To understand the biochemistry of methylmercury (MeHg) that leads to the formation of mercury-selenium (Hg-Se) clusters is a long outstanding challenge that promises to deepen our knowledge of MeHg detoxification and the role Se plays in this process. Here, we show that mercury selenide (HgSe) nanoparticles in the liver and brain of long-finned pilot whales are attached to Se-rich structures and possibly act as a nucleation point for the formation of large Se-Hg clusters, which can grow with age to over 5 μm in size. The detoxification mechanism is fully developed from the early age of the animals, with particulate Hg found already in juvenile tissues. As a consequence of MeHg detoxification, Se-methionine, the selenium pool in the system is depleted in the efforts to maintain essential levels of Se-cysteine. This study provides evidence of so far unreported depletion of the bioavailable Se pool, a plausible driving mechanism of demonstrated neurotoxic effects of MeHg in the organism affected by its high dietary intake.

Particulate HgS is generally thought to be the most abundant Hg species in stored petroleum hydrocarbons stocked onshore. It is also assumed that due to its high stability constant, HgS is chemically inert. However, results from the current study would suggest otherwise. Firstly, a comparison study of the analytical performance of ICP-MS and CV-AFS with respect to matrix effect, showed no significant difference in the measured Hg concentrations in studied samples when CV-AFS is used in the alkali mode. Subsequently, the suitability of three quantification methods during Hg speciation was investigated. Both external calibration and standard addition methods resulted troublesome with the former showing matrix dependence and the latter being hindered by the formation of an emulsion during the derivatisation step. Results from species-specific isotope dilution (SS-ID-GC-ICP-MS), on the other hand, performed at different equilibration times, showed a random variation in the calculated Hg 2+ concentration (RSD 32%), 2 suggesting that factors independent of equilibration time cause the observed variation. Further sedimentation of Hg particulate by means of ultracentrifugation improved the precision of SS-ID-GC-ICP-MS by 10-fold. These results would suggest that Hg particles in petroleum products are reactive at low temperature during Grignard alkylation.

Mercury (Hg) is a global pollutant which occurs in different species, with methylmercury (MeHg) being the critical compound due to its neurotoxicity and bioaccumulation through the food chain. Methods for trace speciation of MeHg are therefore needed for a vast range of sample matrices, such as biological tissues, fluids, soils or sediments. We have previously developed an ultra-trace speciation method for methylmercury in water, based on a preconcentration HPLC cold vapour atomic fluorescence spectrometry (HPLC-CV-AFS) method. The focus of this work is mercury speciation in a variety of sample matrices to assess the versatility of the method. Certified reference materials were used where possible, and samples were spiked where reference materials were not available, e.g. human urine. Solid samples were submitted for commonly used digestion or extraction processes to obtain a liquid sample for injection into the analytical system. For MeHg in sediment samples, an extraction procedure was adapted to accommodate MeHg separation from high amounts of Hg(2+) to avoid an overload of the column. The recovery for MeHg determination was found to be in the range of 88-104% in fish reference materials (DOLT-2, DOLT-4, DORM-3), lobster (TORT-2), seaweed (IAEA-140/TM), sediments (ERM(®)-CC580) and spiked urine and has been proven to be robust, reliable, virtually matrix-independent and relatively cost-effective. Applications in the ultra-trace concentration range are possible using the preconcentration up to 200 mL, while for higher MeHg-containing samples, lower volumes can be applied. A comparison was carried out between species-specific isotope dilution gas chromatography inductively coupled plasma mass spectrometry (SSID-GC-ICP-MS) as the gold standard and HPLC-CV-AFS for biological tissues (liver, kidney and muscle of pilot whales), showing a slope of 1.008 and R (2) = 0.97, which indicates that the HPLC-CV-AFS method achieves well-correlated results for MeHg in biological tissues.

Unprocessed petroleum hydrocarbons often contain high concentrations of mercury (Hg), which can severely damage the metal components of a processing plant and pose a health risk to the workers and the natural environment. Although Hg removal units can significantly reduce the Hg concentration in the export products, they are often installed in the final stage of the processing plant, thus failing to protect the production facilities. In this study, Hg distribution within a natural gas processing plant was studied to identify the most effective place for a Hg removal unit. Additionally, the impact of sampling container materials and their acidification was evaluated, and Hg species in the condensate were quantified. Total Hg concentration was significantly higher in all samples stored in glass in comparison to that with plastic containers. However, the acidification effect of the containers was more pronounced for Hg in nonpolar solutions. Interestingly, the assessment of Hg distribution within the gas plant showed that the export gas is being enriched in Hg, whose concentration rose from 1.25 to 4.11 μg/Sm3 during the processing steps. The second stage separator was identified as the source of excess Hg, which partitioned from the liquid phase of condensate to the gas phase as a result of reduced operational pressure and temperature. The dominant Hg species found in the analyzed gas condensates were elemental Hg (Hg0) and inorganic Hg with the methylmercury fraction comprising up to 18%. However, it was also found that the % fraction of individual Hg species varied along the plant units most likely as a result of Hg0 migration to the export gas. Therefore, to protect all treatment facilities from Hg contamination, the Hg removal unit should be installed after the second stage compressor.

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