Bimodal regulation of organophosphate esters in estuarine systems: Source fingerprints, decoupled drivers, and...

The global phase-out of brominated flame retardants has driven the widespread use of organophosphate esters (OPEs), which readily leach into estuarine ecosystems. However, existing assessments lack a unified framework that decouples water-sediment drivers, links source fingerprints to structure-dependent risks, or addresses aryl-OPE toxicity. By compiling 1920 water and sediment samples from 48 estuaries across five continents (based on 75 peer-reviewed studies), we present the first global synthetic framework linking OPE sources, fingerprints, drivers, and risks. OPEs are ubiquitously distributed across global estuaries, with hotspots in industrialized Asia and Europe. Chlorinated OPEs dominate both water and sediment due to their high solubility and persistence, and sediment cores show a decades-long rise mirroring global consumption after PBDE phase-out. Multivariate clustering reveals three compositional fingerprints, suggesting four plausible input pathways: wastewater, manufacturing, shipping/aquaculture, and atmospheric deposition. Using XGBoost-SHAP, we uncover a bimodal regulation: socioeconomic/urbanization factors (GDP, population, and nighttime lights collectively) drive sediment OPEs with an inverted-U (Kuznets) trend, while climatic factors (precipitation and temperature) are the most important among those tested affecting aqueous OPEs. This matrix-specific decoupling explains why sediment records long-term industrial legacy while water reflects short-term climatic pulses. Multi-index risk assessment (RQ, WFRQ, JPC) identifies TCEP and TPHP as high-priority pollutants. Aryl-OPEs constitute only ∼5% of total OPE concentrations but pose risks comparable to chlorinated OPEs (WFRQ ∼0.24 vs. ∼0.25), revealing a "low-concentration, high-risk" paradox governed by structural toxicity. This study provides a transferable bimodal framework for land-sea contaminants and offers science-based priorities for global estuarine management.