File: ABSTRACT.TXT


                     Acute-to-Chronic Estimation (ACE) 
                   with Time-Concentration-Effect Models

                        Software System Abstract

  

               Center for Exposure Assessment Modeling (CEAM)
       National Exposure Research Lab - Ecosystems Research Division
                  Office of Research and Development (ORD)
              U.S. Environmental Protection Agency (U.S. EPA)
                          960 College Station Road
                         Athens, Georgia 30605-2700

                                706/355-8400



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SUMMARY

Predictive toxicological models, including estimates of uncertainty, are
necessary to address probability-based ecological risk assessments.  Methods
and software (ACE) were developed for estimating chronic toxicity from raw
acute toxicity data (all response observations at all times and exposures).
Three methods were developed - - Accelerated Life Testing (ALT), Multifactor
Probit Analysis (MPA), and two-stage Linear Regression Analysis (LRA).  Of the
three, the method of choice is ALT, in that time to failure (death) of each
experimental unit is independent.  It requires three partial responses over
the time period of acute testing, but will function with one.  The MPA is a
two dimensional probit analysis using both time and concentration to produce a
multiple regression equation, however, each experimental unit is not
independent.  Also, the MPA requires more partial responses than the ALT.  The
LRA calculates LC values for each time period and then regresses the LC values
as the Y axis and the reciprocal of time as the X axis.  The Y intercept is
the chronic no-effect concentration.  The LRA will function when ALT and MPA
fail; no partial responses are required.  All methods provide confidence
limits for the point estimates.  The methods have previously been shown to
estimate chronic no-effect concentrations very well when validated against
actual paired acute and chronic test results with fishes.

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