A modeling approach to study the pesticide dynamics to reduce pesticide residues in Japanese green tea

In this study, a modeling approach is used to clarify and estimate the exposure pathways of pesticides on tea plantations using a case study of Shizuoka Prefecture, Japan, and an improvement to the Japanese good agricultural practice (GAP) is proposed. We develop a dynamic compartment model to project the fate and transport of a pesticide after application in accordance with the Japanese GAP. Two pesticides, Azoxystrobin and Clothianidin, were analyzed using the model for a given set of circumstances. The results indicate that the implementation of a fixed preharvest interval time, which is a crucial provision in the GAP, is not appropriate. The reason for this is that the dissipation rates of pesticides in tea leaves vary with the timing of the pesticide application and are influenced by factors specific to the plantation area. The dissipation rates are 1.5-3.9 days for Azoxystrobin and 3.8-9.5 days for Clothianidin. This study also clarifies that incorporating plantation-area-specific factors, such as temperature, in the GAP guidelines are essential to ensure that pesticide residues are lower than the desired level. Furthermore, to produce good-quality and safe green tea, the GAP should provide detailed and precise guidelines for the timing of pesticide application and formulation of the dosage treatment. These guidelines should be determined by considering specific provisions for the harvest times of fresh tea leaves.