Species-specific isotope tracers to study the accumulation and biotransformation of mixtures of inorganic and methyl mercury by the microalga Chlamydomonas reinhardtii

The present study demonstrates that species-specific isotope tracing is an useful tool to precisely measure Hg accumulation and transformations capabilities of living organisms at concentrations naturally encountered in the environment. To that end, a phytoplanktonic green alga Chlamydomonas reinhardtii Dangeard (Chlamydomonadales, Chlorophyceae) was exposed to mixtures of (199)-isotopically enriched inorganic mercury ((IHg)-I-199) and of (201)-isotopically enriched monomethylmercury ((CH3Hg)-C-201) at a concentration range between less than 1 pM to 4 nM. Additionally, one exposure concentration of both mercury species was also studied separately to evaluate possible interactive effects. No difference in the intracellular contents was observed for algae exposed to (IHg)-I-199 and (CH3Hg)-C-201 alone or in their mixture, suggesting similar accumulation capacity for both species at the studied concentrations. Demethylation of (CH3Hg)-C-201 was observed at the highest exposure concentrations, whereas no methylation was detected. (C) 2014 Elsevier Ltd. All rights reserved.