| According to the national soil pollution survey Bulletin released in 2014,the over standard rate of cultivated land soil points in China is 19.4%,and cadmium（Cd）is one of the most important pollutants.In order to understand the Cd pollution characteristics of paddy soil and rice in Guizhou Province,taking some rice producing areas in 9 cities（prefectures）of Guizhou Province as the study area,the soil and corresponding rice samples were collected,and the soil p H and Cd content of all samples were tested;Then,through the pollution index evaluation model and the health risk evaluation method recommended by the US Environmental Protection Agency,the pollution status of soil and rice Cd in rice field and the possible health risks of soil and rice Cd to local residents are analyzed.At the same time,according to the above Cd pollution characteristics of paddy soil and rice,the paddy soil in the area where the soil belongs to safe utilization and the agricultural products exceed the standard（Pingba District,Guizhou Province）is collected,and the remediation experiment of soil Cd pollution is carried out by applying biochar,sulfhydryl modified palygorskite,foliar inhibitor,etc.The main research results are as follows:（1）Affected by the soil forming parent material（parent rock）and man-made emission,the average content of Cd in the topsoil of rice fields in some rice producing areas of 9 cities（prefectures）in Guizhou is 0.88 mg/kg,96.43%of the soil samples exceed the risk screening value,and the soil Cd pollution is not optimistic.The Cd content of soils in Southwest Guizhou,Bijie,Guiyang,Southern Guizhou,Anshun,Liupanshui,Tongren,Zunyi and Southeast Guizhou decreased gradually.The soil Cd accumulation index(Igeo)showed that the proportion of non-polluted,non polluted to moderately polluted and moderately polluted soils were 76.43%,20.00%and 3.57%respectively.However,the soil Cd Single factor pollution index（Pi）shows that there are 5,101,21 and 13 non-polluted,slightly polluted,moderately polluted and heavily polluted soils respectively.（2）The average Cd value of rice is 0.04 mg/kg,of which 3.65%of rice samples exceed the safety limit of rice（0.2 mg/kg）,which are located in Guiyang,Anshun and Southeast Guizhou respectively.During the grain filling and ripening stage of rice,due to the poor water conditions of paddy field,the high frequency of soil oxidation environment or the long duration of oxidation environment may be one of the main reasons for the excessive Cd of rice.（3）For adults,the average non carcinogenic risk quotient（HQ）of Cd in soil and rice were 2.04×10-3 and 3.37×10-1,respectively;For children,the average HQ of Cd in soil and rice were 1.34×10-2 and 7.22×10-1,respectively.The average HQ of soil and rice Cd to adults and children is less than 1,and the non carcinogenic risk of children and adults can be ignored.The average carcinogenic risk values（CR）of Cd in soil and rice were 3.82×10-6 and 8.80×10-4,respectively;The average CR for children was 9.09×10-6 and 6.29×10-4,respectively.The CR of soil Cd to adults and children is in the range of 1.00×10-6～1.00×10-4,which is acceptable;The CR of rice Cd for adults and children exceeds the maximum acceptable level(1.00×10-4).Therefore,it has potential cancer risk for adults and children,which should be paid attention to.（4）The soil Cd content of 1%biochar（B1）,5%biochar（B3）,0.01%sulfhydryl modified palygorskite（C1）,5%biochar+0.1%sulfhydryl modified palygorskite（B3+C3）and 7%biochar+0.01%sulfhydryl modified palygorskite（B4+C1）potted plants is high,and the Cd content in the corresponding rice（brown rice）is low,indicating that the application of biochar and sulfhydryl modified palygorskite can reduce the activity of soil Cd,and then reduce the absorption of rice;In addition to the application of palygorskite,the application of biochar and leaf barrier decreased the Cd content in rice roots,stems,leaves and rice step by step;After applying biochar,sulfhydryl modified palygorskite and leaf barrier,the content of Cd in brown rice was lower than the limit value（0.2 mg/kg）;Compared with the blank control,adding sulfhydryl modified palygorskite and leaf barrier decreased the Cd enrichment ability of rice grains in soil.The above results showed that the application of sulfhydryl modified palygorskite and foliar barrier had better remediation effect on Soil Cd.However,when biochar,sulfhydryl modified palygorskite,leaf barrier and the mixture of biochar and sulfhydryl modified palygorskite were applied,the rice yield decreased compared with the blank control.This study can provide theoretical support for the next step of restoration and utilization of rice fields with production barriers in Guizhou Province. |
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