Assessment of Organohalogen Contaminants and Heavy Metals Pollution in Soil from Central and Southwest Part of Kenya


Supervisor:wang jun


Degree Year:2019





Anthropogenic activities alter the quality of the environment on a global scale,which can adversely affect life on earth.A typical example of such environmental damage and harmful biological effects is that caused by persistent human made chemicals,particularly organohalogen compounds and heavy metals.The rapid population growth,expansion of urban areas,and growth of agricultural activities have led to the importation of large number of pollutants.In Kenya,deficient urban planning and management,weak or non-existence of monitoring human activities,lack of technical capacity,shortage of trained personnel,and lack of enforcement of relevant environmental law compound the problem.Hence,these pollutants are likely to cause harm to Kenya’s ecological environment and human health.Therefore,assessment of concentrations,sources,ecological and human health risk was conducted in this study.We focused on 16 OCPs,7 indicator PCBs,7 PBDEs,in soil samples from the southwest part of Kenya(from Kiambu to Mombasa)in the first study and 11 polycyclic aromatic hydrocarbon and 9 heavy metals from Nyeri and Mombasa urban soils.Agilent 7880A gas chromatography electron capture detector did/was used for the identification and quantification of OCPs,PCBs and PBDEs and high performance liquid chromatography(HPLC)(Agilent 1220 Infinity LC)system with a UV detector and inductively coupled plasma-Mass spectrometry.(ICP-MS)was used to identify and quantify PAHs and heavy metals respectively.The total concentrations of OCPs ranged from 7.62 and 76.09 ng/g,with a total mean of 16.62 ng/g.dominated by HCHs and heptachlor.The seven indicator PCBs ranged from 9.90-20.8 ng/g with an average of 14.41 ng/g with almost equal contribution of PCBs congeners dominated by penta-PCBs from old transformers’ leakages.Total PBDEs were in the range of 1.89-38.36 ng/g with a mean of 11.38 ng/g,dominated by tri-and hepta-PBDE Congeners and,electric and electronic equipment waste were identified as the sources of PBDE.A weak correlation between TOC and concentrations of OCPs,PCBs and PBDEs showed that other physicochemical properties or closeness to pollution sources might be the influencing factors to levels of the contaminants in the soil.Pollution source identification pointed at mixture of recent and historical inputs of DDTs,which are widely used for control of malaria causing mosquitoes.Moreover,HCHs and endosulfans ratios indicated recent inputs of Lindane and endosulfan in regards to α-/γ-HCH and α/βendosulfans ratios respectively.Risk assessment of OCPs and PCBs showed low potential human health risk could be posed by OCPs while PCBs showed a higher risk.Local authorities are urged to put in place more effective mechanisms to attain Stockholm standards.The second study investigated 9 heavy metals and 11 polycyclic aromatic hydrocarbons in urban soil from Nyeri and Mombasa city.The total concentrations of 11 PAHs ranged between 0.24-364.39 mg/kg with a total mean of 43.51 mg/kg dry weight.Pearson’s correlation showed a significant relationship among individual PAHs;however,monomial PAHs showed trivial correlation with TOC.Diagnostic ratios(DRs),hierarchical clusters analysis(HCA)?and principal component analysis(PCA)suggested pyrogenic sources as predominant inputs of PAHs with a slight contribution from petrogenic sources.Principal component analysis(PCA)disclosed biomass combustion,vehicular emissions,and oil spillage as the major sources of PAHs.Risk quotient(RQ)and incremental lifetime cancer(ILCR)models were employed to assess ecological and human health risk,respectively.RQ and ILCR revealed that these study sites bear potential acute and chronic environmental and human health effects.Heavy metals total concentrations ranged from 22.08-1046.65 mg/kg with a total average concentration of 486.55 mg/kg.All the heavy metals measured were found to be below the maximum permissible concentrations.Pearson’s correlation showed the relationship between individual heavy metals and minimal correlation with TOC.HCA and PCA revealed anthropogenic activities to be the major contributors of heavy metals at the study sites.PCA exhibited traffic emissions,industrial,and municipal wastes disposal as inputs of heavy metals.Based on the potential of ecological risk,carcinogenic,and non-carcinogenic health risks,the study area was found to bear mild risks;however,non-carcinogenic risk showed moderate effects on children.The results of this thesis stress the urgency for the mitigation of organic and inorganic pollutants in Kenya.