Science Inventory

THE CHALLENGES OF AIR POLLUTION AND RESIDUAL RISK ASSESSMENT (EDITORIAL)

Citation:

SAHLE-DEMESSIE, E. THE CHALLENGES OF AIR POLLUTION AND RESIDUAL RISK ASSESSMENT (EDITORIAL). M.K. Banks (ed.), JOURNAL OF ENVIRONMENTAL ENGINEERING. American Society of Civil Engineers (ASCE), Reston, VA, 132(5):431-432, (2006).

Description:

The Clean Air Act (CAA), a comprehensive federal law that regulates air pollution from stationary and mobile sources, was first passed in 1963. The act has provided the primary framework for protecting human health and the environment. The CAA divides air pollutants into "criteria" pollutants, which include CO, NO2, SO2, lead, particulate matter and ozone, and hazardous air pollutants that consist of 188 chemicals and compounds. During the past three decades the CAA has resulted in reduction of several major air pollutants while the United States (U.S.) gross domestic product and energy consumption have increased briskly by 187 percent and 47 percent, respectively. During the same time period, the total criteria pollutants decreased 54 percent. For example, since 1970 emissions of lead (a neurotoxin that is particularly harmful to children) have been reduced by 98 percent because of the national unleaded gasoline program. Despite the progress that has been made toward cleaner air, serious air pollution problems remain, and more needs to be done to improve the nation's ability to confront future air pollution challenges.

While air quality in the U.S. has steadily improved over the past few decades, more than one hundred million Americans still live in communities where pollution causes the air to be unhealthy at times, according to the U.S. Environmental Protection Agency (U.S. EPA). In April 2004, the U.S. EPA reported that 159 million people lived in areas of the U.S. where air pollution levels exceeded the federal air quality standards for ground-level ozone. Despite major achievements in improving air quality, the number of smog days has been increasing in many areas during the past years.

Exposure to air pollution has been associated with cancer or numerous health problems, including decrease in lung functions, neurological damage, miscarriages, birth defects and increase in respiratory symptoms. Even short-term exposure to particle pollution is associated with cardiac arrhythmia, heart attacks and premature death. Recent studies have linked air pollution and lung cancer, and it has been suggested that the efffects of air pollution on the reduction of life expectancy are not uniformly distributed, but depend on factors such as education and antioxidant vitamin status. This implies that life expectancy could be reduced more in disadvantaged populations that are often disproportionately represented in neighborhoods near industrial sites.

The CAA Amendments of 1990 authorized the U.S. EPA to promulgate and implement technology based standards on emissions of nearly 188 hazardous air pollutants. These emission limits were to reflect the "maximum achievable control technology" (MACT) for categories of source and were adopted by the year 2001. The use of MACT relies on the engineering judgment about the amount of the reduction in emission. The U.S. EPA establishes emission limits as a percent reduction or a concentration limit that the regulated source must achieve. This strategy worked better than the risk-based approach to implement hazardous air pollutant standards that was used between 1970 and 1990. The result of risk-based standards was inefficient and ineffective, and the U.S. EPA listed only eight pollutants and regulated only seven air pollutant standards.

Implementing MACT standards has resulted in a significant reduction of toxic air emissions. However, the emission reductions that have been achieved as a result of the MACT program may not be sufficient to protect the public health and the environment. An assessment of the residual risk of toxic air emissions from MACT-regulated sources is needed to determine whether further controls are needed. For many source categories, this assessment may be challenging since it must encompass concerns of the people regularly exposed to toxic air pollutants, the data gap and the concerns in the model uncertainty, complexity of the assessment and economic concerns of the industries. A report from the Risk Commission states "local, regional and national levels of air toxics, by pollutants and by source categories must be put in the context of exposure from other air pollutant sources....". The context for a source category could depend on the health effects posed by a particular pollutants emitted from a given category, or on the extent to which other sources of the same pollutants contribute to the total air pollutant level. Therefore, the U.S. EPA has developed risk assessment methodologies with the help of internal scientists and the aid of the scientific community.

The U.S. EPA now has a Total Risk Integrated Methodology (TRIM) to evaluate the residual health risks and ecological effects associated with exposure to criteria and toxic air pollutants from different source categories. The method depends upon dispersion model to assess human exposure to toxic compounds. TRIM includes a multimedia exposure model, which can be used to conduct bioaccumulation and toxicity evaluations, fate and transport modeling, food web modeling, probabilistic exposure analyses; and the implementation of both screening-level and comprehensive weight-of-evidence assessments to characterize risks. This type of risk analysis could be expensive and resource intensive. The lack of data could likely pose problems and limit the use by state and local risk managers. However, regulatory dispersion models have become increasingly more accurate and less conservative.

The U.S. chemical industry has received a low favorable rating by state legislators, people who live in communities close proximity to chemical plants, and educators. These low favorable ratings were given despite a significant reductiion in accidental releases and transfer of toxic chemicals. On the other hand, three in four U.S. adults (74%) agree that "protecting the environment is so important that requirements and standards cannot be too high, and continuing environmental improvement must be made regardless of the cost." The chemical industry has understood that sustainable development that emphasizes reducing raw material and energy consumption, and minimizing waste will support sustainable environment, healthy population and competitive economy.

The high cost of further measures to reduce air pollution, an increased knowledge about the health effects of air pollution, and a push for more stringent standards, will warrant much scientific and regulatory interest. Risk assessors and decision makers may have to consider how to structure the analysis and present the scientific inferences in an appropriate way based on computer models and scientific uncertainty estimates. As environmental problems become more complex, the traditional approach may not be sufficient to solve them. Continued improvements will depend on an ability to consider risks collectively. The U.S. EPA is broadening its focus to include environmental health impacts from a perspective of public health. To strengthen the scientific understanding necessary to implement this strategy, more interdisciplinary research and broad participation of industrial and academic researchers are needed.

Record Details:

Record Type:DOCUMENT( JOURNAL/ NON-PEER REVIEWED JOURNAL)
Product Published Date:05/01/2006
Record Last Revised:05/31/2006
OMB Category:Other
Record ID: 144764