Synergistic toxicity of glyphosate- and 2,4-Dichlorophenoxyacetic acid-based formulations on <i>Caenorhabditis elegans</i>

The use and marketing of herbicides are increasing worldwide. Glyphosate and 2,4 dichlorophenoxyacetic acid (2,4D) are the most prominent herbicides in this progression, used alone and in combination. There are few reports on the effects of these herbicides in combination. The <i>Caenorhabditis elegans (C. elegans)</i> experimental model has a complete system and is easy to manipulate and maintain. This study evaluated the toxicity of glyphosate and 2,4D alone and in combination with the parameters of survival, development, and reproduction in <i>C. elegans</i> at 4 different concentrations of the herbicides (0.115-0.925 mg/mL for glyphosate and from 1.046 to 8.375 mg/mL for 2,4D). The nature herbicides' interaction was evaluated using SynergyFinder software with the Highest Single Agent (HSA) probabilistic model. The survival results indicated an LC50 (Lethal Concentration 50) of 0.66 mg/mL for glyphosate alone and 0.164 mg/mL when combined with 2,4D. The LC50 for 2,4D alone was 9.41 mg/mL and 3.011 mg/mL when combined with glyphosate. There was a significant reduction in nematode development and reproduction as well as greater herbicide toxicity when combined (<i>p</i> < 0.05). The HSA indicated synergistic effects at different concentrations of the mixture, demonstrating greater toxicity of these herbicides in combination. This is the first time that the synergistic effect of glyphosate and 2,4D on <i>C. elegans</i> has been reported in the literature. This highlights the importance of further studies to understand the impact of using these herbicides alone and in combination, as they are widely used and can affect populations and ecosystems.