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The Air We Breathe

Does animal agriculture affect air quality? Here’s what the former CEO of the Institute of Toxicology and Safety says.

by Wendy Powers

According to Roger McClellan, science alone cannot set standards. Judgment is required to determine how low is low enough for air emissions and their effect on human and environmental health.

McClellan is the former CEO for the Institute of Toxicology and Safety, and his data show that aggregate air emissions have decreased by 49 percent since 1980, despite a 32 percent increase in the U.S. population.

But where does animal agriculture fit in?

McClellan said that animal agriculture will play an important role in meeting future air emission regulations, pointing out recent and increasing interest in greenhouse gas emissions and the implication of animal agriculture in worldwide methane production. At the recent conference on Balancing Animal Agriculture and Communities, McClellan shared data showing how aggregate emissions have decreased in the past two decades, despite an increasing gross domestic product (GDP).

"Remarkable progress has been made in improving air quality," he said. "While the GDP increased 121 percent since 1980, vehicle miles traveled increased by 101 percent and energy consumption is up by 29 percent."

Further improvements in air quality remain an important topic, however, and talk continues about setting more regulations, particularly for the livestock industry.

Policy choices can be informed by science, McLellan said. Ideally, standards are based on epidemiological studies. In the absence of such studies, inhalation chamber studies are used. When these, too, are unavailable, mice are used as surrogates for a human response. The challenge in using such studies as the basis for policy is that it is difficult to draw relationships between factors when factors are variable.

McClellan gave examples such as the daily variation that occurs in pollutant concentrations in the environment and variation in mortality rates. As a result, policies are based on relative risk, typically set to accommodate sensitive populations. The EPA is not required to eliminate risk when setting standards, he noted.

"Rather, a judgment must be made in a ‘comparative health’ context when deciding what risks are acceptable in the world in which we live," McClellan said.

McClellan discussed other challenges in drawing the link between an activity and human health impacts. No unique disease is caused by air pollution—air pollution changes what already exists by increasing the prevalence of a disease, for example. Data collected under a specific scenario are not applicable to other areas. An example that McClellan provided is the use of air monitoring data collected in Detroit to represent air quality throughout the rest of Michigan.

Michigan faces challenges in making progress toward meeting the ozone standard, despite the progress made between 2004 and 2007, McClellan observed. Under a proposed change in the ozone standard, many counties throughout Michigan would be out of compliance. As standards become more stringent, the incremental cost of compliance becomes greater.

The presentation concluded with McClellan pointing out that "science and policy make awkward bedfellows, and it’s going to get more contentious in the bedroom."

This article was originally published in the May 2008 issue of the Scoop. Click here to read the entire issue.