| Herbicides are indispensable for modern agriculture in recent years. However, Due to their massive emission into environments, toxic herbicides have become global environmental problems. Recent studies have shown that herbicides are frequently detected as pollutants in soils, rivers and even foods. The mobility of herbicides into groundwater via soil media has become one of the primary approaches leading to the widespread pollution to ecosystems. Moreover, when practically used, herbicides are also accumulated in soils or where crops are growing. Contamination with herbicides not only affects the quality of crops which directly accumulate herbicides, but also serves as a food chain threatening human health. As herbicides are readily uptaken by crops, overload of herbicides into crop tissues is most likely to disrupt many biological processes. Thus, it is very important to dissect residue and degradation of herbicides in the environment and food. With the development of liquid chromatography coupled to mass spectrometry(LC-MS) technology, it plays an important role in prospective pesticide residue monitoring. Compared with the traditional technology, praticular advantages of faster analytical speed and higher analytical sensitivity for LC/MS. In this doctoral paper, a new analytical methods of 50 herbicides and some catabolites in soil, cereal grain and human serum were developed by ESI-UPLC/MS/MS. Optimization and validation were made for sample pre-concentration method, separation of chromatography, analysis of mass spectrum and validation of the proposed method. And it is a very important theoretical and practical significance for improving the quality of soil and water, ensuring the safety of agricultural products, safeguarding people’s health and realizing agricultural sustainable development.In chapter one, study process of the properties, environmental behavior, detection method and degradation of herbicides was summarized.In chapter 2, A rapid and sensitive method was developed for the determination of 51 herbicides by ultra-performance liquid chromatography-electrospray ionization-mass spectrometry(UPLC-ESI-MS) and MS fragmentations were analyzed. Chromatographic separation was achieved within 12 min using gradient elution with acetonitrile–water as a mobile phase for 22 triazine and phenylurea herbicides, and with 5 m M ammonium acetate containing 0.1% formic acid aqueous solution–acetonitrile as a mobile phase for other 29 herbicides.In chapter 3 and 4, methods for determination of herbicides in soils and cereal grains were developed. Using acetonitrile effectively extracted triazine and other basic herbicides, and using 90:10 v/v acetonitrile-phosphate buffer(p H=7.5) effectively extracted sulfonylurea and phenoxyacid herbicides. The response was linear over two orders of magnitude with a correlation coefficients(r2) higher than 0.99. The limits of detecion for the herbicides varied from 0.06 to 6μg/kg. The intra- and inter-day precisions(relative standard deviation, RSD) were 2.2–9.3% and 5.7–17.1%, respectively. The average recovery varied from 61.6 to 112% with the RSD of 1.9–11.3%. Analyzing 41 soil samples evaluated this method. Most of the positive samples are below 10 g/kg. Nicosulfuron residue in soil for two samples was found, high up to 133 or 1317 μg /kg. A sensitive method was developed for the determination of 51 herbicides in cereal grains by using liquid-liquid extraction combined with C18 SPE purification to detach fat. The response was linear over two orders of magnitude with a correlation coefficients(r2) higher than 0.992. The matrix effects of most herbicides are less than 20%. The limits of quantification for the herbicides varied from 0.2 to 25.6 μg/kg. The recovery were over 70% for all the herbicides in corn, with RSDs below 11%; and above 70% except 4-phenoxybutyric acid(66.9%) and clomazone(69.2%), with RSDs of less 12% in soybean; and varied from 68.1 to 110% with the RSD less than 12% in wheat. Analyzing some soybean, corn and wheat samples evaluated this method. The method has high sensitivity, satisfactory recovery and precision for multi-class multi-residue and high-throughout analysis. And the result of all the positive samples were less 10μg/kg, below the MRLs of US and EU. So the herbicides in cereal grains in this region are within a safety scope.In chapter 5, serum sample preparation was carried out by one-step protein precipitation and analytes extraction using acetonitrile. After centrifugation, an aliquot of 5 μL of supernatant was injected into a C18 column for the separation. The limits of quantification(LOQs) ranged from 0.1 to 20μg/L. Intra and inter day precisions at three spiked levels were satisfactory for the 51 herbicides with the RSD of 1.02 –10.0% and 1.09 –12.0%, respectively. Extraction recoveries of 51 herbicides were satisfactory and ranged from 63.6% to 109% with the RSDs of 1.06% to 12.0%. This UPLC-ESI-MS/MS method is simple, accurate, and useful for multi-class multi-residue determination of herbicides and benefits clinical analysis and diagnosis.In chapter 6, 300 samples of soil, soybean, corn and wheat from 17 counties of shijiazhuang in 2013 and 2014 were analyzed by using this method. Almost all the soil samples contain atrazine or its catabolites. As for cereal grains, the positive rate of wheat is 42.5%, followed by soybean with 35.5% and corn with 34%. Atrazine is the most positive rate herbicides in this test, 98.8% in soils, 38% in wheat, 33% in soybean and 26% in corn. In addition, it was detected nicosulfuron with the content of 1317μg/kg, followed by atratone, propazine and cyanazine, Clomazone, propachlor, triallate in soils. And it was also detected nicosulfuron, atratone, propazine in three cereal grains. Although all the cereal samples herbicide levels were within the MRLs, but the long-term accumulation remains a threat to the people. The results suggest that departments should increase monitoring, supervision efforts, and should monitor herbicides in other products.In chapter 7 and 8, the degradation of atrazine in unsterilized soil were studied by natural bacteria and UV irradiation. In this study, the effects of temperature, moisture, and the coexistence of other herbicides were investigated, the results showed that:Different environmental conditions obvious influence on the degradation of atrazine. When the soil water is 10% and temperatures at 5℃, 25℃, 35℃, respectively, the rate of degradation of atrazine increased with temperature increasing. The rate of degradation are 59.8%-95.6%, 62.2%-96.3%, 63.1%-95.9% in 3 kinds soils after 60 days, respectively. This indicated that atrazine degraded faster at high temperature than low temperature. As well as the kinds and concentrations of catabolites increased with the increasing temperature. The degradation rate of atrazine increased with water increasing, as well as degradation products. But the total atrazine likeness poisons are declined. So, in practice, atrazine degradation can be accelerated by regulating soil temperature and soil moisture. A certain concentration of nicosulfuron was promoted at atrazine degradation, and atrazine- nicosulfuron mix pesticides on crop injury smaller, are more useful in the actual production practice.Photolysis of atrazine is another way of disappearing in nature. The thickness of samples, water, initial concentration coexistence and catalyst are responsible for atrazine photolysis. The results indicate that photolysis of atrazine occurs only in soil surface. More soil moisture was advantageous to the photolysis. The rule of atrazine degradation was similar by different initial atrazine, but the lower the initial atrazine, the faster the degradation rate. In this study, nicosulfuron restrained the photolysis rate of atrazine. The most factor is catalyst, especially influence the photolysis products. In practice, it is beneficial of photolysis by increase soil moisture, reducing herbicides concentrations. |
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