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EPA BACKGROUND PAPER OUTLINING RISK ASSESSMENT RATIONALE,
REGULATORY PLAN FOR CONTROLLING BENZENE UNDER CLEAN AIR ACT
(Dated December 15, 1983)
National Emission Standards for Harardces Air Pollutants
for BENZENE
PURPOSE
The U.S. Environmental Protection Agency (EPA) intends
to estabish emission standards for certain industrial sources
of benzene. This paper wil] discuss (1) the statutory basis for
this action, (2) background information on benzene, (3)
EPA's standard-setting process, and (4) a summary of the
final standard, the proposed standard and those the agency
proposes to withdraw.
‘ INTRODUCTION
Section 112 of the Clean Air Act of 1970 requires EPA to
identify and list pollutants which cause or contribute air
pollution which “may reasonably be anticipated to result in
an increase in mortality or an increase in serious irreversibie, or incapacitating reversibie, illness," and to issue Na-
tional Emission Standards for Hazardous Air Pollutants
(NESHAPS) for classes of sources o1 these pollutants. EPA
listed benzene as a hazardous air pollutant on June 8, 1977.
On April 18, 1980, EPA proposed a benzene emission standard for maleic anhydride plants. On December 18, 1980,
EPA proposed a benzene emission standard for ethylbenzene
and styrene plants. On December 19, 1980, EPA proposed a
benzene emission standard for benzene storage vessels; and
oo January 5, 1981, EPA proposed a benzene emission
standard for fugitive emissions from petroleum refineries
and chemical manufacturing plans. A lawsuit brought by
environmental and industry groups to compe! EPA to act on
benzene standards is now pending in the Federal District
Court in Washington.
EPA intends to promulgate final regulations soon on the
proposed standard for benzene fugitive sources and to propose a standard for a new source category, coke by-product
recovery plants. The agency intends to propose to withdraw
the standards for maleic anhydride plants, ethylbenzene and
styrene plants, and benzene storage vessels, based on its
assessment that the risks to public health are small and that
the proposed standard would minimally reduce those risks.
Consequently, EPA has concluded that the three source
categories do not warrant regulatory concern at the federal
BACKGROUND ON BENZENE
Benzene is a major industrial chemical, ranking among
the top fifteen with the U.S. production volume of almost 6
Million megagrams (or 6.6 million tons) in 1979. In addition
to industrially produced benzene, roughly an equal arnount
is found in gasoline. The vast majority of benzene is derived
from petroleum, with a smaller percentage produced as a
by-product of coke ovens. Most benzene is used to produce
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other industrial chemicals, which in turn are esed to manufacture a wide range of products including nylon, plastics,
insecticides, and polyurethane foams. Stationary source
categories of benzene include “fugitive” emissions (non-
stack emissions, such as leaks) from petroleum refineries
and chemical manufacturing plants, the gasoline marketing
system, process vents at several types of chemical manulfac-
turing plants, coke oven by-product plants, and benzene
storage and handling facilities.
Numerous occupationa! studies conducted over the past 50
years provide evidence of the health hazards resulting from
prolonged inhalation of benzene. Benzene has been recognized since 1900 as a toxic substance capable of causing
acute and chronic effects. Benzene attacks the hematopoie-
tic (blood-forming) system, especially the bone marrow, and
its toxicity is manifested primarily by alterations in the
level of the formed elements in the circulating blood (red
cells, white cells and platelets). The degree of severity of
these effects ranges from mild and transient episodes to
severe and fatal disorders. The mechanism by which ben-
gene produces its toxic effects, although under investigation,
is still unknown. The adverse effects on the blood forming
tissues have been documented in studies of workers in a
variety of industries and occupations including the manufac-
turing and processing of rubber, shoes, rotogravure, paints,
chemicals, and natural rubber cast film. These studies in-
clude single case reports, cross-sectional studies and retrospective studies of morbidity and mortality amonga defined
cohort of workers industrially exposed to benzene.
Occupational exposure levels are much higher than ambient concentrations of benzene. In addition, EPA believes
that non-cancer effects of benzene exposure are unlikely to
occur at ambient concentations. Discussions of these issues
are included in documents supporting EPA's regulation of
benzene prepared by or for EPA entitled the “Assessment of
Health Effects of Benzene Germane to Low Level Exposure,” the “Assessment of Human Exposures to Atmospheric
Benzene,” and the “Carcinogen Assessment Group's Report
on Population Risk to Ambient Benzene Exposures.”
Benzene exposure is causally related to a number of blood
disorders, including acute myelogenous leukemia {a cancer
of the blood-forming system in adults.) Benzene does not
appear to cause another form of leukemia, acute lyrnphocytic leukemia which occurs almost totally in children. Acute
myelogenous teukemia, which is caused by benzene, almost
never occurs in children.
Although the health studies of benzene involve industrial
exposure to benzene at higher levels than those found in the
ambient air, in the absence of sound scientific evidence to
the contrary, prudent public health policy requires that
carcinogens be considered for regulatory purposes to pose
some finite risk of cancer at any exposure level above zero.
Because of its widespread use, benrene emissions in the
ambient air from some sources result in significant human
exposure. Therefore, in June 1977, the Administrator of
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