United States	Air and Radiation	EPA420-F-02-043
Environmental Protection	September 2002
Agency
Office of Transportation and Air Quality
vvEPA
Fact Sheet
Summary of the Acute Behavioral
Effects of Exposure to Toulene and
Carbon Monoxide from Snowmobile
Exhaust
The U.S. Environmental Protection Agency (EPA) has completed an
analysis that estimates potential acute health risks to snowmobile riders
from exposures to carbon monoxide and volatile hydrocarbon emissions
present in snowmobile exhaust. This analysis was intended to allow an
assessment of the monetary benefits associated with reductions in
behavioral impairment from these exposures and comprises a portion of
the benefit-cost analysis for the final rule making on emission controls
of off-road recreational vehicles. It is not intended as risk haracterization
because of uncertainties associated with estimates of exposure. The
Regulatory Support Document for the final rulemaking on emission
controls of off-road recreational vehicles is available to the public
(www. epa.gov/otaq/cleanrec. htm).
Summary
The EPA analysis suggests that blood carbon monoxide (CO) and tolu-
ene concentrations resulting from following a lead snowmobile in typical
snowmobile use are within the range associated with measurable deficits
in behavioral performance. Based on these results, it is predicted that the
behavioral deficits may be linked to increased rates of accidents during
and after snowmobile use. The EPA anticipates that substantial benefits
may be achieved by controlling this exposure.
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The analysis*s conclusions are based on modeling the potential neuro-
logical deficits associated with hydrocarbon and CO emissions from 2-
stroke engines. This was accomplished by using emissions data and
modeling to estimate exposures to a snowmobile rider following behind
a lead sled in plausible group riding scenarios. The EPA also used physi-
ologically-based pharmacokinetic models to estimate blood concentra-
tions resulting from these exposure conditions. Following that, changes
in performance of behavioral tasks were estimated using a meta-analysis
of the existing scientific literature for exposures to two exhaust compo-
nents, toluene and carbon monoxide, the only constituents with a suffi-
cient behavioral database to enable modeling. Finally, the effects of
toluene, but not CO, were compared to equivalent doses of ethanol in
order to facilitate estimates of monetary costs.
Background
The Clean Air Act gives EPA the responsibility and authority to control
emissions from off-road recreational vehicles such as snowmobiles and
other similar machines. The EPA previously proposed a rule for control-
ling emissions from new off-road recreational vehicles and other equip-
ment. After its review of the rule, the Office of Management and Budget
suggested that the EPA had not sufficiently quantified the monetary
benefits of the proposed emission controls (littp: //www. whitehouse.gov/
omb/inforeg otlier_letter.html).
In response to OMB's request, the Office of Transportation and Air
Quality (OTAQ) in the EPA Office of Air and Radiation and the National
Health and Environmental Effects Research Laboratory (NHEERL) in
the EPA Office of Research and Development have completed a three
part analysis that includes: (1) estimating emissions from off-road recre-
ational vehicle engines and exposures to operators during typical use
(OTAQ); (2) estimating health effects of exposures with emphasis on
acute impairments in performance of behavioral tasks (NHEERL); and
(3) developing techniques for estimating monetary costs associated with
behavioral impairment from these exposures (OTAQ).
The two-stroke engines typically used in snowmobiles emit large
amounts CO and of hydrocarbons, a major component of which is tolu-
ene. Because of limitations in available exposure models, the analysis
focused on a scenario in which a snowmobile rider follows in the exhaust
plume of a lead snowmobile down a fixed trail, as is common practice in
national parks. Measurements of snowmobile engine emissions and
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modeling were used to estimate exposures to the second rider in the
wake of the first vehicle. Although there are uncertainties with the
exposure predictions, the estimated blood concentrations of CO and of
toluene rose enough to impair behavioral performance. Therefore, these
analyses suggest that snowmobile exhaust emissions present an exposure
situation of potential concern.
In order to better understand the costs of behavioral deficits from toluene
exposure, a comparison was made to ethanol consumption because it
was not possible to evaluate the costs associated with behavioral deficits
directly. The effects of exposure to toluene were compared to those of
alcohol on the basis of blood concentrations causing equivalent degrees
of behavioral impairment. This novel approach would enable estimates
of accident rates and associated benefits resulting from the ethanol
equivalent to toluene exposure.
For calculation of the monetary value of controls, two components could
be evaluated: accidents while operating snowmobiles and accidents
while driving motor vehicles on the way home. There are substantial
uncertainties in baseline exposure estimates, snowmobile accident data,
in knowing how quickly people get into their cars and how far they
drive. Based on published U.S. Department of Transportaion, National
Highway Traffic and Safety Administration data on relative risks for
accidents, the range of effects is consistent with increased relative risk of
fatal, non-fatal injury and property damage accidents while driving
home.
For More Information
You can access documents on the summary of the acute behavioral
effects of exposure to toulene and carbon Monoxide from snowmobile
exhaust electronically on the Office of Transportation and Air Quality
Web site at:
http: //www. epa. gov/otaq/cleanre c. htm
You can also contact:
William K. Boyes, Ph.D., U.S. Environmental Protection Agency, 919-
541-7538; Fax: 919-541-3335, or
Patricia D. Koman, U.S. Environmental Protection Agency, 734-214-
4955; Fax: 734-214-4816.
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