Pesticides Research, 84 – The Effects of Selected Pyrethroids on Embryos of Bombina bombina during different Culture and Semi-field Conditions

The Effects of Selected Pyrethroids on Embryos of Bombina bombina during different Culture and Semi-field Conditions

Summary

Part I

In the present study, the developmental effects of the pesticide esfenvalerate on the fire-bellied toad Bombina bombina were studied at different temperatures and in different media. Additionally, the effect studies were prolonged in order to include recovery experiments of the tadpoles after transfer to fresh medium without the pesticide for the purpose of studying the possible effects occurring up to 6-7 weeks after the exposure to esfenvalerate was ended as well.

Spasmodic twisting was the most obvious effect on embryos of exposure to esfenvalerate, and at the end of the experiment after 216 h this effect was seen in the embryos exposed to as low as 1 μg/l esfenvalerate. At concentrations above 50 μg/l, the embryos were immobilised caused by constant spasmodic twisting and blistering and oedema were often seen. At concentrations above 100 μg/l, blistering and oedema were frequently seen as well as head and brain malformations. The heartbeat was very slow and severe heart malformations were seen at 100, 150 and 300 g/l. The most significant malformations observed included cardiac malformations, severe lateral flexure, oedema, brain and gut malformations.

Neither growth nor mortality was distinctly affected by the concentrations of esfenvalerate used in this study (1-300 μg/l).

When pond water was used instead of the FETAX solution used in standard FETAX tests few effects of esfenvalerate treatment were seen. It is suggested that difference in ion composition and content of dissolved organic matter may cause the observed difference. Apparently, the pond water used in the study was more appropriate in ion composition and concentration than the FETAX solution, since the EC₅₀ values for malformations were 43.7 and 24.7 μg/l in pond water and FETAX solution, respectively. It is well-known that pyrethroids strongly absorb to organic matter and the bioavaliability may be reduced in this way. Since no organic substance are added to the FETAX solution it is evident that the low toxicity in pondwater may be due to high contain of dissolved organic matter.

The effects of esfenvalerate added in different concentrations were almost comparable at two different temperatures, although displaced in time. The same pattern of malformations was found at both temperatures, however, the embryos at 20°C had more malformations and low EC₅₀ (32.7 and 24.7 μg/l at 24 and 20 °C, respectively).

In the group pre-exposed to 20 μg/l esfenvalerate about 70% of the organisms recovered after 24 h in pesticide free medium, while only 20% of the embryos pre-exposed to 125 μg/l esfenvalerate recovered. After two days all living larvae were swimming around and eating algae like the controls. A distinct effect of esfenvalerate was, however, seen six weeks after the transfer to the fresh medium without esfenvalerate. During the metamorphosis it got evident that esfenvalerate at both concentrations induced malformed forelimbs of Bombina bombina still six weeks after the exposure was ended.

The many malformations recorded in the study as well as the above mentioned results of the recovery experiment as a consequence of exposure to sublethal concentrations of esfenvalerate emphasize the severe impact that this toxicant can have on populations of amphibians in natural environments. From the present study it can be concluded that Bombina bombina is very sensitive to sublethal exposure of pyrethroids and will probably die as a consequence of the developmental abnormalities caused by even a few days' short exposure to rather low concentrations of pyrethroids.

Part II

Developmental toxicity effects of four pyrethroids, sprayed simultaneously to an artificial pond, on caged embryos of Bombina bombina were studied for the purpose of examining the possibility of using natural conditions when monitoring for effects of toxicants on embryos of amphibians in the environment.

A new toxicity test using Bombina bombina as test organism (Larsen & Sørensen, 2004) was used. The embryos were inspected for in vivo effects of pyrethroids every day during the experimental period until day 9. Malformations, growth inhibition and mortality were recorded at the end of the test.

Spasmodic twisting was seen as one of the effects of the pyrethroid treatment, and it caused immobilisation of more than half of the embryos. The effect decreased when the water concentration of pyrethroids decreased due to absorption by sediment and macrophytes. Furthermore, the pyrethroids caused the mortality to increase from 5-10% in the controls to 51%, and had also obvious developmental effects, since 85% of the embryos possessed multiple malformations by the end of the experiments. The growth of the embryos was, however, not affected.

From this study it can be concluded that the new toxicity test guideline using Bombina bombina as test organism (Larsen & Sørensen, 2004) can be modified and used under in situ conditions for testing developmental toxicity of toxicants, thereby increasing the realism of toxicity tests by including natural food webs, decomposers, sediment, natural physical conditions, etc., in the tests.