Risk assessment and GIS-based mapping of heavy metals in the secondary rock deposits derived soils of Islamabad, Pakistan

Soil contamination poses a severe threat in terms of deteriorated environmental quality and badly influences human health. Agricultural soils, mainly in the suburban areas, need detailed investigations for their heavy metal contents to avoid food chain contamination. This study was done to examine the heavy metals (Cu, Ni, Pb, Cr, Zn, and Mn) enrichment and accounts for contamination in arable soils of the Islamabad Capital Territory of Pakistan. Forty soil samples (soil depth 15-25 cm) were collected from cultivated areas of 41.88 km(2) using a predefined GIS-based grid. Soil samples were analyzed for physico-chemical properties and total heavy metal content. Different types of environmental factors to assess the ecological risk were calculated to examine the contamination level in soils of the surveyed area. Results indicated that soil pH, in the surveyed area ranged from 7.27 to 7.98 with the mean value (7.54 +/- 0.19). The Average Cu, Ni, Pb, Cr, Zn, and Mn contents in the soils were 11.7, 31, 33, 42, 86, and 1407 mg kg(-1), respectively. The spatial dependence ranged from moderate to strong, provided an opportunity to prepare contour maps. The pollution load index of the surveyed area indicated a need for a more detailed study to monitor the enrichment of heavy metals. The whole area was classified into various zones based on differential heavy metal content for regional-scale information.