Dietary risk analysis of heavy metal and metalloid pollution in rice: case study of Nanning City in China.

Abstract

Heavy metal contamination of rice represents an important dietary exposure pathway in southern China. This study evaluated heavy metal and metalloid contamination and associated health risks in rice from Nanning City. A total of 1,844 rice samples collected between 2014 and 2020 were used for probabilistic risk assessment, and 538 recent samples (2019-2020) were analyzed to characterize contamination levels. Deterministic and Monte Carlo approaches were applied to assess non-carcinogenic and carcinogenic risks. Among four elements analyzed (Cd, Pb, Hg, and inorganic As), cadmium was the predominant contaminant, with a maximum concentration of 1.28 mg/kg (6.4 times the national limit) and an exceedance rate of 16.36% in recent samples. The combined hazard index (HI) was 1.13, indicating potential non-carcinogenic concern. The total carcinogenic risk (CCR) was 1.75 × 10-5. Monte Carlo simulation showed a mean THQ of 0.61, with 15.8% of the simulated population exceeding THQ = 1. Sensitivity analysis identified cadmium concentration as the primary determinant of exposure risk. Cadmium remains the dominant contributor to dietary risk from rice in Nanning City. Targeted monitoring and risk management in high-exposure areas are warranted.