Studies On The Mobility Of Roxarsone In Soil

Roxarsone is an additive added to poultry and livestock feed for resisting bacteria and coccidiosis, improving feed conversion, stimulating growth and so on. Roxarsone is excreted mostly as its parent drug in animal manure. It was excreted unchanged in the manure and introduced into enveronment when animal litter was applied to farmland as fertilizer, which may pollute soils and ground water. The mobility characters of roxarsone in soils were investigated by the thin layer chromatography of soil and the leaching experiment of soil columns for understanding the transfer of roxarsone in soil and ground water which is useful to evaluate the safety of roxarsone in environmemt.Laboratory studies using soil thin layer chromatography were conducted determine mobility of roxarsone in selected soil. The different developing solvents of water, anionic surface active agent (Cetyltrimethylammonium bromide, CTAB); anionic surface active agent (Sodium dodecylbenzene sulphonate, SDBS) and non-ionic surfactants active agent (Tween-80) were used in soil thin layer experiments. The observed Rf value of roxarsone in soil layer chromatography with water as mobile phase was 0.66. The average Rf values were from 0.63 to 0.73 in SDBS. The Rf value were from 0.61 to 0.65 in CTAB. The Rf value were from 0.68 to 0.70 in Tween-80. According to the classification of the pesticide transferability, the mobility of roxarsone is very strong. The important parameter of a surfactant to mobilize roxarsone was the critical micellar concentration(CMC). Compared with the average Rf value of roxarsone in water, the mobility of roxarsone was enhanced in CTAB with 2CMC or 1CMC concentration, whereas it was declined in 0.5CMC or 0.2CMC. The Tween-80 non-ionic surface agent increased the mobility of roxarsone in soil in every tested concentration to a certain extent. However, the positive ion surface active agent SDBS descended the transference of roxarsone in soil extent in all experimental concentration.A leaching experiment of roxarsone in soil columns was also used to evaluate its transfer potential. The soil columns were made of soils in different depth 0～20 cm, 20～50 cm and 50～80 cm. In this study transport sorption of roxarsone to various depth Grayfluvo-aquicsoils leached by water, 0.01mol/L CaCl₂, 0.01mol/L EDTA-Na₂ and water-extract of chicken manure were determined using soil column experiment. Results showed all measured breakthrough curves (BTCs) of roxarsone exhibited extent of asymmetry with sharp adsorption and slow desorption fronts leaching by water, 0.01 mol/L CaCl₂,0.01 mol/L EDTA-Na₂. Comparing the dose of roxarsone added to soil column, the leaching rate in different depth soils was 92.3～97.1% by water, 71.0～84.9% by 0.01mol/L CaCl₂, 75.4～91.2% by 0.01 mol/L EDTA-Na₂ respectively. When the water-extract of chicken manure was frist through these soil columns, the peak time of BTCs was all shortened and the content of roxarsone leached from soil was all increased, with leaching rate 96.4～110.4% by watwe, 94.5～106.8% by 0.01 mol/L CaCl₂, 90.8～103.2% by 0.01 mol/L EDTA-Na₂. It is come to a conclusion that roxarsone into soil with the manure appalication can be fastly leached into groundwater from different deapth soils, being a risk to water environment.