| This study was conducted to assess the level of PCBs and heavy metal concentrations in soil from Vientiane,Laos.The soil samples were randomly collected from 30 roadside locations in the city.Sampling sites were divided into and chosen from 4 different types of land use:1)Inner urban(IU,locations in the city center),2)Outer-urban(OU,locations on the outskirts of the city),3)Agricultural Areas(AA,locations near rice paddy fields in the city),4)Industrial zones(IZ,sites nearby factories and manufacturing areas).PCBs were determined according to their level of concentration and congeners profile;thus,PCBs distribution was conducted according to the degree of contamination in each location as well as land type.Principal component analysis(PCA)was performed to indicate the significant accumulation of PCBs sources.Additionally,Toxicity Equivalency Values(TEQs)were conducted to identify possible risks to human health.For heavy metals,mathematical models such as the Index of Geo-accumulation(Igeo),Contamination Factors(CF),Pollution Load Index(PLI),were employed to identify possible levels of contamination and pollution in soil caused by human activity.Thus,in order to assess the possible carcinogenic and non-carcinogenic health risks to children and adults,Hazard Index,Hazard Quotient(HQ/HI),and Total Cancer Risk(TCR)were performed to determine potential adverse health risks in accordance with the level of heavy metals in the study areas.Laos imported PCBs into the country as electrical equipment and hydraulic oil in transformers and capacitors.However,information about the PCBs contamination of soil in Laos is not readily available.Research on PCBs in the soil of Vientiane is new.It has been conducted as a vital reference for future studies and policy making for an eco-sustainable city.The results of this research show that PCBs were contaminated in the environment,particularly in urban topsoil.In this study,17 PCB congeners(PCB28,52,77,81,101,105,114,118,123,126,138,153,156,157,167,169,and 180)were detected in all samples from Vientiane soil with the total concentration ranging from n.d(non-detected)to 333.17 ng/g(dry weight)and with total average 65.24 ng/g(±89.36 ng/g).This study was compared to the same types of studies in other countries.The comparison revealed that the level of PCB s contamination in the soils of Vientiane was rated as low.The distribution of PCBs contamination levels in the city center was higher than in other areas.More than 70%of PCBs were low chlorinated congeners such as tri-CBs,tetra-CBs,and penta-CBs among all PCB-homologues.Principal component analysis(PCA)was used to determine source apportionment suggesting that low-chlorinated congeners were the original sources of PCBs in Vientiane soil.3 PCs suggested that PCBs were widely used in electrical equipment and transformers.The high load of low-chlorinated congeners such as CB81,-123,-77,-118,-114,-153,-138,-101 originated from local sources as they were the composition of commercial mixture.PCB congeners CB126,-156,-157,-167 were found to be associated with PCB mixtures that are primarily used in industrial applications.Additionally,the total dioxin-like PCBs level was recognized as having high potential risks to human health due to its TEQs being over the limitation value.The concentrations of TEQ of 11 dioxin-like PCBs in Vientiane soil resulted in a toxic potency of 2,3,7,8polychlorinated dibenzodioxins and dibenzofurans PCDD/Fs in soil samples from Vientiane,The potential environmental and human risk in Laos,due to the total of TEQs was 0.5765 ng/g,out of which,PCB 169 and PCB 126 were the highest toxic congeners.However,the observed tolerable daily intakes of TEQs were compared to those of the Public Health Agency of Canada,whose standards state that daily intake must fall within an acceptable range(1-4 pgTEQkg-1d-1).The lifetime average daily dose(LADD)for children falls within the range while the value for adults is less than the acceptable range.Seven heavy metal elements were selected.These metals appeared in contaminated areas.The selected elements were:Cadmium(Cd),Chromium(Cr),Copper(Cu),Lead(Pb),Zinc(Zn),Nickel(Ni),and Manganese(Mn).All were detected in soil samples with averages of 1.40(mg/kg),40.87(mg/kg),32.92(mg/kg),37.21(mg/kg),197.64(mg/kg),18.43(mg/kg),313.71(mg/kg),respectively.Zn and Mn had the highest levels of concentration among all elements with a maximum level of 197.64(mg/kg)and 313.71(mg/kg),respectively.The concentrations of 6 metals such as Cd,Cu,Cr,Pb,Zn,and Ni in this study were compared to the standard value of the neighboring countries and to Dutch standard values.The concentration level of heavy metals from Laos was comparable to countries in the region and was within the range of standard values of international countries.The Contamination factor(CF)of seven metals(Cd,Cr,Cu,Pb,Zn,Ni,and Mn)in soil samples was rated as low to moderate contamination,as the CF values of Cd,Cr,Ni,and Mn resulted in less than 1(CF<1).In contrast,Cd and Zn were higher than 1 but less than 3(1<CF<3)indicating moderately polluted soils.The CF results indicated that most metals were not among the contaminants in the soils of the study areas.More than half of Pollutant Load Index(PLI)values of the sampling sites were less than 1,which means only some sample sites were contaminated by heavy metals.PLI showed that the most polluted sites included the locations from Inner Urban,which was the city center and residential areas.The values of the HQ and HI of soil with heavy metals in Vientiane,Laos indicated that there were no noncarcinogenic risks in the study area.Children were considered to have a high probability of having non-carcinogenic risks,due to the considerably higher quantity from ingestion of pollutants as well as lower tolerance for pollutants compared to adults.Mn appeared as the highest non-carcinogenic risk with the highest HQ values for both children and adults,while the lowest non-carcinogenic risk was associated with Zn as it displayed the lowest HQ values for both children and adults.Cancer risk for carcinogenic elements was considered to be safe as all calculated values of CRs and TCRs were in the range of the threshold limit(1×10-6 to 1×10-4). |
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