Geochemical stability of chromium in sediments from the lower Hackensack River, New Jersey

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a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m

w w w. e l s e v i e r. c o m / l o c a t e / s c i t o t e n v

Geochemical stability of chromium in sediments from the lower Hackensack River, New Jersey Victor S. Magar a,⁎, Linda Martello b , Barbara Southworth b , Phyllis Fuchsman c , Mary Sorensen d , Richard J. Wenning b a

ENVIRON International Corporation, 123 N. Wacker Drive, Suite 250, Chicago, IL 60606 USA ENVIRON International Corporation, 6001 Shellmound Street, Suite 700, Emeryville, CA 94608 USA c ENVIRON International Corporation, 13801 West Center Street, Suite 1, Burton, OH 44021 USA d ENVIRON International Corporation, 1600 Parkwood Circle, Suite 310, Atlanta, GA 30039 USA b

AR TIC LE I N FO

ABS TR ACT

Article history:

Elevated levels of chromium, partly attributable to historical disposal of chromite ore

Received 23 August 2007

processing residue, are present in sediment along the eastern shore of the lower Hackensack

Received in revised form

River near the confluence with Newark Bay. Due to anaerobic conditions in the sediment,

4 January 2008

the chromium is in the form of Cr(III), which poses no unacceptable risks to human health or

Accepted 4 January 2008

to the river ecology. However, as water quality conditions have improved since the 1970s, aerobic conditions have become increasingly prevalent in the overlying water column. If

Keywords:

these conditions result in oxidation of Cr(III) to Cr(VI), either under quiescent conditions or

Chromium

during severe weather or anthropogenic scouring events, the potential for adverse

Hexavalent chromium

ecological effects due to biological exposures to Cr(VI) is possible, though the reaction

Sediment

kinetics associated with oxidation of Cr(III) to Cr(VI) are unfavorable. To investigate the

Oxidation

stability of Cr(III) in Hackensack River sediments exposed to oxic conditions, sediment

Geochemical stability

suspension and oxidation experiments and intertidal sediment exposure experiments that

Hackensack River

exposed the sediments to oxic conditions were conducted. Results revealed no detectable concentrations of Cr(VI), and thus no measurable potential for total chromium oxidation to Cr(VI). Furthermore, total chromium released from sediment to elutriate water in the oxidation and suspension experiments ranged from below detection (b 0.01 mg/L) to 0.18 mg/L, below the freshwater National Recommended Water Quality Criteria (NRWQC) of 0.57 mg/L for Cr(III). These results support conclusions of a stable, in situ geochemical environment in sediments in the lower Hackensack River with respect to chromium. Results showed that chemicals other than Cr(VI), including copper, lead, mercury, zinc, and PCBs, were released at levels that may pose a potential for adverse ecological effects. © 2008 Elsevier B.V. All rights reserved.

1.

Introduction

Sediments located offshore from the site designated as “Study Area 7” by the New Jersey Department of Environmental Protection (NJDEP) Hudson County Chromate Project are known to contain elevated concentrations of chromium.

Study Area 7 (SA7) is located along the eastern shore of the lower Hackensack River near the confluence with Newark Bay, Jersey City, New Jersey. The sediment-associated chromium is attributable, in part, to historical releases from a 0.14-km2 former waterfront commercial property that was used for the disposal of approximately 800,000 m3 of chromate ore proces-

⁎ Corresponding author. ENVIRON International Corporation, 123 N. Wacker Dr., Suite 250, Chicago, IL 60606 USA. Tel.: +1 312 873 9730; fax: +1 312 853 9025. E-mail address: [email protected] (V. Magar). 0048-9697/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2008.01.007

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sing residue from 1905 to 1954 (Martello et al., 2007). Other potential sources of chromium in SA7 sediments include bay and upriver sources associated with historical releases from combined sewer outfalls, paint and pigment manufacturers, tanneries, smelters, and metal plating facilities that operated up to the mid-1900s (Iannuzzi and Ludwig, 2004). Chromium commonly exists in the environment in one of two stable oxidation states, trivalent chromium (Cr(III) or Cr3+) and hexavalent chromium (Cr(VI) or Cr6+). The valance state of chromium affects its physiochemical characteristics, mobility in the environment, chemical and biochemical behavior, bioavailability, and toxicity (Martello et al., 2007; Sorensen et al., 2007; Berry et al., 2004). Whereas Cr(III) is an essential nutrient and is considered minimally toxic (Sorensen et al., 2007; Becker et al., 2006), Cr(VI) compounds are considerably more toxic due in part to their greater solubility, mobility, and bioavailability (Nieboer et al., 1988). Anaerobic conditions in the sediments located offshore from SA7 establish the valence state of chromium as Cr(III) (Martello et al., 2007), which poses no unacceptable risks to human health or the river ecology (Sorensen et al., 2007). However, since the 1970s, water quality conditions have improved due to decreasing organic loads, resulting in oxic conditions in the overlying water column. At issue is whether exposure of the sediments to oxic conditions due to increased dissolved oxygen (DO) concentrations, exposure of surface sediments at low tide, or resuspension during storm or anthropogenic scouring events could result in the oxidation of Cr(III) to Cr(VI), thereby increasing the potential for biological exposures to Cr(VI) and adverse ecological effects. It is critical to understand the long-term geochemical stability of Cr(III) in sediments in order to evaluate the effectiveness of an in situ remedy for the site such as monitored natural recovery (MNR) or capping. The distribution between Cr(III) and Cr(VI) in the environment is regulated by redox reactions and the prevailing redox condition. Cr(VI) is thermodynamically stable when released to oxygen-rich environments, but is unstable in anaerobic environments commonly encountered in sediments, where Cr (III) predominates (Martello et al., 2007; Berry et al., 2004). In sediments, Cr(III) is generally favored because the concentrations of reducing agents (e.g., Fe(II), sulfides, and natural organic matter) typically outweigh the concentrations of the oxidizing agents known to oxidize Cr(III) to Cr(VI) (Schroeder and Lee, 1975, Goodgame et al., 1984; Boyko and Goodgame, 1986), and because the kinetics of Cr(VI) reduction to Cr(III) tend to be much faster than the kinetics of Cr(III) oxidation to Cr(VI) (Stanin, 2005; Eary and Rai, 1987). The decomposition of organic matter and reduction of sulfate and iron generate H2S and Fe(II), the primary electron donors that reduce of Cr(VI) to Cr(III) in the environment (Schroeder and Lee, 1975; Masscheleyn et al., 1992; Vitale et al., 1997). Cr(VI) also can be reduced by organic matter such as simple amino acids (Schroeder and Lee, 1975) or humic or fulvic acids (Goodgame et al., 1984; Boyko and Goodgame, 1986). Reduction of Cr(VI) is rapid under reducing or even mildly oxidizing conditions, occurring within minutes to days depending on the reducing agent(s) (Schroeder and Lee, 1975; Stollenwerk and Grove, 1985; Richard and Bourg, 1991; Lin, 2002; Berry et al., 2004). Masscheleyn et al. (1992) reported Cr(VI)

reduction under nitrate-reducing conditions and at a reduction–oxidation potential as high as +500 mV, demonstrating the instability of Cr(VI) even under mildly oxidizing conditions. DeLaune et al. (1998) asserts that Cr(VI) is reduced to Cr(III) at an aerobic redox potential of +350 mV in both soils and sediments. Eary and Rai (1987) reported a rapid reduction of aqueous Cr(VI) by aqueous Fe(II) at pHs ranging from 2.0–10.0, even in oxygenated solutions. In contrast, the oxidation of Cr(III) is typically very slow taking weeks to months (Eary and Rai, 1987). Manganese oxide (Mn oxides, MnO2) and hydrogen peroxide (H2O2) are the only proven natural oxidants for Cr(III) at pH b 9 in the environment (Nico and Zasoski, 2000; Kim et al., 2002). However, the oxidation of Cr(III) by MnO2 under typical environmental conditions is limited by the low solubility of Cr(III) (Saleh et al., 1989), the presence of natural organic matter (Masscheleyn et al., 1992; Eary and Rai, 1987; Kozuh et al., 2000; Kim et al., 2002; Wu et al., 2005), and the presence of cations, such as Ca2+ and Mg2+, that compete for sorption sites on the MnO2 particles (Schroeder and Lee, 1975). As a result, Masscheleyn et al. (1992) found that, in wetland soils, Cr(VI) reduction dominates over possible Cr oxidation even in the presence of high MnO2 concentrations. Although the body of literature uniformly supports the conclusion that Cr(III) is stable in sediments, there is little direct evidence to demonstrate this behavior in the environment. This paper presents the results of two experiments designed to determine chromium oxidation potential under aerobic conditions. Sediment resuspension and oxidation experiments were conducted to investigate the potential for release of Cr(III) or Cr(VI) and other chemicals of concern (e.g., divalent metals, PAHs, PCBs, dioxins/furans, and DDE) in sediment to the water column in response to a sediment disturbance event. An intertidal sediment exposure experiment was designed to investigate potential aqueous release of Cr(III) or Cr(VI) from intertidal surface sediments during low tide, the conditions under which sediments experience the greatest level of oxygen exposure.

2.

Methods

2.1.

Sediment resuspension and oxidation tests

The sediment resuspension and oxidation experiments began with a 1-hour procedure using the methods described by Digiano et al. (1995), followed by a 24-hour prolonged aqueous suspension procedure. One test (Test 1) was performed at the Columbia Analytical Services (CAS), Rochester, NY laboratory and focused on the potential for Cr(III) oxidation to Cr(VI). Another test (Test 2) was performed at Calscience Environmental Laboratories (CEL), Garden Grove, CA and evaluated the release of chemicals other than chromium, including divalent metals, PAHs, PCBs, dioxins/ furans, and DDE, in addition to repeating the evaluation of the potential for Cr(III) oxidation to Cr(VI). Lower Hackensack River sediment located offshore from SA7 was collected from three locations for Test 1 in July 2006, and from one location for Test 2 in October 2006 (Fig. 1), using a hand-held push coring device operated from a sampling vessel. Coordinates were measured using a portable global positioning system (GPS) device. For Test 1, sediment cores

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Fig. 1 – Site map showing sampling locations for the sediment resuspension and oxidation experiment and the intertidal surface sediment exposure experiment.

were used to collect samples from multiple depth intervals (i.e., 0–15 cm, 15–30 cm, and 95–125 cm), representing varying degrees of historical sediment exposure and aging. A ponar grab sampler was used to collect surface (0 to 15 cm) sediment for Test 2. A control sediment sample was obtained from Sequim Bay, Washington. Prior to the start of the tests, sediment samples were homogenized and debris removed using an anaerobic glove box or anaerobic bag under nitrogen. Sediment samples were analyzed for total chromium, moisture content, particle size distribution, and total organic carbon

for Test 1. Test 2 included analyses of metals, polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), organochlorine pesticides, and dioxins/furans. Analytical methods are shown in Table 1. River water collected from the lower Hackensack River, adjacent to SA7, was used for both tests. Water was collected from approximately 30 cm below the water surface from a floating dock located at the SA7 bulkhead during ebb tide for Test 1, in July 2006, and during flood tide for Test 2, in October 2006. All river water was field filtered through an inline 5 μm

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Table 1 – Analytical methods Measurement

additional hour. The remaining water was removed and discarded, and the post-1-hour-test sediment was analyzed for acid volatile sulfide (AVS). The elutriate was analyzed for total chromium, Cr(VI), and TSS (both tests), chloride (Test 1), and for total analyte list (TAL) metals, PAHs, dioxins/furans, PCBs, and pesticides (Test 2). Following collection of samples for chemical testing for Test 1 only, the elutriate was added to beakers and stirred vigorously for another 24 h under aerobic conditions to examine the potential for Cr(III) oxidation to Cr(VI) in dilute aqueous solids suspensions. Aliquots of water were removed at 5, 10, 20, and 24 h during aeration and analyzed for total chromium, Cr(VI), chloride, and TSS. Dissolved oxygen was determined using a DO probe at each time interval. All analyses for Test 1 were conducted by CAS (Rochester, NY), with the exception of the sediment grain size analysis, which was performed by EMCON/OWT (Harriman, NY). The grain size analysis for the Sequim Bay control sediment had previously been characterized by USACE Engineer Research and Development Center (ERDC). All analyses for Test 2 were conducted by CEL (Garden Grove, CA), with the exception of the following analyses: dioxins/furans and PCBs were conducted by Vista Analytical Laboratory (El Dorado Hills, CA), AVS was conducted by Severn Trent Laboratory (Colchester, VT), and grain size analysis was conducted by PTS Laboratories (Santa Fe Springs, CA). Analytical methods are shown in Table 1. Standard QA/QC practices were followed as required by each of the methods used. When analyzing for Cr(VI) in aqueous samples, USEPA Method 7199 requires filtration (0.45 µm); hence, all aqueous samples were filtered prior to analysis of Cr(VI). The CAS method detection limit for Cr(VI) was 0.005 mg/L, and the CEL method detection limit for Cr(VI) was 0.01 mg/L. USEPA Method 6010B, for measurement of total chromium in aqueous samples, is less specific and offers procedures for filtered (0.45 µm) and unfiltered samples. For this reason, aqueous total chromium analyses were conducted on both filtered and unfiltered samples. The CAS and CEL method detection limit for total chromium was 0.01 mg/L. Whole sediment samples relied on total chromium analyses only, based on results reported by Martello et al. (2007) who showed that analytical artifacts can lead to Cr(VI) false positives in whole sediment samples, and based on the understanding that the high solubility of Cr(VI) dictates that, if present, Cr(VI) should be readily detectable in aqueous phase samples.

Method

Total chromium Cr(VI) TAL metals PAHs Organochlorine pesticides Dioxins/furans PCBs TSS TOC DOC Chloride DO Moisture content (% solids) Acid-volatile sulfide (AVS) Grain size

EPA 6010B EPA 7199 EPA 6010B + 7471 EPA 8270C EPA 8081A EPA 8290 EPA 1668 EPA 160.2 Lloyd Kahn or 9060 EPA 9060 or 415.1 EPA 325.2 EPA 360.1 EPA 160.3M 1991 Draft AVS/SEM ASTM D422

prefilter followed by a 0.35 μm filter. A matrix spike was performed for Cr(VI) as required for EPA Method 7199 for the analysis of Cr(VI) in the filtered river water prior to the initiation of the Test 1. The result met quality control requirements, indicating that Cr(VI) could be measured with sufficient accuracy and precision in the existing water matrix. For both tests, wet sediment equivalent to 40 g dry weight was added to 4 L of field-filtered river water in graduated cylinders. The sediment was disaggregated and stirred with stirring rods every 10 min, and aerated aggressively for 1 h; aeration also contributed to mixing and maintained the sediment in suspension. During aeration, water samples were removed from the top of each cylinder and analyzed for total suspended solids (TSS). Dissolved oxygen was monitored at routine intervals by inserting a DO probe into the sediment/water slurry during aeration. Plasticware (graduated cylinders, stir rods, etc.) was used for all metals analysis, and glassware was used for PAH, dioxin/furan, PCB, and pesticide analyses. After 1 hour continual aeration and mixing, the air supply was shut off, the tubing removed, and the sediment was allowed to settle for 1 h. Dissolved oxygen continued to be monitored using a DO probe during the settling period. After 1 h of settling, the elutriate was siphoned, leaving the settled sediment and a small amount of water in each cylinder. For Test 1, the sediment/water remaining in the cylinders was stirred, poured into beakers and allowed to settle for 1

Table 2 – Baseline sediment analysis for Test 1 Analysis

Total Cr (mg/kg) % Solids Grain size (%)

Sample location and depth interval

Gravel Sand Silt Clay

TOC (%) Pre-test AVS (μmol/g) Post-test AVS (μmol/g)

SD-1 (0–15 cm)

SD-1 (15–30 cm)

SD-2 (0–15 cm)

SD-3 (95–125 cm)

Control

4110 63.8 31.4 50.9 14.9 2.8 3.9 31.5 27.3

1570 67.0 12.1 47.3 33.5 7.1 6.3 16.1 13.1

2290 64.8 19.9 57.5 18.9 3.7 3.7 12.6 6.96

1235 60.0 0.0 24.6 73.8 1.6 7.4 31.8 14.9

33.7 45.9 0.0 6.7 50.3 43.0 1.4 b2.18 b5.79

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Table 3 – Baseline sediment analysis for Test 2 (mg/kg, unless indicated otherwise) Chemical

Core (0–15 cm)

Arsenic Barium Cadmium Total Cr Cobalt Copper Iron Lead Mercury Zinc Pre-test AVS (μmol/g) Pre-test AVS (μmol/g) Pyrene 4,4'-DDE Total PCB

2.2.

Grab b1.29 132 3.88 1230 18.5 231 26,400 233 7.32 528 37.1 17.5 4.4 0.024 1.16

49.4 242 6.4 913 10.9 605 26,900 452 20.7 679 33.7 77.3 41 0.33 4.64

Intertidal surface sediment exposure experiment

The intertidal experiment employed two methods for the measurement of Cr(VI) in porewater. For the first method, porewater was extracted via centrifugation at two time points, as soon as possible after collection (approximately 1 h) and approximately 5 h after collection from surface sediment (b1 cm depth) samples. For the second method, in situ porewater samples were collected during low tide (Fig. 1) via direct extraction from the surface 1 cm of sediment using 60mL plastic syringes. This method relied primarily on free standing water skimming the sediment surface. If Cr(VI) were liberated during low tide, the aerobic, thin layer of water skimming the sediment surface would be expected to contain the highest potential in situ Cr(VI) concentrations. Surface sediments (0–1 cm) were collected at low tide from three locations plus one replicate in the intertidal zone in the northern cove area (Fig. 1). Sample locations were selected to represent a range of total chromium concentrations in intertidal areas exposed at low tide (ENVIRON, 2006). Coordi-

Table 4 – Baseline river water analyses for Tests 1 and 2 (mg/kg) Chemical

River water (mg/L)

Chemical

Test 1 suspension and oxidation Total Cr b 0.01 Chloride Cr(VI) b 0.005 DOC Test 2 suspension and oxidation Total Cr b 0.005 Total TCDD Cr(VI) b 0.01 Total PeCDD Arsenic b 0.01 Total HxCDD Barium 0.054 Total HpCDD Cadmium b 0.005 Total TCDF Cobalt b 0.005 Total PeCDF Copper 0.198 Total HxCDF Iron b 0.1 Total HpCDF Lead b 0.01 Pyrene Mercury b 0.0005 4,4'-DDE Zinc 0.153 Total PCB pH 7.2 DOC

River water (mg/L)

6065 5.6

b2.17 × 10− 9 b2.65 × 10− 9 b2.55 × 10− 9 b2.38 × 10− 9 b1.48 × 10− 9 b2.32 × 10− 9 b1.29 × 10−9 b4.54 × 10− 9 b 0.01 b 0.0001 8.07 × 10− 7 1.8

Chemical

Core (0–15 cm) −4

Total TCDD Total PeCDD Total HxCDD Total HpCDD Total TCDF Total PeCDF Total HxCDF Total HpCDF TCDD equiv. % Solids TOC (%) Grain size % Gravel % Sand % Silt % Clay

Grab 6.36 × 10− 3 2.94 × 10− 3 1.69 × 10− 2 6.38 × 10− 2 8.79 × 10− 3 1.51 × 10− 2 3.13 × 10− 2 6.13 × 10− 2 3.59 × 10− 4 58.2 5.7 0.0 49.9 40.6 9.5

3.62 × 10 1.63 × 10− 4 4.20 × 10− 4 1.30 × 10− 3 1.07 × 10− 3 7.15 × 10− 4 6.00 × 10− 4 7.43 × 10− 4 3.02 × 10− 4 47.3 5.6 0.0 0.0 52.1 47.8

nates were measured using a portable GPS device. Sampling was conducted on March 19, 2007 between 13:00 and 15:30, during the lowest tides of the month, and during the period when surface water elevations were less than −1.0 ft mean low–low water (MLLW). Fig. 1 shows that the 0 MLLW and −1.26 MLLW elevations adequately expose intertidal sediment areas at the three target sample locations. On March 19, 2007, the lowest tide elevation was − 1.13 MLLW at 14:42. The following procedures were used to collect and process sediment samples. Visual observation of the sediment bed suggested anaerobic sediment with high sulfide content (black, with noticeable sulfide odors) covered by a thin veneer of brown sediment at the surface. Footprint depressions in the sediment showed that the oxidized layer could be readily identified by its distinctive color, which did not penetrate surface sediment more than a few millimeters. The upper few millimeters of oxic sediment were scraped using clean, location-specific plastic spatulas, and the underlying black, anaerobic, cohesive sediment layer was avoided. Sediment was placed into 2-gallon plastic buckets for further on-site processing and analysis. Sample depths were generally less than 1 cm. Approximately 4 L of sediment was collected from each of the three locations plus one field replicate location. Once inside the on-site work area, the sediment was homogenized by hand mixing in the buckets. Debris (leaf litter, twigs, pebbles and rocks) removal was not required, because the sampling approach allowed for careful collection of sediment avoiding small debris. After homogenization, sediment was distributed onto flat, 1-inch deep plastic trays,

Table 5 – Baseline sediment analysis for the intertidal experiment Sample ID Total Cr TOC Solids AVS AVS (mg/L) (%) (%) (time = 0) (time = 5-h) SD012-250 SD003-050 SD009-050 SD009-050R

71.9 126 158 162

ND = Not detected.

1.5 3.5 3.4 3.3

63.1 36.3 42.7 42.8

ND ND ND ND

ND ND ND ND

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Table 6 – Dissolved oxygen and total suspended solids results for Test 1 SD1 (0–15 cm) SD1 (15–30 cm) SD2 (0–15 cm) SD3 (95–125 cm) Control DO (mg/L)

TSS (mg/L)

1-Hour aeration (15, 30, 45, 60 min) Settling (15, 30, 45, 60 min) Elutriate (after siphoning) 24-Hour aeration (5, 10, 20, 24 h) 1-Hour aeration Elutriate/24-h test

9.6–10.2

9.5–10.1

10.1–10.3

9.0–10.2

9.4–9.6

10.0–10.4

8.0–8.2 9.0 8.1–8.4 954 98

8.0–8.6 9.3 8.1–8.5 1005 212

9.0–9.3 10.3 8.0–8.5 872 106

8.1–8.5 9.9 7.9–8.4 815 71

8.2–8.4 9.0 7.8–8.6 1940 423

8.2–8.3 8.9 8.1–8.4 b 16.7 b1

in a layer no more than 1 cm thick, checked with a ruler. The trays were exposed to the atmosphere for approximately 5 h. Sediment samples (approximately 50 mg) were transferred to amber glass sample containers for total chromium testing and acid volatile sulfide analyses, and to clear glass sample jars for total organic carbon analyses. After 5 h, DO, oxidation– reduction potential (ORP or redox), and temperature were measured using a combination probe field meter inserted into the wet sediment samples. AVS was not detected at time 0, or after 5 h exposure. Porewater samples were collected from sediment via centrifugation. At 0 and 5 h, samples were collected in 60mL centrifuge tubes and centrifuged at 10,000 rpm for 20 min per sample. Multiple tubes were required to collect sufficient porewater for off-site laboratory analyses. After centrifugation, porewater was withdrawn using 60-mL plastic syringes and filtered through disposable 0.45 µm filters. Filtered samples were collected in 20-mL VOA vials with Teflon septa for off-site analyses of Cr(VI). After filtration, if sufficient porewater remained for DO analyses, DO measurements were collected from the centrifuged (unfiltered) porewater samples. In situ porewater samples also were centrifuged for 10 min before being filtered (0.45 µm) to fill 20-mL VOA vials for offsite Cr(VI) analyses. Remaining samples were measured for DO, ORP, and temperature using a combination probe field meter. The use of dedicated disposable plastic equipment throughout the study (e.g., to collect sediment, transfer the material to sample jars, centrifuge and filter samples, and transfer liquid samples) eliminated the potential for sample cross contamination. Samples were stored in coolers with ice until shipment to the chemical testing laboratory. Coolers were delivered by hand at 07:00 the next morning for Cr(VI) analysis within the 24-hour holding period specified for EPA Method 7199.

3.

Blank

Results

Fig. 1 shows sample locations, whole sediment total chromium and AVS concentrations, and porewater hexavalent chromium concentrations for the two suspension and oxidation tests and the intertidal porewater oxidation experiment. Baseline sediment characteristics and chemical concentrations for Tests 1 and 2 are shown in Tables 2 and 3, respectively. Table 4 presents baseline chemical concentrations in Hackensack River water used for Tests 1 and 2. Baseline sediment characteristics and chemical concentrations for the intertidal experiment are shown in Table 5.

Total chromium for the suspension and oxidation experiments ranged from 1235 mg/kg to 4110 mg/kg for Test 1 (Table 2), and from 913 to 1230 mg/kg for Test 2 (Table 3). Total chromium concentrations ranged from 72 to 162 mg/kg for the intertidal experiment. These concentrations represent the broad range of total chromium concentrations recorded at the site (ENVIRON, 2006); the concentration ranges for the suspension and oxidation tests represented some of the highest total chromium concentrations observed in surface or buried sediments in the vicinity of SA7, while the intertidal experiment represented some of the lowest surface sediment concentrations measured at the site. The Sequim Bay sediment control for suspension and oxidation Test 1 contained 34 mg/kg total chromium. Total chromium and Cr(VI) were not detected in baseline river water samples collected for both experiments (Table 4).

3.1.

Sediment resuspension and oxidation tests

Dissolved oxygen was maintained at saturation levels throughout the 1-hour aeration periods of Tests 1 and 2 and the 24-hour aeration period of Test 1 (Tables 6 and 7). The DO results show that aeration generated highly oxygenated conditions in both tests and that elevated DO concentrations persisted during settling periods following aggressive aeration. In Test 1, chloride concentrations were used to monitor evaporation. The baseline chloride concentration was 6065 mg/L. Chloride increased by approximately 10% after 1 hour aeration, and by approximately 4% more after 24 h aeration. Therefore, analytical results for the elutriate are approximately 10% higher than they would have been in the absence of evaporation. Total suspended sediment concentrations in the two resuspension tests are presented in Tables 6 and 7. The higher TSS level measured during Test 2 (2940 to 4520 mg/L) than Test 1 (815 to 1005 mg/L) may be due to differences in aeration and mixing or source differences in particle size distributions. Elutriate TSS concentrations were slightly higher in Test 1 (71 to 212 mg/L)

Table 7 – Dissolved oxygen and total suspended solids results for Test 2

DO (mg/L) TSS (mg/L)

1-Hour aeration (0, 50 min) Settling (50 min) 1-Hour aeration Elutriate/24-h test

Core (0–15 cm)

Grab

8.4–9.7 8.6–9.0 2940–3140 54

8.0–9.3 8.7–9.3 4170–4520 53

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Table 8 – Test 1 suspension and oxidation test results SD1 (0–15 cm)

SD1 (15–30 cm)

SD2 (0–15 cm)

SD3 (95–125 cm)

Control

Blank

Test 1: 1-hour suspension and oxidation test Cr (VI) (mg/L) b0.005 Total Cr (mg/L) UF 0.0678 Filt b0.01

b 0.005 0.1765 b 0.01

b 0.005 0.08955 b 0.01

b 0.005 0.133 b 0.01

b 0.005 0.0212 b 0.01

b0.005 b0.01 b0.01

Test 1: 24-hour suspension and oxidation test Cr (VI) (mg/L) t=5 h b0.005 t = 10 h b0.005 t = 20 h b0.005 t = 24 h b0.005 Total Cr (mg/L) t=5 h UF 0.062 Filt 0.051 t = 10 h UF 0.059 Filt 0.039 t = 20 h UF 0.063 Filt 0.035 t = 24 h UF 0.065 Filt 0.039

b 0.005 b 0.005 b 0.005 b 0.005 0.178 0.097 0.148 0.086 0.116 0.070 0.177 0.083

b 0.005 b 0.005 b 0.005 b 0.005 0.098 0.065 0.084 0.053 0.077 0.038 0.087 0.050

b 0.005 b 0.005 b 0.005 b 0.005 0.109 0.066 0.102 0.057 0.101 0.051 0.107 0.047

b 0.005 b 0.005 b 0.005 b 0.005 0.022 0.018 0.019 0.016 0.017 0.013 0.022 0.018

b0.005 b0.005 b0.005 b0.005 b0.01 b0.01 b0.01 b0.01 b0.01 b0.01 b0.01 b0.01

than Test 2 (53 to 54 mg/L). Higher TSS levels were measured in the Sequim Bay control (423 mg/L), which was likely due to the higher percent silt and clay content of sediments from Sequim Bay as compared to sediments from SA7. Chemical testing of the elutriate after the 1-hour resuspension and oxidation experiment for Test 1 are summarized in Table 8. Cr(VI) was not detected (DL = 0.005 mg/L) at any time in any sediment treatment, despite the vigorous mixing and elevated DO levels maintained for the duration of the tests. After 24 h continued aeration, Cr(VI) remained below the method detection limit of 0.005 mg/L. Hence, there was no evidence that Cr(III) was oxidized to Cr(VI) during Test 1, despite vigorous aeration with relatively high suspended solids concentrations, saturated DO levels, and prolonged mixing and aeration for over 24 h. Total chromium concentrations in filtered water samples were below the method detection limit (0.01 mg/L) at the end of the 1-hour tests. Total chromium was detected in all the unfiltered suspended sediment test samples, including the control sample (0.02 mg/L), and ranged from 0.07 to 0.18 mg/L (0.12 ± 0.05 mg/L) in the four test samples. During the prolonged 24 hour test, total chromium was detected in filtered and unfiltered water samples at each time point (i.e., at 5, 10, 20, and 24 h). The appearance of total

chromium in filtered samples may be due to vigorous stirring and disaggregation of suspended solid particles into colloidal material small enough to pass through the 0.45 µm filters. There were no discernable temporal trends in filtered (p = 0.46) or unfiltered (p = 0.86) total chromium concentrations. Chemical testing of the elutriate after 1-hour suspension and oxidation in Test 2 are shown in Table 9. Once again, Cr(VI) was not detected in any treatment, so there was no evidence of Cr(III) oxidation to Cr(VI). Total chromium concentrations were below the detection limit (0.005 mg/L) in filtered samples and were measured at trace levels (0.034 and 0.068 mg/L) in unfiltered samples. Barium, copper, and zinc were detected in both filtered elutriate samples. Lead was detected in filtered elutriate sample from the grab sample. Chromium and iron were detected in whole elutriate only; therefore these metals were mostly associated with suspended particles in the elutriate. Pyrene, DDE and all other PAH and pesticides were not detected in elutriate, while PCBs and dioxins/furans were detected. Although the holding time of 35 days for mercury was exceeded, no effect on total mercury concentrations measured in sediment is expected. Table 2 shows the concentrations of chromium and AVS before and after the 1-hour resuspension and oxidation

Table 9 – Test 2 suspension and oxidation test results Chemical

Arsenic Barium Cadmium Total Cr Cobalt Copper Iron Lead Mercury Zinc Cr(VI)

Core (mg/L)

Grab (mg/L)

Filtered

Unfiltered

Filtered

Unfiltered

b 0.01 0.068 b 0.005 b 0.005 b 0.005 0.214 b 0.1 b 0.001 b 0.0005 0.137 b 0.01

b 0.01 0.070 b 0.005 0.034 b 0.005 0.221 1.96 0.0196 b 0.0005 0.115 NA

b0.01 0.0608 b0.005 b0.005 b0.005 0.0388 b0.1 0.0467 b0.0005 0.192 b0.01

b0.01 0.070 b0.005 0.068 b0.005 0.319 2.34 0.044 0.0015 0.145 NA

Chemical

Total TCDD Total PeCDD Total HxCDD Total HpCDD Total TCDF Total PeCDF Total HxCDF Total HpCDF TCDD equiv. Pyrene 4,4'-DDE Total PCB

Core (mg/L)

Grab (mg/L)

Unfiltered

Unfiltered

NA NA NA NA NA NA NA NA NA b0.01 b0.0001 NA

2.78 ×10− 8 6.28 ×10− 9 5.19 ×10− 8 2.03 ×10− 7 2.92 ×10− 8 9.72 × 10− 8 1.89 ×10− 7 3.49x10−7 2.15 × 10− 8 b 0.01 b 0.0001 7.58 × 10− 5

110

SC IE N CE OF T H E TOT AL E N V I RO N ME N T 3 9 4 ( 2 00 8 ) 1 0 3–1 11

Table 10 – Dissolved oxygen and ORP results for the intertidal experiment

In situ sediment In situ porewater Centrifuged porewater (t = 0)

DO (mg/L)

ORP (Mv)

0.5 to 2 12.2 to 12.4 11.0 to 12.4

−65 to −148 207 to 250 − 44 to 16

experiment for Test 1. While some AVS was oxidized during the test, substantial concentrations remained, indicating that aeration alone did not fully oxidize AVS.

3.2.

Intertidal surface sediment exposure experiment

Sediment and porewater DO and ORP results are presented in Table 10. Results are for in situ sediment samples (temperatureb 5 °C), in situ porewater (3 of 4 samples for DO, and 2 of 4 samples for ORP, due to sample-size limitations), and centrifuged porewater at time zero. The results indicate that the oxidized layer was successfully collected without introducing underlying anaerobic sediment that could have created reducing conditions during the experiment. Total chromium concentrations ranged from 71.9 to 162 mg/kg in the whole sediment samples. The relatively low total chromium concentrations are consistent with the understanding that total chromium concentrations are lowest at the sediment surface due to natural recovery via natural sedimentation and surface sediment dilution processes, as reported by ENVIRON (2006). Cr(VI) concentrations were not detected (with a detection limit of b0.012 mg/L) in all aqueous samples, demonstrating no measurable oxidation of Cr(III) to Cr(VI). Unlike the suspension and oxidation tests, AVS was not detected in surface sediment porewater.

4.

Discussion

This study was conducted to investigate the stability of sediment-associated Cr(III) exposed to oxygenated water. The 1-hour suspension and oxidation experiment was based on a dredge elutriate test procedure designed by the USACE to simulate sediment and surface water conditions at the point of dredging or other disruption events. The 24-h of additional aeration and mixing were intended to evaluate the potential for Cr(III) oxidation to Cr(VI) during prolonged exposure to oxygenated water. The intertidal experiments were designed

to identify the presence of Cr(VI), if any, in sediments exposed to oxygenated water in situ. Hexavalent chromium was not detected in either of the experiments; therefore there appears to be no measurable potential for total chromium oxidation to Cr(VI) in the presence of saturated dissolved oxygen concentrations. Because the suspension and oxidation experiment was preformed twice using two different laboratories, the results have been shown to be reproducible. The lack of chromium oxidation to Cr(VI) in the presence of saturated dissolved oxygen concentrations is consistent with Martello et al. (2007) who reported the absence of measurable Cr(VI) concentrations in surface sediment (0–15 cm) porewater, and with the slow oxidation kinetics observed by Saleh et al. (1989) and Eary and Rai (1987). Eary and Rai (1987) also found that increases in dissolved oxygen did not influence the rate of oxidation of aqueous Cr(III) by MnO2. The lack of measurable Cr(III) oxidation also is consistent with studies that have found that the oxidation of Cr(III) by MnO2 is limited by the low solubility of Cr(III) under typical environmental conditions (Saleh et al., 1989), the presence of natural organic matter (Masscheleyn et al., 1992; Eary and Rai, 1987; Kozuh et al., 2000; Kim et al., 2002; Wu et al., 2005), and the presence of cations that compete for sorption sites on the MnO2 particles (Schroeder and Lee, 1975). The prolonged residual presence of AVS in the suspension and oxidation experiment demonstrates the large reducing capacity of the sediments in suspension, and is consistent with the literature that shows that chemical reductants in the natural environment are much more prevalent than oxidants (Schroeder and Lee, 1975, Goodgame et al., 1984; Boyko and Goodgame, 1986). The existence of DO in intertidal sediment samples, the saturated DO concentrations in the in situ and centrifuged porewater, and the absence of measurable AVS further demonstrate that the presence of oxygen and relatively oxidized conditions do not drive the measurable oxidation of Cr(III) to Cr(VI) in sediment. These results indicate that, once reduced, Cr(III) remains stable even in oxygenated waters and even in the absence of AVS. Precautions were taken during all experiments to make sure that sampling methods would not contribute to the reduction of chromium. These included the rapid measurement of Cr(VI) within 8 h for the suspension and oxidation tests and within 24 h for the intertidal experiment, and the centrifugation and filtration of all samples on-site before shipping for the intertidal experiment to eliminate organic and inorganic solids that could have contributed to the chemical reduction of chromium during transport and before analysis.

Table 11 – Comparison of chemical concentrations in elutriate to chronic saltwater criteria Chemical

Copper (mg/L) Lead (mg/L) Mercury (mg/L)1 Zinc (mg/L) Total PCB (mg/L)

Core (0–15 cm)

Grab

Filtered

Unfiltered

Filtered

Unfiltered

Chronic saltwater criteria

0.214 b 0.001 b 0.0005 0.137 NA

0.221 0.0196 b 0.0005 0.115 NA

0.0388 0.0467 b 0.0005 0.192 NA

0.319 0.044 0.00145 0.145 7.58 × 10− 5

0.0031 0.0081 0.00094 0.081 3 × 10− 5

Bold and underlined values denote concentrations higher than chronic saltwater criteria.

S CIE N CE OF T H E TOT AL E N V I RO N ME N T 3 9 4 ( 2 00 8 ) 1 0 3–1 11

Although Cr(VI) was not released from SA7 sediments exposed to oxic conditions, there is a potential for releases of other chemicals due to exposure to the conditions maintained during the suspension and oxidation experiment. Table 11 compares the concentrations of chemicals in elutriate with National Recommended Water Quality Criteria (NRWQC). All chemicals with chronic saltwater criteria are shown. Copper, lead, mercury, zinc, and total PCBs exceeded the criteria in one or both samples. Maximum concentrations of total chromium in filtered (0.10 mg/L) and unfiltered elutriate (0.18 mg/L) were below the freshwater acute criterion of 0.57 mg/L for Cr(III) (USEPA, 2002). NRWQC for Cr(III) have not been established by USEPA for saltwater/estuarine environments due to well established limits on Cr(III) solubility and toxicity. These results indicate that there is a potential for releases of chemicals other than chromium at levels that may pose a risk to ecological receptors in response to dredging or other episodic events that disrupt and suspend contaminated sediment.

5.

Conclusions

The conditions established for the experiments reported here were designed to maximize the oxidation potential in surface and suspended sediment samples due to exposure to oxygen. Despite this, no sign of Cr(III) oxidation to Cr(VI) was observed. Therefore, Cr(III) is expected to remain geochemically stable in lower Hackensack River sediments under ambient conditions, severe weather conditions, and anthropogenic scouring events. However, there is a potential for releases of chemicals other than chromium, including copper, lead, mercury, zinc, and PCBs, at levels that may pose a risk to ecological receptors in response to dredging or other episodic events that disrupt and suspend contaminated sediment.

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