Impacts of triclosan exposure on zebrafish early-life stage: Toxicity and acclimation mechanisms

Triclosan (TCS) is a broad spectrum antibacterial agent widely used in personal care products and present in most aquatic ecosystems. This study investigated the occurrence of triclosan acclimation and the biological mechanisms underlying the stress response triggered in early-life stage of zebrafish. Zebrafish eggs were first exposed to four different sublethal concentrations of TCS (2, 20, 50 and 100 mu g/L) for 7 days following fertilization and subsequently exposed to a lethal concentration of TCS (1000 mu g/L). During the time-to-death exposure (TTD), mortality was continuously recorded to evaluate if increased resistance occurred. Overall, larvae exposed to 50 mu g/L of TCS demonstrated higher sensitivity, with delayed hatching and increased mortality during the sub-lethal exposure and significant lower mean time-to-death (TTD) value compared to the other groups. Interestingly, fish exposed to the highest concentration of TCS (100 mu g/L) presented a similar mean TTD value as controls and a significantly better survival in comparison with embryos exposed to 50 mu g/L, suggesting that acclimation process has been triggered at this concentration. Proteomic and enzymatic analyses were conducted on 7 days post fertilization (dpf) larvae exposed to 50 mu g/L and 100 mu g/L of TCS giving insights into the functional changes triggered at those specific concentrations. TCS seemed to affect proteins involved in cytoskeleton, stress response, eyes and neuronal development. This was endorsed by the enzymatic results, which suggest impairment in glutathione metabolism and acute neurotoxicity. A significant 2.5-fold and 3-fold increase of AChE activity was observed following TCS exposure. Moreover, GPx activity was significantly increased whereas a significant inhibition of GR activity was observed, suggesting that de novo synthesis of reduced GSH might occur in order to maintain the ratio between reduced and oxidized GSH. Proteomic results revealed possible candidate protein involved in the acclimation process of larvae exposed to 100 mu g/L of TCS. Our integrative analysis revealed complex non-monotonic concentration-related effects on zebrafish early-life stages with increased resistance between 50 and 100 mu g/L exposures. This research highlighted oxidative stress and neurotoxicity as major toxicity mechanisms of TCS during development.