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Issues in Risk Assessment (1993)

Chapter: RESULTS

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Suggested Citation:"RESULTS." National Research Council. 1993. Issues in Risk Assessment. Washington, DC: The National Academies Press. doi: 10.17226/2078.
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TABLE G-5 Vinyl Chloride*

 

Dose Rate (mg/kg-d)

Tumor Incidence

Males

Females

Liver tumors (neoplastic nodules, hepatocellular carcinomas, angiosarcomas)

0

0/55

2/57

1.7

2/58

26/58

5.0

17/56

42/59

14.1

58/59

56/57

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

Source: Feron et al., 1981.

RESULTS

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.
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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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