Effects Of Silicon Application Rates On The Accumulation Of Arsenic In Rice-Wheat Rotation System

In recent years,arsenic（As）pollution in farmland soil has attracted more attention in China,especially the environmental behavior of arsenic in paddy soil.Arsenite mainly exists in the flooded soil.Silicate acid and arsenite acid share the same transporters due to their similar molecular radius and PKa.Therefore,silicon（Si）application in soil can inhibit the uptake of arsenic by rice,and the suitable silicon application amount of arsenic polluted soil in different degrees needs to be further explored.Moreover,it is not clear whether Si application during rice growing season affect the accumulation of arsenic in edible parts of wheat in the rotation system of rice-wheat,which will pose a threat to human health via food chain?Therefore,in the rice-wheat rotation system,the experiments were conducted to explore the effects of silicon application rates in light,moderate and heavy As-contaminated soils on the accumulation of arsenic in rice-wheat rotation system.Furthermore,it was clarified whether Si application rates in rice season controlled the accumulation of As in edible parts of rice and wheat.Finally,the assessment of health risks of arsenic accumulation in edible parts of rice and wheat had been carried out.The results might provide the feasible pathway to reduce As accumulation in crops and grantee food safety in arsenic contaminated areas rice-wheat rotation system.The main results are as follows:（1）It was certified that effects of Si application rates（25,50,100 mg SiO₂/kg）in lightly,moderately and heavily arsenic-contaminated soil on arsenic accumulation in rice.In the lightly arsenic contaminated soil,100 mg SiO₂/kg significantly promoted the rice growth and development（p<0.05）,especially increased grain dry weigh by 38.6%,and the inorganic arsenic content in rice bran was decreased,but the difference was not significant.In the moderately As-contaminated soil,the dry weight of rice grains increased by 32.6%and 47.9%with silicon application of 50 and 100 mg/kg（p<0.05）,respectively.In heavily As contaminated soil,Si reduceed the effective tiller numbers,inhibited the growth of rice,and increased the inorganic arsenic in brown rice,rice bran,rice,polished rice.The silicon application of 50 mg/kg significantly increased the inorganic arsenic levels in brown rice and rice bran（p<0.05）,accounting for 106.0%and 33.9%,and 100 mg SiO₂/kg significantly increased the concentrations of inorganic arsenic in rice,brown rice and white rice（p<0.05）,accounting for 48.8%and 52.5%.The inorganic arsenic in rice bran from the three As-contaminated soils exceeded the safety limit of inorganic arsenic in food safety in China.（2）In the rice-wheat rotation system,the effect of residual effect of silicon application in rice season on arsenic accumulation in wheat in the second season was clarified.In lightly As-contaminated soil,Si application in rice season still reduced the accumulation of arsenic in wheat grain.the application rates of 25 mg SiO₂/kg and 100 mg SiO₂/kg reduced the levels of arsenic in whole wheat,wheat bran,and wheat flour by 47.1%and 21.8%,62.2%and 26.0%,53.0%and 29.5%,respectively.In the moderately and heavily arsenic contaminated soil,the Si application in rice season increased the cumulation of arsenic in wheat edible parts.In addition,the arsenic concentrations of wheat bran exceeded the safety limit of wheat total arsenic in China’s national food safety standard.（3）The health risk of inorganic As in brown rice and wheat grain has assessed in the rice-wheat rotation system.In the three arsenic-contaminated soils,the daily inorganic arsenic intake of inorganic arsenic from whole wheat and brown rice by adults and children was associated with health risks,and children were higher than adults.In the lightly and moderately As-contaminated soil,the risk of inorganic arsenic intake from whole wheat was higher for adults and children than that from brown rice.In heavily arsenic-contaminated soils,the risk of inorganic arsenic intake in brown rice was gradually higher than that in whole wheat with the increase of silicon application.The risk of arsenic accumulation in wheat grains to human health should not be ignored.In summary,it would be better to apply 225 kg SiO₂/hm² in lightly As-contaminated paddy field with irrigation to promote rice growing and reduce As accumulation in edible parts of rice and wheat in the rice-wheat rotation system,however,silicon application could not be recommended for rice in moderately and severely arsenic-contaminated soil.