Extraction of methylmercury from tissue and plant samples by acid leaching

A simple and efficient extraction method based on acidic leaching has been developed for measurement of methylmercury (MeHg) in benthic organisms and plant material. Methylmercury was measured by speciated isotope-dilution mass spectrometry (SIDMS), using gas chromatography interfaced with inductively coupled plasma mass spectrometry (GC-ICP-MS). Reagent concentration and digestion temperature were optimized for several alkaline and acidic extractants. Recovery was evaluated by addition of MeHg enriched with CH3 201Hg+. Certified reference materials (CRM) were used to evaluate the efficiency of the procedure. The final digestion method used 5 mL of 4 mol L(-1) HNO3 at 55 degrees C to leach MeHg from tissue and plant material. The digest was further processed by aqueous phase ethylation, without interference with the ethylation step, resulting in 96 +/- 7% recovery of CH3 201Hg+ from oyster tissue and 93+/-7% from pine needles. Methylmercury was stable in this solution for at least 1 week and measured concentrations of MeHg in CRM were statistically not different from certified values. The method was applied to real samples of benthic invertebrates and inter-laboratory comparisons were conducted using lyophilized zooplankton, chironomidae, and notonectidae samples.