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Research Programs: Clean Air
Air Toxics
NHEERL Research Programs
Problem: The Clean Air Act Amendments of 1990 defined a two-stage regulatory program for hazardous air pollutants (HAPS, or air toxics). The two stages are: 1) apply maximum achievable control technologies to control emissions of 188 HAPs from numerous sources; and 2) evaluate health risks remaining after compliance with control requirements and apply new controls if needed. In the next decade, the risk-based provisions will be prominent and require improved risk assessment methods and data for confident decision making. Available risk methods and data, however, are limited and research is needed to reduce uncertainties to support improved risk assessments and management of air toxics. In addition, the mobile sources program faces submission of industry data on new fuels/fuel additives and they rely on research to help evaluate the relevance of these data in making management decisions.
Scientific Questions:
- What are the mechanisms or mode of action of HAPs in initiating and exacerbating human disease?
- How can we extrapolate dose-response among members of HAP groups, between animals and humans, across routes and scenarios of exposure?
- How can we identify and characterize factors that increase susceptibility to HAP compounds?
- Can we develop exposure-dose-response models that could be incorporated into the OAR TRIM model?
- How can we identify mixtures of HAP compounds for which the hazard is greater than predicted by a default assumption of additive toxicity?
- Can we develop biomarkers and models addressing adverse health outcomes for the biomarkers?
Approach: NHEERL is performing in vivo and in vitro toxicology studies in animals -- and in some cases humans-- to elucidate mechanisms of action and understand exposure-dose- response relationships and factors affecting HAP toxicity. We are developing animal models of human disease to study factors affecting susceptibility, and we are providing consultation on new fuels and fuel additives.
Recent Highlights:
- We have found that inhalation of trichloroethylene (TCE), a volatile organic solvent, causes a unique mid-frequency hearing loss in test animals.
- When evaluating effects of short-term exposures, we found that simple concentration-duration models may not predict responses as well as peak concentration or other estimators
- Using rodents, we found a direct link between DNA adducts formed in the lungs and mutations found in lung tumor oncogenes for certain PAHs.
