Transgenerational toxicity assessment of [C8mim]Br: Focus on early development, antioxidant defense, and transcriptome profiles in zebrafish

1-Methyl-3-octylimidazolium bromide ([C₈mim]Br), one of the most widely used and studied ionic liquids, is a contaminant of emerging concern. Acute exposure to high doses of [C₈mim]Br has been shown to induce a variety of toxicity effects in exposed animals. However, the detrimental effects of chronic parental exposure to low doses of [C₈mim]Br on unexposed offspring and the underlying mechanisms remain largely unknown. To this end, spawning-capable female and male zebrafish (F0 generation) were separately exposed to 25, 250, and 2500 μg/L of [C₈mim]Br for eight weeks and were then mated to spawn. The resulting eggs (F1 generation) were collected and cultured in [C₈mim]Br-free media for 96 h. We found that the early growth and development of F1 embryo-larvae, which were not directly exposed to [C₈mim]Br, were significantly inhibited. This was evidenced by delayed hatching, increased mortality, reduced body weight, slowed heartbeat, poor motility (decreased spontaneous tail-coiling movements and diminished escape responses to touch stimuli and water swirling), and uninflated swim bladders. Furthermore, fluorescent probe labeling and biochemical analyses revealed an accumulation of reactive oxygen species and impairment of the antioxidant defense system in F1 larvae from [C₈mim]Br-exposed F0 parents, indicating the induction of oxidative stress. Finally, transcriptomic sequencing demonstrated that the differentially expressed genes in F1 larvae were primarily involved in muscle development and contraction performance, offering mechanistic insights into the poor motility and associated developmental defects observed in F1 embryo-larvae. Overall, this transgenerational toxicity assessment underscores the adverse outcomes of parental [C₈mim]Br exposure on unexposed offspring, providing a crucial aspect of the ecological risks of [C₈mim]Br.