Contamination status and assessment of urban and non-urban soils in the region of Sulaimani City, Kurdistan, Iraq

Soil contamination, especially in urban areas, is a globally increasing threat. Yet, knowledge on the status of urban soils in recently and rapidly developing regions and semiarid areas is still scarce. In this study, soils were investigated from Sulaimani city that underwent rapid growth and urbanization in past decades. Properties and contamination of 91 topsoils from 11 areas of different anthropogenic impact were determined. Differences between urban and non-urban soils were attributed by principal component analysis to differences in contents of pedogenic oxides, carbonate, organic nitrogen and carbon, pH and CEC. Also total contents of potentially toxic elements (PTE) were higher; mean contents of Cd, Pb, Cu and Zn in urban soils were 0.35, 51.8, 78.6 and 163.0 mg kg−1. The PTE contents increased with traffic volume and industrial emissions. The anthropogenic origin of contamination was further evidenced by significant enrichment of PTE in the top 0–5 cm compared to deeper topsoil layers. Additionally, mobility of PTEs was low in the clayey, alkaline soils. Contamination was substantially lower compared to many other cities, being explained by the short history of urban development in Sulaimani. Correspondingly, contents of polycyclic aromatic hydrocarbons were mostly not detectable. Contamination with PTEs was assessed using pollution indices and classified as ‘moderate’ to ‘considerable’ in roadside soils and significant’ to ‘very high’ in soils from industrial areas, depending on the single element. Toxicity indices >0.5 revealed that adverse effects on ecosystem functions must be expected at several urban and especially industrial sites.