Iodoacetic acid causes developmental toxicity in zebrafish.

Water disinfection can generate disinfection byproducts (DBPs) such as iodoacetic acid (IAA) by reacting with organic matter in water supplies. In vitro studies have shown that IAA is a cytotoxic and genotoxic DBP. In vivo studies using animal models further indicate that IAA has toxic effects on reproductive function and the endocrine system. Yet, its developmental toxicity remains unknown. In this study, we show that exposure to IAA at concentrations ranging from 1 to 100 µM induces dose-dependent embryonic mortality, with the greatest sensitivity observed during the first 24 hours of development. Sublethal concentrations cause delayed or failed hatching and disrupt the development of multiple vital organs. Notably, IAA exposure impairs swim bladder inflation, reduces otolith size, and decreases heart rate. Moreover, IAA reduces intestinal mucus production by suppressing genes essential for mucin production. Given the crucial role of intestinal mucus in defending against pathogens and maintaining host and gut microbiota homeostasis, the deleterious effect of IAA on mucus production highlights its potential pathogenic role in driving disorders linked to epithelial barrier dysfunction and microbiome dysfunction. Together, these findings demonstrate that IAA induces pronounced developmental toxicity affecting multiple organ systems in zebrafish. This study provides the first in vivo evidence that IAA disrupts embryonic development and intestinal function.