Heavy Metals in Rice Fields at a Typical Southeast Coastal Industrial Site: Spatial Distribution and Toxicity Centroids with Health Risk Assessment

This study investigated heavy metals (Cd, Pb, Cr, Cu, Zn) in the soil-rice system of Sanming, a typical industrial and rice-growing region in China, to analyze their spatial patterns, sources, and ecological and health risks. Standard deviation ellipses based on the geoaccumulation index (Igeo), single ecological risk index (Er) and comprehensive ecological risk index (RI) were used to visualize spatial disparities of pollution and risk. Cd was the primary pollutant with the widest distribution; its average (Igeo) reached 2.29, and roughly 80% of samples presented moderate to heavy pollution. The highly matched (Igeo) and (Er) ellipses of Cd resulted from its high toxicity and low background value. Zn and Pb exhibited local hotspots: Zn pollution clustered around Shaxian industrial sites, while Pb spread east–west along the Shaxi River basin. The RI centroid was at 26.334° N, 117.379° E. The hazard index (HI) of rice intake for children exceeded 1, indicating notable non-carcinogenic risks, whereas HI values for other populations were below 1. Zn, Cr and Cd dominated non-carcinogenic risks, and pH drove elevated Zn-related health risks. The Unmix model showed mixed industrial and agricultural sources contributed 55% of heavy metals. This study implies concentration-based spatial analysis may underestimate ecological and health hazards of low-toxic metals. These findings support effective soil management and the protection of local residents from dietary heavy metal exposure. Future studies should apply repeated standard deviational ellipse analyses to track pollution and risk centroid shifts and thus support adaptive management.