Toxicological assessment of the effects of CuCl2 and CuO nanoparticles on early developmental stages of the South American toad, Rhinella arenarum by standardized bioassays

Abstract

The release in aquatic environments of emergent contaminants such as copper oxidenanoparticles (CuO-NPs) has generated concerns on their short- and long-term toxicityand the potential risk for more vulnerable animal groups, such as amphibians. In thissense, the aim of this work was to evaluate the toxicity of CuO-NPs in comparison withits respective salt (CuCl2) in embryos and larvae of a native amphibian, Rhinellaarenarum, by acute (96 h) and chronic (504 h) standardized bioassays. Lethality andsublethal effects such as developmental, morphological, and ethological alterationswere assessed in a wide range of concentrations (0.001-100 mg/L). Neurotoxic effectsby acetyl (AChE) and butyrylcholinesterase (BChE) activity levels and changes in thelipid content were also assessed at sublethal concentrations. Results showed thatCuCl2 caused higher lethality than CuO-NPs in both developmental periods. Embryoswere more sensitive than larvae with LC50-96h= 0.080 mg CuCl2/L and 1.26 mg CuONPs/L and 0.21 mg CuCl2/L and 20.17 mg CuO-NPs/L, respectively. At acuteexposure, embryos exhibited several developmental abnormalities such asdevelopmental delay, edema, axial flexure, and microcephaly. Larvae presentedspasmodic contractions and weak movements. Regarding neurotoxicity, a significantincrease in AChE activity at low concentrations as well as an inhibition of BChE activityat all tested concentrations were evidenced for both substances at acute exposure.Moreover, an increment in phospholipid and triglyceride levels was observed at thehighest concentration of CuO-NPs (10 mg/L) at chronic exposure. The chromatographic separation of lipids showed no apparent differences in acylglycerols and free fatty acid bands, between the treatments and the control. The differences in toxicity between CuO-NPs and CuCl2 could be due to structural and physicochemical characteristics that influence their bioavailability and toxicity. Considering the exponential growth in the production and use of these substances, it is expected that the levels of contamination would rise considerably in the future, so that wildlife,particularly aquatic organisms, would be more increasingly exposed, representing a potential risk for their populations.