Acute and chronic effects of Cr (VI) on Hypsiboas pulchellus embryos and tadpoles

Abstract

In the last few years there has been a great concern about declines in the abundance of several species of amphibians around the world. Among amphibians, anurans have a biphasic life cycle, mostly with aquatic tadpoles and terrestrial adults, and they have an extremely permeable skin, playing as excellent indicators of the health of the environment. A number of different causes for anurans global decline have been suggested, being the pollution of their habitat by chemical stressors considered one of the major factors. Among chemical stressors, heavy metals are known for their high toxicity at very low concentrations. This study assess short (96 h-acute) and long term (1272 h-chronic) exposure to Cr(VI) at lethal and sub lethal concentration levels (between 3 and 90; and 0.001 and 12 mg/L, respectively) on Hyla pulchella tadpoles (Fam. Hylidae) from central eastern Argentina. Fertilized eggs collected from a clean pond near La Plata (Buenos Aires Province) were used for acute and chronic toxicity testing. Assays were done under laboratory controlled conditions (pH 7.6-8.3; hardness 250 mg CO3Ca/L, continuous aeration, temperature 25°C±1, light:darkness 16:8 h). Results of chronic exposure were used to assess the effect of factors such as toxicant concentration and age of organisms at the beginning of exposure on the response variables (growth, development and survival until the time of first metamorphose). Results indicate higher sensitivity to Cr(VI) of larvae respect to embryo during acute and chronic exposure. Exposure to the highest sub lethal concentrations (6 to 12 mg/L) of the toxicant shows on all treated organisms early inhibitory effects on growth, compensated at longer exposure periods with an increment in the growth rate, even higher than control groups.