In this study we investigated the effect of temperature and humic acid on the uptake of Ag, Cd, Co, Cu, Hg and Pb by the common blue mussels, Mytilus edulis. Effect on metal uptake in mussels was tested at two levels (i) in isolated gills and (ii) with whole animals at long term exposure. For the study of the effect of temperature, mussels were gradually acclimated to the test temperatures (6, 16 and 26°C) for 4 weeks. To assess the effect of temperature of acclimation on the general biological functions of mussels, Scope for growth (SFG) before and after acclimation were measured. Lower temperature (6°C) had no effect on overall SFG though maximum clearance rate decreased relative to 16°C. At higher temperature (26°C) SFG was negative indicating animals were utilising their energy reserves. Effect of temperature on metal uptake in isolated gills showed increase of uptake with increase of temperature. Generally, the trend was similar with whole animals, but with exceptions. Copper uptake decreased with increase in temperature. This could probably be related to some biological functions and regulation of copper by mussels at varying temperatures. Uptake of mercury and silver were highest at 16°C, no direct explanation for this was found. Uptake of metals in the presence of I and 2.5 mg/1 humic acid in isolated gills showed a clear decrease in metal uptake as a result of complexation of metals with humic acid, consistent with FIAM concept. However, with whole mussels, the uptake of Ag, Cu and Pb increased with in the presence of HA. The uptake of Cd and Hg showed a general decrease in the presence of HA, while the uptake of Co was unaffected in the presence of HA. These results suggest that metal fractions complexed by humic acid are somehow bioavailable to mussels. It is therefore, suggested that for these metals, uptake by mussels can not be explained entirely by the FIAM concept. |
