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 I : The effects of esfenvalerate on embryos of Bombina bombina during different culture conditions and prolonged studies for identifying effects after recovery of a short embryological sublethal exposure

1 Introduction

Populations of many amphibians have declined in and some species have disappeared from, certain localities around the world. The phenomenon appears to have accelerated recently.

While evidence for widespread reduction in numbers of amphibians is rapidly accumulating, the reasons for the declines are less clear. Complicating matters are the apparent decline of many species in relatively unaltered habitats (e.g. parts of the rain forest of Costa Rica (Crump et al. 1992) and the difficulty of appropriately monitoring and censoring these highly variable populations (Pechmann et al. 1991; Blaustein et al. 1994). Possible causes include loss of suitable habitats (Cooke, 1970), acid rain (Phillips, 1990), climate changes (Pounds and Crump, 1994), Wyman 1990), ultraviolet radiation (Wyman, 1990), and other environmental contaminants.

Due to their thin and permeable skins, and prolonged exposure first to the aquatic environment and then to the terrestrial, amphibians may be particularly sensitive to environmental stress. Embryonic and larval anurans have shown sensitivity to a number of environmental pollutants, such as hydrazine and its methylated derivatives (Greenhouse, 1976; Greenhouse, 1976), phthalate esters (Larsson and Thuren, 1987), and metals (Miller and Mackay, 1987; Birge et al., 1985).

Agricultural pesticides in particular may 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.

In the present study the possible role of one of the widely used synthetic pyrethroid pesticides, esfenvalerat, on amphibian declines has been investigated. Synthetic pyrethroids are increasing in number and used because they have retained the high insecticidal activity and low avian and mammalian toxicity characteristic of natural pyrethrins. Effects on amphibians are less well-known, but some sensitivity has been observed. Berrill et al. (1993) and Phillips (1990) exposed five species of amphibians to permethrin and fenvalerate at concentrations between 10 and 200 μg/l with no mortality resulting but with a notable reduction in growth rates. In the present study the main goal has been to test whether amphibians are sensitive to low levels of contaminants and whether gross sublethal effects do occur.

The only internationally recognized test with amphibians is FETAX (Frog Embryo Teratogenesis Assay-Xenopus) using embryos of Xenopus laevis, the South African clawed frog. As this species is not ecological relevant for Denmark and the rest of Europe a new toxicity test guideline with the fire-bellied toad Bombina bombina as test organism has been developed (Larsen & Sørensen 2004). The present work is a further application of this new test with Bombina bombina where the developmental effects of esfenvalerat at different temperatures and in different media have been investigated. Additionally, the effect studies were prolonged in the present study to examine the recovery of the organisms after transfer to a fresh medium without pesticide 6-7 weeks after the exposure was ended.