Pollution characteristics and source identification of heavy metals in farmland soils around a tailing pond in Zhejiang Province

The safety of the ecological environment around tailing ponds has received high attention, and soil heavy metal pollution is one of the risk sources of cultivated land management and protection. The concentrations of eight heavy metals Cd, Hg, As, Pb, Zn, Cu, Cr and Ni were measured in the soil of a copper mine tailing pond in Zhejiang Province, which was located in the hilly mountainous area of east Zhejiang Province, and the degree of soil heavy metal pollution and ecological risk around the tailing pond were evaluated by using the geo-accumulation index method, pollution index method, potential ecological risk index method and ecological risk warning index method. The sources of heavy metals in farmland soils were quantitatively analyzed by combining the positive definite matrix factor (PMF) receptor model. The results showed that: 1) The concentrations of Cd, Hg, Cu and Zn with a character of high variability in farmland soils in the study area were 5.36, 2.06, 8.19 and 5.36 times higher than the background values of soil elements, respectively. The pollution index showed that the percentage of heavy pollution of Cu, Zn and Cd all reached 10.5%, the percentage of moderate pollution was 5.26%, and 15.8% of the points near the tailing pond (<300 m) were in the severe pollution level. The geo-accumulation index indicated that Cd, Cu, Zn and Hg might have cumulative risks. 2) The results of the ecological risk index showed that Cd was with high potential ecological risk, Hg was with considerable potential ecological risk, Cu was with moderate ecological risk and the remaining heavy metals were minor risk. The comprehensive potential ecological risk index (RI) was 308.91, which belonged to high risk level. The results of the ecological risk warning index indicated Cu was severe warning, Cd and Zn were medium warning, Hg was mild warning, As was early warning, Pb, Cr and Ni were no warnings. The comprehensive ecological risk warning index (IER) was 16.06, which belonged to severe warning level. The spatial distribution patterns of RI and IER were similar, and Cd, Cu, Zn and Hg were the main warning elements and ecological risk factors in the study area. 3) The sources apportionment of heavy metals in the farmland soil based on PMF indicated that the heavy metal contamination in the area mainly came from three sources. Specifically, Cd, Zn and Cu pollution was mainly influenced by mixed of tailings from copper tailing pond and seepage water under the dam, and the corresponding contribution rate was 94.4%, 94.3% and 67.1%, respectively. Agricultural activities such as chemical fertilizer and pesticide application had the highest contribution to Hg, and its contribution rate was 61.5%. Natural parent material and transportation activities had the highest contribution to Cr, Ni, Pb and As, and the corresponding contribution rate was 89.7%, 82.7%, 75.0% and 68.3%, respectively.