When toxicity of plastic particles comes from their fluorescent dye: a preliminary study involving neotropical Physalaemus cuvieri tadpoles and polyethylene microplastics

The toxicity of microplastics (MPs) has been demonstrated in several previous studies, exposing different model organisms to fluorescent-labeled particles. However, many of these studies did not report the use of control groups for unbound and leaching dyes, which limits the conclusions about the bioaccumulative potential of these micromaterials and their (eco)toxicological effects. Thus, considering the need to evaluate the possibility of the toxicity of MPs resulting from the leaching of their dyes, we used Physalaemus cuvieri tadpoles to investigate whether the leachate of fluorescently labeling polyethylene MPs (PE-MPs) with Nile red dye induces behavioral changes, redox imbalance, anticholinesterasic effect, as well as changes in the growth/development of animals. By observing that the response of P. cuvieri tadpoles exposed to fluorescent PE-MPs and their respective leachate were similar, we confirmed the hypothesis that, alone, the fluorescent PE-MPs leachate can induce changes in antioxidant activity (inferred by SOD and CAT activity), in the mechanisms that mediate/regulate the production of NO and MDA, as well as in the animals' AChE activity. These results suggest that the Nile red dye eluted from PE-MPs can induce toxicological effects. Furthermore, we observed that the Nile red dye, when binding to the lipid components of the feed (and later being ingested by the animals), can induce interpretive biases on the bioaccumulative potential of PE-MPs. Therefore, for the evaluation of the (eco)toxicity of PE-MPs, it is important that extensive post-labeling cleaning steps of the PE-MPs (e.g.: via dialysis) and monitoring of the elution of fluorescent probes not bound to these particles be carried out before being added to the exposure water and that control groups for unbound and leaching dyes be established in future experimental designs, accounting for fluorescence induced by any other confounding factors.