The Degradation, Adsorption And Leaching Of Ethiprole In Soil

In this paper, the degradation, adsorption—desorption, leaching behaviors of ethiprole wereinvestigated in five agricultural soil samples from China And the photochemical degradation behaviorsof ethiprole was studied in different aqueous solution.The effect of surfactants and commercial humicacid on the fate of ethiprole in soil was also been evaluated. The main results are described as followed:1. Ethiprole is a moderate persistent pesticide and had potential environmental risk afterapplication to soil. Soil pH value had a negative significantly effect on ethiprole degradation underaerobic condition while clay%had some positive effect on ethiprole degradation under anaerobicconditions. Under xenon simulated sunlight, ethiprole was relatively stable under both acidic andneutral conditions, while it was readily hydrolyzed under alkaline condition. The half-lives of ethiprolein the water from rice field was shorter than that in the water from reservoir and much shorter than thatof in CaCl2solution.2. The adsorption—desorption behaviors of ethiprole in five cultivated soils was performed by thebatch equilibrium method, using solutions of0.01MCaCl2or different surfactants (cetyltrimethylAmmonium Bromide, sodium dodecyl benzene sulfonate,tween80) or adding different commercialhumic acid (biochemical fulvic acid, coal humus acid). The adsorption—desorption isotherms were welldescribed by the linear and freundlich equation. The absorption behavor was significantly positivecorrelated with the soil organic matter content and soil pH value, though the effect of soil pH was muchlower than that of organic matter. The ethiprole adsorption in soils was a spontaneous exothermicprocess and can be well explained by physical adsorption and meanwhile, it showed some degree ofirreversible process. Red soil and meadow solonchak had the higher hysteresis effect while fluvo-aquicsoils had the lowest hysteresis effect. The pH of the soil solution had little effect on theadsorption-desorption of ethiprole. For the low organic carbon adsorption constant (Koc<200), ethiprolecould readily lead to leaching problems. The coal humus acid (solid state organic matter) significantlyenhanced the sorption of ethiprole in soils (red soil, fluvo-aquic soil). The sorption of ethiprole in thesoils was slightly enhanced by the biochemical fulvic acid (soluble organic matter) when its amountbelow2%. With the amount of biochemical fulvic acid increasing, the sorption of ethiprole in the soilsshowed a decreasing trend. Application of tween80, sodium dodecyl benzene sulfonate andcetyltrimethyl ammonium bromide at the concentration below400mg/kg to soils increased the sorptionof ethiprole. The effect of surfactant on ethiprole absorption in soils was in the range of cetyltrimethylammonium bromide> sodium dodecyl benzene sulfonate> tween80. With the amount of surfactantincreasing, the effect of surfactant on ethiprole absorption was gradually weakened. When the amountof surfactants was higher than800mg/kg, the sorption of ethiprole in the three soils (black soil, red soil,fluvo-aquic soil) showed a decreasing trend.3. Effects of different surfactants (cetyltrimethyl ammonium bromide, sodium dodecyl benzenesulfonate, tween80) and different commercial humic acid (biochemical fulvic acid, coal humus acid) on ethiprole mobility were studied using approaches of soil thin-layer chromatography. Soil organic mattercontent had a significant negative effect on ethiprole mobility. According to the classification of thepesticide transferability in china, the mobility of ethiprole in red soil was very strong and it hadpotential to leaching. Study indicated that coal humus acid were quite effective in reducing the mobilityof ethiprole in the thin layer of soils (red soil,. fluvo-aquic soil) while biochemical fulvic acid had littleeffect on the mobility of ethiprole in the thin layer of soils. All the surfactants showed little effect on themobility of ethiprole in the thin layer of soils. Coal humus acid played a significant role in control ofleaching losses of ethiprole while biochemical fulvic acid enhanced the leaching losses of ethiprolefrom soil column. Cetyltrimethyl ammonium bromide slightly decrease the leached amount of ethiprolewhile sodium dodecyl benzene sulfonate and tween80showed little or no effect on the leaching lossesof ethiprole from soil column. In soils amended with coal humus acid, ethiprole mainly remained in theupper layer (0～5cm) of soil column. Biochemical fulvic acid and surfactants also changed thedistribution of ethiprole in the soil profile. This study contributes to the general understanding of thefate of ethiprole in agricultural the soils of China, which was essential to prevent its permeation fromthe surface to the groundwater and its negative effects on non-target organisms. The characteristic ofsoil have the same effect on the fate of ethiprole in soil when using batch equilibrium method, soilthin-layer chromatography or soil column.