Ecotoxicological Evaluation of Safener and Antimicrobial Additives in Isoxaflutole-Based Herbicide Formulations

by Eszter Takács 1,*  Diána Lázár 2,3, Augustine Siakwa 1, Szandra Klátyik 1, Mária Mörtl 1, László Kocsányi 4, Attila Barócsi 4, Sándor Lenk 4, Edina Lengyel 2,5 and András Székács 1

1 Agro-Environmental Research Centre, Institute of Environmental Sciences, Hungarian University of Agriculture and Life Sciences, Páter Károly u. 1., H-2100 Gödöllő, Hungary
2 Limnology Research Group, Center of Natural Science, University of Pannonia, Egyetem u. 10., H-8200 Veszprém, Hungary
3 Aquatic Botany and Microbial Ecology Research Group, HUN-REN-BLKI, Klebelsberg Kuno u. 3, H-8237 Tihany, Hungary
4 Department of Atomic Physics, Institute of Physics, Budapest University of Technology and Economics, Műegyetem rkp. 3., H-1111 Budapest, Hungary
5 Limnoecology Research Group, ELKH-PE, Egyetem u. 10, H-8200 Veszprém, Hungary
* Author to whom correspondence should be addressed.

Toxics 2024, 12(4), 238;
Submission received: 22 February 2024 / Revised: 18 March 2024 / Accepted: 22 March 2024 / Published: 24 March 2024
(This article belongs to the Special Issue Impacts of Agrochemicals: Environmental Fate, Ecotoxicology, Risk Assessment, and Remediation)


The environmental load by isoxaflutole and its formulated herbicide products has increasingly become apparent because, after the ban of atrazine, isoxaflutole has become its replacement active ingredient (a.i.). Obtaining information regarding the fate of this a.i. in environmental matrices and its ecotoxicological effects on aquatic organisms is essential for the risk assessment of the herbicide. In this study, the effects of Merlin Flexx- and Merlin WG75 formulated isoxaflutole-based herbicide products and two selected additives (cyprosulfamide safener and 1,2-benzisothiazol-3(2H)-one antimicrobial agent) were investigated on Raphidocelis subcapitata in growth inhibition assays. In ecotoxicological tests, two conventional (optical density and chlorophyll-a content) and two induced fluorescence-based (Fv*/Fp: efficiency of the photosystem PSII and Rfd* changes in the observed ratio of fluorescence decrease) endpoints were determined by UV-spectrophotometer and by our FluoroMeter Module, respectively. Furthermore, dissipation of isoxaflutole alone and in its formulated products was examined by an HPLC-UV method. In ecotoxicological assays, the fluorescence-based Rfd* was observed as the most sensitive endpoint. In this study, the effects of the safener cyprosulfamide and the antimicrobial agent 1,2-benzisothiazol-3(2H)-one on R. subcapitata is firstly reported. The results indicated that the isoxaflutole-equivalent toxicity of the mixture of the isoxaflutole–safener–antimicrobial agent triggered lower toxicity (EC50 = 2.81 ± 0.22 mg/L) compared to the individual effect of the a.i. (EC50 = 0.02 ± 0.00 mg/L). The Merlin Flexx formulation (EC50 = 27.04 ± 1.41 mg/L) was found to be approximately 50-fold less toxic than Merlin WG75, which can be explained by the different chemical characteristics and quantity of additives in them. The additives influenced the dissipation of the a.i. in Z8 medium, as the DT50 value decreased by approximately 1.2- and 3.5-fold under light and dark conditions, respectively.

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