A Study on Environmental Behaviors of 2,4-D Butylate
|School||Nanjing Agricultural College|
|Keywords||2，4-D butylate environmental behavior absorption mobibity hydrolysis photolysis soil degradation|
A study to environmental behaviors of 2,4-D butylate was aimed at elucidating 2,4-D butylate fate and potential hazards,and providing a seientifie basis for reasonable using, and evaluating environmental safety.A method for residue determination of 2,4-D butylate was developed. Via this method,environmental behavior of 2,4-D butylate was studied, such as absorption, mobibity,hydrolysis,soil degradation.An analytical method for determining 2,4-D butylate residues in water and soil by GC-ECD was described. The line equation was y=33371x-7189.8 with the linearty ranging from 0.05-10 mg-L"1, the correlation coefficient r=0.9974. The method had been validated by spiking different concentrations of 2,4-D butylate to soil and water. The result showed that the average recovery for water was 100.63%, spiked at 0.005-0.1 mg-L-1, while the coefficient of variability was 1.30%. The average recovery for soil was 102.15%, spiked at 0.01-0.1 mg-kg-1, while the coefficient of variability was 4.99%. The LOD were 0.005 mg-L-1,0.05 mg-kg-1, for water and soil samples, respectively. It indicated that the developed method could be applied for residue determination and environmental behavior of 2,4-D butylate.Hydrolysis velocity of 2,4-D butylate in different buffer solutions was in order of pH9>pH7>pH5, while hydrolysis half lives (25℃) were 10.7 min,5.8 d and 23.5 d, reseparately.2,4-D butylate,s hydrolysis was base-catalyzed hydrolysis,which indicated that the pH was a crucial factor. Temperature had a significant effect on 2,4-D butylate’s hydrolysis,which was increased with temperature increasing. The hydrolysis velocity increased 1.57 times for each temperatur increase of 10℃. There existed no obvious correlations between the activation energies of 2,4-D butylate hydrolysis and temperatures,but the activationentropy absolute values of 2,4-D butylate hydrolysis increased with the increasing temperatures in the environment. The activationentropy absolute values of 2,4-D butylate hydrolysis was negative,suggesting that hydrolysis of 2,4-D butylate in the aqueous solutions was driven by the activation entropy. The hydrolytic products of 2,4-D butylate were identified as 2,4-dichlorophenoxyacetic acid and 2,4-dichlorophenol by GC-MS, suggesting that the degradation route of 2,4-D butylate was mainly via ester bonds and aryl ether bond cleavage.There was significant difference with the photolytic rate of 2,4-D butylate in different solvents. The photolytic rate of 2,4-D butylate in n-hexane was faster than in methanol, and it would not be degraded in acetone solvent. The photolytic rate was influenced by initial concentration of 2,4-D butylate.The photolytic rate became faster when decreasing concentration of 2,4-D butylate in n-hexane, maybe because higher concentration cause competitivly absorb certain light energy, each molecule got less energy and probability of photolysising.Half lives of 2,4-D butylate in sand, loam and clay were 10.85d,8.38d and 6.94d, respectively, while in those three sterilized soils,the half lives were46.2d,27.28d and 38.93d, respectively.It indicated that soil microorganisms had s significant effect on the degradation of 2,4-D butylate in soil. The soil organic content influence degradation of 2,4-D butylate in soil through influencing microorganism sort and number.Under field environment, degradation of 2,4-D butylate in soil couldn’t followed the first order reaction well,its maybe because degradation often accompanied by hydrolysis, photolysis and volatilize, affected by light intensity, difference in temperature and some other factors.The adsorption of 2,4-D butylate in three kinds of soils were studied with batch equilibrium technique.Adsorption isotherms of 2,4-D butylate on the soils could be described well by Freundlich equation,correlation coefficent r>0.95. Adsorption isotherm of 2,4-D butylate in clay and loam exhibited L-type isotherm. However, adsorption isotherm of 2,4-D butylate in sand loam was S-type; The adsorption constant (Kd) of 2,4-D butylate in sand, loam and clay was 0.96,1.73 and 5.90 respectively, which suggested that 2,4-D butylate did’t easily been adsorbed in soils. Intense extent of 2,4-D butylate adsorbed by three soils in order to clay> loam>sand, which suggested that the soil adsorption capacities of 2,4-D butylate were positively related with the contents of soil organic matter.The amounts of the adsorption free energy (ΔG) of 2,4-D butylate on sand,loam and clay soils were 12.40 kJ-mol-1,12.18 kJ-mol-1,13.82 kJ-mol-1,respectively, (ΔG<40kJ-mol-1)which indicated that the 2,4-D butylate adsorption was dominated by physical adsorption, its adsorption mechanism could be the actions of H-band, dipolar bond, van der waals force and hydrophobic bond, while the chemical bond adsorption action was not existed.The mobility of 2,4-D butylate in three kinds of soils were studied with soil thin layer chromatography. Rf(relative flow) of 2,4-D butylate in clay, loam sand were 0.19, 0.45,0.56,respectively. The mobility of methomyl in three soils above mentioned was shown as don’t easily mobile and belonged to grade IV pesticide,middling mobile and belonged to grade III pesticide, middling mobile and belonged to gradeⅢpesticide, respectively.The transportation sequence of 2,4-D butylate in the tested soils was sand> loam> clay.2,4-D butylate move to weaken with the increas of soil organic matter content.