Bioaccumulation and transformation of methylmercury and selenite using zebrafish (Danio Rerio) larvae as a model.

Bioaccumulation and possible transformation of methylmercury and selenite has been checked on a 72 h-cycle of bioaccumulation and depuration using larvae from zebrafish. The larvae were exposed to methylmercury and selenite at concentrations of 1% and 0.1% of their LC(50) values. Quantitative extraction of methylmercury and selenite from exposed larvae was achieved by using ultrasonic probe-assisted extraction (USP), thus reducing extraction time and solvent consumption. Extracted species collected at different exposure times were characterized and quantified by liquid chromatography coupled to ICP-MS. Bioconcentration factors (BCFs) were estimated by two procedures: (i) as the ratio of the contaminant concentration in larvae and exposure media (BCF(48 h)) and (ii) fitting contaminant concentration in larvae to bioaccumulation models that describe uptake and depuration processes (BCF(k)). The BCFs obtained for methylmercury were 5000 and 2333 for larvae exposed to 1 μg L(-1) and 10 μg L(-1), respectively; while for selenite the BCF was 74 for larvae exposed to 10 μg L(-1). The good correlation between the BCFs found and those previously reported in the literature shows the proposed method as a good and promising alternative to the OECD Bioconcentration Test 305. Actually, the use of zebrafish larvae reduces the bioaccumulation test time from forty two (OECD Bioconcentration Test 305) to three days. In addition, potential biotransformation of both methylmercury and selenite was evaluated by LC-ICP-MS. For this purpose, a method for species extraction in small size samples by using ultrasonic probe sonication was developed.