Investigation of Daphnia magna Sub-Lethal Exposure to Organophosphate Esters in the Presence of Dissolved Organic Matter Using 1H NMR-Based Metabolomics

Abstract

Organophosphate esters (OPEs) are frequently detected in aquatic environments. Hydrophobic OPEs with high octanol-water partition coefficients (Log KOW) will likely sorb to dissolved organic matter (DOM) and consequently alter OPE bioavailability and sub-lethal toxicity. 1H nuclear magnetic resonance (NMR)-based metabolomics was used to evaluate how DOM (5 mg organic carbon/L) alters the metabolic response of Daphnia magna exposed to sub-lethal concentrations of three individual OPEs with varying hydrophobicity. D. magna exposed to the hydrophilic contaminant (Log KOW = 1.43) tris(2-chloroethyl) phosphate (TCEP) did not have substantial metabolic changes and DOM did not alter the metabolic response. There were significant increases in amino acids and a decrease in glucose from exposure to the hydrophobic contaminant (Log KOW = 3.65) tris(2-butoxyethyl) phosphate (TBOEP) which DOM did not mitigate, likely due to the high sub-lethal toxicity of TBOEP. Exposure to DOM and the hydrophobic contaminant (Log KOW = 4.76) triphenyl phosphate (TPhP) resulted in a unique metabolic response which was unlike TPhP only exposure, perhaps because DOM may be an additional stressor with TPhP exposure. Therefore, Log KOW values may not always predict how sub-lethal contaminant toxicity will change with DOM and there should be more consideration to incorporate DOM in sub-lethal ecotoxicology testing.

Targeting the Lowest Concentration of a Toxin That Induces a Detectable Metabolic Response in Living Organisms: Time-Resolved In Vivo 2D NMR during a Concentration Ramp

“…First, as mentioned above, the lack of temporal resolution would mean the inflection point of the metabolic responses would be hard to pinpoint, which would lead to considerable errors in the LCDR. Because of this, in traditional environmental metabolomics studies, the experiments are repeated at varying concentrations. , If attempted in vivo , for example an experiment involving three controls and three replicates (per concentration) at 16 different concentrations and each run lasting 24 h, then a study on a single chemical would take 51 days. In contrast, by using TR NUS in combination with a concentration sweep, the same experiment with both a more continuous concentration interpolation and a higher temporal resolution could be completed in just 6 days (three replicates and three controls), making it much more amenable to future toxicity screening.…”

Selective Amino Acid-Only in Vivo NMR: A Powerful Tool To Follow Stress Processes

“…69−72 In order to monitor and delineate processes that are taking place inside a living system via NMR spectroscopy, it is important to optimize data acquisition in the shortest time possible. 19,20,40,41,73 Here, the applicability of NUS is tested to see if 2D metabolite profiles can be captured in an accelerated fashion while still retaining spectral information.…”

Understanding the Fate of Environmental Chemicals Inside Living Organisms: NMR-Based 13C Isotopic Suppression Selects Only the Molecule of Interest within 13C-Enriched Organisms

“…As such, 300 ms was chosen as the best compromise that minimizes relaxation losses while still providing additional discrimination between macromolecules and low molecular weight species of interest. Reducing background signals in the aromatic region is critical given that molecules including contaminants/drugs and biochemicals, such as ATP and ADP, which are closely correlated to toxicity-induced energetic impairment in aquatic organisms, , resonate in this 1 H chemical shift region.…”