Review of the Environmental Protection Agency's Draft IRIS Assessment of Tetrachloroethylene (2010) / Chapter Skim
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8 Hematopoietic Effects
8 Hematopoietic Effects
Pages 75-80
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From page 75... ...
. The committee similarly questions the use of the tetrachloroethylene exposure bioassays in the F344 rat for cancer risk assessment for those reasons and others discussed below.
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From page 76... ...
On the basis of 34 NTP studies that yielded evidence of a chemically related increase in the incidence of leukemia, which included the 1986 NTP study of tetrachloroethylene, the authors conducted a reanalysis of dose-response data by comparing results with four statistical methods: Fisher's test for pair-wise comparison of leukemia incidence between a dose group and a control group, the Cochran-Armitage test for incidence trend, logistic regression for incidence, and life tables for survival-adjusted incidence. Tetrachloroethylene was one of five chemicals shown by the authors to produce leukemia in both sexes of rats.
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From page 77... ...
rats weakens the ability to separate the background response from possible chemically induced responses, particularly when the chemically induced response above background is low. The committee recommends that the statistical approaches applied by Thomas et al.
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From page 78... ...
Epidemiologic studies of the association vary with study design, validity, specificity of exposure assessment, type of population studied, and sample size, all of which contribute to the inconsistency of results and reduce the committee's confidence in the conclusions that can be drawn from the data. The committee also noted a number of factual errors in this section of the IRIS draft that should be corrected; such errors detract from overall confidence in the draft's conclusions.
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From page 79... ...
The data suggest a reversible bone marrow depression. Inhibited production of both red cells and various forms of white cells have been reported after exposure to a variety of leukemogens (such as anticancer alkylating agents or benzene)
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From page 80... ...
However, MCL resulting from tetrachloroethylene exposure has not been observed in other strains of rats or other animal species, and no definitive evidence is available to support a hypothesized MOA by which tetrachloroethylene increases MCL in F344 rats. Those are all sources of uncertainty surrounding the relevance of MCL to human cancer risk.
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