A multi-approach analysis of the toxicity of a commercial formulation of monensin on Rhinella arenarum embryos and larvae.

Monensin, an antibacterial commonly used in animal fattening, can enter aquatic ecosystems and harm non-target organisms. Since there are no previous studies about the effects of monensin on amphibians, the aim of the present study was to evaluate the lethal and sublethal toxicity of a commercial formulation of monensin (CFM) through standardized bioassays with embryos and larvae of the amphibian Rhinella arenarum. Oxidative stress (catalase and glutathione S-transferase activities, and reduced glutathione and lipid peroxidation levels), cholinesterasic effect (acetylcholinesterase and butyrylcholinesterase activities) and mutagenicity (micronuclei frequency) biomarkers were evaluated. The CFM produced teratogenic effects, with a teratogenic index of 6.21. Embryos (504 h-LC50: 273.33 µg/L) were more sensitive than larvae, as no significant mortality was observed on larvae exposed up to 3000 µg/L for 504 h. However, oxidative stress, cholinesterasic effect and mutagenicity biomarkers were altered on larvae exposed for 96 h to environmentally relevant concentrations (4, 12 and 20 µg/L of monensin active ingredient). The CFM caused adverse effects on the exposed organisms, primarily on embryos, leading to lethal and sublethal effects, which could impact the wildlife when it reaches aquatic ecosystems.

Metals, pesticides, and emerging contaminants on water bodies from agricultural areas and the effects on a native amphibian.

In the Paraná River lower basin, an important agro-productive area of Argentina, crop fields and cattle breeding activities are common and may affect water quality. So, the aim of this study was to analyze the impacts of cattle breeding and agricultural activities on a stream from Buenos Aires, through physicochemical parameters (metals, pesticides, and emerging contaminants) and ecotoxicological parameters with Rhinella arenarum larvae, a native amphibian species. Three sites were selected on an ordinary plain stream that goes through agricultural fields and a cattle breeding establishment (upstream -S1-, near -S2- and downstream -S3- the establishment). Physicochemical parameters were measured in situ (in water) and in laboratory (in water and sediment samples: metals, pesticides, ivermectin and oxytetracycline). A semi-static chronic toxicity bioassay (504 h) was performed with water samples, and neurotoxicity, oxidative stress and genotoxicity biomarkers were measured after acute exposure (96 h). According to the index, a degradation in the water quality was observed in all sites. Ivermectin (8.03 mg/kg) and oxytetracycline (1.9 mg/kg) were detected in sediment samples from S2. Pesticides were detected in all sites, mainly in water samples: S1 presented the highest variability (7 residues) and in S3 AMPA, glyphosate and acetochlor concentrations were higher (10.3, 22.4 and 23.8 µg/L). Also, all sites significantly produced lethality at chronic exposure. Lethality at 504h was 40% for S1, 56.66% for S2 and 93.33% for S3. At acute exposure, the oxidative stress biomarkers were altered on R. arenarum larvae exposed to all sites and the neurotoxicity biomarkers were altered on larvae exposed to S1 and S3. Water quality was severely degraded by the surrounding agricultural and cattle breeding activities, which may represent a threat to the ecosystems.