New Sources of Very Persistent and Very Mobile (vPvM) Substances: A Case Study of the Fluorinated Herbicide Pyroxasulfone

Abstract

With the increasing use of fluorinated agrochemicals, more fluorinated compounds enter into the environment. Pyroxasulfone (PYS), a broad-spectrum herbicide containing an aromatic CF₃ (Ar–CF₃), is expected to grow significantly in application. Although several transformation products (TPs) of PYS have been reported, their distribution and contribution to transformation processes remain largely unknown. This study combined laboratory simulations and a field study. In soil incubation and soil surface photolysis experiments, (5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)-1H-pyrazol-4-yl)methanesulfonic acid (TFPSA) was identified as the main TP of PYS in soil, accounting for over 90% of all TPs. Field study results showed that PYS and TFPSA were the main species in soil (6.48 ± 1.82 and 1.54 ± 0.90 ng g^–1 wet weight) and corn plants (2.55 ± 2.61 and 31.1 ± 39.6 ng g^–1 dry weight in roots) before harvest. Surface water photolysis experiments showed that TFPSA and TP₂₄₆ were the major TPs of PYS and no significant photodegradation of TFPSA was observed. Persistent (P) and mobile (M) property assessment indicated TFPSA, TP₂₄₆, and other Ar–CF₃ containing TPs of various fluorinated agrochemicals could be potential very P and very M (vPvM) substances. More attention should be paid to Ar–CF₃ containing agrochemicals and their TPs.