Quality standard for pesticides

1. Purity purity is the content of the active ingredient in the original drug , expressed as a percentage. Purity is the main indicator of the quality of the original drug, and the higher the percentage of the active ingredient, the better the quality. The quality standards for pesticides published by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO) should be more than 90% pure. In China's pesticide quality standards, the purity of the original drug can generally reach more than 90%. The content of impurities in the original pesticide with low purity is high, and the excessive impurities in the original drug have the following disadvantages: (1) may cause phytotoxicity to crops. In 2000, the use of bensulfuron-methyl in rice fields in Meihekou City, Jilin Province, caused phytotoxicity, resulting in rice seedling death. Bensulfuron-methyl has good safety to rice seedlings and generally does not cause phytotoxicity. According to preliminary research, the cause of the phytotoxicity is that the impurities JP-003 and JP-004 in the bensulfuron-methyl are excessive. (2) More impurities will increase the toxicity of plateau drugs to humans. For example, the pure LD50 of methamidophos is 30mg/kg body weight in rats, while the LD50 of 50% methamidophos emulsifiable concentrate produced by some domestic manufacturers is 13.6mg/kg, indicating that the toxicity is increased. There are five kinds of impurities in the amine-phosphorus crude oil, and the toxicity of these five impurities is higher than that of the pure methamidophos. (3) The impurities in the original drug lose the original accuracy by the chemical analysis method of calculating the content of the active ingredient in an amount of an element or an atomic group in the active ingredient molecule. Since the impurities also contain the same elements or atomic groups as the active ingredients, the results of the measurement are biased and do not reflect the true content of the active ingredients in the original drug and its preparation. (4) The impurities in the original drug also bring difficulty to the processed powder, because the presence of the impurities lowers the freezing point of the original drug and is not easily pulverized. (5) The impurities of the original drug can reduce the stability of the active ingredient, and with the use of the pesticide, the impurities enter the environment and cause pollution. Therefore, it is necessary to increase the purity of the original drug as much as possible and reduce the content of impurities.
2. pH is the quality index of the original drug and the quality index of the preparation. The pH refers to the amount of free acid or free base in the original pesticide and its preparation, or its hydrogen ion concentration. The purpose of limiting the pH is mainly to reduce the decomposition of the active ingredients in the pesticides and preparations during storage, to prevent the physical properties of the preparations from changing and to cause phytotoxicity when used. It can also be used as a reference for assessing the corrosivity of pesticides on packaging materials. FAO's quality standards for the original drug and preparations and preparations are expressed in terms of acidity (% of H2SO4) or alkalinity (% of NaOH). The original powder is generally required to be <0.1% to 0.2%. The pH is sometimes expressed in terms of pH. In China, the prescriptions for pesticides are expressed in acidity or alkalinity, and most of the preparations are expressed in terms of PH value.

3. Moisture content Moisture content is both the original drug and the quality index of the preparation. The purpose of limiting the moisture content of the original powder of the pesticide is to reduce the decomposition of the active ingredient and maintain chemical stability. For powders and wettable powders, the moisture content is limited to maintain a good dispersion state of the preparation, and it can be well dispersed on the foliage when sprayed. In the pesticide quality standards promulgated by 1971 after FAO, the pesticides have the moisture content index for the pesticides, emulsifiable concentrates and some soluble powders, while the powders and wettable powders have no moisture content. China's water content requirements for powders are not more than 1.5%. However, due to the different types of fillers used in processing powders, their water absorption properties are different, and some fillers have strong water absorption. Even if the moisture content is high, the dispersion properties of the powders are not affected; some fillers have weak water absorption properties, even if the moisture content is not too high. It also affects the dispersibility of the powder. Therefore, it is unreliable to control the moisture content to ensure the dispersibility of the powder. It is more effective to control the dispersibility of the powder by using the fluidity index of the powder than the method of controlling the moisture content. In China, there is no liquidity index in the quality standard of powder pesticides, and the dispersibility is controlled by limiting the moisture content.

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