Risk Assessment Of Heavy Metals In Atmospheric Deposits From Lead Smelting Contaminated Areas

Henan Province is the top lead(Pb)producer in China.Lead smelting has led to heavy metal accumulation in farmland soils in some areas in Henan Province,and it also threatened the health of nearby residents.Inhalation and ingestion is the main pathways of heavy metals by entering human bodies in smelting polluted areas,however,the effect of particulate matters from the lead smelters to local residents has not been investigated yet.In this work,windowsill dust samples were collected from areas with different distances to a lead smelter to study the heavy metal content in different particle sizes and the risk of heavy metals in inhalation particulates.The quantity and risk of heavy metals ingested by residents of lead smelting areas in Jiyuan City were also assessed.In addition,we collected dry and wet deposition samples in different pollution areas of Jiyuan City during six months.The variation of heavy metals in atmospheric dust-fall and the contribution of heavy metals in dusts to the soilwere explored by measuring the total amount of heavy metals in dust.The main results and conclusions are as follows,(1)Investigation of heavy metal content of the windowsill dusts from different areas illustrated that,the average contents of Pb,Cd and As in 10-45 ?m portions of the dusts in the lead-smelting contaminated areas were 28205,1222,1969,6292 and 1922 mg·kg-1,respectively,these values are much higher than the Level 2 concentration in the National Standard for Soil Quality,and the highest Pb value reached 70,455 mg·kg-1.The heavy metals in the samples from Jiyuan polluted areas and Jiyuan urban area were mainly found in 10-45?m and particle size<10 ?m particles,and the highest content in samples collected in Mianchi were found in samples>45 ?m except for Pb,which was mainly found in<10 ?m portions.The maximum lead content of the sample with particle size<10?m reached 70,545 mg·kg-1 in the polluted area.The in vitro inhalation bioaccessibility of heavy metal were different,with the highest bioaccessibility being observed for Cu,while the value of Pb is only 0.04%.According to the human health risks,when the total concentration of heavy metal was used to calculate hazard quotient and carcinogenic risk,the total sum of hazard quotient of heavy metal in the polluted region to the human body reached 0.67,and the carcinogenic risk of Cd was 5.27×10-4,beyond the safety limit 10-6-10-4.However,when we calculated the value with the bioaccessible concentration,the results were 2-3 orders of magnitude smaller,the non-carcinogenic and carcinogenic risk posed by these metals to human were acceptable.(2)The above dust samples were subjected to Extended X-Ray Absorption Fine Structure(EXAFS)spectrometry for Pb species,the results indicated that,the difference of lead species of dusts from areas with different pollution characteristics mainly existed in the proportions of mineral bound lead and organic bound lead.Lead in the samples from Mianchi was mainly organic bound lead,with a proportion of about 85%,the rest was PbS.Lead in the polluted area from Jiyuan were mainly PbS,PbSO4,and mineral bound lead,the proportions were 20%,20%and 40%,respectively;the lead form the urban area of Jiyuan was mainly mineral lead,with the proportion of about 70%,and the rest were PbS and Pb3(PO4)2.(3)The in vitro inhalation bioaccessible fraction of heavy metals in windowsill dust samples with particle sizes<10 ?m in different contaminated areas indicated that,the bioaccessibility of Cu was the highest(45.3%-75.8%),while that of the Pb was the lowest(0.178%-0.735%).Compared with the bioaccessibility in the lung phase,the bioaccessibility of these four heavy metals in the stomach phase were much higher,and the values reached 32.3%-98.8%.Except for Pb,the bioaccessibility of each heavy metals in the samples with different pollution characteristics ranked Jiyuan polluted area>Jiyuan urban area>Control area.In the Jiyuan polluted area,the bioaccessibility of Pb in the samples was the lowest(68.5%),and the bioaccessibility of Cd,Cu and Zn were higher,being 98.8%,91.6%and 93.9%,respectively.However,the bioaccessibility of these four heavy metals from all three areas in gastro-intestine phase all sharply declined,decreased by 65.6%-81.6%,55.5%-88.1%,51.9%-72.6%and 25.0%-87.8%,respectively.The results of human health risk assessment of heavy metals showed that the rankings of hazard quotient and carcinogenic risk for adults and children in different areas are Jiyuan contaminated>Jiyuan urban area>Contral area,with Cd and Pb as the main elements,and children were affected more than adults.The low HQ and HI indicated that the non-carcinogenic risks posed by these metals to both adults and children via inhalation were acceptable.For adults,the hazard quotient caused by heavy metals in the exposure pathway to the human is lower than the safe value limit(HQ=1),but due to the influence of Cd and Pb,the HI of non-carcinogenic risks to adults in Jiyuan polluted area is 0.987,which is close to the safe value limit.However,the HI values to children in Jiyuan polluted area(7.05)and Jiyuan urban area(2.20)exceed the safe value.(4)The heavy metal content in atmospheric deposition samples from different sampling positions in Jiyuan City showed that,the order of heavy metal content was Pb>Zn>Cu>As>Cd.The maximum contents of Pb,Cd,Cu,Zn,and As in atmospheric dust-fall samples in Jiyuan polluted areas were 7371,229,879,2860,and 414 mg·kg-1,respectively,both of which occurred in winter(December and January).The mean deposition fluxes of Pb,Cd,Cu,Zn and As at QD village sites(close to the smelter)were 51.7,1.41,4.77,15.5 and 1.98 kg·(km2·30d)-1,respectively.The background site which is 24.5 km from the smelter exhibited the lowest deposition fluxes(12.3,0.0849,0.707,2.30 and 0.296 kg(km2·30d)-1).Annually,the atmospheric deposition enriched agricultural soil near the smelting plant with 2.38,0.065,0.220,0.716 and 0.008 mg kg-1 Pb,Cd,Cu,Zn and As,respectively.