Cadmium and lead contamination in Iranian wheat grains and soils: Nationwide assessment of spatial distribution and food safety implications.

Abstract

Wheat is a major staple crop worldwide, making the assessment of heavy metal contamination a critical concern for food safety and public health. This study presents a nationwide evaluation of cadmium (Cd) and lead (Pb) concentrations in wheat grains and corresponding agricultural soils across five major agroecological zones in Iran. A total of 2016 wheat grain samples and 690 soil samples were collected from representative wheat-growing regions during 2018-2021 and analyzed using validated analytical methods. The results revealed that the mean concentrations of Cd (0.011 mg/kg) and Pb (0.032 mg/kg) in wheat grains were below the maximum permissible limits set by national and international standards. However, spatial analysis identified localized contamination hotspots, particularly in northern and western provinces, where metal concentrations approached regulatory thresholds. Soil pollution indices generally indicated low contamination levels and low ecological risk at the national scale, with slight enrichment observed in limited areas. Soil-grain relationships were weak but statistically significant, suggesting that Cd and Pb uptake is influenced by soil pH, organic matter content, wheat cultivar, and agricultural management practices. The predominantly alkaline nature of soils in the studied regions appears to reduce Cd and Pb bioavailability and imit their transfer into wheat grains. Health risk assessment based on estimated dietary intake revealed Hazard Quotient values (HQ < 1) for both metals, indicating no significant non-carcinogenic risk associated with wheat consumption under average dietary scenarios. Overall, although current contamination levels do not pose a significant public health risk, the findings highlight the need for continued regional monitoring to sustain safe wheat production and prevent future accumulation.