Abstract
Many anthropogenic chemicals, especially from agricultural and environmental practices are generating global ecological concerns. The fact that many of these substances have been linked to endocrine system modulation, particularly the thyroid homeostasis is becoming a topical issue. Several studies support the hypothesis that the thyroid system represents major target of endocrine disruption. Using a Xenopus Metamorphosis Assay, this study assessed the comparative thyroidal impact of three glyphosate-based formulations including Roundup, Kilo Max and Enviro glyphosate. The result showed that Roundup at 0.6 mg/L significantly increased whole-body length (WBL),and reduced the whole-body mass (WBM) alongside a significant increase in the thyroid gland, but without impacting stage development. The Kilo Max significantly reduced both WBL and snout-vent length (SVL) at 190 and 280 mg/L, while it increased the full-limb length (FLL) at 90 mg/L only. Kilo Max also significantly reduced the stage development at 190 mg/L and 280 mg/L, without impacting the thyroid gland. Although, Enviro glyphosate, reduced WBL, SVL and WBM of the tadpoles at 28 mg/L, without impacts the stage development and thyroid histology. This result confirms that Roundup formulation is thyroid active as it affect the thyroid gland, while Kilo Max and Enviro glyphosate formulations only showed extra-thyroidal effects, since it has no effect on thyroid gland. This result points to the underlying role of surfactant in the thyroid disruption and not the main glyphosate. Regulatory agencies must do the needful, to subject all aquatic formulations to relevant physiological endpoints to characterize their amphibian’s impacts, given their global declining status.
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