Development of pre-concentration procedure for the determination of Hg isotope ratios in seawater samples

• The method for the quantitative pre-concentration of Hg from seawater was developed.
• First report of Hg isotope ratios in seawater is presented.
• A unique mass independent 200Hg isotope fractionation was observed.
• This fractionation has unique potential to distinguish anthropogenic and natural Hg.

Hg concentrations in seawater are usually too low to allow direct (without pre-concentration and removal of salt matrix) measurement of its isotope ratios with multicollector-inductively coupled plasma mass spectrometry (MC-ICP-MS). Therefore, a new method for the pre-concentration of Hg from large volumes of seawater was developed. The final method allows for relatively fast (about 2.5 L h−1) and quantitative pre-concentration of Hg from seawater samples with an average Hg recovery of 98 ± 6%. Using this newly developed method we determined Hg isotope ratios in seawater. Reference seawater samples were compared to samples potentially impacted by anthropogenic activity. The results show negative mass dependent fractionation relative to the NIST 3133 Hg standard with δ202Hg values in the range from −0.50‰ to −1.50‰. In addition, positive mass independent fractionation of 200Hg was observed for samples from reference sites, while impacted sites did not show significant Δ200Hg values. Although the influence of the impacted sediments is limited to the seawater and particulate matter in very close proximity to the sediment, this observation may raise the possibility of using Δ200Hg to distinguish between samples from impacted and reference sites.

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