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EPA Report on Thyroid Cancer

In today's Federal Register (page 15842), the EPA announced the availability
of a report dealing with risk assessments regarding thyroid follicular cancer.
The announcement is interesting in that it is the first time that the EPA has
considered a nonlinear dose response relationship.  The conditions under which
this relationship is allowed may have some impact on the LNT debate currently
underway.  The summary out of the Federal Register is as follows:

The Environmental Protection Agency (EPA) is today announcing the availability
of an EPA Risk Assessment Forum report entitled, Assessment of Thyroid
Follicular Cell Tumors (hereafter ``Forum Report''). The Forum Report presents
science policy guidance that describes the procedures the Agency will use in
the evaluation of potential human cancer hazard and dose-response assessments
from chemicals that are animal thyroid carcinogens. The Forum Report describes
when, under clearly specified conditions, chemical carcinogenesis in thyroid
follicular cells can be analyzed as a nonlinear phenomenon, rather than
assuming low dose linearity as EPA customarily does for carcinogenic
compounds. Four hypothetical case studies are summarized which illustrate how
to evaluate toxicological data and make hazard and dose-response estimation
choices. The procedures and considerations developed in the Forum Report
embody current scientific knowledge of thyroid carcinogenesis and evolving
science policy. Should significant new information become available, the
Agency will update its guidance accordingly.

Brian Kelly, CHP, PE