Nolde N, Drobne D, Horvat M, Jereb V
[ pdf ] [ site ] Environmental Toxicology and Chemistry, 2005

Reduction and methylation of inorganic mercury in Porcellio scaber (Isopoda, Crustacea) and its environment were studied, using a purpose-built experimental setup where Hg cycling was followed using ²⁰³Hg²⁺ tracer in experiments without and with isopods. In experiment without isopods, daily reduction of ²⁰³Hg²⁺ to ²⁰³Hg⁰ under sterile and nonsterile conditions was measured for three weeks to assess the contribution of bacteria to this process. In experiments with isopods, daily release of ²⁰³Hg⁰ was measured for two weeks. Total mercury (T203Hg) and monomethylmercury (T²⁰³Hg) in whole animals, gut, digestive glands (hepatopancreas), food (hazelnut leaves), and feces were measured to obtain the assimilation and distribution of mercury in the animals, to investigate the origin and fate of Me²⁰³Hg, and, finally, to assess the mass balance of mercury in the experimental system. Experiment without isopods showed the important role of bacteria in reduction of ²⁰³Hg²⁺ to ²⁰³Hg⁰, especially in the first day of the experiment. Experiments with isopods showed that formation of ²⁰³Hg⁰ depended on the ²⁰³Hg²⁺ concentration in the food. The contribution of the isopod’s digestive flora in reduction of ²⁰³Hg²⁺ to ²⁰³Hg⁰ was negligible. Approximately 3% of T²⁰³Hg and 2% of Me²⁰³Hg consumed was assimilated by the animals. Methylation of ²⁰³Hg²⁺ occurred already in the leaves before they were consumed by the isopods. Assimilation of Me²⁰³Hg from the food surprisingly was low. Also, a loss of Me²⁰³Hg was noticed when comparing assimilated and excreted Me²⁰³Hg versus consumed Me²⁰³Hg. This may be explained by the assumption that demethylation of MeHg prevailed over methylation of Hg²⁺ in the animal’s digestive system, leading to excretion of ingested mercury as Hg²⁺..