Differernt Sources Of Heavy Metal Fractionation And Rice Paddy Soil Absorption Characteristics

Heavy metal pollution in paddy soil is an important issue of current rice safety production.The absorption and enrichment of heavy metals by rice is related to the bioavailability of heavy metals in the soil.The fractionation of heavy metals in soil is not only related to soil physical and chemical properties such as soil p H,organic matter content and texture,but also the migration and transformation characteristics of heavy metals input from different pollution sources in paddy soil.This paper takes the field polluted rice fields as the research object,and screens the industrial sources such as metal plants and steel plants in Zhuzhou（ZZ）,Fubei（FB）,Zhuji（ZJ）,Fuyang（FY）,Tongling（TL）and Yifeng（YF）regions.36 pairs of rice plants and their rhizosphere soil samples in the surrounding contaminated paddy fields.Simultaneous screening of long-term application of organic fertilizers in Changsha（CS）,Xiangtan（XT）,Yixing（YX）,Suqian（SQ）,Changzhou（CZ）,Zhugang（ZG）,Dingshu（DS）and Zhanping（ZP）areas Forty-eight pairs of rice plants and their rhizosphere soil samples were collected from the agricultural pollution source rice fields with chemical fertilizers and no industrial pollution.Analyze the content and fractionation characteristics of heavy metals in the soil of different pollution sources,compare the transport characteristics of heavy metals in the soil-rice system,evaluate the risk of heavy metal pollution in soil and rice,and explore the main controlling factors affecting the accumulation of heavy metals in rice roots in two pollution sources In order to provide a theoretical basis for the prevention and control of heavy metal pollution in paddy soils,the research results are as follows:（1）Compared with the soil background values in the 1990s,the heavy metal content in the soils of industrial and agricultural sources showed a significant accumulation trend.The accumulation of Cd was the most serious,and the P_B^*values of Cd in the soils of industrial and agricultural sources were as high as 11.82 and 6.17.The excess rates of Cd in the paddy fields of industrial and agricultural sources were as high as 100%and 87.5%,respectively,and the excess rates of Pb in industrial and agricultural sources were 33.3%and 4.1%,respectively.Cu and Zn only exceed the standards in industrial polluted rice fields,and the exceeding standards were divided into 22.2%and 2.7%.The results of single factor index method and Nemerow index method showed that the PI_Cd value of industrially polluted paddy field soil was 3.01,which was considered to be severely polluted,while the PI_Cd value of agriculturally sourced paddy field soil was 1.74,which was considered lightly polluted.The Nemerow index of heavy metals in the soil from industrial sources and agricultural sources polluted paddy fields is 2.33 and 1.56,which belong to moderate pollution and slight pollution,respectively.From the Geoaccumulation index method,it can be seen that the accumulation of Cd is the most obvious in both industrial and agricultural sources polluted soils,with I_geo values of 2.93 and 2.04,respectively,representing moderate to strong pollution.The potential ecological risk indexes of heavy metals in industrial and agricultural sources of soil were respectively 99.38 and 65.53,showing that the industrial source is significantly higher than the agricultural source,but the two typical pollution sources belong to the light pollution risk level.（2）The average and median values of Cd,Pb,Cu and Zn content in rice grains in rice fields polluted by industrial sources are higher than those of agricultural sources.Compared with the quality of national food safety standards,Cd and Pb in rice grains from industrial sources were severely exceeded,and their PI values were 1.12 and 2.11,respectively.Cd and Pb in rice grains from agricultural sources exceed the standard to a certain extent,and their PI values were 0.68 and 0.79,respectively.The median values of Cd,Pb,Cu and Zn in rice roots from industrial sources were 2.28,1.34,2.08 and 2.73 times of those from agricultural sources,respectively.The rice root system had the strongest ability to accumulate Cd,and its ability to accumulate Pb,Cu and Zn was relatively weak.The enrichment coefficients of industrial and agricultural rice roots for Cd are in the range of 0.51 to 2.68 and 0.26 to 1.76,respectively.Cd was reflected in the industrial pollution source rice root enrichment coefficient was significantly higher than that of agricultural sources.The enrichment ability of Pb,Cu and Zn did not show obvious difference.（3）In paddy soils polluted by industrial and agricultural sources,the four heavy metals Cd,Pb,Cu and Zn are mainly present in the residual fractionation,and their content ranges from 40.12%to 57.80%.Compared with different pollution sources,the Fe-Mn-oxieds fractionation（F5）Cd and Pb of industrial source soils accounted for 25.28%and 28.40%,which were 2.69 times and 1.87 times that of agricultural sources,respectively.The average percentages of exchangeable fractionation（F2）Zn,Cd,and Cu in industrial source soils reached 33.46%,22.26%,and 7.46%,respectively,which were 4.81%,3.59%,and 2.26%higher than that of agricultural sources.The proportion of humic acid-bound（F4）of soil Cd and Pb from agricultural sources is higher than that of industrial sources,and the proportion of Cd and Pb from industrial sources increases by 14.18%and 13.32%,respectively.In terms of bioavailability,the bioavailability of Cd and Zn in industrial sources is higher than that of agricultural sources,and the bioavailability of Pb and Cu in agricultural sources is higher than that of industrial sources.（4）The correlation analysis results showed that the content of Cd,Pb,Cu in the roots of rice polluted by industrial sources was significantly positively correlated with the bioavailability of heavy metals in the soil.The content of Cd,Pb,Cu,and Zn in the roots of rice polluted by agricultural sources was related to the bioavailability of heavy metals in the soil.There is a significant positive correlation between the content of soil,and the biologically available soil heavy metals and the physical and chemical properties of the soil are important factors that affect the accumulation of heavy metals in the rice roots.The results of principal component analysis and redundancy analysis show that the content of bioavailability soil heavy metals and soil physical and chemical properties were important indicators that affect the accumulation of heavy metals in rice roots.Redundant analysis results showed that the content of heavy metals in rice roots was positively correlated with the content of available heavy metals in the soil.It shows that the bioavailability of heavy metals in soil was the most important main controlling factor affecting the accumulation of heavy metals in rice roots.The uptake of Cd,Pb,Cu and Zn by rice roots from industrial sources was negatively correlated with soil p H.The absorption of Cd,Pb,and Zn by the rice roots showed a negative correlation with the soil organic matter content.The root system of rice in industrial polluted rice fields was p H as the most important controlling factor in the physical and chemical properties of the soil,while in agricultural polluted rice fields was based on the content of soil organic matter as the main controlling factor.The absorption of Pb and Zn by the roots of agricultural rice showed a certain degree of positive correlation with the content of humic acid combined state.