Increased ecological and health risks associated with potentially toxic trace elements in agricultural soil adversely affected by gold (Au) mining activities

Zaozigou gold mine is located in the Qinghai-Tibet Plateau, and it is one of the largest gold (Au) mines in China. Agricultural soil pollution of toxic trace elements (TTEs) in Au mining area has become an increasingly common issue and potentially harms the environment and human health. In this paper, 78 samples were collected from a typical Au mining area to evaluate pollution degree of TTEs in the soils and assess related human health risk. In this study, a total of 78 samples including 36 agricultural soil, 21 sediment, and 21 river samples were collected from the Au mining area. The soil chemical properties of soil samples were analysed. The geo-accumulation (Igeo), contamination factor (CF), and pollution loading index (PLI) were used to analyse the degree of contamination by TTEs. In addition, potential ecological and health risks to local residents via different three exposure routes were revealed using potential ecological risk index and US-EPA health risk assessment models. Pearson correlations between soil chemical properties and toxic elements concentration were calculated. Results showed that the mean concentrations of As, Cd, Zn, Pb, Cr, and Hg in soils were 27.02, 4.22, 1.57, 1.46, 1.17, and 4.88 times higher than the background values, respectively. The Igeo index and CF values indicated that As pollution was the most severe and Hg and Cd pollution was moderate. Additionally, PLI indicated that soil As and Hg posed extremely high risks. The average potential ecological risk value of all TTEs was 602.34, and As had a higher contribution rate than the other elements, suggesting that the study area was under very high risk, mainly posed by soil As. The hazard index values for Pb, Cr, Cd, Hg, and Zn were below safe value of 1. However, the hazard index values of As for local adults and children were 1.66 and 10.25, respectively. Meanwhile, As presented the unacceptable carcinogenic risks for local residents. The presence of As was related to mining activities, based on the Pearson correlation (between soil chemical properties and TTE contents) and As levels in rivers and sediments near the mining area. As pollution from Au mining activities has posed potential ecological risks to the ecosystem and caused human health risk in the Au mining area. Therefore, more efficient policies to control As contamination in the soils should be implemented as soon as possible.