Incorporating Species Sensitivity Distribution (SSD) Curves and the Comprehensive Quality Impact Index (IICQ) into the Risk Assessment of Heavy Metal(loid)s Synergistic Pollution in the Soil-Rice System of a Selenium-Enriched Area in Northern Anhui, China

To assess the pollution risk of heavy metal(loid)s in the soil-rice system of a selenium (Se)-enriched area in northern Anhui Province, we collected 30 paired samples of rice grains and their corresponding root soils in October 2023. The pollution risk of the soil-rice system was assessed using the comprehensive quality impact index (IICQ), while the soil heavy metal(loid)s thresholds were derived from species sensitivity distribution (SSD) curves. The SSD-IICQ-pollution risk assessment (PRA) model was developed to accurately assess heavy metal(loid)s pollution risks in the soil-rice system of the study area. The results showed that the mean soil concentrations of Se, arsenic (As), cadmium (Cd), and copper (Cu) exceeded the background values for Anhui Province. The mean Se concentration in rice grains met the Se-enriched standard, while As concentrations at some sampling sites exceeded the safety limit. The IICQ results indicated slight pollution by heavy metal(loid)s in the soil-rice system of the study area. Based on SSD and reliability verification, the soil Se threshold was determined to be 0.17–1.29 mg·kg−1 at pH 5.5–7.5. For soil Cd, the thresholds were 0.70 mg·kg−1 at pH 5.5–6.5 and 1.08 mg·kg−1 at pH 6.5–7.5. The thresholds for other heavy metal(loid)s were based on GB 15618-2018. When compared with the PRA using GB 15618-2018 and GB/T 44971-2024, the risk derived from the SSD-IICQ-PRA model was generally lower, but the pollution risk in the northern part of the study area still could not be ignored.