Pesticides Research, 83 – The Effect of Esfenvalerate and Prochloraz on Amphibians with special reference to Xenopus laevis and Bombina bombina

The Effect of Esfenvalerate and Prochloraz on Amphibians with special reference to Xenopus laevis and Bombina bombina

Summary

The South African clawed frog, Xenopus laevis is the test organism used in the only internationally recognised test with amphibians. However, this test has a number of deficiencies, which make it less suited for ecotoxicological risk assessment in Denmark. The purpose of this study has therefore been to develop and to test a new test guideline with the fire-bellied toads Bombina since this organism has widespread wild living species represented in Europe. When choosing Bombina bombina as a test organism, it has become possible to make an important comparison between laboratory tests and field test. The results from the present study have revealed that it is possible to breed Bombina bombina throughout the year and get a sufficient number of healthy embryos for ecotoxicological testing. A new test guideline using Bombina was tested with two pesticides (the insecticide esfenvalerate and the fungicide prochloraz). We also conducted standard tests with Xenopus with the two pesticides to compare their sensitivity as bio-indicators.

Esfenvalerate has only a small effect on the mortality on both Bombina and Xenopus embryos and the LC₅₀ values were higher than 150 µg/l in both species. However, when the number of malformations were used as an end point it was demonstrated that the EC₅₀ values for malformations were only 3 µg/l and 29 µg/l for Xenopus and Bombina, respectively. It should be noted that Xenopus and Bombina responded to esfenvalerate in the same way and that the change in sensitivity was less than a factor of 10. Such a difference can easily be ascribed to normal differences in species sensitivity. Furthermore, it is interesting that the in vivo observation revealed an effect as low as 1 µg/l in both species. These effects are twisting and apparent partial paralysis of the embryos.

For Xenopus and Bombina, no significant mortality was seen at prochloraz concentrations below 3 mg/l and the LC₅₀ values were found to be 4.5 mg/l and more than 10 mg/l for Xenopus and Bombina, respectively. As for esfenvalerate the most sensitive end point which can easily be quantified is the malformation where an EC₅₀ value of 1.4 and 1.5 mg/l were calculated for Xenopus and Bombina, respectively. Many embryos possess multiple malformations, and the same malformations were seen in both Bombina and Xenopus. The present study has also demonstrated that the jelly coat has no significant influence on the effect of prochloraz on the embryos of Xenopus. Even though the LC₅₀ value is higher in Bombina as compared with the value found in Xenopus it should be noted that the difference in effect concentration was only about a factor of 2. Thus, it can be concluded that prochloraz has the same effect on Bombina and Xenopus and at the same concentrations as well.

If mortality was our only measure of response to pesticide exposure, we would conclude that these amphibians were relatively tolerant to these pesticides. However, the sublethal effects that we witnessed are likely to have serious implications on the long-term success of the exposed individuals.

Additional research on environmental concentrations, more chemicals, effects of temperatures, and life-stage sensitivity should be investigated before the toxicity of pesticides to amphibians can be evaluated properly.