Evaluation of heavy metal and total petroleum hydrocarbon contamination of roadside surface soil

The present study was conducted along three major highways namely State Highway (SH49), National Highway (NH66 and 45A) connecting Puducherry (India) for assessing heavy metals and total petroleum hydrocarbon contamination from surface soils in close proximity at a depth of 0–15 cm into automobile repair workshops and agricultural fields located beside the highways. Contamination levels of copper, lead, zinc, manganese, cadmium and chromium were assessed in the surface sediments soil on the basis of geoaccumulation index, contamination factors and spatial variability. The results revealed that sampling sites in the proximity to automobile workshops were moderately to considerably pollution impacted as compared to soil from agricultural fields along highways suggesting a direct influence of anthropogenic activities on levels of contamination. The concentration of heavy metals in the surface soil of automobile workshops close to NH66 ranged between 143.07 and 319.28 mg kg−1 copper; 68.72–396.41 mg kg−1 lead; 162.42–284.91 mg kg−1 zinc; 212.72–401.33 mg kg−1 manganese; 0.12–15.41 mg kg−1 chromium; and 0.73–1.06 mg kg−1 cadmium in dry soil. However, in agricultural fields, the concentrations varied between 33.68 and 66.62 mg kg−1 copper; 27.22–73.66 mg kg−1 lead; 26.24–75.59 mg kg−1 zinc; 137.88–242.07 mg kg−1 manganese; 0–0.21 mg kg−1 chromium; and 1.04–1.58 mg kg−1 cadmium. Total petroleum hydrocarbon concentration near automobile workshops ranged between 90.72 and 121.79 mg kg−1 in contrast to 44.94–83.4 mg kg−1 in agricultural fields. Total petroleum hydrocarbon concentration indicated strong positive correlation with zinc (r = 0.811), copper (r = 0.761); lead (r = 0.642), Mn (r = 0.571), chromium (r = 0.530) and strong negative correlation with cadmium (r = −0.765) at 0.05 significance level. Pearson correlation indicated a strong association of total petroleum hydrocarbon with copper, lead and zinc suggesting that the metal contaminants from roadside surface soil had emanated from a common source.