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4
Key Scientific Problems Limiting Application of Ecological Risk Assessment

EXTRAPOLATION ACROSS SCALES

The most common scientific limitation exemplified in the case studies is the problem of extrapolating across scales of space, time, and ecological organization. For the most part, scientific data related to a specific stressor are limited to what can be obtained in a controlled laboratory setting or in a limited field study. Observations of environmental contamination and ecological effects of tributyltin were limited to a few marinas. Testing of pesticides even in the best of circumstances is limited to small field plots and carefully controlled applications. Table 4-1 shows, for all the case studies, the scales at which the data used in the assessments were collected and the scales of interest in decision-making. In most cases, the scales of interest in decision-making are substantially larger in space and of longer duration than could be accommodated in any practical assessment effort. Some form of extrapolation, either with explicit mathematical models or with judgment-based decision rules, is necessary to make the risk assessments useful for decision-making. The PCB study discussed by Di Toro (Appendix E) clearly illustrated the value of explicit models for estimating recovery times in response to hypothetical management actions. In the pesticide registration process described by Kendall (Appendix E), extrapolation is based primarily on qualitative evaluation of test data and information on expected use patterns. Kendall argued that models of ecological effects of pesticides are needed to reduce uncertainty and to account for effects



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KEY SCIENTIFIC PROBLEMS LIMITING APPLICATION OF ECOLOGICAL RISK 259 ASSESSMENT 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. 4 Key Scientific Problems Limiting Application of Ecological Risk Assessment EXTRAPOLATION ACROSS SCALES The most common scientific limitation exemplified in the case studies is the problem of extrapolating across scales of space, time, and ecological organization. For the most part, scientific data related to a specific stressor are limited to what can be obtained in a controlled laboratory setting or in a limited field study. Observations of environmental contamination and ecological effects of tributyltin were limited to a few marinas. Testing of pesticides even in the best of circumstances is limited to small field plots and carefully controlled applications. Table 4-1 shows, for all the case studies, the scales at which the data used in the assessments were collected and the scales of interest in decision- making. In most cases, the scales of interest in decision-making are substantially larger in space and of longer duration than could be accommodated in any practical assessment effort. Some form of extrapolation, either with explicit mathematical models or with judgment-based decision rules, is necessary to make the risk assessments useful for decision-making. The PCB study discussed by Di Toro (Appendix E) clearly illustrated the value of explicit models for estimating recovery times in response to hypothetical management actions. In the pesticide registration process described by Kendall (Appendix E), extrapolation is based primarily on qualitative evaluation of test data and information on expected use patterns. Kendall argued that models of ecological effects of pesticides are needed to reduce uncertainty and to account for effects

OCR for page 259
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 original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be retained, and some typographic errors may have been accidentally inserted. Please use the print version of this publication as the authoritative version for attribution. TABLE 4-1 Scales of Observation and Management in Case Studies Evaluated by the Committee Case Study Observational Scale Management Scale Spatial Temporal Spatial Temporal ASSESSMENT Tributyltin 5 yr ~ 1 ha (laboratory) < 5 yr (field) Agricultural chemicals ~ 1 ha 5 yr PCB and TCDD 10 yr Spotted owl ~ 300 km2 100 yr Species introduction > 1 yr Georges Bank ~ 104 km2 last 30 yr ~ 104 km2 next 5 yr KEY SCIENTIFIC PROBLEMS LIMITING APPLICATION OF ECOLOGICAL RISK 260