| Nowadays, greenhouse vegetables have already made up most of the market in China. The high temperature and humidity in the greenhouse may induce the spread of the insect pest and disease. Imidacloprid and chlorothalonil are widely used in the greenhouse. The increasing use of imidacloprid and chlorothalonil may induce the residue amount to exceed the safe limit. Imidacloprid is a broad spectrum neonicotinoid insecticide, which had high activity, low toxicity, strong absorbability and long period validity. Chlorothalonil is one of the substitutive benzene fungicides, which was broad spectrum, highly effective and everlasting protectant fungicide. The present study involved four sections:(1) An improved analytical method was developed for quantification of imidacloprid and chlorothalonil in the vegetables and soil; (2) The degradation and residue of the two pesticides in the vegetables and soil were studied in the greenhouse and field; (3) The differences of the residue amounts of pesticides were found in different crop samples; (4) The influences of environment factors in degradation of imidacloprid were studied. The aim of this study was to find out the differences of the degradation and residue of pesticides between greenhouse and field, and the main environmental factor. This paper made a forecast of pesticides prospective development in the greenhouse.The methods for the quantification of imidacloprid and chlorothalonil in eight crops and soil were established by HPLC and GC, respectively. Results showed that the recoveries of imidacloprid ranged from 72.98 to 99.75% within its respective linear range (0.01～10 mg/L), and the relative standard deviation (RSD) ranged from 0.54 to 2.88%. The limit of detection (LOD) of imidacloprid was 2.0×10-10 g, and the limit of quantification (LOQ) was 0.01 mg/kg. The recoveries of chlorothalonil ranged from 73.28 to 104.60% within its respective linear range (0.001～1 mg/L), and the RSD ranged from 0.28 to 3.68%. The LOD of imidacloprid was 1.0×10-12 g, and the LOQ was 0.001 mg/kg.The degradation rates of the two pesticides in soil, bok choy, calabash leaves, eggplant and edible rape in the greenhouse were lower than that in the field. And the residue amount in the greenhouse was higher than that in the field. Meanwhile, the primary residues of imidacloprid and chlorothalonil were diverse in the vegetables with different types of leaves.The initial deposit amount of imidacloprid in different vegetables (bok choy, calabash leaves, eggplant, and edible rape) were 1.009 mg/kg,2.735 mg/kg,0.186 mg/kg and 0.155 mg/kg, respectively. For chlorothalonil, the values were 7.068 mg/kg,9.562 mg/kg,3.245 mg/kg and 3.082 mg/kg, respectively. The initial deposit amount of imidacloprid in different types of leaves such as bok choy, edible rape, cabbage and mater convolvulus were 3.900 mg/kg,1.947 mg/kg,2.655 mg/kg, and 3.769 mg/kg, respectively. For chlorothalonil, the values were 4.628 mg/kg,4.200 mg/kg,4.615 mg/kg, and 4.473 mg/kg, respectively.Our study showed that the residues of imidacloprid and chlorothalonil in bok choy had a negative correlation with the rainfall intensity, but it had a positive correlation with the rainfall interval. Half-lives of imidacloprid in soil were 45.60 d,135.91 d at 25℃and 5℃, respectively. Imidacloprid was sensitive to light, photolysis half life tested with 4000 Lux was 2.09 h. Imidacloprid was broken down into 1-(6-chloro-3-pyridine meth)-2-imidazole ketones via photodegradation. Hydrolysis half lives (pH 7) of imidacloprid at 50℃was 126.03 d, and at 25℃was 385.03 d, respectively.The preset study found the rainfall, light intensity and temperature were the main environmental factors which caused the differences of residues between greenhouse and field. Otherwise, we compared the initial deposit amount of imidacloprid and chlorothalonil in different vegetables and provided the recommended dosage in different types of crops.
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