Characteristics And Health Risk Assessment Of Heavy Metal Pollution In Dust And Soil In Guangzhou

With the accelerating urbanization process,many factors such as industrial and agricultural production and traffic emissions have caused a large number of heavy metals to enter the soil and dust,affecting the healthy life of human beings,and the problem of heavy metal pollution has become a hot spot in the current global environmental research.Guangzhou,one of the central cities in China,has serious heavy metal pollution in soil and dust.In order to investigate the heavy metal pollution in dust and soil of Guangzhou city and to accurately evaluate their health risks,this study sampled dust and agricultural soil of Guangzhou city and determined the content of heavy metals such as As,Pb,Cd,Cu,Zn and Ni in dust and soil,and used the geological accumulation index(Igeo),Nemero index(INI),ecological risk index(RI),Arc GIS spatial interpolation,positive definite The spatial distribution and morphological changes of heavy metal concentrations in dust and soil of Guangzhou city were analyzed by using the matrix factor model(PMF),in vitro digestion experiments and Monte Carlo simulations.The main findings of this study are as follows:(1)The mean concentrations of all heavy metals in the dust of the Guangzhou Industrial Park were higher than the local background values,indicating that the local environmental samples were prone to enrichment of heavy metals.The modified Nemero index(INI)indicates that all dust samples have potential ecological risk of heavy metal contamination(INI> 1),with86% of dust samples reaching "moderate to severe contamination and above" and 53% of samples reaching "severe contamination".The spatial distribution of the RI was spatially distributed,with the highest RI of 1698.51% of the Cd samples were at "high risk",which was the primary pollutant in the dust ecological risk of the study area.(2)The concentrations of heavy metals in the soils of vegetable fields in Guangzhou were Zn > Pb > Cr > Cu > Ni > As > Cd,with the highest mean value of 152.9 mg/kg for Zn.The heavy metals in the soils were all higher than the local background values,and the percentages of Cd,Zn,Pb and Cu samples exceeding the background values were 100%,98%,94% and 77%,respectively.The mean Igeo value of Cd in soil was the highest(2.9),which was moderately to strongly contaminated,and 33% of the Cd samples were strongly contaminated and above.The mean value of RI for soil heavy metals was 528,which is a considerable ecological risk,and 48% of the Cd samples were at "high risk",making Cd the primary contaminant in the ecological risk of vegetable soils in Guangzhou.(3)The stepwise extraction results showed that As and Ni in dust existed mainly in the residue state(9.0-98.2%),Cd and Zn in the carbonate-bound state(ND-69.9%),and Cu in the organic-bound state(22.0-80.0%).The water-soluble and carbonate-bound states are most easily absorbed and utilized by organisms,so the risk of environmental hazards from Zn and Cd in dust is higher.Heavy metals in the soil were mainly present in the residue state(7.9-99.8%),followed by the Fe-Mn oxide-bound state(0.1-43.3%)and the organic-bound state(ND-50.9%).A comprehensive comparison of the stepwise extraction results showed that the easy-to-migrate fraction of heavy metals in Guangzhou soils is low and dust is of greater environmental risk.(4)The PMF receptor model was applied to resolve the possible sources of urban heavy metals in Guangzhou.As and V were natural sources;Fe and Mn were industrial sources;Cr,Cu,Ni and Pb were industrial and traffic sources;Zn and Cd were natural and industrial sources in dust from industrial parks.Mn,Fe,V,As and Cr in the vegetable soil are natural and agricultural sources;Cu,Zn and Ni are industrial sources;Pb and Cd are traffic sources.The results of source analysis can provide some theoretical basis for the source management of heavy metal pollution.(5)In vitro extraction simulation experiments such as IVG and PBET analysis revealed that the bioavailability of heavy metals in dust samples was higher than that in soil,similar to the results of stepwise extraction comparison.The total bioavailability of heavy metals in the gastrointestinal phase was basically similar in both methods,but the bioavailability of heavy metals in the gastrointestinal phase was higher than that in the intestinal phase for soil samples under the IVG method,except for As,while the PBET method was the opposite for most elements.The bioaccessibility ranged from 5.2-62.6% for dust and 5.2-54.0% for soil.The bioavailability of Zn in dust was the highest,up to 62.6%;the bioavailability of As varied widely in different environmental media,from 11.1% in soil to 43.2% in dust.(6)Monte Carlo simulations were applied to comparatively assess the health risks of total and bioavailable fractions of heavy metals in dust and soil in Guangzhou for different populations.The carcinogenic risk(TCR)and non-carcinogenic risk(HI)of both dust and soil were children > adult females > adult males,with the largest contribution from As.The cumulative risk probabilities indicated that there was a non-carcinogenic risk for children after the calculation of total dust heavy metals,but the non-carcinogenic risk disappeared after the correction of bioabsorbable heavy metals,indicating that the non-carcinogenic risk of heavy metals in dust and soil for the population in Guangzhou was basically controllable.In overall comparison,the carcinogenic risk(TCR)of dust and soil were similar,but the non-carcinogenic risk(HI)of dust was higher because dust was more readily absorbed by the human body and posed a greater health risk.The mean carcinogenic risk values for both TCR and BAC exceeded1.0E-06 for all three populations and the risk was not negligible.Compared with the total concentration,the risk of heavy metals in the samples was reduced by more than 80% after correction of bioavailable,and the assessment using bioavailable fraction was closer to the actual situation and was a more reasonable method for human health risk evaluation.