Study On Spatial Variability Of Heavy Metals In Soil-Rice System And Pollution Risk Assessment In Wanjiang River Basin

The Wanjiang River Basin is the most economically developed area in Anhui Province.It is not only an important part of the symbiotic circle of industrial development in the Yangtze River Delta,but also one of the important grain production areas in Anhui Province.Its importance is self-evident.However,with the rapid economic development,the Wanjiang River Basin,as one of the important rice producing areas in Anhui Province,is not optimistic about the environmental quality,especially the soil quality is worrying,which is inconsistent with its economic status.In recent years,food safety issues have received increasing attention.As the main food crop in China,rice quality is related to human health.More and more researchers are beginning to explore the distribution and internal relationship of heavy metals in soil and rice in different regions.Based on the previous survey of heavy metal pollution in the study area,this paper fully considered the uniformity of the sampling distribution and the differences in the rice maturity period in the study area.Since 2017,rice has been collected in 46 counties in the Wanjiang River Basin Grain and corresponding soil samples of rice fields.In this study,according to the distribution of paddy fields in various administrative regions,the sampling density is about 1 sampling point every 10km~2.At the same time,938 soil-rice samples were collected,taking into account the areas where the potential risk of historical pollution is greater.This paper studies the heavy metals in soil and rice in the Wanjiang River Basin.Based on GIS geostatistics,the best models for different heavy metals in soil and rice are selected for Kriging interpolation,and the single pollution index,pollution load index and potential ecological risk are used.The index evaluates the soil and rice heavy metal pollution risk in the study area.In this paper,based on Arc GIS and SPSS data statistical analysis software,the distribution of heavy metals in the soil-rice system in the study area,the spatial variability and internal relationships are as follows:(1)From the perspective of the spatial variability of heavy metals in soil and rice in the study area,the block-base ratio of five heavy metals in the soil is Cr>Hg>As>Pb>Cd,of which Cd,Hg,As,and Pb are medium-space Correlation,Cr spatial correlation is weak;the block-base ratio of 5 heavy metals in rice is Cr>As>Hg>Cd>Pb,and the spatial correlation of 5 heavy metals in rice is weak.(2)Judging from the risk distribution of soil and rice heavy metal pollution in the study area,the contents of five conventional heavy metals in the soil of the Wanjiang River Basin as a whole gradually decreased from south to north,and the areas with higher Cr content were mainly presented along the Yangtze River.Strip-shaped distribution.In addition,the Cr content in Mingguang City and Lai’an County are relatively high,but they all exceed the risk screening value.Cd,Hg,As and Pb showed certain pollution characteristics in the central and southern Yangtze River coastal areas,especially Cd in the soil,which was more serious.The content of five heavy metals in rice in the Wanjiang River Basin also showed the characteristics of high in the south and low in the north.Among them,Hg was not exceeded in all rice samples,Cd and As exceeded rates were between 10%and 20%,and Pb and Cr exceeded rates were lower than 10%.The areas with higher risk of Cd and As in rice are mainly in Tongling,Chizhou and Xuancheng areas along the Yangtze River;the areas with higher risk of Pb and Cr in rice are less and more concentrated,mainly in Tongling.(3)From the results of the correlation analysis of the total amount of heavy metals in rice and soil in the study area,the correlations between Cd,Hg,Pb in rice and the corresponding heavy metals in the soil have reached extremely significant levels,and Cr has reached a significant level.However,the correlation coefficients are low,and the correlation of As is not significant.This paper selects the enrichment index to measure the ability of rice to migrate and accumulate heavy metals in soil.Studies have shown that the strength of rice to enrich heavy metals in soil is in order Cd>Hg>As>Cr>Pb.Cd,Hg,As,and Cr migration models were established by factors such as total heavy metal content,available heavy metal content in soil,and physical and chemical properties of soil.However,no good fitting model was found for Pb elements in the soil-rice system.The model’s decision coefficient is low and may be related to the impact factors involved in the analysis,so this log-linear model still needs to be improved in subsequent studies.