Hazardous Air Pollutants
electroplating; and halogenated solvent cleaners (Ref.
Hazardous Air Pollutants (HAPs), sometimes referred to
as air toxics, are chemicals and trace metals present in
In the state of  Michigan’s air regulation, toxic air
the atmosphere as gases, liquid droplets and solid
contaminants (TACs) are defined as all non-criteria
particulates.  HAPs are released into the atmosphere as
pollutants that may be Ňharmful to public health or the
Volatile Organic Compounds (VOCs) or particulates
environment when present in the outdoor atmosphere
from a variety of  sources.
in sufficient quantities and duration.” (Ref. 25)
The U.S. Clean Air Act of  1970 required the U.S. EPA to
The Canadian Environmental Protection Act defines a
set National Emission Standards for Hazardous Air
substance as being Ňtoxic” if  it is entering, or may enter
Pollutants (NESHAPS) to provide an Ňample margin of
the environment in a quantity or concentration or under
safety to human health.” However, by definition, many
conditions that:
HAPs are chemicals that cause serious health and
have or may have an immediate or long-term
environmental hazards and have no exposure threshold.
harmful effect on the environment or its biological
No minium exposure is to be considered safe.  As a
result, national emission standards were developed for
constitute or may constitute a danger to the environ-
only eight HAPs some twenty years later (Ref. 22).
ment on which life depends; or
Under the 1990 Clean Air Act, a new approach for
constitute or may constitute a danger to human life
regulating HAPs was established.  Emissions standards
or health in Canada.
are now determined on the basis of  Maximum Achiev-
able Control Technology or MACT.  The U.S. EPA is
required under the Clean Air Act to regulate 188 HAPs.
International Joint Commission
Sources of  HAPs are categorized as either major or area
As discussed previously, in 1989, the International Joint
Commission formed the International Air Pollution
Major sources are considered to be those which have the
Advisory Board for the Detroit-Windsor/Port Huron-
potential to emit ten or more tons per year of any
Sarnia Region (the Board), at the request of  both
individual HAP or 25 tons per year of  any combinations
Federal governments, to study the trends in ambient air
of  HAPs.  A distinction is made between new and
quality, particularly the risks to human health associated
existing sources of  HAPs in regard to the implementa-
with airborne toxic chemical pollutants in the regions.
tion of  MACT.  All new sources of  HAPs are required
to adopt the MACT for that industry.  Existing sources
To complete this task, the Board developed a risk
are required to implement MACT to ensure that they
assessment protocol based on a ŇLevels of  Concern
achieve emissions which are equivalent to the average of
Algorithm,” which is a screening technique to identify
the best-performing 12 percent of  the existing sources.
the chemicals that present the greatest concern from a
Existing sources have three years to comply with the
human health perspective, based on the direct inhalation
applicable MACT standard (Ref. 23).
route of  exposure (Ref. 26).  The risk to human health
is based on knowledge of  the severity of  toxic effects
Area sources are stationary sources which do not qualify
(Toxicity Rating), the population of  the region exposed
as major sources.  If  the area source poses a threat to
to the chemical (Exposure Index), and whether the
public health or the environment, an emission standard
levels of  the chemical in the air exceed screening levels
must be developed.  To date, MACT has been applied to
used by government agencies (Level of  Exposure).
eight area source categories.  These categories include:
Based on this assessment, the Board identified fifteen
asbestos processing; chromic acid anodizing; commercial
chemicals present in the region which posed the highest
dry cleaning transfer machines; commercial dry cleaning
level of  concern relative to direct inhalation.
dry-to-dry machines; commercial sterilization facilities;
decorative chromium electroplating; hard chromium