Monohaloacetamide disinfection by-products are potential risk factors for the quality of mouse oocytes.

Haloacetamides (HAcAms) are nitrogenous disinfection by - products (N - DBPs) that are not currently regulated and possess high toxicity. Their prevalence in both drinking water and reclaimed water has been thoroughly documented. This study aimed to systematically evaluate the reproductive toxicity and underlying molecular mechanisms of monohaloacetamides (monoHAcAms) in female mice. Female mice were allowed ad - libitum access to drinking water containing 6.3 mg/L of monoHAcAms for a period of 5 weeks. Reproductive toxicity was assessed through fertility, ovarian histopathology, oxidative stress biomarkers, mitochondrial function assays, and single-cell RNA sequencing (Smart-seq2). The findings indicated a toxicity hierarchy as follows: iodoacetamide (IAcAm) > bromoacetamide (BAcAm) ≫ chloroacetamide (CAcAm). IAcAm exposure significantly impaired oocyte developmental competence, disrupted meiotic spindle integrity, and induced excessive oxidative stress accompanied by mitochondrial dysfunction. Transcriptomic profiling identified more than 700 differentially expressed genes involved in oxidative stress and energy metabolism pathways, suggesting that iodoacetamide perturbs the ovarian microenvironment through multiple molecular routes. These findings highlight haloacetamides as emerging environmental risk factors threatening female fertility, providing mechanistic insights into their reproductive toxicity and emphasizing the need for continuous monitoring of such contaminants in drinking water.