A study in zebrafish shows that even tiny amounts of the flame‑retardant chemical TBBPS can mess up the hormone system that controls reproduction, leading to poorer eggs and embryos. These problems show up not only in the fish that were directly exposed but also in their children and grandchildren, even when the chemical is no longer detectable.

Tetrabromobisphenol S (TBBPS) is one of the most extensively used brominated flame retardants detected in the environment. Despite its widespread presence, the effects of persistent environmental exposure to TBBPS on the reproductive system remain unclear, raising significant health concerns. Here, using the zebrafish (<i>Danio rerio</i>) model, we identified significant intergenerational endocrine disruption and reproductive toxicity induced by TBBPS after a life-cycle (150 days) of parental exposure to environmentally relevant concentrations of TBBPS (0.01, 0.1, 1, 10, and 100 &#x3bc;g/L). TBBPS interfered with hormone levels and the expression of genes within the hypothalamic-pituitary-gonadal (HPG) axis in both F0 males and females, leading to reduced embryo quality. The parental transmission of TBBPS also impacted the endocrine and reproductive systems of the F1 fish, including the increase of gonadotropin-releasing hormone 3 neuron numbers, changes in hormone levels, and a decrease in embryo numbers. F2 fish also displayed endocrine disruption, even in the absence of detectable TBBPS residues, evidenced by altered fertilization rates and vitellogenin levels. Together, our findings show that exposure to environmentally relevant concentrations of TBBPS can induce reproductive toxicity that persists across generations, weakening the endocrine system and early growth in offspring by disrupting the HPG axis. These data provide critical insight into the persistent health risks posed by TBBPS.