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

1 Introduction

There is strong evidence that many amphibian species from a variety of taxa are declining at a drastic rate world-wide (Blaustein and Wake, 1990). Although much of the present decline may be due to loss of suitable habitats or due to swamp drainage, predation and disease, and local development, aquatic contaminants are likely to be involved (Cooke, 1972; Harte and Hoffman, 1989; Bradford, 1991). The increasing use of pesticides in modern agriculture has been mentioned as one of the reasons for the decline of the amphibian fauna stated over the last 40 years. A number of tests of field water ponds/streams in intensive grown farm lands have shown content of pesticides coming directly from spraying, wind drift, surface runoff/drain flow and washing of spraying equipment (Gomme et al. 1991; Berrill et al. 1993). Amphibians are potentially sensitive indicator organisms of environmental stress because of their permeable skins and bi-phasic life cycle (Duellman and Trueb, 1986).

Amphibians are not likely to be killed by normal exposures, due to low concentrations that are likely to occur in aquatic systems. Recognition of a need to identify sublethal effects of contamination in order to assess sensitivity is therefore growing. It is important to measure embryo mortality, malformation and growth inhibition because they can often occur at concentrations far less than those required to affect adult organisms.

The idea of the present study is to investigate the effect of two pesticides with different mode of action on embryos of two different amphibian species. The selected pesticides are

esfenvalerate which is an insecticide used against insect pest in agriculture, gardening, fruit farming and forestry and
prochloraz which is a contact fungicide and is primarily used in cereals, grasses and rape against a number of important diseases.

We use an in vitro standard biological test (FETAX) that is designed to use on embryos of the South African clawed frog Xenopus laevis. This bioassay gives data on the lethal, teratogenic and growth retardation effects caused by xenobiotic exposure. It is possible to test pure chemicals or complex mixtures (even with an unknown composition) that are soluble in water. The test can be realised in a short time and with low costs. Because of the sensitivity of embryonic and early life stages, FETAX provides information that may be useful when estimating the chronic toxicity of a test material to aquatic organisms. However, the sensitivity of embryo and tadpole stages of a particular species may vary significantly. Thus, the effect of many pesticides, e.g. pyrethroids, is found to be highly dependent on the temperatures, and therefore varies with latitude and season (Coats et al., 1989; Materna et al., 1995). The effect of pesticides on populations in northern latitudes as well as spring-breeding species may therefore be different from the effect found in test with an African frog.

A new standardised toxicity test with Bombina bombina, which has a European distribution and an aquatic lifestyle outside the hibernation season, was therefore developed. The species has a wide distribution in nature, from Denmark in the West to the Urals in the East and Greece in the South (Corbett, 1989). B. bombina inhabits lowlands of Northern and Central Europe, and breeds most typically in lakes, for example ox-bows, fish ponds or flooded areas alongside larger rivers (Madej, 1973). It is declining in especially the north-western part of its range.

Acquired knowledge from the laboratory tests in the present study is validated with field and semi-field data from Funen's County, the National Forest and Nature Agency, the University of Roskilde (RUC), and the adjoining projects by the Danish National Environmental Research Institute. The Danish Technological Institute's part of the total pond project will thus make up the necessary laboratory counterpart for the field test of the direct and indirect effects of pesticides. This makes the important comparison between laboratory tests and field tests possible.