Sampling and storage of natural waters for trace metal analysis

Water Research Vol. It, pp. 745 to 7,;6. Pergamon Press 1.977. Printg.d in Great Britain.

SAMPLING AND STORAGE OF NATURAL WATERS FOR TRACE METAL ANALYSIS G. E. BATLEYand D. GARDNER Analytical Chemistry Section, Australian Atomic Energy Commission Lueas Heights. NSW. Australia and CSIRO Division of Fisheries and Oceanography, Cronulla, NSW, Australia (Received 22 December 1976; accepted 31 March 1977)

Alntract--Methods for the collection, preservation and storage of natural water samples for the analysis of trace levels of heavy metals have been critically reviewed, with particular reference to the analysis of zinc, copper, lead, cadmium and mercury. Recommended prodecures are given which minimise the problems of sample contamination and adsorption losses. Carefully cleaned high-density polythene or Teflon containers are recommended for both sampling and storage, with a storage temperature of 4°C. Acidification to 0.05 M H" with nitric acid is desirable, except in speciati0n studies. For mercury analysis the addition of an oxidant or complexing agent is also necessary.

INTROD UCTION

formation of chemical species can occur during storage. Because of the nature of the liquid phase, water samples unlike non-volatile solid samples are particularly susceptible to storage problems, Natural waters are mixtures containing biological and chemical species in dynamic equilibrium. The mere act of sampiing, when the water sample is brought into contact with oxygen and container walls, or subjected to physical changes of temperature and pressure, is often sufficient to disturb this equilibrium. Often, in a haste to provide numbers, such problems have been overlooked and many accepted procedures assumed to be free of contamination or losses have been shown to be otherwise on later, more careful examination (Summers, 1972; Hume, 1973). In this paper, we have reviewed previous reports of sampling and storage procedures for trace metal analyses in natural water systems and, together with results from our own investigations, have attempted to formulate acceptable sample collection, preservation and storage conditions to permit the accurate analysis of trace metal species.

As a result of improvements in instrumental techniques in the past decade, it has been possible to extend the detection limits of analytical methods for many heavy metals to the #g 1-1 level and below. Increasing public concern for the impact of man on his environment, has led to greater demands on the analytical chemist to provide data for trace metals in environmental materials. Methods have now been developed which permit the reporting of the concentrations of most heavy metals in an uncontaminated environment. In the past, there have been many cases of unquestioned acceptance of such data, without cognisance of possible errors. Although the statistical error limits for the particular analytical measurements may be low, large errors can be unwittingly introduced during sampling and storage, either by contamination of the sample or by changes during storage. While such errors have not previously concerned those working at the parts/10 s concentration ranges, their effect can be catastrophic when parts/109 concentrations are being studied (Tolg, 1972; Hume, 1973; Mitchell, 1973). As has been stressed repeatedly before, ~mple colSAMPLE COLLECTION lection is possibly the most important step in trace Ideally, it should be possible to circumvent the many analysis (Hume, 1973; Hamilton, 1976). It~is therefore problems associated with sample collection by the use of essential that sampling be'performed with an aware- in sit~ measurement methods. Although measurement ness of all possible sources of contamination, and pre- probes have been developed for the analysis of copper,, ferably under the direction of an analytical chemist cadmium, lead and other heavy metals in waters (Orion since he is generally responsible for the ultimate pro- Research, 1973; Alexander, 1976), their detection limits under optimum conditiqns are 10-7-10 -s M, which is induction of meaningful result~ Since there is often a sufficiently sensitive for the analysis of unpolluted water delay between the times of collection and anal~,sis, samples. With the possible exception of anedic stripping specific methods for the preservation and storage of voRammetry (a.s.v.) and neutron activation analysis, the sample after collection must be followed to pre- methods for the analysis of heavy metals in natural waters vent contamination and storage losses during this in- generally require the use of a preconcentration step, which precludes their in situ application. While there arc obvious terval. This is expecially important where chemical limitations in the latter case, there are po-~aibilities for the speciation of trace metals is being studied, and trans- use of a.s.v, measurements in situ (Schimpf, 1971; Zirino 745 w.R. t I/'9--A

"6

G.E. BATLEY and D. GARDNER

and Lieberman. 1975). Sample collection is therefore unavoidable in most instances and. because of the ease of heavy metal contamination at #g l - t concentrations, it is essential that the correct type of sampling apparatus be chosen (Brewer, 1975; Riley, 1975). A variety of sampling devices, from plastic buckets to discrete depth samplers have been used (IAEA, 1970). For surface sampling, a plastic or polypropylene bucket attached by a nylon rope is commonly used (IAEA, 1970; Preston et al., 1972; Stem. 1975; Kubota et al., 1974). This technique, however, is likely to collect some of the surface film which is enriched in heavy metal species (Duce et el.. 1972). This problem can be obviated to some extent by the use of high density polyethylene (Polythene) bottles or jerry cans which can be immersed by hand to well below the surface (Zirino, 1970; Florence, 1972). These are advantageous as they do not present a large exposed surface capable of collecting airborne contaminants as do buckets. Care should be taken that cardboard or plastic inserts in the caps of these bottles are removed, or suitably covered, before use. All components of these and other sampling systems should be soaked for several days with 2 M HCI to remove surface contamination. Careful rinsing with distilled water followed by several sample aliquots is then required before sample collection. For depth sampling, samplers are best constructed of Polythene, polypropylene, polycarbonate, Teflon or Perspex (Plexiglas). In all cases, samplers should be free of metal, neoprene rubber or other contaminating materials (Robcrtson, 1968a; IAEA, 1970; Spencer and Brewer, 1970). Metal components should be Teflon.coated; rubber bands should be replaced by Teflon coated springs; and Teflon and PVC caps and O-rings used in boule caps to replace rubber components, With depth samplers, contamination from the hydro-wire in the form of either rust or grease can be a problem, (Betzer and Pilson. 1975) and coated wires have been used (Duursma, 1967). A summary

of commercizlly available water samplers is given in Table i. For heavy metal anabses, several laboratories ha~e reported the use of Van Dorn (Matson, 1968; Kubota e: al., i974: Carpenter er a/.. 1975) or Niskin (Windom and Smith, 1972: Fukai et aL, 1975, Bender and Gagner. 19701 sampling bottles, while Hood (1966) used Nansen bottles for samples to be anal)sed for copper, zinc and manganese. To minimise chemical interaction between sample and sampler walls it is advisable to minimise the surface to volume ratio. The adsorption and leaching characteristics of a I litre Van Dorn botde, constructed from PVC with gum rubber closures, was tested by Matson (1968). A synthetic seawater lost 16% of a 0.03 ~g I- : lead spike by adsorption in one hour, however leaching of up to I #g l- i of cadmium and copper occurred over this time interval. Casts requiring 5-10 rain or less were considered adequate to avoid contamination. We have observed no contamination when using National Institute of Oceanography (NIO) bottles in which the rubber closures were wrapped in thin Potytherie film. Segar and Berberian (t975) compared trace metal contamination introduced by a variety of Niskin samples and a pumping system. Niskin bottles having silicone rubber springs introduced iron and zinc impurities. Zinc contamination occurred after 3 h in bottles having a Teflon-coated coil spring but no contamination was observed using a newly designed "top-drop" Niskin bottle. Pumping systems provide alternative, eXl:)edient ways of obtaining uncontaminated samples (Jeffrey et at., 1973) while permitting, continuous sampling of either vertically or horizontally 'fine" water mass structures (Si~love and Pcarlman, 1972), For shallow waters (<100m), a simple vacuum pump drawing water through Pglythene tubing into a large Buchner flask is all that is required (Abdullah and Royle, 1974). This system, if flask and tube are pro, cleaned with acid, is likely .to be contamination freel For

Table 1. Water sample bottles for trace metal analysis Type Standard sample;'s NIO

Supplier

Institute of Oceanographic Sciences. Wormley, Surrey. U.K.

Keference

Volume (])

Herdman (1963}

1.3

Materials

Special comments

Polypropylene Most other lin/e~ls plutic; weil~ht 1.4ks: and low filler r e v ~ I d~a'e~mNr included; up to 20 p~ neoprene rubber ho/~; also Itrile boVA~ .p to 91 ava/la~e;

colou~ yellow; ~ : n~mm N auer~-n~dilied

Van Dorn

Niskin

Hydrobios KieI-Hokenan. West Germany

Fisher (1968)

Hydro Products San Diego The Kahl Sdentific Instrument Corp. San Dido, Calif. USA. Genend Ocmalcs Inc, Miami. Florida. USA.

Van Dora (19~6)

~,oertl ~

Polycarbonate

~d

replacement with Teflon or Teflon coated corapoeen ct A ~ird 0¢ the wei&ht of original Nan.'n;

transparent pobesrYaouze:~tled by rule apcn~tre p l a ~ bmU valves; memeallerdo~-d; 3-60

Plastica~d

rubber

Finucan~ & M ~ tt961)

ste~ .~r Nhddn Top-drop

1.7

operated lid): mme~ser

rUbb~ . u h and ~

1

strong ~'uld~rb~m4 in Od,Oilat b~ oow a~tldiabie with coeu~ured coat:el PVC ~,topl~rs; nu~dns and safinll llood. Alternative to rubber components required

3-60

ModiScauon or" above

5-9O

PVC

Rcpttce xubb~ bazxd w/th FIFE ~ d ~ m g for tra~ mettl work. External la~x bsndL S~np/~ ~¢mzactsPVC o.iy

<5

Per,~o~

CoDe~on and ~l~ral/~t in .d~u of w ~ . r m

09e~) e~

at.

ln~

~CW~D. IUwo-CSlltO Milehaa. Vie,. 3132 A~slralia

Nisldn b~dlowsbag

Gt-rl~l O ~ u i ~

Go-Flow

General Oceanics inc.

Inc.

Niddn (1%2)

--

Stenie plzst~

1.7-60.

PVC

slafa(~ Hydros',ad¢ pres:;ure activated mechanism opens valves a~ preset depth.

Sampling and storage of natural waters for trace metal analysis deeper waters, a multistage, water-lubricated, axial flow pump made from, or coated with, noncontaminating materials, is required to keep the flow turbulent to overcome friction with the walls of the tubing, and to permit passage of large particles without attrition. Such a system was found by Segar and Berberian (1975) to introduce substantial copper contamination. Carpenter et al. 1975) used a nylon pump and Polythene hose for the collection of 1001 samples for heavy metal analysis from Chesapeake Bay and the Susquehanna River. Alternative pumping systems have been reported by other authors (Preston et al., 1972; Wolfe et al., 1975). When sampling, it is necessary to avoid surface oil slicks, ships' discharges and antifouling paints, in close proximity to the sampling point (Grasshoff, 1969). Shipboard sampling should be performed on the windward side. preferably near the bow. Sampling below oil slicks or surface contamination is best performed by pumping methods or samplers which open and close at the required depths (Table l). An in situ sampling and preeoncentration technique has been reported by Davey and Soper (1975) in which the sample is filtered through Nuclepore filter bags in Polythene containers, and heavy metals are concentrated on a Chelex-100 resin column. In sire concentration techniques eliminate the uncertainties as to the fate of trace metals during storage. Chelex-100 will not of course remove all the dissolved metal fraction of the sampled water (Florence and Batley, 1976). In unpolluted seawater samples the resin-removable fractions for cadmium, lead and copper lie in the range 30-70~ of the total metal concentrations. In polluted waters this fraction will be higher since metal pollutants usually consist of ionic species. The nonretained metal is present primarily as metal adsorbed on fine organic and inorganic colloidal particles. SAMPLE PRETREATMENT

Unless analyses are to be performed immediately following sample collection, care.ful consideration must be given to the manner in which the sample is to be treated prior to storage. This treatment will depend on the analyses required. In general, for trace metal analysis, particulate matter is first removed from the sample by filtration or centrifugation. Preservative reagents may then be added to the sample, and the sample stored in an appropriate container under conditions which minimise contamination or losses of metals from solution. Filtration

Metal analyses are generally reported both on suspended particulate matter and on the 'soluble' metal fraction of the water sample. That fraction which passes a 0.45/am pore size filter is now accepted as defining the dissolved or soluble fraction (Riley, 1975), while the suspended matter is that retained by the filter. In unfiltered samples, contact of the dissolved fraction with particulate matter for extended periods of time is likely to lead to changes in the distribution of chemical forms of heavy metals in solution. Several workers (Duke et al., 1968; Murray and Murray, 1972; Gardiner, 1974) have shown that the equilibrium times for adsorption and desorption of heavy metals in sediment-water mixtures are rapid and less than 72 h. Maximum adsorption occurs at pH values above 7.5. Concentration factors for metals in sediments may be as high as 50,000. With any change in solution equilibrium after collection, adsorption sites provided by particulate matter will provide a path for removal of metal species (Murray and Meinke, .1974) while under some conditions, resorption of adsorbed metal is possible. High bacterial concentrations associated with sedimentary material will also lead to depletion of soluble metal species (Lee and Hoadley, 1967). McLerran and Holmes

747

(1974) have reported the removal of 85~o of added 65Zn, and 70~/o of added t°gCd, by a bacterial culture in two hours. The growth of bacteria and algae involves photosynthesis and respiration which will give rise to changes in the carbon dioxide content of the water and therefore in its pH. Changes in pH may result in precipitation, changes in the degree of complexation and adsorptive behaviour, and in the rate of redox reactions involving heavy metal species in solution. Because of the unpredictable nature of bacterial growth in stored samples (Moebus, 1972) it is advisable that filtration be performed as soon as possible after sample collection. If this time is in excess of several hours, the sample should be chilled (not frozen) to near 4°C to retard bacterial growth (Carpenter et al., 1975) until filtration can be completed. For filtration of water samples a wide variety of membrane filters is now commercially available. These are made from cellulose, cellulose esters, Teflon, nylon, polycarbonate, polyvinylchloride, polyamide, glass fibres and silver foil. For trace metal analysis of water samples, polycarbonate or cellulose ester filters under the brand names Nuclepore, Sartorius, Millipore and Gelman are commonly used. Filters of the same nominal pore size have been shown to vary in the speed of filtration and particulate retention (Stem, 1975; Wagemann and Brunskill, 1975) and in trace metal contamination (Robertson, 1968a, 1972; Spencer and Manheim, 1969; Chau, 1971; Bate et al., 1975). Spencer and Manheim (1969) indicated that metal contamination from filters is not significant for sample volumes greater than 101. Our experience suggests that for smaller sample volumes careful washing of the membranes in the filter holder, with dilute nitric acid (20 ml) followed by distilled water (10Oral) and sample (500 ml) prior to collection of the filtrate is necessary to minimize contamination. Filters of 0.45 #m pore size retain all phytoplankton and most bacteria. Continued filtration can lead to clogging of pores with a reduction in pore diameter as filtration proceeds. This can be overcome by more frequent replacemerit of filters in samples with a high content of suspended matter, or by use of stirred pressure filtration. The type of filtration apparatus to be used is also an important consideration. Thought should be given to the material of construction, Pyrex, glass or polypropylene, and the mode of filtration, vacuum or pressure. We routinely use a Millipore all Pyrex glass vacuum filter unit having a male, standard-taper joint on a one litre filter flask; the unit is readily decontaminated by soaking with 2 M HC! for several days before use. Polypropylene units are also available. Rubber bungs and ground glass joints are potential sources of contamination if likely to contact the sample (Robertson, 1968a, 1972). Pressure filtration (Spencer and Brewer, 1969; Segar and Berberian, 1975) offers advantages in terms of speed of filtration and is preferable with freshwater samples having a high suspended sediment load, where filtration rates using vacuum, may be as low as 100ml h -t for 47ram diameter, 0.45/am filters. Stirring will prevent the formation of concentration gradients and clogging of filters, Pressure filtration is commonly used with ultrafiltration membranes (Smith, 1976). With either vacuum or pressure filtration, it is essential that only low pressures are used (Guillard and Wagnersky, 1958; IAEA, 1970). Rupture of phytoplankton cells will occur at pressures greater than 20 cm H8, and this may lead to increases in heavy metal concentrations in the filtrate and to changes in heavy metal speciation as a result of the increase in dissolved organic matter (Barley and Gardner, unpublished results). Concentration factors of 3 x I0'Lfor zinc, lead and copper in phytoplankton have been reported by Martin and Knauer 0973). Filtration can also result in losses of trace metals. Depending on the speed of filtration, losses of between

-~."

G.E. BATLEYand D. GARD\ER

10-30",, of dissolved mercur3 from seawater have been observed when using untreated membrane filters IGardner. 1971 ): boy, ever silicone treatment of glass fibre filters was successful in reducing losses to less than 7o, 1Gardner. unpublished results). Gardiner 119741 reported losses of mercury. copper and cadmium during filtration. Approximately 7°0 of cadmium was lost during the filtration of 25 ml of a sample of tapwater. To a~)id contamination during filtration it is preferable that this operation be performed in dust-free conditions preferably in a clean room or at least in a laminar flow. clean hood IMitchell. 1973: Hughes. 1974: Workshop on Interlaboratory Lead Analyses. 19741. This is especially true for seawater samples where the trace metal concentrations are low. For difficult-to:filter samples, centrifugation can be a useful alternative tlAEA. 19701. however this may lead to significant contamination (Abdullah et el.. 1976b~. The effectiveness of centrifugation in separatmg particulates is a function of the centrifuge speed, time and particle density. For continuous centrifugation it is necessary to use Teflon or Polythene liners, which must be rigorously cleaned before use. Similar precautions apply to Polythene or Teflon tubes for batch centrifugation. Insignificant mercury losses were also observed when using these techniques {Gardner and Rilev. 19731. The problems ofadsorption of trace metals on container surfaces can be overcome by the use of freeze-drying to concentrate samples. Filby et el. (1974) used this technique effectively for lake and river water samples. Filtrates were collected directly in Polythene bags, frozen m dry iceacetone then freeze-dried. No losses of volatile elements such as antimony and arsenic were reported. This technique is particularly suited to samples for neutron activation analysis. MATERIALS USED IN ANALYSES In addition to sample bottles, there are a number of materials such as glassware, cells, pipette tips with which the sample will come into contact during the anatysis, and which represent potential sources of contamination. The trace metal contents of a large number of laboratory materials have been thoroughly reviewed by Robedson (1968a. 1972). Pyrex glass, Polythene, Teflon and Perspex were all shown to be low in heavy metals. The purest of these materials, Perspex, being transparent and easily machined, is ideal for the construction of a.s.v, cells for water analysis. Teflon and Polythenc are preferable mater, ials for water sampling bottles. Polyvinylchloride (PVC) was found to be high in zinc. iron, antimony and copper, while structural nylon was highly contaminated with cobalt (Robertson. 1968a). Materials to be avoided include rubber, talcum powder, galvanised metal stands, brass fittings, metal syringe needles, paper tissues, soda glass coniainers, and l~adbased paints, all of which are capable of contribttting metal contamination to the sample for analysis (Spencer and Brewer. 1970; Chau. 1971; Robertson, 1972). Smoldng should be prohibited in the working area. Plastic pipette tips volumes of reagents to s~ sis. These tips have ho~ of copper, zinc, iron and, trations of 0.8-16 fB!mj 0.5-5.9 (Sommerf¢ld et al respectively, for the abo~ reduced if the tips wen before use. It is desirable by soaking in 2 M HCI remove surface metal ira, ~. troduced during the manufacturing process. The addition of unwanted trace metal impurities in analytical reagents must be avoided by ensuring that only

ultra-high purit? chemicals are used I'vasilevska~a et ~l.. 1965: Robertson. 196~al. A ~tde range of such reagents are now available from several manufacturers tMerck. B.D.HI. Ahernatively. analytical grade reagents may be further purified in the laboratory before use. Controlled potential electrolysis, for long periods of time. has been successfull) used to purify reagent solutions tAbdullah et el.. 1967a~. Solvent extraction or ~on exchange procedures can also be used to purify reagents. Mercury has been removed from sulphuric acid using dithizone tn carbon tetrachloride (Gardner and Riley. 19741. Traces of organic chemicals introduced by such treatments may be detrimental in metal speciauon studies. High purity distilled water is conveniently prepared by distillation using a quartz still of demineralised water in the presence of potassium permanganate iBatley and Florence. 19751. A second distillation of this product is sometimes required. Higher purity can be achieved by the use of sub-boiling distillation from either Teflon or silica stills lKuehner et el.. 1972). Sub-boiling distillation has also been used for purifying nitric, hydrochloric, hydrofluoric. perchloric and sulfuric acids (Little and Brooks. 1974: Dabeka et al.. 1976}. Hydrochloric acid is conveniently purified by isothermal distillation using two Polythene beakers filled with concentrated acid and distilled water respectively in a large dessicator. In all such operations, careful cleaning of all glassware and polythene containers is necessary, otherwise metal contamination will occur in the clean-up operation.

SAMPLE STORAGE Sample containers

Despite the many papers on the analysis of natural waters for heavy metals which have appeared in the recent literature, little has been reported on the ixoblems of sample storage and preservation dn~e the early work- of Robertson (1968b1. These studies measured the krss in activity of radioti'acer spikes of Ag, Co, Z ~ St, Sb, As, Fe, In, Sc, U, Rb and CS, added to seawater m l l ~ t ~ A major problem in storage experiments has been the a~.Lual measurement of natural levels of heavy, metals, and for this reason many workers have resor~d to m ~ & a ¢ ¢ r s to follow storage Iosse~ Such studies h o w e ~ r ~ i ~ ' b l y overestimate these losses since the time 0f. ~ t ~ i b ~ t i o n of added radiotracer will differ for different chemical species of the same metal. While the equilibl~tti0t~ time is very rapid for ionic metal and radiotracer S~kes, Barley and Florence (1976) showed that for lead a n d : c , o ~ , for example, a significant percentage of the total rnetals in an una¢idified seawater sample are 'irreversibly' associated with organic and inorganic matter in solution to. t ~ extent that they are not exchanged with added radialmeet alter five days. While 100V~ or" the tracer m a y b e lost- daring

a testperiod,thismay representa miCa'smaller,~ n t a g e of the totalmetal oribdaallypresent,The ~ 1 ~ of s t a g e experiments based on the addition of ionic rnettl or mdib-

As the following pages will show, results generally support the conclusion that Teflon or high density Polythene

Sampling and storage of natural waters for trace metal analysis or polypropylene are preferred materials for storage containers (IAEA, 1970; Bowditch et al., 1976). Pyrex (borosilicate) glass, preferably siliconized, is also suitable but soft or soda glass containers should be avoided. The choice of container is def,'mined both by its adsorptive properties and the presence of surface impurities. Glasses have been shown to function as weak ion exchangers (Helfferieh, 1962}. In weakly acidic and slightly alkaline solutions, the negativdy-charged silicic acid groups on the surface permit cation exchange (Doremus. 1969; Adams, 1972). Doremus (1969) showed that the potential ion exchange capacity of soda glass is significantly higher than a standard polysulfonate resin. The introduction of borosilicate groups alters the adsorptive behaviour of the glass, resulting in an order of magnitude decrease in ion exchange "capacity'. The adsorption of metal ions on glasses and oxide surfaces has" been the subject of many investigations and it is now well-established that the degree of adsorption is dependent on the ability of the metals to be hydrolyzed. Little adsorption occurs in acid solutions where simple ionic metal species are present, but with increasing pH and the formation of hydroly-zed metal ions having a reduced positive charge, increased adsorption is observed (James and Healy, 1972). Significant adsorption occurs at a lower pH for the more readily hydroly-zed metal ions such as Fe(llI) and Cr(lll). The adsorptive behaviour of hydrophobic organic polymers such as Polythene or Teflon is believed to involve ion exchange at a charged double layer on the polymer surface (Benes and Smetana, 1969). It has been proposed that, on Teflon, this layer comprises hydroxyl ions sorbed by either Van der Waals forces or by hydrogen bonding (Starik et al., 1963). The existence of a negative surface charge has been confirmed by electro-osmosis measurements. In general adsorptive losses appear, to be lower on Polythene or Teflon than on Pyrex glass. The application of a hydrophobic silicone coating to Pyrex surfaces has been shown to significantly reduce the adsorption of a number of heavy metals (Eichholz et al., 1965; West et al.. 1966; Bubic et al., 1973). Heavy metal impurities in polymer materials may contaminate the sample. These generally result from catalysts, promoters or metal dies used in the manufacturing process. For example, traces of nickel or molybdenum may be present in Polythene depending on the type of catalyst system used (Cresser, 1957). These and other surface metal impurities may be readily leached out with dilute hydrochloric or nitric acids. Karin et al. (1975) recommended a 3-day leach with 8 N nitric acid for optimum removal of trace element contamination from Polythene surfaces. Their studies revealed a basic inherent inhomogeneity of metal contamination which may be found within the polymer matrix, just below the surface, or adsorbed onto the surface. For the metals examined, AI, Mn, Cu, V, Au, Sb, Cr, Co and La, leach ratios, defined as the ratio of leached metal to metal present in unleached Polythene. had diminished to a constant value after 3 days' leaching. Organic plasticisers may also be released during storage (Robertson, 1972) and these may affect metal speciation, either as a result of their redox properties or through metal complexation. While treatments such as acid-leaching are essential to remove surface contamination from container material, such treatments can activate adsorption sites capable of removing trace metal from solution. For this reason it is essential that, after acid treatment, the containers be wellrinsed with distilled water and sample. For the collection •of unpolluted seawater samples, we reuse the same aged containers with only sample rinsing, not acid rinsing, between samples, so that the surfaces are well-equilibrated with the natural levels of heavy metals.

749

Where only a total metal analysis is required, it is usual to minimise adsorptive losses by acidif~Sng the sample after filtration to 0.05 M H" with either hydrochloric or nitric acids (ASTM. 1.975]. Acidification before filtration, however, will release metals from particulate matter and is not advisable. Note that corrections must be made for acid blanks, and if these are measured by the addition of acid to distilled water, it should be borne in mind that often carefully distilled water will be higher in trace metals than the natural water samples being studied. Acid addition is of course detrimental in metal speciation studies. In addition to storage losses associated with the sample container, losses and transformations of metal species may occur as a result of physical and biological changes in the stored sample. Sheldon et al. (1967) showed that after filtration of seawater through 0.45/am membrane filters. regrowth of particles occurred to the extent that, after several days, large numbers of particles were present in sizes greater than 4/~m diameter. Evidence was obtained that particle formation occurred by growth and a~regation of bacteria, possibly involving syntrophic growth of more than one bacterial species. Changes in the bacterial content of samples during storage are unpredictable. Giltbricht (1957) observed that in closed systems, the overall concentrations of organic matter decreased during storage, losses most probably occurring as CO2 during periods of high bacterial growth. Moebus (1972) found that the number of colony forming marine bacteria fluctuated over three orders of magnitude during several months. Such changes can provide pathways for the removal of metals or transformations of metal species. Bacterial activity can be reduced by storage at 4°C and several authors (Carpenter et al., 1975; Fukai et al., 1975) have reported a decrease in storage losses of heavy metals under these conditions. Our own experiments with seawater samples (Batley and Gardner, 1977), indicated no significant differences with respect to cadmium, lead and copper speciation between samples stored at room temperature and 4:C over a three-month period. Similar results were obtained for freshwater samples (Florence, 1977). Species were measured using a.s.v, and the speciation scheme described previously (Barley and Florence, 1976). A number of laboratories practice freezing o f water samples after filtration (Bevan et al., 1975; Holliday and Liss, 1976). Freezing has been used as a means of concentrating organic materials from water samples (Baker, 1967a, b) and intuitively one might expect freezing to affect the distribution of heavy metal species unless a flash-freezing technique was adopted. We observed that the total cadmium, lead and copper concentrations in unacidified seawater samples stored at -45~C for three months, were unchanged with the only changes in metal speciation being a decrease in labile copper associated with colloidal organic and inorganic matter (Batley and Gardner, 1977). Baier (1971) reported no differences in lead concentrations between frozen and unfrozen seawater samples; however, freezing of freshwater samples was found to reduce the concentrations of labile copper and lead species, although the total metal concentrations were unchanged (Florence, 1976}. Freeze-drying may also provide a convenient method for preconcentration and storage of water samples for total metal analyses. An evaluation of lyophilisation by Harrison et al. (1975) confirmed that, with the exception of mercury, more than 95% of a large number of heavy metals was retained in the residue. Filby et al. (1974) applied this procedure to riverwater samples for trace metal analysis by neutron activation analysis. Specific storage data have been reported for a number of trace heavy metals in waters and these will be discussed separately in the following pages. Special consideration will be given to samples for mercury analysis since their storage and preservation requirements are unique.

750

G.E.B.¢TLEY and D. G.~,~s~R

Zinc

Petrie and Baler 11976) recently reported results for losses of ionic lead during anodic stripping measurements on unfiltered seawater samples. At pH 4.6, after 95 rain of repeated plating-stripping cycles, in a seawater sample spiked with : t ° P b to W e an ionic lead concentration of 1.3 #g 1-~. only 22°0 of the initial lead activity remained in solution, with 23°~ lost to the Pyrex glass cell walls and 417 o associated with the counter electrode. This, however, represents an unusually ions exposure. A-typical exposure for seawater samples in routine analysis would be 20 min. and under these conditions only 25% of the initial activity was lost. The use of acid rinses between measurements probably enhances these losses, by reactivating the adsorption sites on the glass and may not occur with acid-washed and seawater-equilibrated glass. Matson (1968) examined a number of container materials for sorption and leaching characteristics withrespect to cadmium, lead and copper. Although lead was leachable from Pyrex containers, if correctly cleaned before use, quartz, Teflon and Polythene showed little tendency to adsorb and release the above metals. Polythene containers washed with hot concentrated nitric acid lost more than 50% of a 5.6#g 1-~ lead spike in 6 h from 0.6M NaCI at pH 6. No losses were observed if the acid washed bottles were presoaked in 0.01 M EDTA or in lake or river water. Alexander and Corcoran (1967) reported no removal of copper from seawater by aged PVC bottles over a 5 h test period; however PVC has been shown to contain copper impurities (Robertson, 1968a). Struempler (1973) studying metal losses from distilled water solutions reported no losses of a 1 gg 1- t cadmium addition at pH 6 from a Polythene container after 32 days. Losses on borosilicate glass reached 20% after 20 days at this pH. No losses occurred on either container at p H 2. Only borosilicate glass was effective in maintaining a 10 pg l-~ ionic lead addition in solution beyond a 4 day period and then only at pH 2. At pH 4, losses were low for the first four days, but at pH 6, almost complete adsorption had occurred in this time on b o ~ polythene and borosilicate glass. Similar high losses of lead were reported by Issaq and Zielinski (1974) for deionised water spiked with 400/~g 1-t lead.

Literature data for losses of zinc for stored water samples are summarised .in Table 2. These show general agreement that for seawater or estuarine water samples stored in Teflon or Polythene containers at 4"*C for up to 75 days, no significant losses of zinc occur, but losses may be greater at room temperature, or in Pyrex glass containers. Bubic et al. (1973) examined losses from seawater of zinc, lead and copper on the walls of a.s.v, cells. Adsorptive losses at pH 8 followed the order Pyrex glass > siliconised Pyrex > Polythene, but losses on all surfaces were negli~ble at pH ,g.<6. For freshwater samples, studies at natural levels using direct measurement techniques revealed only small losses on storage (Benes and Steinnes. 19751 with little change in zinc speciation (Florence. 1977). Experiments using large ionic spikes showed no losses at pH 5 from distilled water stored in Polythene (Struempler, 1973). Anomalously high losses (rom pond water observed by Dokiya et at. (1974a) were attributed to biological activity alone. Cadmium, lead and copper

Despite the limited data available on storage l o - ~ s of cadmium, lead and copper from natural water samples, results support the conclusions that minimal losses occur using Potythcne containers, if p o s s i b l e w i t h refd~.'ration to 4°C. Under these conditions, no change in cadmium, lead and copper concentrations in seawater were observed over one month's storage by Fukai and H u y n h - N g o c 11976), and these results were confirmed by our own studies of metal speciation in natural water samples referred to previously. King et at. (1974) examined the losses of cadmium using carrier.free |°gCd additions to distilled water samples. Losses of cadmium activity we.re n ~ l i s i b l ¢ from Polythaae, polypropylene and PVC bottles in the p H raas¢ 3-!0, For soft glass containers, no losses occurred below pH6.9, with 10% loss at pH 8.0, and 80% loss a t p H 9,0, after 2Oh= Cadmium losses on borosilicate glass were found to be about 70% of that of soft glass.

Table 2. Selected literature data on zinc storage losses from natural waters storage Period

e~mple° Unflltarcdseawaler Unfiltered.~awater

pH

Zinc Con~ntl~ttion

Container

Days

% Loss

Natural Naturallevels+ ~sZaa Natural Natural levels+ °SZn

Pyrex,polythene Pyrex

75 60

0 0

Unfilteredseawater

Natural Natural levels+ 6sZn

Polythnne

15

0

Unfllt~

Unfilteredseawater

Natural Naturallevels Natural Namr~lllevels

Talon Polytl~me

14 30

0 0

Estuarine water

Natural Natural levels

Polythcae

75

seawater

Rderence Rob~tson, 1968'O Schutzand Turck/aa, 1965 Dokiya e~aL. 1974b Bradford. 1972 Falrai and HuyahNIIo¢. 1976 Fukai er al.. t975

zero at 4~C chanl~ in chemical form <5 at 4°C Carpenter~ a/.. 4.5 at room temp. [975 0 Flore.m~ 1977 n o ellaall¢ in cl~mical form 5 Bcn~sand 1975 40 Bab/¢ ~ e/., 1973 no

Estuarine water

Natural Natural levels

Teflon

35

River watur

Natural Natural levels

Polyth~'~e

~

Unfllt¢l~lriver ,**cater

Natural Natural levels

Polytl~me

Spied smgratcr

16

8 8

20a$1 -I

,~DilaKIRa~ltcr

S

2014g I"1 +~s~

POlylh¢ltc

15rain

8

Rl~c ~ a/.. 1973

Spiked uzwaler

<6

20/41 L"1 +eSZn l$.lqtI" ' + "sgn

I~rax

15rain

0

B a l ~ el a/., 1973

6

.~0

Spilled ~ m a t e r

U d l l ~ pond wa~'r Di~dlled water

Di~ll¢'d water

20 ~

. 6sZn

I " z + ~sZn

NaturaJ Natural 151411-t ~ ssZa 5 100NI I-I 5 100~g I"j

15rain

~ ~ l m ~

~eX

~y~enc

~ ~ 1 ¢ ~

~ poly-

propylene

* Unless otherwise indicated samples have been filtered.

I5 ~n

30 60 60

I5

0 20 0

B~

r~ ~

1973

Do~!la et al., 1974a D o ~ y a ~ a L 197ga

SIm~ll~". 1973 Slga¢lsap~r. 1973

Sampling and storage of natural waters for trace metal analysis

751

Mercury

reducing agents in the solution. These may be in the form

During the past decade, concern for mercury as an environmental pollutant has exceeded that for any other heavy metal, probably as a result of the several disasters associated with its release at Minimata and Niigata in Japan. It is not surprising therefore, that a large body of literature now exists concerning the sampling and storage of water samples for mercury analysis. (Chilov, 1975; Jenne and Avotins, 1975; Platell and Wehb, 1974.) These problems are of particular importance with mercury, since the pathways by which mercury may be lost from solution are more numerous than those for other heavy metals. In addition to adsorptive losses of ionic mercury both on container wails and on colloidal matter, there are also the possibilitiesof losses of organo-mercury complexes or of metallic mercury through adsorption on, and diffusion through the container surface and by vaporisation at the air-water interface.Conversely, Robertson (1972) reported increases in the dissolved mercury content of acidified samples stored in Polythene containers in areas of high atmospheric mercury content. The high reduction potential of the Hg(ll)/Hg(1) couple means that mercury(If) ions present in natural waters will be susceptible to reduction by traces of mild

ol plasticiser material leached from the container, organic detritus or naturally occuring bacterial reductants. The mercury(I) ions so formed are then capable of disproportionation to metallic mercury and mercury(II). Studies by Shimomura et al. (1969) and Toribara et al. (1970) suggested this as a likely mechanism for metallic mercury formarion. More recently Baler et al. (1975) suggested the bacterial conversion of/~g 1- t concentrations of inorganic mercury in waters to the organic and/or elemental form as an alternative biochemical route for the production of volatile mercury forms. Data obtained by Avotins (1975) and Avotins and Jenne (1975) indicated that only a fraction of mercury loss from solution was attributable to the amount absorbed on the container walls but, because of' the nature of bacterial growth in solution, these amounts are subject to some variation. It was verified that mercury loss was less from sterile solutions Such decomposition can be controlled by refrigeration or freezing of the sample (Gassaway and Cart, 1972; Avotins and Jenne, 1975). Freeze-drying of water samples, however, does appear to lead to some losses of mercury (Filby et al., 1974; Harrison et al., 1975). Table 3 contains a summary of some relevant literature

Table 3. Selected literature data on mercury storage losses from natural waters

Sample

Mercury Concentration pg I" t

Reagents Added

Container

Storage Period Days % Loss

Reference

Distilled water Distilled water

1.65 6

Z°~Hg only
Polythene Polythcne

l0 25

90 30

Distilled water

6

>pH 2 + 2OJHg

Polythene

25

80

Pyrex Teflon • Polythene Polythene Polythene

10

0

15

50

Litman et at., 1975

15 " 30 21

70 0 2

Litman er aL, 1975 Limum et at, 1975 Lo and Wai, 1975

5

[ N HNO3 +--:°JHs [ N HNO) + Z°)Hg I N HNO3 + 2°~Hs " i N H N O 3 + Z°)Hg 0.05% K2Cr20~ + HNO3, pH 0.5 + 2°~Hg 0.05% K2Cr207 + 2°JHg

Polythene

21

25

Lo and Wai, 1975

5

0.2ms I -I Au 3. + H N O ) . pH 0.5

Polythene

21

25

Lo and Wai. 1975

Soft glass, PVC polythene Soft glass, PVC polythane Polythene

16

Distilled water Distilled water Di~iiled water Distilled water Oeminerali~d water Demineralissd water Demineralised water Creek water

20 ' 15 "

68 3400 5

+ZO~Hg

25

HNO 3 to pH 0.5

Creek water

25

HNO~ or HzSO, to pH 2

Pond water

15

0.1 M HCL I nM cysteine + ~O3Hs 5% HNO), 0.05~ K~Cr207 5~ HNO3, 0.05% K2Cr~O, 5~ HNO3 + 0.01%K2CrzO7 5% HNO~ 0.5% H2SO. 0.01% KMnO, 0.5 M HNO3 + :°3H s 0.3 M HNO~/HAaCI, + 2°~Hg 0.1 N H : S O , + :°3Hg

Distilled water Distilled water Distilled water Distilled water Distilled water Distilled water Distilled water Lake water River water River water Distiilad water

.0.1 0.2 0.2 0.2 0.2 I [ 0.05-0.5

Seawater Seawater Seawater Seawater

0.01 0.0[ 0.01 0.01

Feldman, 1974 Fcldman, 1974 Feldman, 1974 Feldman, 1974 Feldman. 1974 Rook and Moody, 1974 Rook and Moody, 1974 C'hau and Saitoh. 1970

0 20 50 40 ' 20 0 0

0 0

0.1 M HCI + I nM cysteinc + 2°3H s :O)Hg only 0.1 N H~SO, ~O3Hs only

Polythene

15

I

Acid washed pol~hene Acid washed polytheae Glass winchester Silicone canted

9 9 40 42

>50 6 35 0

10mg I "L cysteine + 2°3Hg 0.02-0.065 0.02--0.065 . 20~H$ only

<0.01

Dokiya et al., 1974b

0

5O

3% NaCI + 2°~Hs

Lake water Seawater

Seawater

0

10 10 5 5 5 30 30 14

21

Ze3Hg only

0.02--0.065

0.006

15

Teflon. pyrex

0.02-0.065

Lake water

Seawater

Rosain and Waio 1973

0.18 M HNO3

Lake water

0.007-0.00.-4

Romin and Wai. 1973

80

HCI, pH 1.5

l 0.02-0.065

Seawater

Teflon

<2

Pyrex, polythene polypropylane Flint glass Flint glass Hot acid leached polythene Hot acid leached polythene Hot acid leached polyOtene Untreated polythcnc Hot acid leached polythene Polythene. pyrex

0.1 M HNO~ + 2°~Hg 0.01 M HNO3 + KMnO~ + 2°~Hg 2°~Hg only

I

Borosilicate glass Polythene Poiythene Po[ythene Polythene Teflon

4.6

0.2 N H ~ S O 4

winchester

Avotins and Jenne. 1975 Benes and Rajman, 1969 Iknes and Rajman, ~969 Litman et aL, 1975

28 28 21

0 Gaston and Lee, 1974 0 Gaston and Lee, 1974 0.3 Weiss et al.. 1976

58

20

Weiss et aL. 1976

47

0

Weiss et aL. 1976

30 58

0 0

W~ss el aL, 1976 Weiss ¢t aL, 1976

Bothner and Robertson. 1975 Fitzlp~"ald and Lyons, 1975 Dokiya er aL, 1974a Gardner, 1971 Gardner, 1971 Gardner. 1971 Gardner and Riley, 1974

752

G.E. BATLEYand D. GARDNER

results on mercury storage experiments on filtered water samples. Losses v,ere found to vat,, with container material and its surface to volume ratio. ~,ith the composition of the water sample and with t,~,e concentration of dissolved mercury'. Unfiltered samples behave differentl,~ during storage and these have been the subject of more derailed studies by Baler et al., 1975 and Weiss et al. (19761. Both Polythene and borosilicate glass ha~e been widely used for the storage of water samples and mercury losses from these containers have been thoroughly investigated. Benes and Rajman (1969) showed that adsorptive losses were greatest in the pH range 4-13 where hydrolysed mercury species Hg(OH):. HgCIOH or HgOH- were present. In seawater, the formation of complex chloro species diminished the extent of adsorption, particularly at the lower pH values. Significant losses of mercury have been reported even from acidified water samples stored in polythene {Benes and Rajman. 1969: Gardner. 1971: Feldman. 1974; Gaston and Lee. 19741 although losses appear to be reduced from Pyrex glass, siliconised Pyrex or Teflon (Fitzgerald and Lyons. 1975: Gardner and Riley, 1974). It has been shown that pretreatment of containers ~s important m determining their adsorptive properties and this possibly explains the wide variations in the results of mercury storage experiments. Weiss er al. 11976) suggested that adsorptive losses on Potythene occur by a reductive process involving active sites on the surface. These sites were successfully eliminated by a hot nitric acid leach, with a resultant decrease in adsorptive losses. Despite this treatment, so me waters still suffered losses which were attributed to soluble reducing agents in the sample. Losses were greatest from unacidified freshwater or distilled water samples (Coyne and Collins. 1972: Dokiya er al.. 1974a, b). However. in saline waters, or by the addition of salt to non-saline waters, the changes in redox potential were shown to si~ificantly inhibit losses due to soluble reducing spectes lWeiss er al.. 1976). Many workers have effect[~,-ely reduced mercury losses by the addition of chemical preservatives in the form of bactericides, complexing agents or oxidants, including CN-. EDTA. cysteine, AuC12. K:Cr20,, KMnO,~ and H2Oz. With the exception of cysteine (Weiss et al.. 19761 and HzOz (Gardner and Dal Pont. 1977). these reagents generally are only effective in acidified solution (Feldman. 1974; Gaston and Lee. 1974: Lo and Wai. 1975). For mercury speciation studies, such additions cannot be made and if possible the analysis should be performed immediately, or otherwise the sample should be stored in hot acidleached polythene or Teflon containers, under refrigeration at 4~C. Iron

The adsorption of iron on glass and Polythene surfaces from aqueous solutions has been studied in some detail by Benes and co--workers (1968, t969), As expected, adsorption was shown to be very low in the pH range 0-3 increasing over the pH range 3--6.4 with the formation of hydrolys~d iron(Ill) species. Above pH 6.6 almost quantitative adsorption of ferric hydroxide occurred on either glass or Polythene. Benes and Steinnes (1975) reported significant losses of dissolved iron from unaeidified lake and river water samples after four days storage in Polythene. Over 70% of the iron was adsorbed from seawater samples onto glass or Potythene surfaces after 55 days at the natural pH (Robertson, 1968b); however, adsorption could be eliminated by acidif~ation to pH 1.5. Lewin and C'hen (1973) showed that, in unfiltered seawater samples, there is a gradual trandormation of iron from soluble to particulate species during storage. In filtered samples, removal of soluble iron occurxed by adsorption on polycarbonate container surfaces. ~ high fet,rous iron content of seawater was almost completely transformed to ferric species after 40 h storage, but could be stabilised by the addition of EDTA.

Chromium

Radiotracer experiments by Schutz and Turekian ~19651 showed no significant adsorptive losses of chromium after two months storage of seawater in Pyrex containers, Shendrikar and West {i974) showed that. while losses of chromium(VI) from natural waters were negli~ble, in excess of 15°~, of a lmg l -t chromium(Ill) spike was lost from distilled water at pH 6.95 after 10 days storage in Pyrex or Polythene containers. This behaviour is predictable cor~sidering the hydrolysis beha~iour of trivalent chromium. Benes and Steinnes 0975) reported up to 50.°~ loss of chromium in 40 days from a fiver water which was high in trivalent chromium. Other heacy metals

Storage losses of a number of other heavy metals are referred to in the comprehensive studies by Robertson I1968b) and Benes and Steinnes (1975). Manganese, cobalt and thorium are among those metals for which high losses were obtained from seawater or lakewater stored at the natural pH in glass of Polytbene containers, but in all cases losses could be reduced by acidification. High losses of gold have been observed on Polythene from acidified solutions, (Kepak. 197[). West et al. ~1966) observed negti. gible losses of l mg I- z levels of silver from distilled water of pH 7.0 in Polythene. Struempler (1973), however. showed that. while no losses of 0.5/tg l- t silver occurred at pH 2 from distilled water, losses of up to 25~ were observed after 4 days at pH 4.5 in Polythene or borosilicate glass. Losses could be reduced by exclusion of light. The adsorption of ions in tracer concentrations has received considerable attention in radiochemistry laboratories (Eichholz et al.. 1965). Details of losses from water samples of zirconium, plutonium and selected radionuclides are discussed by Eiehholz et al. {1965), in the review by Kepak (1971) and in the two IAEA reports (1970. 1975) on manne radioactivity studies.

CONCLUStONS AND RECOMMF-NDATIONS F r o m the preceding discussion it ts apparent that well-defined techniques are now available for the collection of natural water samples which wilt avoid heavy metal contamination. For surface samples we recommend the use o£ Polythene bottles or jerry cans, precleaned by soaking with dilute HCI, distilled water and then rinsed wen with sample. For depth sampiing, the least chance of contamination is offered by PVC bottles without internal closures, such as the top drop Niskin bottle. Bottles ha~Sng internal rubber closures are to be avoided, unless these can be satisfactorily covered with a plastic coating or film. and any internal metal components must be Teflon coated. Potythene or PVC bag samplers also appear suitabl~ Simple pumping systems offer acceptable alternatives for shallow depths, but for deep samples the more complex pumps required, and the greater surface area exposed to the sample, will result in a greater opportunity for sample contamination. In all cases it is r e c o m m ~ d e d that the time of contact of sample with sampler should be as short as possible. The problems of adsorptive losses and contamination during sample prctrcatment and analysis arc now better understood, and surmountable with the use of careful housekeeping and an acute awareness of potential sources of heavy metal interferences. As

Sampling and storage of natural waters for trace metal analysis soon as possible after collection, the sample should be filtered, using membrane filter papers and apparatus, which have been pre-washed with acid, distilled water and sample. Alternatively, centrifugation should be performed using pre-cleaned Polythene or Teflon tubes. If the delay before filtration is to exceed several hours, the sample should be chilled to below 4'C to inhibit bacterial growth, but must not be acidified. A more vexing problem is that of sample storage, and certainly, to quote Struempler (1976) "'the last chapter on container adsorption of metal ions at low concentrations in an aqueous solution has not been written". Clearly, more careful attention needs to be given to the design of experiments to predict such losses. Since most analyses are concerned with natural levels of metals in water samples, a study of changes in these data from the time of collection and filtration should be of interest and not data from systems that have been artificially perturbed by the addition of high concentrations of ionic metal species, or of radiotracer spikes which equilibrate with the different natural metal species at different rates. A significant variability in storage behaviour has been observed in experiments on the same container material, as a function of container surface pretreatment, the composition of the stored water sample and temperature and place of storage. In view of this, it is advisable. whichever storage method is selected for a particular sampling program, that it be tested using the identical methodology to be used on field samples, using the natural waters to be analysed, at the natural concentrations found and in the containers to be used in the field. For the analysis of heavy metals, samples should be stored in high density Polythene or Teflon containers which have been cleaned in the manner described previously and thoroughly rinsed with filtered sample. To minimise losses the sample should be kept at 4°C. Freezing of samples is also acceptable although not recommended for speeiation studies. For the analysis of most metals with the notable exception of mercury, acidification of the sample with high purity nitric acid to 0.05 M H ÷ is recommended to reduce adsorption losses, although this too is undesirable in studies of metal speciation. For mercury analysis both acidification and the addition to the sample of an oxidant or complexing agent, such as H202 or cysteine, are necessary to prevent losses. REFERENCES Abdullah M. I., Berg B. R. & Klim E. K. R. (1967a) The determination of zinc, cadmium, lead and copper in a single seawater sample by differential pulse anodic stripping voltammetry. Analytica china. Acta. 84, 307-317. Abdullah M. I., EI-Rayis O. A. & Riley J. P. (1967b) Reassessment of chelating ion-exchange resins for trace metal analysis of sea-water. Analytica chim. Acta. 84, 363-368. Abdullah M. I. & Royle L. G. (1974) A study of the dissolved and particulate trace elements in the Bristol Channel. J. mar. biol. Ass. UK. 54, 581-597.

753

Adams P. B. (t972t Glass containers. In Ultrapurity, Methods and Techniques. (Edited by M. Zief and R. Speights`L pp. 297-351. Marcel Dekker Inc. New York. Alexander J. F. & Corcoran E. F. q1967) The distribution of copper in tropical seawater. Limnol. Oceanoor. 12, 236-242. Alexander P. W. (19761 Continuous-monitoring with electrode sensors, Prec. R. Aust. Chem. Inst. 43, 358362. ASTM (1975) Standard Methods of test for copper in water and waste water. In Annual Book of ASTM Standards Part 3[. Water, p. 292. ASTM. USA. Avotins P. V. (1975) Adsorption and coprecipitation studies of mercury on hydrous iron oxide. Thesis, Stanford University. California. USA. Avotins P. & Jenne, E. A. (1975). The time stability of dissolved mercury in water samples--II. Chemical stabilization. J. envir. Qual. 4, 515-519. Baier R. (1971). Lead distribution in.coastal waters. Thesis, University of Washington. Washington, USA. Baler R. W., Wojnowich L. & Petrie L. (1975) Mercury loss from culture media. Analyt. Chem. 47, 2464-2467. Baker R. A. (1967a) Trace organic contaminant concentration by freezing--I. Low inorganic aqueous solutions. Water Res. 1, 61-77. Baker R. A. (1967b) Trace organic contaminent concentration by freezing--II: Inorganic aqueous solutions. Water Res. 1, 97-113. Bate L. C.. Lindberg S. E. & Andren A. W. (1975) Elemental determination of water and air particulates by use of neutron activation analysis, in Prec. Int. Conf. Heavy Metals in the Environment, Toronto Canada, 1975, page 1:)94. Batley G. E. and Florence T. M. (1975) An evaluation and comparison of some techniques of anodic stripping voltammetry. J. electroanalyt. Chem. 55, 23-43, Batley G. E. and Florence T. M. (1977) Determination of the chemical forms of dissolved cadmium, lead and copper in seawater. Mar. Chem. 4, 347-363. Barley G. E. and Gardner D. (1976) A study of copper, lead and cadmium speciation in some estuarine and coastal marine waters. Estuar. Coast. mar. Sci. in press. Bender M. L. and Gagner C. (1976) Dissolved copper, nickel and cadmium in the Sargasso Sea. J. mar. Res. 34, 327-339. Benes P. and Rajman I. (1969) Radiochemical study of the sorption of trace elements. V. Adsorption and desorption of bivalent mercury in polythene, Coll. Czech. Chem. Commun. 34, 1375-1386. Benes P. and Smetana J. (1969). Radiochemical study of the sorption of trace elements. IV. Adsorption of iron on polythene and its state in aqueous solution. Coll. C:ech. Chem. Commun. 34, 1360-1374. Benes P., Smetana J. & Majer V. (1968) Radiochemical study of the sorption of trace elements. III. Adsorption and resorption of iron on glass. Coll. C:ech. Chem. Commun. 33, 3410-3421. Benes P. & Steinnes E. (1975) Migration forms of trace elements in natural fresh waters and the effect of the water storage. Water Res. 9, 741-749. Benjamin M. M. & Jenne E. A. (1976) Trace element contamination. 1. Copper from plastic microlitre pipet tips. Atom Absorpt. Newsletter, 15, 53-54. Bernhard M. & Zattera A. (1975). Radiotracer experiments with phytoplankton. In Design of Radiotracer Experiments in Marine Biological Systems. IAEA Technical Report No. 167, pp. 35-58. Betzer P. R. & Pilson M. E. Q. (1975) The effect of cotreded hydrographic wire on particulate iron concentrations in seawater. Deep-Sea Res. 22, 117-120.

"54

G E. BATLEY and D. GARD\ER

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7'5~

G.E. BATLE~ and D. OARDNER

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