Environmentally relevant concentrations of triclosan induce lethality and disrupt thyroid hormone activity in zebrafish (Danio rerio)

Uptake, tissue distribution, and biotransformation pattern of triclosan in tilapia exposed to environmentally-relevant concentrations

Although triclosan has been ubiquitously detected in aquatic environment and is known to have various adverse effects to fish, details on its uptake, bioconcentration, and elimination in fish tissues are still limited. This study investigated the uptake and elimination toxicokinetics, bioconcentration, and biotransformation potential of triclosan in Nile tilapia (Oreochromis niloticus) exposed to environmentally-relevant concentrations under semi-static regimes for 7 days. For toxicokinetics, triclosan reached a plateau concentration within 5-days of exposure, and decreased to stable concentration within 5 days of elimination. Approximately 50 % of triclosan was excreted by fish through feces, and up to 29 % of triclosan was excreted through the biliary excretion. For fish exposed to 200 ng·L-1, 2000 ng·L-1, and 20,000 ng·L-1, the bioconcentration factors (log BCFs) of triclosan in fish tissues obeyed similar order: bile ≈ intestine > gonad ≈ stomach > liver > kidney ≈ gill > skin ≈ plasma > brain > muscle. The log BCFs of triclosan in fish tissues are approximately maintained constants, no matter what triclosan concentrations in exposure water. Seven biotransformation products of triclosan, involved in both phase I and phase II metabolism, were identified in this study, which were produced through hydroxylation, bond cleavages, dichlorination, and sulfation pathways. Metabolite of triclosan-O-sulfate was detected in all tissues of tilapia, and more toxic product of 2,4-dichlorophenol was also found in intestine, gonad, and bile of tilapia. Meanwhile, two metabolites of 2,4-dichlorophenol-O-sulfate and monohydroxy-triclosan-O-sulfate were firstly discovered in the skin, liver, gill, intestine, gonad, and bile of tilapia in this study. These findings highlight the importance of considering triclosan biotransformation products in ecological assessment. They also provide a scientific basis for health risk evaluation of triclosan to humans, who are associated with dietary exposure through ingesting fish.

Assessment of thimerosal effects in sublethal concentrations on zebrafish (Danio rerio) embryos exploring NMR-based metabolomics profile

Thimerosal, a preservative commonly used in the pharmaceutical and cosmetic industry, has raised concerns regarding its potentially toxic effects as an organic mercury compound. Within this context, using an NMR-based metabolomics profile and chemometric analysis, zebrafish embryos were used as an in vivo model to study the effects of thimerosal in metabolic profiles after exposure to sublethal concentrations of the mercury compound. The thimerosal concentrations of 40 and 80 nM were employed, corresponding to 40% and 80% of the LC50, respectively, for zebrafish embryos. The most significant alterations in the metabolic profile included changes in carbohydrates, amino acids, nucleotides, trimethylamine-N-oxide, ethanolamine, betaine, and ethanol. Furthermore, thimerosal exposure affects various metabolic pathways, impairing the nervous system, disrupting protein metabolism, and potentially causing oxidative damage. Therefore, adopting a metabolomics approach in this investigation provided insights into the potentially implicated metabolic pathways contributing to the deleterious effects of thimerosal in biological systems.