Contamination characteristics, source apportionment, and risk assessment of heavy metals and metalloids in the soil-crop-human system within the typical high geological background region of the Yangtze River Delta

Anji County, Zhejiang Province, is a typical high geological background region within the Yangtze River Delta. Our study aimed to address gaps in fragmented traditional heavy metal and metalloid research by comprehensively exploring the soil-crop-human system. In surface soil, all eight heavy metals and metalloids (As, Hg, Cr, Cu, Pb, Zn, Ni, and Cd) exceeded the background values, especially Cd (3.75 times), and their spatial distribution correlated with the black rock series. Spearman correlation analysis, principal component analysis (PCA), and positive matrix factorization (PMF) models were utilized to identify sources: industrial (25.76 %), traffic (23.16 %), agricultural (16.94 %), mixed (15.55 %), and lithogenic (18.60 %). Ecological risk assessment with Nemerow's synthetical pollution index (P_n) and potential ecological risk index (RI) showed that Cd had a single pollution index of 2.32, which drove P_n to 1.77, signifying mild pollution, and contributed 97.11 % to RI. In the planting system, dry land enriched more heavy metals than paddy and tea fields, and crop levels were vegetables > tea > rice. Phytoaccumulation heterogeneity was pronounced. Leafy vegetables exhibited a relatively strong accumulation ability for heavy metals. Dietary differences drove divergent risk susceptibilities. Limited tea consumption reduced children's carcinogenic risk (CR), whereas increased hickory intake amplified their risk. Despite the contamination of the soil-crop system, population health indicators did not show significant negative effects. Biomonitoring revealed urinary Cd exceedance against normative hair Cd levels, suggesting effective renal clearance mechanisms counteracting environmental exposure, albeit long-term risks necessitate continued monitoring. These findings provide new insights into the impact of heavy metal pollution on human health in high-background areas.