| In this paper, the dissipation, residues and cumulative residues of Fluazinam, Cymoxanil, Phoxim and Dimethachlon were studied to the regional soil in three different ecological environment in Changsha, Guangzhou and Hangzhou. Taking the earthworms (Elsinia-foetida) as experimental material, the acute toxicity and toxicity effects to earthworms of this four pesticides in lab were studied, and the environmental safety of this four pesticides were evaluated. These researches would be helpful to provide basic data to develop the scientific and reasonable usage standards of these pesticides, and comprehensively evaluate their ecological toxicity. The main results were as follows:1. The dissipation of these four pesticides in soil was accorded with the first-order kinetics equation, in the natural environment conditions of rural areas in Changsha, Guangzhou and Hangzhou. In the natural environment conditions, the half-lives of Fluazinam, Cymoxanil, Phoxim and Dimethachlon in soil were2.00～8.03d,2.33～5.52d,3.14～6.12d,3.31～4.64d, respectively, showing that these pesticides belonged to non-persistent and low-residual pesticides, the dissipation rate of them were fast in soil. The dissipation rate of these four pesticides was:Dimethachlon>Phoxim>Cymoxanil>Fluazinam. The different dissipation rate of pesticides were related to the type of soil, rainfall, temperature, light and spray time.2. The Fluazinam, Cymoxanil, Phoxim and Dimethachlon were sprayed in soil, according the recommended applying dose of pesticide (the dose of active ingredients) and high dosage (1.5times the recommend dose) applying2times and3times (interval7d), and the residues of this four pesticides are not detected in the soil from the15d after the last application. Thus, the usage of these four pesticides hadn’t cumulative residual damage in soil, according to the recommended dosage. But residues in soil increased with the increase of spray times and dosage, and the shortened application time.3. Three methods were adopted in this experiment to study the acute toxicity of Fluazinam, Cymoxanil, Phoxim and Dimethachlon to earthworms. The results showed that: the48h-LC50of these four pesticides on earthworms were2.109μg/cm2,55.765μg/cm2,40.751μg/cm2and41.401μg/cm2, respectively, by the test of contacting filter paper; the14d-LC50were59.069mg/kg,139.251mg/kg and99.160mg/kg,87.924mg/kg, respectively, by the method of artificial soil. The14d-LC50were28.332～30.093mg/kg,89.018～114.109mg/kg,74.498～83.948mg/kg and65.225～90.241mg/kg, respectively, by the method of natural soil. The half lethal concentration measured through the test of contacting filter paper (48h) and the method of artificial soil (14d) showed that the toxicity of this four pesticides to earthworms was:Fluazinam>Phoxim>Dimethachlon>Cymoxanil, and the trend was slightly different by the method of natural soil. Two soil methods’experimental results showed that the LC50of these four pesticides were greater than10mg/kg, therefore, these pesticides belong to the low toxicity of pesticides to earthworms, and they were safe to earthworms if been used reasonably.4. In the test of earthworm’s avoidance response to Fluazinam, Cymoxanil, Phoxim and Dimethachlon, the earthworms is not sensitive to the dangers of these four pesticides in time, with poor sensitive to the toxicity of them. Activities of earthworms in soil can increase the fertility of the soil, therefore, we should to reduce the use of pesticides and control the impact of pesticides to earthworms.5. According to the coefficient of poisoning, in the natural environment, only when the use dosage of Fluazinam, Cymoxanil, Phoxim and Dimethachlon were controlled less than2124.9g/ha,6676.35g/ha,5587.35g/ha and4891.875g/ha, respectively, the usage was safe to the environment. |
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