Distribution characteristics, speciation and risk assessment of mercury in surface sediments of urban lakes in Nanchang city, China

Mercury is a toxic and harmful heavy metal pollutant that is prone to migration and accumulation. The increase of mercury emission and the aggravation of mercury pollution have attracted the attention of many scholars. The study focused on six urban lakes in Nanchang city, China as the research area. By determining the content of total mercury (THg) and mercury speciation in the surface sediments, Pearson correlation analysis, Tessier continuous extraction method and multiple ecological risk assessment methods were employed to investigate the distribution characteristics, migration and transformation, and ecological risks of mercury in the surface sediments of urban lakes in Nanchang. The results showed that the total mercury concentrations ranged from 0.109 ~ 0.377 ng/g, with an average of 0.197 ± 0.103 ng/g. The mercury pollution was relatively severe, and the closer to the city center, the more serious the mercury pollution. Mercury primarily existed in the form of residue, accounting for approximately 48.3% to 63.6% of the total mercury. The proportions of bioavailable mercury was also relatively high, ranging from 36.4% to 51.7%. Among the six urban lakes, the content of bioavailable mercury in the sediments of Qingshan Lake was the highest, which was significantly affected by human activities and easy to be released back into water. The overall mercury pollution in the sediment of six urban lakes in Nanchang was moderate pollution with high risk, while the biological toxicity and release possibility of mercury were moderate risk.