Grantee Research Project Results
2015 Progress Report: Rapid Methods to Estimate Exposure to SVOCs in Indoor Environments
EPA Grant Number: R835606Title: Rapid Methods to Estimate Exposure to SVOCs in Indoor Environments
Investigators: Little, John C , Marr, Linsey C.
Institution: Virginia Tech
EPA Project Officer: Aja, Hayley
Project Period: July 1, 2014 through June 30, 2017 (Extended to June 30, 2018)
Project Period Covered by this Report: July 1, 2014 through June 30,2015
Project Amount: $900,000
RFA: New Methods in 21st Century Exposure Science (2013) RFA Text | Recipients Lists
Research Category: Chemical Safety for Sustainability
Objective:
The major goals are to: (1) develop a novel method to measure the gas-phase SVOC concentration (y0) adjacent to the material surface in a consumer product; (2) measure the occurrence of SVOCs in consumer products (C0) and use resulting data to establish the nature of equilibrium relationship between C0 and y0; (3) conduct single-source experiments to characterize emissions of various SVOCs from the representative sources; (4) develop a novel method to determine surface/air partition coefficients (Ks) for selected SVOCs and six interior surfaces, including airborne particles (Kp) and dust (Kdust), and compare results to available correlations for Ks, Kp, and Kdust; (5) validate the single-source model using results from the chamber experiments for representative sources and the single-phase model using data collected from the literature; and (7) evaluate assumptions on which the rapid single-source and single-phase methods are based and characterize the uncertainty inherent in model predictions, especially for the low volatility SVOCs.
Progress Summary:
Results to date and their relationships to the goals of the project are summarized in the abstracts of each publication. Substantial progress has been made towards meeting project goals 1, 2, 3 and 4.
The mass content of plasticizers in six backpacks and seven toys was measured by extracting them in tetrahydrofuran. Bis(2-ethylhexyl) terephthalate (DEHT) was the most common plasticizer, dominating the composition of plasticizers in four backpacks (average mass content in product polyvinyl chloride, 5.38 ± 1.98%–25.5 ± 3.54%) and six plastic toys (8.17 ± 1.85%–21.2 ± 1.11%). The surface of each product was wiped with three dry and three wet (by isopropanol) cotton wipes, so as to evaluate the mass transfer of plasticizers to clothing and human skin, respectively. DEHT was the most common plasticizer detected on wipe samples. There were strong correlations (backpacks r = 0.90; plastic toys r = 0.96) between average mass transfer of DEHT to wet wipes and its average mass content in the product. The mass transfers of the five dominant plasticizers in one backpack to both dry and wet wipes were also correlated (both r = 1.00) with their mass contents. This work focused on the mass content of plasticizers in children’s backpacks and toys, and their mass transfer from product surfaces to cotton wipes. These results suggest that the mass transfer of plasticizers from products to clothing or human skin is strongly associated with their mass content.
Semi-volatile organic compounds (SVOCs) are present in many indoor materials. SVOC emissions can be characterized with a critical parameter, y0, the gas-phase SVOC concentration in equilibrium with the source material. To reduce the required time and improve the accuracy of existing methods for measuring y0, we developed a new method which uses solid phase micro-extraction (SPME) to measure the concentration of an SVOC emitted by source material placed in a sealed chamber. The experimental time was shortened from several days (even several months) to about 1 day, with relative errors of less than 5%. The measured y0 values agree well with results obtained by independent methods. The saturated vapor pressure (Vp) of one typical indoor SVOC, DEHP, was measured. Based on the Clausius-Clapeyron equation, a correlation that reveals the effects of temperature, the mass fraction of the target SVOC in the source material, and Vp on y0 was established. The proposed method together with the correlation should be useful in estimating and controlling human exposure to indoor SVOCs.
Semi-volatile organic compounds (SVOCs) are indoor air pollutants that may have significant adverse effects on human health. Although emissions of volatile chemicals from building materials and consumer products are usually characterized in small chambers, few chamber studies have been conducted for SVOCs due to the challenges associated with analysis and the lack of validation procedures. There is an urgent need for a reliable and accurate chamber test method to verify these measurements. A reference method employing a specially-designed chamber has been developed and is undergoing extensive evaluation. A pilot inter-laboratory study (ILS) has been conducted with six laboratories performing chamber tests at identical conditions for di-2-ethylhexyl phthalate (DEHP). Results from this study showed inter-laboratory variations of 24% for DEHP emission rates, with greater agreement observed between intra-laboratory measurements for most of the participating laboratories. The mechanistic emissions model fit well to the measured concentration profiles, demonstrating the feasibility of the proposed reference method to independently assess laboratory performance and validate SVOC emission tests.
Semivolatile organic compounds (SVOCs), such as phthalates, are ubiquitous in the indoor environment. Airborne particles play an important role in the distribution of SVOCs. The interactions between airborne particles and SVOCs increase the total airborne SVOC concentrations and consequent human exposure. In this study, a specially-designed pipe chamber with laminar flow regime was used to investigate the particle-mediated mass transfer of SVOCs, with di-2-ethylhexyl phthalate (DEHP) selected as the target compound. As the particles were introduced at concentrations of 40-110 µg/m3, the gas-phase DEHP concentrations maintained at a constant level, and the total concentrations increased by a factor of 2 to 3. The particle/air partition coefficient (Kp) and vapor pressure of DEHP was determined as 0.011 m3/µg and 2.7 µg/m3, respectively, based on the experimental measurements. The experimental quantification was combined with the Computational fluid dynamics (CFD) model analysis of transport phenomena. The results showed that SVOC transport between emission source and air is significantly enhanced in the presence of particles. This work reveals quantifiable influence of particles on overall SVOC dynamics and allows for a more comprehensive exposure assessment.
Future Activities:
We will focus on goal 4 during the next reporting period, although we will continue to work on the other project goals. A thermal desorber coupled with GC/MS will be used to include more SVOCs for analysis, including flame retardants. Different materials, including glass, aluminum, wood, plastic, artificial skin and dust, will be studied to determine partition coefficients between these materials and air.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 35 publications | 11 publications in selected types | All 11 journal articles |
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Wu Y, Cox SS, Xu Y, Liang Y, Won D, Liu X, Clausen PA, Rosell L, Benning JL, Zhang Y, Little JC. A reference method for measuring emissions of SVOCs in small chambers. Building and Environment 2016;95:126-132. |
R835606 (2015) R835606 (2016) R835606 (2017) |
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Xie M, Wu Y, Little JC, Marr LC. Phthalates and alternative plasticizers and potential for contact exposure from children’s backpacks and toys. Journal of Exposure Science and Environmental Epidemiology 2016;26(1):119-124. |
R835606 (2015) R835606 (2016) R835606 (2017) |
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Supplemental Keywords:
Risk assessment, pollution prevention, toxics, environmental chemistry, SVOCs, indoor air;Relevant Websites:
Annual Conference of the International Society of Exposure Science located in Utrecht, The Netherlands, 9 to 13 October, 2016 ExitProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.