Deleterious effects of benzotriazoles on zebrafish development and neurotransmission: 5-Chloro-benzotriazole versus 1H-benzotriazole.

Benzotriazoles are heterocyclic compounds typically presenting a benzene ring fused with a triazole molecule. The industry uses these compounds as anti-corrosion agents and recently, they have been employed in the pharmaceutical industry and in detergent formulations. Benzotriazoles persist in the environment, and water treatment plants cannot degrade them completely. Consequently, these compounds have been detected in rivers, lakes, and drinking water, which makes assessing their safety for the human and aquatic animal populations crucial. Here, we have evaluated and compared how exposure to 1H-benzotriazole or 5-chloro-benzotriazole affect the zebrafish embryo-larval stages. We have determined the acute toxicity, morphometric alterations, and acetylcholinesterase activity on zebrafish embryos, as well as behavioral endpoints using the tail coiling assay. The estimated LC of 5-chloro-benzotriazole was 19 mg/L, whereas 1H-benzotriazole caused no mortality. The zebrafish embryos exposed to 20 and 25 mg/L 5-chloro-benzotriazole had decreased hatching rate and exhibited pericardial and yolk sac edemas. Furthermore, the embryo length and eye area were decreased, in contrast with an increased yolk sac after exposure to 20 mg/L 5-chloro-benzotriazole. In turn, 1H-benzotriazole also decreased the eye area of zebrafish embryos, but no other significant morphological alterations were observed. The tail coiling assay showed that the zebrafish embryos increased the percentage of time moving and the number of embryonic movements per minute after exposure to 1H-benzotriazole (15 mg/L) or 5-chloro-benzotriazole (20 and 25 mg/L), indicating that these compounds were potentially neurotoxic. However, acetylcholinesterase activity was not significantly altered in embryos exposed to 1H-benzotriazole, but significantly decreased when exposed to 0.05 mg/L 5-chloro benzotriazole confirming its neurotoxicity at a much lower concentration. Our findings showed that 5-chloro-benzotriazole seems to induce more harmful alterations to zebrafish embryos than 1H-benzotriazole. Nevertheless, 1H-benzotriazole seems to induce a direct effect on eye development for concentrations lower than the ones of 5-chloro-benzotriazole affecting zebrafish embryos.