Contamination of arable topsoil by organic and inorganic pollutants around petroleum products handling facilities

The concentrations of heavy metals (inorganics) and poly aromatic hydrocarbons (organics) were determined in soils around fueling stations and automobile workshops. Mean concentrations of nickel, lead, cadmium and vanadium were 636, 1379, 12.0 and 18.0 µg/kg, respectively. Flourene, benzo (a) pyrene, benzo (b) fluoranthene and benzo (ghi) pyrelene recorded means of 2.01, 2.014, 1.14 and 1.12 µg/kg, respectively, but other poly aromatic hydrocarbons recorded means <1. Heavy metals levels were higher at sites of activities than the control site. Phenanthrene, naphthalene and benzo (k) fluoranthene were present at control site but absent in some locations of activity. These showed they were not only from petroleum products handling facilities. Mean levels of both inorganics and organics were below world standards for agricultural soil quality. Principal component analysis of heavy metals produced two principal components that explained 40.72% and 36.90% of the total variance. These reflect geological weathering, automobile exhaust and petroleum combustion sources. Analysis of poly aromatic hydrocarbons data produced four principal components, which explained 36.30%, 19.96%, 15.19% and 12.81% of total variance. The sources of these organics are internal combustion of gasoline, kerosene and rock weathering. Diagnostic ratios ranged from 0.3-0.94 showing that poly aromatic hydrocarbons are of pyrogenic and petroleum combustion origin. Single pollution index means ranged from 0.0002-0.02 and Numerov composite pollution index attained a mean of 0.028. Therefore, the soil is unpolluted and heavy metals levels are not toxic to human health. The study provides information on sources of soil pollutants and their environmental and health risks.