Cytogenotoxicity of 2,4-D and Glyphosate Herbicides: Effects of Isolated and Combined Environmental Concentrations on Onion Root Tips (Allium Cepa)

Glyphosate and 2,4-dichlorophenoxyacetic acid (2,4-D) are the most widely used pesticides in the world. In this work, the cytogenotoxic potential of these herbicides and their binary mixtures was investigated using A. cepa test. 2,4-D was assayed at 0.4 – 400 μg L⁻¹ and glyphosate at 0.65 – 650 μg L⁻¹ concentration range. The concentrations evaluated cover those permitted by Brazilian legislation for the protection of aquatic life and human health. Sixteen binary mixtures were examined to replicate different contamination scenarios. When analyzed separately, 2,4-D at 400 μg L⁻¹ inhibited the mitotic index, while glyphosate at 0.65 and 65 μg L⁻¹ increased it. In addition, the herbicides increased the frequency of chromosomal aberrations (2,4-D at 0.4, 4, and 40 μg L⁻¹ and glyphosate at 0.65, 65, and 650 μg L⁻¹) and micronuclei (2,4-D at 400 μg L⁻¹ and glyphosate at 650 μg L⁻¹). Regarding the mixtures, six of them were cytotoxic while eight were genotoxic. Additive, synergistic, or potentiated effects were observed. However, none of the mixtures tested increased the frequency of micronuclei. The results showed that even concentrations allowed by Brazilian legislation pose a potential risk to exposed organisms. There is little research on the cytogenotoxic effects of 2,4-D + glyphosate mixtures, so this is the first study to analyze a large number of combinations. The detection of additive, synergistic, or potentiated toxicities highlights the need for better pesticide legislation and discussions among regulators and environmental managers regarding pesticide mixtures in water.