Emerging
Issues in Air Toxics Regulation
Urban Air Toxics Strategy
EPA's Integrated Urban Air Toxics Strategy focuses on reducing the human
health threats from air toxics in urban areas. Toxic and hazardous
air pollutants are of special concern in urban areas because large concentrations
of people live and work near a variety of pollution sources. The
goals of the program are three-fold:
- To reduce by 75% the risk of cancer associated with air toxics from
both large and small commercial and industrial sources;
- To substantially reduce noncancer health risks (e.g., birth defects
and reproductive effects) associated with air toxics from small commercial
and industrial sources; and
- To address and prevent disproportionate impacts of air toxics hazards,
such as those in areas known as "hot spot," and on sensitive
populations in urban areas, including children, the elderly, minority
and low-income communities.
To accomplish these goals, EPA identified 33
of the 188 hazardous air pollutants posing the greatest threat
to public health in urban areas. This list is based on the quantity
of pollutants released to the air, the harm caused by these pollutants,
and the estimated concentration in the air.
To date, EPA has identified a total of 70 area source categories which
represent 90% of the emissions of the 33 listed air toxics. Of
these 70 area source categories, MACT standards have been developed
for 15 and the remaining area source standards are under development
or will be developed in the future. A list of the source categories
is available on EPA's website at http://www.epa.gov/ttn/atw/urban/arearules.html. A
fact sheet further explaining the Urban Air Toxics Strategy is available
at http://www.epa.gov/ttn/atw/urban/strategyfs0303.pdf.
Maine is working with EPA and other states to draft rules for the remaining
area source categories. In particular, Maine is working with EPA
on these categories: auto refinishing, stationary internal combustion
engines, industrial boilers, gasoline distribution, and fabricated metal
work.
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Residual Risk
The 1990 Clean Air Act (CAA) Amendments directed EPA to evaluate the
risks remaining after the application of maximum achievable control
technology (MACT) standards. These are known as residual risks. EPA
is to consider the need for additional standards following MACT implementation
to protect public health and the environment. The CAA also specifies
that such residual risk standards “provide an ample margin of
safety to protect public health” and requires EPA to determine
whether residual risk standards are necessary to prevent “an adverse
environmental effect,” taking into consideration “costs,
energy, safety, and other relevant factors” in deciding what level
is protective.
In the first step of this residual risk assessment, the CAA required EPA
to report to Congress on the methodology it would use to assess the
residual risk. EPA's framework for risk assessment consists
of four steps:
- Hazard Identification. The first step in
a risk assessment is to determine whether to pollutants of concern
can be causally linked to health effects in question (cancer and/or
non-cancer health effects). Factors such as the route of exposure,
the type and quality of the effects, the consistency of findings
across studies, and the potential for bioaccumulation all contribute
to the strength of the hazard identification statement.
- Dose-response Assessment. This step is the
quantitative characterization of the relationship between the concentration,
exposure (or dose) of a pollutant and the resultant health effects. When
adequate data exist, a dose-response assessment for non-cancer effects
is the identification of exposure level that humans could experience
daily for a lifetime without appreciable probability of ill effect.
Dose-response assessment may also look at short-term exposure levels
and the probability of ill effect.
- Exposure Assessment. An exposure assessment
for air toxics has four major components: (1) emissions characterization;
(2) environmental fate and transport analysis; (3) characterization
of the study population; and (4) exposure characterization for both
inhalation and non-inhalation pathways.
- Risk Characterization. The final steps is where
all the information from the previous three steps is integrated to
describe the outcome of the analysis and where the uncertainly and
variability in the results are described.
As of 2005, one residual risk assessment had been completed (Coke
Ovens) and EPA continues to work on many others.
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