Impact of Biochars on the Bioavailability and Enviornmental Fate of Oxyfluorefen
Supervisor:zheng yong quan
As representative of diphenyl ether herbicides,which is widely used in the whole world,oxyfluorefen has been massive and persistent used to control the growth of broadleaf weeds causing potential adverse impacts on sensitive crops and organisms even at a low environmental residue due to its high activity and selectivity.It may seriously increase the health risks and ecological safety problems.However,oxyfluorfen could be easily into soil during using in agroforestry,so it is critical to select proper method to control pollution.As a new material for soil remediation and pollution control,biochar is widely used to absorb pollutants to remediate soil.Moreover,its impact is significant difference,due to its different raw materials and preparation methods.Therefore,this paper comprehensively considered the different properties of soil and biochar,and aging time impact biochar,systematically studied the impacts of oxyfluorfen on adsorption,disspation,microogranism and bioavailability in the soil environment.The main results are as follows:(1)Prepare different biomass raw materials(rice hull,mazie,peanut,chestmut,bamboo)and pyrolysis temperature(300,500,700℃)biochar,and characterize the physical and chemical properties and surface structure of biochar.The results show that because of the difference of pH,elemtary content,surface area and ash content,the physical and chemical properties of the biochar are significant differences.Result also indicate that biochar’s surface ash content,specific surface area and C content increased with increase of temperature;however,O and H content,and the ratio of H/C,O/C,(O+N)/C shows the decrease with increase of temperature.The surface of biochar treated with acid shows more pore structure,while the property of biochar treated with H2O2 is similar to that of natural aging.The surface chemical treatment with H2O2 can effectively simulate the state of natural aging.(2)Through the adsorption isothermal experiments of five kinds of biochar,the results indicate that the adsorption capacity of biochar under same temperature(Kf value)is from 481 to 4125(μg/g)/(mg/L)n.The order of adsorption capacity of the five biochar from large to small as follow: rice hull biochar(BCR)>bamboo biochar(BCB)>mazie straw biochar(BCM)>chestnut biochar(BCC)>peanut biochar(BCP).With increase of temperature from 300 to 700 oC for BCR,the Kf value increase from 4125 to 7120(μg/g)/(mg/L)n.Combined with the characterization structure of biochar,SSA,ration of elementary(O/C,H/C,(O+N)/C)and functional group,adsorption of oxyfluorfen is mainly affected by pore size filling,hydrophobic distribution and π-π interaction.(3)After addition of biochar,the pH,organic content and TN of soil are increase,and the adsorption capcity of three-type soil are increase.The results showed that the adsorption capacity of the three soils without biochar was from small to large,namely,red soil,chao soil and black soil.Moreover,after the addition of biochar(0.5~2%),the adsorption capacity(Kf)of oxyfluorfen was significantly improved 1.4~3.2-time.Moreover,the Kf decrease with aging time,however,after aging for 6 months,the adsorption capacity of rice hull biochar was still 1.5~2.5 times compared with control(without biochar).Therefore,the structure feature and the properties of biochar and soil and aging effects of biochar determined the sorption mechanisms(4)After addition five biochar,the disspation rates of oxyfluorfen accelerate after the addition of BCR-500.Addition different ratio of biochar(0~2% w/w)in the three soils,the DT50 of three soils decrease from 45~108d to 35~77d,the degradation rates are increase with quantity of biochar.Through the experiments of sterilization degradation conditions,for HNS the after addition of BC remove rate increase from 29% to 35%,and DT50 decrease from 192 d to 176 d after addition of 2% BCR,it shows that both chemical and biological degradation are involved.Through addition of salicylic acidand adjust pH of biochar suspension,leaching suspension,and ash suspension,the impact of biochar on the chemical degradation of oxyfluorfen by biochar could be through pH of soil,dissolve metal ion,surface active indigrent and generation of free radicals(5)Using Illumina Miseq high-throughput sequencing to analyze the changes of soil microbial community composition and structure under the application of 2% rice hull biochar.The results showe that when the soil was treated with 10 times of the recommended dose of oxyflurofen,the bacterial community diversity is inhibited,and the soil microbial community recovered relatively quickly after the improvement and repair treatment by adding biochar,which may even stimulate the microbial abundance and diversity.PCo A analysis indicate that the treatment with oxyflurofen had a significant effect on the bacterial community structure within 90 days.Although the treatment with 2% rice hull biochar had an impact on the community structure during the first 60 d,at the end of the 90 d test,the bacterial community structure slowly recovered and tended to the CK control level.LEf Se analysis find that the emergence and abundance change of Rhodococcus,Mycobacterium,Sphingomonas,Pseudomonas in the biochar restoration soil system verify that BCR-500 accelerated the degradation of oxyflurofen by microorganisms in the soil to some extent,but further research and discussion are needed.(6)The studies of bioavailablilty of soybean,maize,and earthworm,BCR-500 is added in three type soils.After addition of biochar,the cotent of oxyfluorfen in soybean and earthworm is significant decrease,and increase of addition(0.5~2%)of biochar,the content is decrease by 20% and 63%.The content of soybean root was significantly lower than that of stem due to the different functions of plant tissues and organs.Biochar adsorption capacity decreased with aging time,and the amount of oxyfluorfen accumulated in plants and earthworm is decrease.However,the accumulation amount of plants in the biochar-soil remediation system was still lower than that without biochar even after aging 6 months.Tenax is used to evaluate bioavailability of soybean and earthworm,the oxyfluorfen in Tenax and soybean and earthworm is good correlation,even after aging,the oxyfluorfen in Tenax and soybean and earthworm are also good correlation(R2=0.8013 and 0.9476).Therefore,Tenax could well predict bioavailability of soybean and earthworm.To further study the impact of biochar addition on subsequent crops,after addition of biochar,the height and biomass are 9.73 and 21.8 time copmpared with control group.To sum up,addition of BCR-500 could effectively reduce the bioavailability,and alleviate the side-effects for crops.