Research On Safety Threshold Value And Risk Assessment Of Heavy Metals In Vegetable Soils

The concentrations of lead, cadmium, chromium, mercury and arsenic in267vegetable samples including rapes, celeries, cabbages, carrots, lettuces, cayenne peppers, tomatoes and cowpeas and their corresponding soil samples in primary vegetable production areas of Zhejiang Province, China. Through correlation analysis between concentrations of vegetable and corresponding soil samples, we proposed20safety thresholds of heavy metals for vegetable soils. The environmental risk assessment was based several evaluation standards and methods at home and abroad. The health risk assessment developed by the U.S. EPA (United States Environmental Protection Agency) was used to explore the potential health hazards of heavy metals contamination in vegetable soils in the study areas. The results are presented as follows:(1)The heavy metals contamination level and bio-accumulation ability differed among soil heavy metals and vegetables. The ranges of heavy metal contents in soils were Pb(4.54～350.48mg·kg-1), Cr(23.25～82.22mg·kg-1), As(4.34～50.12mg·kg-1), Cd(0.09～2.53mg·kg-1), and Hg(0.08～1.65mg·kg-1), and leafy vegetable soils>root vegetable soils>solanaceous vegetable soils>legume vegetable soils. Among all the soil physical and chemical properties, pH was the dominating factor which influenced heavy metal content of soils. Next was CEC. Limits of contaminants in foods (GB2762-2005) was used as the standard, and heavy metals safety thresholds in vegetable soils were established for the metals, Pb (783mg·kg-1) being the highest safety threshold.(2) Compared with single pollution index method, soil pollution as reflected by the results of Nemerow comprehensive pollution index method was more serious, especially in the soil of leafy vegetables and root vegetables, which were higher than the national standards. The results of Hakanson accessment method showed that Cd pollution was the most serious in four kinds of vegetable soils, followed by Hg.Comprehensive potential ecological risk was high in the soil of leafy vegetables and root vegetables. (3) The results of carcinogenic risks showed that diet pathway was the dominating exposure route of all the heavy metals to humans. As the main carcinogenic factor, Cd in soils showed carcinogenic risk value on the level of10-4～10-5for children. Carcinogenic risk values of As for children were between4.33×10-5～1.17×10-4, and the effect of As on local human health was not serious. Diet pathway was also the dominating exposure route for non-carcinogenic risk. The non-carcinogenic risks of Pb, Cr and As for children exceeded the limit value1in leafy vegetable soils and root vegetable soils.The highest total non-carcinogenic risk of children existed in celery, followed by rape, and they both exceeded the safety limit. In different groups, carcinogenic risk should be controlled for adults and non-carcinogenic risk for children. Cr was the primary heavy metals posed non-carcinogenic risks while Cd generated the greatest carcinogenic risk. For these reasons, effective control measures should focus on Cd and Cr to reduce health risk in the study areas.