Comparative Aquatic Risk of Three Glyphosate–Based Herbicides Using Early-Stage Development of Clarias gariepinus (Burchell, 1822)

TL;DR

This study shows that glyphosate-based herbicides harm the early development of Clarias gariepinus fish, with effects varying by herbicide formulation and concentration.

Contribution

The study compares the aquatic toxicity of three glyphosate-based herbicides on fish development, revealing formulation-specific risks.

Findings

Higher concentrations of glyphosate-based herbicides significantly reduced fertilization and hatching rates in Clarias gariepinus.

Early-stage development was disrupted by herbicides, with effects linked to imbalances in reactive oxygen species and antioxidant enzymes.

The recommended application rates of some herbicides exceed the lowest concentrations causing significant developmental effects.

Abstract

Clarias gariepinus' (Burchell, 1822) early-stage development was assessed in microconcentrations of glyphosate-based herbicides (GBHs), Forceup, Roundup, and Uproot. Using the default ecological trigger value of 0.37 mg L−1 of glyphosate as a reference, herbicides were diluted to microconcentrations containing 0.006, 0.013, 0.025, 0.05, and 0.10 ([v/v] %) of herbicide using borehole water, which served as control. Concentrations and control were replicated three times. Fertilization (%), time to morula formation and to commencement of hatching (minutes), hatching (% fertilized eggs), and 96-h larval survival (% hatched larvae) in microconcentrations were monitored. Within formulation, concentration significantly affected fertilization and hatching rates (p < 0.001), time to morula formation and hatching, and 96-h larval survival ([χ2] 5 = 16,648, p = 0.010; [Kruskal–Wallis H test]). Morula formation, fertilization, hatching, and larval survival rates were significantly affected by formulation in Concentrations 2 and 3, while fertilization rate was significantly affected at all concentrations ([χ2] 3 = 6.49, p = 0.039). The glyphosate ecological trigger value of 0.37 mg L−1 as well as the recommended application rate of Roundup Proactive in aquatic and riparian environments of 0.32% (v/v) are higher than the lowest significant effect concentrations of the herbicides. Reactive oxygen species (ROS) and superoxide dismutase (SOD) in control embryos, were higher but not significantly, than levels in freshly stripped eggs (p > 0.05) (Mann–Whitney U test). Early-stage development was normal in controls, suggesting a balance between ROS and SOD. This was, however upset in treatments, leading to deleterious effects on early-stage development. GBHs pose a greater risk to fish reproduction, varying in severity with the formulation. This should be considered in regulations for their use in aquatic and riparian environments, balancing herbicide effectiveness with the risk of aquatic toxicity.

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