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. The total mercury (THg) concentration and mercury speciation in surface sediments were determined. Pearson correlation analysis, Tessier continuous extraction method and multiple risk assessment methods were employed to investigate the distribution characteristics, migration and transformation, and potential risk of mercury in the surface sediments of urban lakes in Nanchang. The results showed that THg concentrations varied from 109 to 377 ng/g, with an average of 197 ± 103 ng/g. The mercury pollution was relatively severe, and the closer to the city center, the more serious the mercury pollution. Residual mercury was the dominant speciation, accounting for 48.3% to 63.6% of THg. The proportions of bioavailable mercury was also relatively high, ranging from 36.4% to 51.7%. Among all six lakes, Qingshan Lake had the highest content of bioavailable sediment mercury, which was significantly affected by anthropogenic activities and prone to re-release into overlying water. The overall mercury pollution in the sediment of six urban lakes in Nanchang was mild pollution with high risk, while the potential risk and release possibility of mercury were moderate risk.