[Comprehensive Quality Assessment of Soil-Maize Heavy Metals in High Geological Background Area]

The aim of this study was to analyze the pollution degree and causes of soil and agricultural products in high geological background areas and to provide a basis for the safe production of agricultural products and the risk control of soil heavy metals. A total of 36 sets of soil-corn collaborative samples were collected in the farming area of Baolong Town, Wushan County, Chongqing City; the contents of heavy metals (Cd, Hg, Pb, As, and Cr) and soil pH in the soil-maize were analyzed, the pollution degree of heavy metals in the soil-maize was evaluated using the Nemerow comprehensive pollution index method (P_N) and comprehensive quality impact index (IICQ). The sources of heavy metals in the soil and the influencing factors of heavy metal excess in corn were also analyzed. The results showed that the average value of soil heavy metal content in the study area was higher than the national and Chongqing soil background values, and the soil heavy metal enrichment effect was obvious. Cd was the main factor of soil-maize exceeding the standard, and the overall exceeding rates of soil and corn Cd were 91.67% and 30.55%, respectively. The evaluation results of the Nemerow comprehensive pollution index showed that the soil was dominated by heavy pollution, accounting for 63.89%. The soil-maize comprehensive quality impact index was dominated by moderate and severe pollution, accounting for 44.44% and 47.22%, respectively. From the perspective of the spatial distribution of heavy metal pollution, corn and soil pollution areas were inconsistent. Soil heavy metal pollution was mainly affected by the Permian and Triassic strata and was related to the secondary enrichment of black rock series and limestone areas. The Cd content of maize was mainly affected by soil pH, and maize was relatively safe under alkaline conditions. It is suggested that the soil in the study area should be divided into risk zones according to the stratum distribution, and the planting structure should be adjusted in the high-risk areas. For the low- and medium-risk areas, it is recommended to strengthen the monitoring of agricultural inputs and reduce the input of heavy metals in the soil. Additionally, we recommend carrying out agronomic regulation in acidic soil areas to improve soil acidification, plant corn varieties with low accumulation of heavy metals, and reduce the risk of agricultural products exceeding the standard.