Phenanthrene toxicity during early development of the neotropical tree frog Dendropsophus branneri

Abstract

Phenanthrene is considered a priority polycyclic aromatic hydrocarbon due to its ubiquitous presence in aquatic and terrestrial environments and its toxic potential. Tadpoles are sensitive ecotoxicological models that provide important information regarding effects of contaminants in amphibian species. The goal of the present study was to generate information regarding the acute and chronic toxicity of phenanthrene to the neotropical tree frog Dendropsophus branneri early life stages. Tadpoles at Gosner stage 25 were exposed to environmentally relevant concentrations of 10.8, 18.6, 76.2, 187.7, and 279.6 µg phenanthrene L−1 in two experiments with 15 and 60 days of exposure. Lethality, progression of development, final weight, swimming behavior and enzymatic biomarkers were analyzed. The lethal concentration of dissolved phenanthrene for 50 % of D. branneri tadpoles after 15 days of exposure was 154.8 µg L−1, typical of a sensitive species. Significant developmental delay was verified, with a lowest observed effect concentration (LOEC) of 76.2 µg L−1 and 10.8 µg L−1 after exposures of 15 and 60 days, respectively. Delay was measured based on the difference between the mean Gosner stage of controls and exposed tadpoles (Deltagosner). Deltagosner after 60 days of exposure ranged from 10 at 10.8 µg L−1 to 13 at 187.7 µg L−1, and tadpoles remained in the early stages of hind limb development (Gosner stages 28–32), in contrast to controls that reached stage 42 with fully formed forelimbs and hind limbs with toes at metamorphic climax. Glutathione-S-transferase and Catalase were induced in exposed tadpoles, possibly due to oxidative stress. Thigmotaxis was decreased in phenanthrene exposed tadpoles, indicating loss of anti-predatory behaviors. Final wet weight of exposed D.branneri tadpoles significantly decreased. Delayed development and slower growth rate are crucial factors for tadpole survival, and these effects of phenanthrene on D.branneri early stages potentially affects its recruitment to the adult stage.