Pharmacokinetics and Distribution of Dietary Tributyltin and Methylmercury in the Snow Crab (Chionoecetes opilio)

Abstract

The pharmacokinetics and distribution of a single 5-μg dietary dose of radiolabeled [113Sn]tributyltin (TBT) and [203Hg]methylmercury (MeHg) were studied over 154 days in the snow crab, using in vivo gamma counting and whole-body autoradiography. Experiment was done under conditions typical of those encountered in the cold natural habitat of this crustacean. Retention efficiency was high for both compounds (80−100%), and two kinetic pools could be distinguished. Elimination of the first pool proceeded within 20−80 days, 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 and 520−650 days for MeHg. Autoradiographic and dissection data revealed a less homogeneous distribution of the radiolabel and much higher radioactivity in gut lumen for TBT compared to MeHg. This suggests that the larger size of the first pool in the case of TBT resulted from metabolization in the hepatopancreas and fecal elimination of the metabolites. The whole-body biomagnification factor (BMF) that would result from the long-term chronic exposure of snow crab to TBT-contaminated food was estimated as 0.1−0.6. Although 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 TBT via food may be an important accumulation route.