to many other states in the region, Vermont enjoys clean air.
Few Vermonters, however, realize that atmospheric concentrations of
several toxic chemicals exceed state ambient health standards, many
of which were established in the 1980s to protect public health from
the adverse impacts of toxic chemicals in the air we breathe. One
contaminant of particular concern is a known human carcinogen: benzene.
is a volatile organic compound emitted from both natural and human-created
sources. Natural sources in Vermont include forest fires and organic
chemicals emitted by trees and other vegetation through their natural
physiological processes. Of much greater concern, however, are the
benzene sources linked to our modern mobile lifestyle, which frequently
revolves around the internal combustion engine.
snowmobiles, outboard marine engines, and lawnmowers all release benzene
into our atmosphere. According to the U.S. Environ-mental Protection
Agencys National Scale Assessment Project for 1996, approximately
48 percent of benzene emissions nationwide come from mobile sources.
In Vermont, where automobiles and other forms of transportation contribute
a greater percentage to total toxic emissions, this percentage is
likely to be higher. Vermont ranked 11th in the nation in 1999 for
per capita vehicle miles traveled; on average, each Vermonter drove
11,566 miles. Total vehicle miles traveled in the state has increased
by approximately 450 percent since 1950 (Figure 1); this increase
has offset a lot of the pollution savings from improved emissions
technology in the past three decades.
sources of benzene in Vermont include the combustion of wood and oil
for home heating and the industrial storage and distribution of gasoline.
Indoor air can also contain high concentrations of benzene from common
household cleaning products, glues, paints, and cigarette smoke.
are regularly exposed to benzene air emissions through short-term
acute exposures or long-term chronic exposures. The principal human-made
source of benzene in outdoor air is the motor vehicle. Evaporative
emissions (unburned fuel) at gasoline station pumps may expose people
to acute, high levels of benzene, although vapor recovery systems,
now featured at larger gasoline stations, have greatly reduced this
source of exposure. Recent advances in on-board automobile vapor recovery
have decreased the potential for gasoline vapor exposure even further.
Breathing combusted gasoline and evaporative emissions from automobiles
results in considerable exposure. In addition, multiple sources of
ambient benzene create a background level in the atmosphere that consistently
exceeds the state health standard, leading to chronic exposure.
can be found in the air, water, or soil, although it evaporates quickly
from the soil and water surfaces. Once in the air, the pollutant reacts
with other atmospheric chemicals and breaks down within a few days.
Benzene in the air may be returned to the ground by rain or snow.
better assess the concentrations of toxic air pollutants in Vermont,
the Air Pollution Control Division initiated the Hazardous Air Contaminants
Monitoring Program, a monitoring network that measures a wide range
of chemicals over a broad portion of the state. Starting in 1993,
monitoring of air toxics has consistently occurred at four sites,
ranging from an urban location in downtown Burlington to a rural background
site on the western slope of Mount Mansfield in Underhill. Monitoring
is currently taking place at five sites in the state.
concentrations are generally higher in more populated urban sites
than rural locations (Figure 2); however, median concentrations of
benzene exceeded the Vermont Hazardous Ambient Air Standards of 0.12
µg/m3 (micrograms per cubic meter) many times from 1993 through
2000, even at the rural Underhill site. (The 0.12 µg/m3 standard
is the concentration equal to the risk level at which 1 person in
1 million is expected to develop cancer due to a continuous lifetime
exposure to benzene in the air.) At urban sites, median concentrations
of benzene were as much as 30 times the state health standard (Figure
3). Annual median concentrations in Brattleboro, Burlington, and Rutland
consistently posed a cancer risk of 1 in 100,000, while at Underhill,
benzene concentrations exceeded the 1 in 1 million risk level at least
84 percent of the time.
analytical minimum detection limit is the level below which a pollutants
concentration cannot be quantified accurately. The minimum detection
limit during the six-year period for benzene was 0.38 µg/m3,
a value 3.2 times higher than the standard itself. As the minimum
detection limit is above the standard, it is possible that non-detect
levels of benzene still exceed the health standard. Of the 619 samples
collected at the four monitoring sites during the period, only 5 percent
were below the minimum detection limit (0.38 µg/m3), and 80
percent of the non-detects occurred at Underhill, the rural site.
The maximum concentration measured in Vermont (15.4 µg/m3),
on the other hand, occurred in Rutland on February 19, 1994. This
concentration exceeded the air standards by 128 times.
addition to vapor recovery systems on cars and at gasoline stations,
the Air Pollution Control Division is taking other measures to deal
with benzene emissions in Vermont. The Division is in the process
of developing toxic action plans, technical documents that will provide
detailed analysis of available air toxics data and toxicological information
for critical target pollutants. The action plans will serve as technical
and policy guidelines to reduce target pollutant concentrations to
levels below the Vermont Hazardous Ambient Air Standards.
can also be exposed to benzene through drinking water. Information
provided by the Vermont Health Department indicates that few of the
private wells tested for benzene actually have detectable concentrations
of this pollutant. However, rare instances of well water contamination
exist due to leaking underground gasoline storage tanks or gasoline
Agency at this time cannot estimate the combined average of benzene
exposure due to inhalation and ingestion, but the Agency believes
that the majority of the health risk associated with this carcinogen
comes from inhalation exposure.
Vermonts population continues to grow and the demand for transportation
increases, it is likely that, unless extensive strides are made to
counter toxic emissions, the percentage of emissions derived from
combustion sources will continue to increase. This implies potentially
greater environmental and health problems, including higher cancer
risks for Vermonters.