Investigation of the status of heavy metals in soils of Iran: A comprehensive and critical review of reported studies

In the world, attention to the content of heavy metals in the soil has increased due to their potential risks to the environment and human health. In recent decades, many studies have been reported on soil contamination by heavy metals in Iran, but most studies do not show heavy metal status in soils on a national scale. On the other hand, despite the importance of background concentration of heavy metals for the assessment of pollution and environmental risks of these metals, no study has yet been published for soils of Iran at the national scale. In this study, an attempt was made to provide a comprehensive understanding of the status of heavy metals in soils of Iran on a national scale based on quantitative and qualitative analysis of the results of studies reported. To conduct this research, a total of 247 studies (both articles and final reports of research projects on field monitoring of heavy metals in soils of Iran that were published until November 2021 were collected. The required information (analysis results of about 21,400 soil samples) were extracted from the studies and first evaluated in terms of quality assurance and quality control criteria. Then, studies were classified into agricultural, urban and industrial based on the type of land use, and after screening and selecting studies that had the minimums required in terms of quality control, various statistics such as weighted average, median, background concentration and pollution index for heavy metals As, Pb, Cd, Cr, Co, Ni, Cu and Zn were calculated and analyzed....