Reactivity Of Different Modified Biochar Characteristics And Its Effect On The Mercury Accumulation Of Rice

Mercury(Hg)is a global environmental pollutant.Various forms of mercury are highly toxic,and organic mercury is generally more toxic than inorganic mercury.in particular,Methyl mercury(MeHg)has strong bioaccumulation and biological amplification effect,which can cause serious impact on human health through the food chain.Previous studies have found that the harm of MeHg mainly comes from the aquatic food chain.However,recent studies have found that rice has a strong ability to enrich MeHg,and rice consumption has become an important source of human MeHg exposure.Therefore,how to reduce the methylation of mercury in rice fields and reduce the bioaccumlation of MeHg in rice grains has become an important practical problem to be solved urgently.Recent studies have confirmed that the addition of biochar can effectively reduce mercury methylation in rice fields and MeHg enrichment in rice.However,the amount of biochar used in these studies is very large and the cost is high,which makes it difficult to be applied in practice.Considering that the modified biochar not only changes the structural characteristics of biochar,but also enriches the functional groups and improves the adsorption performance.It is worth studying whether adding a small amount of modified biochar with controllable cost can reduce the methylation of mercury in rice fields and the content of MeHg in grains.Preparation for this,this study first six kinds of functional groups of modified biochar(amino,ethoxy,epoxy,sulfhydryl,chitosan and selenium,respectively),using SEM,BER/BJH,FTIR,TGA and three-dimensional fluorescence technique characterization and analysis of the characteristics on the basis of reactivity,again through the rice pot experiment,the different modified biochar on rice is studied the influence of mercury enrichment,and analyzed the characteristics and reactivity of modified biochar rice correlation of mercury enrichment,purpose is to seek economic and efficient rice materials provide the basis for production safety.Specific research results are as follows:(1)The UV spectra and 3D fluorescence spectra of modified biochar DOM and unmodified biochar DOM are significantly different.Compared with unmodified biochar,the biodegradation ability of modified biochar DOM was improved,and the electronic supply capacity(EDC)was significantly decreased(P<0.05),but the photodegradation ability of modified biochar DOM was not significantly different.In addition,two optical indexes(SUVA254 and S275-295)were significantly correlated with the biodegradability and EDC of DOMBC(p<0.05).More importantly,it was observed that the color change and biogeochemical activity of DOMBC were mainly dominated by aromatability,so SUVA254 can be used as a basic index to evaluate the biogeochemical activity of DOMBC.More importantly,it was observed that SUVA254 was the main factor affecting the color variation of DOMBC(a355),so the optical characteristics of DOMBC could be used as a basic indicator to evaluate its biogeochemical activity.(2)In pot experiments,biochar(especially modified biochar)significantly reduced the content of MeHg in soil and rice tissues compared with blank control group(p<0.05).In addition,there were significant differences in the effect of different modified biochar treatments on the levels of MeHg in soil and rice plants(p<0.05).Selenium-modified biochar had the most significant effects on inhibiting MeHg production in soil and reducing the uptake of MeHg in rice grains by 86.69%and 85.78%,respectively.The second was chitosan modified biochar,which decreased by 63.02%and 75.75%,respectively.Therefore,among the six functional group modified biochar,selenium modified biochar and chitosan modified biochar were selected for remediation of mercury pollution in rice fields in this study.(3)Rice plants transfer MeHg in a similar way to the absorption of nutrients such as inorganic salts and water,first taking up MeHg from the soil through the roots and then to the above-ground parts of the grain,stem and leaf,respectively.The distribution of MeHg content in the tissues of rice plant was as follows:rice grain>rice husk>root>stem>leaves.The trend of leaf change as follows:new leaves>up leaves>middle leaves>old leaves.Therefore,the grain is the main part of rice plant to uptake MeHg,and the percentage of MeHg in THg is significantly higher than other tissues(p<0.05),and the range is 79.44%-97.41%,that is,the grain has the strongest biological ability to enrich MeHg,and MeHg is the main form of the grain to enrich mercury.However,the distribution of THg in rice tissues was different from that of MeHg,the trend was as follows:root>rice grain>rice husk>stem>leaves,so the root was the main site of Hg enrichment.(4)Hg in soil and pore water was the main source of Hg in rice plants,and soil MeHg content was slightly positively correlated with grain MeHg content,which could be used as a basic parameter to evaluate and predict grain MeHg content.Soil and grain MeHg content was correlated with biochar DOM,and was significantly positively correlated with CDOM content(a355)and aromatics(SUVA254),but was not significantly positively correlated with S275-295.