Concentrations of Metals in Water,Sediment, Biofilm,Benthic Macroinvertebrates,and Fish in the Boulder River Watershed,Montana, and the Role of Colloids in Metal Uptake

To characterize the partitioning of metals in a stream ecosystem, concentrations of trace metals including As, Cd, Cu, Pb, and Zn were measured in water, colloids, sediment, biofilm (also referred to as aufwuchs), macroinvertebrates, and fish collected from the Boulder River watershed, Montana. Median concentrations of Cd, Cu, and Zn in water throughout the watershed exceeded the U.S. EPA acute and chronic criteria for protection of aquatic life. Concentrations of As, Cd, Cu, Pb, and Zn in sediment were sufficient in the tributaries to cause invertebrate toxicity. The concentrations of As, Cu, Cd, Pb, and Zn in invertebrates from lower Cataract Creek (63, 339, 59, 34, and 2,410 μg/g dry wt, respectively) were greater than the concentrations in invertebrates from the Clark Fork River watershed, Montana (19, 174, 2.3, 15, and 648 μg/g, respectively), that were associated with reduced survival, growth, and health of cutthroat trout fed diets composed of those invertebrates. Colloids and biofilm seem to play a critical role in the pathway of metals into the food chain and concentrations of As, Cu, Pb, and Zn in these two components are significantly correlated. We suggest that transfer of metals associated with Fe colloids to biological components of biofilm is an important pathway where metals associated with abiotic components are first available to biotic components. The significant correlations suggest that Cd, Cu, and Zn may move independently to biota (biofilm, invertebrates, or fish tissues) from water and sediment. The possibility exists that Cd, Cu, and Zn concentrations increase in fish tissues as a result of direct contact with water and sediment and indirect exposure through the food chain. However, uptake through the food chain to fish may be more important for As. Although As concentrations in colloids and biofilm were significantly correlated with As water concentrations, As concentrations in fish tissues were not correlated with water. The pathway for Pb into biological components seems to begin with sediment because concentrations of Pb in water were not significantly correlated with any other component and because concentrations of Pb in the water were often below detection limits.     

Relationship Between Wetlands and Mercury in Brook Trout

The purpose of this study was to determine if wetlands influence mercury concentrations in brook trout (Salvelinus fontinalis), benthic macroinvertebrates, and stream water. On September 26, 2005, water samples, benthic macroinvertebrates, and brook trout were collected from four streams in western Maryland under low-flow conditions. Water samples were also collected in these four streams under high-flow conditions in January 2006. The watersheds of Blue Lick and Monroe Run did not contain wetlands, but the watersheds of the Upper Savage River (3% of upstream area) and Little Savage River (7% of upstream area) contained wetlands. We found significantly (p = 0.05) higher average total mercury concentration in brook trout from Little Savage River (129 ± 54 ng g⁻¹); intermediate concentrations (66 ± 19 ng g⁻¹) in brook trout from Upper Savage River; and lowest concentrations in brook trout from Blue Lick (28 ± 11 ng g⁻¹) and Monroe Run (23 ± 19 ng g⁻¹). Brook trout in all streams accumulated mercury at the same rate over their lifetimes, but the youngest fish had significantly different mercury concentrations (Little Savage > Upper Savage > Blue Lick = Monroe Run), which may be due to differences in mercury concentrations in the eggs or food for the fry. Mercury concentrations in brook trout were not consistent with mercury concentrations in stream water and benthic macroinvertebrates. The Little Savage River had significantly higher total and methylmercury concentrations in stream water, but mercury concentrations in the other streams and in the benthic macroinvertebrates were not significantly different among streams. The unusually high methylmercury concentrations (0.5 to 2.1 ng L⁻¹) in the Little Savage River may have been caused by production of methylmercury in the pools. The relatively low methylmercury concentrations in the Upper Savage River may be caused by a mercury concentration gradient downstream of the wetland.     

Background Concentrations of Heavy Metals in Benthos from Transboundary Rivers of the Transbaikalia Region, Russia

The concentrations (mg/kg dry weight) of Cu, Zn, As, Cd, Hg, and Pb were measured in benthic macroalgae and invertebrates collected in the upper transboundary tributaries of the Onon River, Transbaikalia, Russia. The background concentration ranges in Cladophora fracta, Ulothrix zonata and Zygnemataceae were: 6.4–9.1 for Cu, 27.2–73.1 for Zn, 0.4–0.9 for Cd, 6.7–35.3 for As, 0.01–0.02 for Hg, and 1.9–4.3 for Pb. In Brachycentrus americanus and Lymnaea media the concentration ranges were: 9.0–25.5 for Cu, 21.4–96.0 for Zn, 0.1–0.3 for Cd, 1.7–5.6 for As, 0.004–0.02 for Hg, and 0.4–2.2 for Pb. The concentrations of Cu, Zn, Pb, and Hg were consistent with data for uncontaminated areas. Under contamination conditions the concentrations in C. fracta were: 938 for Zn, 513 for Pb, and 9.5 for Cd; in Lymnaea media were: 46.8 for Cu, 176 for Zn, 52.3 for Pb, and 3.0 for Cd. All the organisms showed a common response to contamination, and consequently can be used as biomonitors of contamination by heavy metals.     

Distribution of Trace Elements in Streambed Sediment Associated with Mining Activities in the Upper Colorado River Basin, Colorado, USA, 1995–96

Streambed-sediment samples were collected in the Southern Rocky Mountains physiographic province in the Upper Colorado River Basin in Colorado to characterize the occurrence and distribution of trace elements in mined and nonmined areas of the basin. During October 1995 and September 1996, streambed sediment was collected at 37 sites, and the samples were analyzed for trace elements. The ranges in concentrations of As, Cd, Cu, Pb, and Zn at mining sites generally were orders of magnitude higher than the ranges of concentrations at nonmining sites. Sampling sites located in two predominant rock types in mining areas were not significantly different (p > 0.05) for concentrations of As, Cd, Pb, and Zn. Cu was significantly different (p < 0.05) between sites in the two predominant rock types. Concentrations of As, Cd, Cu, Pb, and Zn were not significantly different (p > 0.05) between main-stem sites and tributary sites. Concentrations of As, Cd, Cu, Pb, and Zn exceeded established guidelines for adverse effects on aquatic biota at some sites in the study area. The patterns in concentrations of Cd and Zn, Cd and Pb, and Pb and Zn were highly correlated to one another in this study. Concentrations of trace elements in the <63-μm fraction were higher than in the total particle-size fraction analysis. Comparison of reference sites to sites affected by a mine source indicated that trace-element concentrations initially increased downstream of the source and then gradually decreased in concentration with distance from the source. Received: 31 August 1998/Received: 11 January 1999     

Accumulation of heavy metals in Caspian seals (Phoca caspica)

Concentrations of heavy metals (Fe, Mn, Zn, Cu, Pb, Ni, Cd, Co, and Hg) were determined in the muscle, liver, and kidney of 42 Caspian seals and fishes collected from the Caspian Sea in 1993. Higher Mn and lower Fe and Cu concentrations were found in the liver in comparison with other marine pinnipeds. Lower Cu concentrations in the liver appear to be a common feature in small seals belonging to subgenus Pusa, which include ringed, Baikal, and Caspian seals. However, low Fe and high Mn in livers were specific to Caspian seal. Concentrations of toxic metals such as Hg and Cd were relatively low. Pinniped species can be divided into two groups, based on accumulations of Cd or Hg in the liver. Interestingly, it was found that Cd-accumulating groups feed on invertebrates, whereas the preferred diet of Hg accumulators is fish. Caspian seals seemed to belong to the Hg-accumulating group. Cd and Hg concentrations in the liver and kidney of young animals increased with age. Mercury concentrations in adult animals increased with age continuously, whereas Cd concentrations in adult animals decreased. This trend might be due to preferential feeding habits and shift in ratio of Hg and Cd in the diet (i.e., invertebrates to fish). Received: 10 July 2001/Accepted: 7 January 2002     

Impacts and Pathways of Mine Contaminants to Bull Trout (Salvelinus confluentus) in an Idaho Watershed

Metals contamination from mining activities is a persistent problem affecting aquatic ecosystems throughout mining districts in the western USA. The Gold Creek drainage in northern Idaho has a history of mining within its headwaters and contains elevated sediment concentrations of As, Cd, Cu, Pb, and Zn. To determine system-wide impacts of increased metals, we measured concentrations of metals in water, sediment, and benthic macroinvertebrate tissues and related them to whole-body fish tissues and histopathological alterations in native salmonids. Water concentrations were higher than those in reference areas, but were below water quality criteria for protection of aquatic biota for most of the study area. Sediment and benthic macroinvertebrate tissue concentrations for all metals were significantly higher at all sites compared with the reference site. Fish tissues were significantly higher for all metals below mine sites compared with the reference site, but only Cd and Pb were higher in fish tissues in the furthest downstream reach in the Gold Creek Delta. Metals concentrations in benthic macroinvertebrate tissues and fish tissues were strongly correlated, suggesting a transfer of metals through a dietary pathway. The concentrations within sediments and biota were similar to those reported in other studies in which adverse effects to salmonids occurred. We observed histopathological changes in livers of bull trout, including inflammation, necrosis, and pleomorphism. Our study is consistent with other work in which sediment-driven exposure can transfer up the food chain and may cause adverse impacts to higher organisms.     

Leachability of Protein and Metals Incorporated into Aquatic Invertebrates: Are Species and Metals-Exposure History Important?

To partially simulate conditions in fish intestinal tracts, we leached six groups of metals-contaminated invertebrates at pH 2 and pH 7, and analyzed the concentrations of four metals (Cd, Cu, Pb, and Zn) and total protein in the leachates. Four of the groups of invertebrates were benthic macroinvertebrates collected from metals-contaminated rivers (the Clark Fork River in Montana and the Coeur d’Alene River in Idaho, USA); the other two groups of invertebrates (one of which was exposed to metals in the laboratory) were laboratory-reared brine shrimp (Artemia sp.). Additionally, we fractionated the pH 2 leachates using size-exclusion chromatography (SEC). Protein content was 1.3 to 1.4× higher in Artemia than in the benthic macroinvertebrates, and leachability of metals and protein differed considerably among several of the groups of invertebrates. In SEC fractions of the pH 2 leachates from both groups of Artemia, Cu and protein co-eluted; however, Cu and protein did not co-elute in SEC fractions of the leachates from any of the benthic macroinvertebrate groups. Although none of the other three metals co-eluted with protein in any of the pH 2 leachates, one or more of the metals co-eluted with lower-molecular-weight molecules in the leachates from all of the groups of invertebrates. These results suggest fundamental differences in metal-binding properties and protein leachability among some invertebrates. Thus, different invertebrates and different histories of metals exposure might lead to different availability of metals and protein to predators.     

Acute toxicity of cadmium, lead, zinc, and their mixtures to stream-resident fish and invertebrates

The authors conducted 150 tests of the acute toxicity of resident fish and invertebrates to Cd, Pb, and Zn, separately and in mixtures, in waters from the South Fork Coeur d'Alene River watershed, Idaho, USA. Field-collected shorthead sculpin (Cottus confusus), westslope cutthroat trout (Oncorhynchus clarkii lewisi), two mayflies (Baetis tricaudatus and Rhithrogena sp.), a stonefly (Sweltsa sp.), a caddisfly (Arctopsyche sp.), a snail (Gyraulus sp.), and hatchery rainbow trout (Oncorhynchus mykiss), were tested with all three metals. With Pb, the mayflies (Drunella sp., Epeorus sp., and Leptophlebiidae), a Simuliidae black fly, a Chironomidae midge, a Tipula sp. crane fly, a Dytiscidae beetle, and another snail (Physa sp.), were also tested. Adult westslope cutthroat trout were captured to establish a broodstock to provide fry of known ages for testing. With Cd, the range of 96-h median effect concentrations (EC50s) was 0.4 to >5,329 μg/L, and the relative resistances of taxa were westslope cutthroat trout ≈ rainbow trout ≈ sculpin < other taxa; with Pb, EC50s ranged from 47 to 3,323 μg/L, with westslope cutthroat trout < rainbow trout < other taxa; and with Zn, EC50s ranged from 21 to 3,704 μg/L, with rainbow trout < westslope cutthroat trout ≈ sculpin < other taxa. With swim-up trout fry, a pattern of decreasing resistance with increasing fish size was observed. In metal mixtures, the toxicities of the three metals were less than additive on a concentration-addition basis.     

Distribution of Metals in Surface Sediments from a Small River Flowing Through Urban and Agricultural Areas

The characteristic distributions of 12 metals (Al, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Cd and Pb) were investigated in surface sediments from a small river (Niitsu River) flowing through both urban and agricultural areas by comparison with those from the upper main stream (Nodai River). Among the investigated metals, the mean concentrations of Al, Cr, Fe, Zn, Cd and Pb in the Niitsu River were significantly higher than those in the Nodai River. The investigated sites can be characterized by the principal components 1–3.     

Perfluorinated Compounds in Aquatic Organisms at Various Trophic Levels in a Great Lakes Food Chain

Trophic transfer of perfluorooctanesulfonate (PFOS) and other related perfluorinated compounds was examined in a Great Lakes benthic foodweb including water–algae–zebra mussel–round goby–smallmouth bass. In addition, perfluorinated compounds were measured in livers and eggs of Chinook salmon and lake whitefish, in muscle tissue of carp, and in eggs of brown trout collected from Michigan. Similarly, green frog livers, snapping turtle plasma, mink livers, and bald eagle tissues were analyzed to determine concentrations in higher trophic-level organisms in the food chain. PFOS was the most widely detected compound in benthic organisms at various trophic levels. Concentrations of PFOS in benthic invertebrates such as amphipods and zebra mussels were approximately 1000-fold greater than those in surrounding water, which suggested a bioconcentration factor (BCF; concentration in biota/concentration in water) of 1000 in benthic invertebrates. Concentrations of PFOS in round gobies were two- to fourfold greater than those in their prey organisms such as zebra mussels and amphipods. Concentrations of PFOS in predatory fishes (Chinook salmon and lake whitefish) were 10 to 20-fold greater than those in their prey species. Concentrations of PFOS in mink and bald eagles were, on average, 5- to 10-fold greater than those in Chinook salmon, carp, or snapping turtles. Because of the accumulation of PFOS in liver and blood, the biomagnification factor (BMF) of perfluorinated compounds in higher trophic-level organisms such as salmonid fishes, mink, and eagles were based on the concentrations in livers or plasma. Overall, these results suggest a BCF of PFOS of approximately 1000 (whole-body based) in benthic invertebrates, and a BMF of 10 to 20 in mink or bald eagles, relative to their prey items. Eggs of fish contained notable concentrations of PFOS, suggesting oviparous transfer of this compound. PFOA was found in water, but its biomagnification potential was lower than that of PFOS.     

Concentrations of Metals Associated with Mining Waste in Sediments, Biofilm, Benthic Macroinvertebrates, and Fish from the Coeur d'Alene River Basin, Idaho

Arsenic, Cd, Cu, Pb, Hg, and Zn were measured in sediments, biofilm, benthic macroinvertebrates, and fish from the Coeur d'Alene (CDA) River to characterize the pathway of metals transfer between these components. Metals enter the CDA Basin via tributaries where mining activities have occurred. In general, the ranking of food-web components from the greatest to smallest concentrations of metals was as follows: biofilm (the layer of abiotic and biotic material on rock surfaces) and sediments > invertebrates > whole fish. Elevated Pb was documented in invertebrates, and elevated Cd and Zn were documented in sediment and biofilm approximately 80 km downstream to the Spokane River. The accumulation of metals in invertebrates was dependent on functional feeding group and shredders-scrapers that feed on biofilm accumulated the largest concentrations of metals. Although the absolute concentrations of metals were the largest in biofilm and sediments, the metals have accumulated in fish approximately 50 km downstream from Kellogg, near the town of Harrison. While metals do not biomagnify between trophic levels, the metals in the CDA Basin are bioavailable and do biotransfer. Trout less than 100 mm long feed exclusively on small invertebrates, and small invertebrates accumulate greater concentrations of metals than large invertebrates. Therefore, early-lifestage fish may be exposed to a larger dose of metals than adults. Received: 3 April 1997/Accepted: 8 September 1997     

Anthropogenic Sources of Heavy Metals in the Indian Ocean Coast of Kenya

Water and surface sediment samples from Rivers Sabaki, Ramisi and Vevesi that flow into the Indian Ocean coast of Kenya were analysed for heavy metals. The sediment concentrations of exchangeable cations (in μg/g) for Co, Cu, Mn, Ni, Pb, Sn and Zn ranged from 0.10 to 506.75 (for Mn at Sabaki), constituting between 2% and 20% of the total metal concentrations obtained by digestion with strong acid. Cu, Mn, Ni, Pb and Zn were more leachable with 0.1 N HCl. The total dissolved metal in water and the total sediment concentrations for Ag, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sn and Zn are given in the text. For dissolved metals, the metal/Mn ratios indicated higher concentrations of Ag in Sabaki River, Cd in Ramisi, Ni in Sabaki and Pb in Ramisi, respectively. In sediments, the metal/Mn ratios showed higher enrichment of Ag in Ramisi, Cd in Sabaki and Vevesi, and Zn in Sabaki, respectively. Enrichment factors showed elevated levels of Cd, Pb and Zn in sediment in River Sabaki and River Vevesi that were due to anthropogenic inputs through Athi River. The total dissolved metal concentration ranges for the three rivers were comparable with those ranges reported in rivers in South Africa but the sediment concentrations were below those of rivers in Europe and Asia where anthropogenic addition of some of the toxic elements such as Cu, Pb and Cd is evidently higher.     

Heavy Metals in Livers of Waterbirds from Spain

Wetlands tend to accumulate heavy metals from local sources, such as Pb shot used for waterfowl hunting, and from regional sources, such as atmospheric deposition and riverine or marine inputs. We determined concentrations of six heavy metals (Cr, Mn, Cu, Zn, Cd, and Pb) in livers of waterbirds shot by hunters in five Spanish wetlands to study the different factors that can contribute to the accumulation of these metals (sex, age, diet, grit, and Pb shot ingestion). Differences among wetlands were observed only for Cr, Cu, and Cd. Differences among species were observed for all the metals, and Cu was notably higher in pochards (Aythya and Netta genus) than in other waterfowl. Cu, Zn, and Cd concentrations increased with age, and only Pb showed differences related to sex, with males having higher concentrations than females. Most metals other than Pb were correlated with each other. Lead was dependent on Pb shot ingestion. Grit ingestion positively correlated with concentrations of Cr and to a lesser extent with Mn, Zn, and Cd. Ingestion of grit or shot may obscure relationships between metals and diet. Herbivorous species, which had more grit in the gizzard, had higher Cr, Zn, and Cd concentrations. Granivorous birds, which have the highest rates of Pb shot ingestion, had the highest concentrations of Pb. Grit and Pb shot ingestion are both important sources of heavy metals for waterbirds. Lead was the single metal studied whose concentrations exceeded toxicity thresholds. Received: 5 March 2002/Accepted: 12 June 2002     

Variations of heavy metals and arsenic in fish and other organisms from the Calcasieu River and Lake,Louisiana

The edible parts of several species of fish and other marine organisms inhabiting the Calcasieu River/Lake, Louisiana were analyzed for Cd, Cr, Cu, Pb, Hg, Ag, Zn, and As. Concentrations of all metals measured in both intra and interspecies showed no significant variation with sample location. Differences in elemental concentrations were related to organism mobility and not to site-specific variations in metal loadings. Different species of finfish contained only trace amounts of Cd (0.02-0.08), Ag (<0.01–0.3), Pb (<0.2–0.5), and As (<0.1–0.3) mg kg^–1. Concentrations of Cu and Cr were highly variable, in contrast to Zn, which was present in relatively constant amounts across all species (28 ± 7 mg kg^–1). Sessile organisms such as oysters had the highest concentrations of heavy metals, including Cd. Periphyton and Zooplankton were the only groups that showed differences in metal concentrations with sampling location.     

Mouthpart deformities and community composition of Chironomidae (Diptera) larvae downstream of metal mines in New Brunswick,Canada

The effect of metal enrichment on chironomid communities was examined in streams receiving mine drainage from metal mining operations in New Brunswick, Canada. At five sites receiving mine drainage, metal concentrations were significantly (p < 0.05) elevated in water (Zn), periphyton (Cd, Co, Cu, and Zn), and chironomid tissue (Cu, Cd, and Zn) relative to five paired reference locations. Metal concentrations in chironomid larvae were significantly correlated with concentrations in both water and periphyton. Chironomid communities were severely affected at sites receiving mine drainage as demonstrated by reduced genera richness and altered community composition. Sites receiving mine drainage exhibited an increased abundance of metal-tolerant Orthocladiinae and a reduced abundance of metal-sensitive Tanytarsini relative to reference sites. The incidence of mentum deformities was significantly elevated at sites receiving mine drainage (1.43 +/- 0.24%), with the mean percentage approaching a doubling of that observed at reference sites (0.79 +/- 0.22%). Trace metal concentrations at mine-associated streams in New Brunswick significantly affected the benthic community and have the potential to alter the structure and function of these aquatic ecosystems.     

Distribution of Metals in the Tissues of Benthic, <Emphasis Type="Italic">Euryglossa orientalis</Emphasis> and <Emphasis Type="Italic">Cynoglossus arel.</Emphasis>, and Bentho-Pelagic, <Emphasis Type="Italic">Johnius belangerii.</Emphasis>, Fish from Three Estuaries,Persian Gulf

Concentrations of Cd, Co, Cu, Ni, Pb, Fe and Zn were determined in the muscle, liver and gills of three commercial benthic and pelagic fish species (Johnius belangerii, Euryglossa orientalis and Cynoglossus arel) from three estuaries in the northwest Persian Gulf. Metals levels varied significantly depending on the tissues, species and locations. Generally, the results showed that liver accumulate higher concentrations of the metals in comparison to muscle and gills, except in few cases. Among the species, E. orientalis showed the highest levels of Co, Cu, Ni and Fe, while the highest concentrations of Pb and Zn were observed in C. arel. J. belangerii accumulated the highest level of Pb element.     

Determination of selected heavy metal concentrations and distribution in a southwestern stream using macrophytes

Since the reduction of the arsenic standard from 50 to 10 μg L⁻¹ by the US Environmental Protection Agency in 2006 many small town and rural water municipalities were left with the task of preventing or mitigating arsenic contamination of drinking water supplies. In this study macrophytes and sediments were used to determine the concentration and distribution of heavy metals (As, Cd, Cu, Pb, and Zn) within the primary source of drinking water (Gallinas River watershed) to the residents of Las Vegas, New Mexico. Sampling was done in the spring and fall at four sites, two above the city and two below, and samples were analyzed using ICP-MS. Results showed significantly higher (p<.05) metal concentrations in plant roots than shoots for most metals. Spearman’s correlation showed positive correlations (r>.3) between plant and sediment concentrations of Cd, Pb, Zn, As, and a negative correlation for Cu. The site above waste water treatment plant (AWWTP) had the highest plant tissue concentrations of Cd, Pb, Zn, and As. All of these concentrations attained critical toxicity levels exceeding sediment quality guidelines. High concentration factor values and levels of metals detected in macrophyte tissues indicate that heavy metals within sediments in the Gallinas River occur in bioavailable forms. Correlations between plant and sediment metal concentrations indicate that metal concentrations in macrophyte tissues are a good reflection of metal concentrations within the sediment in the Gallinas River.     

Distribution and Association of Trace Metals in Soft Tissue and Byssus of Mytilus edulis from the East Coast of Kyushu Island, Japan

Concentrations of Cd, Pb, Zn, Cu, Ag, Cr, Co Ni, Mn, and Fe in soft tissues and byssi of blue mussel (Mytilus edulis) from three sites along the east coast of Kyushu Island, Japan, were determined by AAS method. Large inter-regional differences in metal concentrations in both soft tissues and byssi (Cu, Cd, and Pb and Cu, Pb, Co, Ni, Mn, and Fe, respectively) were recorded. Highly significant correlations (p < 0.01) were observed between tissue and byssal concentrations of Pb, Cu, Zn, and Mn. The tissue concentrations of Cu, Cd, and Pb were two orders of magnitude greater in Mytilus edulis from expected to be the most contaminated locations compared to those from a nonindustrialized area. Intercomparison of the present study data with those published previously indicates that the soft tissue and especially byssus are useful in detecting some areas of some metallic contaminants. The high concentrations of Cd, and especially Pb and Cu, in Saganoseki mussels and moderately elevated concentrations of these metals in Akamizu mussels may be attributed to the anthropogenic emissions from a metallic refinery and an artificial fiber factory, respectively. It is evident that, compared to the soft tissue, the increase of Cu levels relative to Zn levels in the byssi of M. edulis are eight times higher, with a slope b (Cu/Zn) of 7.5 for byssus and 0.93 for soft tissue. This suggests that byssus, as compared to soft tissue, is a more sensitive bioindicator for Cu. From the data obtained, the soft tissue and especially byssi of M. edulis appear to be good bioindicators for identification of coastal areas exposed to metallic contaminants. Received: 29 January 1996/Revised: 19 June 1996     

Metal-metal interactions of dietary cadmium, copper and zinc in rainbow trout, Oncorhynchus mykiss

The influence of metal-metal interactions on uptake, accumulation, plasma transport and chronic toxicity of dietary Cu, Cd and Zn in rainbow trout (Oncorhynchus mykiss) was explored. Juvenile rainbow trout were fed diets supplemented with (μg/g) 500 Cu, 1000 Zn and 500 Cd singly and as a ternary mixture at 2.5% body weight daily ration for 28 days. Complex interactions among the metals dependent on the tissue/organ, metals ratios and duration of exposure were observed. While Zn did not accumulate, whole-body Cd and Cu concentrations increased following linear and saturation patterns, respectively. Early enhanced whole-body Cu accumulation in fish exposed to the metals mixture was correlated with reduced Cd concentration whereas late enhancement of Cd accumulation corresponded with elevated Cd concentration. This suggests early mutual antagonism and late cooperation between Cd and Cu probably due to interactions at temporally variable metal accumulation sites. At the level of uptake, Cd and Cu were either antagonistic or mutually increased the concentrations of each other depending on the duration of exposure and section of the gut. At the level of transport, enhanced Cd accumulation in plasma was closely correlated with reduced concentrations of both Zn and Cu indicating competitive binding to plasma proteins and/or antagonism at uptake sites. Compared to the Cu alone exposure, Cu concentrations were either lower (gills and carcasses) or higher (liver and kidney) in fish exposed to the metals mixture. On the other hand, Cd accumulation was enhanced in livers and carcasses of fish exposed to the mixture compared to those exposed to Cd alone, while Zn stimulated Cu accumulation in gills. Chronic toxicity was demonstrated by elevated malondialdehyde levels in livers and reduced concentrations of Zn and Cu in plasma. Overall, interactions of Cd, Cu and Zn are not always consistent with the isomorphous competitive binding theory.     

Uptake of lead, cadmium, and other metals in the liver and kidneys of cattle near a lead-zinc mine in Kabwe, Zambia

Concentrations of lead, cadmium, and other metals in the liver and kidneys of cattle near a lead-zinc mine in Kabwe (Zambia), which is ranked among the 10 worst polluted places on earth, were compared with other Zambian towns. Metal concentrations were measured in the liver and kidneys of 51 cattle from Kabwe and other Zambian towns. The maximum metal concentrations, expressed in mg/kg and dry weight, in the liver or kidneys were 398.4 (Cu), 252.6 (Zn), 77.81 (Cr), 19.37 (Cd), 7.57 (Ni), 1.8 (Pb), 1.04 (Co), 0.112 (Hg), and 0.05 (As). Concentrations of Pb and Cd in Kabwe cattle were higher than levels in other Zambian towns. The mean concentration of Cd exceeded benchmark values in offal destined for human consumption. Levels of Ni and Cr may also pose public health concerns. Concentrations of Pb and Cr, Pb and Cu, Cd and Zn, Cd and Hg, Zn and Cu, Cu and Co, as well as Co and Ni were positively correlated. The present study also highlighted the dangers of exposure of animals and humans to a mixture of toxic metals.