Behaviors Of New Herbicide HW-02 In Environments

HW-02 is an organic phosphorus herbicide invented by Institute of Pesticide Chemistry, Central China Normal University, can be used to control broad-leaved weeds in corn field and lawn. The environmental behavior of HW-02 was systemically investigated in this dissertation, including the soil adsorption of HW-02, photolysis, hydrolysis, the degradation mechanism and the effect of HW-02 on four enzymes. In addition, the analysis method for HW-02 residue in maize grain was established, and the determination of the final residue and the risk assessment of MRL were conducted. The detailed results can be seen as follows:1. Absorption of HW-02 on different types of soilThe absorption of HW-02 on five types of soil (i.e. meadow black, sandy loam, clay loam, baijiang soil and chernozem) was investigated by the method of the classical oscillation balance. The results indicated that the absorption of HW-02 on all five types of soil followed Freundlich equation. The absorption velocity was rapid. The absorption balance could be reached in 3-5 h. The absorption capability of these five soils was meadow black>sandy loam> chernozem>clay loam>baijiang soil. The absorption free energy was -22.25--28.57 (kJ/mol). This indicated that the absorption of HW-02 in soil was mainly physical adsorption. The absorption capability of HW-02 on soil was significant correlative with the content of soil organic matter, but little correlation with soil pH and cation exchange capacity was observed. All the results above showed that the absorption capability of HW-02 on these five soils was from medium to relatively strong. Contrarily, the eluviation of HW-02 in soil was from relatively weak to medium.2. Photolysis of HW-02 in different organic solventsThe photolysis of HW-02 in four organic solvents was conducted, and the photolysis velocity of HW-02 matrix compound was determined by using GC-MS. The photolytic products were separated and analyzed, too. The results indicated that the photolysis of HW-02 in all four organic solvents followed the first order kinetics. After 40 min UV illumination (1.641×10~5 lux), the photolysis velocity was n-hexane > methanol > xylene>acetone in these four organic solvents, the photolysis rate were 99.3%,72.72%, 54.4% and 42.9%,the half life were 11.72,21.74,30.27 and 39.40 min, respectively. This indicated that the photolysis velocity of HW-02 in these four organic solvents varied greatly, which was due to the different UV light adsorption in these four organic solvents. Anyhow, the photolysis of HW-02 in these four organic solvents could be conducted rapidly. Under UV light, HW-02 could be photolyzed in organic solvents and eight photolytic products were identified by GC-MS. According to the HW-02 matrix and the photolytic products, it could be seen that three different reactions occurred in the photolytic processes: (i) ester bond cleavage, (ii) dechlorination and (iii) esterification reaction. The photolysis mechanism included photo-hydrolysis, photoreduction and esterification. Additionally, the Intermediate product of photolysis could photolyze further and did not accumulate. Phosphate and carbon oxides might be the final products.3. The hydrolysis of HW-02The hydrolysis rate of HW-02 was tested by GC-MS under the condition of different buffer, temperature and water. The result indicated that the hydrolysis of HW-02 followed the first order kinetics. The half lifes were 0.40-167.99 h、0.81-4.08 h�'�5.09-6.50 h, respectively. The hydrolysis rate in buffer was enhanced with the increasing of pH value. The range was 5-400 times than control. In general conditions, HW-02 will not accumulated in water. The products of HW-02 hydrolysis indicated in different buffer were also different. The result indicated that the products were different in different buffers. The concentrations were increased with the extending of hydrolysis time. The two products were 2,4 -dichlorophenoxyacetic acid methyl ester and 2,4-dichlorophenoxy acetic acid. The hydrolysis reaction mechanism was the typical nucleophilic substitution, dued to the C-O bond cleavage and formed 2,4-dichlorophenoxy acetic acid. Since the composition of HW-02 were bridged by organophosphates and phenoxyacetate, the C-O bond cleavage could also formed 2,4-dichlorophenoxy acetic acid. The 2,4 -dichlorophenoxyacetic acid methyl ester was formed by esterification with methanol. The result also indicated that HW-02 was easier to hydrolysis and will not residue for long in aquatic environment. The influence of HW-02 to the environment was small.4. The influence of HW-02 on the enzyme activityThese studies test the enzyme activity of phosphatase, urease, catalase and invertase. After the usage of HW-02, the soil urease and catalase activity were stimulated at first and were inhibited in the end. The invertase was inhibited after useage and was stimulated after that. The phosphatase was stimulated. The inhibition rate of HW-02 on the soil enzyme was -33.41-43.95%, most of them were under 20%. The result indicated that the influence of HW-02 on soil enzyme was low.5. The residue levels and risk assessment of HW-02 in cornThe study established the analytical method of HW-02 in maize kernel. This method has the characteristics of high accuracy, good reproducibility and easier to extraction and purification. This method was tested maize kernels for two years field experiment. The result suggested that the MRL of HW-02 in maize kernel was 0.25mg/kg and the risk assessment were also done. The result was that the MRL was safe when the usage of HW-02 under the dosage of 450-900 g a.i/hm ~2.