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HEALTH EFFECTS OF AIR TOXICS
Air
toxics can be broadly grouped into two categories according
to their health effects: carcinogens (cancer-causing)
or noncarcinogens. Carcinogens are those chemicals
that have been shown to cause cancer, either in people
or animals. Noncarcinogens have other kinds of health
impacts, affecting such things as development, reproduction,
respiration, the liver, kidney or other organs. Health
effects of chemicals are discovered in a number of
ways. Researchers can study groups of people that have
been exposed to the chemicals in the past, usually
at the workplace. They can also expose volunteers to
specific amounts of a chemical and record the effects.
Most health effects information comes from studies
of animals that are exposed in the laboratory to specific
doses of a chemical for specific periods of time.
USING
HEALTH BENCHMARKS
Groups
of experts at government agencies, such as USEPA and
California EPA , are brought together to look at all
of the studies done on the health effects of a chemical,
and to recommend toxicity values that can be used to
evaluate public exposure to that chemical. These toxicity
values are known as unit risk factors and reference
concentrations.
Unit
risk factors are
toxicity values used for carcinogens, that estimate
the increased risk of getting cancer associated with
the concentration of the chemical in the air that
you are breathing. A risk of less than one in a million
is usually considered to be negligible.
Reference
concentrations are
toxicity values developed for noncarcinogens. Exposure
to a chemical below its reference concentration,
even over a long period of time, is not expected
to have any negative effect on health.
These
unit risk factors and reference concentrations can
be used as health benchmarks, to evaluate the potential
health effects of the air toxic concentrations measured
by air monitors, or predicted by air pollution models,
such as that used for NATA. For carcinogens, the health
benchmark is the air concentration that would result
in a one in a million increase in the risk of getting
cancer if a person inhaled that concentration over
a whole lifetime. For noncarcinogens, health benchmarks
are set at the reference concentration.
Comparing
a health benchmark to an air concentration gives a
risk ratio. Risk ratios equal to or less than
one (below
the health benchmarks) are not expected to be harmful
to human health. It is not always clear, however, how
far above the health benchmark an air concentration has
to be before it becomes harmful. Types of harmful health
effects and actual harmful levels will vary substantially
from pollutant to pollutant. Still, comparison to a health
benchmark is a useful tool for evaluating air
concentrations like those predicted in NATA. If the modeled
air concentration is below the health benchmark (the
risk ratio is less than or equal to one), there is
probably no need for further concern. If the risk ratio
is greater than one (the air concentration is above
the health benchmark), there may be some cause for
concern, and further assessment is warranted. The risk
ratio also indicates just how much higher the air concentration
is than the health benchmarks.
SOURCES OF INFORMATION
The NJDEP Air Quality Permitting Program uses unit risk
factors and reference concentrations in a risk screening
process to evaluate potential health effects from facilities
seeking permits to emit air toxics. The tools used in
this risk screening process are available here:
Risk
Screening Tools
For more information on compiling a risk assessment,
see:
Technical
Manual 1003: Guidance on Preparing a Risk Assessment
Protocol for Air Contaminant Emissions.
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