Quantifying the Role of Simultaneous Transformation Pathways in the Fate of the Novel Aquatic Herbicide Florpyrauxifen-Benzyl

Abstract

Predicting the fate of organic compounds in the environment is challenging due to the inability of laboratory studies to replicate field conditions. We used the intentionally applied aquatic herbicide florpyrauxifen-benzyl (FPB) as a model compound to investigate the contribution of multiple transformation pathways to organic compound fate in lakes. FPB persisted in five Wisconsin lakes for 5−7 days with an in-lake halflife of <2 days. FPB formed four transformation products, with the bioactive product florpyrauxifen persisting up to 30 days posttreatment. Parallel laboratory experiments showed that FPB degrades to florpyrauxifen via base-promoted hydrolysis. Hydroxy-FPB and hydroxy-florpyrauxifen were identified as biodegradation products, while dechloro-FPB was identified as a photoproduct. Material balance calculations using both laboratory rates and field product concentrations demonstrated that hydrolysis (∼47% of loss), biodegradation (∼20%), sorption (∼13%), and photodegradation (∼4%) occurred on similar timescales. Furthermore, the combined results demonstrated that abiotic and plant-catalyzed hydrolysis of FPB to florpyrauxifen, followed by biodegradation of florpyrauxifen to hydroxy-florpyrauxifen, was the dominant transformation pathway in lakes. This study demonstrates how combined field and laboratory studies can be used to elucidate the role of simultaneous and interacting pathways in the fate of organic compounds in aquatic environments.

Laboratory measurements underestimate persistence of the aquatic herbicide fluridone in lakes

“…57,70–74 Previous studies on aquatic herbicides such as 2,4-D and florpyrauxifen-benzyl similarly observed biodegradation only in the presence of the sediment microbial community, with no loss observed due to microbes exclusively in the water column. 57,75 Ultimately, the microcosm incubations showed that biodegradation has the potential to be a key fluridone loss mechanism and that sorbed fluridone can serve as a reservoir of the herbicide.…”

“…, t 1/2 ∼ 25 and 2.2 days, respectively). 57,75 We hypothesize the more rapid biodegradation of 2,4-D and florpyrauxifen-benzyl contributed to better laboratory to field comparisons than the fluridone microcosms, 73 but future research specifically on fluridone biodegradation is needed. While the second set of microcosms could have been primed for fluridone degradation due to the sediment being collected after initial treatment, similar fluridone loss rates were observed in microcosms conducted with pretreatment lake water and sediment (Fig.…”

Limitations of conventional approaches to identify photochemically produced reactive intermediates involved in contaminant indirect photodegradation

“…Slower photodegradation is expected in the field due solar light intensity, light attenuation within the water column, and other environmental factors as described previously. 4,67–69…”