Targeted metabolomics reveals varying impairments of 17α-ethinylestradiol exposure in the presence of dissolved organic matter to <i>Daphnia magna</i>

17α-ethinylestradiol (EE2) is a highly potent endocrine disrupting chemical (EDC) that pollutes aquatic ecosystems, leading to biological impairment in freshwater organisms such as Daphnia magna. Bioavailability of EE2 may be affected by the presence of dissolved organic matter (DOM), also found in aquatic ecosystems; however, these interactions are not fully understood. To address this, EE2 interactions with two DOM types with varying chemistry (Suwannee River [SR] DOM and Leonardite-derived DOM) are explored by examining molecular-level perturbations to the polar metabolic profile of D. magna. D. magna were acutely (48 hr) exposed to sublethal concentrations of EE2 (high = 1 mg/L and low = 0.1 mg/L) and mixtures of each DOM type. Targeted metabolomics using liquid chromatography-tandem mass spectrometry was used to measure 52 polar metabolites from individual adult daphnids. In the absence of DOM, EE2 exposure at both concentrations significantly affected key metabolites and pathways that are essential for growth and survival in D. magna. Exposure to the DOM-SR and EE2 mixture resulted in the highest number of significant metabolite and pathway perturbations, whereas exposure to the Leonardite DOM and EE2 mixture demonstrated the least disruptions. These results suggest that the Leonardite DOM likely lowered the bioavailability of EE2 through binding, whereas the DOM-SR enhanced metabolic disruptions. Thus, these findings affirm that different types of DOM can distinctively affect EE2 behavior and biological response at the molecular-level, highlighting the importance of considering DOM chemistry when examining its interactions with pollutants and subsequent impacts to aquatic organisms.