Assessment of Mercury Pollution of Coastal Waters in Ussuriysky and Amursky Bays Using Macroalgae

Abstract—Mercury concentrations were determined in the thalli of common macroalgae species, Ulva lactuca, U. linza, Sargassum miyabei, S. pallidum, Stephanocystis crassipes and Costaria costata from the northwestern Sea of Japan in June–July 2017–2022. Macrophytes on average contain low mercury concentrations, not exceeding the maximum permissible concentrations (MPC) for commercial algae (500 ng/g based on dry weight) and corresponding to the third quartiles of global samples for green and brown algae (170 and 105 ng/g, respectively). Coastal sea waters around Vladivostok are not contaminated with mercury, except for local areas on the western coast of Ussuriysky Bay in the Sea of Japan. The maximum mercury concentration of 1071 ng/g dry weight was detected in the green alga Ulva lactuca in the region adjacent to the reclaimed solid waste landfill Gornostay, where previously the algae with elevated contents of Cu, Pb, Fe, and Zn have been noted. Threshold values of Hg concentrations were calculated as the median plus double median of deviations from the median. They are 34 ng/g of dry weight for U. lactuca, 36 for U. linza, 43 for S. miyabei, 38 for S. pallidum, 115 for S. crassipes and 83 ng/g for C. costata (blade without rhizoids). The dependence of mercury concentration on the age of the thallus is considered.