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U.S. Environmental Protection Agency
Office of Inspector General
At a Glance
21-P-0129
May 6, 2021
Why We Did This Audit
We conducted this audit to
determine whether the
U.S. Environmental Protection
Agency's residual risk and
technology review, known as
RTR, process has sufficiently
identified and addressed any
elevated cancer risks from air
toxics emitted by facilities.
The Clean Air Act requires the
EPA to conduct residual risk
reviews to assess the health
and environmental risks that
remain after implementation of
technology standards limiting
air toxics emissions. If health
risks are determined to be
unacceptable, the EPA is
required to revise the standards
to reduce the risks. Separately,
the EPA is required to review
each of the technology-based
standards at least every eight
years and, if necessary, revise
them, considering
developments in practices,
processes, and control
technologies. The EPA calls
this the technology review.
For efficiency, the EPA
combines RTRs in the same
regulatory package.
This audit addresses the
following:
• Improving air quality.
This audit addresses a top EPA
management challenge:
• Integrating and leading
environmental justice.
Address inquiries to our public
affairs office at (202) 566-2391 or
OIG WEBCOMMENTS@epa.gov.
List of OIG reports.
EPA Should Conduct New Residual Risk and Technology
Reviews for Chloroprene- and Ethylene Oxide-Emitting
Source Categories to Protect Human Health
What We Found
Results from the EPA's modeling and
monitoring efforts indicate that people in
some areas of the country may be exposed
to unacceptable health risks from
chloroprene and ethylene oxide emissions.
Despite the EPA classifying chloroprene as
a likely human carcinogen in 2010 and
The EPA should conduct new
RTRs for chloroprene- and
ethylene oxide-emitting source
categories to address elevated
individual lifetime cancer risks
impacting over 464,000 people, as
found in a modeling tool, and to
achieve environmental justice.
ethylene oxide a carcinogen in 2016, the
EPA has not conducted new RTRs for most types of industrial sources, referred
to as source categories, that emit chloroprene or ethylene oxide. The EPA
should take the following steps to ensure its RTR process sufficiently identifies
and addresses these emissions:
•	Conduct new residual risk reviews for four major source categories that emit
chloroprene or ethylene oxide using new risk values for these pollutants.
•	Conduct a residual risk review for the hospital sterilizers area source
category using the new risk value for ethylene oxide.
•	Conduct overdue technology reviews for four source categories.
•	Develop new National Emission Standards for Hazardous Air Pollutants, or
NESHAPs, for chemical plant area sources that emit ethylene oxide.
•	Develop a process to initiate timely reviews of existing and uncontrolled
emission sources when new or updated risk information becomes available.
New RTRs should be conducted because the EPA issued new risk values for
chloroprene and ethylene oxide in 2010 and 2016, respectively, to reflect their
potent carcinogenicity, as found in newer scientific evidence. The EPA should
exercise its discretionary authority to conduct new residual risk reviews under the
Clean Air Act whenever new data or information indicates an air pollutant is more
toxic than previously determined. Use of such discretionary authority is consistent
with the Agency's position, stated in its April 2006 commercial sterilizer RTR rule.
Recommendations and Planned Agency Corrective Actions
We recommend that the assistant administrator for Air and Radiation (1) develop
and implement an internal control process with specific criteria to determine
whether and when new residual risk reviews of existing NESHAPs and
uncontrolled emission sources are needed to incorporate new risk information;
(2) conduct new residual risk reviews for Group I polymers and resins, synthetic
organic chemical manufacturing industry, polyether polyols, commercial
sterilizers, and hospital sterilizers; (3) revise the NESHAP for chemical
manufacturing area sources to regulate ethylene oxide and conduct a residual
risk review; and (4) conduct overdue technology reviews for the source
categories listed in Recommendations 2 and 3. Recommendations 1, 2, and 3
are unresolved. Recommendation 4 is resolved with corrective actions pending.

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