CONICET | Buscador de Institutos y Recursos Humanos

Ivermectin (IVM) is an antiparasitic widely used in veterinary medicine around the world. Approximately 45% of administrated IVM is eliminated by livestock faeces. In wetlands of Middle Paraná River, cattle injection with IVM is a common practice. Immediately after injection, cattle enter wetland for feeding and drinking, incorporating faeces with IVM into aquatic systems, where it accumulates in the substrate, especially in sediments rich in organic matter. Thus, our objective was to experimentally assess the habitat selection of nektonic (Boana pulchella) and benthic (Physalaemus albonotatus) tadpoles between patches of substrate with and without IVM. The experimental units consisted of quadrangular plastic trays with the bottom divided in four internal quadrants, two of them filled 1 cm depth with the substrate free of IVM and the other two filled with substrate with IVM (nominal IVM concentrations were 3000 ng g-1 substrate fresh weight) and filled with water(3 cm depth). We placed one tadpole in the centre of each tray (B. pulchella: n = 22; P. albonotatus: n = 50) and visually registered its position (IVM-free or IVM quadrants) every 1 h during the first 10 h, and a final observation at 24 h. The recovery concentration of IVM in the IVM quadrant substrate was 73.95 % (percentage of target concentration) and was not detectable in the IVM-free quadrant. The frequency of observations of tadpoles was significantly higher in IVM-free quadrants than in IVM-quadrants (B. pulchella: 57 %; P. albonotatus: 58 %), and this pattern did not differ between nektonic and benthic tadpoles. Thus, tadpoles of both species selected the quadrants free of IVM. The response of tadpoles to IVM should be investigated in a wider spectrum of species and different concentrations to better depict the effects of this emergent pollutants on amphibians.

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