Uncovering the Fate and Global-Scale Risk-Based Threshold Contents of Organophosphate Esters in Indoor Environments: A Tiered Modeling Approach

Abstract Organophosphate esters (OPEs) are ubiquitous indoors, posing threats to public health. However, limited information on both the permissible levels and environmental behavior makes global regulation challenging. Herein, a closed-loop mechanistic framework, termed the Indoor OPE Source Identification and Exposure Direct Assessment (IOSIEDA) model, tracing the cause-and-effect chain from OPE source contents to health impacts, was developed to forecast indoor OPE emissions and fate, rapidly screen risks, prioritize high-risk OPE-material combinations, and back-calculate risk-based threshold contents (RTCs). Model evaluation via Monte Carlo simulation and a residential case study revealed a total Σ13OPEs influx of ∼2053 μg day–1, predominantly originating from indoor source emissions (99.4%), with 95% loss via air exchange. Notably, the IOSIEDA model back-calculated the RTCs within a risk-based framework built upon the source-specific relationship between OPE contents and emission characteristics, developing health-prevention-oriented thresholds for a set of unregulated OPEs across five types of understudied source materials. Global application across 16 countries provided emissions and an RTC database for indoor OPEs, filling in the missing values for global national thresholds of OPEs in specific source materials. Total residential OPE emissions were estimated at ∼74,500 kg yr–1; Asia constitutes the major emission region, and RTCs exhibit distinct regional disparities across continents.