Evaluation of the developmental toxicity of 2-phenoxyethanol and clove oil anaesthetics using the Frog Embryo Teratogenesis Assay: Xenopus (FETAX)

The developmental toxicity of two anaesthetics, 2-phenoxyethanol and clove oil, used in aquaculture was evaluated using the Frog Embryo Teratogenesis Assay: Xenopus (FETAX) and the results were compared to outcomes in fish. Xenopus laevis embryos were exposed to 50, 100, 300, 500, 700 and 1000 mg/l of 2-phenoxyethanol or 1, 5, 10, 20, 30 and 40 mg/l of clove oil. Values of 96 h LC50, 96 h EC50 (malformation) and teratogenic index (ratio of 96 h LC50 and 96 h EC50) were determined and the types and severities of the induced malformations and minimal concentration inhibiting the growth of embryos were estimated. Teratogenic index values for 2-phenoxy-ethanol and clove oil were estimated at 1.69 and 0.61 respectively. The most frequently observed malformations produced by 2-phenoxyethanol were axial flexure and oedema and for clove oil, axial flexure, gut malformation, microphthalmia and oedema. 2-phenoxyethanol was found to induce growth inhibition of frog embryos at concentrations above 300 mg/l and clove oil at concentrations above 20 mg/l. In summary, both 2-phenoxyethanol and clove oil affected the growth of Xenopus embryos, while only 2-phenoxyethanol represented a teratogenic risk.