Acute and chronic toxicity of Betanal(®)Expert and its active ingredients on nontarget aquatic organisms from different trophic levels

Abstract

As a way to improve the efficacy to target organisms, new pesticide generation is based on technologically advanced coformulations of two or more active ingredients. One example is Betanal(®)Expert, a postemergence herbicide composed of an Advanced Micro Droplet coformulation of phenmedipham, desmedipham, and ethofumesate. Although its composed formulation brings an increase in the pesticide performance, it can also enhance its toxicity to nontarget species. Therefore, the present study intends to contribute with relevant information on ecotoxicological effects of Betanal(®)Expert and its active ingredients on a battery of bioassays using aquatic species from different trophic levels: bacteria (Vibrio fischeri), microalgae (Pseudokirchneriella subcapitata, Chlorella vulgaris, and Chlamydomonas pseudocostata), macrophyte (Lemna minor), and cladocerans (Daphnia magna and Daphnia longispina) species. Across the organisms tested and endpoints measured, different responses concerning the toxicity of the active ingredients were found: (i) phenmedipham was the most toxic to V. fischeri and L. minor; (ii) desmedipham was the most toxic to P. subcapitata, D. magna, and D. longispina; (iii) and ethofumesate was the most toxic to C. pseudocostata and C. vulgaris. Furthermore, for C. pseudocostata and daphnids, the toxicity observed for some active ingredients was higher than the toxicity of the commercial formulation. In fact, in an attempt to evaluate the contribution of each active ingredient to the overall toxicity of Betanal(®)Expert, it was observed that, in general, the toxicity values obtained for desmedipham and phenmedipham were close or even lower to the values determined for Betanal(®)Expert, indicating that the ethofumesate can act as an antagonist in the three-way coformulation. In spite of the most impaired species being the photosynthetic ones, this study also showed pernicious effects on nonphotosynthetic organisms with distinct target sites. Therefore, our results underline the importance of clarifying the mode of action and metabolic pathways of these compounds on nonphotosynthetic species.