Dynamic Accumulation and Co-occurrence of Phthalates and Squalene in Settled Dust: Implications for Assessing Indoor Phthalate Homology and Exposures

Abstract

Phthalate esters, as prevalent semi-volatile organic compounds (SVOCs) indoors, tend to accumulate in settled dust, posing lasting health risks. However, the dynamic process of this accumulation and the interactions with dust organic constituents remain poorly characterized, leading to uncertainties in their homology analysis and exposure assessment. This study investigated the dynamic accumulation and co-occurrence of phthalates and squalene (a major human skin lipid component) in settled dust from university dormitories over a 56-day period with longitudinal sampling. Results demonstrated that dust-phase phthalates and squalene required approximately 28 days to approach near-steady conditions under the present dormitory setting. Importantly, squalene was found to co-occur strongly with phthalates in settled dust, suggesting that correlation-based homology analysis of phthalates may be biased if potential confounding by dust composition is not considered. After adjustment for squalene, fewer phthalate–phthalate correlations remained significant, suggesting that source commonality inferred from settled-dust correlations alone may be overestimated. Furthermore, applying equilibrium models to dust samples collected before near-steady conditions were reached led to lower model-derived airborne concentrations and associated exposure estimates, particularly for high-molecular-weight compounds such as di-2-ethylhexyl phthalate (DEHP, up to 30%). These findings highlight the need to account for dust residence time in sampling protocols and to incorporate dust accumulation stage into settled-dust-based phthalate exposure assessment. This study provides critical insights into the dynamic accumulation of SVOCs in indoor dust, with direct implications for refining indoor SVOC homology and exposure assessment.