Making mercury measurements in food more reliable
JRC scientists developed a new certified reference material (CRM) to improve the accuracy of methylmercury measurements in food. This CRM (ERM-AE671) consists of isotopically labelled methylmercury with certified values for the isotopic composition. Used as internal standard, it will make the measurements of methylmercury more accurate.
Regulation 466/2001/EC sets limits for the total mercury content in foodstuffs. However, like some other elements, mercury can be present in different forms ("species"), which can have different toxicity. For mercury in fish, methylmercury is especially important, as its acute toxicity is a factor 1000 higher than the one of elemental mercury and also has a high chronic toxicity. This was tragically demonstrated by the massive poisoning of humans by methylmercury in the Minamata bay, Japan between the 1950ies and 1970ies. Therefore, measuring the total mercury content alone is not sufficient to ensure that a product poses no risk. The European Food Safety Authority (EFSA) reacted to this fact by setting provisional limits for the tolerable consumption of methylmercury to complement the legal limits on total mercury.
Determination of metal species is significantly more challenging than determination of the total element content, as one must not only ensure absence of contamination and absence of loss, but one must also ensure that the methylmercury is not converted into elemental mercury and vice versa. Use of an isotopically labelled internal standard can correct for many of the problems in the determination of element species. To respond to this need, the JRC's Directorate for Health, Consumers and Reference Materials developed the Certified Reference Material ERM-AE671 consisting of methylmercury which virtually entirely contains 202Hg in contrast to natural mercury, which is a mixture of seven different isotopes. The homogeneity and stability of the material was demonstrated and the certified values were calculated from the purity and precision-weighing of the materials. These data were confirmed by independent measurements.