Pollution Evaluation And Environmental Risk Assessment Of Heavy Metals From Atmospheric Deposition In Lanzhou

In order to evaluate the contamination,analysis the sources,assess the ecological and health risks of heavy metals from atmospheric deposition in Lanzhou,samples of atmospheric deposition were collected from sampling sites respectively and their concentrations of heavy metals were determined.An analysis was made simultaneously of the atmospheric deposition flux of Lanzhou published by Lanzhou Environmental Protection Agency per year and per week.All dustfall samples were analyzed for concentrations and fractions of Cu,Pb,Mn,Cr,Cd,Ni and Zn.And the source and the accumulation level of the atmospheric deposition were also researched.The main conclusions can be summed up as follows.1.The atmospheric deposition flux concentrations in Lanzhou city decreased year after year since 1996,especially when it comes to the autumn and winter.The data also demonstrates that the dustfall flux is highest from March to May whereas decreases since June every year,and reached the bottom when October,increases then in the November.The atmospheric deposition flux of Lanzhou city show significant U-shaped variation during the heating period.And it present a spatial distribution of Chengguan District>Xigu District>Qilihe District>Anning District>Yuzhong County.2.Average contents of Cu,Pb,Cd,Cr,Ni,Zn,Mn are 82.22,130.31,4.34,88.73,40.64,369.23,501.49mg·kg-1.Each functional area of elements is quite different except Mn.3.According to the results,the enrichment factor score of Mn is close to 1,while the enrichment factors scores of Ni,Zn,Cu and Cr are arrange from 1 to 10 which effected by human at different levels.But among them,the enrichment factor of Pb,Cd presents a high level that mainly due to the human activity.Enrichment factor of Cr,Ni,Zn in the industrial areas are larger than other functional areas.Cu and Pb are most enriched in traffic area.Cd is most concentrated in the suburban area.4.Principal component analysis(PCA)was performed and three main sources were identified.(1)In heating period:first,Pb and Cd are correlated to coal combustion exhaust;The second principal component mainly composed of Fe composition,the second factor can be considered representative of natural sources;thirdly,Cr,Cu,Zn have the connection with industrial pollution and traffic exhaust.(2)In Non-heating period:first,Cu,Pb and Zn are correlated to traffic exhaust and coal combustion;secondly,Ni and Cr have the connection with industrial emission;thirdly,Fe and Mn derive from soil particles(natural sources).5.Cu in atmospheric deposition of Lanzhou is mainly in the residual fraction and organic matter.Pb mainly Exist in Fe-Mn oxides fraction and residual fraction because of A large number of vehicle exhaust emissions and metal processing industry.Ni,Cr and Cd are mainly in the residual fraction.Zn mainly bound to organic and Fe-Mn oxides,exchangeable fraction are very small in all functional areas.The index of bioavailability of heavy metals show that Cd and Zn are provided with potential ecological risk,bioavailability of Cr,Cu,Ni,Pb is lower.6.The assessment results of geoaccumulation index of potential ecological risk indicate that the pollution of Cd in the atmospheric deposition of Lanzhou is classified as extreme degree,and that of Cu,Ni,Zn,Pb as between slight and extreme degrees,and Cr practically uncontaminated.Contaminations of heavy metals of atmospheric dust in October to next March are more serious than from April to August.7.The assessment results of potential ecological risk of heavy metal pollution indicated that the pollution degree of single element showed the order of Cd>Pb>Ni>Cu>Zn>Cr.The potential ecological risk of Cd is strongest,other elements is low ecological hazard.The total potential ecological risk index reached its highest level,is very strong ecological hazards.Distinction between the various functional areas is not obvious.The conclusions those between Potential ecological risk assessment and geoaccumulation index method to evaluate environmental risks are similar.8.Health risk assessment indicated that the heavy metals in atmospheric deposition are mainly ingested by human bodies through hand-mouth ingestion.Non-cancer risk is higher for children than for adults.The order of non-cancer hazard indexes of heavy metals is Pb>Cr>Cd>Cu>Ni>Zn.The non-cancer hazard indexes and carcinogen risks of heavy metals are both lower than their threshold values,and it suggests that it will not harm the health.