Molecular weight of humic acids as a major property of the substances influencing the accumulation rate of cadmium by a blue mussel (Mytilus edulis)

The influence of marine humic substances and their molecular weight fractions on accumulation of cadmium by a blue mussel Mytilus edulis was investigated in laboratory conditions. Mussels, collected from the western part of the Gulf of Gdansk, were exposed to cadmium (25 mu gCd/L) or to radiocadmium (3 or 10 kBq(115m)Cd/L) and to varying concentrations of humic substances (HS) or their molecular weight fractions (0-8 mgHS/L) in Baltic Sea water (7 mg/L salinity, 10 degrees C +/- 1 degrees C temperature). It was found that marine HS, a fraction of naturally occurring matter, stimulate the accumulation of cadmium by the mussels. Molecular weight of HS is an important factor influencing the uptake of the metal by Mytilus edulis, due to its different complexing capacity toward cadmium. Low molecular weight HS influenced the accumulation rate of metal by the mussels more than high molecular weight ones. Cadmium was accumulated mainly in the hepatopancreas, next in gills, and least in mantle and muscles, independent of the molecular weight of HS.