Factors affecting trace element uptake in the black mussel Septifer virgatus

The variability of the influx rates of Cd, Cr(VI), Se(IV), and Zn in the black mussel Septifer virgatus from Hong Kong coastal waters was examined under different environmental and biological conditions using the radiotracer technique. The uptake of trace elements generaiiy proceeded linearly over time and a short-term exposure (4 h) was therefore employed to measure the influx rate of trace elements. The uptake rates were directly proportional to the concentration of trace elements in the dissolved phase. The calculated uptake rate constant was 0.286, 0.085. 0.031, and 0.460 1 g-' d-' for Cd, Cr(VI), Se(IV), and Zn, respectively. Transport of Cd and Zn was primarily a faclhtated process that was significantly inhibited by N-ethylmaleimide due to its specific binding with SH-containing ligands. Uptake rates of Cd and Zn were closely coupled, whereas no relationship of their uptake with Cr(V1) or Se(1V) uptake was found. Uptake of Cr(V1) and Se(1V) was decoupled, indicating that they were transported via different pathways into the mussels. The Ca channel was not involved in the transport of all trace elements. A decrease in salinity greatly enhanced the i n f l u of all 4 trace elements. Changes in metal speciation and Ca concentration were not responsible for the underlying effects of salinity. The allometnc scaling of Cr(V1) and Se(IV) uptake was cornparable to the allometric scaling of the mussels' filtration rate, suggesting that gill surface area may determine their uptake rate. The uptake of Cr(V1) and Se(IV) may simply be predicted based on the measurements of the n~ussel's filtration rate. For Cd and Zn, the allometry of meta1 uptake may also be controlled by other processes such as SH-containing ligands available for metal binding.