National Academies Press: OpenBook

Issues in Risk Assessment (1993)

Chapter: RESULTS

« Previous: DATA
Suggested Citation:"RESULTS." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.

TABLE G-5 Vinyl Chloride*


Dose Rate (mg/kg-d)

Tumor Incidence



Liver tumors (neoplastic nodules, hepatocellular carcinomas, angiosarcomas)













*Oral lifetime exposure. Surviving males and females were sacrificed at 135 and 144 weeks, respectively.

Source: Feron et al., 1981.


For the 14 candidate agents on which comparable quantitative data are available, the right side of Table G-2 shows the observed TD50 as calculated by Krewski's procedures with the one-stage model. The last three columns in Table G-2 show the log10TD50 predicted by Krewski's model, the deviation from the regression line (observed - predicted log10TD50), and the standardized deviation (observed deviation divided by r.m.s. error). The data are plotted in relation to Krewski's regression line in Figure 1. Most of the 14 candidate chemicals are within the 95% confidence limits (standardized deviation, 1.96); this is illustrated in Figure 2, which plots the calculated TD50s for each of the 14 chemicals. For five of the 14 agents (the three benzidine dyes, carbon tetrachloride, and 1,3-butadiene), the calculated TD50s are below the lower confidence limit on the regression line, i.e., inside Region C (Figure 2). Among the four agents on which comparable quantitative data are not available, only plutonium has a low ratio of TD50 to HDT (1:13), but its HDT caused premature deaths and would not be accepted as an MTD in a conventional bioassay.

Neither of the TD50s calculated for vinyl chloride fall in Region C. The TD50 based on the data selected by the committee falls below the

Suggested Citation:"RESULTS." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.
Page 181
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,'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!