Occurrence, human exposure and dynamics of phthalates in ACMV indoor environments : method development and field studies

Phthalates are a group of common indoor semi-volatile organic compounds (SVOCs) that can concurrently exist in gas-phase, airborne particle-phase and settled dust phases, due to their special physicochemical properties. Human exposure to phthalates in indoor environments has raised public concerns owing to the identified associations between phthalates and a number of adverse human health effects. This study first develops sampling and analytical methods for field studies of airborne phthalates. Based on the methods, the study investigates occurrence of typical phthalates in indoor air of air-conditioned environments and assesses the impacts of air-conditioning and mechanical ventilation (ACMV) system on indoor phthalate concentrations. The study further examines phthalate concentration differences in indoor air and in personal air. More importantly, the study investigates the impacts of human induced particle resuspension and generation on airborne phthalates concentrations. Meanwhile, it evaluates gas/particle partitioning of selected phthalates when there are different levels of particle concentrations in real indoor environments. In the development of sampling and extraction method, works mainly focus on testing homemade two-bed sorbent tubes with silanized glass wool and Tenax TA as sorbents for airborne phthalate sampling. The sorbent tubes can sample airborne phthalate at low air flow rate for shorter sampling times, improve detection limits of low-volatile phthalates, and are compatible with thermal desorption (TD) method. The development of analytical method tests the extraction efficiency of the tubes. The extraction procedures and parameters are optimized. Important issues including carry-over, recovery, repeatability and linearity are considered. The study investigates occurrence of five typical phthalates in 24 ACMV indoor environments that are covered with different flooring materials. The results show that bis(2-ethylhexyl) phthalate (DEHP) has higher airborne concentrations in the involved indoor environments when compared with the literature data. There is also evidence that the rooms covered by polyvinyl chloride have apparently higher DEHP concentrations than those covered by carpets. The calculated whole room emission rates suggest that there are strong source strengths of DEHP and DBP (di-n-butyl phthalate) in the indoor environments. The study evaluates the impacts of operations of the ACMV system on indoor concentrations of DEHP and DBP in a typical office. The results indicate that indoor DEHP and DBP concentrations accumulate when the ACMV system is off, but decrease continuously to certain quasi-stable levels when the ACMV system is on. The evidence demonstrates that the ACMV system does have certain level of impacts on the indoor concentrations of the both high-volatile and low-volatile SVOCs. The study compares personally sampled phthalates with the corresponding phthalates in the bulk indoor air in three rooms. The results show that there is no detectable difference between the personal concentrations and the environmental concentrations. The explanation may be that the sedentary subjects’ activities are not strong enough to resuspend settled particles, which carry significantly higher phthalate concentrations. This study conducts intentional particle resuspension and generation in well-controlled real rooms to understand the impacts of human activities on airborne phthalate concentrations as well as their gas/particle partitioning variations. The results suggest that increased airborne particle concentration due to both particle resuspension and generation can result in obvious increases in airborne concentrations of phthalates with low volatilities. The increases are because of either resuspension of phthalates bound to settled dust or partitioning of gas-phase phthalates to the airborne particles. The findings also demonstrate that the gas fractions of the low-volatile phthalates decrease when the airborne particle concentrations increase.Doctor of Philosophy (CEE