The Effect Of Study On Reducing Inorganic As In Rice Grain Using An Improved Si-rich Rice Husk Ash

Due to Mining of mines and smelting of ores,unreasonable use of agricultural materials such as pesticides and fertilizers,and random stacking of solid waste,a large area of soil around the world is contaminated by heavy metal As.Rice is seriously affected by soil As pollution,which is mainly because the chemical speciation of As in the paddy field that has been in flooded environment for a long time is mainly As（III）and As（III）shares transporters Lsi1 and Lsi2 with Si in rice roots.Therefore,in view of the unique characteristic that arsenite（As（III））is the main chemical speciation of As in porewater and the transporter proteins of As（III）is the same as Si,this provides a very advantageous condition for using Si to reduce the absorption and utilization of As by rice.In order to obtain rice husk ash with high Si solubility,the rice husk is burned with alcohol in our work.And,the purpose of effectively reducing the absorption and utilization of As by rice is achieved by increasing the concentration of Si in the soil solution.Firstly,chemical methods are used to explore the four Silicon forms in rice husk ash,and combined with FTIR,XRD and SEM to further reveal the internal mechanism of high Si solubility in rice husk ash.Secondly,rice husk and rice husk ash are added to long-term flooded rice pots,and the specific effects of Si on rice absorption and utilization of As are systematically analyzed and discussed through diversification of porewater chemical indicators,rice plant As/Si accumulation,soil As/Si form,soil available As/Si,and XRF fluorescence images of rice roots,nodes I and grains.Finally,rice husk ash is added to the paddy field to further explore the specific effects that rice husk ash reduce the absorption of As by rice.The main conclusions obtained are as follows:（1）Compared with rice husk,the available Si and amorphous Si concentrations in rice husk ash increased by 3.0 times and 7.7 times,respectively,which supported the release potential of Si.In addition,XRD data showed that Si in rice husk ash is mainly amorphous Si O₂;FTIR data shows that the Si-O-Si stretching vibration peak of rice husk ash is stronger,and aromatic C with low solubility is observed in rice husk ash;SEM data shows that there is a structure of Si wrapped C in rice husk ash.The above results show that open burning not only improves the availability of Si in rice husk ash,but also makes C solidify in the soil.（2）Compared with the control,the Si-rich treatment increased the available Si in the rhizosphere soil of rice by 40.3-49.1%,and the available As also increased by 33.3-35.3%,which indicated that the Si-rich treatment not only improves the bioavailability of Si in the rhizosphere of rice,but also improves the bioavailability of As.In addition,compared with the control,the rice husk ash treatment reduced the Fe on Fe plaque by 24.1%,but increased the concentration of As on Fe plaque by 26.9%,which indicated that rice husk ash treatment increased the retention efficiency of As by root plaque-Fe,thereby reducing the transport of As to the above-ground tissues.（3）XRF data shows that,in rice roots,the highest fluorescence intensity of As does not have a strong correlation with the highest fluorescence intensity of Fe,while the fluorescence intensity of Si has a strong correlation with the fluorescence intensity of Fe;at node I,the fluorescence intensity between As and Si are negatively correlated,which indicates that Si can effectively reduce the accumulation of As in rice;in brown rice,S,Fe,and Zn are distributed in the aleurone layer,which may indicate that the concentration of S,Fe and Zn will be reduced in the grains rice grains due to polishing to remove the aleurone layer.（4）Compared with the control,the Si-rich treatment reduced the inorganic arsenic（As_i）concentration in the grain by 31.0-54.0%,and the rice husk ash made the As_iof the grain lower than the national food safety standard（0.2 mg/kg）.At the same time,the Si-rich treatment did not have a serious negative effect on the intake of nutrient elements.（5）In the field experiment,compared with the control,the silicon fertilizer and rice husk ash treatments increased the available Si in the rhizosphere soil of rice by 28.1-33.1%,which indicated that the Si-rich treatment increased the bioavailability of Si.At the same time,compared with the control,the non-specifically adsorbed-As and the specifically adsorbed-As increased by 23.8-28.1%and 8.1-10.6%,respectively,while the crystalline hydrous Fe/Al oxide-bound As is reduced by44.3-52.2%,which indicates that As is converted to bioavailable state,thereby increasing the bioavailability of As.In addition,compared with the control,the silicon fertilizer and rice husk ash treatments increased the As concentration in white roots by 11.6-51.6%,while the As concentration in straw and rice husks decreased by 2.0-25.4%and38.9-56.0%,and rice husk ash treatment reduced the transfer coefficient _{straw/white root}from 0.02 to 0.01,which indicated that the retention ability of white root on As was enhanced and the migration and transport of As to the aboveground tissues of rice was inhibited.（6）In the field experiment,compared with the control,the rice husk ash treatment reduced the As_iconcentration in rice grains by 33.9%compared with the control,and was lower than the national food safety standard（0.2 mg/kg）,while the silicon fertilizer treatment increased the grain As_iby 29.7%,which indicated that the treatment effect of rice husk ash is better than that of silicon fertilizer.