Incense and Candle Burning: A Major Source of Phthalate Exposure in Indoor Environments

Abstract

Incense and candle burning, deeply rooted in cultural and aesthetic practices, are increasingly recognized as a significant source of indoor air pollution. The present study employed spectrometry-based techniques to characterize candle and incense emissions at the molecular level, focusing on diethyl phthalate (DEP), a widely used plasticizer raising concerns over its endocrine-disrupting and neurotoxic effects. Experiments were conducted under controlled chamber conditions and in realistic indoor environments to quantify DEP emission factors, temporal profiles, chemical stability, and phase partitioning. As the dominant ester species, DEP was consistently detected across all samples examined, comprising on average ~18.8% and ~2.4% of the identified molecular features in incense and candle aerosols, respectively. Moreover, DEP demonstrated sustained stability under acidic and photolytic conditions, suggesting its persistence in indoor environments. Notably, incense smoke retained DEP primarily in the particle phase, whereas candle emissions exhibited a more dynamic distribution yet still maintained a particle fraction exceeding 80%. These results contrast with other household sources that primarily release DEP as vapors, implying that combustion-derived DEP poses a greater exposure risk due to its efficient pulmonary deposition in particle-bound form. A further exposure assessment integrating our airborne measurements with literature data revealed that inhalation is the dominant exposure pathway, exceeding the combined intake from dermal absorption and ingestion by nearly an order of magnitude. This dominance driven primarily by incense emissions underscores the need for further investigation into the long-term health risks associated with chronic DEP inhalation.