Environmental pollution status and health risk assessment of selective heavy metal(oid)s in Iran's agricultural soils: A review

Abstract

The assessment of heavy metal(oid) concentrations in agricultural soil holds significant importance due to its impact on crop safety and quality, as well as the potential risks it poses to human health. This review utilized secondary online published data to evaluate the contamination levels of seven HMs (As, Cd, Cu, Cr, Ni, Pb, and Zn) in Iranian farmland soils. As a result, 31 research papers were collected to compile a dataset offering a comprehensive analysis of HM concentrations, distribution, sources, ecological risks, and potential health risks. The findings indicated that mean concentrations of Ni and Cd exceeded their corresponding permissible levels in farmland soils, while other HMs remained below this threshold. The mean Igeo (geoaccumulation index) values followed the sequence Ni > As > Cu > Cr > Zn > Pb > Cd, with Igeo values suggesting low to slight enrichment for the studied HMs. Pollution index (PI) results revealed notable contamination of As in various provinces, including Kurdistan, Hamedan, Tehran, Mazandaran, West Azerbaijan, Kermanshah, Hormozgan, Golestan, and the Kamfiruz region of Fars. Elevated contamination of Pb and Cd was observed in Fars (Shiraz region), and Cr and Ni in the Sabzevar area farmland soils. As, Cd, and Cu exhibited higher ecological risks (EI) compared to Zn, Cr, Ni, and Pb. The potential ecological risks (PER) ranged from 9.9 to 244.6, indicating low to moderate risk levels. Non-carcinogenic assessments indicated that ingestion was the primary exposure pathway to HMs in Iranian farmland soils, followed by inhalation and dermal contact. Total hazard index (HI) values for studied HMs did not exceed 1, indicating no significant non-carcinogenic risk for both population age groups. This study highlights the current lack of well-documented scientific reports on the status of HMs in agricultural farmland soils across 12 other provinces in Iran, emphasizing the need for further investigation. Moreover, the bioavailability of HMs in agricultural soils significantly influences HM content in crops, underscoring the need for future research to ascertain HM concentrations in different soil fractions.