Differences in Mercury Concentrations in Water and Hydrobionts of the Crimean Saline Lakes: Does Only Salinity Matter?

Of significant scientific and public concern is the high toxicity, significant bioaccumulation, and magnified concentration within the food web of mercury (Hg). Hg content both dissolved and in suspended forms in water as well as in biomass of different hydrobiont taxa was studied in 18 saline lakes in Crimea from 2012 to 2021. The impact of different factors (salinity, seasonality, anthropogenic activities, geological background, etc.) was analyzed. The generalization of data for all lakes showed that the average concentration of Hg in dissolved form was 129 ng L⁻¹, varying over a wide range. The content of Hg in total suspended substrates was an average of 151 ng L⁻¹, and the total content of Hg in lake water averaged 291 ng L⁻¹. Geological background and anthropogenic activities can determine the total Hg content in lakes. In most lakes, a significant positive correlation was noted between the concentration of one, two, or all three indicators of Hg content and the month of the year, with indicators increasing from winter through to autumn. When analyzing the entire data array, a significant positive correlation was found between the concentration of the suspended form of Hg and salinity; such correlation between the concentration of the dissolved form of Hg and salinity was absent. The highest average Hg concentrations in biomasses were noted in Artemia and were the lowest in plants. Geological background and human activity contribute to high Hg content in lakes. Hydrobionts can significantly influence the distribution and behavior of Hg, being an important factor of its cycle in the lakes.