Mercury speciation in fish tissue by eco-scale thermal decomposition atomic absorption spectrometry: method validation and risk exposure to methylmercury

Abstract

A non-chromatographic method for Hg speciation in fish muscle using eco-scale thermal desorption atomic absorption spectrometry was validated according to the demands of the Decisions 2007/333/EC, 2011/836/EC and 2002/657/EC. The method is based on the determination of total Hg in solid sample and MeHg+, respectively, after double liquid–liquid extraction (47% HBr, toluene, 1% l-cysteine) according to a procedure recommended by the European Commission. The method was applied for the speciation of Hg in fish muscle to asses the weekly intake and health risk exposure to MeHg+. The method provided calibration coefficients better than 0.999, limits of detection of 0.2 µg kg−1 total Hg and 3.0 µg kg−1 MeHg+. The accuracy of the method assessed by the analysis of CRMs was 100 ± 9% for total Hg and 101 ± 13% for MeHg+ for a coverage factor k = 2. The figures of merit of the method comply with the requirements in the European legislation. Total Hg in the analyzed fish species was in the range 12–108 µg kg−1 wet mass, of which 83–97% as MeHg+. Although significant variation in total Hg was observed among fish species, no differences in terms of distribution of organic and inorganic Hg species were identified. No risk exposure to MeHg+ was ascertained from muscle fish consumption from reliable sources, since weekly intake was below 30% of provisional tolerable weekly intake of 1.6 µg kg−1 body weight. Speciation is recommended as MeHg+ is much more helpful than total Hg to evaluate the dietary risk exposure.