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

PART II : The effects of selected pyrethroids on embryo development of Bombina bombina under semi-field conditions

5 Introduction

There has been a worldwide trend of decreasing amphibian populations in different types of habitats and some species have disappeared from certain localities around the world. (Howe et al., 1998). Due to their thin and permeable skins, and prolonged exposure first to the aquatic environment and then to the terrestrial, from herbivorous tadpoles to carnivorous adults, amphibians may be particularly sensitive to toxic substances (Gutleb et al., 1999).

Agricultural pesticides are under suspicion to cause or contribute to the decline in amphibian populations (Phillips, 1990; Dutta and Mohanty-Hejmadi, 1978; Berrill, et al., 1994). Much of the amphibian life cycle occurs in ponds, streams, and temporary pools that are often associated with agricultural areas receiving pesticide applications. In addition, breeding and larval development of amphibians occur in spring and summer at the same time that heavy application of pesticides on agricultural lands occurs.

The only internationally standardized test with amphibians is FETAX (Frog Embryo Teratogenesis Assay-Xenopus, Dumont, 1983). FETAX is a standard method for developmental toxicity tests of chemicals using embryos of Xenopus laevis, the South African clawed frog. As Xenopus laevis has all its life stages only in water and only represents a limited African ecosystem, with restricted ecological relevance for e.g. Denmark, a new toxicity test guideline with the fire-bellied toad Bombina Bombina as test organism has been developed (Larsen & Sørensen, 2004).

Bombina bombina is widespread throughout Europe and since several species are closely related to Bombina bombina this species is highly relevant as a test organism. Bombina bombina proved to be easy to maintain and breed throughout the year in the laboratory, provided that the adults are fed properly (only "moving" food, i.e., various invertebrates), and have access to both water and land area in the vivarium (Larsen & Sørensen, 2004). The new test guideline using Bombina bombina has been tested with two pesticides (the insecticide esfenvalerate and the fungicide prochloraz). Esfenvalerate had only a small effect on the mortality on Bombina bombina. However, when malformations in the embryos were examined, effects from as low as a concentration of 1g/l of esfenvalerate were seen (Larsen & Sørensen, 2004).

Standard toxicity tests where chemical substances are tested for toxicity on one organism at a time have been criticized for not being realistic, since they are carried out in the laboratory under artificial conditions. There is a need for evaluating the validity of such toxicity tests by applying the tests under natural conditions, where food chains are intact and vegetation, sediment, decomposers etc. influence the behaviour of the test substances as well as the test organisms in the habitats. In the present study, effects of four pyrethroids, applied to an artificial pond, on caged embryos of Bombina bombina were studied for the purpose of examining the developmental toxicity effects under more realistic conditions. Furthermore, the potential of caging Bombina bombina embryoes/tadpoles under in situ conditions was evaluated with reference to monitoring for effects in the environment.