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Human Health
IEMB is working, in cooperation with the other Laboratories within EPA's Office of Research and Development (ORD), to help develop better approaches and models to aid the Agency in directing its regulatory and research efforts to most effectively improve the health of the U.S. population.
Most of IEMB's projects in this area have been initiated fairly recently.
- Under the "Buy Clean" initiative, the Branch is providing modeling support to the Office of Pollution Prevention and Toxics (OPPT) and to the Office of Radiation and Indoor Air. The Buy Clean program is intended to provide guidance to vendors and school systems, encouraging the manufacture and procurement of building materials and consumer products that will reduce the exposure of children with respiratory problems to airborne irritants in school buildings.
- In a joint program with other ORD Laboratories under the Children's Health Initiative, IEMB has been characterizing the sources of Stachybotrys chartarum and other microbial aerosols, and investigating risk management approaches to reduce the exposures of children to these microbial agents indoors. This work is described in a separate page on this web site (follow the Children's Health Initiative link on the menu bar to the left).
- IEMB is working with other ORD Laboratories, in a project under the Asthma and Children's Health Initiatives, to develop methods for addressing the asthma end-point within the National Children's Study (NCS), as part of EPA's contribution to this multi-agency (NIH/EPA/CDC) effort. IEMB's current role in this project is to develop simplified methodology for estimating the indoor exposure of NCS cohort participants to gaseous combustion-related pollutants (SO2, NOx, and O3) and to a full range of bioaerosols (including non-viable fragments of fungal organisms), to enable assessment of the role of these contaminants in NCS asthma outcomes.
- IEMB will be providing input to the source module of ORD's multi-media/multi-pathway source-to-effects model for estimating aggregate and cumulative exposures of the U.S. population to a wide range of contaminants. Among currently planned IEMB activities is an evaluation of the effect of a building's heating and cooling system (including air filters) on indoor exposure to pollutants that are: a) generated indoors; and b) penetrating from outdoors.
Buy Clean Program
As indicated above, the overall objective of the Buy Clean program is to reduce the exposure in schools
of children with respiratory problems, by providing guidance to:
- school systems, to promote procurement and proper use of "clean" products; and
- to manufacturers, to promote development and marketing of clean products.
OPPT has the lead responsibility under the Buy Clean program, and currently has pilot program grants to 9 of the 10 EPA Regional Offices. Among the product categories receiving emphasis in OPPT's current effort is ‘custodial products.'
Accordingly, IEMB's initial effort addresses water-based cleaners used in schools. Specifically, IEMB is proceeding to develop and validate a simple source model describing how the emissions of VOCs from wet cleaner films are impacted by the surfactants present in these cleaners as the active cleaning agents. Such VOCs are present as solvents, fragrances, and disinfectants. This source model will then be incorporated into a user-friendly "exposure model" (that predicts how cleaner emissions translate into concentrations encountered by the children), that can be used for decision-making by school personnel and manufacturers as part of OPPT's Buy Clean outreach effort.
The first step in developing the source model will be the development of a fundamental structure activity model, estimating how surfactants of various molecular configurations modify the Henry's Law constant for VOCs of various structures, solubilities, etc., as a function of surfactant concentration. The Henry's Law constant will be modified by surfactants because the surfactant will tend to draw VOCs into micelles, increasing their solubility in water (and hence inhibiting their ability to vaporize out of aqueous solution).
Laboratory headspace testing to develop this structure activity model is about to begin, using laboratory-generated aqueous surfactant/VOC mixtures that systematically vary the parameters of concern. These tests will include a range of nonionic, anionic, and cationic surfactants commonly found in cleaners (such as nonylphenol polyethoxylates, alkyl alcohol polyethoxylates, alkyl dimethyl benzyl ammonium chloride, and sodium dodecyl benzene sulfonate), and a range of VOCs (such as ethylene glycol monobutyl ether solvent, d-limonene fragrance, and o-phenyl phenol disinfectant).
The second step in developing the source model will be the incorporation of the fundamental structure activity model into a mass-transfer-based source model equation, and the validation of this source model equation using films or pools of aqueous surfactant/VOC mixtures in EPA's 53-L dynamic test chambers.
The validated source model will then be incorporated into one of IEMB's IAQ component-network mass balance models, such as IAQX or RISK (follow the Indoor Air Quality Modeling link at left for more information). This mass balance model will be equipped with a user-friendly interface, and will incorporate default values for any basic parameters needed for model use, to reduce the effort required by the user. IEMB would then assist with the incorporation of this user-friendly model in OPPT's Buy Clean outreach.