Heavy metal contamination in rice-growing regions, along with its associated ecological and human health risks, remains insufficiently characterized in many parts of Iran, including Darreh Shahr. This study evaluated the ecological, carcinogenic, and non-carcinogenic risks posed by heavy metals (Zn, Cu, Cr, Fe, Pb, Ni, and Mn) in the soil–rice system of Darreh Shahr, western Iran. To assess the degree of soil contamination, several indices were applied, including Igeo, CF, ER, IPI, RI, ΣTU, CD, PLI, and NIPI. In addition, the bioconcentration factor and human health risk indices were calculated for rice consumers. The results of the Igeo, CF, and ER indices identified Ni contamination in paddy soils as the most critical concern in the study area, followed by Zn, Cr, and Pb, which collectively contributed to the highest ecological risk in the ecosystem. Based on the mean values of IPI, RI, ΣTU, CD, PLI, and NIPI, as well as the distribution of sampling points among their respective classes, the paddy soils were characterized by acute toxicity and moderate to high ecological risk. The bioconcentration factor revealed that rice exhibited a high potential for Pb accumulation, while the accumulation potential for the other metals ranged from low (Ni and Fe) to moderate (Zn, Cu, Cr, and Mn). Consumption of contaminated rice was associated with a higher non-carcinogenic risk in adults than in children. The carcinogenic risk (CR) values for Pb were estimated at 1×10⁻⁴ for children and 4×10⁻⁴ for adults. The estimated CR for Pb in adults exceeded the USEPA acceptable threshold of 1 × 10⁻⁴, placing it in Category 3 (significant carcinogenic risk). In children, although the mean CR remained within the acceptable range, some sampling points exceeded the threshold, corresponding to Category 2 (acceptable/tolerable risk). Overall, these findings identify lead as a major health concern for the local population through rice consumption. They also demonstrate a substantial ecological and human health threat from heavy metal contamination in the Darreh Shahr soil–rice system, underscoring the urgent need for stricter monitoring of irrigation water and major pollution sources, particularly road traffic emissions and fertilizer inputs, in order to mitigate metal accumulation in paddy soils and rice. • The results of calculating the Geoaccumulation index (Igeo), Contamination factor (CF) and Potential Ecological Risk (ER) indices showed that Ni has the highest ecological risk for the studied ecosystem. • The non-carcinogenic risk of heavy metals from rice consumption for adults was higher than for children • Rice is a hyperaccumulator for Pb and has moderate accumulation ability for Zn, Cu, and Cr.
Solgi et al. (Fri,) studied this question.