Elucidating sources of mercury in the west coast of Korea and the Chinese marginal seas using mercury stable isotopes

Nearshore systems play an important role as mercury (Hg) sources to the open ocean and to human health via fish consumption. The nearshore system along East Asia is of particular concern given the rapid industrialization, which contributes to significant anthropogenic Hg emissions and releases. We used Hg stable isotopes to characterize Hg sources in the sediment and fish along the west coast of Korea, located at the northeast of the East China Sea. The Hg isotope ratios of the west coast sediments (delta Hg-202; -0.89 to -0.27 parts per thousand, Delta Hg-199; -0.04 to 0.14 parts per thousand) were statistically similar with other nearshore sediments (delta Hg-202; -0.99 to -0.30 parts per thousand, Delta Hg-199; -0.04 to 0.19 parts per thousand) and overlapped with the industrial Hg source end-member (delta Hg-202; -0.5 parts per thousand, Delta Hg-199; 0.01 parts per thousand) estimated from the Chinese marginal seas. Using a ternary mixing model, we estimated that industrial Hg sources contribute 83-97% in the west coast of Korea, and riverine and atmospheric Hg sources play minor roles in the Korean west coast and the Chinese marginal seas. The comparison between Hg isotope ratios of the sediment and nearshore fish revealed that the fish in the most west coast sites are exposed to MeHg produced in the sediment. At a few southwest coast sites, external MeHg produced in rivers and the open ocean water column appears to be more important as a source in fish. This is supported by much higher delta Hg-202 (0.74 parts per thousand; similar to oceanic fish) and lower delta Hg-202 (-0.71 parts per thousand; similar to riverine sources) compared to fish collected from other west coast sites influenced by sedimentary MeHg. The substantial Hg contributions from industrial activities suggest the national policies regulating anthropogenic Hg releases can directly mitigate human Hg exposure originating via local fish consumption. This study contributes to the growing regional and global inventories of Hg fluxes and sources exported into coastal oceans.

Automated summary

This study investigates the sources of mercury (Hg) in the west coast of Korea using Hg stable isotopes. The results show that industrial Hg sources contribute significantly to the west coast of Korea, while riverine and atmospheric Hg sources play minor roles. The study also reveals that fish in the west coast are mainly exposed to methylmercury (MeHg) produced in the sediment, but in some southwest coast sites, external MeHg from rivers and the open ocean water column is more important as a source in fish.