Impact of dredged urban river sediment on a Saronikos Gulf dumping site (Eastern Mediterranean): sediment toxicity,contaminant levels,and biomarkers in caged mussels

Impacts of chemical contaminants associated with dumping of dredged urban river sediments at a coastal disposal area in Saronikos Gulf (Eastern Mediterranean) were investigated through a combined approach of sediment toxicity testing and active biomonitoring with caged mussels. Chemical analyses of aliphatic hydrocarbons (AHs), polycyclic aromatic hydrocarbons (PAHs), Cu, and Zn in combination with the solid phase Microtox® test were performed on sediments. Concentrations of PAHs, AHs, Cu, and Zn as well as multiple biomarkers of contaminant exposure and/or effects were measured in caged mussels. Sediments in the disposal and neighboring area showed elevated PAHs and AHs concentrations and were characterized as toxic by the solid-phase Microtox® test during and after dumping operations. Biomarker results in the caged mussels indicated sublethal effects mainly during dumping operations, concomitantly with high concentrations of PAHs and AHs in the caged mussel tissues. Cu and Zn concentrations in sediments and caged mussels were generally not elevated except for sediments at the site in the disposal area that received the major amount of dredges. High PAHs and AHs levels as well as sublethal effects in the caged mussels were not persistent after termination of operations. The combined bioassay–biomarker approach proved useful for detecting toxicological impacts of dredged river sediment disposal in sediments and the water column. Nevertheless, further research is needed to evaluate whether sediment toxicity will have long-term effects on benthic communities of the disposal area.     

Distribution and relationships of selected trace metals in molluscs and associated sediments from the Gulf of Aden, Yemen

Concentrations of Cd, Pb, Zn, Cu, Ni, Co, Cr, Mn and Fe in the soft tissue of Turbo coronatus, Acanthopleura haddoni, Ostrea cucullata and Pitar sp., as well as in associated surface sediments (bulk and bioavailable metal concentrations) from the Gulf of Aden, Yemen, were determined by atomic absorption spectrophotometry method. Large differences between size-classes of molluscs in metal concentrations were recorded. Significant spatial differences in metal concentrations in both the soft tissue of the molluscs and associated sediments studied were mostly identified. Statistically significant correlations (p<0.01) between concentrations of selected metals were observed. A slope of the linear regression is significantly higher than unity for Fe (9.91) and Cd (3.45) in A. haddoni and for Ni (4.15) in T. coronatus, suggesting that the bioavailability of these metals is disproportionally increased with a degree of enrichment of the sediments in Fe, Cd and Ni, respectively. A slope constant approximating to unity (1.14) for Cu in A. haddoni relative to its concentration in sediment extract implies that bioavailability of this metal proportionally increased with growing concentrations of its labile forms in the associated sediment. The degree of contamination of Gulf of Aden waters by the metals studied is discussed and the potential ability of molluscs, especially A. haddoni and T. coronatus, as biomonitors of metallic pollutants is postulated.     

Speciation of heavy metals in marine sediments vs their bioaccumulation by mussels.

Total contents and speciation of selected heavy metals, including Al, Fe, Co, Ni, Pb, Zn, Cu, Cr, were measured in sediment samples and mussels Mya arenaria and Astarte borealis collected in the Horsund Fjord off Spitsbergen (Norwegian Sea) and the Bay of Gdansk (Baltic Sea). The investigation aimed at revealing differences in the accumulation pattern of heavy metals in mussels inhabiting sediments characterized by varying metal bioavailability. The contents of metals adsorbed to sediments and associated with iron and manganese hydroxides, which were obtained by sequential extraction, were utilized as a measure of metal bioavailability. The contents of Cd, Pb, Zn, Cu and Cr in mussels collected off Spitsbergen were generally lower than those in mussels from the Baltic Sea. In sediments collected off Spitsbergen the bioavailable fraction represented a small proportion (0-3.7% adsorbed metals and 0-11% associated with metals hydroxides) of total heavy metal contents. In sediments from the Baltic Sea the percentages of metals adsorbed and bound to hydroxides were 1-46% and 1-13%, respectively. The differences in bioavailable metal contents measured in sediments were utilized to explain the different contents of metals in mussels collected in the corresponding sites.     

Heavy metal concentrations in molluscs from the Atlantic coast of southern Spain

Trace metals were determined in the two most abundant species of bivalve molluscs along the Atlantic coast of southern Spain (Donax trunculus and Chamelea gallina) and in the sediments where they live. The results show that the area near the mouth of the Huelva estuary is where the highest metal concentrations are found in sediments and in the two bivalve species. This is not surprising, considering that the Huelva estuary is the mouth of the Tinto and Odiel rivers, which have one of the highest levels of metal pollution of all the rivers of Europe. The two species of bivalves have different amounts of metals in their tissues. The concentrations of Cr, Cu, Pb, Zn, As and Hg in D. trunculus were significantly higher (p < 0.05) than in C. gallina; however, C. gallina contained more Ni and Cd. In both species the most abundant elements were Cu and Zn, while Hg showed the lowest values. There is a significant correlation (p < 0.05) for concentrations of Cu, Pb, Zn and Hg in D. trunculus and C. gallina relative to their concentrations in surface sediments.     

A comparative study of metal pollution and potential eco-risk in the sediment of Chaohu Lake (China) based on total concentration and chemical speciation

Total and extractable concentrations of Cu, Pb, and Zn were determined in surface sediments of west Chaohu Lake (China) by HCl-HNO₃-HF-HClO₄ digestion and an optimized BCR sequential extraction procedure, respectively. The metal pollution was evaluated by the enrichment factor approach, and the potential eco-risk was evaluated by the sediment quality guideline (SQG) and risk assessment code (RAC) assessments. The results indicated that both total and extractable metal concentrations were highly variable and were affected by sediment properties, even though the sediments were predominantly composed of <63-μm particles (>89 %). Enrichment factors of the metals based on the total and extractable concentrations all showed higher values in the northern lake area and decreasing values towards the south. This distribution indicated an input of anthropogenic metals via the Nanfei River. Anthropogenic Cu, Pb, and Zn in surface sediments showed comparable values for each metal based on the total and extractable concentrations, suggesting that anthropogenic Cu, Pb, and Zn resided predominantly in the extractable fractions. Sediment Cu had low eco-risk, and Pb and Zn had medium eco-risk by the SQG assessment, whereas the eco-risk rankings of Cu, Pb, and Zn were medium, low, and low–high, respectively, by the RAC assessment. Referencing to the labile (dilute acid soluble) metal concentrations, we deduced that the eco-risk of Cu may be largely overestimated by the RAC assessment, and the eco-risk of Pb may be largely overestimated by the SQG assessment. Overall, sediments Cu and Pb may pose low eco-risk, and Zn may pose low–high eco-risk.     

Heavy metal concentrations in green-lipped mussels collected from Tolo Harbour and markets in Hong Kong and Shenzhen

Green-lipped mussels, Perna viridis, were collected from Kat O, Yim Tin Tsai, Ma Liu Shui and Tap Mun around Tolo Harbour and six local markets in Hong Kong (Aberdeen, Shau Kei Wan, Kowloon City, Mongkok, Yuen Long) and Shenzhen (Dongmun) between July 1994 and February 1995 and analysed for cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn). The metal concentrations of mussels collected from the study sites were Cd (0.45-1.44 microg/g), Cr (0.82-4.89 microg/g), Cu (6.02-23.99 microg/g), Ni (3.25-6.87 microg/g), Pb (2.02-4.36 microg/g) and Zn (90-135 microg/g), while those from the markets were Cd (0.27-1.44 microg/g), Cr (1.09-3.30 microg/g), Cu (9.05-17.8 microg/g), Ni (2.44-5.25 microg/g), Pb (1.17-5 microg/g) and Zn (51-103 microg/g). The metal concentrations were below the maximum permissible levels set by the Hong Kong Government. In addition, seasonal variation of metal accumulation in mussels was investigated in Yim Tin Tsai and Ma Liu Shui and a reduction in the total heavy metal concentrations during winter was noted. The non-carcinogenic hazard index of mussels collected from Tolo Harbour and from Hong Kong markets was between 0.46 and 1.36 compared with those from Shenzhen markets (0.85-1.46), which indicated a low but possible risk in consuming the mussels.     

Copper, zinc and lead speciation in salt marsh sediments colonised by Halimione portulacoides and Spartina maritima

Total concentrations and fractionation of Cu, Zn and Pb in seven operationally defined phases (exchangeable, carbonates, manganese oxides, organic complexes, amorphous iron oxides, crystalline iron oxides and residual) were determined in sediments colonised by the halophyte species Halimione portulacoides and Spartina maritima in a Tagus estuary salt marsh (Portugal). We aimed to determine whether the speciation of these metals was different in areas colonised by each halophyte. Higher concentrations of Cu, Zn and, in particular Pb, were found in the rhizosphere of S. maritima than in the root sediments of H. portulacoides. Geochemical fractionation of Cu, Zn and Pb in sediments of the salt marsh depended upon the metal, and for Zn and Pb clearly varied with depth and with the colonising species. The higher redox potential observed in sediments colonised by H. portulacoides may in part explain the observed differences in the speciation of Cu, Zn and Pb.     

Distribution and coassociations of trace elements in soft tissue and byssus of Mytilus galloprovincialis relative to the surrounding seawater and suspended matter of the southern part of the Korean Peninsula

The concentrations of Cd, Co, Cu, Cr, Fe, Hg, Mn, Ni, Pb, Sn, Ti and Zn were analyzed by AAS, ICP MS and AFS in soft tissues and byssal threads of Mytilus galloprovincialis from Masan Bay and Ulsan Bay, Korea. Spatial variations in metal concentrations were found. The levels of Cd, Pb, Hg, Cu, Zn, Co and Mn were very high in the mussels from Ulsan Bay (Sts. U1, U2) and comparable with elevated concentrations of these elements in Mytilus sp. reported to date for other geographical areas. Seasonal differences in some metal concentrations were also observed. These variations may be caused by factors such as: a large difference in seawater temperature, food supply for the mussel population and/or freshwater runoff of particulate metal to the coastal water and weight changes brought about by gonadal development and the release of sexual products. Pb, Cu, Zn, Co, Ni, Fe and Mn were more enriched in byssal threads than in the soft tissues, hence the byssus seems to be more sensitive in reflecting the availabilities of trace metals in the ambient waters. Concentrations of trace metals varied with respect to the size of mussels and season, depending on many factors like sexual development, and seawater temperature, etc. The levels of some trace metals in seawater, especially in suspended matter were correlated significantly with those in soft tissues and byssal threads. There were spatial variations in metal concentrations in the soft tissue and byssus attributed to different sources of trace elements located near the sampling sites. There were significant relationships between concentrations of some metals (Cd, Cu, Pb, and Zn) in mussel soft tissues and byssal threads and suspended matter. This suggests that M. galloprovincialis can be used as a sensitive biomonitor for the availabilities of trace elements in the coastal waters off Korea.     

Use of sedimentary metals to predict metal concentrations in black mussel (Mytilus galloprovincialis) tissue and risk to human health (Sydney estuary, Australia)

Filter-feeding bivalves have been used extensively as an indicator of ecosystem condition and in management of estuarine environments. The current study aimed to determine whether sedimentary metals could predict metal concentrations in tissue of filter-feeding mussels (Mytilus galloprovincialis) and to identify areas of the estuary where mussel consumption posed a human health risk. Mussel tissue Cu and Zn concentrations (wet weight) were below guideline values for human consumption in all parts of the waterway, whereas Pb tissue concentrations exceed these guidelines (2.0 μg?g^?1 wet weight) in the upper reaches of some embayments of the estuary. Concentrations of Cu and Pb in the fine fraction (<62.5 μm) of bottom sediment reasonably predicted concentrations (dry weight) of these metals in mussel tissue (r ²?=?0.460 and p?=?0.001 and r ²?=?0.669 and p?<?0.0001, respectively) as these materials are resuspendable and available to filter-feeding estuarine animals, whereas total sediment and mussel tissue were poorly related. Lead concentrations (>350 μg?g^?1) in fine sediments indicated areas of this estuary where human health was at risk due to high tissue concentrations of this metal. These results give encouragement for the use of the metal concentration in fine sediments as an indicator of estuarine condition and risk to human health in this waterway. Mussels were distributed in all parts of the estuary, even in areas where metal concentrations exceeded sediment quality guidelines.     

A comparative assessment of heavy metal accumulation in soft parts and byssus of mussels from subarctic, temperate, subtropical and tropical marine environments

Existing data on metal concentrations in mussels from subarctic, temperate, subtropical and tropical waters were analyzed using multivariate statistics in order to assess regional variations in metal contamination. Potential errors were reduced by only analyzing data from surveys that employed the same protocols, analytical methodologies and analysts. Factor analysis demonstrated that mussels inhabiting extremely contaminated areas (e.g. from Japanese and Swedish metallurgy sources) could be separated from mussels from other contaminated areas, and that metals such as Cd, Pb, Cu and Zn could be used to identify heavily contaminated samples while Co, Fe, Cr and Ni concentrations were good markers for exposure to inputs from different industrial sources. Furthermore byssus, like soft tissue, selectively and sensitively reflects variations of certain metal concentrations in ambient waters and thus serves as a reliable biomonitor for these contaminants in a variety of coastal and estuarine areas.     

Spatial distribution and ecological risk assessment of sediment metals in a highly industrialized coastal zone southwestern Taiwan

Spatial variations of Cr, Cu, Hg, Ni, Pb, and Zn in the surface sediments from 34 stations of the Kaohsiung coastal zone southwestern Taiwan were studied to address the current pollution status, sediment quality, and potential ecological risk. The study revealed that the concentrations of sediment metals in Kaohsiung Harbor were alarmingly high compared to the other region of Kaohsiung coast. The concentrations of Cr, Cu, Hg, Ni, Pb, and Zn in the harbor sediments were as high as 351, 247, 1.93, 61.8, 60.9, and 940 mg kg⁻¹, respectively. The current situation of metal pollution was assessed by different pollution indices and results showed moderate to severe enrichment of Cu, Hg, and Zn in the harbor sediments. According to the degree of contamination, pollution load index, and contamination severity index, the sediments from the inner Kaohsiung Harbor show high degree and high severity of metal contamination, while the rest of Kaohsiung coastal areas show uncontaminated or low-level pollution. Results of mean ERM quotient and potential ecological risk index also indicated that the harbor sediments posed a 49% probability of biological toxicity and very high ecological risk. The toxic units indicated that the negative biological effects of the six metals in the harbor sediments were Zn > Cu > Cr > Ni > Hg > Pb. In contrast to Kaohsiung Harbor as a trap where considerable amount of anthropogenic metal loadings accumulated in sediments, low metal concentrations were observed in most Kaohsiung coastal sediments. It probably resulted from the limited fine-grained sediment deposition. In the wave-dominated Kaohsiung coastal zone, fine-grained sediments associated with polluted metals tend to be easily resuspended and transported offshore via waves and wave-induced currents. The results of this study can provide valuable information for river and coastal zone management.

     

Spatial Distribution Patterns,Sources of Heavy Metals,and Relation to Ecological Risk of Surface Sediments of the Cyprus Northern Shelf (Eastern Mediterranean)

In this study, the spatial distribution of metals and the sources of metal pollution were investigated along the Northern Shelf of Cyprus (Mediterranean Sea). The concentrations of heavy metals and organic matter were measured in sediments collected from the Gemi Konagi, Girne, and Gazi Magusa areas. Measured metal values were compared with Mediterranean background concentrations. Cu and Zn concentrations at the Gemi Konagi area and all of the Cr values were higher than Mediterranean backgrounds. The metal levels were evaluated by the enrichment factor (EF), contamination factor (C_f) and degree of contamination (C_d). EF results indicated that heavy metal sources were probably originated from natural processes and mining activities. The C_f values of Hg indicated low contamination. The C_d (degree of contamination) values for all heavy metals also showed a low degree of contamination at the study area. Metal levels were also compared with the numerical Sediment Quality Guidelines (SQG) for an environmental risk assessment. Results showed that sediments were classified as heavily polluted by Cu and moderately polluted by Zn at Gemi Konagi and heavily polluted by Cr and Ni contamination at all sampling areas per the SQG.     

Modification of trace metal accumulation in the green mussel Perna viridis by exposure to Ag, Cu, and Zn

To examine the Cd, Hg, Ag, and Zn accumulation in the green mussel Perna viridis affected by previous exposure to Cu, Ag, or Zn, the dietary metal assimilation efficiency (AE) and the uptake rate from the dissolved phase were quantified. The mussel's filtration rate, metallothionein (MT) concentration, and metal tissue burden as well as the metal subcellular partitioning were also determined to illustrate the potential mechanisms underlying the influences caused by one metal pre-exposure on the bioaccumulation of the other metals. The green mussels were pre-exposed to Cu, Ag, or Zn for different periods (1-5 weeks) and the bioaccumulation of Cd, Hg, Ag, and Zn were concurrently determined. Pre-exposure to the three metals did not result in any significant increase in MT concentration in the green mussels. Ag concentration in the insoluble fraction increased with increasing Ag exposure period and Ag ambient concentration. Our data indicated that Cd assimilation were not influenced by the mussel's pre-exposure to the three metals (Cu, Ag, and Zn), but its dissolved uptake was depressed by Ag and Zn exposure. Although Hg assimilation from food was not affected by the metal pre-exposure, its influx rate from solution was generally inhibited by the exposure to Cu, Ag, and Zn. Ag bioaccumulation was affected the most obviously, in which its AE increased with increasing Ag tissue concentration, and its dissolved uptake decreased with increasing tissue concentrations of Ag and Cu. As an essential metal, Zn bioaccumulation remained relatively stable following the metal pre-exposure, suggesting the regulatory ability of Zn uptake in the mussels. Zn AE was not affected by metal pre-exposure, but its dissolved uptake was depressed by Ag and Zn pre-exposure. All these results indicated that the influences of one metal pre-exposure on the bioaccumulation of other metals were metal-specific due to the differential binding and toxicity of metals to the mussels. Such factors should be considered in using metal concentrations in mussel's soft tissues to evaluate the metal pollution in coastal waters.     

Heavy metal concentrations in sediments from Manila Bay, Philippines and inflowing rivers

Concentrations of Fe, Mn, Zn, Cu, Pb, Ni, Cd and Co were determined in surface and core sediments collected from Manila Bay and in surface sediments from inflowing rivers. Core profiles revealed highly fluctuating and enriched Pb, Cd, Zn and Cu concentrations on the surface, suggestive of recent inputs coming from anthropogenic sources. Concentrations of Pb, Zn, and to a lesser extent Cu and Cd were higher in riverine sediments as compared with marine sediments, which may be attributed to the proximity of these riverine sites to pollutant sources. Comparison of metal concentration levels obtained with other areas in the world revealed elevated values for Pb and Cd, indicating a considerable amount of pollution in the area. Continuous monitoring and further studies of the area are recommended to ascertain long-term effects that may have not yet been reached.     

Use of zebra mussel (Dreissena polymorpha) to assess trace metal contamination in the largest Italian subalpine lakes.

Trace metal (Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn) contamination was evaluated in zebra mussels from the lakes Maggiore, Lugano, Como, Iseo and Garda, which are located in the most highly populated and industrialised area in Italy. Zebra mussels from Lake Maggiore contained the highest concentrations (3.44, 1.51, 4.97, 0.158, 5.87, 346 microg g(-1) for Cd, Co, Cr, Hg, Pb, Zn, respectively) of all metals analysed except Cu and Ni. The lowest levels of most metals were in animals from Garda and Lugano (0.78 and 0.60 microg g(-1) for Cd, 2.87 and 2.03 microg g(-1) for Cr, 0.065 and 0.049 microg g(-1) for Hg, 12.1 and 11.9 microg g(-1) for Ni, 1.96 and 2.46 microg g(-1) for Pb, 158 and 163 microg g(-1) for Zn). The most contaminated sites and possible local sources of metals were identified for each lake, and the lakes classified into quality classes concerning metal pollution.     

Total,dissolved, and bioavailable metals at Lake Texoma marinas

Dissolved metals in water and total metals in sediments were measured at marina areas in Lake Texoma during June 1999 to October 2001, and October 2001, respectively. The metals most often found in the highest concentrations in marina water were Na and Ca, followed by Mg and K. Elevated Cu levels detected in lake water appeared to be associated with Cu based anti-fouling paint used on boats. Metal concentrations in sediment were much higher than in water. The relative order of the concentration in sediment was Ca > Al > Fe > K > Mg > Na. Elevated Cu level at specific locations appeared to be associated with local anthropogenic sources of boat repair activities. There were positive relationships between several metal elements in water and sediment. Metals in 16 sediments from lake marinas were extracted with a weak electrolyte solution [0.1 M Ca(NO3)2] to predict the bioavailability of metals. Among the five heavy metals studied (As, Cd, Cr, Cu and Zn), Cu was the most bioavailable in Lake Texoma marinas.     

Speciation distribution and mass balance of copper and zinc in urban rain, sediments, and road runoff

Heavy metal pollution in road runoff had caused widespread concern since the last century. However, there are little references on metal speciation in multiple environmental media (e.g., rain, road sediments, and road runoff). Our research targeted the investigation of metal speciation in rain, road sediments, and runoff; the analysis of speciation variation and mass balance of metals among rain, road sediments, and runoff; the selection of main factors by principal component analysis (PCA); and the establishment of equation to evaluate the impact of rain and road sediments to metals in road runoff. Sequential extraction procedure contains five steps for the chemical fractionation of metals. Flame atomic absorption spectrometry (Shimadzu, AA-6800) was used to determine metal speciation concentration, as well as the total and dissolved fractions. The dissolved fractions for both Cu and Zn were dominant in rain. The speciation distribution of Zn was different from that of Cu in road sediments, while speciation distribution of Zn is similar to that of Cu in runoff. The bound to carbonates for both Cu and Zn in road sediments were prone to be dissolved by rain. The levels of Cu and Zn in runoff were not obviously influenced by rain, but significantly influenced by road sediments. The masses for both Cu and Zn among rain, road sediments, and road runoff approximately meet the mass balance equation for all rainfall patterns. Five principal factors were selected for metal regression equation based on PCA, including rainfall, average rainfall intensity, antecedent dry periods, total suspended particles, and temperature. The established regression equations could be used to predict the effect of road runoff on receiving environments.     

Impact of products of a ferronickel smelting plant to the marine benthic life

The determination of heavy metal concentrations in the tissues of biota is an accurate method to estimate the abundance and the bioavailability of metals in the marine environment. The concentration of Fe, Cr, Cu and Zn were measured by atomic absorption spectrophotometry in molluscs, algae and angiosperms from a marine area adjacent to a ferronickel smelting plant (situated at North Evoikos Gulf, Greece), in order to investigate the spatial distribution of metals along the coast and their impact on marine benthic life. Results showed higher levels of Fe and Cr in biota from the sampling sites situated near the smelting plant or the dumping site of the nretalliferous slag in contrast with the obviously lower levels of the more distant sites. Molluscs showed generally higher concentrations of Fe and Cr in their tissues than plants. Cu and Zo were distributed quite undonnely in the tissues of the studied species. Furthermore the concentration of Fe and Cr in mussels collected from two localities at Evoikos Gulf and kept in clear seawater under experimental conditions decreased by almost 50% in comparison to their initial concentration within 18–48 hours of detoxification.     

Metal partitioning in river sediments measured by sequential extraction and biomimetic approaches

We quantified the concentrations and distributions of metals (Cd, Cr, Cu, Ni, Pb, and Zn) in the sediments of Tuen Mun River, Hong Kong. The potential bioavailability of metals was assessed with a biomimetic extraction method using the sipunculan gut juices. The sediments were characterized by relatively high concentrations of trace metals. Field collected sediments were highly anoxic and the ratio of simultaneously extractable metal (sigmaSEM) to acid volatile sulfide (AVS) was much less than one in these sediments. The majority (>67%) of Cd, Pb, and Zn were bound to AVS, thus their concentrations in the sediment porewater were low. In contrast, Ni was little bound to AVS due to its lower ratios of SEM-Ni to total Ni concentrations. For Cu, relatively high concentrations in the sediment porewater was found, and total organic carbon, AVS and other resistant sulfide phase were the controlling factors for sedimentary Cu partitioning. Net metal adsorption from gut juices to anoxic sediments was observed in metal extraction experiments, suggesting that AVS determined the bioaccumulation and potential bioavailability of most metals in these sediments. Extraction of metals from the oxidized sediments by the gut juices was mainly attributed to metal redistribution from AVS to other geochemical phases. The gut juices were the most effective solvent or extractant than the simple electrolyte solution [I (NaNO(3)) = 0.01 M] and the natural overlying water. Cd was more easily extracted from the oxidized sediments than Zn that tended to have a stronger binding affinity with Fe-Mn oxide, clay and organic matter. The application of partial removal techniques in metal extraction experiments further demonstrated the differential controls of various sediment geochemical phases in affecting metal bioavailability, with the order of TOC > Fe-Mn oxides > carbonate.     

Biomonitoring of heavy metals in the Western European Rivers Rhine and Meuse using the freshwater mussel Dreissena polymorpha

Since 1976, active and passive biological monitoring programs using the freshwater mussel Dreissena polymorpha have been carried out to study trends in the bioavailability of heavy metals in the rivers Rhine and Meuse. The Cd concentration in mussels exposed in the river Rhine has decreased from 74 mg kg(-1) in 1976 to 1.5 mg kg(-1) in 1988. In the river Meuse, however, the Cd concentration in Dreissena polymorpha has increased from 6 mg/kg (-1) to 22 mg kg(-1). Cu concentrations in mussels have not changed. Comparison of heavy metal concentrations in mussels from Lake Heerhugowaard, Lake Markermeer, Lake Maarsseveen and the river Dieze demonstrated that background concentrations for Cu, Zn, Cd and Pb in Dreissena polymorpha are about 12, 110, 1 and 0.5 mg kg(-1), respectively. Mussels from these four locations showed seasonal variation in heavy metal concentrations. This may be caused by both changes in the bioavailability of the metals and by the annual growth and reproductive cycle of the mussels. Therefore, one should take care that animals are collected at the same location and in the same section in long-term active biological monitoring programs.