Toxicity of PAHs and jelly protection of eggs in the Common frog Rana temporaria

Polycyclic Aromatic Hydrocarbons (PAHs) are damaging for aquatic organisms such as amphibians. In this study, toxicity of a mixture of three PAHs (naphthalene (2 rings), phenanthrene (3 rings) and pyrene (4 rings)) was tested on Common frog (Rana temporaria) embryos. The protective role of the jelly coat surrounding the eggs was studied by exposing embryos with and without jelly coat to PAHs dissolved in an aqueous solution without organic solvent. Results showed that the mixture of these three PAHs significantly increase embryonic mortality rate after a few hours of exposure. Embryos with jelly coat tend to suffer a lower mortality rate than embryos without jelly. The jelly surrounding eggs is filled by water of the breeding site, which can contain pollutants. Because jelly characteristics vary among species, sensitivity to environmental pollutants and levels of embryonic protection could be different among amphibian species. Polycyclic aromatic hydrocarbons (PAHs) are transported through the atmosphere over long distances and are now widely distributed in the ecosphere (Aceves et al., 1993, Fernandez and Grimalt, 2003). PAHs are naturally produced by volcanic eruptions, forest fires and decomposing organic matter in sediment (Blumer, 1976). Human activities, especially urbanisation, as well as incomplete combustion of living or fossil organic matter, exhaust fumes from vehicles, gasand oil-fired heating and steel mills, for example (Nykolaou et al., 1984; Van Schooten et al., 1997) are major sources of PAH emissions into the environment. Despite their hydrophobic nature, PAHs can be highly damaging to aquatic organisms (Bowling et al., 1983; Eisler, 1987; Landrum et al., 1987). Because of their unique physiology and habitat requirements, amphibians are often regarded as potentially more vulnerable to changes in their environment than many other vertebrates (Sparling et al., 2000,