Globally, amphibians are experiencing widespread abnormalities and population declines. One potential contributor to these challenges is the use of pesticides, particularly aquatic
herbicides applied to aquatic habitats inhabited by amphibians. Critical issues of concern are the potential toxicity and teratogenicity of these
herbicides towards amphibians. Using the FETAX protocol, three globally used formulations, including
diquat dibromide (Midstream),
glufosinate ammonium (
Basta), and
imazapyr (Arsenal), were assessed for embryotoxicity, teratogenicity, and growth inhibition. Developing Xenopus laevis embryos were exposed for 96 h at concentrations of 0.5-3.0 mg/L, 1.6-3.0 mg/L, and 20-45 mg/L for Midstream,
Basta, and Arsenal respectively. The 96-h LC50 estimates were 0.83 mg/L
acid equivalent (a.e.), 36 mg/L a.e., and 2.2 mg/L a.e., whereas the EC50 estimates were 0.24 mg/L a.e., 28.13 mg/L a.e., and 2.01 mg/L a.e. for the Midstream, Arsenal, and
Basta formulations, respectively. These two estimates produced Teratogenic Index of 3.5, 1.3, and 1.1 for Midstream, Arsenal, and
Basta, respectively, indicating a high risk of malformation induction by Midstream and moderate risk for Arsenal. Regarding growth inhibition, lowest observable effect concentrations of 0.5 mg/L, 25 mg/L, and 2.0 mg/L were computed for Midstream, Arsenal, and
Basta, respectively, producing the minimum concentration inhibiting growth (MCIG) ratios of 0.62, 0.69, and 0.89 for the three formulations. These
MICG values are higher than the standard 0.30
growth inhibitors benchmark, suggesting that the formulations are not
growth inhibitors at the evaluated concentrations. This study provides evidence of the embryotoxic and teratogenic status of Midstream and the embryotoxicity of
Basta. There is a need to further characterise the physiological and ecological impacts of these formulations to ensure responsible use and the safety of amphibians and other wildlife.