Zebra mussels (Dreissena polymorpha) were translocated in cages to 56 water bodies in Flanders (Belgium) during summer 2001. After six weeks, concentrations of polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), p,p'-DDE, and trace metals were measured in the transplanted mussels. It was investigated whether total dissolved water and sediment pollutant levels or bioaccumulation factors (BAFs) and biota-sediment accumulation factors (BSAFs) were predictive for mussel tissue levels. The sample sites covered a broad range both in terms of the type and concentration of the pollutants, and this was reflected in large differences in tissue concentrations of all pollutants among the sites. The highest pollutant levels in mussels were among the highest reported in the literature. For Cd and Zn levels up to 33 and 1994 microg/g dry wt. respectively were found. The lowest levels were comparable to those from uncontaminated sites in Europe and the U.S. For Cd and Zn respectively 51 and 75% of the variation in tissue levels was described. For both metals, dissolved and particulate metal contributed to the variation in accumulation. For other pollutants, relationships between tissue concentration and water or sediment concentration were weak or nonsignificant. Then the measured environmental factors (dissolved calcium, pH, oxygen, organic carbon and clay content in the sediment) were taken into account applying multiple regression analysis, and no increase in the described variation of pollutant accumulation was observed. The BAF and BSAF for all pollutants varied up to 1000-fold even after TOC-normalization. Clear negative relationships were found between BAFs/ BSAFs and environmental levels. However, even at constant environmental concentrations a 10- to 100-fold variation in BAFs/BSAFs was observed. This study illustrated the need for biological monitoring since neither environmental

Zebra mussels (Dreissena polymorpha) were exposed at 12 canals and lakes situated in Flanders (Belgium), in cages for six weeks during the summer of 2002. Accumulation of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), hexachlorobenzene, and trace metals were measured in the transplanted mussels and levels compared to levels in indigenous mussels. Additionally, zebra mussels were exposed at a small lake in the vicinity of Antwerp (Belgium), and accumulation of contaminants was followed for an extended period from December 2001 to April 2002. Analysis of the pollutants in the indigenous mussels showed that the selected sites displayed a wide range of pollution from near to background to very high levels of metals and/or organic contaminants when compared to the literature. For organic contaminants and for most metals, comparison of levels between caged and resident mussels revealed no significant differences. Only for cadmium and nickel, significant differences were observed, with levels being either higher (cadmium) or lower (nickel) in caged mussels. For organic contaminants, significant correlations between levels in caged and resident mussels were found with r2 values up to 0.98. For some metals, no or poor correlations were found. At most sites, concentrations of those metals were of the same order of magnitude and comparable to levels in mussels from unpolluted sites. This might explain the absence of significant correlations. When mussels were exposed for an extended period, the concentration of some pollutants increased, whereas others decreased with time. Only in the case of certain metals did levels differ significantly because of the slow depuration of metals already present in the transplanted mussels. This is an additional indication that measured concentrations in transplanted mussels indeed reflected the local situation. With this study, we were able to prove the applicability of transplanted mussels as a biomonitoring tool for the accumulation of pollutants over a wide range of pollution.

a b s t r a c tOrganisms are able to detoxify accumulated metals by, e.g. binding them to metallothionein (MT) and/or sequestering them in metal-rich granules (MRG). The different factors involved in determining the capacity or efficiency with which metals are detoxified are not yet known.In this work we studied how the sub-cellular distribution pattern of cadmium, copper and zinc in whole tissue of zebra mussels from clean and polluted surface waters is influenced by the total accumulated metal concentration and by its physiological condition. Additionally we measured the metallothionein concentration in the mussel tissue. Metal concentration increased gradually in the metal-sensitive and detoxified sub-cellular fractions with increasing whole tissue concentrations. However, metal concentrations in the sensitive fractions did not increase to the same extent as metal concentrations in whole tissues. In more polluted mussels the contribution of MRG and MT became more important. Nevertheless, metal detoxification was not sufficient to prevent metal binding to heat-sensitive low molecular weight proteins (HDP fraction). Finally we found an indication that metal detoxification was influenced by the condition of the zebra mussels. MT content could be explained for up to 83% by variations in Zn concentration and physiological condition of the mussels.

Metal speciation in aquatic systems is mainly determined by the type and concentration of ligands present in solution. A very important group of complexing agents is dissolved organic matter (DOM), e.g., humic and fulvic acids. According to the free-ion activity model, only the free metal ion is available to biota. Nevertheless, DOM has been reported to decrease or increase metal uptake, leading to uncertainty concerning the bioavailability of metal-DOM complexes. In this work the effect of Aldrich humic acid on cadmium accumulation by the zebra mussel, Dreissena polymorpha, was studied under laboratory conditions. Mussels, collected in a drinking water reservoir, were exposed to varying environmentally relevant concentrations of cadmium in the presence and absence of humic acid. Cadmium concentrations in the mussel tissues were analyzed, and measurements with a cadmium-ion-selective electrode were made to determine the free cadmium ion activity in the exposure waters. The uptake of humic acid by the zebra mussels was measured by the decrease of the total organic carbon (TOC) concentration in the water over time. The free cadmium ion activity in the water decreased from 51.6% to 19.9% of the total cadmium concentration in the presence of humic acid. This decrease by a factor of 2.6 resulted in a decrease in the cadmium uptake rate in the soft tissue of zebra mussels from 12.9 to 7.9 nmol/g dry wt/day, which corresponds to a decrease by a factor of 1.6. This implies that cadmium uptake rates were higher than predicted by the free-ion activity model and indicates that cadmium-humic acid complexes are partly available to zebra mussels.

No abstract

The levels and distribution of PBDEs in zebra mussels and several freshwater fish species (eel, carp and gibel carp) were investigated for different sites in Flanders, Belgium. In parallel, other organohalogenated contaminants, such as polychlorinated biphenyls (PCBs), p,p[prime or minute]-DDE and hexachlorobenzene (HCB) were also measured and their relationship with PBDEs was investigated. At most sites, individual PBDE congeners were present at detectable levels in mussel tissue, with the mean [summation operator]PBDE concentration ranging from 0.15 to 1.8 ng g(-1) wet weight (ww). The PCB concentrations in mussels ranged from 6.2 to 102 ng g(-1) ww. HCB and p,p[prime or minute]-DDE could be measured in mussels from most sites, mean values ranging from below the limit of quantification (LOQ) to 0.58 ng g(-1) ww and from 0.66 to 6.5 ng g(-1) ww, respectively. Except for one site (Blokkersdijk, Antwerp) where PBDEs were below the LOQ in carp muscle, all fish samples from other sites contained detectable PBDE levels, with the highest concentrations (14 +/- 14 ng g(-1) ww) being measured in eel liver from Watersportbaan (Ghent). The sampled sites covered a broad concentration range of organohalogenated pollutants with the highest values being consistently measured in eel liver. With few exceptions, all correlations between PBDEs and organochlorine pollutants for each species were low (r < 0.50) and most were statistically not significant (p > 0.05). This suggests that the exposure to contaminants arises from local sources possessing different signatures of PBDEs and organochlorine pollutants.

The advantages of ABM for biomonitoring purposes are: Experiments can be performed for a known exposure period . All organisms have a similar life history at the start of the exposure. It is easy to compare different sites , even if the organisms are not normally present at the exposure locations. A comparison between transplanted and indigenous organisms can indicate to what extent the indigenous organisms are adapted to the location or can give information about uptake kinetics of pollutants. Indigenous species can be “genetically protected,” and thus the use of transplanted organisms can circumvent this adaptation processes, making the comparison among different sites more precise and the use of nonadapted species more sensitive. Compared with laboratory‐bred organisms, transplanted organisms are better acclimated to changing environmental conditions, and thus the impact of field exposure through, e.g., climatological shock, will be less pronounced.

Zebra mussels (Dreissena polymorpha) originating from a drinking water reservoir were exposed at seven sites in metal polluted watercourses in Flanders (Belgium), including to a cadmium and zinc pollution gradient. At each site one cage, containing twenty-five mussels, was exposed for six weeks. Mussels were collected after 10, 21 and 42 days. At each sampling, five mussels were taken from each cage and analysed for metal content and condition. Significant metal accumulation in zebra mussel was measured as a function of time at all sites for at least one metal. However, a steady state in accumulation was not always reached. Depending on the site, extremely high levels of cadmium, copper, nickel and zinc were measured in the mussels. Despite differences in metal accumulation, no significant differences in two condition indices were observed among the different sites. When data of all the sites were pooled there was no significant relationship between the condition and the metal load in the mussels, although a threshold could be distinguished. However, when this relationship was examined for the separate rivers, significant relationships were found. This indicates that besides metal pollution other environmental factors such as food availability affect the mussel condition.