From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Wednesday, January 07, 2004 11:03 AM
Subject: [epa-water] The Feasibility of Performing Cumulative Risk
[Federal Register: January 7, 2004 (Volume 69, Number 4)]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
ENVIRONMENTAL PROTECTION AGENCY
The Feasibility of Performing Cumulative Risk Assessments for
Mixtures of Disinfection By-Products in Drinking Water
AGENCY: Environmental Protection Agency.
ACTION: Notice of availability.
SUMMARY: This notice announces the availability of a final report
titled, ``The Feasibility of Performing Cumulative Risk Assessments for
Mixtures of Disinfection By-Products in Drinking Water (EPA/600/R-03-
051F),'' which was prepared by the U.S. Environmental Protection
Agency's (EPA) National Center for Environmental Assessment (NCEA) of
the Office of Research and Development (ORD).
DATES: This document will be available on or about January 7, 2004.
ADDRESSES: The document will be made available electronically through
the NCEA Web site (<A
HREF="http://www.epa.gov/ncea">http://www.epa.gov/ncea</A>). A limited
number of paper
copies will be available from the EPA's National Service Center for
Environmental Publications (NSCEP), P.O. Box 42419, Cincinnati, OH
45242; telephone: 1-800-490-9198 or 513-489-8190; facsimile: 513-489-
8695. Please provide your name, your mailing address, the title and the
EPA number of the requested publication.
FOR FURTHER INFORMATION CONTACT: The Technical Information Staff,
National Center for Environmental Assessment/Cincinnati, Ohio office
(MS-117), U.S. Environmental Protection Agency, 26 W. Martin Luther
King Drive, Cincinnati, OH 45268. Telephone: 513-569-7257; fax: 513-
569-7475; e-mail: <A
HREF="mailto:[log in to unmask]">[log in to unmask]</A>.
SUPPLEMENTARY INFORMATION: In 1996, the Safe Drinking Water Act
Amendments were passed, requiring the EPA to consider the risk
assessment of contaminant mixtures in drinking water and prompting this
current research on disinfection by-product (DBP) mixtures. Humans are
exposed daily to hundreds of DBPs via oral, dermal, and inhalation
routes. Some positive epidemiologic studies suggest cancer and
reproductive/developmental effects are associated with consumption of
chlorinated drinking water. However, in other epidemiologic studies
significant health effects have not been observed, and current single-
chemical toxicology studies fail to corroborate epidemiologic findings.
Furthermore, human health risk estimates made using animal data based
only on oral exposures do not reflect the same magnitude of risks found
in positive epidemiologic studies. Thus, it is hypothesized that this
difference can be accounted for by evaluating simultaneous exposures to
multiple DBPs via all three exposure routes. This report addresses the
feasibility of such an assessment, yielding the following interim
* Exposure estimates are made for an adult female and an
adult male, each of reproductive age, and for a child (age 6) of total
absorbed doses inclusive of exposures via oral, dermal and inhalation
* Estimates are made for 13 major DBPs, accounting for human
activity patterns that affect contact time with drinking water (e.g.,
tap water consumed, time spent showering, building characteristics) and
physicochemical properties of the DBPs (inhalation rates, skin
permeability rates, blood:air partition coefficients, etc.).
* A novel cumulative risk assessment method, Cumulative
Relative Potency Factors, is advanced that integrates the principles of
dose addition and response addition to produce multiple-route, chemical
mixture risk estimates using total absorbed doses.
The report acknowledges the need for additional research, such as,
to conduct a more complete uncertainty and sensitivity analysis on the
exposure estimates, and to conduct a more comprehensive analysis of
toxic mode of action for the DBPs. This report makes two significant
contributions to the science. First, external exposure modeling is
conducted and linked with physiologically-based pharmacokinetic
modeling to produce internal dose measures of drinking water
disinfection by-products (DBPs) for multiple route exposures to be used
in mixture risk assessments. Thus, a comprehensive exposure estimate is
made for 13 of the major DBPs of concern, including the four
trihalomethanes and five haloacetic acids that are currently regulated.
Second, a mixtures risk assessment method, based on additivity concepts
is proposed to logically evaluate human health risks using total
internal doses and oral toxicology dose-response data based on
knowledge or assumptions regarding toxic mode of action. This new
method is a novel approach to evaluating multiple route exposures that
can be generalized for the evaluation of other environmental mixtures.
Dated: December 23, 2003.
Peter W. Preuss,
Director, National Center for Environmental Assessment.
[FR Doc. 04-322 Filed 1-6-04; 8:45 am]
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