Degradation Behaviors Of Novel Soil Fumigant,Dimethyl Disulfide

Dimethyl disulfide(DMDS)is a new type of fumigant.It is a perfect alternative for Methyl bromide due to its high activity to soil-borne disease and no ozone-depleting potential.DMDS is a high volatility pesticide and eliminate harmful organisms by gas form.The environment conditions of soil and soil amendments affect diffusion and degradation of fumigant,which influences efficacy of fumigant futher.Therefore,definite the degradation dynamic in different condition is the scientific application DMDS to control soil-borne disease.In order to clarify the influence of the dosage of Dimethyl Disulfide on its biodegradation,we use 16S rRNA to explore the effect of different doses of Dimethyl Disulfide on the microbial diversity.The results are as follows:A simple method for the determination of DMDS residue in soil was developed by GC-MS.The results showed that DMDS extraction from soil by ethyl acetate and stirred for 1 min(2500 rpm),then static for 60 min gave the best recovery.Recovery studies were performed at five spiked levels of 5,10,100,1000 and 5000?g/kg,in three different blank soils,and the overall recoveries ranged from 70.2to 98.8%and relative standard deviations(RSD)lower than 19.1%for all analytes.The linearity was good in the range from 0.05 to 5 mg/L,and the regression equation was Y=171.92 x–13137(r~2=0.9992).The method is efficient and reliable for the determination of DMDS residue in soil.Degradation of DMDS in soil was influenced by such the factors as soil type,microorganisms,temperature,water content and DMDS addition dosage.The half-life of DMDS in soil ranged from 0.75to 7.88 d in ten different soils.Generally,DMDS degradation was significantly slower in acidic and high organic content soils.After sterilization,the degradation rate of DMDS in soil decreased significantly,and the half-life of DMDS in sterilized samples was higher than in non-sterilized samples by 4.00,20.36,17.37,1.71 and 2.73 times in Harbin,Jining,Fangshan,Shaoyang and Qujing soils,respectively,the results showed that biodegradation is the main pathway for DMDS removal in soil.The degradation rate increased with temperature and water content.However,when the temperature exceeded 35°C the degradation rate decreased with temperature,and when the soil water content rose to10%the change in DMDS degradation was not significant in Fangshan soil.The degradation of DMDS in soil depended on the initial application rate.In general,degradation slowed down as the fumigant application rate increased.DMDS degradation in soil was restrained by the addition of organic matter to soil,and the effect was enhanced by increased dosage.DMDS degradation in soil was also restrained by the use of chemical fertilizers except when amended with sodium dihydrogen phosphate and sodium thiosulfate.Bacterial diversity was affected by different treatments which affect the biodegradation of DMDS in soil.Seven out of the eight tested biochar amendments delayed the degradation of DMDS in soil,increasing the half-life of DMDS in Fangshan soil from 1.05 d to 1.16-5.87 d following amendment with 1%(w/w)biochar.The results showed that DMDS hydrolysis rates were accelerated by increases in pH and temperature.There existed no obvious correlations between the activation energies of DMDS hydrolysis and temperatures.However,the activation entropy absolute values of DMDS hydrolysis increased with increasing temperatures,suggesting that the hydrolysis of DMDS in aqueous solutions was driven by activation entropy.The hydrolysis rates of DMDS in natural water samples are as follows:rice paddy field water>Grand Canal water>tap water,and the biodegradation accounted for 21.52%,8.82%and4.08%.Our study provides a theoretical basis for developing effective DMDS application strategies and environmental assessment for achieving good soil-borne diseaes control.