Dynamic assessment of phthalate exposure: Linking internal and external monitoring in diverse indoor environments

Phthalates (PAEs), as prevalent endocrine disruptors, are widely distributed in indoor environments and enter the human body through dermal contact, respiratory inhalation, and ingestion, subsequently participating in metabolic processes across various organs and tissues. Existing studies primarily focus on predicting regional exposure scenarios to assess internal or external exposures risks; however, limited studies have systematically examined the correlation and discrepancies between internal and external exposures. This study collected PAEs samples from three phases (gas, particle, and dust phases) across three representative indoor environments and conducted urinary biomonitoring of phthalate metabolites (mPAEs) among exposed populations. Results showed that PAEs concentrations in the gas phase (21.67 μg·m^-3) and particle phase (2.38 μg·m^-3) were significantly higher in laboratories than in dormitories and offices, whereas office desktops exhibited the highest dust phase concentration (312 μg·g^-1). Urinary analysis revealed distinct metabolic profiles across populations: MBP was the dominant metabolite in office and dormitory groups (median: 19.3 ng·mL^-1 and 10.4 ng·mL^-1, respectively), while MMP prevailed in laboratory populations (median: 18.3 ng·mL^-1). Seasonal variation analysis indicated that urinary mPAEs concentrations were 4.28 times higher in summer than in winter. Demographic analysis showed that mPAEs levels were higher in males, individuals with obesity, and those with frequent plastic use compared to females, individuals with normal BMI, and those with infrequent plastic use. Furthermore, external exposure estimated from ambient PAEs concentrations exceeded internal exposure derived from urinary mPAEs concentrations by 17.3 %. These findings provide critical insights into exposure pathway differentiation and risk assessment optimization for indoor PAEs contamination.