Herbicides vs herbicidal ionic liquids - does the herbicide application form affect the properties of active components?

Abstract

Despite extensive research on ionic liquids (ILs), their environmental fate remains poorly understood. Cation toxicity is generally considered the primary determinant of the final properties of the ILs. However, the relevance of cation-anion interactions after ILs are released into the environment requires insightful investigation. This study aimed to assess how natural-origin cations with varying toxicities, specifically choline and a derivative of morpholine, influence the degradation of ILs containing herbicidal anions-2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA), in four distinct agricultural soils. We also examined the impact on soil microbial biodiversity and the potential hormonal activity of these compounds. The results from 28-day degradation assays indicated that the addition of non-toxic hydrophilic cations did not significantly affect the environmental fate of IL-based herbicides. Phospholipid fatty acid (PLFA) analysis further confirmed that these cations had no discernible impact on soil biodiversity. However, a range of synthesized ILs displayed dose-dependent antiestrogenic activity, notably in benzyldecylmorpholinium chloride and ILs containing this cation. This suggests that the presence of specific cations, rather than anions, could contribute to unanticipated hormonal effects. This study is critical as inappropriate actions could lead to adverse effects not evident from the anions alone. Given the limited investigation into the environmental impact of ILs, our findings underscore the importance of understanding the behavior and interactions of IL-derived cations and anions in ecosystems. Our results suggest that, once released into the environment, ILs dissociate into independent ions, indirectly influencing the environmental fate of the ILs.