National Academies Press: OpenBook

Issues in Risk Assessment (1993)

Chapter: CASE STUDY 3B: ECOLOGICAL RISK ASSESSMENT OF TCDD AND TCDF

« Previous: CASE STUDY 3A: MODELS OF TOXIC CHEMICALS IN THE GREAT LAKES: STRUCTURE, APPLICATIONS, AND UNCERTAINTY ANALYSIS
Suggested Citation:"CASE STUDY 3B: ECOLOGICAL RISK ASSESSMENT OF TCDD AND TCDF." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.
×

partition coefficient, Kow. The range of uncertainty in the predicted concentrations also varied among the chemicals. In-lake removal processes (sedimentation, volatilization, and degradation) were important for all chemicals.

CASE STUDY 3B: Ecological Risk Assessment of TCDD and TCDF

M. Zeeman, U.S. Environmental Protection Agency

This paper is based on a full-scale ecological risk assessment of chlorinated dioxin and furan emissions from paper and pulp mills that use the chlorine bleaching processes (Schweer and Jennings, 1990). Although the risk assessment addressed potential risks to terrestrial and aquatic wildlife exposed to TCDD and 2,3,7,8-tetrachlorodibenzofuran (TCDF) via a number of environmental pathways, the case study was limited to exposure of terrestrial wildlife to TCDD resulting from land disposal of paper and pulp sludges. This route of exposure was identified as one of the most hazardous in the multiroute risk assessment.

The specific exposure pathway considered was uptake of TCDD by soil organisms (earthworms and insects) from soil to which pulp sludge has been applied, and the consumption of soil organisms by birds and other small animals. Transfer factors were estimated both by modeling and from data collected in a field study in Wisconsin, in which an average soil TCDD concentration of 11 ppt led to concentrations of up to 140 ppt in a composite of six robin eggs. The models used three alternative sets of assumptions: low estimate, best estimate, and high estimate. The best estimates of tissue concentrations derived from the model were often similar to those observed in the field study: the low and high estimates were lower and higher, respectively, by a factor of roughly 10.

Risk estimates for terrestrial wildlife were derived by comparing exposure estimates (usually converted to daily intake rates) with benchmark toxicity values. The values used as benchmarks were either lowest-observed-adverse-effect levels (LOAELs) or no-observed-adverse-effect levels (NOAELs) for reproductive toxicity in birds and mammals

Suggested Citation:"CASE STUDY 3B: ECOLOGICAL RISK ASSESSMENT OF TCDD AND TCDF." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.
×
Page 299
Next: Discussion »
Issues in Risk Assessment Get This Book
×
Buy Paperback | $65.00
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

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.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    Switch between the Original Pages, where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text.

    « Back Next »
  6. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  7. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  8. ×

    View our suggested citation for this chapter.

    « Back Next »
  9. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!