Study On The Process Of Residue And Metabolism Of Pyrethrins In Tea

In recent years,the hygiene quality of tea is the focus of attention,and also is the main factor affecting the competitiveness in the international trade.In recent years,the health and safety of tea has become a kind of technical barriers in international trade.Now,buprofezin, fenpropathrin and fenvalerate are the three excess-standard pesticides in export tea of our country.How to use scientific methods to quickly and accurately detect pesticide residues in tea plays an important role in the proper use of pesticides,improvement of the quality of tea,and enlargement of the export.In this thesis,the pollution background of pyrethrins was investigated in tea-garden soils and teas in the southwest region of China,the pollution status of pyrethrins were evaluated using the single-factor pollution index and Nemerow pollution index,and the health quality of tea-garden soils and teas were analyzed.Thus,the basic data were obtained for the sustainable development of tea industry in the above region.Based on the background investigation,the three pesticides including buprofezin,fenpropathrin and fenvalerate were selected as research objects,and the dynamic characteristics of residue and metabilosm of them in tea were studied. This study can provide theoretics foundation to scientically know the residual problem of pyrethrins in tea in southwest region and prevent the pollution of pyrethrins in tea.The results were summarized as follows.1.The background investigation of pyrethrins in tea-gardens:the contents of three kinds of pyrethrins in tea in southwest region were in the scope of quality standards,with the single-factor pollution indices and Nemerow pollution indices of less than 1.0.No pesticide pollution was found in the tea-gardens in Mount Jinyun and Guizhou,and these tea-gardens could be developed as the bases with no public hazard.However,the three pesticides were detected in the tea-gardens in Fuding and Yongchuan,and the use of pesticides must be payed attention to avoid highly residual amounts,and affect the quality of tea.In addition,the use of fenvalerate must be payed attention in the tea-gardens in Leshan,Beibei.2.The dynamic characteristics of residue and metabolism of pyrethrins in tea at different culture times were studied by using liquid cultivation.The results showed that the residual amounts in tea increased with the concentrations of the sprayed pesticides increasing.Among them,buprofezin was the easiest one to be residual,and then fenpropathrin,fenvalerate was the last one.3.The process of residue and metabolism of pyrethrins in tea was studied by potted cultivation in different culture period.The results showed that the degradation rates of the three pesticides in tea increased with culture time increasing.Among them,fenvalerate was degraded the fastest,and the degradation rates of buprofezin and fenpropathrin were close.4.From liquid cultivation and potted experiments,it can be found that the residual amounts of the three pestcides in tea could be described as a first order dynamic equation,i.e.C_t = C₀e^-kt, where t is the culture time,k is the degradation rate constant of pesticide,C₀ is the initial concentration of pesticide,and C_t is the concentration of pesticide at t.Among them,the degradation rate constant of fenvalerate was maximum,and then fenpropathrin,and that of buprofezin was minimum.The half-lives of the three pesticides were also obtained,with the order of buprofezin,fenpropathrin and fenvalerate from high to low.