Spatio–Temporal Distribution of Polycyclic Aromatic Hydrocarbons in Urban Soils in Cape Town, South Africa

The spatial and seasonal distribution of eight US Environmental Protection Agency priority poly aromatic hydrocarbons (PAHs); namely benzo(b)fluoranthene, benzo(a)pyrene, indeno(1,2,3-cd)pyrene, benzo(k)fluoranthene, chrysene, benzo(a)anthracene, dibenz(a,h)anthracene and fluoranthene were investigated in 35 soil samples. Gas chromatography with flame ionization detection was used for the quantification of the PAHs in the residential, roadside and industrial soil samples collected in proximity to an industrial area, including a petrochemical plant, in Cape Town. The sum of the concentrations of the detected PAHs (ΣPAHs) in winter ranged between nd (not detected) and 13.88 mg/kg, with a mean concentration of 4.08 mg/kg and a standard deviation of distribution of 2.64 mg/kg, while in summer, ΣPAHs ranged between nd and 10.43 mg/kg, with a mean concentration of 0.50 mg/kg and standard deviation of distribution 1.83 mg/kg. The presence and concentration level of the PAHs detected in the soil samples vary significantly under climatic change (p < 0.05). The maximum concentrations of individual PAHs in the soil samples were higher in winter compared to the maximum concentrations of the PAHs detected in summer. The diagnostic ratios of selected PAH compounds showed that petrogenic processes were the most likely sources of the PAH compounds in the soil samples. In summer and winter, the total PAH concentration increased in order of residential soil < industrial soil ≤ roadside soil.