Assessment and sources of heavy metal accumulation in the soil of Erbil Governorate, Kurdistan Region-Iraq: Using pollution indices and principal component analysis

This study evaluates the ecological risks and pollution levels of nine heavy metals (As, Cr, Co, Cu, Mn, Ni, Pb, V, and Zn) in stream sediments of the Erbil Governorate in the Kurdistan Region of Iraq, bordered by the Upper and Lower Zab Rivers to the northwest and southeast, respectively. Average concentrations of heavy metals from 100 sediment samples collected across ten districts in Erbil Governorate were ranked as follows: Choman > Rawanduz > Soran > Erbil Plain > Koysinjaq > Shaqlawa > Mergasur > Khabat > Erbil Center > Makhmur. Notably, Ni, Cu, As, and Cr emerged as the primary contaminants, particularly in the northeastern areas of the Governorate, specifically Choman and Erbil Plain Districts. Enrichment factor analysis revealed slight to moderate pollution levels, except for Ni, which indicated moderate to heavy pollution. Principal component analysis (PCA) grouped the majority of metals (Cr, Co, Cu, Mn, Pb, Ni, V, and Zn) into three components, suggesting a natural origin. The fourth component indicated salinity effects related to cation and anion exchange processes that facilitate the leaching of other metals, while the fifth component, comprising arsenic, was associated with the application of arsenical pesticides in agricultural practices. Both As and Ni present significant concerns due to their toxicity, with as occurring at low to moderate levels and Ni at moderate to high concentrations. Overall, a low potential ecological risk index was calculated for soil samples from the Erbil Governorate.