Unregulated heavy metals in Chinese rice pose greater health risks and economic costs than regulated metals

The concentrations of certain heavy metals in rice, such as cadmium (Cd), are regulated by governments or international organizations due to their toxicity to human health, referred to as “regulated metals”. In contrast, other metals, despite their potential health risks, remain unregulated and are classified as “unregulated metals”. Compared to regulated metals, unregulated metals have received relatively limited research attention due to the absence of regulatory standards in rice. This study collected 408 heavy metals concentration data from 204 published articles, covering on four regulated metals (Cd, Asi, Pb, Cr) and four unregulated metals (Ni, V, Mo, Co). We compared health risks and economic costs of regulated and unregulated metals across 32 Chinese provinces using health risk and economic cost assessments methods. Results show that the HQ value for each individual unregulated metal is below 1, indicating low non-carcinogenic risks. However, Ni poses a significant carcinogenic risk, highlighting its potential health threat. Monte Carlo simulation shows that 82.28% and 92.96% of the population face accumulated non-carcinogenic and carcinogenic risks from unregulated metals, significantly exceeding the 65.76% and 82.27% associated with regulated metals. Significant regional variations were observed, with higher health risks in Hunan, Guangdong, Guangxi, and Sichuan provinces. Furthermore, the total economic costs of unregulated metals, estimated at USD 661.28 billion and USD 25.05 billion yuan (VSL and COI methods, respectively), are 1.45 and 1.47 times higher than those of regulated metals. Regions in southern China bear the greatest economic burden. Our findings suggest unregulated heavy metals in Chinese rice pose greater health risks and economic cost than regulated metals, highlighting the urgent need to prioritize them in future risk and economic assessments for rice safety and sustainability. However, the uncertainties arising from heterogeneous data sources and assumptions in cost estimation require further investigation.