Fate of pyribambenz propyl (ZJ0273) in anaerobic soils revealed by position-specific 14C labeling

Pyribambenz propyl, or ZJ0273, is a new and widely used pyrimidynyloxybenzoic herbicide; however, its behavior and safety in anaerobic soils remain poorly understood. In this study, ZJ0273 was labeled with 14C on its benzoate-, pyrimidyl- and benzyl- rings respectively, and applied to anoxic flooding soils to characterize its anaerobic fates. Over the 100 d incubation, the amended 14C-ZJ0273 was slightly mineralized to 14CO2 (<4%) or redistributed into the overlaying water (<10%), with the majority of the 14C (82-98%) remaining in the soil. The residues in soil underwent a gradual transformation from extractable residues (ER) to bound residues (BR), with the percentage of 14C-BR increasing from 1.1 to 2.5% at day 5 to 23.2-47.2% at day 100. The proportion of 14C-ER, 14C-BR and 14CO2 depended both on the soil property and the labeling position. Generally, ZJ0273 has the highest tendency to form BR in fluvio-marine yellow loamy soil, and the mineralization on both the benzoate and benzyl rings tends to be more extensive in red-clayed soil than the other soils. The ring-specific labeling 14C on three aromatic rings respectively provides full molecular information and yield information on sub-molecular level, i.e., the benzoate ring was generally more susceptible to cleavage than the pyrimidyl or benzyl rings (P < 0.01).