Cover Image

PAPERBACK
$49.00



View/Hide Left Panel

safety. Work is needed to understand the mechanisms of the response that occur at the threshold in the stress-response function.

Expression of Uncertainty

The functional expression of the stress-response relationship is stochastic and distributional; the assessor must consider extremes and discontinuities, not just central tendencies. Assessments should recognize the natural variability in systems, and conclusions should be accompanied by a description of uncertainty and probability.

Understanding the Stressor

Qualitative and quantitative aspects of the stressors should be clearly articulated without bias with respect to desirability of outcome. The effect of other anthropogenic or natural stressors should be included in the analysis, because most ecological systems are affected by multiple stresses. For example, assessments of ecological risks of chemicals could increase reliance on field experiments in which test organisms are exposed to a suite of compounds and a range of natural conditions (this approach is already being widely used to set water quality criteria). One might also use a stressor classification to locate sensitive systems and sensitive components (e.g., species). Such a classification could include the components of the system potentially affected by the stressor, the pathway(s) of movement of the stressor, and the capacity of the affected component(s) to recover. Assessors should consider developing a matrix that considers the analytical method used to quantify stress versus class of stressor.

A good understanding of mechanisms of action can substantially improve understanding of stress-response relationships. Knowledge of mechanisms is not, however, a prerequisite for a useful risk assessment. Before a theory of mechanisms is used in a risk assessment, it must be validated in a realistic and comprehensive fashion.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 314
APPENDIX F 314 original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the retained, and some typographic errors may have been accidentally inserted. Please use the print version of this publication as the authoritative version for attribution. safety. Work is needed to understand the mechanisms of the response that occur at the threshold in the stress-response function. Expression of Uncertainty The functional expression of the stress-response relationship is stochastic and distributional; the assessor must consider extremes and discontinuities, not just central tendencies. Assessments should recognize the natural variability in systems, and conclusions should be accompanied by a description of uncertainty and probability. Understanding the Stressor Qualitative and quantitative aspects of the stressors should be clearly articulated without bias with respect to desirability of outcome. The effect of other anthropogenic or natural stressors should be included in the analysis, because most ecological systems are affected by multiple stresses. For example, assessments of ecological risks of chemicals could increase reliance on field experiments in which test organisms are exposed to a suite of compounds and a range of natural conditions (this approach is already being widely used to set water quality criteria). One might also use a stressor classification to locate sensitive systems and sensitive components (e.g., species). Such a classification could include the components of the system potentially affected by the stressor, the pathway(s) of movement of the stressor, and the capacity of the affected component(s) to recover. Assessors should consider developing a matrix that considers the analytical method used to quantify stress versus class of stressor. A good understanding of mechanisms of action can substantially improve understanding of stress-response relationships. Knowledge of mechanisms is not, however, a prerequisite for a useful risk assessment. Before a theory of mechanisms is used in a risk assessment, it must be validated in a realistic and comprehensive fashion.