Evolution and spatial variability of heavy metals in mussels (<i>Mytilus edulis</i> L.) in the Scheldt estuary (1996-2002)

This paper presents data on the heavy metal contamination of the soft tissues of marine mussels along the Scheldt Estuary. The study considered both arms of the Scheldt estuary, i.e. the relatively polluted Western Scheldt (WS) and the now marine tidal bay of the Eastern Scheldt (ES). The two systems present an ideal opportunity to investigate, in a field situation, the role of physico-chemical and pollution gradients on metal accumulation in mussels. In the WS, depending on the metal, tissues concentrations decreased by 2 - 6 times from Hansweert (the landward limit for mussels) to Westkapelle on the North Sea coast. Similar decreases were also observed in the ES. With a few exceptions (i.e. Cd, Cu), there were no clear differences in tissue metal concentrations between WS and ES. The study also showed strong positive correlations between tissue metal concentrations and distance from the sea in both systems for most metals. Similar trends were observed for both WS and ES indicating that salinity and metal gradients are not entirely responsible for increasing metal tissue levels towards the inland. Additionally, the influence of the constructed storm surge barrier was evident as heavy metal levels in mussels at sites around the barrier were considered elevated. Furthermore, there were only modest decreases in metal concentrations in mussel tissues between 1996 to 2002, further indication that even in the cleaner ES, efforts to reduce the impact of environmental metal pollution take time to give results

Differences in metal sequestration between zebra mussels from clean and polluted field locations

Organisms 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

Effect of hydrogen ions and inorganic complexing on the uptake of copper by the brine shrimp <i>Artemia franciscana</i>

The effect of hydrogen ions and inorganic complexing on copper uptake in the brine shrimp Artemia franciscana has been studied in chemically defined saltwater solutions. Uptake increases with decreasing hydrogen ion concentration and decreases with increasing carbonate complexation. A simple non-linear model that combines the effect of hydrogen ions on the transport of the metal across the solution-body interface and the effect of hydrogen ions and complexation on the speciation of the metal provided a close functional description of the observed variation in copper uptake by brine shrimp

Assessment of the myoglobin variation in the periwinkle <i>Littorina littorea</i> along the Scheldt estuary

The Scheldt estuary (The Netherlands) consists of two tributaries, of which the western part is heavily polluted (i.e. domestic and industrial pollutants, including heavy metals) and the eastern is relatively clean. Pollutants generally follow downstream decreasing concentration gradients, thus opposing a natural occurring salinity gradient, which decreases upstream. Hence, the Scheldt estuary forms an interesting setting to investigate the effects of both anthropogenic and natural kind.The population genetic structure of the periwinkle, Littorina littorea, has already been studied in this estuary using esterases and RAPD markers. Both studies revealed an estuary based genetic structuring. This genetic patterning is unexpected since L. littorea has a planktonic larval development and thus little genetic differentiation is expected. However, radular myoglobin studies have shown intraspecific variation in L. littorea on a macrogeographical scale. In this contribution, myoglobin profiles of the radular muscle were phenotypically analysed along the Scheldt estuary, using isoelectric focusing.A total of 395 periwinkles, descending from four eastern estuarine, five western estuarine and one marine sampling site were collected and morphometrically characterized after which their individual Mb profile was determined. Four Mb bands could be identified and the distribution of each of these bands differed significantly between the western and eastern Scheldt estuary. In addition, eight different Mb phenotypes were detected of which the distribution differed between both estuaries as well, yielding a significantly higher phenotypic variability in the Western Scheldt. A Dice similarity distance based multidimensional scaling minimum spanning tree (MDS-MST) analysis revealed no clear differentiation between both estuaries. Likewise the MDS-MST analysis failed to detect phenotypic structuring along the pollution-salinity gradient of the Western Scheldt sampling sites. However, the only marine sampling site was clearly separated from the nine remaining estuarine locations in the MDS-MST plot. These preliminary data suggest, in the presence of intense gene flow, (1) a high level of phenotypic Mb variability and (2) a marine versus estuarine phenotypic Mb structuring