Mobility And Bioavailability To Weeds Of Acetochlor In Soils

Acetochlor is a selective soil-treating herbicide.Because of its high herbicidal activity after soil treatment and a moderate effective period,the application area of acetochlor is expanding in China.However,excessive application of acetochlor also contributes to a series of environmental problems that threatening soil,water,crops,animals and humans.Therefore,in order to reduce the occurrence of phytotoxicity and acetochlor resistance of crops and protect the ecological environment,the adsorption/desorption and migration behavior of acetochlor in three soils including yellow-brown soil(NJ),fluvo-aquic soil(YC)and red soil(YT),and the bioavailability of acetochlor in soil to four weeds commonly found in fields were studied.The adsorption/desorption behavior of acetochlor in three soils from Nanjing(yellow-brown soil),Yancheng(fluvo-aquic soil),and Yingtan(red soil)was studied.The adsorption dynamics of acetochlor in yellow-brown soil was determined by batch equilibrium experiment.The experiment was carried out at 25 ±1℃.The concentration of acetochlor in 0.01 mol/L of CaCl2 aqueous solution was 16 mg/L,the ratio of soil to water was 1:5.The time for acetochlor to reach adsorption equilibrium in the soil was 24 h.Then,under the same temperature and soil-water ratio conditions,the adsorption test was carried out with the 0.01 mol/L CaCl2 aqueous solution of acetochlor at a concentration of 0.5,1.0,2.0,4.0,8.0,and 16.0 mg/L.It indicated that the adsorption and desorption processes of acetochlor in the three soils were consistent with the Freundlich isotherm,R2 was between 0.9813～0.9925,and the adsorption coefficient Kf(mL/g)was between 1.04～1.57.In order,it was yellow-brown soil,fluvo-aquic soil and red soil from large to small.The slope 1/n was between 0.4938～0.9462,indicating that the adsorption of acetochlor in the soil was nonlinear.The desorption coefficient Kf(mL/g)of acetochlor in the desorption process of three soils was between 2.08～2.42.It was the same order to the absorption processes.For the same soil,the desorption coefficient was greater than the adsorption coefficient,which indicated that the desorption of acetochlor in the soil had a hysteresis effect.Once acetochlor was absorbed by the soil,it was not easy to be desorbed into the soil solution.The migration behavior of acetochlor in three soils was studied by soil thin layer chromatography and soil column leaching.The Rf of acetochlor in yellow-brown soil,fluvo-aquic soil and red soil were 0.35±0.01,0.64±0.01 and 0.77±0.04,respectively.The results of soil column leaching experiments showed that the peak shape of the penetration curve of acetochlor in red soil was relatively symmetrical and reached the peak first.The peak shape of yellow-brown soil had a tailing phenomenon and finally reached the peak.It can be seen that the mobility of acetochlor in red soil was the strongest and the mobility of acetochlor in yellow-brown soil was the weakest.The bioavailability of acetochlor in soil to four weeds was studied.The barnyard grass exposed to the concentration of 0～0.20 mg/kg acetochlor in soil,and the growth of the barnyard grass was strongly inhibited cultured at the concentrations of 0.10 and 0.20 mg/kg.The two concentrations were selected for the same culture for 20 days.The growth of barnyard grass at 0.10 mg/kg was inhibited,while the barnyard grass cultured at 0.20 mg/kg died.A residue detection method for acetochlor in barnyard grass was also established The accumulation of acetochlor in the barnyard grass at 0.10 and 0.20 mg/kg was measured at the 15 days of culture.The results showed that the latter was 2.19 times as high as the former.Chloris virgata Sw.exposed to acetochlor at a concentration of 0-0.16 mg/kg.There was the strongest inhibitory effect when cultured at concentrations of 0.08 and 0.16 mg/kg.The two concentrations were selected for the same culture for 20 days.The growth of chloris virgata Sw.at 0.08 mg/kg was inhibited,while the chloris virgata Sw.cultured at 0.16 mg/kg died.The amaranthus exposed to acetochlor at a concentration of 0～0.16 mg/kg.There was the strongest inhibitory effect when cultured at concentrations of 0.08 and 0.16 mg/kg.The two concentrations were selected for the same culture for 5 days.The growth of amaranthus at 0.08 mg/kg was inhibited,and the amaranthus cultured at 0.16 mg/kg died.The chenopodium glaucum L.exposed to acetochlor at a concentration of 0～0.40 mg/kg.There was the strongest inhibitory effect when grown at the concentrations of 0.20,0.30 and 0.40 mg/kg.The three concentrations were selected for the same culture.After 10 days,the chenopodium glaucum L.died which cultured at a concentration of 0.40 mg/kg.After 20 days of culture,the growth of chenopodium glaucum L.at 0.20 mg/kg was inhibited,and the chenopodium glaucum L.at 0.30 mg/kg died.At the same time,the acetochlor residue in the soil was also determined.It was found that the planting of weeds had no significant effect on the residue of acetochlor in soil.It was indicated that the main part of of acetochlor degradation in soil was natural degradation.