| As one of the main ways of resource utilization of livestock and poultry manure,pig manure composting may bring serious heavy metal pollution problems while promoting economic benefits of crop growth,and may even pose risks to the ecological environment and human health.Therefore,it is of great significance to explore the migration and transport of heavy metals in soil-vegetable system in pig manure composting area,and to scientifically evaluate its pollution degree,potential ecological risk and health risk.In this paper,based on a large-scale pig farm in Jingdezhen City,Jiangxi Province,the contents of heavy metal elements such as Cr,Ni,Cu,Zn,As,Cd and Pb in the soil-vegetable system of pig manure composting area were determined by ICP-MS,and the occurrence characteristics and bioavailability of heavy metals in rhizosphere soil were analyzed by improved BCR method.The migration and transport of heavy metals in soil-vegetable system were analyzed by bioconcentration factor and migration coefficient.The enrichment factor method based on the total amount of heavy metals,the geo-accumulation index method,the Nemero index method and the pollution load index method,as well as the secondary phase and primary phase comparison method based on heavy metal forms and the risk assessment coding method were used to evaluate the degree of soil heavy metal pollution.The comprehensive quality impact index method was used to evaluate the overall heavy metal pollution degree of the soil-vegetable system in the study area.The potential ecological risk and health risk of heavy metals in soil-vegetable system were evaluated by potential ecological risk index and health risk assessment model.The main conclusions are as follows:(1)The contents of Cr,Ni,Cu,Zn,As,Cd and Pb in the rhizosphere soil of the study area were 48.74±4.21,28.80±1.05,49.25±6.50,201.42±46.74,9.53±0.78,0.11±0.03 and 15.86±1.84 mg/kg,respectively.The average contents of Ni,Cu,Zn and Cd were higher than their background values,and the average contents of other elements were lower than their background values.(2)In the rhizosphere soil of the study area,the contents of Cr,Ni and As are mainly F4 residuals,the contents of Cu,Cd and Pb in residuals and non-residuals(F1+F2+F3)are equivalent,and the contents of Zn are mainly F1 in the soluble state of weak acid.The bioavailability coefficient(K_i)indicated that Zn had the highest bioavailability,Cu,Cd and Pb had certain bioavailability,while As,Cr and Ni had low bioavailability.In addition,the bioavailability of heavy metals in rhizosphere soil of rhizome vegetable growing areas was relatively higher than that of solanaceous vegetabels and leafy vegetables growing areas。(3)In the evaluation of rhizosphere soil pollution based on the total amount,the results of enrichment factor method showed that Ni,Cu and Zn were slightly,mildly and moderately polluted,respectively,and other heavy metal elements were not polluted.The results of the geo-accumulation index method showed that Cu and Zn were slightly polluted,and other heavy metal elements were not polluted.The evaluation results are consistent,and Cu and Zn are the main pollution factors of rhizosphere soil in the study area.The evaluation results of Nemerow index method and pollution load index method showed that the whole study area was moderately polluted.In the evaluation of the pollution degree of rhizosphere soil based on morphology,the results of the secondary phase compared with the primary phase showed that Zn and Pb were slightly polluted,and other heavy metals were not polluted.The results of risk assessment coding method showed that Zn was at high risk level,Cd was at medium risk level,Cu and Ni were at low risk level,and Cr and As were not at risk.(4)The average contents of seven heavy metal elements in the edible parts of vegetables in the study area were Zn(6.22 mg/kg)>Cu(1.23 mg/kg)>Ni(0.50mg/kg)>Cr(0.39 mg/kg)>As(0.11 mg/kg)>Pb(0.03 mg/kg)>Cd(0.003 mg/kg),respectively,which were lower than the national food limit standard,but the content of Cr in the edible parts of some solanaceous and leafy vegetables exceeded the standard.The content of most heavy metals in edible parts of vegetables was leaf vegetables>root vegetables>solanaceous fruits,and the content distribution of heavy metals in different tissues of various vegetables was root>stem>leaf.The enrichment coefficient of Cd in vegetables in the study area was the largest,followed by Cu and Zn,while the enrichment coefficient of As and Pb was relatively low.The enrichment coefficients of most heavy metals in solanaceous vegetables were higher than those in other two types of vegetables.Cr,Ni,Cu,Zn and Pb had the largest transfer coefficient between stem and leaf tissues,and As and Cd had the largest transfer coefficient between root and stem tissues.The evaluation results of the comprehensive quality impact index method show that the soil-vegetable system in the study area is at a slight pollution level as a whole.The IICQ mean value of the Soil-Vegetable System in different vegetable planting areas is leafy vegetables>root vegetables>solanaceous vegetable.(5)The average potential ecological risk index(E_i~r)of Cr,Ni,Cu,Zn,As,Cd and Pb in the rhizosphere soil of the study area were 1.58,5.55,9.67,2.51,7.70,30.73and 3.06,respectively.Cd was at a medium risk level and other elements were at a low risk level.The average comprehensive potential ecological risk index of heavy metals in rhizosphere soil of the study area was 59.72,which was at a low risk level.(6)The Soil-Vegetable System in the study area has a certain non-carcinogenic risk and an intolerable carcinogenic risk to both adults and children.As is the main contribution factor,and the vegetable intake pathway is the main way to produce health risks.For different populations,the non-carcinogenic health risk of the Soil-Vegetable System to adults in the study area was lower than that to children,while the carcinogenic health risk was higher than that to children.In addition,the non-carcinogenic and carcinogenic health risks of different Soil-Vegetable Systems to adults and children were leafy vegetables>root vegetables>solanaceous vegetable. |
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