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DATA

Twelve of the candidates were already included in the CPDB and in Krewski's study (upper portion of Table G-2). For two other agents (benzo[a]pyrene and 1, 3-butadiene), the committee identified dose--response data that could be analyzed quantitatively (Tables G-3 and G-4). For another agent (vinyl chloride), the committee identified an ingestion study that gave results (Table G-5) markedly different from those of the inhalation study included in the first part of Table G-2. The ingestion study (Feron et al., 1981) appears to have met the inclusion criteria of the CPDB, and it is not clear why it was not included in the CPDB. The data in Tables G-3, G-4, and G-5 were analyzed by Krewski with the same methods as those used in his workshop paper, and the resulting estimates of TD50 are tabulated in the lower portion of Table G-2.

For four agents listed in Table G-1, comparable numerical estimates of carcinogenic potency could not be obtained, for the following reasons:

  • Dimethyl sulfate. The only reported studies are unsuitable for quantitative analysis, but show tumors at the MDT and MDT/2 (IARC, 1974).

  • Dibenz[a,h]anthracene. The only reported studies are unsuitable for quantitative analysis (ATSDR, 1990).

  • Methyl bromide. Data purporting to show induction of forestomach tumors within 90 days (Danse et al., 1984) have been discredited (EPA, 1986; Reuzel et al., 1991).

  • Plutonium. Dose data on this and other radionuclides are not commensurable with those customarily applied to chemical carcinogens. For plutonium, the radiation dose that causes early death (within 1.5 years) due to radiation pneumonitis and pulmonary fibrosis in animals exposed by inhalation is about 45 Gy (Scott et al., 1990), whereas the TD 50 for animals similarly exposed is 3.3 Gy (Diehl et al., 1992). (In this case, early death is used as the measure of toxicity for the purpose of determining the MTD.)



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OCR for page 177
APPENDIX G 177 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. DATA Twelve of the candidates were already included in the CPDB and in Krewski's study (upper portion of Table G-2). For two other agents (benzo[a] pyrene and 1, 3-butadiene), the committee identified dose--response data that could be analyzed quantitatively (Tables G-3 and G-4). For another agent (vinyl chloride), the committee identified an ingestion study that gave results (Table G-5) markedly different from those of the inhalation study included in the first part of Table G-2. The ingestion study (Feron et al., 1981) appears to have met the inclusion criteria of the CPDB, and it is not clear why it was not included in the CPDB. The data in Tables G-3, G-4, and G-5 were analyzed by Krewski with the same methods as those used in his workshop paper, and the resulting estimates of TD50 are tabulated in the lower portion of Table G-2. For four agents listed in Table G-1, comparable numerical estimates of carcinogenic potency could not be obtained, for the following reasons: • Dimethyl sulfate. The only reported studies are unsuitable for quantitative analysis, but show tumors at the MDT and MDT/2 (IARC, 1974). • Dibenz[a,h]anthracene. The only reported studies are unsuitable for quantitative analysis (ATSDR, 1990). • Methyl bromide. Data purporting to show induction of forestomach tumors within 90 days (Danse et al., 1984) have been discredited (EPA, 1986; Reuzel et al., 1991). • Plutonium. Dose data on this and other radionuclides are not commensurable with those customarily applied to chemical carcinogens. For plutonium, the radiation dose that causes early death (within 1.5 years) due to radiation pneumonitis and pulmonary fibrosis in animals exposed by inhalation is about 45 Gy (Scott et al., 1990), whereas the TD50 for animals similarly exposed is 3.3 Gy (Diehl et al., 1992). (In this case, early death is used as the measure of toxicity for the purpose of determining the MTD.)

OCR for page 177
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.APPENDIX G 178

OCR for page 177
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.APPENDIX G 179

OCR for page 177
APPENDIX G 180 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. TABLE G-3 1,3 Butadiene* Dose Rate (mg/kg-d) Tumor Incidence Males Females Lymphocytic lymphoma 0 2/70 2/70 3.8 1/70 4/70 12 2/70 6/70 38 4/70 3/70 120 2/70 11/70 380 62/90 36/90 *Inhalation exposure, 6h/day, 5d/wk for up to 2 years. Most animals died in high exposure groups by 65 weeks because of high tumor incidence. Source: Melnick et al., 1990. TABLE G-4 Benzo[a]pyrene* Dose Rate Tumor Incidence (mg/kg-d) Male and Female Stomach, squamous cell carcinomas and 0 0/289 papillomas 0.13 0/25 1.3 0/24 2.6 1/23 3.9 0/37 5.2 1/40 5.85 4/40 6.5 24/34 13.0 19/23 32.5 66/73 *Oral exposure in diet. Mice, CFW, male and female. Duration of exposure: 110 days. Duration of experiment: 183 days. Source: Neal and Rigdon, 1967.