MOLECULAR-WEIGHT OF HUMIC ACIDS AS A MAJOR PROPERTY OF THE SUBSTANCESINFLUENCING THE ACCUMULATION RATE OF CADMIUM BY A BLUE MUSSEL (MYTILUS-EDULIS)

The influence of marine humic substances and their molecular weight fr actions on accumulation of cadmium by a blue mussel Mytilus edulis was investigated in laboratory conditions. Mussels, collected from the we stern 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 concentrat ions 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 degr ees C temperature). It was found that marine HS, a fraction of natural ly occurring matter, stimulate the accumulation of cadmium by the muss els. Molecular weight of HS is an important factor influencing the upt ake of the metal by Mytilus edulis, due to its different complexing ca pacity toward cadmium. Low molecular weight HS influenced the accumula tion 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.