Unraveling co-contamination characteristics of heavy metals in soil-crop system and collaborative management of their health risk across China

Abstract

Heavy metal pollution in farmland soil and crops directly affects the food safety and public health. A comprehensive national-scale assessment from an integrated soil-crop perspective in China remains limited. To address this gap, this study conducted a systematic review using an optimized bibliometric approach enhanced with uncertainty control and case mining. 1157 publications reporting on eight heavy metals (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in agricultural soils, grains, and vegetables across China were analyzed. Key findings include: (1) Cadmium (Cd) was the most widespread pollutant in soils, whereas mercury (Hg) showed highly concentrated hotspots. (2) A discrepancy was observed between soil pollution levels and the corresponding crop contamination indicating that the relationship between them is not fully synergistic. (3) Health risk assessment revealed that the total carcinogenic risk from soil exposure (10⁻⁶ - 10⁻⁵) was significantly lower than that from ingestion of contaminated grains and vegetables (10⁻⁴ - 10⁻³). Arsenic (As) and Cd were identified as the primary risk contributors in most provinces. (4) Geographically, integrated high-risk areas were classified as Class I (Guangdong, Guizhou, Yunnan) and Class II (Hunan). Risk sources in Yunnan and Guizhou were attributed to both geogenic and anthropogenic activities, with exposure dominated by vegetable and grain ingestion, respectively. In contrast, risks in Guangdong and Hunan were primarily linked to human activities (industrial, mining, and agricultural), with comparable exposure from both crops. Based on these findings, tailored risk mitigation strategies are proposed for the identified high-risk provinces, considering their distinct exposure pathways and contamination sources.