Concentrations, source identification and eco-toxicological risk of polycyclic aromatic hydrocarbons in agricultural soils of Kenya, Eastern Africa

Abstract

This study evaluated the concentrations, distribution, source and potential toxicological risk of 16 polycyclic aromatic hydrocarbons (PAHs) in agricultural soils in Kenya, East Africa. A total of 69 soil samples were analysed from five agricultural sites. Matrix solid-phase extraction was used for sample extraction before analysis using high-performance liquid chromatography. A total organic carbon analyser was used to assess the organic carbon content of all of the soil samples. The overall concentrations of PAHs varied from 2593.05 ng/g (Maai Mahiu) to 4356.15 ng/g (Mount Suswa) with a mean value of 3353.04 ± 2179.81 ng/g. Lower-molecular-weight (2-, 3- and 4-ring) PAHs were dominant in the soils. Anthracene had the highest mean concentration with a value of 1048.92 ng/g and ranged from 614.37 ng/g in Narok to 2416.95 ng/g in Mount Suswa. Identification of potential sources of PAHs revealed that pollution from PAHs in Kenyan soil samples was primarily derived from pyrogenic sources linked to biomass combustion and from vehicle and coal combustion. The risk assessment indicated a high eco-toxicological risk associated with the majority of the 16 PAHs in Kenyan agricultural soils. All of the RQ∑16PAHs (NCs) in all of the study sites showed values higher than 800. Similarly, all of the RQ∑16PAHs (MPCs) were also found to be greater than 1.00 in all study sites, which indicated potential risk. Therefore, certain measures need to be established to control and mitigate pollution.