Impact of Newly Build Lead-Acid Battery Agglomeration Area on the Surrounding Soil Environment: A Study Based on the Spatial Characteristics of Heavy Metals

Abstract

To determine whether the newly built lead-acid battery agglomeration area in a town in northern Zhejiang had an impact on the surrounding soil environment after seven years of operation, 76 samples of surface soil around the lead-acid battery concentration area were collected, and the contents of Hg, As, Cu, Zn, Pb, Cd, Ni, and Cr in the soil were determined. Based on the spatial distance of the agglomeration area and 50, 450, and 850 m from the agglomeration area boundary, the soil environmental quality was evaluated using the single factor index, Nemerow comprehensive pollution index, and potential ecological risk index methods. The spatial distribution characteristics of the heavy metals were analyzed using the geostatistical method, and the sources of heavy metals affecting the soil environment were determined by correlation analysis. The results showed that the average contents of Hg, Zn, and Pb in eight heavy metals were higher than their corresponding background values at all spatial scales. The average Cd content in spatial scales other than the agglomeration area was larger than its background value. Only As at 50 m was greater than its background value, whereas the average content of other elements at all spatial distances was lower than their corresponding background values. The spatial variability was high for Hg and Cd but not obvious for other elements. This implies that the influence of regional activities was concentrated mainly on Hg and Cd; the content of both increased with distance from the agglomeration area. Hg and Cd exceeded the risk screening values and were distributed mainly at 450 m and 850 m; 33.33% and 38.89% Hg points and 27.78% and 55.56% Cd points were observed at these distances, respectively. The spatial distribution characteristics of Hg and Cd were consistent with their contents; only Zn and Pb had scattered points that exceeded the risk screening values and generally no obvious spatial distribution characteristics. According to the risk analysis of soil comprehensive pollution caused by the eight heavy metals, Cd was the main source of soil comprehensive pollution risk at a contribution rate of 36.73%, which caused the soil at 850 m to be in a state of alert. Soil ecological risk at a medium level occurred mainly at 450 m and 850 m outside the agglomeration area from Hg and Cd. The contribution rates to the soil quality at these distances were 46.30% and 39.37% for Hg and 38.98% and 49.30% for Cd, respectively. This indicates that regional activities caused Hg and Cd to be the main elements affecting soil quality in the study area. The results of geostatistics and multivariate statistical analysis showed that Hg and Cd were diffused inward from the periphery of the agglomeration area on the axis of the local main wind direction (northeast-southwest), and the main sources of both were coal-burning activities of enterprises in the periphery of the agglomeration area. In summary, the newly build lead-acid battery agglomeration area has not significantly affected the accumulation of heavy metals in the agglomeration area and in the surrounding soil after seven years of operation.