Sorption-Desorption And Degradation Of Dufulin In Soils

Dufulin is a novel antiviral agent which was discovered and developed by the Research and Development Center for Fine Chemicals of Guizhou University. It has been widely used to prevent and control viral diseases in tobacco, cucumbers, tomatoes and rice. Dufulin has brought great benefits to crop production. Therefore, in order to assess correctly the environmental safety and provide guidance on the reasonable application of Dufulin, it is essential to research the sorption-desorption and degradation of this new virus inhibitor in soils.A method for determining Dufulin residues in soil, water and wheat by HPLC-UVD was developed. Soil sample was extracted ultrasonically with aceton-water, cleaned up by the liquid-liquid extraction and the column filled with the silica gel; wheat sample was extracted ultrasonically with petroleum ether and then purified by the column with the silica gel; water sample was directly purified and collected by solid-phase extraction (SPE). The calibration curve was linear in the range of 0.05～20.00 mg L-1, with the correlation coefficient of 0.9996. The spiked recoveries of Dufulin in soil sample ranged from 91.5% to 99.7%, the wheat sample from 91.5% to 105.7% and the water sample from 94.7% to 106.1%, respectively. The relative standard deviations in soil, wheat and water samples were from 1.1% to 4.5%,1.1% to 6.4% and 1.3% to 7.0%, respectively. The limits of detection for soil, wheat and water samples were 0.013mg kg-1,0.013mg kg-1 and 0.007mg L-1.The sorption-desorption characteristics of Dufulin in the three kinds of soils (Eutric Gleysols, Cumulic Anthrosols and Dystric Regosols were collected from Nanjing, Guiyang and Yingtan) were investigated by using the standard batch equilibration method. The correlation coefficients for the three soils (R2> 0.98) have shown that all sorption-desorption isotherms were fitted in well with Freundlich equation. The adsorption coefficients (Kf) of Dufulin in Eutric Gleysols, Cumulic Anthrosols and Dystric Regosols were 13.71,10.40 and 7.98, respectively. The adsorption ability of soils to Dufulin was regarded as follows:Eutric Gleysols> Cumulic Anthrosols> Dystric Regosols, suggesting that the soil adsorption capacities of Dufulin were positively related with the content of organic matter. The values of Kf in the desorption isotherms were observed following the same order. Adsorption free energy (AG) of Dufulin in three soils was all less than 40 kJ mol-1, indicating that the adsorption largely resulted from the physical adsorption involving in hydrogen bond, hydrophobic bond, dipolar bond and van der waals force.HPLC and LC-MS were used to study the degradation behavior of Dufulin in three soils. Furthermore, influence factors and degradation products were analyzed in Eutric Gleysols. The results showed that degradation of Dufulin was fastest in Eutric Gleysols (DT50=17.59 d) and slowest in Dystric Regosols (DT50=43.32 d). The elevated moisture accelerated the decay of Dufulin in soil. The degradation rate of Dufulin increased slightly with the initial concentration from 1.0 to 5.0 mg kg-1 and the DT50 reduced from 21.87 to 17.33 d. But the dosage of Dufulin between 5.0 and 20.0 mg kg-1 had no significant influence on the rate of degradation. Degradation of Dufulin increased obviously with temperature between 15 and 25℃. However,25～35℃ were supposed to be the optimal temperature because there was only a small change of DT50 for Dufulin at 25 and 35℃. The values of DT50 in sterilized and SOM-free soils were 108.30 and 150.68 d, respectively. They were far more than that in control soil, suggesting that Dufulin degradation was largely governed by microbial process and the organic matter in soil could promote the decay of Dufulin. Photodegradation was an effective way of Dufulin degradation. Under different light sources, the most effective degradation occurred with 100 W UV light, followed by 15 W UV light and Xenon light. Analysis by LC-MS revealed that 2-amino-4-methylbenzothiazole was one of the major decayed products of Dufulin in soils, suggesting that elimination of diethyl phosphate and 2-fluorobenzaldehyde was most like the degradation pathway of Dufulin in Eutric Gleysols.