The effect of surfactants on the extraction-atomic absorption spectrophotometric determination of copper, iron, manganese, lead, nickel, zinc cadmium and cobalt

Nine surfactants representing pure cationic, anionic and non-ionic detergents, three industrially prepared detergents. sodium pyrophosphate. sodium tripolyphosphate, and a soap were investigated for their effect on the extraction-atomic absorption spectrophotometric determination of copper. iron, manganese and lead. Some results are also given for nickel, zinc, cadmium and cobalt. Cations were extracted into 10 ml of MIBK as APDC chelates. To Avoid emulsion formation, maximum concentration of LAS was 1 mg 1⁻¹, and for formulated and non-ionic detergents and washing powders it was 5 mg 1⁻¹.A standard addition procedure was used to obtain correct results for copper and nickel. Two extractions of iron, cobalt and lead, and one extraction of manganese, zinc and cadmium gave a recovery of 100 ± 5%. Soap gave high recoveries for iron and copper. NTA in concentrations up to 25 mg l⁻¹ did not interfere. EDTA in concentrations up to 25 mg l⁻¹ interfered with iron and nickel determinations, but the addition of 3 mg of aluminium removed the EDTA interference in the determination of copper, manganese, lead, zinc, cadmium and cobalt.For the determination of trace metals in polluted natural waters the amount of 4% APDC was increased to 10 ml and for manganese to 25 ml. An addition of 3 mg aluminium as nitrate after the addition of buffer with subsequent 20 min reaction time is required for the determination of all eight metals by the recommended procedures. The effect of humic acid was also investigated.     

Preliminary studies on the leaching of some trace metals from kitchen faucets

Preliminary studies were carried out on the leaching of copper, zinc, chromium, cadmium and lead from eight kitchen faucets by samples of raw, filtered and distributed Ottawa water, a sample of well water and deionized water containing 2 mg l⁻¹ aqueous fulvic acid. Leaching was effected by allowing the test solutions to stand in the inverted faucets for two successive 24-h periods. Concentrations of the metals found in the leachates were copper: first leaching, 0.12–28.0 mg l⁻¹, second leaching, 0.08-3.54 mg l⁻¹; zinc: first leaching, 0.13-10.25 mg l⁻¹, second leaching, 0.06-2.85 mg l⁻¹; chromium: first leaching, < 1.0 × 10⁻³ − 0.395 mg l⁻¹, second leaching, < 1.0 × 10⁻³−0.032 mg l⁻¹; cadmium: first leaching, < 0.05 × 10⁻³−0.01 mg l⁻¹, second leaching, < 0.05 × 10⁻³−4 × 10⁻³ mg l⁻¹; and lead: first leaching, < 0.2−110.0 mg l⁻¹, second leaching, < 0.2−82.0 mg l⁻¹. The faucets containing lead-soldered copper joints released high concentrations of lead, particularly in the case of leaching with the aqueous fulvic acid solution. Under the conditions of the present investigations it is indicated that in some cases the concentrations of metals leached could lead to intakes in excess of the maximum permissible limits for these metals. However, further investigations will be required to determine the possible contribution of these faucets to metal intake under normal usage.     

The effect of photochemical treatment of water on algal growth

A new method for the destruction of algae in surface waters by dye-sensitized photooxidation is described. The algae (Peridinium, Pediastrum and Cosmarium) used as test organisms were inoculated in an artificial culture medium, containing a dye-sensitizer, with subsequent incubation in a controlled environment (20 ± 2°C, 14 h light, 10 h darkness). Water samples from Peridinium bloom in Lake Kinneret underwent similar treatment. The algicidal effect of various sensitizer concentrations and of different sunlight exposure times was investigated. Complete destruction of algae was obtained in about 2 weeks of incubation after exposure to solar radiation for 30–60 min in the presence of 0.25, 0.15 and 0.75 mg 1⁻¹ methylene blue or 0.5, 0.8 and 0.8 mg 1⁻¹ rose bengal in Peridinium, Pediastrum and Cosmarium cultures, respectively.     

Algae as a chemical speciation monitor—I A comparison of algal growth and computer calculated speciation

An alga, Selenastrum capricornutum, was used to monitor the relationship between metal speciation and toxicity. The principal effect of copper on the algae was a decrease in growth rate constant as the total concentration of copper increased. A 24-h growth experiment was used to monitor the effect of metal on the algae. Chlorophyll measurements at 17 and 23 h were used to estimate the growth rate constant. A plot of growth rate constant versus the speciation variable (total copper, pCu, pCuL, etc.) was used to determine the toxic species and the algicidal concentrations. Solutions containing EDTA, TRIEN, NTA, HIMDA and bicine became algicidal at pCu of 8.0 whereas solutions containing ethylenediamine and citric acid became algicidal at pCu 8.65 and 9.5, respectively. A comparison of growth and calculated speciation suggests that Cu en⁺² and Cu CIT OH⁻² were toxic species.     

Removing metals from waste solutions with low rank coals and related materials

Ion exchange media were produced by contacting brown coal, peat or wood sawdust with a solution of calcium hydroxide, preferably as an aqueous slurry of lime. The resultant calcium loading on the media, which ranged up to 8% for sawdust, 12% for peat and to 19% for brown coal, was exchanged for many metals in solution.Preliminary work showed the method to be amenable to extraction of copper, nickel, chromium, cadmium, lead, zinc, mercury, cobalt, silver, iron, manganese, vanadium, germanium, gallium, aluminium, antimony and uranium. For most of the metals more than 99% was removed from I g 1⁻¹ solutions.In more detailed work, confined to calcium loaded brown coal and solutions having metal concentrations more typical of industrial operations, minimum residual metal concentrations of 0.0005 mg l⁻¹ mercury; 0.02 mg 1⁻¹ copper; 0.02 mg 1⁻¹ zinc; <0.05 mg l⁻¹ cadmium; 0.1 mg 1⁻¹ lead and 0.2 mg l⁻¹ manganese were obtained. These results compare favourably with those reported for other relevant processes and there might be operational advantages in the method.The method can be applied either by agitating the calcium loaded media in the solution and then filtering, or by passing the solution through packed beds of the media. Where appropriate, dilute solutions can be up-graded for re-use by stripping the metals from the media which can also be re-used. Alternatively, the loaded media can be combusted and the metals recovered from the residues.The method might be applicable to mine drainage and to effluents from metallurgical processing and electroplating, but more work is required to assess costs.It is suggested that the method is environmentally preferable to other common effluent treatment procedures because it enables collection and recycling of heavy metal pollutants.     

Studies on the toxicity of copper sulphate to stone loach Noemacheilus barbatulus (L.) in hard water

The toxicity of copper sulphate to Noemacheilus barbatulus was studied for 64 days in a water of total hardness 249 mg l⁻¹ as CaCO₃. The 63-day lc₅₀ was approximately 0.25 mg Cu l⁻¹. Larger fish survived longer, and at concentrations greater than 0.29 mg l⁻¹ fish hid less during daylight. Noemacheilus surviving 0.12 mg Cu l⁻¹ for 64 days shed copper when placed in clean water for 7 days: gill, muscle, eye and vertebrae lost significant amounts of copper during this period. The opportunity to shed copper during a short period when the poison supply to their tank failed, may have allowed fish exposed to 0.49 mg l⁻¹ to live 12 days longer than expected. The sensitivity of Noemacheilus to copper, cadmium and zinc was compared with that of rainbow trout. Salmo gairdneri.     

Effects of manganese, copper and lead on Selenastrum capricornutum and Chlorella stigmatophora

Algal assays were conducted to observe the responses of Selenastrum capricornutum and Chlorella stigmatophora to the metals manganese, copper and lead, added singly or in combination to both artificial media and natural waters. A 50% reduction in the total algal cell volume of Selenastrum in standard algal assay medium (SAAM) occurred by the addition of either 3.1 mg manganese 1⁻¹ 85 μg copper 1⁻², or 140 μg lead 1⁻¹. For Chlorella grown in 28 ppt artificial seawater plus full SAAM nutrients, the corresponding numbers were 50mg manganese 1⁻¹, 70 μg copper 1⁻¹ or 700 μg lead 1⁻¹. Of the metals tested, only lead was found in higher concentrations in urban and agricultural runoff than at least one of these levels.Theoretical considerations show that a product model is a more reasonable reference for no-interaction than an additive model for experiments in which toxic metals are added in combination. Combination experiments, in which any combination of the three metals act at the same time, indicate (1) synergism between manganese and copper, (2) antagonism between manganese and lead, and (3) antagonism between copper and lead. As to the manganese-lead interaction, it is shown that the lead-induced inhibition of cell division is offset, partially for Selenastrum and completely for Chlorella by the addition of manganese.     

Chronic toxicity of a copper, cadmium and zinc mixture to the fathead minnow (Pimephales promelas rafinesque)

Fathead minnows were exposed to a series or concentrations of a copper, cadmium and zinc mixture during a 12.5 month chronic test in water of 200 mg 1⁻¹ total hardness. The metal concentrations in the mixture were selected on the basis of results obtained during previous chronic exposures to each of the metals individually in the same water. Strict summation of the chronic toxicities of the metals was not indicated when they were tested in combination. Toxic effects of the mixture attributable to copper appeared to be increased, but that attributable to cadmium was reduced. The effects thought to be due to zinc were similar in degree to those observed in the single chronic exposure. Summation of effects resulting from a mixture containing about the same proportions of copper, cadmium and zinc occurred at a much higher, acutely lethal concentration. A lethal threshold was attained in the mixture when each metal was present at a concentration of 0.4 or less of its individual lethal threshold.     

The toxic effect of copper on algae and rotifers from a Soda Lake (Lake Nakuru, East Africa)

The effect of Cu(II) ions on the photosynthetic oxygen production of the phytoplankton, the growth rate of the blue-green algae Spirulina platensis and the population of rotifers (Brachionus sp.) in water from the soda lake Nakuru in Kenya was investigated experimentally. The photosynthetic production was reduced to 80% of the control by the addition of 0.1 mg Cu l⁻¹ and 50% by addition of 0.15–0.20 mg Cu l⁻¹. The growth rate of Spirulina platensis was more affected by copper than the photosynthesis of phytoplankton. Addition of 0.05 mg Cu l⁻¹ reduced the growth rate to about 40% of the control. The rotifiers were less sensitive to copper than the algae, but after 8 days exposure to 0.5 mg Cu l⁻¹ or more the population was severely affected.     

The effect of surfactants on the mixed chelate extraction-atomic absorption spectrophotometric determination of copper, nickel, iron, cobalt, cadmium, zinc and lead

Twelve surfactants representing pure cationic, anionic and non-ionic detergents, three commercial detergents, sodium pyrophosphate, sodium tripolyphosphate, a soap, nitrilotriacetic acid (NTA), EDTA, and humic acid were investigated for their effect on the extraction-atomic absorption spectrophotometric determination of copper, nickel, iron, cobalt, cadmium, zinc and lead. Cations were extracted into 10 ml of a solution containing diphenylthiocarbazone, 8-quinolinol and acetyl acetone in ethyl propionate. To avoid emulsion formation, the maximum concentration of linear alkylate sulphonate (LAS) was 10 mg l⁻¹ and for solid industrial LAS-type detergent was 50 mg l⁻¹, but washing powder did not interfere at 100 mg l⁻¹. Cationic and non-ionic detergents gave low recoveries for cobalt. Condensed phosphates at a concentration of 20 mg l⁻¹ did not cause significant interference. NTA interfered with nickel extraction and EDTA with all metals. Humic acid, however, gave no interference. A standard addition procedure can be used to correct the results.A comparison is made between the APDC-MIBK and the mixed chelate-ethyl propionate methods for the determination of trace metals in the presence of various surfactants in natural waters; the latter is preferable.     

Electrodeposition of six heavy metals on reticulated vitreous carbon electrode

Six heavy metals, copper, cadmium, chromium, lead, uranium and zinc were deposited on cathodes made of a newly developed form of carbon, Reticulated Vitreous Carbon, in a laboratory scale electrochemical reactor. Different metals varied in the extent of their removal with copper depositing 100% at a flow rate of 0.24 cm min⁻¹ in a single pass while it would require a maximum of 20 passes for 100% chromium deposition at a flow rate of 1.8 cm min⁻¹, initial concentrations for both metals being 50 μmol 1⁻¹.Experiments conducted using 0.5 × 10⁻³ M CuSO₄ in 0.5 M Na₂SO₄ supporting electrolyte resulted in a mass transfer coefficient of the order of 10⁻³ cm s⁻¹ and a current efficiency of 64% for the electrodeposition of copper at a cell voltage of 4.0V. Because of very high porosity, 97%, high specific surface area, up to 66 cm² cm⁻³ for RVC grade 100, and useful electrochemical characteristics, RVC can be advantageously used as electrode material for heavy metal removal from dilute industrial effluents.     

Accumulation of zinc, cadmium and lead by field populations of Lemanea

A study has been made of the concentrations of zinc, cadmium and lead in populations of the red alga Lemanea growing in fast-flowing rivers in Britain, France. Germany, Ireland and Sardinia (Italy). The sites were selected to provide a wide range of aqueous concentrations of these metals. Many of the sites are influenced by past or present mining activities and Lemanea was found at aqueous concentrations of zinc up to 1.16 mg 1⁻¹. In contrast to previous studies with filamentous green algae, no evidence could be found to support the hypothesis that populations differ genetically in their ability to tolerate these heavy metals. Samples of alga consisted of pooled 2 cm long terminal tips of filaments detached from approx. 1 cm² rock surface. Significant positive correlations were found between the logarithm of the mean concentration of zinc, cadmium and lead in four such samples collected from within 10 m reaches at 59 sites and the logarithm of the concentration of each metal in both unfiltered and filtered water. The enrichment ratios for each metal decreased with increasing aqueous metal concentrations. Although the aqueous concentrations of the three metals were strongly intercorrelated, differences in the ratio of metal concentrations were reflected in the composition of Lemanea filaments. The results suggest that high levels of calcium (and/or magnesium) result in decreased uptake of zinc. Intensive sampling from a single population showed that part of the zinc content of filaments is sensitive to short-term fluctuations in concentrations in the surrounding water. In the particular population studied this was about 20%; a similar percentage could be eluted in the laboratory with EDTA. Transplants of Lemanea were made between reaches with different aqueous concentrations of zinc and in all cases the zinc concentration in filament tips increased or decreased to stabilise at a concentration similar to that in filaments native to the reach. It is suggested that chemical analyses of natural or transplanted populations of Lemanea could provide a valuable aid in monitoring contamination of rivers by zinc, cadmium or lead.     

Zinc, cadmium and lead in water, sediments and submerged plants of the Derwent Reservoir, Northern England

A partial budget is presented of the zinc, cadmium and lead entering the Derwent Reservoir. The mean levels in the water column upstream of the site of inflow are: Zn, 0.216 mg 1⁻¹ ; Cd, 0.003 mg 1⁻¹; Pb, 0.065 mg 1⁻¹; the levels after passage through the 4.1 km² reservoir fall by: Zn, 70.3%; Cd, 98.3%; Pb, 89.2%. Most of these metals are deposited in sediments, the mean values for which are: Zn, 1035 μg⁻¹; Cd, 13μg⁻¹; Pb, 827μg⁻¹. Lead, a higher percentage of which occurs as particulate material, is deposited more rapidly than zinc; this effect is especially obvious when streaming of colder water along the bottom of the reservoir takes place at the time of floods. Macroscopic plants are only occasional in this reservoir, due perhaps in part to heavy metal toxicity. Of the two most common submerged species, Nitella flexilis probably accumulates almost all of its metal content directly from the water, but the data suggest that sediments are a source of some of the heavy metals accumulated by Glyceria fluitans.     

Role of bacterial extracellular polymers in metal uptake in pure bacterial culture and activated sludge—II Effects of mean cell retention time

A gel filtration technique afforded a good separation between metal complexed with bacterial extracellular polymers and free metal ions. The complexation of polymers extracted from cultures of Klehsiella aerogenes and activated sludge with cadmium, nickel, manganese and cobalt was demonstrated. The extraction of extracellular polymers from cultures of K. aerogenes and activated sludge reduced the capacity of the cells and flocs to adsorb metal. Adsorption and complexation of metals by cells of K. aerogenes and extracellular polymers extracted from activated sludge were fitted to Freundlich equilibrium isotherms. Saturation of activated sludge polymer binding sites occurred at 10 mg 1⁻¹ metal additions for all the metals studied except manganese which was complexed to a very limited extent. Cells of K. aerogenes exhibited no saturation effects in the range of metal concentrations studied.Precipitation of metals below a concentration of 1 mg 1⁻¹ was minimal, with the exception of cadmium precipitation. At a concentration of 10 mg 1⁻¹, precipitation of cadmium, cobalt and manganese may have been the major mechanism of metal removal. The more soluble metals generally displayed the lowest removals. Concentrations of extracellular polymers and soluble chelating agents may be important in controlling removals of metals which are largely soluble in activated sludge.     

The toxic effects of trinitrotoluene (TNT) and its primary degradation products on two species of algae and the fathead minnow

The effects of alpha trinitrotoluene (alpha TNT) and its primary degradation product (TNTcc), commonly referred to as “pink water”, were determined on members of two trophic levels. The growth responses of the algae Selenastrum capricornutum and Microcystis aeruginosa were examined through static bioassays. Death and behavioral responses of the fathead minnow (Pimephales promelas) were determined using a proportional diluter. Alpha TNT and TNTcc were both more toxic to the fathead minnow than to either species of alga. Five and 15 mg l⁻¹ alpha TNT inhibited S. capricornutum and M. aeruginosa growth, respectively. TNTcc inhibited S. capricornutum growth at concentrations above 9 mg l⁻¹; it was lethal to M. aeruginosa at 50 mg l⁻¹, but stimulated growth at lower concentrations. The 96-h lc₅₀ values based on the death response of the fathead minnow to alpha TNT and TNTcc were 2.58 and 1.60 mg l⁻¹, respectively. The 96-h ec₅₀ values based on the behavioral responses were 0.46 and 0.64 mg l⁻¹, respectively. There was no response to concentrations of 0.05 mg l⁻¹ alpha TNT and 0.07 mg l⁻¹ TNTcc.     

The distribution of cadmium between the marine alga Chlorella stigmatophora and sea water medium: Effect on algal growth

Distribution of dissolved cadmium between Chlorella stigmatophora and sea water medium—and possible effects of cadmium on the alga's growth—were investigated at cadmium concentrations between 1–10 mg 1⁻¹. Results show considerable cadmium uptake by Chlorella stigmatophora along the growth curve. No effect of cadmium uptake on growth expressed by number of cells was recorded but a considerable decrease in chlorophyll content per cell was established. A mathematical expression was developed for the distribution of cadmium between Chlorella stigmatophora and sea water medium.     

Effect of copper and hexavalent chromium on the specific growth rate of ciliata isolated from activated-sludge

After growing mass and monoxenic cultures of three species of Ciliata (Vorticella microstoma, Colpidium campylum, and Opercularia sp.) with Alcaligenes faecalis as the sole protozoan food, and confirming that copper and hexavalent chromium did not affect the bacterial growth, the effect of these metals on the specific growth rate of each protozoa was examined. The term IL_m (median inhibitory limit) was used to define the metal concentration required to reduce the specific growth rate of protozoa to one-half of that of a control. The IL_m for copper was: 0·25 mg 1⁻¹ (V. microstoma), 0·32 mg 1⁻¹ (C. campylum), and 0·27 mg 1⁻¹ (Opercularia sp.). Regarding hexavalent chromium, IL_m for V. microstoma, C. campylum, and Opercularia sp. were 0·53, 12·9 and 20·2 mg 1⁻¹, respectively. Acclimation of each protozoa to these metals for 96 h resulted in IL_m enhanced values of 1·2–2·2 times as large as that for the control.     

Removal of heavy metals from electroplating rinsewaters by precipitation, flocculation and ultrafiltration

Chromium, nickel, copper and zinc can be effectively removed from electroplating rinsewaters by hydroxide precipitation, flocculation and ultrafiltration. Prior to precipitation, chromium is reduced from the hexavalent to the trivalent form by ferrous sulfate and cyanide in copper and zinc rinsewaters are oxidized by sodium hypochlorite. Minimum metal concentrations in the permeate from separate batches of chromium, nickel, copper and zinc rinsewaters were found to be, respectively, 0.17 mg 1⁻¹ Cr (T), 0.26 mg 1⁻¹ Ni, 0.30 mg 1⁻¹ Cu and 1.84 mg 1⁻¹ Zn. These solubilities are in good agreement with the theoretical solubility curves, except for copper where the formation of stable copper cyanide complexes appears to increase the solubilities at least two orders of magnitude relative to those predicted on the basis of the equilibrium constants for copper hydroxides and oxides. A simple mass balance model, assuming concentrate recycle and constant metal concentration in the permeate, is adequate for the prediction of feed and permeate concentrations as a function of the volume filtered up to a relative volume of about 0.3. Above this value, the feed concentrations are lower than predicted, apparently because of entrapment of metal precipitate in the strainer. Water recoveries are strongly dependent on the specific metal removed and are found to be 24% for Ni with a 0.20 μm membrane, 10% for Cr with a 0.80 μm membrane, 6.5% for Cu and 3.7% for Zn, both with a 0.45 μm membrane.     

Bioconcentration of vanadium in American flagfish over one reproductive cycle

Flagfish (Jordanetta floridae Goode and Bean) were exposed to constant concentrations of vanadium (V) in the water from age 10 days to maturity, and second-generation fish were continued in the same concentrations to age 30 days. Residues of vanadium were directly related to exposure concentrations but bioconcentration factors were inversely related to them. Both residues and bioconcentration factors increased with exposure time up to 70 days, after which they remained stable to the end of exposure at 96 days. Residues and bioconcentration factors did not differ significantly between first- and second-generation fish, nor between males and females.Adults accumulated 21–29 μg V g⁻¹ (whole body dry weight) during exposure to 0.48 or 1.50 mg V 1⁻¹. These residues were significantly higher than values of 15–17.5, 4.4–4.8, and 0.27–0.54 μg V 1⁻¹, found after exposure to 0.17, 0.041 mg V 1⁻¹, and control conditions, respectively. Residues for these two lowest concentrations and control were significantly different from each other.Bioconcentration factors were 2.0–28 × two or three orders of magnitude lower than the factors for cadmium and zinc in the same species of fish, as determined by other investigators. The bioconcentration factors appeared, in fact, to be at the low end of the range found for metals, and danger to fish from bioaccumulation of vanadium was accordingly judged to be low.     

Accumulation de quelques metaux lourds (Cd, Cu, Pb et Zn) chez l'eperlan (Osmerus mordax) preleve sur la rive Nord de l'Estuaire du Saint-Laurent

Heavy metals in trace amounts are normal constituents of marine organisms. At sufficiently high concentrations, heavy metals are toxic to living organisms and so it is important to know by how much their concentration may be increased before effects on marine or estuarine populations can be detected or commercial species become unsuitable as food. A method of removing metals is by storage in a particular tissue. Several different sites for storing metals were investigated and concentrations of Cd, Cu, Pb and Zn were examined in muscle, liver and gonads of the smelt (Osmerus mordax) from the North shore of the St Lawrence estuary. Copper and zinc are constituents of several enzymes and are absolutely essential for normal growth and development, while cadmium and lead are not known to have necessary physiological function. A modified wet digestion procedure was used to prepare biological samples for the determination of trace elements by flameless atomic absorption spectrophotometry procedure, using calibration standards made up in a matrix of similar acidity (Table 1). NBS reference material bovine liver was analyzed along with the samples and the results were within the specified tolerance (Table 2). Analyses were reported on a dry weight basis (Table 3) and the correlations with total body weight were determined by regression analysis. Copper (range 0.3–3.3 μg g⁻¹) and zinc (range 19–38 μg g⁻¹) in muscle fillets were found to be negatively correlated with total body weight (Fig. 1). Apparent decreasing concentrations in these two metal levels in muscle sample with increasing body weight were possibly due to factor such as dilution with growth. Growth may dilute metal concentrations in an organism if tissue is added faster than metal. Livers and gonads contained greater levels of the four metals than somatic muscle. Liver metal concentrations of Zn (range 29–108 μg g⁻¹) and Cd (range 0.06–0.37 μg g⁻¹) increased with total body weight. All equations fit data at P < 0.01 (Fig. 2). Positive correlations between size and metal concentrations suggest that net uptake may occur. Inessential, slowly exchanging metals such as Cd appear to reflect an uptake which tend to become a cumulative process (age dependence of concentrations). The occurrence of insignificant correlation between liver concentrations of Cu (mean value: 4 μg g⁻¹) and environmental concentrations of this metal was consistent with equilibration. Since fish are known to possess the metal binding protein metallothionein, a sequestering agent, detoxification of these metals in fish liver may be by sequestration rather than elimination. Increasing metal concentrations in liver may represent storage of sequestered products in that organ. In the gonads, no significant relationship exists between total body weight and trace metal contents. Results of t-test indicated that females had significantly greater Cu and Zn concentrations, but no significant difference existed between males and females for Cd concentrations (Figs 3 and 4). Thus, the relation between concentration and total body weight appears to be specific as to the species, tissues analyzed and environmental conditions. The comparison of metal concentrations in fish to assess variations in contamination levels requires understanding the relationship between metal concentration and body size within each population.