Exposure Impacts of Environmentally Relevant Concentrations of a Glufosinate Ammonium Herbicide Formulation on Larval De
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Exposure Impacts of Environmentally Relevant Concentrations of a Glufosinate Ammonium Herbicide Formulation on Larval Development and Thyroid Histology of Xenopus laevis Oluwaseun O. Babalola1,2 · J. Christoff Truter1,4 · Edward Archer1,3 · Johannes H. van Wyk1 Received: 12 April 2020 / Accepted: 5 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Thyroid hormones play critical roles in body growth and development as well as reproduction. They also influence the activities of a wider variety of tissues and biological functions, such as osmoregulation, metabolism, and especially metamorphosis in organisms, such as frogs. These complex activities of thyroid hormones are prone to disruption by agricultural pesticides, often leading to modulation of growth and the reproductive system in particular. These substances include Glufosinate ammonium, Glyphosates, Imazapyr, Penoxsulam, and Diquat dibromide among other herbicides. In this study, the standardized Xenopus Metamorphosis Assay protocol was used to assess the potential thyroid-modulatory properties of the Glufosinate ammonium Basta formulation, at relevant environmental concentrations (0.05 mg/L, 0.15 mg/L, and 0.25 mg/L) for 21 days. The results showed that this formulation only reduced the hind-limb length among the morphological endpoints. Histological evaluation showed that the mean thyroid gland area and the mean thyroidal follicle epithelium height were significantly increased following 0.15 and 0.25 mg/L exposures. The present study confirmed that this Basta formulation interacts with the thyroid axis and therefore potentially pose health hazard to amphibian in particular and potentially metamorphic aquatic vertebrates. Furthermore, the result is a signal of inherent potential thyroid disrupting activities that must be further investigated and characterised in some of the aquatic herbicide formulations to safeguard the aquatic biodiversity. Keywords Thyroid disruption · Herbicide · Glufosinate ammonium · Amphibians · XEMA · EDC
Introduction A decline of amphibian populations on a global scale has been suggested (Hayes et al. 2010; Wagner et al. 2013), and pollution has been highlighted as one of the main contributing factors responsible for habitat degradation or physiological modulation (Hayes et al. 2010). Chemical compounds, in particular linked to agricultural practices (pesticides and * Oluwaseun O. Babalola [email protected] 1
Department of Botany and Zoology, Stellenbosch University, Stellenbosch, South Africa
2
Zoology and Environmental Biology, Lagos State University, Lagos, Nigeria
3
Department of Microbiology, Stellenbosch University, Stellenbosch, South Africa
4
Department of Paraclinical Sciences, University of Pretoria, Pretoria, South Africa
fertilizers) and waste water treatment discharges, have been shown to compromise the health of aquatic vertebrates (Jobling and Tyler 2003; Nugegoda and Kibria 2017), including amphibians (Kloas et al. 1999; Hayes et al. 2010), but
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