Pollution assessment of heavy metals in soils of India and ecological risk assessment: A state-of-the-art.

Soil is substantive component of biosphere, which is exposed to plethora of pollutants including heavy metals. These are added by natural as well as anthropogenic activities. Upsurge in heavy metal content affects all organisms by biomagnification. So, it becomes vital to create a database of heavy metals concentration in soil. This is relevant in countries where unsustainable intensive agriculture, industrial and urban development is in progress. The present review of the scientific literature from 1991 to 2018 on heavy metals in soils in India shows that Zn and Pb exceeded their limits for Indian natural soil guidelines (Zn 22.1 and Pb 13.1 μg/g), Canada (Zn 200 μg/g), Swedish (80 μg/g) and Poland (Zn 300 μg/g) soil guidelines. The mean values of As and Cu for all soil types except for roadside soils, exceeded the limits. The average value of Cd for all soil types exceeded their limit. The mean values obtained for soils of India are Fe (23774.84 μg/g), Mn (872.54 μg/g), Zn (359.94 μg/g), Cu (183.67 μg/g), Cr (161.42 μg/g), As (148.70 μg/g), Ni (112.41 μg/g), Pb (61.87 μg/g), Co (37.63 μg/g) and Cd (14.16 μg/g). Cluster analysis and factor analysis were employed to different soil types and showed multiple sources of these metals. The contamination factor (CF), enrichment factor (EF) and potential contamination index (Cp) showed that Cd and As are the main contaminants. The results of ecological risk index indicated that Cd is the main pollutant in the different soils of India.