Adsorption and Its Mechanisms of Novel Insecticide HNPC-A9908 on Clay Minerals and Humic Acids

OU Xiao-ming1, LUO Ling2, WANG Xiao-guang1, FAN De-fang3 (1. Hunan Branch of National Pesticide R&D South Center, Hunan Research Institute of Chemical Industry, Changsha 410007, China; 2. Changsha Environmental Protection College, Changsha 410004, China; 3. Institute of Pesticide & Environmental Toxicology, Zhejiang University, Hangzhou 310029, China)

oxime insecticide; HNPC-A9908; clay mineral; humic acid; adsorption and mechanism

HNPC-A9908 [O- (3-phenoxybenzyl)- 2-methylthio- 1-(4-chlorophenyl) propyl ketone oxime] is a novel oxime insecticide that is discovered and developed by Hunan Branch of the National Pesticide R & D South Center. It can be used to control effectively various pest insects such as imported cabbageworm Pieris rapae, rice leafhopper Nephotettix cincticeps, oriental armyworm Mythimna separata, tea tussock moth Euproctis pseudoconspersa, tea geometer Ectropis oblique, tea green leafhopper Empoasca spp, etc on vegetable, rice, tea and other crops. Adsorption and its mechanisms of HNPC-A9908 on clay, humic acid and their complexes in the laboratory using batch equilibrium. Adsorption isotherm of HNPC-A9908 on the Ca-saturated montmorillonite (Ca-Clay) was S-type, the adsorption active site of HNPC-A9908 on the clay surface decreased gradually with the concentration increasing of HNPC-A9908, and finally reached a plateau level. However, adsorption of HNPC-A9908 on humic acid exhibited L-type isotherm, suggesting that the humic acids have a great affinity to HNPC-A9908. Adsorption of HNPC-A9908 on clay and humic acids fitted Freundlich equation very well, and under the same conditions, adsorption coefficient KF of HNPC-A9908 on Ca-Clay was 5.45 times of that on humic acids. The IR chromatograph of Ca-Clay and HNPC-A9908 complexes showed that there existed some absorbance peaks of HNPC-A9908, and the major characteristic of absorbance peaks, such as sites, shapes and intensity, also changed, demonstrating that hydrogen bonding and coordination formed between HNPC-A9908 and Ca-Clay. Meanwhile, there also appeared the similar results in the humic acids and HNPC-A9908 complexes. The binary complexes of Ca-Clay and humic acids could reduce obviously the adsorption amount of HNPC-A9908 on Ca-Clay and humic acids, but adsorption amount varied with ratios of Ca-Clay and humic acids, the lowest adsorption of HNPC-A9908 appeared at 50∶50 complex of Ca-Clay and humic acids. There appeared a different adsorption of HNPC-A9908 on the complexes that formed at different times. Adsorption amount of HNPC-A9908 on the complexes decreased gradually with prolonging action time of Ca-Clay and humic acids. When the action time of the complexes went on, the adsorption amount began to increase and reached the maximum at 21 d, after that, it decreased, close to the initial level at 28 d.