Appreciation for "Remembering Alice Stewart". (Correspondence).

EHP deserves appreciation for publishing "Remembering Alice Stewart" (Mead 2002). However, I would like to address a few inaccuracies and important omissions about this scientist's contributions that warrant comment.

The Oxford Survey of Childhood Cancers (OSCC) did not limit itself to "children [who] had died of lymphatic leukemia," (Mead 2002) but it included all children who had died of any form of cancer, anywhere in the United Kingdom. Mead's statement that Stewart found

   that children who died of cancer had received
   prenatal X-rays twice as often as healthy children

should read that

   among the children that had died of cancer, twice
   as many had been exposed to prenatal X-rays, as
   compared to the group of healthy children serving
   as controls.

Mead correctly stated Stewart's conclusion that

   radiation protection committees ... had grossly
   underestimated the [unavoidable] number of
   cancers due to background radiation,

but failed to refer to her pivotal study linking variations in local background exposure levels over a narrow grid all across the British Isles with variations in local childhood cancer (Knox et al. 1988). This observation led Stewart to infer that while about 7% of all childhood cancers for 1950-1980 were associated with prenatal X-rays (declining thereafter with declining doses), more than 70% were associated with unavoidable in utero exposures to natural background radiation (Knox et al. 1988). This study contradicted the popular contention that small anthropogenic increases in population exposures from radioactive fallout or environmental contamination have no detectable detrimental health consequences.

Based on her findings, Stewart developed a model of cancerogenesis that links a strongly age-dependent risk for radiation-induced cancer (highest during early fetal development, lower by at least a factor of three before birth, lowest in young adults, then rising again sharply after 40 years of age) with an age- and general health-dependent variation in individual immune defense competence. The evidence for this relation combines the findings of the OSCC with those of nuclear workers studies.

Mead's article (2002) and other reports have focused primarily on the politically explosive challenges that Stewart's work presented to official radiation risk assessments. However, for the history of pioneering scientific ideas it is far more significant to note that most of these contradictions derive from Stewart's unconventional insights into the confounding effects of selection (such as healthy worker and healthy survivor effect) and of competition between malignant and nonmalignant causes of deaths on epidemiologic mortality studies. Ignoring these factors have led to dramatically different outcomes in the analysis of the same statistical database.

Rudi H. Nussbaum
Department of Physics and
Environmental Sciences
Portland State University
Portland, Oregon
E-mail: [e-mail]

REFERENCES

Knox EG, Stewart AM, Gilman EA, Kneale GW. 1988. Background radiation and childhood cancers. J Radiol Prot (GB) 8(1):9-18.

Mead MN. 2002. Remembering Alice Stewart. Environ Health Perspect 110:A56.