Risk assessment of heavy metals in north of Iran (Sari) rice and implications for human health

Rice, as a global staple food, requires safety monitoring to protect public health. This study evaluated heavy metal contamination in rice crops in Sari, Iran using hazard quotients (HQ) and cancer risk assessment (ILCR). In this study, 144 rice samples were collected-comprising 48 samples from each of the three dominant local brands (H, Sh, and B)-across 16 rice mills situated in the four cardinal directions (north, south, east, west) of Sari (Iran) between June and September 2022. The concentration of Lead (Pb), Cadmium (Cd), Copper (Cu) and Zinc (Zn) was performed using a Metrohm 797 VA Computrace polarographic trace analyzer (Metrohm, Germany). Results showed mean concentrations of 2.77 ± 2.14 (Pb), < 0.0001 (Cd), 3.95 ± 2.11 (Cu), and 11.73 ± 5.62 mg/kg (Zn), with Pb exceeding safety limits (0.2 mg/kg) in all samples. Risk assessment indicated significant non-carcinogenic risk from Pb (HQ > 1), while other metals posed acceptable risks. Spatial analysis revealed Pb hotspots near the Caspian Sea (9.88 mg/kg) versus southern regions (0.38 mg/kg), reflecting anthropogenic pressures from tourism and wastewater irrigation in coastal areas. Contamination patterns followed land use: northern highways (Pb), eastern farms (Zn/Cu from fertilizers), and urban centers (multiple metals). These findings mirror global coastal pollution dynamics, showing cleaner rural versus polluted urban-adjacent fields. We recommend immediate agricultural interventions including source identification and remediation strategies, particularly for Pb mitigation. Comprehensive coordination between environmental management and agricultural practices represents the optimal approach for simultaneously protecting human health and ecosystem stability in Mazandaran vital rice production areas.