论文部分内容阅读
There are far reaching and long term implications of the presence of heavy metals on the environment and human health.The need to identify the sources of these pollutants with a view to mitigating their effects has necessitated the present investigation.This study was therefore conducted to assess the level of heavy metal contamination of road deposited sediments(RDS)from paved roads in Enugu metropolis in south east of Nigeria.A total of 32 RDS samples were collected from 10 selected roads.The RDS was digested with a mixture of concentrated HNO3,HF and HClO4(2:2:1,by volume)and analyzed for the metals: Cr,Mn,Fe,Co,Ni,Cu,Zn,Cd and Pb using Flame Atomic Absorption Spectrophotometer(FAAS).The physico-chemical parameters: pH,electrical conductivity(EC),total organic matter(TOM)and total organic carbon(TOC)were also determined.The results showed that the metal concentrations(mg/kg)were in the following ranges: Cr(0.67-3.67),Mn(2.33-7.67),Fe(408.33-512.33),Co(3.00-61.75),Ni(39.67-193.67),Cu(11.50-90.00),Zn(1.00-31.67),Cd(0.00-1.33),and Pb(0.00-46.67).The pH of the RDS samples ranged from 6.75-8.39,EC from 556-578.67 μS/cm,while TOC and TOM ranged from 0.43%-3.49%and 1.27%-10.35%,respectively.The correlations among the metals and the physico-chemical parameters were determined using correlation co-efficient analysis.The possible sources of metals were identified with such multivariate analyses as principal component analysis(PCA)and hierarchical cluster analysis(HCA).Further,enrichment factors were used to quantitatively evaluate the influence of human activities on heavy metal concentrations.Other mathematical models like Index of Geo-accumulation,Contamination Factors and Degree of Contamination were used to assess anthropogenic influence on the pollutants.Potential Ecological Risk Index(PERI)was applied to evaluate the potential ecological risk of heavy metal pollutants.The results showed that Mn concentrations did not exceed the crustal level.However,significant Pb and Cd contamination was observed in the RDS samples.The results acquired from the models showed good consistency,giving moderate to significant levels of pollution for most parts of the selected roads.The results of the PCA indicated three major sources of heavy metal pollutants in RDS in Enugu metropolis: the crustal,vehicular(emissions and corroded vehicular parts)and industrial sources.