Dibromoacetic acid impairs spermatogenesis: integrative evidence from human epidemiology, network toxicology, and mechanistic validation

Global declines in sperm quality urgently demand the identification of modifiable environmental risk factors. Dibromoacetic acid (DBA), a prevalent yet unregulated drinking water disinfection byproduct, is a suspected reproductive toxicant, but population evidence and clear mechanisms are lacking. By integrating epidemiology, network toxicology, and mechanistic validation, we first identified a significant negative association between urinary DBA (100% detection rate) and sperm concentration/count in 282 men. Histone-to-protamine replacement constitutes a critical step in sperm chromatin remodeling. In follow-up mechanistic experiments, we further verified that disruption of this process acted as a novel, central mechanism by which DBA triggered spermatogenic impairment in experimental models. Mechanistically, DBA activated the USF1-PIWIL1 axis to induce a specific piR-rno-9885 that post-transcriptionally suppressed Tnp1. Concurrently, it inhibited the chromatin remodelers CHD4/5. This dual-pathway synergy (piRNA-mediated Tnp1 suppression and CHD4/5 inhibition) compromised chromatin condensation. Moreover, DBA exposure perturbed hormonal homeostasis and triggered testicular inflammation, further disturbing the spermatogenic microenvironment. Collectively, our epidemiological data reveal an adverse human exposure association, while animal and cellular mechanistic assays validate DBA as a reproductive toxicant with a defined molecular mode of action. More broadly, our integrated approach establishes a translatable paradigm that bridges population-level association identification with in-depth mechanistic insight. This paradigm offers an actionable framework for drinking water monitoring, risk assessment, and regulation of DBA and analogous unregulated disinfection byproducts.