Transcriptome Analysis Suggests Chronic Toxic Effects of 1‐Ethyl‐3‐(3‐Dimethylaminopropyl)carbodiimide in <scp> <i>Daphnia magna</i> </scp> via Induction of Endoplasmic Reticulum Stress

Plastics have revolutionized modern life, yet their persistence in the environment poses a growing ecological threat. Biodegradable plastics, like polycaprolactone (PCL), offer a promising alternative, but their degradation can release toxic byproducts. In this study, we evaluated the ecotoxicological impact of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), a carbodiimide-based additive used to stabilize PCL, using Daphnia magna as a model organism. Chronic toxicity assays revealed that EDC exposure at concentrations as low as 1 mg/L significantly impaired reproduction, and concentrations above 7.5 mg/L caused complete lethality. To clarify the underlying molecular mechanisms, RNA-seq analysis was conducted using four developmental stages. Surprisingly, the highest number of differentially expressed genes appeared at Day 2, prior to visible phenotypic changes. Gene ontology and pathway analysis revealed that EDC exposure induced endoplasmic reticulum (ER) stress, indicated by suppressed ribosomal gene expression and enhanced protein folding and degradation pathways. Concurrently, sphingolipid metabolism and glutathione metabolism were altered, suggesting adaptive responses to maintain cellular homeostasis. These findings suggest that EDC leaching from degrading plastics can cause profound cellular and organismal toxicity, even at environmentally relevant concentrations. Our study highlights the need to assess the toxicity of not only intact polymers, but also their degradation byproducts, offering essential insights for safer plastic chemistry and for environmental risk evaluation.