Concentration,Distribution And Health Implications Of Heavy Metals And Organochlorine Pesticides In Suburban Soils From Kenya

Chemical pollution in soil arising from anthropogenic sources continues to pose a significant challenge to community wellbeing and the environment.In Kenya,poor management of resources,poor planning,and absence of coherent municipal policies has accelerated the problem of environmental damage.Persistent human-made chemicals cause a notable example of such ecological destruction.The use of these synthetic chemicals in agriculture and manufacturing has raised concerns about the dangers of heavy metals and organochlorine pesticides（OCPs）in the environment.By examining these chemical pollutants in suburban soils of Kenya,our study evaluated the distribution,levels,and the danger posed to the environment and human health.Our study focused on soil samples from five suburban areas of Kenya,including Juja,Ngong,Kapsabet,Voi,and Nyeri.In the first study,eight heavy metals were examined,including zinc（Zn）,lead（Pb）,arsenic（As）,copper（Cu）,chromium（Cr）,nickel（Ni）,cadmium（Cd）,and mercury（Hg）.While in the second study,we focused on two organochlorine pesticides,including hexachlorocyclohexane（HCH）and dichlorodiphenyltrichloroethane（DDT）.An inductively coupled plasma–Mass spectrometry（ICP-MS）and a gas chromatography-electron capture detector（GC-ECD,Agilent 7890B）were used to examine and quantify the heavy metals and OCPs,respectively.Source apportionment of the contaminants was examined by principal component analysis and validated using cluster analysis.Whereas the relationship between compounds and Total Organic Carbon（TOC）was analyzed using Pearson’s correlation.Further,the ecological and carcinogenic risk was calculated to determine the degree of contamination and the threat posed to human health.The heavy metal concentration of Zn,Pb,As,Cu,Cr,Ni,Cd,and Hg,and were1.65-99.16,0.2-12.50,n.d-2.28,0.59-17.22,0.18-4.93,0.17-1.55,0.01-0.23 and n.d.-0.03 mg kg^-11 respectively.The results demonstrated that both natural and anthropogenic activities influenced the distribution of heavy metals in the soils.Correlation coefficients highlighted an association amongst metals suggesting a similar origin.The strongest relationship was detected between Cd vs.Cr（r²=0.841）,and Pb vs.Zn（r²=0.701）.Moreover,Total Organic Carbon showed an association with the heavy metals highlighting the significance of organic carbon in the adsorption and the distribution of heavy metals in soil.Pollution indices revealed that pollution decreased in the order Juja>Ngong>Kapsabet>Nyeri>Voi with the overall ecological index indicating a low level of pollution.The concentration of As and Pb was found to be high in all the study sites posing a potential hazard to the environment while Juja and Ngong regions were at a higher risk of threat.The human health risk evaluation revealed a potential risk from As and Cr.Children were at a greater danger of exposure to carcinogenic or non-carcinogenic risks.Moreover,the highest possible exposure route was through ingestion and skin contact for both children and adults.The inappropriate disposal of industrial and municipal effluents,agricultural practices,and the burning of fossil fuels,were identified as the key causes of metal pollution.The second study reported hexachlorocyclohexane（HCH）and dichlorodiphenyltrichloroethane（DDT）in soils of Kapsabet,Voi,and Nyeri towns.The results showed concentrations ranging from 0.03–52.7,0.06–22.3,and 0.24–24.3 ng g^-1,respectively.The highest HCHs mean value was in Kapsabet with an average of6.12±13.09 ng g^-1(range:0.03-48.05 ng g^-1)whereas the DDTs highest mean level was3.18±5.61 ng g^-1(range:n.d.-15.51 ng g^-1)detected in Voi town.In all the study sites,β-HCH was detected at high frequencies,with Kapsabet having the highest value of n.d.-37.8 ng g^-1.Source identification revealed that the OCPs pollution originated from the current usage of DDT pesticides to control insect-borne disease and from the use of lindane to control agricultural pests.Based on the correlation test,an association was observed between total organic carbon and OCPs,and amongst the DDTs and HCHs compounds in all the sampling points.The ratios ofα-HCH/γ-HCH were 2.51,0.66,and 0.51 for Kapsabet,Voi,and Nyeri,respectively indicating the use of lindane while those of DDE/DDT were<1 in all the study sites,suggesting recent input of DDT.The incremental cancer risk assessment showed values of 8.70E-07,5.45E-07,and 8.94E-07 for the child,adolescent,and adult,respectively.These values were close to the set risk level of 10^-6,suggesting the likelihood of exposure to cancer was not low enough,and there was a need for control measures to be established.In conclusion,this study highlights the importance of monitoring organic and inorganic pollutants and the necessity for legislating strict environmental policies aimed at protecting the environment and the community health.