Modern indoor environments contain a vast array of manufactured materials, many of which emit toxic contaminants. Of special concern are indoor levels of phthalate plasticizers, which have increased substantially in recent decades. These semi-volatile organic compounds (SVOCs) enhance product performance, and are ubiquitous, redistributing from their original sources to indoor air, and subsequently to all interior surfaces. Because they partition so strongly to surfaces, many SVOCs persist for years after the source is removed. Biomonitoring (measuring concentrations in blood and urine) provides direct evidence of the virtually universal human exposure to plasticizers, which may result in profound and irreversible changes in the development of the reproductive tract. A recent report by the National Academies urgently recommends that the most important sources of phthalate exposure be identified. While biomonitoring alone cannot provide this answer, the PIs have developed and validated a fundamental approach that can be used to identify the most important sources of exposure to plasticizers. Building on this promising conceptual leap in understanding, their research objectives are to: (1) Select several indoor polyvinyl chloride products (PVCPs) based on the measured concentration of different phthalates present in the materials (C0); (2) Develop a novel, direct, solid-phase microextraction (SPME) method to measure (y0) the gas-phase concentration in equilibrium with C0, and use the resulting C0 vs y0 data to establish the nature of the equilibrium relationship as a function of temperature; (3) Characterize emissions of the target phthalates from nine of the selected PVCPs and validate their emissions model for the new phthalates in chamber experiments over a range of temperatures; (4) Extend the chamber approach to simultaneously measure emissions from two sources of phthalates (with each material acting as a sink for the phthalate from the other material); (5) Test the effect of temperature on phthalate emissions, sorption and condensation in vehicles under controlled conditions, and compare the results with analogous chamber studies; and (6) Use the measured/predicted y0 values to estimate screening-level exposure for the entire range of PVCPs studied and combine exposure with toxicity from ToxCast? to get risk, providing a simple method for the rapid prioritization of indoor sources most harmful to human health.
This research builds on the first successful elucidation of the fundamental mechanisms governing the release of phthalates from polymer materials. The PIs will, for the first time, develop an innovative new SPME method to measure y0; establish the equilibrium relationship between C0 and y0 as a function of temperature; and test the temperature effect on phthalate emissions and sorption in cars and homes. The temperature effect could be of great significance when sunlight shines directly on a PVCP surface in a room or car, increasing the emission rate by orders of magnitude. When a person enters a hot car and turns on the air conditioning without opening the windows, the cooling phthalate vapor will condense, coating interior surfaces, including human skin, with a thin film of liquid phthalate, imposing potentially significant health risks. The PIs also will develop a powerful yet simple screening-level exposure assessment approach for PVCPs, and substantially enhance our ability to predict exposure (via inhalation, dermal sorption and oral ingestion of dust) to all phthalate plasticizers.
Their fundamental approach to predict exposure to phthalates in PVCPs can almost certainly be generalized to a wide range of other SVOCs (PBDEs, organotins, and pesticides) emitted from a host of materials and products found in homes, cars, schools, offices, and factories. The new mechanistic understanding will enable the conscious design of green materials because the chemical and material properties that govern emissions are clearly understood. Diversity will be inculcated through their ACE (Academic Credit for Experimentation) program, as well as through personal relationships with colleagues at three HBCUs. The undergraduate ACE students at Virginia Tech will estimate exposure to some of the PVCPs in their own homes, enabling identification of new phthalate-laden PVCPs entering the market as well as some of the ?legacy? products that are no longer produced. Given that most PVCPs emit phthalates for decades, this constitutes a vital aspect of the project. The undergraduate students at UT Austin will be engaged in the first temperature controlled tests of automobile cabins. Their approach for estimating screening-level health risks can be used to prioritize cost-effective action, and could revolutionize how human health effects of indoor materials are evaluated.
