Characteristics Of Heavy Metals Pollution In Paddy Soils And Soil-Rice Heavy Metal Coupled Relationship In Typical Research Areas

With the continuous acceleration of my country’s urbanization and industrialization process,and the gradual improvement of the level of agricultural modernization,heavy metal pollutants caused by industrial and agricultural production activities enter the farmland environment through atmospheric deposition,runoff input and other methods,which seriously affect the safety of crops.In order to ensure the safety of agricultural products,strengthen the classification and control of farmland soil,realize the prediction of the heavy metal content of rice,and construct a soil-rice heavy metal coupled Relationship model is a simple and effective method.In this paper,a combination of field sampling and pot experiment was used to study heavy metal-contaminated farmland in three typical research areas including Changzhutan,Shaoguan,and Doumen Xinhui.Based on the analysis of pollution characteristics and risk assessment of the three study areas,a soil-rice heavy metal cadmium(Cd),lead(Pb),zinc(Zn),and copper(Cu)coupling relationship model was constructed.The main research results of this article are as follows:1.Soil physical and chemical properties and determination of heavy metals in soil and rice in typical areasThe soils in the three research areas are mainly weakly acidic.The pH in the Changzhutan and Doumen Xinhui research areas is mainly between 5.0 and 6.5,and the Shaoguan research area is mainly between 6.0 and 7.0.The average soil pH value in the three regions was 5.99,6.02 and 5.75,respectively.The soil organic matter content in the Doumen Xinhui research area was the highest,followed by Changzhutan and Shaoguan research areas.The average values of the three research areas were 32.67,27.18 and 34.93 g/kg,respectively.The value of soil cation exchange in Changzhutan and Shaoguan research areas is not much different.Due to the strong influence of soil leaching,the amount of cation exchange in the Doumen Xinhui research area was low.The average total amount value of total Cd,Pb,Zn and Cu in Changzhutan research area is 0.9880,64.21,116.7,28.74 mg/kg,the average effective soil content is 0.0660,0.0250,0.608,0.129 mg/kg,the average content of rice grain values were 0.374,0.054,27.80,and 4.853 mg/kg.The average total amount value of Cd,Pb,Zn,and Cu in Shaoguan research area were 4.865,609.1,904.3,and 213.7 mg/kg,and the average effective soil content was 0.397,0.386,114,0.294 mg/kg,the average content of rice grain is 0.342,0.158,27.5,5.40 mg/kg.The average total amount value of soil Cd,Pb,Zn,Cu in the Doumen Xinhui research area is 0.3890,40.36 127.4,47.16 mg/kg,the average effective soil content is 0.0280,0.0270,0.899,0.0200 mg/kg,and the average content of rice grain is 0.166,0.235,26.5,4.45 mg/kg.2.Risk assessment of heavy metal pollution in soil in typical research areas and Study on the Characteristics of Rice Enrichment of Heavy MetalsThe single factor pollution index indicates that the main pollutants of heavy metals in the three study areas are all Cd elements.There are soil pollutions of Cd,Pb and Cu in the Changzhutan research area,and the pollution of the four elements of Cd,Pb,Zn and Cu in the Shaoguan research area are relatively serious.The soil Cd and Cu in the Doumen Xinhui research area are polluted.The Merlot Comprehensive Pollution Index in the three regions reached moderate pollution,severe pollution and light pollution.Among the four heavy metals,the Cd element is the easiest to concentrate into rice,and the Pb enrichment ability is the worst.Rice in the Changzhutan research area has a significantly stronger enrichment capacity for heavy metals Cd,Zn,and Cu(the average enrichment coefficients of Cd,Zn,and Cu are 0.645,0.319,0.215).Although the Shaoguan research area has serious soil pollution,the ability of rice to accumulate heavy metals is not strong(the average enrichment coefficients of Cd,Pb,Zn,and Cu are 0.357,0.003,0.171,and 0.094).Duo to the strong stability of heavy metals in the Doumen Xinhui research area,the ability of rice to accumulate heavy metals Weak(Cd,Pb,Zn,Cu enrichment coefficient average values are 0.612,0.006,0.236,0.121).3.Construction of soil-rice heavy metal coupled relationship model in typical areaThe soil-rice heavy metal coupled relationship models constructed in different research areas have both common characteristics and different characteristics.The commonality is that the effective state content of heavy metals in the soil significantly affects the enrichment of heavy metals by rice.The difference is that the main control factors that determine the coupled model are affected by the pollution characteristics of different research areas.The effective Zn content of the soil in the Changzhutan research area plays a major role in the absorption of heavy metals Pb and Zn by the rice in the area,while the effective Cd content of the soil in the Shaoguan research area plays a major role in the absorption of Cd,Pb and Zn by the rice.The model of each heavy metal element in the Doumen Xinhui research area is affected by the effective content of the element in the soil.The determination coefficients of the Cd,Pb,and Zn models in the underground parts of rice in the Changzhutan Research Area are 0.535,0.709,and 0.484,and the determination coefficients of the Cd,Pb,and Zn models in the underground parts of Shaoguan Research Area are 0.519,0.779,and 0.758.The determination coefficients of the Pb and Zn models in the underground parts of rice in the Doumen Xinhui research area are 0.284 and 0.425.Therefore,the higher the degree of pollution,the stronger the explanatory power of the model,and the model of rice shoots and grain content has the same rules.