Potential Harmful Metal Particle Size Occurrence Effects Of Typical Pollution Sources And Their Health Risks

Toxic Metal Elements（TMEs）can cause several human diseases by impairing metabolic functions and functions of important organs and glands since they accumulate in plant tissues or animal organs due to irreversibility,strong toxicity and persistence.Therefore,it is of great importance to explore the occurrence and the risk of TMEs in soil and dust,the major environmental media,under the typical sources of TMEs pollution.In order to explore the further effect and risk of TMEs in soil and dust,associated with different size particles in soil and dust,this study obtained different size particles through wet extraction,discussed chemical speciaton and bioaccessibility,found TMEs phase source through the X-ray diffraction,electron microscopy technology,and revealed the graded effect of TMEs health risks.On this basis,combined with different sizes and bioaccessibility established synthesis method of health risk assessment under typical pollution source.In addition,the phase characteristics and geochemical process of TMEs under typical pollution sources were interpretated.First,samples from typical sources of TMEs pollution（soil and dust around power plants,industrial lead-contaminated soil and urban road runoff sediments）were collected.Different particle size fractions（50-250μm,5-50μm,1-5μm,<1μm）of soil and dust were extracted by wet extraction,and the distribution characteristics of TMEs in each particle size were determined.The experiment results showed that 5-50μm was the main particle size of soil,50-250μm was the main particle size of dust and 5-50μm was the main particle size of runoff sediment.The concentration of TMEs in soil and dust around power plants,industrial lead-contaminated soil and runoff sediments were significantly different.Compared with the soil background value in Shaanxi Province,the contents of Cu,Fe,Mn,Ni,Pb and Zn were all greater than the background value.All TMEs,except Cu,were enriched in small particle size（<1μm）in soil and dust around power plant,industrial lead-contaminated area.Secondly,the particle size effect of chemical speciaton and bioccessibility of TMEs under typical contamination sources was investigated.The results showed that with the decrease of particle size,the concentration of exchangeable,carbonate-bound and Fe/Mn hydroxide-bound of TMEs increased,which was contributed to the release of TMEs in the environmental media.Especially,the average concentration of carbonate-bound was 35.58%in industrial lead-related contaminated soil,but only 6.52%in residual.This indicates that strong solubility to organic matter and strong adsorption to carbonate when Pb was combined with soil mineral interface,which also indicated that Pb was easy to migrate and transform.Similarly,the bioaccessibility of TMES also showed a certain size effect.The bioaccessibility of small particle size of most elements was greater than that of coarse particle size,and the bioavailability of most elements was greater in<1μm.Then,the potential ecological risk and human health risk of TMEs were calculated by the concentration of carbonate-bound and Fe/Mn hydroxide-bound of TMEs and bioaccesssibility from typical pollution sources.The results showed that,in the soil/dust around the power plant,the comprehensive potential ecological risk index of<1μm was the highest,followed by 1-5μm,and finally 50-250μm and 5-50μm.When the TMEs particle size load was taken into account,the contribution of 1-5μm to the soil was greater,and the contribution of 5-50μm to the dust was greater.In lead-contaminated soils,the comprehensive potential ecological risk index of each grain size component was as follows 1μm>1-5μm>bulk>50-250μm>5-50μm.The comprehensive potential ecological risk of each grain size was more than 240,and its risk level was significantly higher than that of the road runoff sediment and the power plant.When TMEs particle size load was taken into account,the contribution of 5-50μm to the total particle size was greater.In urban road runoff sediments,The average intensity of ecological risk was ranked as Cu>Pb>Ni>Zn>Cr>Mn.The multi-element comprehensive potential ecological risk was greater than 60,which was considered as high risk or very high risk.According to the health risk assessment,the risks of TMEs of adults and children in leadcontaminated soil was significantly greater than that of soil/dust around tpower plants and urban runoff sediments.When the size effect of TMEs was taken into account,the risk was overestimated by both coarse size（50-250μm）and small size（1-5μm and<1μm）assessments,and the risk value is closest to most closely approximated the true health risk by the bioaccessibility concentration in the 5-50μm.Finally,the phase source of TMEs was found by X-ray diffraction and electron microscopy.The results showed that with the decrease of particle size,the content of primary minerals such as quartz and albite decreased,while the content of secondary minerals such as calcite and chlorite increased.Clay minerals have strong adsorption capacity for TMEs,which was also the reason for the concentration of TMEs in different particle size fractions.TMEs was more dependent on Ca-and Fe-containing minerals for<1μm fraction.Based on SEM/EDS,fly ash particles were obviously found in the soil and dust samples around the power plant,while a large number of Pb particles were observed in the soil samples contaminated by industrial lead.In addition,after settling for 48 h,the suspended particles of road runoff samples were mostly presented as spherical or regular square,and most of them were single particles.It was found that these suspended particles were highly likely to be Cu-containing substances,and trace amounts of TMEs such as Cr,Zn and Pb had been adsorbed on their surfaces through EDS.