Study on the occurrence characteristics, bioavailability and risk assessment of mercury and arsenic from thesurface sediments inLake Gahai

The results of heavy metal elements Hg and As from the surface sediments of Lake Gahai in Qaidam Basin determined by Tessier sequential chemical extraction procedures are reported. Based on the enrichment factor (EF), geo-accumulation index (I_geo), potential ecological risk index (PERI), risk assessment code (RAC) and the ratio of secondary to primary phase distribution (RSP) methods, the pollution degree, potential ecological risk level and bioavailability of Hg and As in the study area were evaluated. The results showed that the average contents of Hg and As element was 0.07 mg/kg and 37.28 mg/kg, respectively, showing an uneven spatial distribution and asynchronous trends in content variation. Hg and As were predominantly presented in the residual phase, accounting for 81.12% and 60.49% of their total amounts, respectively, the subordinate fractions were the carbonate-bound forms, accounting for 2.27% and 0.52% of their total amounts, respectively. The RAC evaluation results suggested Hg>As, while the RSP evaluation results indicated As>Hg. The I_geo and PERI evaluation results showed that the overall ecological risk trends for mercury and arsenic were generally consistent, with the ecological risk of Hg being much higher than that of As. The impact of anthropogenic sources generated by human activities is becoming increasingly prominent, and the heavy metal elements such as Hg has become nationwide pollutant that requires sufficient attention.