Trace metals cadmium

Yates J (1982) Technical report TR181. Determination of trace metals (cadmium, copper, lead, nickel, and zinc) in filtered saline water samples. Water Research Centre, Medmenham, UK... 

Emissions from other nonferrous metal facilities are primarily metal fumes or metal oxides of extremely small diameter. Zinc oxide fumes vary from 0.03 to 0.3 jiim and are toxic. Lead and lead oxide fumes are extremely toxic and have been extensively studied. Arsenic, cadmium, bismuth, and other trace metals can be emitted from many metallurgical processes. 

Theory. Conventional anion and cation exchange resins appear to be of limited use for concentrating trace metals from saline solutions such as sea water. The introduction of chelating resins, particularly those based on iminodiacetic acid, makes it possible to concentrate trace metals from brine solutions and separate them from the major components of the solution. Thus the elements cadmium, copper, cobalt, nickel and zinc are selectively retained by the resin Chelex-100 and can be recovered subsequently for determination by atomic absorption spectrophotometry.45 To enhance the sensitivity of the AAS procedure the eluate is evaporated to dryness and the residue dissolved in 90 per cent aqueous acetone. The use of the chelating resin offers the advantage over concentration by solvent extraction that, in principle, there is no limit to the volume of sample which can be used. 

As is the case with assessments of the toxicity of dissolved trace metals, the development of sediment quality criteria (SQC) must be based on the fraction of sediment-associated metal that is bioavailable. Bulk sediments consist of a variety of phases including sediment solids in the silt and clay size fractions, and sediment pore water. Swartz et al. (1985) demonstrated that the bioavailable fraction of cadmium in sediments is correlated with interstitial water cadmium concentrations. More recent work (e.g., Di Toro et al, 1990 Allen et al., 1993 Hansen et al, 1996 Ankley et ai, 1996, and references therein) has demonstrated that the interstitial water concentrations of a suite of trace metals is regulated by an extractable fraction of iron sulfides. 

Topping G (1982) Report on the sixth ICES trace metal intercomparison exercise for cadmium and lead in biological tissue. ICES Cooperative Research Report No in. International Council for the Exploration of the Sea, Copenhagen, Denmark... 

Shen GT, Boyle EA (1988) Determination of lead, cadmium and other trace metals in annually-banded corals. Chem Geol 67 47-62... 

Greater adsorption of trace metals is found at higher pH and C02(g) concentrations. Sites available for Zn2+ sorption are less than 10% of the Ca2+ sites on the calcite surface, and Zn adsorption is independent of surface charge. This indicates a surface complex with a covalent character (Zachara et al., 1991). Furthermore, the surface complex remains hydrated and labile because Zn2+ is rapidly exchangeable with Ca2+, Zn2+ and ZnOH. At the dolomite-solution interface, the carbonate(C03)-metal (Ca/Mg) complex dominates surface speciation at pH > 8, but at pH 4-8, hydroxide (OH) -metal (Ca/Mg) dominates surface speciation (Pokrovsky et al., 1999). Calcite has an observed selectivity sequence Cd > Zn > Mn > Co > Ni > Ba = Sr, but their sorption reversibility is correlated with the hydration energies of the metal sorbates. Cadmium and Mn dehydrate soon after adsorption to calcite and form a precipitate, while Zn, Co and Ni form surface complexes, remaining hydrated until the ions are incorporated into the structure by recystallization (Zachara et al., 1991). 

Most trace metals may be precipitated with phosphate into insoluble metal phosphates (Table 7.5). Most metal phosphates have low solubility. High localization of phosphates reduces the bioavailability of Zn in arid soils. The banded application of P near the seeds depresses Zn uptake by com (Adriano and Murphy, 1970 Grant and Bailey, 1993), causing Zn deficiency. However, both N and P fertilizers increase Cd concentration in plants. Cadmium and Zn are antagonistic in root uptake and distribution within plants. 

Scarponi et al. [93] concluded that filtration of seawater through uncleaned membrane filters shows positive contamination by cadmium, lead, and copper. In the first filtrate fractions, the trace metal concentration maybe increased by a factor of two or three. During filtration, the soluble impurities are leached from the filter, which is progressively cleaned, and the metal concentration in the filtrate, after passage of 0.8 -11 of seawater, reaches a stable minimum value. Thus it is recommended that at least one litre of seawater at natural pH be passed through uncleaned filters before aliquots for analysis are taken... 

In the determination of cadmium in seawater, for both operational reasons and ease of interpretation of the results it is necessary to separate particulate material from the sample immediately after collection. The dissolved trace metal remaining will usually exist in a variety of states of complexation and possibly also of oxidation. These may respond differently in the method, except where direct analysis is possible with a technique using high-energy excitation, such that there is no discrimination between different states of the metal. The only technique of this type with sufficiently low detection limits is carbon furnace atomic absorption spectrometry, which is subject to interference effects from the large and varying content of dissolved salts. 

Electrothermal atomic absorption spectrophotometry with Zeeman background correction was used by Zhang et al. [141] for the determination of cadmium in seawater. Citric acid was used as an organic matrix modifier and was found to be more effective than EDTA or ascorbic acid. The organic matrix modifier reduced the interferences from salts and other trace metals and gave a linear calibration curve for cadmium at concentrations < 1.6 pg/1. The method has a limit of detection of 0.019 pg/1 of cadmium and recoveries of 95-105% at the 0.2 pg of cadmium level. 

Stolzberg [143] has reviewed the potential inaccuracies of anodic stripping voltammetry and differential pulse polarography in determining trace metal speciation, and thereby bio-availability and transport properties of trace metals in natural waters. In particular it is stressed that nonuniform distribution of metal-ligand species within the polarographic cell represents another limitation inherent in electrochemical measurement of speciation. Examples relate to the differential pulse polarographic behaviour of cadmium complexes of NTA and EDTA in seawater. 

Bengtsson et al. [671] found that the high background adsorption of solutions of trace metals containing up to 400 mg/1 can be easily minimised by addition of 2% v/v nitric acid. Of the several agents added in an attempt to eliminate the decrease in sensitivity caused by the salt and the variability in sensitivity between graphite tubes, only lanthanum added at 1 g/1 was effective for both lead and cadmium. 

Figure 5.18 is an absorbance versus time plot obtained by Hoenig and Wollast [681] for the determination of trace metals in seawater. It shows the absorbance profiles of the desired elements as a function of the atomisation temperature. The scale starts with cadmium, for which the absorption signal appears around 400 °C, followed by lead (756 °C), copper (1000 °C), manganese (1200 °C), nickel (1300 °C), and chromium (140 °C). 

A poly(acrylaminophosphamic-dithiocarbamate) chelating fibre hasbeen used to preconcentratrate several trace metals in seawater by a factor of 200 [957]. The elements included beryllium, bimuth, cobalt, gallium, silver, lead, cadmium, copper, manganese, and indium. ICP-MS was used for detection. 

Mart et al. [793] and Valenta et al. [794] have described two differential pulse ASV methods for the determination of cadmium, lead, and copper in arctic seawater. After a previous plating of the trace metals into a mercury film on a rotating electrode with a highly polished glassy carbon as substrate, they were stripped in the differential pulse mode. The plating was done in situ. 

Holzbecker and Ryan [825] determined these elements in seawater by neutron activation analysis after coprecipitation with lead phosphate. Lead phosphate gives no intense activities on irradiation, so it is a suitable matrix for trace metal determinations by neutron activation analysis. Precipitation of lead phosphate also brings down quantitatively the insoluble phosphates of silver (I), cadmium (II), chromium (III), copper (II), manganese (II), thorium (IV), uranium (VI), and zirconium (IV). Detection limits for each of these are given, and thorium and uranium determinations are described in detail. Gamma activity from 204Pb makes a useful internal standard to correct for geometry differences between samples, which for the lowest detection limits are counted close to the detector. 

Stolzberg [143] has discussed potential inaccuracies in trace metal speciation measurement in the determination of copper and cadmium by differential pulse polarography and ASV. 

Gardner and Yates [26] developed a method for the determination of total dissolved cadmium and lead in estuarine waters. Factors leading to the choice of a method employing extraction by chelating resin, and analysis by carbon furnace atomic absorption spectrometry, are described. To ensure complete extraction of trace metals, inert complexes with humic-like material are decomposed by ozone [27]. The effect of pH on extraction by and elution from chelating resin is discussed, and details of the method were presented. These workers found that at pH 7 only 1-2 minutes treatment with ozone was needed to completely destroy complexing agents such as EDTA and humic acid in the samples. 

Gardner MJ (1987) UK Analytical Quality Control for Trace Metals in the Coastal and Marine Environment, the Determination of Cadmium. Report PRS 1516-M, Water Res Centre, Medmenham, UK... 

Bordin, G., J. McCourt, and A. Rodriguez. 1994. Trace metals in the marine bivalve Macoma balthica in the Westerschelde estuary, the Netherlands. Part 2 intracellular partitioning of copper, cadmium, zinc and iron — variations of the cytoplasmic metal concentrations in natural and in vitro contaminated clams. Sci. Total Environ. 151 113-124. 

Devineau, J. and C. Amiard Triquet 1985. Patterns of bioaccumulation of an essential trace element (zinc) and a pollutant metal (cadmium) in larvae of the prawn Palaemon serratus. Mar. Biol. 86 139-143. Dib, A., J.P Clavel, and J.P. Carreau. 1989. Effects of gamma-linolenic acid supplementation on lipid composition of liver microsomal membranes. I. Pregnant rats fed a zinc-deficient diet and those fed a balanced one. Jour. Clin. Biochem. Nutr. 6 95-102. 

The technique is useful for the quantitation of many metals including lead, copper, mercury, cadmium and zinc with detection limits as low as lOpg. Its sensitivity makes it a very suitable method for trace metal analysis in biological samples. 

A significant proportion of the needs for reference materials for seawater trace metal studies would be addressed by the preparation of these materials. Although the total iron concentration of these reference materials should be provided, these materials clearly will be useful for studies of other important metals such as zinc, manganese, copper, molybdenum, cobalt, vanadium, lead, aluminum, cadmium, and the rare earth elements. With careful planning, such water samples should be useful for analysis of dissolved organic substances as well. The collection sites should be chosen carefully to provide both a high and a low concentration reference material for as many metals as possible. 

Concentration profiles from the North Atlantic and North Pacific (a) phosphorus, (b) silicon, (c) iron, (d) nickel, (e) manganese, (f) cadmium, (g) zinc, and (h) copper. Source From Morel, F. M. M., and J. G. Hering (1993) Principles and Applications of Aquatic Chemistry. John Wiley Sons, p. 406. Data sources Bruland, K. W., and R. P. Franks (1983). Trace Metals in Seawater pp. 395-414, C. S., Wong, et al. Plenum Press and Bruland, K. W. (1980). Earth and Planetary Sciences Letters, 47, 176-198. 

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