We report on an international proficiency test (PT) scheme for mercury (Hg) determination in soil, sediment,
fish and human-hair samples (ILAE-Hg-02). For total-Hg determination, 74% of participants had
a satisfactory performance (|z-score| ≤ 2), 8% had a questionable performance and 18% required action
(|z-score| > 3). The best results were obtained for soil, while fish yielded the most-biased results, reflecting
the analytical problems of quantifying Hg at low concentrations. Proficiency in the extraction of
organometallic and available metal fractions was an important goal of the ILAE-Hg-02 and it was concluded
that most laboratories are still not acquainted with the procedures for Hg fractionation; we therefore
discuss their importance and highlight the need for more PT schemes dedicated to this matter, as they
are an important tools in the standardization of procedures and for the development of adequate quality
control/quality analysis protocols and certified reference materials
