Optimization and validation of the methods for the total mercury and methylmercury determination in breast milk

The objective of the work was to develop and validate methods for the total Hg and methylmercury (MeHg) in breast milk that could be further used to obtain first data on chemical contamination of French breast milk. For total Hg determination, the potential of two techniques, namely Advanced Mercury Analyzer (AMA) and ICP MS, was compared. For MeHg determination, ICP MS detection associated to a quantification by isotopic dilution was used and the potential of a preliminary separation by gas or liquid chromatography was evaluated and discussed. The optimization studies have shown that AMA for total Hg determination and HPLC ID ICP MS, after a preconcentration step by freeze-drying, for MeHg quantification were the most relevant methods to use for epidemiologic studies. The figures of merit for both methods were evaluated by means of accuracy profiles in terms of limits of quantification (1.82 and 1.35 mg Hg/kg dry weight, corresponding to 0.22 and 0.16 mu g Hg/kg wet basis for total Hg and MeHg, respectively), repeatability (2-11% and 3-8% for total Hg and MeHg respectively), intermediate precision reproducibility (4-12% and 4-8% for total Hg and MeHg respectively) and trueness bias (-0.1-9% and 4-0% for total Hg and MeHg respectively). The methods were then applied to 180 breast milk samples. Total Hg concentrations ranged from < LD to 16.9 mu g Hg/kg wet basis ( < LD to 142 mu g Hg/kg dry weight) and the MeHg contents from < LD to 0.43 mu g Hg/kg wet basis ( < LD to 3.67 mu g Hg/kg dry weight).