Feature Stories

Pinpointing Contaminant Exposure in a Virtual Home

interior of living room and kitchen in home with student in lab coat amongst various testing materials

The UTest house is a 1300 ft2 manufactured home located at the J.J. Pickle Research Campus at the University of Texas at Austin. The house is a three bedroom/two bathroom home built with conventional materials and has two independent HVAC systems, one in the attic space and one in the belly space beneath the home.

June 25, 2014

Because of the widespread use of phthalates in the environment and the potential for detrimental effects on human health, an urgent need exists to identify the most predominant sources and pathways of exposure. Methods to measure concentrations of chemicals in humans, known as bio-monitoring, can be costly and burdensome. CAEE researchers created a model of a hypothetical residential house with adjustable airflow systems to illustrate how phthalates released by a specific source might be predicted.  They developed an innovative micro-chamber method to quickly measure parameters needed for the model.

Phthalates are a class of chemicals used in numerous consumer products, including floor and wall coverings, car interior trim, clothing, gloves, footwear, wire insulation, artificial leather, and toys. Data from the Centers for Disease Control and Prevention suggest that more than three-quarters of the U.S. population may be exposed to these suspected endocrine disrupting chemicals. Children experience 2 to 10 times greater exposure than do adults.  

Assistant Professor Ying Xu and graduate students Yirui Liang and Chenyang Bi built on an earlier model that described how benzylbutyl phthalate (BBzP) and diethylhexyl phthalate (DEHP) are released from vinyl flooring into air and sorbs strongly to adsorbs strongly interior surfaces (e.g., walls, ceilings, windows, cloth, and furniture) and suspended particles.  They developed a novel method to measure key model parameters controlling phthalate emissions to air, which significantly reduced the test duration from several months (using conventional methods) to less than three days.  The research team conducted actual measurements in the UTest house to validate and refine the model; the UTest house is a 3 bedroom, 2 bath full-scale research house located at the J.J. Pickle Research Campus.

To test which parameters might change the amount of phthalate exposure through different routes, the researchers varied model parameters such as the amount of ventilation and velocity of air moving through a home. They concluded that a fan pushing air through the house would cause more skin contact with phthalates by increasing the release rate from vinyl surfaces to indoor air.  Air flow from fans also thins the boundary layer of air adjacent to skin, thus making it easier for phthalates from air to contact skin.  In addition, the researchers found that temperature has a great influence on phthalate emissions; an increase of room temperature from 20°C to 30°C can increase human inhalation exposure to phthalates by an order of magnitude.    

The team’s research efforts indicate that levels of phthalates measured in adults and children may result in part from contact with surfaces such as clothing and dust that adsorb high concentrations of phthalates. Furthermore, phthalate exposures arising from a single product (vinyl flooring) may differ by as much as 40 times depending on indoor environmental conditions such as temperature, home ventilation rates, and more. This variability underscores the wide range of potential exposures across the population, and the uncertainty of relying on human bio-monitoring alone to identify the most harmful sources.
 
Although their work to date focuses on vinyl flooring, the fundamental approach that Dr. Xu and her students have developed will be generalizable to a host of materials and products emitting various endocrine disrupting chemicals. The research provides an effective and economical way to identify the most important sources of phthalate exposure in the general population. It will be of value to architects and engineers who wish to specify low-emitting materials for use in healthy buildings, and allow the use of validated models for developing standards of product environmental performance or green labels.