Mixture toxicity of microcystin-LR, paraoxon and bromadiolone in Xenopus laevis embryos.

Objectives: Apart from infections and habitat loss, environmental pollution is another major factor of global decline of amphibians. Using the model of Xenopus laevis embryos, we test the hypothesis that combined exposure of amphibians to natural toxins and anthropogenic pollutants induces more pronounced adverse effects than single exposures.

Methods: Experimental procedures adhered to Frog Embryo Teratogenesis Assay - Xenopus standards (FETAX). Exposure groups included controls, solvent (dimethyl sulfoxide) controls, and embryos exposed for 96 h to single, double and triple action of paraoxon (P), bromadiolone (B), and microcystin-LR (M), added to the FETAX medium at a dose of 300, 350, and 500 μg.L(-1), respectively. Studied responses of X. laevis embryos included mortality and malformations, head-to-tail length, total antioxidant capacity, lipid peroxidation, and caspase-3 activity.

Results: The triple combination induced the highest mortality. Malformations in embryos significantly prevailed only in B-, and B+P-exposure groups. Apart from the single exposure to B, the tested substances and their combinations inhibited the embryonic growth. Triple exposure had the most pronounced effect both on the growth inhibition and total antioxidant capacity. Lipid peroxidation was increased after B+M exposure, while single and combined exposures to B and P had an opposite effect.

Conclusions: This study helps to understand adverse effects of environmental pollution by natural toxins and agrochemicals in amphibians. The results allow for risk assessment of environmental pollution and findings of low concentrations of contaminants in aquatic environments. Further research to address issues such as mixture toxicity to metamorphosing and adult amphibians is necessary.