Ecological and Health Risk Assessments Based on the Total Amount and Speciation of Heavy Metals in Soils Around Mining Areas

Abstract

Topsoil and supporting crop samples around a mining area were collected in Longyan City, and the total amounts and speciation of Pb, Cd, and As in the samples were determined. The ecological risk and human health risk assessment of soil heavy metals Pb, Cd, and As were carried out using the Hakanson potential ecological risk assessment method, the ecological risk classification method based on the principle of geochemical statistics, and the health risk assessment method in accordance with the characteristics of human exposure parameters in China. The results indicated that the heavy metal elements in the soil in the study area exceeded the environmental quality standards for Pb and Cd, and the heavy metal contents in cereal grains exceeded the food limit value mainly for Pb. The proportion of the four bioavailable forms except the residue state followed the order of Pb>Cd>As. The ecological risk assessment results based on the total amount of heavy metals and bioavailable forms showed that Cd was the most important ecological risk factor. The single potential ecological risk of Cd and the comprehensive ecological risk of Pb, Cd, and As in the soil based on bioavailable forms were significantly reduced compared with that based on the total amount. The proportion of medium and superior samples decreased from 100% and 50.0% to 17.2% and 7.81%, respectively, and the divided risk zone basically contained all the warning points of exceeding the standard of crops. Oral ingestion was the main carcinogenic and non-carcinogenic exposure route of heavy metals. In terms of carcinogenic risk, the risk of human carcinogenic health exposure to Cd and As was within the acceptable range, regardless of whether bioavailability was considered. Among the non-carcinogenic risks, the non-carcinogenic risk of the heavy metal Cd was negligible. When only the total amount of heavy metals was considered, the non-carcinogenic risk index of Pb and As under the three exposure pathways ranged from 0.14 to 8.65 and from 0.04 to 2.85, respectively. After considering the adjustment of bioavailability, the non-carcinogenic risk of As was greatly reduced and could be considered to no longer have non-carcinogenic risk. Although the non-carcinogenic exposure risk index of Pb was reduced by 84.7%, the maximum value still reached 1.69, which would cause non-carcinogenic harm to the population and was the key to soil remediation in mining areas.