Spatial Distribution Characteristics and Human Health Risk Assessment of Organophosphate Esters in Indoor Dust in...

Organophosphate esters (OPEs), extensively employed as flame retardants and plasticizers, have emerged as ubiquitous contaminants in indoor environments following the phase-out of brominated flame retardants. However, the occurrence patterns, source characteristics, and exposure implications of emerging OPE congeners across diverse urban indoor microenvironments remain inadequately elucidated. In this study, twenty-eight OPE congeners were quantified in settled dust collected from eight representative indoor microenvironments and one outdoor reference site in Beijing, China. Total OPE concentrations exhibited pronounced spatial heterogeneity, ranging from 8.46 to 42.60 mg kg^-1, with the highest levels observed in subway stations and laboratories. Non-halogenated OPEs dominated the contamination profile, accounting for 80.7% of the total OPEs, whereas Tris(2-ethylhexyl) phosphate (TEHP), 2-Ethylhexyl diphenyl phosphate (EHDPP), Tris(1-chloro-2-propyl) phosphate (TCIPP), Tris(2-chloroethyl) phosphate (TCEP), and Triphenyl phosphate (TPhP) collectively contributed 85.1% of the overall burden. Correlation analysis and positive matrix factorization revealed that indoor OPE contamination was primarily associated with emissions from building materials, polymer-containing consumer products, furniture, and electronic equipment. Transformation-associated compounds such as Bis(2-butoxyethyl) hydroxyethyl phosphate (BBOEHEP) were detected in indoor dust, pointing to the plausible presence of OPE transformation processes in such enclosed settings. Exposure assessment demonstrated that dust ingestion accounted for over 98% of total OPE intake, resulting in substantially higher exposure levels in children than in adults. Although estimated non-carcinogenic and carcinogenic risks remained below established health-based thresholds, exposure was disproportionately driven by a limited number of congeners, particularly EHDPP, TCIPP, TCEP, and TEHP. These findings highlight the growing contribution of replacement OPEs to indoor chemical burdens and underscore the importance of incorporating transformation products and indoor aging processes into future exposure and risk assessments frameworks.