Bacterial Transformation Products from Organophosphate Esters and Their Elevated Environmental Risks in Soil and...

Organophosphate esters (OPEs) are chemicals of emerging concern that pose risks to human and wildlife health. Soil microorganisms transform OPEs into diverse biotransformation products (BTPs), thereby broadening the exposure beyond the parent compounds. Therefore, the biotransformation processes, environmental occurrence, exposure pathways, and toxicities of these products have remained poorly characterized. We integrated laboratory and field investigations, high resolution mass spectrometry, and computational modeling to evaluate the risks associated with the use of OPE BTPs in soils and groundwater. We isolated soil bacteria capable of transforming organophosphate esters (OPEs) and integrated culture-derived fingerprints with field measurements to screen for transformation products occurring in the environment. Importantly, our pathway analysis indicates a previously under-recognized step in the transformation of the OPEs that is consistent with methylation, complementing hydrolysis and oxidative reactions. We identified five TPs, including bis(2-butoxyethyl) hydrogen phosphate, bis(2-ethylhexyl) hydrogen phosphate, bis(1-chloropropan-2-yl) hydrogen phosphate, diphenyl hydrogen phosphate, and methyl diphenyl phosphate, as prevalent in soil and groundwater. Relative to their parent compounds, these TPs exhibited higher toxicity (2.58-, 2.08-, 5.51-, 1.33-, and 1.36-fold) and posed greater ecological risks to aquatic organisms (16.31-, 2.32-, 1.41-, 39.45-, and 59.22-fold). Our findings highlight that bacterial biotransformation of OPEs can yield more hazardous transformation products and should be explicitly incorporated into chemical risk assessment and management frameworks.