Approaches For Safety Production In Cadmium-contaminated Paddy Soil:Rice With Low Cadmium Accumulation And Integration With Other Remediation Technology

As the development of economy and society,heavy metal contamination of farmland has become increasingly prominent and cadmium pollution is the major type,which has great effects on the sustainable development of agricultural production and the quality of human living environment.In order to study the safe production measures of rice in cadmium contaminated paddy soils,a field experiment was conducted to investigate the effects of different adding levels of sepiolite,humic acid and the combination of both on immobilization of Cd were discussed;the accumulation characteristics of cadmium in rice seeds and the effects of agronomic measures(management of water and fertilizer)in contaminated paddy fields were studied.The main results were as follows:As the development of economy and society,heavy metal contamination of farmland has become increasingly prominent and cadmium pollution is the major type,which has great effects on the sustainable development of agricultural production and the quality of human living environment?Measures such as variety screening,amendments and proper agronomic measures,are widely applied to the remediation of soils polluted by heavy metals.In order to study the safe production technology of rice in cadmium contaminated paddy soils,a field experiment was conducted to investigate the effects of rice with low accumulation and combined regulations under different contamination levels.The main results were as follows:1.Study on approaches for safety production in heavily cadmium-contaminated soil by using low cadmium accumulation rice and amendments.(1)A field experiment was conducted to assess the effects of different adding levels of sepiolite,humic acid and the combination of both on Cd concentration in rice seed and different organs.Results showed that the application of amendments could decrease the Cd contents in rice seeds.When no amendments were applied,the cadmium contents of Jia-33 and Xiu-128 were 0.215 mg·kg-1and 0.245 mg·kg-1,respectively.The former is less and both of them exceeded the national food safety standard(GB2762-2012)of 0.2 mg·kg-1.Under the treatments of sepiolite,the content of Cd in rice seeds of Jia-33 and Xiu-128,decreased by 5.58%?37.67%and 7.76%?28.98%,respectively.The contents of Cd in seeds of both Jia-33 and Xiushui-128 were less than 0.2 mg·kg-1when the addition of sepiolite was more than 0.67 kg·m-12(Treatment H2).When the treatment of sepiolite was 1.12 kg·m-2,the Cd contents of Jia-33 and Xiushui-128 could reduce to 0.139 mg·kg-1 and 0.181 mg·kg-1,respectively.Meanwhile,no significant change was found in the Cd contents in rice seeds when addition of sepiolite exceeded 1.12 kg·m-2(Treatment H3).It suggested that the optimum dosage of sepiolite was 1.12 kg·m-2,which was far less than the dosage of common varieties(2.25 kg·m-2).Under the application of combined amendments,the cadmium contents in Jia-33 rice seed were 0.145 mg·kg-1?0.196 mg·kg-1,all have reached the national safety standards,and it was declined by 8.84%?32.56%,when compared with control.The cadmium contents of Xiu-128 rice seed were 0.174 mg·kg-1?0.231 mg·kg-1,decreased by 5.71%?28.98%than control,and Z4,Z5 treatment(sepiolite 0.79 kg·m-2 +humic acid 0.26 kg·m-2,sepiolite 1.12 kg·m-2 +humic acid 0.37 kg·m-2)were under the national security standard.The optimum combined amendments dosages of Jia-33 and Xiushui-128 were Z4 and Z5,respectively.Compared with unlamented soil,humic acid treatments reduced the rice seeds Cd contents of Jia-33 and Xiushui-128 by 13.49%and 21.63%,and Cd contents in seeds were reduced to 0.186 mg·kg-1 and 0.192 mg·kg-1,respectively.Of all the treatments,the remediation of efficiency of contamination soil treated by sepiolite and combined amendments was superior to that of contaminated soil treated by humic acid.The contents of Cd in different organs of both J-33 and Xiu-128 were found in the order of root>stem>leaf.Basically,the Cd contents of stem and leaf reduced with increasing amendments,and the effects of cadmium reduction in stem and leaf of sepiolite and combined amendments are better than that of humic acid.There are significant differences among the 3 remediation,while specific law of Cd in roots with the amounts of amendments was not found.(2)The soil pH,the available Cd and the speciation transformation of cadmium were employed to explore the mechanisms of amendments in cadmium immobilization in heavily cadmium-contaminated soil.The amendments reduced the uptake of cadmium by converting it from exchangeable form to other forms and the available Cd decreased.Results showed that:Basically,the application of sepiolite and combined amendments could increase soil pH and the change of soil pH was not much.The application of sepiolite and humic acid could increase soil pH up to 2.08 and 2.32,respectively.The exchangeable,Fe-Mn oxide and residual forms were dominants soil cadmium in the tested soil.The contents of exchangeable form of Cd decreased with increasing sepiolite,humic acid and combined amendments,with maximal Cd reduction of 30.23%,17.81%and 25.44%,respectively.Under sepiolite treatments,the concentration of Fe-Mn oxide,residual form increased by 25.69%?95.58%and 53.58%?113.88%,respectively.Under humic acid treatments,the carbonate bound increased by 16.39%?54.1%.The addition of sepiolite,humic acid and combined amendments could reduce the available Cd by 31.16%?65.50%.19.53%?38.10%and 10.53%?60.99%,respectively.(3)The changes of soil nutrients were tested to invest the impacts of amendments on soil environmental quality.Significant impact on the soil alkali-hydrolyzale nitrogen of humic acid application and combined amendments was not found,while sepiolite application could decrease alkali-hydrolyzale nitrogen.All the three amendments could increase the soil available phosphorus and available potassium.Basically,the amendments would not to soil nutrient shortage and can be applied as immobilization materials.(4)In conclusion,it was possible to achieve safety production in heavy Cd-contaminated paddy soil in this area by the application of rice with low cadmium accumulation and integration with immobilization materials.The application of sepiolite and combined amendments had good effects on the cadmium reduction regulation for rice with low accumulation and the optimum dosage of amendments was far less than the common varieties.2.A field experiment was conducted to investigate the accumulation of Cd in rice seeds in moderately and slightly polluted soils.In Xiangyin county,the contents of Cd in rice seeds increased along with the soil Cd,and that the contents were significantly positively correlated with the available Cd contents.In available Cd contents,the calculated security threshold value based on the cadmium limited index of rice(GB2762-2012,0.2 mg·kg-1)for Jia-33 is 0.307 mg·kg-1 and Xiushui-128 is 0.292 mg·kg-1.3.Studies on approaches for safety production in moderately and slightly cadmium-contaminated soil by using low cadmium accumulation rice and agronomic measures.The effects of water and fertilizer management on rice seed Cd contents and yield were studied through the soil moisture management and the application of calcium magnesium phosphate.In Xinlong village(soil cadmium concentration was 0.38 mg·kg-1,under the conventional water and fertilizer management,the contents of cadmium in rice seeds of Jia-33 and Xiushui-128 were 0.181 mg·kg-1 and 0.213 mg·kg-1,respectively.That suggested low Cd-accumulating rice variety Jia-33 could achieve safety production under the conventional water and fertilizer management in this area,while Xiushui-128 could not.The Cd contents in rice seeds decreased with the application of whole season flooding and calcium magnesium phosphate,and both of Jia-33 and Xiushui-128 could meet the national food safety standard.Therefore,the rice safety production is possible through agronomic measures.4.While adjusting soil pH values and soil organic matter content by liming and application of organic manure,the contents of soil available Cd were all decreased,which was morphological transformation to lower validity of soil Cd.Thus,reduction of soil cadmium migration to rice plants and accumulation in polished rice was happened.Results of Pearson analysis revealed that Cd accumulation in polished rice were significantly negatively correlated with the soil pH and organic matter,which indicated soil pH and soil organic matter were two important factors regulating cadmium accumulation polished rice.In summary,the combination of varieties with low Cd accumulation(Jia-33 and Xiushui-128)and measures for adjusting soil pH values and organic matter contents could be an important approach to ensure safe production of polished rice in more Cd contaminated paddy field in Xiangyin county.