Risk assessment for the mercury polluted site near a pesticide plant in Changsha, Hunan, China

- Total concentration and fraction distribution of mercury were characterized.
- Soil physicochemical properties were built-up for fractionation analysis.
- DGH method and model were introduced for risk assessment.

The distribution characteristics of mercury fractions at the site near a pesticide plant was investigated, with the total mercury concentrations ranging from 0.0250 to 44.3 mg kg−1. The mercury bound to organic matter and residual mercury were the main fractions, and the most mobile fractions accounted for only 5.9%-9.7%, indicating a relatively low degree of potential risk. The relationships between mercury fractions and soil physicochemical properties were analysed. The results demonstrated that organic matter was one of the most important factors in soil fraction distribution, and both OM and soil pH appeared to have a significant influence on the Fe/Mn oxides of mercury. Together with the methodology of partial correlation analysis, the concept and model of delayed geochemical hazard (DGH) was introduced to reveal the potential transformation paths and chain reactions among different mercury fractions and therefore to have a better understanding of risk development. The results showed that the site may be classified as a low-risk site of mercury DGH with a probability of 10.5%, but it had an easy trend in mercury DGH development due to low critical points of DGH burst. In summary, this study provides a methodology for site risk assessment in terms of static risk and risk development.