Evaluation of heavy metal distribution characteristics of agricultural soil–rice system in a high geological background area according to the influence index of comprehensive quality (IICQ)

Heavy metal pollution is a global ecological safety issue, especially in crops, where it directly threatens regional ecological security and human health. Selecting scientific evaluation methods is an important prerequisite for understanding the distribution of heavy metals in a region. To evaluate the distribution characteristics of arsenic (As), cadmium (Cd), copper (Cu), and zinc (Zn) in farmland soil–rice system in Doumen District of Zhuhai City, Pearl River Delta, we analyzed the high geological background area and heavy metal contents in soil by inverse distance–weighted interpolation and single-factor pollution index. Bioconcentration factor (BCF) was used to study the migration and accumulation characteristics of heavy metals. Then, the soil–rice system was evaluated comprehensively with a novel evaluation method, i.e., the influence index of comprehensive quality (IICQ). Results showed that As, Cd, Cu, and Zn in the soil of the study area followed normal distribution. Cd and Cu were the main pollutants whose point contamination rates were 50% and 22.86%, respectively. A total of 2.86% of the soil were contaminated by As, and no Zn contamination was observed in the soil. At the same time, As and Cd in rice were partially polluted, and the Cu and Zn were not polluted. The order of bioaccumulation coefficient was Cd > Zn > Cu > As, and no evident enrichment was observed. According to the impact index of IICQ to evaluate the pollution of heavy metals in the soil–rice system, 96.98% of the soil in study area was in a state of moderate, heavy, and extreme pollution, which were concentrated in the northern and central parts of the study area. The soil–rice system in the high geological background area was in a subhealthy state. A total of 90.69% of the soil were polluted, but the rice met the national food safety standards.