[Federal Register: July 23, 1998 (Volume 63, Number 141)]
[Notices]               
[Page 39568-39569]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr23jy98-62]

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ENVIRONMENTAL PROTECTION AGENCY

[FRL-6128-2]

 
Technical Workshop on Exposure-Duration and Toxicity 
Relationships

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notice of meeting.

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SUMMARY: EPA is announcing a meeting organized and convened by Eastern 
Research Group, Inc., a contractor to EPA's Risk Assessment Forum, for 
external scientific peer consultation on the relationship of exposure-
duration and toxicity. The meeting is being held to discuss methods 
under development or currently in use by EPA to characterize exposure-
duration relationships and to explore how to model these relationships 
with respect to risk assessment.

DATES: The meeting will begin on Wednesday, August 5, 1998 at 8:30 a.m. 
and end on Thursday, August 6, 1998 at 5:00 p.m. Members of the public 
may attend as observers.

ADDRESSES: The meeting will be held at the Sheraton Crystal City, 1800 
Jefferson Davis Highway, Arlington, Virginia 22202. Since seating 
capacity is limited, please contact Eastern Research Group, Inc., Tel.: 
(781) 674-7374, or E-mail confmail@erg.com, by July 27, 1998 to attend 
the meeting as an observer.

FOR FURTHER INFORMATION CONTACT: For technical inquires, contact Dr. 
Gary Kimmel, U.S. EPA, Office of Research and Development (8623-D) U.S. 
EPA, 401 M Street S.W., Washington DC., 20460. Tel.: (202) 564-3308.

SUPPLEMENTARY INFORMATION: Current risk assessment procedures are 
typically based on overall daily exposure levels, and tend to emphasize 
effects resulting from continuous exposures over a lifetime. This basis 
is widely recognized to be an oversimplification, and there has been an 
increasing realization that exposures are more likely to be experienced 
as bursts or spikes, or intermittent exposures of varying levels. The 
complexities of exposure effects on toxic responses require 
consideration of the entire exposure profile, including the timing, 
duration, and intermittent nature of exposures reflecting realistic 
scenarios encountered in practical

[[Page 39569]]

settings. The proper metric for exposure may be highly dependent on the 
pharmacokinetic properties of the chemical or exposure in question, and 
the toxic effects considered in models must be carefully chosen to 
reflect the sensitive endpoints based on the exposure characteristics. 
Models have been developed over the last decade which begin to address 
the effect of duration of exposure in addition to exposure levels; 
however, most of these models do not incorporate mechanistic 
information. In addition, only limited work has been done on developing 
efficient designs for studying dose-rate effects, and these designs 
tend to be simplistic.
    The Agency's Risk Assessment Forum is beginning to examine how 
exposure-duration and toxicity relationships are or can be incorporated 
into the risk assessment process for less-than-lifetime exposures. This 
examination is an extension of efforts within EPA as well as 
collaborative work carried out with researchers from the Harvard School 
of Public Health. The next step in this examination of exposure-
duration and toxicity relationships will build upon these prior efforts 
through a peer consultation workshop.
    The workshop is being held for invited participants to discuss the 
current understanding of dose-duration relationships and their 
underlying mechanistic basis, which approaches can be used in modeling 
these relationships, and how to include these methods in risk 
assessment, and future directions in this area. During the meeting, 
several presentations will be made to provide specific examples of the 
various issues. The remainder of the meeting will be organized around 
breakout sessions that will discuss where current risk assessment 
approaches may be improved.

    Dated: July 17, 1998.
William H. Farland,
Director, National Center for Environmental Assessment.
[FR Doc. 98-19654 Filed 7-22-98; 8:45 am]
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