Study On Migration And Enrichment Of Cadmium In Soil-pepper System And Its Coupling Relationship

Karst carbonate rock area has typical high-metal geological background characteristics.In some areas of Guizhou Province,pollution is superimposed due to mining,smelting,etc.,which leads to serious contamination of cadmium in the soil,and there is a risk of cadmium food chain in Guizhou Province.Pepper is a kind of characteristic agricultural product in Guizhou Province,so the migration and enrichment of cadmium in soil-pepper system are worthy of discussion.Selecting the zonal soil yellow earth and limestone soil in Guizhou,and the three types of peppers（Capsicum frutescens L.）including line pepper,hot pepper and hybrid pepper to study the migration and enrichment of cadmium at different cadmium concentration levels.Selecting some counties where the background value of cadmium is high and collecting their soil and fruit samples of pepper to study the coupling relationship between capsicum cadmium and soil total cadmium and available cadmium,and derive the threshold of soil total cadmium and available cadmium concentration based on safe production of pepper for provide a base on controlling pollution and safe utilization of soil cadmium in geological high background areas.The research results are as follows:（1）The distribution of cadmium in all parts of hot pepper,line pepper and hybrid pepper is the same.Its showed roots>stems,leaves>fruits of the pepper on the yellow earth and showed roots,leaves>fruits>stems on the limestone soil.There are differences in cadmium content among different peppers.Roots:line pepper>hot pepper,hybrid pepper;leaf and fruit:hot pepper>line pepper,hybrid pepper.The cadmium content of different types of pepper fruits in yellow soil were:1.08¹.37 mg·kg^-1（hot pepper）,0.70¹.19 mg·kg^-1（line pepper）,1.03¹.06 mg·kg^-1（hybrid pepper）.The cadmium content of different types of pepper fruits in limestone soil is 0.52¹.26mg·kg^-1（hot pepper）,0.56¹.08 mg·kg^-1（line pepper）and 0.46¹.08 mg·kg^-1（hybrid pepper）.The ability of hot pepper to enrich cadmium is higher than that of line pepper and hybrid pepper,which has higher risk of cadmium exposure.（2）The root-stem transport coefficient（TF1）mean values of hot pepper,line pepper and hybrid pepper in acid yellow earth were 0.59,0.81,0.67,stem-fruit transport coefficient（TF2）were 0.51,0.91,0.79,and root-fruit transport coefficient（TF3）was 0.31.0.68,0.55,all less than 1,the bioconcentration factors（BCF）were 1.43,2.11,1.60,all more than 1.On the yellow earth,the characteristics of cadmium absorption in peppers are characterized by high transport and low accumulation.The mean TF1 in limestone soil were 0.36,0.50,0.31.TF2 were 1.38,1.26,1.51.TF3were 0.4,0.62,0.46.BCF were 0.42,0.42,0.41.TF2 are greater than 1,BCF are less than 1,and in limestone soil,cadmium absorption characteristics of peppers are characterized by high transport and low accumulation.Capsicum fruit has higher ability of cadmium enrichment on the yellow earth.（3）The experiment investigated 9 districts and counties,collected 103 pairs of soil and pepper fruit samples.Among them,44 soil samples exceeded the risk screening value of soil environmental quality standards（GB 15618-2018）,there are 10 soil samples super-risk control value,20 pepper samples that exceed the national food safety standards（GB 2762-2017）limit.In those areas,Weining county is a typical geological high background and pollution superimposed area where the ratio of risk screening value of super soil environmental quality standard（GB 15618-2018）is 100%,ratio of super risk control value is 50%and proportion of peppers exceeding the national food safety standards（GB 2762-2017）limit is 100%.The soil and pepper samples in Leishan County that own non-karst geological background are not exceeded.（4）The total cadmium threshold of soils safely produced by linear regression(Cd<0.05mg·kg^-1)was 2.06 mg·kg^-1（P<0.01）,and available cadmium threshold was 0.1099 mg·kg^-1（P<0.01）:pH<6.5,the total cadmium threshold in soil is 1.33 mg·kg^-1（P<0.01）,available cadmium threshold is 0.1783 mg·kg^-1（P<0.01）;6.5≤pH≤7.5,the total cadmium threshold of soil is 2.00mg·kg^-1（P<0.01）,and available cadmium threshold is 0.0455 mg·kg^-1（P<0.01）;pH>7.5,the total cadmium threshold of soil is 2.57 mg·kg^-1（P<0.01）,and available cadmium threshold is 0.0055mg·kg^-1（P<0.01）.Pepper is a cadmium-rich crop.The soil cadmium threshold is greater than the soil pollution risk screening value,which is less than the regulatory value.Planting pepper in the high geological background area has a higher risk of cadmium exposure.