Ecological Risk Assessment And Source Analysis Of Soil Heavy Metals Of Paddy Field In Fujian Province

In recent years,the area of cultivated land contaminated by heavy metal with external source has been continuously increasing in China,and food safety incidents assocated with which have occurred frequently.Paddy field is the production source of rice,which confronts with serious risk of heavy metal pollution.Fujian province is a traditional areas of two season rice cropping,the paddy field guarantees the local food security to a great extent,it has importantly significant to carry out the ecological risk assessment of paddy soil heavy metals in Fujian province.In this study,272 topsoil samples of paddy field were collected from Fujian province,and the contents of 7 heavy metals,Cd,Cr,Pb,As,Cu,Ni and Co,were analyzed by ICP-MS.The GIS and spatial statistics were used to analyze spatial variation and distribution of 7 heavy metals of paddy soil in the main rice producing areas of Fujian province.The ecological risk of heavy metal pollution in paddy soil was evaluated synthetically by Geo-accumulation index,Nemerow index and Potential ecological risk index.Positive definite matrix factorization(EPA-PMF)model was used to analyze the sources of heavy metals.The study aims at providing data basis for the balance management of heavy metals in paddy fields and safe production process of rice in Fujian province.The main results of reasearch are as following:(1)The mean contents of Cd,Cr,Pb,As,Cu,Ni and Co of paddy soil in Fujian province are 0.26±0.12 mg·kg-1,49.08±37.12 mg·kg-1,91.94±41.03 mg·kg-1,22.60±7.99 mg·kg-1,27.98±14.99 mg·kg-1,7.46±15.33 mg·kg-1 and 10.57±4.68 mg·kg-1,respectively,within the National Standard Level Ⅱ value for heavy metal(GB 15618-1995).However,contents of 7 heavy metal exceed the Natural Soil Background value of heavy metal in Fujian province,the mean contents of Cd,As,Pb and Ni in sampled paddy soil are 5.20,3.85,2.63 and 2.03 times of the Natural Soil Background Values of heavy metal in Fujian province,the maximum of contents of 7 elements are greater than the National Standard Level Ⅱ value of heavy metal,indicating that some samples of paddy soil in Fuijian province have been contaminated by Cd,Pb,As,Cu,Ni and Co in various degree.(2)By using ArcGIS software to analyze the spatial distribution of heavy metals of paddy fields in Fujian province,the result shows that the spatial distribution of heavy metal content in paddy soil in Fujian province is quite fluctuant,among which,the area with high Cd content distributes in the southeast of Sanming city and the northeast of Quanzhou city;the area with high Cr content distributes in the southwest of Sanming city and the southeast of Nanping city;the area with high Pb content distributes in the southeast of Quanzhou city;the area with high As content distributes in Zhangzhou city;the high content area of Cu was concentrated in central region of Nanping city;the area with high Ni content distributes in the southeast of Nanping city;and the area with high Co content distributes in the southwest of Sanming city and the southeast of Nanping city.(3)The correlation analysis between the heavy metal content and the pH value of paddy soils in Fujian province shows that Cr and Co,Ni,Cu,Cd,Cu and Cd,Pb,Ni and Cu,Cd,Co and Ni,Cu,Cd and Pb are very significantly positive correlation(P<0.01),indicating that above subgroups of heavy metals may have similar sources.While the average pH value of paddy field in Fujian province was 5.51,with negatively correlated with Cr,Co and Ni content,indicating that the lower pH value(the more acid),the higher content of Cr,Co and Ni in soil.(4)The ecological risk of heavy metals of paddy soils in Fujian province was assessed by the geo-accumulation index,the results show that the Cd and As are in moderate pollution risk level,Pb and Ni are at low pollution risk level,Cr,Cu and Co are at no pollution risk level.However,Cd accumulation in 1.47%soil samples reaches the risk of Level Ⅳ(i.e.intensity risk),Pb and As accumulation in 0.37%soil samples reaches the risk of Level Ⅳ(i.e.intensity risk).(5)The ecological risk of heavy metals of paddy soils in Fujian province is assessed by Nemerow index,the results show that the comprehensive pollution index of heavy metals of paddy soils in Fujian province is 1.12,which hits to mild pollution level.However,the heavy metal of paddy soil in 7 counties,Jianou,Jianyang,Ninghua,Shaowu,Pucheng,Nanan and Zhangpu,are in the mild pollution,Yongchun County and Zhaoan County reach the still-clean(i.e.alert level)level,and Youxi County hits to the level of cleanliness(i.e.safety).(6)The ecological risk of heavy metals of paddy soils in Fujian province is assessed by Potential ecological risk index,the results show that the average potential ecological risk values(Er)of single heavy metals in paddy soils were at low risk level.Among them,the maximum of potential ecological risk index of Cd is 102.05,which is in higher risk of heavy metal pollution.Implying that the heavy metals in paddy soils in Fujian province are in low risk level,but some soil samples are contaminated by Cd.By analyizing the integrated potential Ecological Risk Index(RI),the average potential ecological risk index of heavy metals in paddy soils of Fujian province is 49.06,which is in low risk level.(7)6 souces of Heavy metal pollution of paddy soil in Fujian province are analyzed by exploring the positive definite matrix factorization(EPA-PMF)model.Among them,the contribution rate of atmospheric subsidence pollution source(industrial pollution source)is 27.43%,the contribution rate of sewage irrigation source is 16.23%,the contribution rate of fertilizer source is 14.51%,the contribution rate of pesticide pollution source is 12.62%,the contribution rate of traffic pollution source is 14.35%and the contribution rate of soil parent materials quality is 14.86%,implying that the pollution effect caused by human activities is much greater than that of natural soil-forming parent material in Fujian’s paddy soil.