[Pollution Characteristics of Heavy Metals in Soil-rice System in Geological High Background Area and Related Risk...

Taking the paddy fields in a high geological background area of Guizhou Province as the research object， the total and available contents of eight heavy metals （Hg， Cd， As， Pb， Cr， Ni， Cu， and Zn） in the soil and rice grains， as well as the physicochemical properties （pH， EC）， were analyzed. Multiple evaluation methods were employed， including the single factor pollution index， Nemerow comprehensive pollution index， integrated soil and agricultural product quality index （IICQ）， and human health risk models. Species sensitivity distribution （SSD） curves and multiple linear regression were utilized to determine safe thresholds for heavy metals in the soil-rice system. The results revealed significant exceedances of Hg （48%）， Cd （30%）， and As （53%） in the soil relative to the Chinese Soil Environmental Quality Standard （GB 15618-2018）， while rice grains exhibited elevated Hg （86.29%）， As （50.25%）， Cd （6.09%）， Pb （5.08%）， and Cr （9.14%） levels exceeding the National Food Safety Standard （GB 2762-2017）. The Nemerow index identified Hg， Cd， and As as primary soil pollutants， with Hg posing the most severe grain contamination. IICQ evaluation indicated predominantly severe soil pollution but only mild-to-moderate grain contamination. Health risk assessment identified oral ingestion as the primary exposure pathway contributing to both non-carcinogenic and carcinogenic risks. Through the fitting of SSD and multiple linear regression models， the safety thresholds of Hg， As， Pb， and Cr in the soil of the study area were all lower than the current national screening values for soil pollution risks in agricultural land， while the safety threshold of soil Cd was higher than the screening value. The research results can provide a reference for the prevention and control of heavy metal pollution risks in paddy fields in high background areas.