Handbook of Solvents - George Wypych - ChemTech - Ventech!

20.5 Lymphohematopoietic study of workers exposed to benzene 1369
is not applicable here based on the most recent EPA and IARC positions. 57,58 This linear,
non-threshold model assumes that every increment of dose is accompanied by a commensurate
increment in the excess cancer risk. The use of this toxicological model allows extrapolation
of risks from relatively high dose levels, where cancer responses can be measured, to
relatively low dose levels, where such risks are too small to be measure directly through epidemiological
studies. 61 Figures 20.5.2 and 20.5.3 demonstrate the extrapolation from high
levels of exposure to low levels of exposure utilizing the linear modality.
Indeed, in its most recent publication the U.S. EPA, 10/14/98, 62 further supports that
approach and the panel members who evaluated the data felt that for the leukemogenic effects
of benzene the linear model is consistent with the spirit of the proposed cancer risk assessment
guidelines.
20.5.7 CELL TYPES: HEMATOLYMPHOPROLIFERATIVE EFFECTS OF
BENZENE
The hematopoietic cell type toxicity from benzene have been described in animal data, case
reports, case studies, animal data, and epidemiological data. Essentially, Wong in his
OSHA testimony 63 concludes that for the continuously exposed group the lymphohematopoietic
cancer risk ratio was 3.2 with a statistical significance of p