Organic Contaminants of Emerging Concern (OCECs) in Indoor Air: A Perspective on Global Distribution and Hazard Burden

Abstract The diversity and concentrations of organic contaminants of emerging concern (OCECs) in indoor air are increasing, yet their distribution and potential hazard burdens remain insufficiently understood. This review synthesizes seven major classes of indoor OCECs, encompassing over 130 compounds across diverse indoor environments (residences, offices, schools, and commercial spaces). Acrossmicroenvironments, OCECs exhibit distinct distribution patterns, with phthalate alternatives (PAEAs) dominating residential air (up to 2.08 × 104 ng/m3), per- and polyfluoroalkyl substances (PFAS) in schools (up to 230 ng/m3), organophosphate esters (OPEs) in offices (up to 159 ng/m3), and both PFAS (up to 316 ng/m3) and alternative halogenated flame retardants (AHFRs) (up to 0.340 ng/m3) in commercial environments. Although included in the occurrence synthesis, microplastics (MPs) were excluded from the inhalation hazard index due to inconsistent units and toxicity metrics. Inhalation hazard prioritization revealed that the United States, Germany, Sweden, and China exhibited relatively higher hazard burdens, with PAEAs, chlorinated paraffins (CPs), OPEs, and PFAS identified as the predominant contributors. However, the higher estimated hazard levels in these countries may partly reflect more comprehensive monitoring efforts and broader chemical coverage, rather than indicating inherently greater indoor OCEC contamination. These findings highlight the need for globally standardized monitoring strategies and harmonized assessment frameworks.