Pollution Characteristics,sources Analysis And Risk Assessment Of Heavy Metals In Vegetable Soil Of Livestock Manure Composting Area In Jiangxi Province

With the high-quality development of China’s livestock and poultry breeding industry,there are more and more large-scale and intensive pig farms,and at the same time,a large amount of pig manure such as feces and urine is also generated.Composting and returning to the field is one of the main ways to utilize livestock and poultry manure resources,but long-term composting can cause the accumulation of heavy metals in farmland and vegetable soil.Currently,livestock and poultry manure has become an important source of heavy metals in the environment.At present,research on heavy metals in soil in Jiangxi is mostly focused on the surrounding soil of mining areas and lakes and wetlands,while there are few reports on heavy metal pollution in pig manure composting soil.Therefore,conducting evaluation,source analysis,and risk assessment of heavy metal pollution in composting soil is of great significance to ecology and humanity,providing scientific basis for the recycling and effective prevention and control of heavy metal soil pollution in livestock manure composting soil.This article selected vegetable soil from a pig manure composting area in Jingdezhen,Jiangxi Province as the research object.15 surface soil samples were collected using the diagonal method,and the total and form contents of 7 heavy metals（Cu、Pb、Zn、Cr、Cd、As、and Ni）were analyzed and measured.Enrichment factor method（EF）,land accumulation index method(I_geo),Nemero pollution index method（P_n）were used Evaluation methods such as secondary phase to primary comparison method（RSP）and risk assessment coding method（RAC）were used to evaluate the degree of heavy metal pollution in soil;Using the potential ecological risk index method and health risk assessment model to evaluate the potential ecological and health risks of heavy metals in soil;Combining principal component analysis and absolute principal component multiple linear regression model,the sources of heavy metals in vegetable soil in pig manure composting areas were identified and the following conclusions were drawn:（1）The variation range of Cr、Ni、Cu、Zn、As、Cd and Pb content in the soil of the study area is 41.41～64.38mg/kg、24.72～31.23mg/kg、31.28～68.90mg/kg、71.10～22.80mg/kg、6.04～15.26mg/kg、0.07～0.19mg/kg and 9.38～18.53mg/kg,respectively,with an average of 48.46mg/kg、29.06mg/kg、48.16mg/kg、142.32mg/kg、10.62mg/kg、0.13mg/kg and 15.75mg/kg.The contents of Cu、Zn、Cd and Ni are 1.89,1.77、1.17 and 1.12 times higher than their background values,respectively.The content of As is close to the background value,while the content of Cr and Pb is lower than its background value.The concentrations of seven heavy metals are all lower than the risk screening values specified in the"Soil Environmental Quality Standard for Soil Pollution Risk Control of Agricultural Land（Trial）"（GB 15618-2018）.（2）The distribution of various forms of Cu,Ni,As,and Pb in the soil of the study area is F4>F2>F3>F1,the distribution of Cr is F4>F3>F2>F1,the distribution of Zn is F4>F1>F2>F3,and the distribution of Cd is F4>F2>F1>F3.The soil occurrence of the seven heavy metals is mainly in the residual state.The proportion of reducible states of Pb,Cu,Cd,and Ni is relatively high,accounting for 43.22%,17.99%,13.31%,and 5.55%,respectively;Zn has the highest proportion of weakly acid soluble state,at 29.08%;The proportion of non-residual states of Cr and As is very low.（3）The evaluation results of the single factor pollution index method showed that there was mild pollution of Cu、Zn、Cd and Ni in the soil of the study area,with some sampling points of Cu and Zn showing moderate pollution;The pollution level of As、Cr、and Pb is pollution-free.The evaluation results of the enrichment factor method showed that Cu、Zn、Cd and Ni showed slight enrichment levels,while As、Cr and Pb showed no pollution and no enrichment phenomenon.The results of the ground accumulation index method indicate that Cu and Zn are in a slightly polluted state,while Cd、Ni、As、Cr、and Pb show no pollution.The results of the Nemero pollution index method show that the overall soil in the study area is in a slightly polluted state.The results of the comparison method between secondary and primary phases indicate that the overall environmental risk of heavy metals is very low,with some sampling points of Zn、Cd and Pb showing mild pollution levels.The risk assessment coding method evaluation results show that Zn is at medium risk Cd、Cu、Ni and As are all at low risk,while Cr and Pb show no risk.（4）The results of the potential ecological risk index method indicate that the potential ecological risk index of each heavy metal is ranked in descending order:Cd（35.13）>Cu（9.45）>As（8.58）>Ni（5.60）>Pb（3.03）>Zn（1.77）>Cr（1.57）.Cd presents a moderate risk level,while the other six heavy metals all present a mild risk level;The average potential ecological risk index is 65.14,indicating a slight ecological risk level for heavy metals in the soil of the study area as a whole.（5）The health risk assessment results indicate that the non-carcinogenic risk indices for heavy metals in compost soil in the study area for adults and children are0.07 and 0.11,respectively,with carcinogenic risk indices of 1.01×10^-5and 1.82×10^-5,its non-carcinogenic and carcinogenic risks do not exceed the standard threshold,and the existing risks are acceptable.Oral intake is the main non carcinogenic and carcinogenic risk exposure pathway for heavy metals in soil.As and Cd are the main non carcinogenic factors of heavy metals in compost soil for adults and children.（6）The source analysis results indicate that Cu、Zn、Cd and Ni in the soil of manure composting vegetable fields in the study area are mainly"agricultural pollution sources"caused by pig manure composting,with contribution rates of40.82%、61.01%、66.36%,and 60.26%,respectively.Pb、Cr and As are mainly"industrial sources"caused by coal-fired activities,with contribution rates of20.99%,、19.99%and 25.53%,respectively.