Exposure and Health Risk Evaluation of Heavy Metals in Soils Along Major Roads in Enugu State, Nigeria

This study evaluates the concentrations and potential health risks of selected heavy metals (Lead (Pb), Manganese (Mn), Nickel (Ni), Copper (Cu), Chromium (Cr), Arsenic (As), Mercury (Hg) and Iron (Fe)) in surface soils (0-5 cm) from three major urban roads in Enugu State, Nigeria. Composite soil samples were collected, acid-digested and analysed using Atomic Absorption Spectrophotometry. Contamination levels were assessed through four pollution indices; Geoaccumulation index (Igeo), Contamination Factor (CF), Pollution Load Index (PLI) and Enrichment Factor (EF) while human health risk was evaluated using United States Environmental Protection Agency (USEPA) models considering ingestion, dermal contact and inhalation pathways for both adults and children. Results indicate that concentrations of some metals particularly As were slightly elevated compared to background values. The pollution indices showed low to moderate level of contamination in all the three urban roads except for As with PLI value greater than 1 (PLI > 1) in the commercial road indicating slightly nature of contamination. The assessment of health risk indicated that there were mainly three exposure pathways for people via ingestion, dermal contact and inhalation. The main exposure pathway of heavy metals for both children and adults is ingestion. The values of Hazard Quotients (HQ) and Hazard Index (HI) for all the heavy metals and exposure pathways were < 1, indicating no significant non-carcinogenic health risk. Meanwhile, the HI values for children were higher than that for adults indicating that children have higher potential health risk than adults. Cancer Risk (CR) values for Cr, As, Pb and Ni were within the acceptable risk range (10-6 - 10-4) showing negligible carcinogenic risk. The order of exposure were observed to be adults < children. Though the CR and TCR results were observed to be within the acceptable range for developing cancer, the result however suggest that children could be more susceptible to potential carcinogenic risk following continual exposure to heavy metals from vehicular activity. This leads to a concern about the expansion of unregulated settlements along heavy traffic roads in Enugu State, Nigeria. It is recommended that continuous periodic monitoring should be done to track potential changes due to increasing traffic and urbanization in the state.