UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C, 20460
OFFICE OF THE ADMINISTRATOR
SCIENCE ADVISORY SOAftQ
EPA-SAB-IAQC-94-0093
February 15, 1994
Honorable Carol M. Browner
Administrator
U.S. Environmental Protection Agency
401 M Street, SW
Washington, DC 20460
RE: Draft "Addendum to the Methodology for Assessing Health Bisks Associated with
Indirect Exposure to Combustor Emissions*
Dear Mrs. Browner:
On December 3, 1993, the Indoor Air Quality/Total Human Exposure Committee (the
Committee) of the Science Advisory Board reviewed the draft „ acunient "Addendum to the
Methodology for Assessing Health Bisks Associated with Indirect Exposure to Combustor
Emissions* (the Addendum). In view of pressing EPA and public concerns about
incinerators, this interim letter was prepared to provide you with preliminary information on
some of the major findings of the Committee, A mbre detailed report is in preparation and
will follow soon (EPA-SAB-IAQC-94-009).
The assessment of risks from combustors entails a complex range of issues, including
many different kinds of combustion devices and raw materials, direct and indirect exposure
routes, and concerns regarding transportation and disposal of raw materials and combustion
ash. It is thus important to emphasize, at the outset, that this letter and the report in
preparation address only one of these aspects, namely the questions surrounding indirect
exposure assessment which are die subject of the Addendum, Indirect exposures are those
that occur via, transfer of airborne contaminants into water, soil and the food chain. Direct
airborne exposures from combustor emissions are being addressed with other methodologies
by the Agency and are not the subject of this letter.
To grapple with these complex exposure pathway issues, the Agency needs to be able
to estimate the environmental rate of combustor emissions and their consequent potential for
human exposures. This task requires the development of models to predict accumulations of
chemical contaminants in the environment and identification of the chemicals, environmental
compartments, and exposure pathways most likely to be of concern so that appropriate actions
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can be taken before there is widespread and/or irreversible damage. The Addendum we
reviewed is a critical part of the Agency's effort to deal with these very difficult challenges*
The Committee's, principal conclusion is thai the Addendum is not ready for release
as an "EPA Methodology\ * The major scientific concerns were as follows;
1) There is a general lack of measured data to estimate input parameters and very
littie validation of the exposure models. The general reliance on default input data and the
large number of assumptions left the Committee with many reservations about widespread
appEeation of this document as an EPA methodology for all types of combustors and
chemicals. The Committee recommends that the Agency develop and implement a strategic
plan to collect critical input data for the models and to validate the methodology.
2) The Committee is concerned about the lack of information on the frequency
and impact of upset conditions (e.g., upsets in the combustion process that result in less
complete combustion, as well as breakdown of filters, predpitators, or other controls on stack
emissions) on both the chemical composition and the character of emissions from incinerators.
The model relies on measured data from four California incinerators. These limited data
suggest that upset conditions can contribute significantly to the total emissions from an
incinerator but the frequency of upset conditions has not been determined for sufficient
numbers and types of incinerators to be reasonably confident of the adequacy of the default
values recommended for use.
3) The Committee is concerned that the Addendum does not reigire the risk
assessor to account for the impact of multiple combustor sources. While a single new facility
may not result in a significant risk, the cumulative effect of the addition of a facility to an
area with, a number of existing combustors may well cause an unacceptable health risk.
There is a need for a more regional approach to evaluating risks from indirect exposures.
There were also concerns that the impact beyond 50 km (the maximum distance considered in
the Addendum) may be of concern for areas with large numbers of combustors.
4) Although the Addendum nominally addresses all combustors (incinerator, fossil
fuel, etc.), the document as now written appears to place more emphasis on incinerators and
does not adequately address all combustors. It is known that the chemical nature of the
emissions and the frequency of upset conditions will differ substantially among various types
of combustors but the document does not reflect this body of information. For example,
there is a substantial body of information on emissions from coal combustors that should be
referenced if die document is to be all inclusive.
5) The Committee noted that EPA's re-permitting process for incinerators offers a
unique opportunity to obtain existing data on the frequency and duration of upset conditions
for various types of incinerators in the U.S. Other useful data may be available that could be
required as part of the re-permitting process, such as emissions measurements.
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Many of the above issues have been noted by previous SAB committees in their
review of hazardous waste and domestic waste incineration. In addition, various incineration
studies and emission data sets exist in other countries. It is highly recommended that the
Agency compile and review these previous efforts as a way of focusing its future directions.
•4
In summary, the Committee is very aware of the difficulties inherent in the "state of
the science" nature of the work which the Addendum effort entails, especially when the work
must be done under the combined pressures of severely limited resources and public demands
for "something" to be done quickly. The Committee, however, does not recommend the
release of the Addendum as an "EPA Methodology" due to the substantial scientific
uncertainties in the models and the absence of information in the Addendum concerning these
uncertainties and limitations.
Sincerely,
ievieve
Executive Committee
Science Advisory Board
Chair
Joan M. Dalsey, Chair *
Indoor Air QuaUty/Totaffluman Exposure
Committee
Science Advisory Board
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