Source analysis and human health risk assessment of heavy metal in farmland soil-rice system in Nandu River Basin, Zhanjiang City, Guangdong Province, China

This study aims to characterize heavy metal contamination in rice fields of the Nandu River Basin (subtropical red soil zone) and elucidate its risk mechanisms. Key objectives include assessing pollution levels/ecological risks, identifying contamination sources, and evaluating human health risks from soil-rice systems. Forty paired soil-rice samples were collected. Concentrations of Cr, Ni, Cu, Zn, Pb, Cd, Hg, and As were quantified using ICP-MS and ICP-AES. Contamination status was evaluated via the Nemerow integrated pollution index and Hakanson’s potential ecological risk index. Health risks were assessed using an exposure model. Source apportionment employed a multivariate framework combining correlation analysis, principal component analysis (PCA), and the absolute principal component score–multiple linear regression (APCS-MLR) receptor model. Soil metals generally met screening thresholds, but Hg was significantly enriched (6.44× background), indicating heavy pollution and high ecological risk. Cr exceeded limits in 12% of rice samples; As carcinogenic risk neared thresholds. Hg and Pb in rice showed high spatial variability (CV > 140%), suggesting anthropogenic influence. Source analysis revealed: PC1 (47.3%)—volcanic weathering + traffic/agriculture (Pb-Zn-Ni); PC2 (25.66%)—geogenic + agricultural (As-Cu-Cr); PC3 (10.86%)—electronics/traffic (Hg); PC4 (7.32%)—fertilizers (Cd). Children’s oral intake risk for As/Cr was 78–123% higher than adults; dermal Cr exposure posed notable noncarcinogenic risk ( HQ  = 0.709). Contamination in the basin stems from composite natural-anthropogenic sources, with Hg posing significant ecological risk and Cr/As presenting key health concerns, especially for children via ingestion and dermal pathways. These findings provide a scientific basis for targeted risk management of heavy metals in high-background red soil agricultural regions.