Concentrations and health risk appraisal of heavy metals and volatile organic compounds in soils of automobile mechanic villages in Ogun State, Nigeria.

This report presents the findings of the concentrations, distributions and health risks assessment of heavy metals (HMs) and volatile organic compounds (VOCs) in topsoils of two typical automobile mechanic villages (MVs) situated within Ogun State, Nigeria. One of the MVs is located in basement complex terrain (Abeokuta), while the second is in the sedimentary formation (Sagamu). Ten composite samples were collected at depth of 0-30 cm with the aid of soil auger from spent oil-contaminated spots within the two MVs. The chemical parameters of interest were Pb, Cd, benzene, ethylbenzene, toluene, total petroleum hydrocarbon (TPH) as well as oil and grease (O&G). In addition, soil pH, cation exchange capacity (CEC), electrical conductivity (EC) and particle size distribution were also evaluated in order to find out their impacts on assessed soil pollutants. Results revealed that the soils in both MVs are of sandy loam texture, slight acidic to neutral pH, mean CEC < 15 cmol/kg and mean EC > 100 μS/cm. The mean concentration of each of analyzed HMs and VOCs in soils from the two MVs was < 5 mg/kg, while the mean values of TPH and O&G content were > 50 mg/kg. The mean Cd values in soils of both MVs were higher than the national soil screening level of 0.8 mg/kg, but lower than the Canadian and Italian guidelines. There is no significant correlation between each of HMs/VOCs and any of assessed soil physicochemical variables. The non-cancer risk expressed in terms of hazard index (HI) was > 1 via oral ingestion route for adults and children at the two MVs, indicating adverse non-carcinogenic health risk. The HI > 1 value was obtained for adults only through the dermal absorption pathway in Abeokuta MV. However, HI values for the two age groups at the two MVs via inhalation route were < 1, indicating no likelihood of any non-carcinogenic effects via the breathing exposure. The potential of non-cancer risk via oral ingestion route in both MVs was derived from the contributive ratios of HMs and VOCs in the order: Cd > benzene > Pb > toluene. The carcinogenic risk (CR) values due to ingested Cd, benzene and Pb for both age groups at the two MVs exceed the safe limit range of 10 to 10. Cadmium, benzene and lead made considerable contributions to the estimation of CR through dermal exposure for adults only in Abeokuta MV. The CR values via inhalation pathway for adults and children in both MVs were within the threshold range. Artisans and children should circumvent accidental ingestion of contaminated soils in addition to wearing of protective clothes during routine vehicle maintenance activities.