17
THE POSSIBLE ASSOCIATION BETWEEN
CHRONIC LYMPHOCYTIC LEUKEMIA AND
EXPOSURE TO ELECTRIC AND
MAGNETIC FIELDS
D WARTENBERG
INTRODUCTION
Following Wertheimer and Leeper's seminal study
of childhood cancer in 1979 (1), many investigators have studied the possible
association between cancer and exposure to electric and magnetic fields.
There have been 16 residential childhood cancer studies, 8 residential
adult cancer studies, and several dozen occupational studies (2). Overall,
the studies provide an intriguing but somewhat confusing picture (3). However,
only magnetic fields are believed to show any possible association.
EXPOSURE AND HEALTH EFFECTS
Measures of Exposure
One challenge has been how best to describe exposure
to magnetic fields (eg, distance from power lines, wire codes, direct measurement,
calculations based on historical loads). In addition, a variety of different
metrics have proposed and/ or used to describe the exposure (eg, wire codes,
distance, time weighted average magnetic field, median magnetic field,
percent of time above a specified threshold, variability of magnetic field).
This disparity in exposure assessment provides challenges for the comparison
and interpretation of study results. In occupational studies, early studies
used job titles to infer exposure. Four recent studies combine job
history information with magnetic field measurements of specific tasks
to give integrated exposure estimates.
Health Effects and Confounders
Most studies examined both leukemia and brain cancer
occurrence, either as incidence or mortality. Only some of the studies
reported subdivisions of these classes of cancer. Some have looked at other
cancers in addition. Most studies adjust for some confounding variables
(eg, age, urban/rural, socio-economic status, traffic density, occupational
exposure to solvents or ionizing
radiation), but the array of confounders considered varies from study
to study.
Overall, the studies show a moderately consistent
association between residential proximity to power lines and childhood
leukemia. In occupational studies, there tend to be associations between
leukemia, brain cancer and time weighted average magnetic fields. However,
there is a moderate disparity among reported relative risks, and a sampling
of studies that do not show these associations.
Three of the four most recent occupational studies
report data on chronic lymphocytic leukemia (See Table 1). These data,
as with most magnetic field epidemiology, are suggestive but inconsistent.
Even if magnetic field exposure is a risk factor for chronic lymphocytic
leukemia, and if the time weighted average magnetic field is the appropriate
measure, on average the size of the risk is relatively small.
REFERENCES
1. Wertheimer N, Leeper E. Electrical wiring configurations
and childhood cancer. American
Journal of Epidemiology1979; 109(3):273-84.
2. Savitz D, Ahlbom A. Epidemiologic evidence on cancer in relation
to residential and
occupational exposures. In: D Carpenter.
Biologic Effects of Electric and Magnetic Fields.
New York: Academic Press, Inc., 1994:
233-61.
3. Wartenberg D. EMFs and health: Cutting through the controversy.
Public Health Reports
1996; 111:204-215.
4. Floderus B, Persson T, Stenlund C, Wennberg A, Ost A, Knave
B. Occupational exposure
to electromagnetic fields in relation
to leukemia and brain tumors: a case-control study in
Sweden. Cancer Causes and Control 1993;
4:465-76.
5. Sahl J, Kelsh M, Greenland S. Cohort and nested case-control
studies of hematopoietic
cancer and brain cancer among electric
utility workers. Epidemiology 1993; 4:104-14.
6. Theriault G, Goldberg M, Miller A, et al. Cancer risks associated
with occupational exposure
to magnetic fields among electric utility
workers in Ontario and Quebec, Canada, and Fra.
American Journal of Epidemiology1994;
139(6):550-72.
7. Savitz D, Loomis D. Magnetic field exposure in relation to
leukemia and brain cancer
mortality among electric utility workers.
American Journal of Epidemiology 1995;
141:123-34.
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