Assessment Of Heavy Metal Pollution And Human Health Risk Of Paddy Soils In A Certain Area Of Hunan Province

Hunan is one of the largest rice production bases in the country.The heavy metal pollution in its farmland soil is not only related to the quality and safety of local crops,but also to the health of Chinese residents.In order to study the situation of soil heavy metal pollution in a certain area of Hunan Province,further understand the distribution of heavy metal elements in the soil-rice system caused by local heavy metal pollution,improve the quality of soil environment,improve the quality and safety of local agricultural products,and enhance the health management level of the population,this paper selects the farmland soil and the main crop-rice as the research objects in Hunan Province.The contents of four heavy metals,Cd,As,Cu,and Zn,are obtained by measurement.The distribution characteristics of soil heavy metals in the study are analyzed by using descriptive statistics and enrichment coefficient.The soil heavy metal pollution in the study area is evaluated by single factor pollution index method,Nemerow comprehensive pollution index method,geoaccumulation index method and potential ecological hazard index method,and the human health risk of the population in the study area is evaluated by non-carcinogenic risk index and carcinogenic risk index.The conclusions are as follows:（1）The average value of the heavy metal Cd in the soil of the study area is 0.56 mg/kg,which is 1.4 times the national standard limit.The heavy metal As,Cu and Zn do not exceed the national standard limit.Taking the Hunan soil background value as the reference standard,the average values of Cd,As,Cu and Zn are 4.00,1.08,1.28 and 1.30 times of the Hunan soil background value.The four kinds of heavy metals accumulated in the soil of the study area to a certain extent,and the average value of heavy metal Cd in rice in the study area is 0.26 mg/kg,which is 1.3 times the national standard limit.The contents of heavy metals As,Cu and Zn in rice do not exceed the national hygienic standard limit.The heavy metal Cd is the main pollutant.（2）In soil samples,four heavy metals,Cd,As,Cu,and Zn,are all moderately variable.In rice crop samples,except for the heavy metal Cd,which is highly variable,the rest are medium degree of variation.It shows that the distribution of soil heavy metal pollution in the study area is uneven,the distribution of heavy metal Cd in rice crops is unbalanced,and the spatial difference is large.The enrichment coefficients of heavy metals in rice crops are less than 1.The order from large to small is BCF_Cd=0.46>BCF_Zn=0.17>BCF_cu=0.07>BCF_As=0.01.The migration,transformation and enrichment ability of heavy metals in soil rice crop system is low.（3）The single factor pollution assessment grade of heavy metal Cd in farmland soil in the study area is slight pollution,and the other heavy metals As,Cu and Zn are non-pollution.The Nemerow comprehensive pollution assessment grade of soil heavy metal is mild pollution.The average value of soil geoaccumulation index of four kinds of heavy metals is less than 0,which belongs to no pollution.The potential ecological hazard index of soil heavy metals in the study area belongs to the level of slight ecological risk.Among them,the potential ecological hazard risk of heavy metal Cd belongs to the degree of strong ecological risk,and the other three heavy metals do not cause risks to the ecosystem.The main pollution factor of farmland soil pollution is the heavy metal Cd.（4）The results of human health risk assessment showed that the total non-carcinogenic risk index of heavy metals Cd,As,Cu and Zn in the soil of the study area through all exposure routes is 9.42E-01,less than 1,which is an acceptable risk.The carcinogenic risk index of heavy metals Cd and As in the soil of the study area is 9.40E-05,less than10^-4,which is below the maximum acceptable risk level recommended by the U.S.Environmental Protection Agency（USEPA）.The total non-carcinogenic risk index of heavy metals Cd,As,Cu and Zn in rice in the study area is 3.21E+00,greater than 1,and the carcinogenic risk index is 3.55E-03,greater than 10^-4.Therefore,the medium heavy metals Cd and As will cause unacceptable health risks to human body,and the health risks caused by the heavy metals Cu and Zn to human body are acceptable.