Accumulation of organic and inorganic mercury from food in the tissues of Carcinus maenas: effect of waterborne selenium

Abstract

Accumulation of organic and inorganic mercury from contaminated food into the tissues of seleniumand non-selenium-exposed shore crabs Carcinus maenas were investigated in the laboratory. Crabs fed homogenates of Cardiurn edule collected in the mercury-contaminated Nissum Bredning, Jutland, Denmark, assimilated 50 to 60 % of ingested inorganic and organic mercury. Muscle and midgut gland contained approxin~ately 50 to 60 % and 40 % respectively of both asslmilated mercury species. Simultaneous exposure to selenite augmented accumulation of organic mercury in muscle and increased assimilation of organic mercury from the food. Accumulation of inorganic mercury was not affected by exposure to selenite. When the mercury concentration of the food was increased 10-fold (by the addition of HgClz and CH3HgCl directly to the cockle homogenate), a higher percentage of the ingested inorganic mercury was assimilated by the crabs, 95 % of the inorganic mercury being accumulated in the rnidgut gland. Percent assimilation and tissue distribution of organic mercury was less affected by increasing the concentration in the diet. The subcellular distribution of the 2 mercury species was almost identical. In the soluble fraction both mercury species were bound predominantly to proteins with a molecular weight (MW) of ca 12 000 Da. In the soluble fraction, exposure to selenite diverted mercury from the 12 000 Da region to high (MW > 70 000 Da) or very low (MW c 4000 Da) molecular weight proteins. Injected organic mercury was cleared from the haemolymph more rapidly than inorganic mercury, and clearance of both mercury species from the haemolymph proceeded faster in selenite-exposed crabs.