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Issues in Risk Assessment (1993)

Chapter: EXTRAPOLATION ACROSS SCALES

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Suggested Citation:"EXTRAPOLATION ACROSS SCALES." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.
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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

Suggested Citation:"EXTRAPOLATION ACROSS SCALES." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.
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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

Tributyltin

< 1m3

< 1 yr

Chesapeake Bay

> 5 yr

~ 1 ha

(laboratory)

< 5 yr (field)

Agricultural chemicals

~ 1 ha

< 1 yr (field test)

Agricultural region

> 5 yr

PCB and TCDD

< 1 L

~ 1-month (laboratory)

Lakes or rivers

> 10 yr

Spotted owl

~ 300 km2

< 6 yr

Pacific northwest

> 100 yr

Species introduction

< 100 m2

~ 1 yr (greenhouse)

Agricultural region

>> 1 yr

Georges Bank

~ 104 km2

last 30 yr

~ 104 km2

next 5 yr

Suggested Citation:"EXTRAPOLATION ACROSS SCALES." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.
×
Page 259
Suggested Citation:"EXTRAPOLATION ACROSS SCALES." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.
×
Page 260
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The scientific basis, inference assumptions, regulatory uses, and research needs in risk assessment are considered in this two-part volume.

The first part, Use of Maximum Tolerated Dose in Animal Bioassays for Carcinogenicity, focuses on whether the maximum tolerated dose should continue to be used in carcinogenesis bioassays. The committee considers several options for modifying current bioassay procedures.

The second part, Two-Stage Models of Carcinogenesis, stems from efforts to identify improved means of cancer risk assessment that have resulted in the development of a mathematical dose-response model based on a paradigm for the biologic phenomena thought to be associated with carcinogenesis.

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