| In recent years, Chinese herbal medicines attract people’s more attention with the preference of natural medicine. And Dendrobium candidum is increasingly demanded because of the unique medicinal value. Due to the low output, Dendrobium candidum could not meet the market demand and most of them on the market were artificial cultivation in greenhouse in China. During planting process, the high temperature and humidity in the greenhouse may induce the increasing use of the pesticide for controlling plant deseases.So pesticide residue violative was frequently observed. It affected not only the quality and sales, but also people’s health. In this paper, mixed preparation of difenoconazole and prochloraz manganese chloride complex (two common fungicides) was selected as test pesticides to establish residue analytical methods and investigate the dissipation characteristics in Dendrobium candidum and cultivation substrates. Besides, the influences of substrate types and temperature on the degradation of the mixed preparation within indoor environment were examined in order to provide the basis for the scientific and rational use of pesticides. The main results were summarized as follows:1) Simple, rapid residue analytical methods of mixed preparation in Dendrobium candidum and cultivation substrates were developed. The sample was extracted with acetone, and purified, then determined by HPLC. It was found that the LOQ of difenoconazole were 0.04,0.05,0.026mg/kg in fresh, dry samples and cultivation substrates. The average recovery was 86.53-91.49% and the relative standard deviation (RSD) was 2.34-7.95%. The LOQ of prochloraz-manganese chloride complex were 0.04,0.05,0.026 mg/kg in fresh, dry samples and cultivation substrates.The average recovery was 85.82-91.41% and the relative standard deviation (RSD) was 2.58-4.33%.2) In the greenhouse, the dissipation of difenoconazole and prochloraz-mang-anese chloride complex in Dendrobium candidum and cultivation substrates were fitted to the first-order kinetic equation after the application of the dose (75 g/mu). The half-lives of prochloraz-manganese chloride complex in Dendrobium candidum and cultivation substrates were 10.02 d (Zhejiang),13.81 d (Yunnan) and 8.66 d (Zhejiang),11.66 d (Yunnan).The half-lives of difenoconazole were 11.12 d (Zhejiang),14.62 d (Yunnan) and 11.21 d (Zhejiang),15.40 d (Yunnan).The residue of prochloraz-manganese chloride complex in fresh and dry samples were less than 0.5 and 2 mg/kg, and the residue of difenoconazole in fresh and dry samples were less than 0.5 and 1 mg/kg when 30 days after the application. So Considering the MRL standards at home and abroad, ADI and the test results, it is recommended that the MRL value of prochloraz-manganese chloride complex in fresh and dry samples were 0.5 and 2 mg/kg, the MRL value of difenoconazole in fresh and dry samples were 0.5 and 1 mg/kg and the safety interval is 30 days.3) The degradation of difenoconazole and prochloraz-manganese chloride complex in cultivation substrates under different indoor conditions, such as different substrates and temperature, were all fitted to the first-order kinetic equation. The half-lives of difenoconazole were 18.19 d (Zhejiang),21.00 d (Yunnan),51.71 d (10℃),30.66 d (20℃),21.00 d (30℃).The half-lives of prochloraz-manganese chloride complex were 15.93 d (Zhejiang),19.25 d (Yunnan),42.77 d (10℃),27.39 d (20℃),19.20 d (30℃), According to the result of variance analysis in 95% confidence intervals by DPS, the degradation of mixed preparation in cultivation substrates under different temperature were significant different, while there were no difference in different substrates. The results indicated that high temperature could accelerate the degradation of the two fungicides. |
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