Influences of different selenium species on the uptake and assimilation of Hg(II) and methylmercury by diatoms and green mussels.

We examined the influences of different concentrations and species of Se (selenite, selenate, and seleno-l-methionine) in the ambient environment on the accumulation of inorganic Hg(II) and methylmercury (MeHg) by the diatom Thalassiosira pseudonana and the green mussel Perna viridis. At the experimental concentrations tested (< 500 microgl(-1)), selenite and selenate did not significantly affect the uptake of either mercury species by the diatoms and the green mussels. The assimilation efficiency of Hg(II) and MeHg by the mussels from ingested diatoms was also independent of the inorganic Se loadings in the food particles. In contrast, selenomethionine significantly inhibited the uptake of MeHg and enhanced the uptake of Hg(II) by the diatoms and the mussels, but it did not affect the assimilation from the ingested diatoms. The influence of tissue body burden of Se in the green mussels following pre-exposure to selenite and selenomethionine for different periods (1-5 weeks) on the accumulation of Hg(II) and MeHg was further investigated. Our results showed that tissue Se concentrations did not significantly affect the dietary assimilation of mercury, but the influences on the aqueous uptake were variable. Our study thus, strongly highlights the specificity of the Se-Hg interaction in marine mussels for different Se and Hg species. Both dissolved and dietary uptake appeared to be equally important in the accumulation of Hg(II) and MeHg in the green mussels.