| With the acceleration of industrialization and urbanization,soil heavy metal pollution is becoming more and more serious,which has become one of the world's environmental problems.Heavy metal pollution of soil will not only lead to soil degradation,but also reduce the yield and quality of crops.At the same time,it can harm human health through the enrichment of food chain.Therefore,it is of great significance for people's health and food security to take effective measures to control and repair heavy metal contaminated soil.Guiyu town of Shantou City is a famous e-waste dismantling Center in China.Improper treatment of acid pickling wastewater and e-waste in the process of e-waste dismantling has brought serious heavy metal pollution to local farmland,resulting in excessive heavy metal content in rice produced in local farmland.In this study,the farmland polluted by heavy metals in a village of Guiyu Town,Shantou City,eastern Guangdong Province was taken as the research object.The soil in the farming layer and the rice samples in the corresponding sample points were collected at fixed points in the field,and the single factor pollution index method was used to evaluate the heavy metal pollution of soil and rice.According to the evaluation results,the soil polluted by heavy metals in this area was selected for pot experiment to study the effect of different modifiers on reducing soil available cadmium;then,the best modifiers were selected to carry out low cadmium rice screening experiment in the field,to study the difference of cadmium absorption of different rice varieties,and to screen rice varieties with relatively low accumulation of heavy metals in their grains.The main results of this study are as follows:(1)The rice produced in this area is mainly polluted by heavy metal CD.The over standard rate of CD and Cr in rice is 85.33%,5.3% and other heavy metals are not over standard.There are serious heavy metal pollution in the paddy soil in this area.The over standard rates of CD,Pb and Hg are 61.54%,48.08% and 90.38% respectively.(2)A new compound heavy metal polluted soil improver was developed by pot experiment,which was mainly composed of quicklime,calcium magnesium phosphate and organic fertilizer.The results showed that QD-CPO1 increased the soil pH from 5.50 to 6.72 in slightly polluted farmland,and the available cadmium content decreased by 63.3%;ZD-CPO1 increased the soil pH from 5.50 to 6.72 in moderately polluted farmland The soil pH increased from 5.39 to 6.93,which decreased the available CD content by 46.2%.(3)In the experiment of screening rice varieties with low cadmium in farmland,four treatments were set up: light blank,light treatment,medium blank and medium treatment,we can see that Guanghong 3 and jingliangyouhuazhan met the standard of low accumulation cadmium rice.In lightly polluted farmland,the increase of QD-CPO1 can reduce the cadmium content of two kinds of rice by more than 70%;in moderately polluted farmland,the increase of ZD-CPO1 can reduce the cadmium content of two kinds of rice by more than 65%.The results showed that the model of "soil amendment in situ passivation + low accumulation of cadmium type rice" could produce rice conforming to the national food safety limit standard in moderate and light polluted farmland.The results of this study will be helpful to promote the recovery of production function of Cadmium Contaminated Farmland in eastern Guangdong. |
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