Health Risks of Multiple Air Pollutants Examined by EPA

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By Pat Rizzuto

July 13 — The Environmental Protection Agency is developing an approach to understand the health risks posed by mixtures of different air pollutants.

Barbara Buckley, a toxicologist working in the EPA's National Center for Environmental Assessment, described during a July 12 webinar a conceptual approach the agency is developing to assess mixtures of air pollutants.

Buckley said the Adverse Outcome Pathway approach the EPA is exploring is at the research stage; information would be used to identify additional studies that could address critical data gaps. The approach, however, marks an important shift in the agency from a single-pollutant at a time approach to assessing multiple pollutants in the air people breathe, she said.

The EPA sets national ambient air quality standards (NAAQS) for ozone, lead, particulate matter, nitrogen dioxide, sulfur dioxide and carbon monoxide.

The agency's integrated science assessments of these pollutants, which synthesize the most policy-relevant health studies, provide essential information for those regulatory standards, Buckley said. She spoke during a one of a series of webinars on Alternative Approaches for Acute Inhalation Toxicity” co-hosted by the PETA International Science Consortium Ltd. and the National Toxicology Program's Interagency Center for the Evaluation of Alternative Toxicological Methods.

Can Adverse Outcome Pathways Address Mixtures?

The problem the EPA is addressing is that its standards focus on one criteria air pollutant at a time, even though people breathe air that contains a mixture of pollutants, Buckley said.

The EPA is exploring whether an Adverse Outcome Pathway approach could help, she said.

Such pathways describe a chain of biological changes that must occur to trigger a specific health problem. Analysts can then examine whether a chemical, a group of chemicals, or in this case a combination of air pollutants, would cause the critical biological changes. The EPA, European Joint Research Center, Army Corps of Engineers and the Organization of Economic Cooperation and Development are among the institutions developing Adverse Outcome Pathway approaches to assess the health and ecological effects of chemicals, according to an EPA backgrounder.

The EPA tested the pathway approach using two case studies, Buckley said.

The first case study, Buckley said, examined airway hyper-responsiveness, an excessive response to irritants illustrated by asthma.

Scientific studies have found that people exposed to ozone, nitrogen dioxide and sulfur dioxide for short periods of time may need to use asthma inhalers, have to go to the emergency room and experience other respiratory problems, she said. Long-term exposure is associated with asthma, bronchitis and other more chronic problems, she added.

EPA's analysis showed that all three pollutants cause specific biological changes that could lead to subsequent airway inflammation and asthma.

The second pathway the agency examined focused on lung injuries, oxidative stress and other critical biological changes that cause increased blood pressure, plaque build up in the circulatory system, heart attacks and other health problems.

Particulate matter, in particular, but also ozone can cause the biological changes that can lead to these subsequent problems, Buckley said.

Buckley is the principal author of a paper published July 18, 2015, in the journal Toxicology that described both case studies and limitations of the Adverse Outcome Pathway approach.

To contact the reporter on this story: Pat Rizzuto in Washington at

To contact the editor responsible for this story: Larry Pearl at

For More Information

An abstract of Buckley's paper, Conceptual Model for Assessing Criteria Air Pollutants in a Multipollutant Context: A Modified Adverse Outcome Pathway Approach, is available at, which has instructions to purchase the full paper.

Details on the webinar series are available at

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