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Environmental

Fact Sheet

 Printed on Recycled Paper

United States

Environmental Protection

Agency

Air and Radiation EPA420-F-02-043

September 2002

Office of Transportation and Air Quality

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 toluene 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 neurological 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 physiologically-based pharmacokinetic models to estimate blood concentrations 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 components, toluene and carbon monoxide, the only constituents with a sufficient 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 controlling emissions from new off-road recreational vehicles and other equipment. 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 (http://www.whitehouse.gov/

omb/inforeg/other_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 recreational 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 toluene. 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/cleanrec.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.