Soil Heavy Metal Contamination And Risk Assessmentin Greenhouse Vegetable Fields Of Xi'an Suburb

In this paper,a field study was conducted using vegetable greenhouse fields from the suburb of Xi'an,Soil and the main agricultural products of typical greenhouse vegetable areas were collected in Chang'an District,Baqiao District,Weiyang District and Gaoling District.The contents of heavy metals?Cd,Cr,As,Pb?in soil and vegetable samples were analyzed,and the spatial distribution of heavy metals in the study area was performed using ArGIS 10.2software,The bio-availability of heavy metals in human digestive organs was analyzed in vitro.Finally,the health risk of heavy metals were evaluated and concentrate on the following exposure pathways:three exposure pathways of heavy metals in soil and the oral ingestion of vegetables.The results showed that:?1?The fluctuation range of heavy metal content in soil was large and the maximum levels of three heavy metals?Cd,Pb,As?are higher than the limit values,The order of heavy metal content from high to low was Cd>Pb>As,and Cr was environmentally friendly.according to theindividualfactor,Nemerowcomprehensivepollutionand accumulated pollution,the Cd pollution was most severe in greenhouse vegetable soil,and the order of the other heavy metal content from high to low was Pb>As>Cr.It showed the comprehensive potential ecological risk assessment,the comprehensive soil ecology in this area represented a small hazard potential,however,Cr in vegetable exceeded the standard,and the Cd of vegetable in Weiyang District was significantly influenced by human factors,Pb and As were not exceeding the standard,therefore,The high concentration of Cr in Brassica chinensis L.?2?The heavy metals content in the study area from high to low are follows:Cd was Weiyang District>Gaoling District>Baqiao District>Chang'an District,Cr was Gaoling District>Weiyang District>Baqiao District>Chang'an District,Pb was Weiyang District>Gaoling District>Chang'an District>Baqiao District,As was Gaoling District>Chang'an District>Baqiao District.?3?The pH range of the soil was 7.5⁸.71,which was alkaline.Available Cd content in soil was relatively high.There was a significantly correlation between available Cd,Pb and As in soil.The content of available Cd in soil was significantly correlated with total Cd in vegetables,while there was a significant negative correlation between Cd and Cr in vegetables.?4?The bio-availability of heavy metals was analyzed by in vitro simulation.The results showed that the dissolution rate of As was higher than other heavy metal in oral stage,and the dissolution of Pb in gastric stage was high;the highest dissolution rate of heavy metal in intestinal stage was Cd;The difference of the dissolution rates of heavy metals at different digestion stages may be related to the environment of digestive organs and the forms of heavy metal.?5?The non-carcinogenic index of the four heavy metals in soil were less than 1.The soil Cr of greenhouse vegetable fields was the primary influencing factor of non-carcinogenic risk to the local residents in Weiyang District.The soil As was the main influencing element in the other three region.the HI of four heavy metals in Weiyang area was 1.03 at different exposure routes,which was more than 1.The results indicated that adults in this area could increase the risk of health hazards from three exposure routes,while Cr in vegetables was the main factor of non-carcinogenic risk to local residents.?6?According to the carcinogenic risk index of Cd and As at different exposure routes,the total carcinogenic risk of a single pollutant through three exposure routes was As>Cd,and the carcinogenic risk caused by single pollutant was acceptable.However,it is worth noting that the carcinogenic risk index of heavy metals digestibility in vegetables was 1.31×10^-3,It means that about one in a thousand people had a carcinogenic risk above the threshold of carcinogenic risk index(R=10^-4),which represented an unacceptable carcinogenic risk.Long-term consumption of vegetables contaminated with Cd and As increased the risk of carcinogenesis of local citizen.