Uptake and Biotransformation Govern the Toxicity of Reactive Acrylamides in an <i>In Vivo</i> Zebrafish Embryo Model: Implications for NAM-Based Hazard Assessment

Acrylamides are widely used in polymer manufacturing and adhesives, and their electrophilic nature raises toxicological concerns when released into aquatic environments. However, their physicochemical diversity complicates the prediction of environmental fate and toxicity. To elucidate the main drivers of their toxicity in aquatic organisms, we investigated ten structurally diverse monomeric acrylamides and methacrylamides in zebrafish embryos (<i>Danio rerio</i>) (ZFE). Acute toxicity varied over 2 orders of magnitude (0.16-33 mM) and showed a moderate correlation with hydrophobicity (log<i>K</i>_lipw, <i>R</i>² = 0.87) and intrinsic electrophilic reactivity (log<i>k</i>_GSH). Measured bioconcentration factors of highly polar, reactive compounds (e.g., NMBA) for ZFE deviated up to 16-fold from model predictions, indicating limited uptake or significant biotransformation. This indicates an impact of toxicokinetics on their <i>in vivo</i> toxicity. UPLC-HRMS-based nontarget screening revealed 90 transformation products across the ten compounds. Glutathione conjugation and mercapturic acid formation were dominant pathways, with mercapturic acid-taurine conjugates observed for eight compounds, suggesting a previously undescribed detoxification mechanism for (meth)acrylamides in the ZFE. Our results highlight the need to integrate toxicokinetic data into hazard assessment of electrophilic compounds, as <i>in vitro</i> assays may overestimate risks. The ZFE provides a mechanistically informative <i>in vivo</i> model to reduce misclassifications, especially for polar and reactive chemicals.