Occurrence and risk assessment of heavy metals and organochlorine pesticides in surface soils, Central Kenya

BackgroundThe present study investigated pollution in surface soils of five dominant land use types in central Kenya. The mean concentration of heavy metals (Zn, Hg, Cd, Cu, Cr, As and Ni) in (mg/kg) and two organochlorine pesticides (DDTs and HCHs) (g/kg) were determined.MethodHeavy metal contamination and potential ecological risk using the Nemerow pollution index and Hakanson ecological risk index respectively were used in examining pollution level. With the help of multivariate analysis sources of heavy metal pollution were identified which were mainly from anthropogenic activities. Notably, heavy metal concentration in our study was compared to other regions within the country, results showed regional variation. Total levels of DDTs, HCHs pesticide and their constituent isomers in the surface soil were determined by a gas chromatography (GC-ECD).ResultsPollution level in all land use areas according to Nemerow pollution index indicated low pollution status. Notably, in all land use areas the pollution level decreased in the following order Industrial land>Peri-urban>Agriculture land>Forest>River. In addition, heavy metals had low risks values according to Hakanson ecological risk index ranging from 0.01 to 0.58, with Hg having the highest mean value of 0.58. As expected, organochlorine pesticide were higher in agricultural land use, DDTs levels were comparatively higher than HCHs levels. Results on DDTs ratio (p, p-DDT/p, p-DDD+p, p-DDE) were