Toxicity of diflubenzuron, P-chloroaniline and their mixtures on zebrafish (Danio rerio, Hamilton 1922): effects in adults and in early life stages of development

Fish farmers have used the insecticide diflubenzuron (DFB) to control parasites in fish. One of the degradation products of DFB is p-chloroaniline (PCA), which is highly toxic. These compounds, individually or in a mixture, can be released into water bodies adjacent to production systems and negatively impact aquatic biota. Zebrafish (Danio rerio), in early life stages and in adults, were exposed to six concentrations of the insecticide, its metabolite and its mixtures (75%, 50% and 25% PCA). The highest toxicity was manifested in larvae and was attributed to PCA (LC50-96h = 13.5 mg·L -1), 75% PCA combination (LC50-96h = 12.6 mg·L-1) and 50% PCA combination (LC50-96h = 15.6 mg·L-1). The insecticide showed lower toxicity when evaluated in isolation (LC50-96h = 81.2 to 124.3 mg·L-1. The embryos (1 h post-fertilization “1 hpf”) exposed to mixtures of DFB and PCA for 96 h presented a hatching delay. The LC50-96h value for the most toxic treatment (PCA) in embryos was very close that the related for larvae. The lowest protective concentration that would avoid fish species to chronic adverse effects (PCchronic) was estimated to be in the order of 0.13 mg·L-1 for PCA and 75% PCA mixture. The results contributes to better recognizing the ability of the insecticide (together with its metabolite and the mixtures of both) to harm living organisms and may assist future studies in the establishment of maximum concentration levels in aquatic compartments.