Use of atomic absorption spectrometry for the determination of metals in sediments in south-west Louisiana

Microchemical Journal 66 Ž2000. 73᎐113

Use of atomic absorption spectrometry for the determination of metals in sediments in south-west Louisiana James N. Beck a,U , Joseph Sneddon1,b a

Department of Physical Sciences, Nicholls State Uni¨ ersity, Thibodeaux, LA 7030, USA b Department of Chemistry, McNeese State Uni¨ ersity, Lake Charles, LA 70609, USA

Abstract The relatively recent introduction of atomic absorption spectrometry has produced a rapid and relatively inexpensive method for the determination of metal concentrations in a wide variety of samples. One such application is in the determination of metal concentrations in soils and sediments. Soils and sediments represent concentrated reservoirs for these metals that serve as sinks for introduced trace metals or can become environmental sources. The coastal zone of Louisiana provides a ‘living laboratory’ to investigate the mechanisms of transport, deposition, and dissolution of trace metals into this fragile environment. Investigations done in the coastal zone have found trace metals tend to concentrate near pollution inputs and sources and have not migrated to or significantly impacted the coastal zone of Louisiana. Common trace metals determined and their range of concentrations in coastal soil and sediments are chromium Ž10᎐30 ppm., copper Ž10᎐25 ppm., iron Ž0.6᎐2.1%., manganese Ž200᎐600 ppm., nickel Ž6᎐20 ppm., lead Ž8᎐20 ppm., and zinc Ž30᎐55 ppm.. 䊚 2000 Elsevier Science B.V. All rights reserved. Keywords: Atomic absorption spectrometry; South-west Louisiana; Metals

1. Introduction Atomic absorption spectrometry ŽAAS. was discovered in the early 1950s w1,2x, and has become a U

Corresponding author. Tel.: q1-504-448-4500; fax: q1504-448-4927. E-mail addresses: [email protected] ŽJ.N. Beck., [email protected] ŽJ. Sneddon.. 1 Tel.: q1-3370-475-5781; fax: q1-337-475-5234.

well-used and widely accepted technique for trace metal determination in a wide variety of samples. A detailed presentation of the discovery and history of AAS is given elsewhere w3x. When concentrations in the order of 1 part per million Žppm. or even as low as several parts per billion Žppb. are to be determined with less than four different metals, AAS is frequently the choice of the analyst. If more than four different metals are to be determined, in particular on a simultaneous basis,

0026-265Xr00r$ - see front matter 䊚 2000 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 6 - 2 6 5 X Ž 0 0 . 0 0 0 5 9 - X

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inductively coupled plasma-atomic emission spectrometry ŽICP-AES. or the more recent inductively coupled plasma-mass spectrometry ŽICPMS. can be the choice of the analyst. One factor, which has to be considered, is cost. A flame atomic absorption spectrometer can be obtained in the $10 000᎐$35 000 range, and a fully loaded top-of the line graphite furnacerflame combination will be $75 000᎐$100 000 range. ICP-AES will cost in the range of $75 000᎐$200 000, and ICPMS cost can reach $300 000. The total market for AAS for 1998 has been estimated at approximately $317 million. It is predominately a replacement of old or obsolete instrumentation. A major reason that AAS has been retained by the analyst is that ‘it works’ and fulfills a need when the situation arises where several different metals have to be determined in a complex matrix. This chapter provides a short introduction and review to AAS. The bulk of the chapter describes the results of numerous studies of a number of metals in sediments in south-west Louisiana. A sediment can be defined as a soil or surface under a body of water. Some supporting work on soil is presented for completeness. The majority of the determinations were performed with atomic absorption spectrometry but several used ICP-AES and will be noted.

the ground atoms, and can be represented as follows: T s PrPo

Ž1.

Where T is the transmittance, P is the power of the light source passing through the sample zone, and Po is the power of the light source after it has passed through the sample zone. The sample zone of path length, b, is relatively long to maximize the amount of light absorbed by the atoms. The amount of light absorbed is dependent on the atomic absorption coefficient, k. This value is related to the number of atomsrm3 in the atom cell, n; the Einstein probability for the absorption process and the energy difference between the two levels of the transition. In practice, these are all constants that can be combined to give one constant, called the absorptivity, a. The value k is related exponentially to the transmittance as follows: T s PrPo s eyk b

Ž2.

In practice, the absorbance, A, is used in AAS and is related logarithmically to the transmittance as follows: A sy log T sy log PrPo s log PorP s log 1rT s kb log e s 0.43 kb

Ž3.

The Beer᎐Lambert Law relates A to the concentration of a metal in the atom cell, c, as follows:

2. Basic principles Light of a specific wavelength will impinge on previously generated ground state atoms. The atoms absorb this light and a transition to a higher energy level will occur. The intensity of this transition is related to the concentration of

A s abc or ␧ bc

Ž4.

where a is the absorptivity in grl-cm, ␧ is the molar absorptivity in molrl-cm, and b is the cell length in centimeters.

Fig. 1. Schematic diagram of flame AAS.

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

3. Instrumentation A detailed description of instrumentation for AAS is available elsewhere w4x. Current instrumentation combines all the components briefly described here into a compact bench type unit for the user. A schematic diagram of a typical flame atomic absorption spectrometer is shown in Fig. 1. The radiation source is almost always a hollow cathode lamp ŽHCL. or for more volatile metals such as zinc and cadmium an electrodelesss discharge lamp ŽEDL.. Its function is to provide light of a very specific wavelength with a width of approximately 0.2 nm. A separate lamp is needed for each metal of interest although some multimetal lamps for two or three metals are available. The atom cell is the flame with the air᎐acetylene flame the most widely used. For refractory metals such as molybdenum, the hotter N2 O᎐acetylene flame is recommended. The object of the flame is to create ground state atoms. The sample is introduced in a aqueous form through a pneumatic nebulizer. Various other sample introduction systems have been proposed, often for a particular sample need w5x. The monochromator will isolate the wavelength Žradiation. of interest from other wavelengths, and has a typical resolution of 0.02᎐2 nm. The detection system is most frequently a photomultiplier tube ŽPMT.. Its basic function is to convert a light signal into an electrical signal. Recent work has used the photodiode array ŽPDA. or charge transfer devices ŽCTDs.. Readout devices were originally meters with calibrated scales. Modern instrumentation has digital displays or graphic presentations on video units or external computers. Hard copy can be provided.

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A furnace atomic absorption spectrometer has essentially the same components as a flame AAS and is shown schematically in Fig. 2. The major differences are in the atom cell and the sample introduction system. The atom cell is almost exclusively a graphite furnace and the sample introduction is either manually or via an autosampler. A description of these components is described elsewhere w4,6x. An additional need in furnace AAS is faster electronics to process the transient and faster generated-signal. In practice AAS usually has a fast electronics capability and most commercial systems have interchangeable flame and furnace. The unique properties of mercury have led to the development of cold vapor-AAS as the most widely used method of analysis. Elemental mercury exhibits an appreciable vapor pressure, even at room temperature and the vapor is monoatomic. This results in no need for the flame provided mercury in the sample could be converted into its elemental form. A detailed description of this technique is presented elsewhere w7,8x.

4. Practice of atomic absorption spectrometry AAS in common with many analytical techniques is not an absolute method of analysis. A comparison with standards Žusually aqueous. is the most common method for performing quantitative analysis. A calibration curve is established with Žusually. four standards and a blank. The unknown sample can be compared to the calibration curve and its concentration established. The unknown concentration should be higher than the lowest standard and lower than the highest stan-

Fig. 2. Schematic diagram of furnace AAS.

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dard. If the signal is higher than the lowest standard then a dilution is recommended. If the unknown signal is lower than the lowest standard then preconcentration or another technique is recommended. Linearity of the calibration curve in AAS is Žtypically. 2᎐3 orders above the detection limit. Most analyses are performed on samples which have a more complex matrix than the aqueous standards, in this case the use of matrix matched standards or standard-additions is recommended w4x. Accuracy can be established using a comparison to a different method or more commonly by comparison to a standard reference material. There are numerous agencies around the world, which produce standard reference materials with NIST ŽNational Institutes of Standards & Technology, Gaithersburg, MD, USA. being the most widely used. Flame AAS is an ideal technique when the concentration of the metal in the sample is around one ppm or higher and at least several milliliters of sample are available. If the concentration of the metal is less than one ppm and only a few microliters of volume or milligram masses are available, then furnace AAS is a better choice. Recent developments in furnace AAS methods, frequently called modern furnace technology, have improved the acceptance of furnace AAS. These are summarized in Table 1 and described in detailed elsewhere w6x.

5. Recent development in atomic absorption spectrometry For the most part, AAS has seen few major changes in the last two decades. In the late 1980srearly 1990s several commercial multimetal systems became available, typically 4᎐6 metals on a simultaneous basis w9x. These systems did not attract as much interest because of the ready availability of ICP-AES. Improvements in software, computer control, and data reduction were developed for AAS as for all other atomic spectroscopic techniques. Recent interest in the chemical form or speciation of a metal has led to the development of hybrid techniques involving separation methods Žchromatography, electrophoresis, etc.. and AAS w10x, as well as flow injection analysis w11x. A major reason that few major developments have occurred in AAS in the last few decades is because it has matured as an analytical technique and for many applications ‘it works’.

6. Overview of study area The remainder of this chapter focuses on the analytical procedures required to determine trace metals in sediments. For completeness some work on soils is presented. The coastal zone of

Table 1 Instrumentation and protocols included in modern furnace technology Component

Improvement

Autosampler Chemical modifiers Fast electronics Integrated absorbance

Improved precision compared to manual pipetting Reduced interferences More accurate characterization of transient signal More accurate characterization of transient signal than peak absorbance Atomization in a hot environment that reduces intereferences

Platform atomization with fast heating rates during atomization Pyrolitically coated graphite tubes Transversely heated furnace Use of modern methods of background correction Žself-reversal and Zeeman.

Reduced analyte᎐graphite interactions Increased isothermality compared to longitudinally heated furnaces More accurate correction for background

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Louisiana was chosen as the study area and investigations done there are used to present examples of the use and accuracy of these results to interpret environmental issues. The coastal zone of Louisiana comprises an area south of Interstate 10 Žhighway or major road. and the Gulf of Mexico ŽFig. 3.. The coastal zone can be roughly divided into two main regions: the region east of the Atchafalaya River is open marshland that reaches as far north as the Mississippi River and has elevations ranging from sea level to 1 m. To the west, the Chenier Plains, bound by the Atchafalaya River on the east and the Sabine River on the west, are the dominant feature, often reaching staggering heights of 2 m above sea level, lying along the coast and effectively

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protecting inland marshes. This chapter will focus mainly on the studies done in south-west Louisiana with an emphasis on the Calcasieu River Estuary. Some studies on south-east Louisiana are presented for comparison and completeness. This area typifies the impact of anthropogenic inputs of trace metals into local environments. This area of Louisiana is one of the most productive estuaries in the Continental United States in the production of shrimp, menhaden Žfish., oysters, and other marine species. It is thus, in the nations interest, important to protect and sustain this estuary. The discovery of oil and gas in the coastal zone led to large scale drilling activities. The placement of drilling rigs overland in this zone is virtually impossible because these

Fig. 3. A soil map of Louisiana showing the general location of the coastal zone of Louisiana designated on the map as the coastal marshes.

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

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soils will often not support a man’s weight much less the heavy equipment required for drillers. As

a result, canals were dredged to allow barges supporting the drilling rig to be towed to the

Table 2 Mean concentration ranges of selected metals Žin ppm or mgrkg. in sediments collected from the riverrlake complex, the Calcasieu River, tributaries and ship channel stations Žtheir stations 32 and 33. in the vicinity of the southern end of the industrial area and the gulf intracoastel water way, south to two stations near the northern end of Lake Calcasieu Žtheir stations 34 and 35. Metal

Calcasieu Lake

(a) Ri¨ err lake complexa Arsenic 0.72 Cadmium 0.98 Chromium 9.35 Copper 7 Lead 10 Mercury - 0.05 Silver 0.07 Zinc 36 Iron n.d.

Ship canal

Choupique Bayou

Contraband Bayou

Bayou d’Inde

Bayou Virdinne

Reach 1

0.66 0.48 19 27 12 - 0.05 0.08 45 n.d.

0.70 0.34 34 7 15 - 0.05 0.09 34 n.d.

0.97 0.48 19 34 49 0.10 0.14 85 n.d.

0.56 0.26 15 61 25 0.46 0.16 86 n.d.

0.48 0.09 39 16 9 0.10 0.10 61 n.d.

2.27 n.d. 59 8.01 20 n.d. n.d. n.d. 7688

(b) The Calcasieu Ri¨ er and tributariesb Metal Background Stations station from Cal-18 Bayou Verdine

Chromium Copper Lead Mercury Nickel Zinc

24᎐26 6᎐7 8 Not detected 5᎐6 34᎐37

25᎐21 22᎐58 15᎐129 0.1᎐0.2 11᎐42 73᎐1234

Other northern lake and ship channel sites 710᎐157 7᎐50 7᎐45 0.3᎐0.5 7᎐19 28᎐346

(c) Two ship channel stations and Lake Calcasieu stationsc Metal Ship Channel Lake Calcasieu stations stations 32 33 34 Aluminum 19 113 25 818 6748 Arsenic 2.5 4.6 1.1 Barium 211 303.0 113.0 Beryllium 2.0 3.0 1.0 Chromium 25.0 31.0 10.0 Cobalt 8.0 10.0 4.0 Copper 15.0 19.0 7.0 Iron 17 569 21 818 7555 Lead 7.0 8.0 n.d. Manganese 517 661.0 101.0 Nickel 16.0 19.0 7.0 Silver 2.0 3.0 n.d. Vanadium 31.0 42.0 12.0 Zinc 66.0 88.0 28.0

35 15 993 2.0 117.0 2.0 20.0 7.0 10.0 13 427 2.0 186.0 12.0 2.0 24.0 48.0

Reprinted, with permission, from Derouen and Stevenson w12x and Wade w16x. Reprinted, with permission, from ICF Kaiser Engineers w13x. c Cadmium and Mercury were not Determined. Reprinted, with permission from Cunningham et al. w14x. a

b

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drilling site. This is particularly true of the eastern portion of the coastal zone. In fact, the areas are so criss-crossed with these canals that aerial photos give the impression of city streets traversing the marsh. The presence of these canals has allowed tidal action to erode these fragile soils at the rate of loss of approximately the area of one football field each minute. Many of the canals have become open ponds or lakes accelerating the loss of marshland. During the early 1940s, refining of fossil fuels and production of chemicals became a national emergency and several locations in southern Louisiana were chosen to develop this industry. Louisiana was chosen because of the abundance of fresh water, deep-water ports, and remoteness from imminent attack. The need to produce these products, and lax or absent environmental regulations, led to the widespread introduction of pollutants to the coastal zone. Industrial complexes were developed along the Mississippi River between Baton Rouge and New Orleans and along the Calcasieu River near Lake Charles. Many studies w12᎐17x have attempted to measure the extent of resulting pollution from metals along this riverine system. Table 2a᎐c summarizes some of the results of previous studies w12᎐14,16x on the Calcasieu Estuary and generally give similar results. Elevated concentrations of trace metals are found in every study only in the northern portions of the watershed. The restoration of marshland in Louisiana has become a national priority w18x because the loss of this important estuary will severely impact the diversity and quantity of aquatic organisms. Several restoration methods have been proposed and many have been applied. These methods include the use of dredge spoils from nearby rivers pumped to prepared ponds, dewatered, and allowed to settle to a previously determined elevation, usually only a few feet above sea level. A second method currently being used is to build low dams around areas of marsh that become flooded at high tides. This restoration method effectively reduces tidal action, reducing the impact of erosion. These impoundments allow time for suspended sediments to settle to the bottom, slowly building up bottom sediments. Other less

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successful methods have been periodic flooding of marsh using sediment rich waters from the Mississippi River w18x, however, this method is useful only in remote, uninhabited areas. Another technique is making use of waste products from refining activities, such as the use of red mud from local aluminum refining. The need to establish baseline concentrations of metals in soils and sediments in the coastal zone is apparent when considering the numerous historical inputs. It is also important to establish locations of polluted areas and the extent and movement of the pollution through estuaries w19x. The movement and reentrainment of metals to the environment are affected strongly by variations in pH and Eh Žreduction potential. of overlying waters, the degree and frequency of flooding, and indigenous vegetation w20,21x. The introduction of fill materials to marshes can alter the natural balance and concentrations of nutrients, metals, pH, and Eh, alter the concentrations of metals, and foster migration and bio-availability of trace metals. Dissolution of metals could result in increased bioavailability and affect local biota and natural succession. Lake and reservoir sediments offer unique substrates for investigating the occurrence of many energy-related pollutants since they are the main ‘sink’ for materials entering watersheds and may be dated by radioactive methods providing a depositional history w22᎐25x. Furthermore, accurate coring, e.g. minimal disturbance of sediments, is of great importance to paleolimnological investigations, especially those aimed at reconstructing the deposition history andror inventories of pollutants deposited through atmospheric processes. To properly assess geochronologies of sediments, methodologies must be available for taking a large volume of undisturbed sediment cores, so that multiple parameters can be measured at critical core depths. Commonly used 4᎐7-cm diameter sediment corers often do not yield sufficient sample size to complete all chemical analyzes required. In order to collect large enough samples, multiple cores must be taken and homogenized, thus blurring the geological record. Larger corers are of such size and weight they are difficult to use in sampling lake and river sediments. An-

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other common problem with gravity corers is the frequent washing away of the upper-level sediment as the corer is dropped resulting in the loss of important information. These types of corers often result in vertical compression of the sediment core, thereby producing false chronologies. A simple solution to this problem was the development of large diameter slow penetration sediment corers w26,27x.

7. Soil and sediment collection methods 7.1. A. methods used to collect surface soil samples The need to collect representative samples can be a perplexing problem when one is sampling in the middle of a marsh or a large lake. This can be accomplished by collecting a number of replicates Žas many as 10. in a preselected sampling scheme. For example, an area marked with a template can be sampled in a predetermined pattern, one from middle, north corner, etc., until the required number of replicates has been collected. When the sample area is vegetated, the plants can be scraped to the soil surface before sample collection is started. Sampling depth must also be determined prior to collection. Surficial soil samples are often all that is required and can be collected using scoops samplers over a specified area and depth, i.e. 12 = 12 = 2.54 cm deep. It is often necessary to understand variations of metal content with depth so a sampling pit must be dug. The depth of the pit should be related to soil profiles Žorganic layer at top and clay at depth. w28x. The upper soil layer in well-drained areas will generally be well developed soils, and often uniform in composition down to developed clays Žin Louisiana soils this is generally a red clay, often a sink for trace metals.. The depth to the clay layer can vary from a few centimeters to several meters. Marsh soils are characteristically poorly drained and do not develop the characteristic soil profiles, and are mainly clayey in nature. Usually only surficial soils are required to obtain representative samples. If samples are required in the rhizosphere Žarea around soils in contact with roots.

deeper samples may be required. Sampling equipment can include such exotic equipment as plastic scoops, stainless steel shovels, augers, post-hole diggers, etc. Care must be taken to prevent contamination of collected samples. 7.2. Methods for the collection of sediments using grab samplers In areas where the soils to be sampled are periodically covered by water or are lake or river sediments, a different approach to sampling must be used. Several grab samplers have been developed including devices such as the Ekman grab sampler and others shown in Fig. 4. These samplers range in size from 0.05 to ) 1 m2 in area. These samplers often have a hinged bottom held open by springs. The sampler’s weight allows it to penetrate into sediments after being dropped through the water column. A sending unit is dropped onto a trigger device that releases the hinged bottom trapping the sediment in the sampler. The sampler and sediment sample can then be retrieved. The larger samplers require wenches to drop and retrieve. Handles can be attached to the smaller samplers Žsuch as the 0.1 m2 sampler. when sampling in shallow marsh or lake-sediment to allow better control of the sample collection. Dredge samplers are towed and allowed to drag along the surface of the sediments behind sampling boats to collect surface sediments. This will allow the collection of samples representative of wider sampling areas. The dredge is then retrieved and representative samples are taken from the dredge. 7.3. Techniques in the use of core samplers The collection of core samples requires a device that can be made to penetrate sediments at depth without disturbing or mixing the sample collected in the coring device. A few of the commonly used coring devices are illustrated in Fig. 5. There are many commercial coring devices available. These devices are generally metal cylinders made usually of brass or other metals that surround a plastic inner liner that the sample is collected in. These devices are generally dropped

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Fig. 4. Schematic diagram of grab samplers commonly used to collect sediment and biota.

from the boat and gravity and the sampler weight drives the corer into the sediment. If the sediment is coarse enough the sample will stay in the sampler when pulled from the water. The devise

can be taken apart and the inner liner containing the sample removed, capped, and labeled. The plastic inner liner is replaced; sampler reassembled and is ready to collect a new sample. In

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Fig. 5. Schematic diagram of two types of core samplers commonly used to collect sediment and core samples.

shallow waters the core sampler can be fitted with a handle to allow the operator to control the depth of the core collected. In the coastal zone of Louisiana, there are many areas where sediments are fluid enough at depth that conventional core samplers will not hold these sediments. This difficulty in collecting core samples led to the development of a core sampler w27x made entirely of polyvinyl chloride ŽPVC. pipes and pipe parts as illustrated in Fig. 6. A thin walled plastic tube is attached to a handle using a rubber-plumbing boot and pushed or driven into the sediment to the desired depth. The plastic handle is sealed to produce a vacuum that prevents the loss of sample. The corer is retrieved, capped on the bottom, sampler drained of water, and the sample tube is removed from the handle, labeled and capped.

tioned into desired lengths. This technique often makes it difficult to control the thickness of core sections, so an alternate procedure is to freeze the core in the collection tube and then cutting the frozen core to the desired lengths, the samples are then thawed and sample preparation continued. Each core segment or surficial soil is weighed and dried at 80⬚C for 48 h to constant weight to establish %water content. The samples are ground to a fine powder that will pass through a sieve to a predetermined grain size Žfor example, the fraction that will pass a 20-mesh sieve.. Ground samples are stored in appropriate containers such as polyethylene bottles, polyethylene ziploc bags, etc., until digestion. All samples should be analyzed within 6 months of collection. It is often necessary to determine the long-term effects of vegetation on soil structure and metal chemistry so the concentration of organic matter in the soil is often measured. Organic content of soils can be measured by removing loose litter from the dried sample, weighed and placed in a muffle furnace and heated to 500⬚C for 4 h. The

7.4. Techniques and methods of sample preparation The following procedure is typical of most sample preparation techniques. Sediments from cores can be extracted from the coring tubes by mechanically pushing the core out and then sec-

Fig. 6. Soft sediment coring tool. Reprinted from Meriwether et al. w27x, with permission. The letters on the figure are described in the original paper.

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

%organic content is then determined from the difference in weight of the soil sample after ignition.

Table 3 Composition of metal concentration in 1 M nitric acid leach and bomb digestions for two trials of sediments collected in Bayou d’Inde, Louisiana Metal

8. Extraction techniques 8.1. Techniques and methods for using acid digestions It is often sufficient to digest sediments using dilute solutions Ž1᎐6 M. of acids such as nitric, hydrochloric, acetic, perchloric, etc., or combinations of any of them. This allows the determination of leachable metals in sediments or soils w29x. Generally, a weighed sample of sediment is placed in a beaker or flask, approximately a 10:1 ratio of acid to sediment and a stirring bar added. The sample is then stirred at constant temperature for a period of 16᎐24 h. The samples are often digested at temperatures ranging from room temperature to 90⬚C, depending upon the method used. The digested samples are filtered and brought to volume in a volumetric flask. This method closely approximates the Environmental Protection Agencies Toxicity Characteristic Leaching Procedure ŽTCLP. extraction technique w30x. This method was developed to determine if metals readily leach from contaminated sediments, sludges, etc., under conditions when rainwater and groundwater percolate through the soil. The major difference between the two techniques is the use of dilute organic acids as the leachant in the TCLP extraction procedure. This was done so that the method could simulate long-term leaching of contaminated materials by rainwater or groundwater interacting with the substrate. 8.2. En¨ ironmental studies using acid digestions Beck et al. w15x used 1 M nitric acid to leach metals from sediments collected in the Calcasieu Estuary Žmethod developed by Slowey w31x.. Metals were determined using atomic absorption spectrometry and cold vapor atomic absorption spectrometry for mercury. This work involved a comprehensive study of the extent and location of

83

Arsenic Chromium Copper Lead Silver Zinc

1 M HNO3 leach

Bomb digestions

1

2

1

2

0.66 15 96 26 0.14 141

0.55 27 85 24 0.05 152

0.70 87 110 30 0.19 171

0.76 92 102 35 0.24 160

introduced pollution within the Calcasieu Estuary, far from the direct influence of pollution sources. They concluded that the results obtained were not consistent enough and the method was abandoned. Table 3 compares the results of the determination of trace metals using this extraction technique with the bomb digestions used later. The main problem with this method was the incomplete extraction of chromium and lead, which were often a factor of two or greater than other extraction techniques. Significant statistical variations were found in the measurement of other trace metals suggesting that grain size, clay content, etc., strongly control the leaching rates of the different metals. Wade w16x used a modified elutriate test similar to the TCLP procedure developed by the US EPA w30x to study the resuspension of contaminant metals into the Calcasieu River waters during the dredging activities along the Calcasieu River Ship Channel. The collected sediments were mixed with dredging site water to a slurry concentration of 0.7 g sedimentrl of site water. The samples were stirred vigorously for 15 min and then aerated for 1 h to ensure oxidizing conditions similar to those caused by the dredging activity. The samples were analyzed for metal determination by using ICP-AES, cold vapor-AAS, and flame and furnace AAS. Bulk chemical analysis gave ‘reason to believe’ that the sediments could be contaminated, so the modified elutriate test was developed and used to determine the potential for metal release. The bulk chemical analysis indicated that there were

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Table 4 Modified elutriate test chemical dataa Metals

Antimony Arsenic Beryllium Cadmium Chromium Copper Lead Mercury Nickel Selenium Silver Thallium Zinc Iron a

Reach 1

Reach 2

Reach 3

Total conc. ppm

Dissolved conc. ppm

Total conc. ppm

Dissolved conc. ppm

Total conc. ppm

Dissolved conc. ppm

- 0.0030 - 0.0020 0.001 0.0021 0.012 - 0.001 0.0063 0.0009 0.008 - 0.0020 - 0.010 - 0.020 0.062 7.29

- 0.0030 - 0.0020 - 0.0010 - 0.0020 - 0.0010 - 0.001 - 0.0010 - 0.0002 - 0.001 - 0.0020 - 0.010 - 0.0020 - 0.010 - 0.025

0.0106 0.0648 0.0390 0.00263 1.30 0.659 0.667 0.0042 0.737 0.0184 - 0.010 0.0030 2.16 699

- 0.0030 - 0.0020 0.001 - 0.00020 - 0.0010 - 0.0010 - 0.0010 - 0.0002 - 0.001 - 0.0020 - 0.010 - 0.0020 - 0.010 - 0.025

0.0044 0.0029 0.001 0.00043 0.011 - 0.001 0.0045 0.0003 0.008 - 0.0020 - 0.010 - 0.0020 0.163 0.392

0.0030 0.0023 - 0.001 - 0.00020 - 0.0010 - 0.001 - 0.0010 - 0.0002 - 0.001 - 0.0020 - 0.010 - 0.0020 - 0.010 - 0.025

Reprinted, with permission, from Wade w16x.

detectable metal concentrations over the length of the ship channel. However, the modified elutriate test showed dissolved metal concentrations in the effluent were all below detection limits. There were indications; however, that the total elutriate contained particle-associated metals such as arsenic, chromium, copper, and mercury, in low concentrations. Table 4 presents results from Wade w16x showing that metals were not dissolved using this dissolution technique. Catallo et al. w29x extracted sediments taken from urban and rural Louisiana lakes using heated Ž85⬚C. and constantly agitated 6 M nitric acid to leach metals from the samples. Metals were determined ICP-AES, while mercury was analyzed using cold vapor atomic absorption spectrometry. The object of the study was to determine if there are significant differences in historical contaminant loadings, to identify sources of pollution, and to develop a health assessment strategy. Lac des Allemands located in the Barataria Basin of south-eastern Louisiana was used as one sample site. Core samples were collected, separated into sections and metal concentrations with depth were determined. Since the relative shape of the distribution of trace metals with depth is not strongly influenced by the extraction technique, the data

can be used to interpret changes over time. They found that only mercury and lead profiles indicated historical inputs over the past 100 years. The results of the determination are presented in Fig. 7 to show the change in concentration with

Fig. 7. Concentrations of trace metals at Lac des Alllemands, south-eastern Louisiana, Pb Ž ., Cr Ž ., Ni Ž ., Cu Žq., and Zn ŽU .. Reprinted, with permission, from Catallo et al. w29x.

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

depth for samples collected in Lac des Allemands. The method yields consistent and reliable results and gives information about metal concentrations attached to easily dissolved chemical species. However, most investigators use extraction techniques that more closely approximate a total dissolution of all metals in the sample.

85

Pardue et al. w32x extracted aluminum, cadmium, chromium, and lead from sediments collected from Vermilion Bay, located in southcentral Louisiana, using a nitric-perchloric acid digestion. They closely followed the method outlined in Standard Methods w33x. The metals were determined in diluted extracts using ICP-AES.

Fig. 8. Aluminum and metal concentrations Žlead, cadmium, and chromium. of additional sites in the Louisiana coastal zone compared with metalraluminum regression lines calculated from the larger coastal data set. Sites include Lac des Allemand bottom sediment Žopen circle., Little Lake Žopen triangle., and Airplane lake Žopen square., from Feijtal et al. w21x. Also included are Lake Verret Žopen diamond., Lake des Allemands marsh Žfilled circle., Spring Bayou Žfilled triangle., Grammercy Žfilled square., and Baton Rouge Žfilled diamond.. Chromium data were not available for sites in Feijtal et al. w21x. Reprinted, with permission, from Pardue et al. w32x.

86

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

Using ‘baseline’ concentrations established by Pardue et al. w34x and extending the methods of using regression analysis to explain trends in metal ratios introduced by Windom et al. w35x, they compared all metal concentrations with aluminum. Fig. 8 shows the results of their data analysis for regions of the Louisiana coastal zone not considered contaminated with trace metals. The data all fit the regression lines for ‘baseline’

concentrations suggesting the absence of pollution. Fig. 9 shows the same ‘baseline’ regression lines compared to areas known to be contaminated with heavy metals. They chose Capitol Lake, located in downtown Baton Rouge, and Bayou Trepanier, located in St Charles Parish for the investigation. Both sites are well known for having elevated metal concentrations. It is clear from

Fig. 9. Aluminum and other metal concentrations Žlead, mercury, and chromium. of Capitol Lake and Bayou Trepagnier, Louisiana, compared with metalrAl regression lines calculated from the larger coastal data set. Data are plotted on log᎐log for scale purposes. Reprinted, with permission, from Pardue et al. w32x.

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

Fig. 9 that both sites do indeed have elevated levels of some trace metals. Capitol Lake shows excesses of lead probably resulting from the heavy automobile and commercial traffic that once used leaded fossil fuels. However, Bayou Trepanier shows excess concentrations of chromium and lead but a depletion of cadmium w36x.

87

This study demonstrates the usefulness of using this type of determination to identify areas having elevated metal concentrations. This determination yields rapid and inexpensive methods for obtaining information for assessing environmental impacts. The results of using an acid-leach procedure will yield consistent and useful infor-

Fig. 10. Schematic diagram of bomb digestion technique.

88

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

mation about the distribution of metals in soils and sediments. Metal distributions in soils are not dependent upon the extraction technique but upon the analytical ability of the investigators. 8.3. Techniques and methods using bomb digestions Dissolution of soils using bomb digestions were introduced by Bernas w37x and Fig. 10 illustrates the basic features of the bomb digestion procedure. The method involved the use of stainless steel bombs that surrounded a teflon-lined sealed cup. The sample was weighed into the teflon cup, nitric acid or nitric acidrhydrogen peroxide or hydrochloric acid, or any combination of the acids added depending on the method selected or soil collected. The bomb was sealed and heated in an oven at 140⬚C for 2 h. The bomb, after cooling was opened, the sample filtered, and then brought to standard volume. The introduction of microwavable bombs and the danger of bomb failure have reduced the use of this technique. A newer method of acid digestion utilizes microwave ovens and microwave bombs w25,38,39,73x. A common procedure is to weigh 0.2᎐1.0 g of sediment in a teflon digestion vessel. Five to 10 ml of concentrated nitric or hydrochloric acids are added to the sample and the bomb is sealed. The bomb is placed in a microwave oven for periods ranging from 30 s to several minutes. The bomb is allowed to cool, opened and if the sample contains significant organic materials, hydrogen peroxide is added and the microwave heating is repeated. After cooling the sample is filtered and the sample brought to volume with deionized water. There are a wide variety of microwavable bombs available and a choice of a wide variety of commercial vendors. The choice of microwave ovens varies depending upon the sample load required. The occasional user can make use of an ordinary microwave oven that can be purchased from any well-known retailer. Microwave ovens have been adapted for this use and can be purchased from many commercial vendors. A comprehensive review of microwave methods and equipment can be found in Kingston and Haswell w40x.

These ovens allow the introduction of a large number of bombs at the same time, are programmable and allow the introduction of additional reagents as the experiment proceeds. In case a sample over-pressures, the bomb will vent into a neutralizing solution to prevent cross contamination. The digestion times for samples can be greatly lengthened with these ovens. 8.4. En¨ ironmental studies utilizing bomb digestions The area around Lake Charles, in south-western Louisiana has gained a national reputation as a severely polluted region perhaps deserving the currently proposed designation as a super-fund

Fig. 11. A detailed map of the study area showing the location of all the sampling stations. The insert shows the portion of south-west Louisiana investigated. Reprinted, with permission from Mueller et al. w38x.

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site. Large-scale petrochemical industry grew in the area during the 1940s and developed into the second largest concentration of chemical plants in Louisiana. Lax environmental regulations in the past allowed large-scale emissions, which were primarily dumped into the air or directly into tributaries of the Calcasieu River. This has spurred numerous studies w12᎐17,41x on the estuary to determine the extent of this pollution. The Calcasieu River drains the entire area of southwestern Louisiana ŽFig. 11. and flows past the industrialized city of Lake Charles, entering the Calcasieu Ship Channel before flowing into the Gulf of Mexico approximately 40 km south. The basic structure of the 3-m deep river changed when it was altered by channelization. This occurred after a 12-m deep navigation channel was dredged and the natural levee protecting the mouth of the river was removed. This allowed saltwater to intrude above the city of Lake Charles altering the chemistry of these waters. Major tributaries of the river include Choupique Bayou, Bayou’s d’Inde and Verdinne, Contraband Bayou, South Fork, and Ouiskey Chitto. Previous studies w12᎐17,41x occasionally found moderately high concentrations of chromium, copper, and zinc along the Calcasieu River Ship Channel. High concentrations of these metals

89

were only found in the upper part of the estuary in the vicinity of the industrial complex. This was particularly true of metal concentrations in sediments collected in Bayou’s d’Inde and Verdinne, the main conduits carrying industrial wastes. Table 5 summarizes some of these results; comparing results near the industrial complex and near the Sabine Wildlife Refuge. Maples et al. w42x determined cadmium, chromium, copper, lead, silver, and zinc and the metalloid arsenic concentrations in sediments collected in Calcasieu Lake. The metals selected for this study were chosen because they corresponded to metals measured in the US mussel watch program w43,44x. The only difference between the two studies was the exclusion of nickel in the later investigation. These metals are generally selected for this type of study because they can act as nutrients for biota or as inhibitors to growth and development of healthy ecosystems. They used 0.2-g samples of sediment to which 2 ml of concentrated nitric acid was added. The stainless steel bomb was then sealed and heated at 140⬚C for 2 h. After cooling, the samples were filtered and brought to constant volume with deionized water. The overall purpose of this investigation was to determine the concentration of selected trace

Table 5 Comparison of metal concentrations from previous studies on Calcasieu Ship Channel sediments taken in the vicinity of Sabine National Wildlife Refuge Investigator

Copper Žppm.

Iron Ž%.

Manganese Žppm.

Nickel Žppm.

Lead Žppm.

Zinc Žppm.

19

27

n.d.

n.d.

n.d.

10

45

25 28

7 17

n.d. 1.97

n.d. 589

6 18

8 8

36 36

34 10 59 17

15 11 8 18

1.71 n.d. 0.77 n.d.

670 n.d. n.d. n.d.

15 14 n.d. n.d.

9 12 20 22

84 36 61 70

Mean of all studies

27

15

1.48

630

13

13

53

Site V Žthis work.

21

10

2.10

580

15

6

42

Derouen and Stevenson w12x ICF Kaiser w13x Cunningham et al. w14x Shultz w41x Army Corp. w58x Wade w16x Sneddon w64x

Chromium Žppm.

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

90

metals in oysters, a major industry in south-western Louisiana. A second purpose was to assess water and sediment quality because of the postulated pollution present in Calcasieu Lake due to inputs located further north. Table 6 summarizes the results of the determination of trace metals and arsenic at three sampling locations in Calcasieu Lake. These sampling locations corresponded to known oyster reefs within the lake. The results presented do not vary with location in the lake and generally are consistent with ‘baseline’ concentrations for the lake and surrounding environment. This would appear to suggest that trace metal inputs in the northern portion of the estuary have not impacted sediments or biota in Calcasieu Lake. A multiyear and multidisciplinary study of the Calcasieu Riverine System was begun in 1983 to investigate the ecological health of the estuary. We will concentrate here on the analytical results for some environmentally important heavy metals including cadmium, chromium, copper, lead, mercury, silver, and zinc as well as the metalloid arsenic. The results of this comprehensive study w12x agrees well with the conclusions reached in previous studies on the estuary and is used here to summarize the findings. A map of the sample area including the locations of all sample stations is presented in Fig. 11. Calcasieu Lake, an important estuary for the production of aquatic species such as shrimp, oysters, was selected for sampling in order to determine if contamination was migrating south and affecting this important resource. Choupique Bayou was

selected because it drains mainly marshland, with little anthropogenic impact, and serves as a reference system. The Ship Channel was selected because it is the conduit that drains known inputs of pollutants and potentially carries all potential contaminants to the estuary as a whole. Bayou d’Inde was selected because most industrial outfalls empty into this Bayou and had been previously identified as seriously polluted. Contraband Bayou was selected to determine the impact of urban sources of pollution. Sediment samples were collected using a coring device designed to collect undisturbed cores in extremely soft sediments. The coring sampler illustrated in Fig. 4 was designed so that samples having diameters ranging from 3 to 30 cm could be collected depending on the amount of sample required. Representative samples up to 100-cm depth and 30-cm diameter could be collected using this coring device. The core samples were stored in their labeled coring tube, taken to the lab, and extruded from the core tube in 2.54-cm lengths. All samples were dried at 80⬚C for 24 h and then placed in labeled polyethylene bags until analysis. All samples were digested using 1 M nitric acid leaching techniques in the early stages of the project, but this proved inadequate. Stainless steel digestion bombs became available so the digestion was carried out using the bomb digestion technique. Samples Ž0.2 g. of sediment was weighed in a stainless steel nylon-lined bomb, followed by the addition of 5 ml each of concentrated nitric and hydrogen peroxide. The bomb was sealed and then heated at 140⬚C for 2 h,

Table 6 Mean concentrations of trace metals Žppm. in sediments in Calcasieu Lake, Louisiana Metal

Calcasieu Žnorth.

Calcasieu Žsouth.

West Cove Calcasieu

Arsenic Cadmium Chromium Copper Lead Mercury Silver Zinc

0.51 0.05 16 11 9 - 0.05 - 0.05 35

0.70 0.09 20 10 7 - 0.05 - 0.05 40

0.45 0.06 19 14 11 - 0.05 0.06 37

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allowed to cool, opened, filtered and brought to volume with deionized water. The project called for the determination of cadmium, chromium, copper, lead, mercury, silver, and zinc as well as arsenic. The concentrations of chromium, copper, and zinc were determined using flame atomic absorption spectrometry, while cadmium, lead, and silver were determined using graphite furnace atomic absorption spectrometry. Mercury was analyzed using a separate sub-sample and using the standard potassium permanganate, sulfuric acid leaching method, followed by the reduction of mercury and determined using the cold vapor atomic absorption spectrometric method. As part of the quality assurancerquality control ŽQArQC. procedures w45x, it was necessary to determine the fraction of metal that was actually dissolved by the nitric acidrdigestion bomb leaching procedure. Table 7 gives the percentages of metal extracted from the standard reference sediment wNational Institutes of Science & Technology ŽNIST. Rocky Flats Soil No. 1, Standard Reference Material ŽSRM 4353.x. The method does yield consistent results for the percent of metal extracted for triplicate sub-samples thus not affecting trends in the analysis of data. It is

91

Table 7 Percentage of heavy metals extracted from standard reference sediments ŽNIST Rocky Flats No. 1. using nitric acidrdigestion-bomb leaching Element

Weight digested

% Recovery

Zinc

0.2 0.4 0.6 0.8 1.0

90, 90, 90 72, 95, 76 66, 81, 75 67, 75, 69 61, 66, 66

Copper

0.2 0.4 0.6 0.8 1.0

62, 75, 69 43, 50, 56 44, 46, 54 49, 51, 55 54, 55, 56

Iron

0.2 0.4 0.6 0.8 1.0

32, 35, 35 31, 33, 32 30, 33, 32 32, 32, 30 32, 32, 31

also clear that there is a significant drop in recovery rates for all metals analyzed as the sample size is increased, probably due to decreased contact time with the acid as the sample size increases. Iron results were not used in this study

Fig. 12. The results of the quarterly surveys for the determination of copper in surficial sediments for stations sampled along the three Bayous investigated. The roman numerals ŽI᎐IV. refer to the first through fourth surveys and each graph is one quarterly period. The numbers attached to the data are the date of collection in the year and month ŽYYMM..

92

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due to the poor recoveries. All other metals studied gave recovery rates that fell between the values for copper and zinc. Samples were collected quarterly for 1 year at all sampling sites in order to provide the necessary replicate analysis to assure quality assurance. Repeat sampling at all stations gave reasonably consistent results for all metals analyzed except chromium. This was verified by using the Statistical Package for the Social Sciences ŽSPSS.. A confirmation multivariate analysis of variance ŽMANOVA. was run to verify that metal concentrations measured at different sampling times did correspond to that stations metal profile. Greater than 92% of the samples analyzed grouped with the proper sampling station demonstrating the accuracy of the chemical procedures. Typical results of the quarterly sampling are given in Figs. 12 and 13 for the mean concentrations of copper and chromium, respectively, along the three major Bayous in the study area. The first sampling time labeled I in Figs. 12 and 13 represents the 1 M nitric acid leach procedure which was replaced in all subsequent sampling times with the bomb digestion method. The num-

ber of sampling stations varied along each Bayou due to differences in length. It is evident that little of the chromium in sample I was extracted when compared to the following sample times. The profiles for copper were similar for all sampling times suggesting that extraction technique did not affect dissolution of copper. Other studied metals showed variances in the first sampling period that fell between the extremes represented by chromium and copper. It is evident in Fig. 14 that metal concentrations determined in Choupique Bayou were the lowest values measured and probably reflect baseline concentrations for the region. Measured concentrations in Contraband and d’Inde Bayous are elevated over values found in Choupique Bayou suggesting inputs of contaminant metals to the Bayous. The sources of pollution in these Bayous lie between sample stations 3 and 4 and metal concentrations tend to decrease to baseline values at the mouth and upstream in each Bayou. This suggests that introduced metals to the polluted sediments remain isolated in the general vicinity of the pollution source and is not seriously impacting the remainder of the estuary.

Fig. 13. The results of the quarterly surveys for the determination of chromium in surficial sediments for stations Ž1᎐10. sampled along the three Bayous investigated. The roman numerals ŽI᎐IV. refer to the first through fourth surveys and each graph is one quarterly period. The numbers attached to the data are the date of collection in the year and month ŽYYMM..

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93

Table 8 Variation in mean concentration Žmgrkg or ppm. of selected metals for group stations a Metal

Station group Lake River Bayou Bayou Bayou Choupique Contraband d‘Inde

Chromium 19 Copper 7 Lead 10 Zinc 35 a

30 18 10 44

19 7 15 34

15 34 49 85

39 61 25 86

Reprinted, with permission, from Mueller et al. w70x.

bayous are excluded from the mean, the means at all other river stations fall to baseline concentrations. Fig. 15 shows a plot of mean metal concentration Žcopper, lead, and zinc. vs. sampling stations within the Lake, River and Bayous. This

Fig. 14. The variation in the mean concentration of chromium, copper, lead and surficial sediments and zinc against sampling stations along the three bayous investigated. Reprinted, with permission, from Mueller et al. w38x.

Table 8 gives the mean concentrations of chromium, copper, lead, and zinc for groupings of stations reflecting different environments within the study area. Stations located in Calcasieu Lake and Choupique Bayou have the lowest concentrations of metals in the estuary and also are similar in concentrations. These areas appear to be baseline concentrations for the Calcasieu Estuary and were used to determine excess metal content at other sampling sites. The highest mean metal concentrations were found in Bayou Contraband and Bayou d’Inde because of the presence of major inputs of pollutants located there. The river stations were found to be intermediate between the two extremes, however, if the two stations adjacent to the mouths of the two contaminated

Fig. 15. A comparison of the variation in the mean concentrations of copper, lead, and zinc in surficial sediments measured at all regular stations in the lake, river and bayou. The bayou stations sampled were C1, D1, P1, and V1. Reprinted, with permission, from Mueller et al. w38x.

94

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

again demonstrates the fact that impacted stations are located in and along Bayous d’Inde and Contraband and the river station located near these Bayous. Interesting presentations of this localization of polluted sediments are shown in Figs. 16 and 17. These plots give a demographic view of copper and zinc ŽFig. 16. and mercury and zinc ŽFig. 17. across the sample area with the bars representing the mean metal concentration at each sampling station. It is quite evident that the areas near the sources of pollution have been

Fig. 17. A demographic view of the variation of the concentrations of Pb and Hg in surficial sediments across the Calcasieu RiverrLake Complex. Reprinted with permission, from Mueller et al. w38x.

severely impacted, with the remainder of the study area being little affected by the activity upstream. 8.5. Techniques using total digestion

Fig. 16. A demographic view of the variation of the concentrations of Cu and Zn in surficial sediments across the Calcasieu RiverrLake Complex. Reprinted, with permission, from Mueller et al. w38x.

Total digestion of samples are required when it is necessary to know the total metal concentrations in sediment samples, as opposed to leachable metal content. In pollution studies it is often necessary to compare total metal concentrations between sample replicates to determine the ex-

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

tent of contamination. Because of high silica content of many soils, a fusion reaction is necessary to get metals into solution. Most total digestion techniques require a fusion reaction of the sediment with alkali metal salts. A common technique is as follows; 5 g of sodium hydroxide pellets are added to a 1᎐10-g sedimentrsoil sample and heated over a Meeker burner for 20᎐30 min. A 0.5-g sodium carbonaterg sample is mixed into the fused sample and the heating continued for approximately 30 min or until completely melted. The sample is allowed to cool and the fused material is dissolved in 1 M HCl or 1 M HNO3 . A second illustration of this technique w46x utilizes lithium borate as the flux. Li 3 BO 3 is mixed with a weighed sample and placed in a graphite crucible and melted at 750⬚C in a muffle furnace. The cooled sample is then dissolved in 1:1 HNO3 and analyzed. There are as many variations of this extraction method as there are investigators but all serve the purpose of dissolving soilrsediment and even rocks. There have not been in the recent past any good examples of using this technique to determine metal concentrations in soils in the coastal zone of Louisiana. The method is included for completeness. 8.6. Techniques and methods using sequential extraction procedures A wide variety of reagents can be used to extract sediment-bound trace metals selectively from different fractions within the sediment profile. For example in the extraction of metals from the adsorption and cation exchange fraction of bound metals, examples of reagents that have been used are as follows: BaCl 2-triethanolamine ŽpH 8.1. solutions w47x, MgCl 2 ŽpH 7.0. solutions w48x, andror ammonium acetate ŽpH 7.0. w49x. Metals bound to the carbonate fraction have been extracted using several different techniques and reagents such as CO 2 -treatment of sedimentrwater suspensions w50x and NaOAcr HOAc᎐buffer ŽpH 5.0. solutions w49x. Ammonium oxalate buffer solutions w51x and dithionite᎐citrate buffer solutions w52x are two examples of the

95

reagents that have been employed to fractionate metals contained in the reducible phase. Speciation of metals contained in the organic fraction has been successfully achieved using organic solvents w53x, 0.1 M NaOHrH 2 SO4 solutions w54x, solutions of sodium pyrophosphate w55x, as well as several other reagents. Residual metals have been most commonly speciated using nitric acid andror perchloric acid solutions. 8.7. Summary of a sequential extraction technique Procedures very closely following that of Tessier et al. w49x are widely used for the speciation of particulate trace metals in sediments. A summary of this method is illustrated in Fig. 18. This method was utilized because of its wide acceptance internationally as the method of choice for the speciation of metals. A reference standard has been developed for this method to allow quantification and to measure the reliability of the method. The following presents an example of a typical sequential extraction procedure that closely resembles that developed by Tessier et al. w49x. The procedure gives a summary of the method of extracting metals in five fractions representing: Ž1. exchangeable binding sites; Ž2. metals bound to carbonates; Ž3. metals bound to ironrmanganese oxides; Ž4. metals bound to organic matter; and Ž5. metals bound to the sediment matrix. Ž1. Exchangeable: The exchangeable metals are extracted from a sediment sample by digesting the sample with 20 ml of a 1.0 M MgCl 2 solution adjusted to a pH of 7.0. The mixture is continuously agitated for 1 h. This solution is then centrifuged and the supernatant diluted to 50 ml using a volumetric flask with deionized water. The residue is washed with approximately 20 ml of deionized water and the solution is again centrifuged and the supernatant discarded. Ž2. Metals bound to carbonates: Metals bound to carbonates are extracted by pouring 20 ml of a 1.0 M NaC 2 H 3 O 2 solution, adjusted to a pH of 5.0 with acetic acid, onto the residue from the first procedure and then agitating this mixture continuously for a 4-h period. This solution is then

96

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

Fig. 18. Flow chart of metal extraction procedure employed for 2.5-g soil samples showing the steps in the sequential extraction procedure.

centrifuged and the supernatant diluted to 50 ml using a volumetric flask with deionized water. The residue is washed with approximately 20 ml of deionized water and the solution is again centrifuged and the supernatant discarded.

Ž3. Metals bound to iron and manganese oxides: Metals bound to iron and manganese oxides are extracted by pouring 50 ml of a 0.04 M NH 2 OH . HClr25% HC 2 H 3 O 2 solution onto the residue from the second procedure. Continuous

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

agitation is applied while keeping the solution at a temperature of 96 " 3⬚C for a 5.5-h period. This solution is then centrifuged and the supernatant diluted to 50 ml using a volumetric flask with deionized water. The residue is washed with approximately 20 ml of deionized water and the solution is again centrifuged and the supernatant discarded. Ž4. Metals bound to organic matter: Metals bound to organic matter are extracted by pouring 7.5 ml of a 0.02 M HNO3 solution and 12.5 ml of a 30% H 2 O 2 solution, adjusted to a pH of 2.0, onto the residue from the third procedure and then providing continuous agitation while keeping the temperature of the solution at temperature of 85 " 2⬚C for a 2-h period. An additional 7.5 ml of the 30% H 2 O 2 solution, adjusted to a pH of 2.0, is then added while maintaining continuous agitation and a temperature of 85 " 2⬚C for another 3 h. This solution is then allowed to cool to room temperature Žapprox. 45 min.. An aliquot of 12.5 ml of a 3.2 M NH 4 C 2 H 3 O 2r20% HNO3 solution is added and the entire mixture diluted to approximately 50 ml using deionized water. This solution is agitated continuously for 30 min. Finally, the solution is then centrifuged and the supernatant diluted to 50 ml using a volumetric flask with deionized water. The residue is washed with approximately 20 ml of deionized water and the solution is again centrifuged and the supernatant discarded. Ž5. Residual: Metals in the residual form are extracted by placing the residue from procedure four into digestion bombs and adding 10 ml of concentrated Ž70%. HNO3 . The bomb is then placed into a convection oven set at a temperature of 140⬚C for 2 h or a microwave oven for 45 s. The bomb is taken out and allowed to cool to room temperature. Twenty milliliters of deionized water is added and the solution is centrifuged. The supernatant is poured into a 50-ml volumetric flask and brought up to volume using deionized water. The residue is then discarded. Procedure five digestion parameters have been adjusted according to methods developed previously in Beck et al. w15x.

97

8.8. En¨ ironmental studies using sequential extraction procedures Tessier et al. w49x analyzed the analytical precision of each step of the extraction method using six sub-samples from two sites. Table 9 summarizes the results of this analysis. Precision for samples near the detection limit were generally poor, as expected but improved to 10% or lower when the sample concentration exceeded fivefold the metal detection limit. Lead in one of the Table 9 Detection limits, precision, and accuracy of the sequential extraction procedure as determined on two sediments samples a Fractionb Detection Mean " S.D.c limit Sediments No. 1 ŽSaint Marcel.

Sediment No. 2 ŽPierreville .

Cd 1 2 3 4 5 Z MT

0.1 0.3 0.1 0.2 0.1

- 0.1 - 0.3 - 0.1 - 0.2 - 0.1

- 0.1 - 0.3 0.15" 0.05 - 0.2 - 0.1

0.1

- 0.1

- 0.1

Co 1 2 3 4 5 Z MT

0.5 2.0 0.5 1.4 1

- 0.5 - 2.0 3.6" 0.5 - 1.4 5.4" 0.4 12.9) X ) 9.4 13.2" 1.9

- 0.5 - 2.0 6.4" 0.7 - 1.4 9.2" 0.8 19.6) X ) 16.3 19.5" 1.8

Cu 1 2 3 4 5 Z MT

0.1 0.5 0.4 0.5 1

Ni 1 2 3 4 5 Z MT

0.2 1.1 0.5 0.6 1

1

1

1

0.15" 0.05 3.2" 0.3 4.0" 0.3 5.0" 0.7 7.9" 0.5 20.2" 1.0 25.0" 4.9 - 0.2 1.1" 0.3 6.9" 0.8 1.4" 0.5 17.3" 2.6 26.5" 2.4 28.8" 1.5

0.2" 0 8.2" 0.5 9.1" 0.8 11.3" 1.5 16.4" 1.0 45.2" 1.1 48.6" 4.0d - 0.2 1.9" 0.5 13.2" 0.7 2.7" 0.3 38.4" 3.7 56.2" 4.0 60.2" 1.5

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

98 Table 9 Ž Continued. Fractionb Detection limit

Pb 1 2 3 4 5 Z MT

0.6 0.5 1.0 1.2 1.4 1.4

Zn 1 2 3 4 5 Z MT

0.1 0.5 0.1 0.1 1

Fe 1 2 3 4 5 Z MT

0.4 0.4 50 80 10

1

10

Table 9 Ž Continued. Mean " S.D.c Sediments No. 1 ŽSaint Marcel. - 0.6 2.6" 0.4 3.8" 0.6 2.7" 1.2 7.8" 1.2 16.9" 1.4 18.2" 2.9

Fractionb Sediment No. 2 ŽPierreville . - 0.6 9.4" 5.5d 10.3" 2.9d 7.8" 1.7d 10.1 " 2.0d 37.7" 11.1d 42.5" 6.6d

- 0.1 11.2" 0.6 22.2" 0.5 3.9" 0.2 49.9" 7.8 87.2" 7.2 88 " 2

- 0.1 7.9" 2.0 35.5" 0.6 9.0" 1.3 71.7" 4.8 122.1" 5.4 127 " 5

0.4" 0.1 732 " 33 4630 " 100 620 " 60 30 300 " 1000 36 300 " 1100 36 100 " 260

0.4" 0.1 476 " 21 6910 " 120 1150 " 30 39 500 " 2400 48 000 " 2500 50 400 " 360

sediment samples was found to exhibit low reproducibility, probably due to the heterogeneity of the sediment and not the method. Comparisons of the sum of metals in individual fractions with the total metal concentration showing good agreement for all trace metals with the concentrations measured in completely digested subsamples. Variability in the specific fraction concentrations of lead was also found in the total concentrations. Gauthreaux et al. w17x used the Tessier method of determination of metals in sediments and soils collected at Sabine National Wildlife Refuge located in south-western Louisiana. The work was done to investigate the impact of using dredge spoils to restore lost marshland at the refuge. Table 10 presents typical results of the analysis of two different soils compared to the duplicate sample results. The agreement between results from the sample and sample duplicate was excellent. These variations were within the "10%

Mn 1 2 3 4 5 Z MT e

Detection limit

Mean " S.D.c Sediments No. 1 ŽSaint Marcel.

Sediment No. 2 ŽPierreville .

2.5 9 10 1.2 2

99 " 2 90 " 21 106 " 5 10.9" 0.8 413 " 21

2

768 " 17

38 " 0 314 " 20 265 " 10 30 " 1 456 " 29 1103 " 37 1090 " 30

a

Detection limit, mean value, and standard deviation are expressed in ␮grg of sediment by dry wt. b Following the sequence, 1, exchangeable; 2, carbonate..., Z represents the sum of the five fractions and M T represents the total concentrations. c Unless otherwise indicated, results for six replicate determinations. d A value differing from the mean by more than three times the standard deviation was excluded. e Results for three replicate determinations. This data reproduced with permission, from Table 1, ‘Sequential extraction procedure for the speciation of particulate trace metals’, see Tessier et al. w49x.

expected for differences in sample and duplicate analysis. Table 11 presents the means and standard deviations for chromium, copper, manganese, and zinc for different sites at the refuge and includes samples taken from vegetated and non-vegetated areas. The agreement between sample and duplicate determinations was excellent. No statistically significant differences were found between the concentrations of metals between fractions, except for fractions 2 and 3 for manganese. This difference was explained as being caused by changes in metal chemistry resulting from vegetative growth and decay. Table 12 presents the summed data at each sample site and the standard deviation in the means. The number given in parentheses after the concentrations are the number of samples used to calculate the means and standard deviations. The concentrations of metals measured for sediments taken from the Calcasieu River Ship Channel compare favorably with measurements taken previously in a number of earlier studies ŽTable 5..

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Table 10 Typical results for metal determination in sediment and duplicated using sequential extraction procedurea Sample

Metal Žppm. concentration . Chromium

Copper

Iron

Site IV 11 12 13 1.4 1.5 Total

3.2 2.6 3.6 6.0 9.0 24.4

0.2 0.2 0.2 3.0 7.0 10.6

3.0 5.0 530 2245.0 640.0 3423.0

Site IV 1 D1 1 D2 1 D3 1 D4 1 D5 Total

3.2 2.8 2.6 5.6 10.8 25.0

0.8 0.2 0.8 4.2 7.8 13.8

Site V 11 12 13 1.4 1.5 Total

2.4 2.0 2.0 3.8 6.4 16.6

Site V 1 D1 1 D2 1 D3 1 D4 1 D5 Total

2.0 2.8 3.4 3.4 10.8 22.4

Manganese

Nickel

Lead

Zinc

13.6 10.0 10.0 15.0 2.0 50.6

0.5 0.5 1.0 4.0 7.2 13.2

0.1 0.2 0.9 1.4 1.0 3.6

6.6 2.6 10.0 8.4 14.2 41.8

2.0 5.0 355.0 2430.0 900 3692

13.2 10.0 20.0 20.0 2.0 65.2

0.5 0.5 0.6 1.8 6.2 9.6

0.1 0.5 1.1 1.4 1.2 4.3

4.8 3.0 4.6 6.0 6.2 24.6

0.4 0.4 2.8 7.0 3.0 13.6

2.0 5.0 1500 8820.0 11 100 21 427.0

18.8 50.0 35.0 165.0 20.6 289.4

0.5 1.0 3.6 3.8 6.8 15.7

1.2 1.6 0.2 5.8 3.0 11.8

42.0 5.0 1610.0 8100.0 10 300.0 20 057.0

24.0 30.0 50.0 85.0 3.0 192.0

0.5 0.5 2.6 3.4 5.6 12.6

2.8 4.8 8.0 13.6 13.0 42.2

0.2 0.3 1.4 3.1 1.7 6.7

8.8 2.4 7.0 7.4 2.8 28.4

a Sample identification is as follows; Site Vs ship channel, Site IV s reference site, 1 s replicate, Ds duplicate, and 1᎐5 s fractions 1᎐5.

To better understand the relationship between sampling stations and metal concentrations between stations Gauthreaux et al. w56x used the following statistical tests. This is one of many statistical methods that can be used. The method involved placing of the sampling stations into three predicted groupings representing native soils and a reference marsh; ship channel sediments, sites previously restored and a recently restored site devoid of vegetation, and a third site that was a recently restored site that had become vegetated. These groupings were selected mainly due to the similarities in metal concentrations. In this

determination, chromium, copper, iron, manganese, nickel, lead, and zinc were determined and compared. To test whether the groups could be separated and distinguished by metal concentration, a multivariate analysis of variance ŽMANOVA. was used. Group differences were highly significant with respect to metal concentration Ž P- 0.05.. Since no information is obtained to determine the differences caused by the individual metals between the station groupings, a univariate analysis of variance ŽANOVA. was used to determine the effect of each metal. They found that only the concentrations of iron, manganese,

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Table 11 Means and standard deviations for chromium, copper, manganese, and zinc concentrations Žppm.. Duplicate determinations for Site II vegetated and non-vegetated a Fraction

Metal Chromium

Copper

Manganese

Zinc

Site 1, ¨ egetated 1 1.0" 0.4 2 0.6" 0.5 3 2.4" 1.2 4 1.6" 0.8

0.4" 0.4 0.6" 0.3 0.6" 0.1 2.0" 0.3

13.6" 5.9 246.5" 60.0 158.2" 60.1 35.6" 15.0

1.5" 0.7 5.0" 0.6 19.1" 8.0 5.8" 0.9

Site 1, non-¨ egetated 1 1.8" 0.9 2 1.4" 0.8 3 3.0" 1.4 4 3.4" 1.4

0.7" 0.3 1.1" 0.6 0.6" 0.7 3.2" 1.5

5.9" 4.1 103.6" 18.4 381.2" 13.5 156.3" 28.7

2.0" 0.7 5.8" 2.6 16.3" 9.2 7.6" 2.5

a

Means and standard deviations include three samples and three duplicates for non-vegetated Site II and two samples and three duplicates for vegetated Site II.

and zinc varied significantly between the station groups. The remaining metals showed no variations between station groups. A discriminant analysis using Duncan’s multiple range tests was then used to understand the relationship between metals in each station group and to confirm that group means were different. The results given in Table 13 show that an individual observation could be correctly placed in the predicted grouping 91% of the time. This strongly suggested that sequen-

tial extraction techniques produce reliable and reproducible results that can be analytically important. Another important consideration is the selectivity of the sequential extraction procedure. Tessier et al. w57x found that fraction 1 contained extremely low concentrations of silicon, aluminum, and sulfur and organic matter implying that the treatment with MgCl 2 will not affect the dissolution of silicates, sulfides, or organic matter. They found that all carbonates are dissolved in sodium acetateracetic acid at pH 5.0 based on the absence of dolomite X-ray diffraction patterns in the extracted soil samples. The complete absence of silicon, aluminum, and sulfur suggest that this solution did not appreciably dissolve the silicates, sulfides or organic matter. The metals bound to iron-manganese oxides were extracted in hydroxylamine-hydrochlorideracetic to prevent the dissolution of organic matter and silicates. The low levels of aluminum and silicon in the extracts proved that the matrix materials were not appreciably dissolved and the organic content of the sediments was also undiminished after treatment. The use of peroxide to dissolve the organic phase was found to have a minimal affect on the silicate minerals in the sample. This is shown by the almost complete absence of silicon and aluminum in the extracts. The remaining metals were extracted using a complete dissolution of the residue using HF-HClO4 .

Table 12 Mean metal concentrations Žppm except for Fe which is %. and standard deviations by sampling sites a Site

Chromium

I II III Žbefore. III Žafter. IV V a

18.5 Ž6. "2.0 21.8 Ž22. "2.9 19.5 Ž6. "2.5 18.1 Ž6. "3.8 23.6 Ž14. "2.9 21.4 Ž14. "4.5

Copper

Iron

Manganese

Nickel

Lead

Zinc

11.0 Ž6. "3.1 14.5 Ž22. "6.2 10.0 Ž6. "3.5 13.6 Ž6. "1.8 10.6 Ž4. "6.2 9.9 Ž14. "3.2

1.82 Ž6. "0.61 1.95 Ž11. "0.55 0.41 Ž6. "0.22 1.91 Ž3. "0.35 0.35 Ž4. "0.55 2.10 Ž12. "0.61

210 Ž6. "90 640 Ž22. "120 151 Ž6. "30 648 Ž6. "145 56.2 Ž3. "120 580 Ž14. "220

20.4 Ž6. "2.5 19.5 Ž11. "3.0 10.4 Ž6. "2.8 12.1 Ž3. "3.2 17.8 Ž11. "3.0 14.6 Ž12. "3.5

6.4 Ž5. "0.7 8.3 Ž9. "0.9 6.8 Ž4. "0.8 5.6 Ž2. "0.4 4.3 Ž3. "0.9 5.6 Ž9. "0.8

47.1 Ž6. "5.4 55.5 Ž22. "11.5 36.5 Ž6. "4.1 41.0 Ž6. "8.1 33.0 Ž4. "11.5 41.6 Ž14. "4.1

Numbers in parentheses are the number of samples used in calculating the means.

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Table 13 Discriminant analysis of metal data classifying metal concentration in each station grouping Actual group

Number of cases

Predicted group membershipa 1

2

3

1

45

38 85.0%

5 10.5%

2 4.5%

2

105

2 1.8%

95 90.6%

8 7.6%

3

133

0 0.0%

10 7.8%

123 92.2%

a

Percent of group cases correctly classified were 92.2%.

Gauthreaux et al. w56x used this method of sample digestion to study the impact of using dredge spoils to restore marshland at Sabine National Wildlife Refuge located in south-western Louisiana. Fig. 19 gives a map of the sampling area and shows the location of the sampling sites. The significant loss of marsh have led to proposed restoration projects utilizing dredge spoils from the Calcasieu Ship Channel to restore lost marsh at the Sabine National Wildlife Refuge. The introduction of these spoils appeared to degrade the restored areas and it became necessary to understand this problem and formulate a solution. Samples analyzed were selected based on their location and different characteristics of the sample sites Ži.e. vegetated sediment, non-vegetated sediment, ship channel sediment, etc... Five sample locations were selected and were designated Sites I᎐V. Site I was an area of marsh that had been restored 14 years earlier and was divided into two sections designated Site I ŽINNER. and Site I ŽOUTER.. Site II was a site restored only 3 years prior to study and was divided into two sections designated Site II ŽVEG. and Site II ŽNONVEG.. Site III was a site being restored during the study period and was divided into two parts Site III ŽPRIOR. and Site III ŽAFTER. ᎏ which represented samples collected prior-to and after restoration. Site IV was a undisturbed reference marsh and Site V was the Calcasieu Ship Channel from which dredge spoils were taken. The averaged concentrations for chromium, copper, iron, manganese, nickel, lead, and zinc

are given in Table 14 for each sampling station. The values reported are means for the sums of five summed fractions for each station. No significant variations were observed for the average concentrations of chromium, copper, nickel, and lead across the five sampling sites. Significantly

Fig. 19. A map of the sampling area at Sabine National Wildlife Refuge including the locations of the five sampling sits and the types of samples collected in the sites. Reprinted, with permission, from Gauthreaux et al. w56x.

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Table 14 Mean concentrations Žmgrkg or ppm. and standard deviation on the mean for selected metals in each extracted fraction from selected sample sites Metal

Site I-IN

Site I-OUT

Site III-PRIOR

Site II-AFTER

Site-IV

Copper Chromium Iron Manganese Nickel Lead Zinc

11.5" 2.1 19.8" 1.6 21 934 " 2230 199.6" 75.8 21.6" 2.8 6.2" 0.4 53.7" 4.4

10.6" 4.1 17.5" 1.8 14 157 " 4010 92.0" 9.7 19.5" 2.3 6.4" 1.1 37.2" 5.8

10.8" 6.3 30.1" 2.7 13 064 " 1450 135.7" 44.0 16.0" 2.4 6.6" 0.4 34.6" 6.1

13.6" 1.3 18.1" 3.1 8674 " 685 648.5" 89.6 13.4" 2.1 5.7" 0.7 4.1" 5.2

10.6" 2.8 23.6" 1.4 3160 " 520 56.2" 5.8 10.5" 1.3 4.7" 2.2 33.0" 6.8

higher concentrations of manganese were found at Sites I, II, and V when compared to the reference site ŽSite IV.. A similar pattern was found for iron concentrations with the inclusion of elevated levels of iron at Site III, while zinc concentrations were found to be elevated at Sites I and II in comparison to the reference site. The results obtained using the sequential extraction procedure and summing the fractions yield results that agree well with earlier studies on the Sabine National Wildlife Refuge w12,14᎐16,41,58x. Concentrations of copper, chromium, manganese, and zinc for ship channel sediments found in these studies range from 7 to 27 ppm for copper, 10᎐59 ppm for chromium, 0.8᎐2% for iron, 590᎐670 for manganese, 8᎐22 for lead, and 36᎐84 ppm for zinc. The concentrations found compared favorably with those found in previous studies, which are considered to be baseline levels for the study area. Table 5 summarized some of these results and agreement between investigators is excellent. Another major purpose of this project was to determine whether dredge spoils could be used to reclaim marsh that was lost due to subsidence without affecting local biota. For this to be determined, the availability of the contaminant metals had to be evaluated. Bioavailability of metals is controlled by the metal concentration, the species of the metal, and the surrounding flora and fauna. Sampling locations are grouped according to the project sites from which the samples were taken. Metal concentrations are compared for Ship Channel, vegetated Site II and non-vege-

tated Site II samples in Table 15. Fig. 20 shows greater than 85% of copper is bound in the organic and residual fractions, while 50% of chromium is contained in the residual fraction, with the remainder spread evenly throughout the other fractions. Site V and Site II ŽNONVEG. samples have approximately 50% of the manganese bound in the carbonate and manganese oxide fractions, whereas Site II ŽVEG. samples Table 15 Comparison of the mean metal concentrations in extracted fractions comparing ship channel dredge spoils with vegetated and non-vegetated soils taken from Site II at Sabine National Wildlife Refuge Fraction

SC ppm by fraction Metal Copper

Chromium

Manganese

0.8" 0.5 1.0" 0.5 0.9" 1.2 4.3" 2.4 3.6" 2.0

2.7" 0.8 2.4" 0.5 2.5" 0.5 3.6" 0.6 10.3" 2.8

25.4" 13.7 206 " 202 156 " 141 84 " 48.2 13.4" 5.1

Non-¨ egetated ppm by fraction 1 0.5" 0.4 2.5" 0.8 2 0.8" 0.6 2.1" 0.8 3 0.5" 0.6 2.7" 0.6 4 4.6" 2.1 3.6" 0.9 5 7.1" 3.4 8.5" 1.5

17.7" 7.7 237 " 68.6 236 " 698 117 " 57.1 27.3" 9.7

2.8" 1.7 6.6" 4.6 10.4" 3.4 9.4" 2.2 17.1" 5.1

Vegetated ppm by fraction 1 0.4" 0.2 3.0" 1.3 2 1.0" 0.7 2.4" 1.4 3 0.5" 0.4 3.1" 1.2 4 4.1" 2.3 3.6" 1.2 5 9.7" 9.4 10.2" 2.4

8.1" 7.7 97.7" 66.2 350 " 89.2 163 " 29.8 29.1" 9.1

2.3" 1.0 6.1" 2.1 20.8" 6.1 11.5" 11.4 23.9" 11.3

1 2 3 4 5

Zinc 5.6" 10.1 5.8" 3.0 9.9" 1.7 8.0" 3.7 9.9" 4.1

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

appear to have a different pattern with over 75% in the manganese oxide and organic phases and an increase in the residual phase ŽFig. 21.. This change in pattern is unique for Site II and may suggest uptake of manganese by the local vegetation and subsequent buildup in detritus For Site V sediments, a definite correlation for manganese was observed between samples collected before dredging ŽBD. and those collected after dredging ŽAD.. The highest percentages of manganese are contained in Fraction 2 for BD samples and in Fraction 4 for AD samples. The most probable cause for this sporadic variation

103

seems to be the differences in grain size and composition of the sediments w16x. The total manganese concentrations indicate a large variation in concentrations between Site I ŽINNER. ᎐ Ž332 ppm. and Site I ŽOUTER. ᎐ Ž92 ppm.. Site I ŽOUTER. sampling locations have significantly lower manganese concentrations than Site I ŽINNER. sampling locations. Complete coverage of Site I by dredge spoils from the Ship Channel occurred during the same dredging periods, indicating that variations in manganese concentrations should not be as large as those observed. One possible explanation for this dis-

Fig. 20. Variation of the concentrations of copper, chromium, zinc, iron, nickel, and lead by fraction and site. The sites are identified as Sites: I-IN Ž ., I-OUT Ž ., and IV Ž ..

104

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

Fig. 21. Variation in the concentration of manganese by fraction and sites.

crepancy may be the location of the sampling sites. Site I ŽOUTER. is located just west of the Ship Channel adjacent to several minor streams ŽFig. 19.. Site I ŽINNER. was located in the center of Site I and farther than Site I ŽOUTER. from any waterways. The soils in Site I are typical regional soils and have a very acidic surface layer. This may allow for acid leaching to occur at Site I ŽOUTER., particularly when the area is partially flooded by surrounding streams, causing depletion of manganese. Another explanation may be that Site I ŽOUTER. was never covered by spoils; thus the concentration may reflect the typical soil concentrations.

Samples for Site II were grouped by the existence of vegetation. Indigenous vegetation was slow to repopulate the area where dredge spoils had been used and concern over this impact led to this study. Results in Fig. 21 reveal a shift in manganese from Fraction 2 of non-vegetated samples to Fractions 3 and 4 of vegetated samples. A plausible explanation for the shift of manganese into Fraction 3 Žironrmanganese oxides. is the oxidation of manganese Žq2. increases in aerated soils that are periodically flooded with alkaline, saline water. When vegetation begins to grow on the soils, the root systems allow better aeration and, thus, greater access to oxygen by

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

manganese within the soils. As manganese oxides are produced they are precipitated and then accelerate the oxidation of manganese. Manganous ions are selectively adsorbed onto manganese oxides and as manganese oxides are formed, the surface area is increased, thereby increasing the rate of adsorption of manganese Žq2. ions. The shifting of manganese into Fraction 4 of the vegetative samples is probably due to an increased supply of organic matter caused by decaying vegetation. When the pH is above 6, manganese Žq2. ions form complexes with organic matter causing an increase in manganese concentrations in Fraction 4 for the vegetative samples. Feijtal et al. w21x used a sequential extraction procedure to determine metal accumulation in sediments taken from freshwater, brackish, and saltwater lakes located in the Barataria Bay, south-eastern Louisiana. Their method included the extraction of exchangeable cations using oxygen-free 2 M sodium acetate at a pH of the interstitial waters. The samples were shaken for 12 h, centrifuged, and the supernatant extracted under argon atmosphere w20,59x. Metals released upon reduction were extracted using the method described by Chao w60x and Chao and Zhou w61x. Manganese was converted to soluble manganous ions using 0.1 M hydroxylamine hydrochloride at pH 2. The samples were shaken for 30 min, centrifuged, and the supernatant separated. The separated solids were then exposed to 0.25 M hydroxylamine hydrochloride in 0.25 M hydrochloric acid. The samples were shaken in a hot water bath at 50⬚C for 30 min. Total sediment concentrations of metals were determined using a nitric-perchloric acid digestion w62x. Feijtal et al. w21x found that metal distributions in sediment from Barataria Bay correlated strongly with the organic carbon, while clay and silt content were poor indicators of metal distributions between extracted fractions. The concentration of cadmium, lead, nickel, copper, and zinc correlated strongly with the amount of hydrous iron and manganese oxides. Approximately 50% of heavy metals found in these sediments were bound to the iron and manganese oxides. With the exception of manganese, significant amounts of the studied metals were not found in

105

the dissolved and exchangeable fractions. A significant fraction of the manganese was found to associated with these fractions, suggesting that manganese may actually be present in the soluble manganous ion. The analytical results obtained using sequential extraction techniques can yield accurate, reliable, and significant insights into the geochemistry of metals entering the water sediment interface. Many factors including pH, Eh, organic content, presence of sulfides, etc., significantly affect the distribution and redistribution of trace metals in the environment. However, it is evident that trace metals tend to bind to chemical sites on the sediments that are largely resistant to minor changes in factors that would tend to redissolve these metals, reducing dramatically their environmental impact and ultimate hazard to biota. 8.9. Techniques and methods using toxicity characteristics leaching procedures The Environmental Protection Agency w30x developed the Toxicity Characteristics Leaching Procedure ŽTCLP. to determine the mobility and leachability of contaminant trace metals and organic compounds in waste material such as sludges, industrial process wastes, contaminated soils and sediments, etc. The TCLP extraction method is summarized in the following manner. Dry samples Ž20 g. were weighed into polyethylene extraction bottles along with a 20:1 ratio of liquid extractant to dry sample. Sediment samples were slightly alkaline so US EPA extraction fluid 噛1 was used. This solution was 0.100 M glacial acetic acid and was tested to ensure the pH was 2.88" 0.10. All solutions were made using American Chemical Society ŽACS. reagent grade glacial acetic acid and American Standard Testing and Materials ŽASTM. Type 2 water. The extraction bottles were sealed, placed in a standard tumbler and tumbled for a period of 18 h. This time is theoretically long enough to allow steady state dissolution and mobilization to occur for samples - 9.5 mm in diameter. Samples in this study were ground to - 0.85 mm that has sufficiently small grain sizes to allow steady state conditions to be met. After tumbling, the samples

J.N. Beck, J. Sneddon r Microchemical Journal 66 (2000) 73᎐113

106

were filtered through acid treated ŽHNO3 . 0.6-␮m glass fiber filter paper using pressure filtration. The solid phase was discarded and the eluant was placed in acid ŽHNO3 . rinsed polyethylene bottles. All samples were stored at 4⬚C until analysis. The following is an example of one investigation using the TCLP extraction technique to investigate pollution and the possible leaching of contaminate metals w63x. The study was done along Bayou d’Inde, a major tributary of the Calcasieu River located in south-west Louisiana. This Bayou has historically and is presently receiving industrial and municipal wastes and is locally known for its level of contamination w12,14,15,41,58,64x.. The US EPA TCLP method w30x was designed as an extraction procedure to determine the possibility that extracted metals would exceed the primary drinking water standards for maximum contaminant levels ŽMCLs. in water bodies w30x. Core samples were collected along the Bayou in areas where contamination was known to be the highest. Wide variations in metal concentrations between core depths shows the stratification of

contaminant metals with depth and also the highly localized nature of contamination along the bayou. TCLP extractions of Bayou d’Inde sediments are given in Table 16 along with the primary and secondary maximum contaminant levels ŽMCLs. in drinking water Žreported as mgrl.. This analysis was designed to classify waste as to its ultimate hazard and to predict long-term behavior of the contaminants. The US EPA in an attempt to quantify the hazard established the guidance that metal concentrations in extracts would not exceed 100 times the MCL for that metal. When this criterion is met the waste would not be considered hazardous. The TCLP analyses presented in Table 17 reveal that extracted samples did not exceed the criteria set by the US EPA of 100 times the MCLs. Copper and zinc concentrations were always found to be below the MCLs. Duplicate sample analyses suggest that the TCLP extraction procedure yield reproducible results for the studied sediment samples.

Table 16 TCLP extracts Žin ppm. from sediments taken from Bayou d’Inde along the primary and secondary water quality standards and TCLP limits a Core

Sample depth Žcm.

I

1 29 55

II

III

Copper

Mercury

0.3 1.5 0.5 Ž2.1.

1.2 1.3 1.6 Ž1.6.

- 0.001 0.035 0.003 Ž0.009.

2.0 5.0 3.0 Ž5.4.

18 4.8 2.3 Ž5.1.

1 29

0.5 0.2

1.1 0.3

- 0.001 - 0.001

1.0 1.0

4.6 0.8

1 24

0.2 0.2 Ž0.3. 0.2

1.2 1.1 Ž1.3. 1.2

0.08 Ž0.05. 0.1

0.3 Ž0.05. 0.3

50 IV

1 22

MCLs TCLP MCL = 100 a

Chromium

0.1 10

Reprinted, with permission, from Hardaway et al. w63x.

1.3 130

Lead

0.005 0.002 Ž0.005. 0.006

2.0 1.0 Ž2.0. 2.0

- 0.001 Ž0.004. 0.002

0.8 Ž2.0. 0.8

0.002 0.2

1.3 130

Zinc

11 11 Ž12. 19 0.9 Ž1.3. 2.7 5 500

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107

Table 17 Milligrams of chromium, copper, mercury, lead, and zinc in 20-g sediment samples used in TCLP extraction along with the percentage of metal extracted a Core

Sample depth Žcm.

Chromium

Copper

mg

%ext.

mg

%ext.

I

1 29 29dup. 55 55dup.

1.3 2.4 2.5 4.6

4.5 12.5 16.8 2.2

3.1 10.7 10.5 13.2

II

1 29

1.7 0.3

5.8 15.4

III

1 25 25dup. 50 50dup.

0.9 0.9 0.9 1.3 1.2

IV

1 22 22dup.

0.2 0.3 0.2

Mean S.D. a

Mercury

Lead

Zinc

mg

%ext.

mg

%ext.

mg

%ext.

7.6 2.4 3.0 2.4

0.044 0.038 0.040 0.200 0.220

- 4.5 18.4 ND 3.0 0.8

1.4 2.4 2.2 12.8

29 42 50 5

3.1 3.1 3.4 7.8

12 31 30 6

4.0 0.2

5.5 27.3

0.032 0.002

ND - 9.1

2.3 0.2

9 49

2.6 0.4

35 44

4.6 4.4 6.5 3.1 ND

3.1 2.2 2.4 2.9 3.6

7.8 10.0 10.7 8.3 ND

0.098 0.078 0.070 0.110

1.0 0.5 1.4 1.1

1.6 1.4 1.4 1.6 1.6

26 14 29 25

4.6 3.7 3.7 4.2 3.9

48 60 45 57

8.3 3.6 8.3

0.3 0.2 0.2

23.1 30.0 4.5

0.005 0.001

-4 28.0

0.4 0.3 0.3

40 57 47

0.6 0.4 0.3

31 56 45

7 5

11 10

7 10

32 17

38 16

Reprinted, with permission, from Hardaway et al. w63x. ND, not detectable.

Core samples taken from Bayou d’Inde in south-west Louisiana revealed unusually high metal concentrations in sediments. The concentrations of chromium ranged from 12 to 230 ppm, copper: 10᎐660 ppm, mercury: 0.03᎐11 ppm, lead: 11᎐640 ppm, and zinc: 16᎐390 ppm, showing the extent of contamination. TCLP extractions carried out on fourteen sediment samples indicated that 7᎐40% of the studied metals leach when extractions are carried out in weak organic acids. Metals Ž60᎐90%. were found to bind to sediments, probably to organic andror lattice sites, that are resistant to leaching. Complexation to organic molecules found in high abundance in Louisiana waters or to lattice sites in clay minerals, amorphous solids, etc., probably account for reduced leach rates measured. Metal concentrations in TCLP extracts from sediment samples did not exceed the US EPA maximum contaminant levels. The use of the TCLP extraction procedure

can produce interesting results related to the toxicity of metals bound to sediments.

9. Analysis of mercury in sediments 9.1. Techniques and methods of measuring mercury in sediments The presence of mercury in sediments are measured almost exclusively using the classic cold vapor procedure outlined in Standard Methods Ž1998. and method 245.5 found in US EPA w65,66x, as originally developed by Hatch and Ott w7x. The method involves weighing a sample of soil or sediment into a 250-ml BOD Žbiochemical oxygen demand. bottle to which 6 ml each of concentrated sulfuric and nitric acids are added. Deionized water Ž25 ml. is added followed by the addition of 15 ml of potassium permanganate, the

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sample is then digested at 95⬚C for 2 h in a water bath. After cooling, 10 ml of hydroxylamine hydrochloride is added to reduce the remaining permanganate ion. A set of weighed standards is also prepared along with the samples. A reagent blank or two are also prepared with the standards. Generally the mercury is prepared using serial dilutions of a certified standard solution of mercury, usually with a concentration of 1000 ppm. The standards are prepared by having 0.5, 1.0, 2.0, and 5.0 ␮g of mercury in separate labeled bottles. The samples are then taken to an atomic absorption spectrophotometer fitted with the aerator and mercury cell Žreplaces the burner head. designed for the instrument. A mercury hollow cathode lamp is used as the energy source. Stannous chloride Ž6 ml. is then added and the sample bottle immediately attached to the aerator, because the stannous chloride reduces the mercuric ions to elemental mercury. Mercury is purged from the solution with the airflow and then passes through the sample cell. The peak absorbance is then recorded for each sample and standard. The absorbance of standards are then plotted against known concentrations and a Beer’s Law plot is obtained. The concentrations of mercury in the samples can then be calculated. The choice of spectrophotometers is only dependent on the presence of an atomic absorption spectrophotometer, mercury cold vapor lamp, BOD bottles, and the cold vapor attachment being present in the laboratory. There are also a wide variety of specialized spectrometers available that are designed as a single metal Žmercury. analyzer. 9.2. En¨ ironmental studies of mercury in sediments The presence of mercury in the Louisiana environment has become one of major priority health concerns. Reports of mercury in fish has produced a public mania that led Louisiana state agencies ŽLouisiana Departments of Health and Hospitals ᎏ LDHH and Environmental Quality ᎏ LDEQ. to survey the entire state for ‘hot spots’ contaminated by mercury. Mercury concentration levels have been found to exceed the

United States Food and Drug Administration ŽFDA. action level of 1 ppm in many water bodies, including some in Louisiana. Fish consumption advisories have been posted in 29 individual states of the United States. The state of Louisiana under the guidance of the of LDHH and LDEQ set fish consumption advisories for at risk citizens when the mean concentration of mercury in any water-body exceeds 0.5 ppm, slightly below the FDA consumption limits. Sediments contaminated with mercury are assumed to be one of the major sources of mercury. Louisiana Department of Environmental Quality w67x recently published their Phase 1 report that involved preliminary sampling of 38 waterbodies across Louisiana during 1994᎐1995. This report was quickly followed by their second annual report on mercury in water, sediment, and fish in 30 additional sites w68x. They reported that mean mercury concentrations in sediments was 0.170 ppm with a range in values from 0 to 0.631 ppm. They also discovered that the concentration of mercury in sediments did not correlate with tissue concentrations, probably related to the effect of such parameters as pH, Eh, and dissolved oxygen on the methylation of mercury. Henke et al. w69x reported that uncontaminated sediments in the United States had mean concentrations of mercury ranging from 0.01 to 0.2 ppm. The mean value found for Louisiana sediments of 0.17 ppm would suggest that local sediments have not been impacted severely with mercury contamination. Mueller et al. w70x, however, found elevated concentrations of mercury in sediments collected along Bayou Contraband and Bayou d’Inde in south-western Louisiana. Utilizing the cold vapor atomic absorption method described earlier, they collected core samples across the Calcasieu River Estuary as part of an ecological study of the area. The results of that study are shown in Fig. 22. Elevated mercury levels were found only in sediments collected along Bayou Contraband and Bayou d’Inde. The source of mercury in Bayou d’Inde was, probably, discharges from a chloralkali plant that used mercury cells to produce product. The absence of mercury in sediments prior to the onset of plant discharges is shown clearly from the radiochronologically dated sedi-

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low level inputs of mercury to the lake over the past 20᎐40 years. These kinds of results have been repeated often across the coastal zone of Louisiana, indicating no large-scale inputs of mercury. The state of Louisiana has issued three fish consumption advisories, but none in the coastal zone. Inputs of mercury are seemingly site specific and are related to such activities as sewage out-falls, industrial activity including paper production, military firing ranges, etc. It is comforting to note that mercury does not pose a major health risk to residents in Louisiana. 9.3. Summary of results of en¨ ironmental studies Recent advances in atomic absorption spectrometry over the past 30᎐40 years have allowed a rapid and relatively inexpensive method for the determination of metal concentrations in a wide variety of matrices. This technique allowed a sys-

Fig. 22. Demographic plot of mean mercury concentrations in surface sediments. Reprinted, with permission, from Dupre et al. w71x.

ment core data shown in Fig. 22. The elevated mercury levels in Contraband Bayou, although lower in concentrations found in Bayou d’Inde, appear to be related to sewage discharges into the bayou. Fig. 22 also gives a clear indication of the localization of mercury in sediments. The degree that mercury binds to sediments reduces its bioavailability as shown by the lack of correlation between sediment and fish concentrations w68x. Dupre et al. w71x measured mercury in sediment cores taken from Lake Boeuf, south-eastern Louisiana and found low concentrations of mercury with high values ranging up to 0.25 ppm. Fig. 23 reveals a periodicity in their results indicating

Fig. 23. The variation in the concentration of mercury plotted against the sediment depth in two core samples taken from Lake Boeuf, Louisiana. Reprinted, with permission, from Mueller et al. w70x.

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tematic and accurate determination of metals in soils and sediments, but these matrices must be reduced to an aqueous medium. Prior to the introduction of atomic absorption instrumentation, metals were measured using tedious and labor intensive wet methods of analysis involving chemical separations of each metal, followed by quantitative analysis. The introduction of X-ray technology allowed the qualitative and semiquantitative measurement of metals in many matrices. The development of neutron activation analysis allowed multi-metal, non-destructive, and economical Žbased on cost per element. determination of metal compositions of soils and sediments. The ubiquitous availability of atomic absorption spectrometers reduced these techniques to almost a footnote in history and obsolete. The early beginnings of atomic absorption allowed only single element analysis to be done, but a simple change of hollow cathode lamps and instrument parameters allowed aspiration of samples to be repeated for any number of elements. These repeated aspirations of sample into the

flame required a fairly large volume of sample, often reducing the sensitivity of the measurements. The advent of graphite furnace atomic absorption spectrometers produced greater sensitivity for the determination of many elements. The need to introduce only 20᎐50 ␮l of sample to the graphite tube allowed the technician to make smaller dilutions further increasing sensitivity. More recent spectrometers allow multi-metal analysis through the use of multi-lamp turrets and programmable wave-guides that can scan a wide range of wavelengths in a short time. The introduction of inductively coupled plasma ŽICP.-AES instruments truly allows simultaneous multi-metal analysis of many metals. Many applications of the use of atomic absorption spectrometry are found in the literature. This chapter presented a brief summary of the use of this technique to quantify metal concentrations and distribution of metals in soils and sediments in studies done in south-western Louisiana. In order to determine metal concentrations in soils; metals in the soils and sediments must be leached

Fig. 24. Depth profiles in the concentrations of iron, zinc, mercury, chromium, copper, and lead determined in core samples collected from North Lake, Louisiana.

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from the soils and placed in aqueous solution. The choice of dissolution techniques, outlined in this chapter, depend on the requirements of the study undertaken. If absolute concentrations in the matrix are required, the sample must be completely dissolved to ensure that all bound metals are released to the aqueous solution. Often all that is required is to measure trends in the concentrations across a sampling site or with depth in the sediments to obtain historical information. Specialized leaching procedures such as US EPA w45x and Tessier et al. w49x, etc., allow information such as long-term leachability of metals, the binding sites that metals are chemically bound to, bio-availability of metals, etc. These techniques have been applied over the past 30᎐40 years to determine the extent and magnitude of predicted pollution in the coastal zone of Louisiana. Industrial discharges in Louisiana places the State as producing the second highest total emissions of toxic chemical to the environment in the United States. These large-scale discharges to air, water and land have led to public awareness of the probable impact on

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human and ecological health due to introduction of toxic chemicals, including trace metals to the coastal zone. This public awareness has spurred a great deal of interest in the measurement of these contaminants. It has become clear that environmental pollution is isolated to areas near discharge points, generally within a kilometer of the source. This isolation of pollution can be demonstrated by looking at the results of an investigation of trace metals measured in core samples collected in North Lake, a small isolated brackish lake located in Vermilion Bay, Louisiana w72x. Fig. 24 gives the results for the determination of chromium, copper, iron, lead, mercury, and zinc plotted vs. depth of the core. The data reveal concentrations of metals that are similar to baseline concentrations across the coastal zone. It is also interesting to note that for most of the metals measured in the upper 10 cm of the cores there is an increase in concentration. This apparent increase in concentration has often been interpreted as evidence of the introduction of pollutant metals to the sediment. This apparent increase in metal concentration is due to diagenetic

Fig. 25. Variation in the concentrations of chromium, copper, lead, and zinc in Core IV with depth of the core. The depth profiles and metal concentrations in the remaining cores are similar to the variation observed in Core VI. Core VI is thus used to illustrate the variation in metals in Lake Boeuf, Louisiana.

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processes such as redox reaction retaining metals in the aqueous phase at the waterrsediment interface. Another example is a study by Aucoin et al. w39x who measured similar metals in cores taken from Lake Boeuf, a small freshwater lake in south-eastern Louisiana. Fig. 25 summarizes the results determined in core samples for chromium, copper, lead, and zinc. Concentrations of trace metals were similar to expected baseline concentrations for coastal zone soils and sediments. These studies and others presented earlier do not indicate evidence for large-scale inputs of pollutant trace metals to this region, except for areas near known inputs of these trace metals. The use of dredge spoils and other foreign materials to rebuild lost marshland will need to be carefully studied in the future to assess the impact of using these materials on indigenous species and changes in metal distributions in soils.

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Acknowledgements The authors acknowledge the support of US Environmental Protection Agency Grant R-824143-01-00.

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