[Federal Register Volume 69, Number 4 (Wednesday, January 7, 2004)]
[Notices]
[Pages 919-920]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 04-322]


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ENVIRONMENTAL PROTECTION AGENCY

[FRL-7607-9]


The Feasibility of Performing Cumulative Risk Assessments for 
Mixtures of Disinfection By-Products in Drinking Water

AGENCY: Environmental Protection Agency.

ACTION: Notice of availability.

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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 (www.epa.gov/ncea). 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: [email protected].

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 
results:
    [sbull] 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 
routes.
    [sbull] 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.).

[[Page 920]]

    [sbull] 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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