<p xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" class="first" dir="auto"
id="d9258701e85">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 10-6 to 10-4. 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.
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