Pharmacokinetics and distribution of dietary tributyltin and methylmercuryin the snow crab (Chionoecetes opilio)

The pharmacokinetics and distribution of a single 5 mu g dietary dose of ra diolabeled [Sn-113]tributyltin (TBT) and [Hg-203]methylmercury (MeHg) were studied over 154 days in the snow crab, using in vivo gamma counting and wh ole-body autoradiography. Experiment was done under conditions typical of t hose encountered in the cold natural habitat of this crustacean. Retention efficiency was high for both compounds (80-100%), and two kinetic pools cou ld be distinguished. Elimination of the first pool proceeded within 20-80 d ays, but it accounted for 27-62% of the assimilated TBT, compared to 8-11% for MeHg. Biological half-life of the second pool was 33-187 days for TBT a nd 520-650 days for MeHg. Autoradiographic and dissection data revealed a l ess homogeneous distribution of the radiolabel and much higher radio activi ty in gut lumen for TBT compared to MeHg. This suggests that the larger siz e of the first pool in the case of TBT resulted from metabolization in the hepatopancreas and fecal elimination of the metabolites. The whole-body bio magnification factor (BMF) that would result from the long-term chronic exp osure of snow crab to TBT-contaminated food was estimated as 0.1 -0.6. Alth ough these BMF values were an order of magnitude lower than those estimated for MeHg (1.8-2.4), they are not negligible and indicate that uptake of TB T via food may be an important accumulation route.