Degradation Of Thiamethoxam And Acetamiprid In Aqueous Solution By Ozonation

The neonicotinoid insecticide has been widely used in agriculture replacing the traditional insecticides such as organophosphorus insecticide, organochlorine insecticide, carbamic acid ester insecticide with high toxicity, high remain and great damage to environment since its publication because of its advantages such as high activity, good safety and broad insecticidal spectrum. Thiamethoxam （THIA） and acetamiprid （ACE）, as the outstanding ones, have occupied a larger share in the market. These two neonicotinoid insecticides mainly fount on the normal conduction in central nervous system so that kill the insects. However, more and more waste water will be generated during the using process; besides, the solubility of thiamethoxam and acetamiprid are relatively high, thus these waste water are hazardous and difficult to be biodegraded, and damage to the environment even threat the health of human and animals, therefore to seek effective and economy methods to deal with the waste water containing thiamethoxam and acetamiprid is imperative.Ozone （O₃）, as a strong oxidant with the properties of high efficiency, safety and without secondary pollution, can generate ·OH who has stronger oxidability and has been more and more widely used in the waste water treatment. Studies about ozonation degradation of thiamethoxam and acetamiprid have been reported, while the researches of the reaction mechanism and toxicity changes were rare. In this paper, we conducted the ozonation degradation of thiamethoxam and acetamiprid, expecting to provide scientific theoretical basis and technical guidance for the degradation of thiamethoxam, acetamiprid and any other similar neonicotinoid insecticide, the results are as follows:（1） The primary influencing factors including the pH, the initial thiamethoxam concentration, the ozone concentration and the temperature during the ozonation degradation of water containing thiamethoxam were studied. When pH was increased from 3 to 11, the removal percentage was firstly increased then decreased, and the optimal condition was obtained when pH was 9; within the experimental scope, the removal percentage was increased with the increase of ozone concentration and temperature, but decreased with the increased of initial thiamethoxam concentration. Under the condition that pH was 9, the initial thiamethoxam concentration was 150 mg·L-1, the ozone concentration was 17.8 mg·L-1, and the temperature was 308 K, the removal percentage researched 86.78% after 90-min ozonation degradation.（2） The kinetics of ozonation degradation of thiamethoxam was investigated. The ozonation degradation of thiamethoxam follows pseudo-first-order kinetics under the experimental conditions, and the kinetics models are as following:（3） The intermediates generated during the ozonation degradation of thiamethoxam and acetamiprid were characterized using HPLC-MS and GC-MS, and four and six of them were separated and identified, according to which, the probable ozonation degradation mechanisms were presumed.（4） The toxicity changes of the samples taken during the ozonation degradation of thiamethoxam and acetamiprid were assessed via measuring the inhibition rate of samples to the photobacteria phosphoreum T3 spp, and the mineralization degree was assessed via measuring the change of chemical oxygen demand （COD）. When the initial thiamethoxam concentration was 200 mg·L-1, the relative inhibition rate decreased from 69.19% to 10.58%, and the UV245 and COD decreased to 16.7% and 24.06% respectively after 180-min ozonation; when the initial acetamiprid concentration was 100 mg·L-1, the relative inhibition rate decreased from 86.13% to 19.3%, and the UV245 and COD decreased to 10.05% and 47.6% respectively. Thus, ozonation degradation conducted a well toxicity removal and effective mineralization.