Ecological Risk Assessment and Source Analysis of Heavy Metals in Farmland Soils Around Typical Industrial Agglomeration Areas in the Central Plains

In order to investigate the pollution status and sources of heavy metals in farmland soils around the typical industrial agglomeration area in the Central Plains, taking the farmland soil around an industrial cluster in Henan Province as the research object, this study analyzed the contents, spatial distribution characteristics and ecological risks of eight heavy metals (Cu, Cd, Hg, As, Cr, Zn, Ni, Pb) in both surface and vertical profiles of farmland soils in the study area. Correlation analysis and absolute principal component score-multiple linear regression (APCS-MLR) model were used to analyze the sources of heavy metals in the soil of the study area. The results indicated that the average contents of eight heavy metals in the surface farmland soil of the study area did not exceed the screening values for soil pollution risks of agricultural land stipulated by the national standard. However, the average levels of Cu, Zn, Cd, Hg and As were higher than the background values of the soil in Henan Province. Spatially, the high-value areas of Cr and Zn in the surface farmland soil were mainly concentrated in the eastern part of the study area, the high-value areas of Cu, Ni and Cd were mainly concentrated in the western and southern parts of the study area, and Hg and Pb showed point-source distribution patterns. Vertical distribution characteristics suggested that most of the eight elements in the farmland soil in the study area were enriched in the topsoil and were difficult to migrate downward, which might be caused by the soil compaction resulting from petroleum extraction activities. The comprehensive pollution degree of eight heavy metal elements in the farmland soil of the study area was relatively low, and the comprehensive ecological risk level was medium. Among them, the ecological risk levels of Cd and Hg elements were relatively high, at medium or above levels, while the ecological risk levels of the remaining heavy metal elements were all relatively low. The APCS-MLR model identified three sources of heavy metals. Cr, Ni, Cu and Zn were mainly from industrial sources, namely the production activities of petrochemical enterprises and related industrial enterprises, and the contribution rates of this source to Cr, Ni, Cu and Zn were 92.40%, 56.92%, 62.20% and 84.64%, respectively. Cd, Pb and As were mainly from traffic sources, that is, dust deposition caused by exhaust emissions and tire wear during transportation,and the contribution rates of this source to Cd, Pb and As were 53.25%, 71.26% and 42.78%, respectively. Hg was primarily associated with a comprehensive pollution source caused by the accumulation of agricultural-anthropogenic solid waste. Among them, the contribution rate of agricultural sources to Hg was 33.23%, and the contribution rate of unknown sources to Hg was 48.17%. These findings provide a scientific basis for the precise prevention and control of regional heavy metal pollution and have important practical value for ensuring the environmental quality of farmland soil and the safety of agricultural products around the chemical industry agglomeration area.