Translocation, residues and risk assessment of thiamethoxam applied by root irrigation in tomato plant ecosystems

Thiamethoxam (TMX) has been registered for use on a wide range of crops due to its broad pest spectrum, high efficiency and versatile application methods. However, there is limited literature evaluating the residue behaviors of TMX applied through root irrigation. In this study, the uptake and translocation of TMX, its degradation to clothianidin (CLO) and risk assessment of TMX application in a tomato plant ecosystem were evaluated. TMX applied through root irrigation was transferable within the tomato plant, including stems, leaves and fruit at different heights. TMX concentration in the four sections of stems was ordered as C lower > C mid > C upper > C top , while in the leaves the order was the opposite and the top had the highest concentration. The degradation product CLO was detected in the tomato plant, and the concentration order was C leaf > C root > C stem > C tomato . In the leaves, the concentrations of CLO were even higher than those of TMX. The translocation factor (TF) in the same section generally followed the order of TF leaf > TF stem > TF tomato. Both long-term and short-term risks were lower than 0.44% for all the subgroups in China, which indicated that the application of TMX was comparably acceptable. This study promotes the evaluation of TMX applied through root irrigation for use in tomato ecosystems from a dietary safety perspective.