Extraction of low-level methylmercury from sediments for species-specific isotope ratio determination by GC-MC-ICP-MS.

Reliable species-specific isotope ratio analysis of methylmercury (MMHg), the most toxic form of mercury, is essential for advancing our understanding of mercury sources, transformations, and biogeochemical cycling. Existing methods are time-consuming, often require preconcentration, and are restricted to samples with high concentrations of MMHg. Here we present a fast and straightforward distillation-based extraction method for sediments, that is applicable to samples with low-levels of MMHg, without imparting any fractionation. The method can process up to 5 g of sediment, making it applicable to samples with concentrations as low as 0.1 ng/g of MMHg. Using gas chromatography prior to MC-ICP-MS allows complete isolation of MMHg from residual inorganic mercury, preventing contamination of the isotope ratio measurements. This method enables rapid species-specific isotope ratio measurements across sediments with varying MMHg concentrations, providing a valuable tool for investigating mercury cycling and environmental fate.