Sources apportionment and spatio-temporal changes in metal pollution in surface and sub-surface soils of a mixed type industrial area in India

• Faridabad area shows high surface soil metal pollution with an average PLI of 2.77.
• Soils are moderately to heavily polluted for Cd Cr, Cu, Ni, Pb, and Zn.
• Sampling sites around small scale metal industries show high Igeo of metals.
• Among four identified sources, industrial emissions explained 46% of data variance.
• Soil pollution and seasonal changes are specific to the sampling site(s) and metal(s).

Metals in the urban soils of industrial townships adversely affect human health and ecosystem. In the present work, surface and sub-surface soils collected at 0–10 cm and 10–20 cm depth, respectively, in pre and post monsoon seasons from twenty sites in an urban industrial area adjoining New Delhi are studied for the total metal concentrations (Al, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, V and Zn) seasonal changes and pollution sources. Both surface and sub-surface soils are affected by high metal pollution with the contamination factor (CF) > 2 and the average pollution load index (PLI) of 2.77. The geo-accumulation index values of 6.6–8.2 (pre and post monsoon samples) for Zn, 6.7–8.2 for Cr and 5.6–5.1 for Cd in surface soils indicate extreme levels of pollution in the region. A total four metal sources, industrial emissions for Fe, Mn, Cu, Ni, Co and Cd, electroplating industry for Zn and Cr, geogenic for Al and V, and vehicular and biomass burning for Ba and Pb in the surface soils were identified using the principal component analysis. Industrial emissions, explaining 46% of data variance, are the major source of metals. Surface soils around small scale industries are more polluted with Zn, Cr and Cd (CFs = 25–31), and Cu and Pb (CFs = 7–11) and have high PLI (range: 3.28–8.77) compared to other sampling sites. Higher geo-accumulation indices and pollution load of metals in the urban soils are expected to have long term impact on human health, plants and crop productivity in this area.