Geochemical assessment of heavy metals and Pb isotopic characterization of soils of automobile garage areas in Chandigarh, India

The study here focuses on the range and extent of selected heavy metals found in contaminated soils of automobile workshop sites in one of the better-planned and environmentally aware cities of northern India. Soil samples from four motor markets in Chandigarh were analyzed for heavy metals. Multivariate statistical analysis and Pb isotopic source apportionment were done to understand better the source of the heavy metals including Pb in the soils. Results showed that the decreasing average metal concentrations (mg kg⁻¹) were in the following order: Mn (547) > Zn (217) > Cu (95) > Pb (94) > Ni (37) > Cr (34) > Cd (1.4). The Pb concentration had a minimum value of 32.98 mg kg⁻¹ and a maximum value of 565.20 mg kg⁻¹. Among the analyzed heavy metals, the mean I_geo ranged from − 1.32 (Cr) to 3.5 (Cd) with Cd also having the highest enrichment. Similarly, high contamination of the affected soils was indicated as the pollution load index (PLI) value ranged from 1.07 to 2.58. Principal component analysis of the heavy metal data extracted four components with Pb having the highest loading factor in the fourth component. Similarly, in cluster analysis, the metals Cd, Pb, Cu, Ni, Cr, and Zn had the least interelement distance between them signifying their common anthropogenic source. Lead isotopic analysis of the soils revealed that the ²⁰⁸Pb/²⁰⁴Pb ratio ranged between 37.16 and 38.71, the ²⁰⁷Pb/²⁰⁴Pb between 15.56 and 15.69, and the ²⁰⁶Pb/²⁰⁴Pb ratio between 17.30 and 18.34. The plot between the ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb ratios showed that Pb in the soils could be from vehicular exhausts and not from coal combustion.