United States
Environmental Protection
Agency
Health Effects Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S1-84-009 Oct. 1984
&EPA Project Summary
Thermoregulatory
Consequences of Long-Term
Microwave Exposure at
Controlled Ambient
Temperatures
Eleanor R. Adair, Donald E. Spiers, Robert 0. Rawson, Barbara W. Adams,
Douglas K. Sheldon, Philip J. Pivirotto, and Gillian M. Akel
This study was designed to identify
and measure changes in thermoregu-
latory response systems, both behav-
ioral and physiological, that may occur
when squirrel monkeys are exposed to
2450-MHz CW microwaves 40 hours/
week for 15 weeks. Microwave power
densities explored were 1 and 5
mW/cm2 (SAR = 0.16 W/kg per
mW/cm2) and were presented at con-
trolled environmental temperatures of
25, 30, and 35 °C. Standardized tests,
conducted periodically, assessed chang-
es in thermoregulatory responses. De-
pendent variables measured included
body mass, certain blood properties,
metabolic heat production, sweating,
skin temperatures, deep body temper-
ature, and behavioral responses by
which the monkeys selected a preferred
environmental temperature. Results
showed no alteration of metabolic rate,
internal body temperature, or thermo-
regulatory behavior by microwave ex-
posure although the ambient temper-
ature prevailing during chronic exposure
could exert an effect. An increase in
sweating rate occurring in the 35 °C
environment was not enhanced signif-
icantly by microwave exposure. Skin
temperature, reflecting vasomotor
state, was reliably influenced by both
ambient temperature and microwaves.
The most robust consequence of micro-
wave exposure was a reduction in body
mass which appeared to be a function
of microwave power density.
This Project Summary was developed
by EPA's Health Effects Research Lab-
oratory, Research Triangle Park. NC, to
announce key findings of the research
project that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Committees of both houses of the
Congress(U.S. Senate, 1978; U.S. House
of Representatives, 1979) have urged the
establishment of research programs
which would investigate the biological
effects of long-term exposure to low-level
radiation. Held to be of particular impor-
tance is "...basic research into the physio-
logical mechanisms by which biological
and/or behavioral effects of exposure to
nonionizing radiation may occur..." The
final report on this(project describes some
results of a four-year program of research
for which.the above description is highly
appropriate. Specifically, the study invest-
igated the changes in thermoregulatory
mechanisms that may occur when squir-
rel monkeys are chronically exposed to
low-level microwave fields at controlled
environmental temperatures.
Thermoregulation refers to the ability
of an organism to achieve and maintain a
characteristic internal body temperature.
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Two classes of responses can accomplish
thermoregulation, behavioral and physio-
logical (or autonomic). Behavioral re-
sponses, voluntary actions by the organ-
ism, control the thermal characteristics of
the air-skin interface and can take two
forms, either direct manipulation of the
environment itself of bodily movement
into a more favorable microclimate. The
heat exchange between the organism
and the environment is thereby closely
regulated, which results in stability of the
internal body temperature. Both types of
behavior have been shown to change
when an organism is exposed briefly to a
microwave field.
Physiological responses are involuntary
in endothermic species and may occur
automatically whenever behavioral re-
sponses are impossible or inadequate, or
under special circumstances; e.g., during
exercise or febrile disease. Specific phys-
iological responses include shivering and
non-shivering thermogenesis, changes
in peripheral vasomotor tone, sweating
and/or panting. These responses also
have been shown to change when endo-
therms are exposed briefly to a microwave
field.
That long-term exposure to low-level
microwave fields may alter thermoregu-
latory function is suggested by some of
the Eastern European clinical literature.
A neurocirculatory syndrome involving
cardiac, neural, and metabolic function
was often found in Soviet workers who
had labored in close proximity to micro-
wave sources for 10 years or more. The
literature describes long-term alterations
in body weight, blood pressure, body
temperature, and certain conditioned
reflexes. It has been reported that workers
exposed to microwaves for more than 10
years are copious sweaters compared to
short-term workers. However, in these
Eastern European clinical studies, aver-
age microwave exposures are estimated,
proper dosimetry is nonexistent, and
other relevant environmental factors,
such as temperature and humidity, are
usually neither assessed nor controlled.
To date, laboratory investigation of the
effects of long-term microwave exposure
in animals has been carried out almost
exclusively on small mammals(i.e., mice,
rats, guinea pigs, and rabbits). No pub-
lished study has stated as a specific
purpose the assessment of the thermo-
regulatory consequences of such expo-
sure, although a metabolic compensation
in exposed animals has been inferred
from measurements of body mass and
food consumption. In general, rats and
rabbits 'exposed for several weeks or
months to low doses of microwaves eat
less than controls but maintain body
weight and increase fluid intake. Such
findings have led some to conclude that
the exposed animals profited from the
microwave energy and the reduced ener-
gy demands of their bodies was reflected
by a lowered food intake.
The effects of periodic and chronic
microwave exposure at high power dens-
ities on the regulated body temperature of
dogs was an early topic of investigation.
Repeated exposure to 2800-MHz pulsed
microwaves at 165 mW/cm2 produced
smaller and smaller increases in rectal
temperature. Also reported was an adapta-
tion to the procedure that took the form of
a lower-than-normal body temperature.
A very important variable appears to be
the ambient temperature at which such
chronic exposures are performed, high
ambients emphasizing thermoregulatory
abnormalities and low ambients de-em-
phasizing them.
Few primates have been chronically
exposed to radiofrequency fields and
none for the express purpose of measur-
ing changes in thermoregulatory function.
The literature describes several studies in
which rhesus monkeys, living outdoors in
large family groups, irradiate themselves
with 9.3 GHz pulsed microwaves at a
range of power densities as they work
daily for apple juice rewards. No dele-
terious effects on the eyes have been
observed after several years, and operant
responding, social behavior, health, and
fecundity are all normal. Another study
exposed rhesus monkeys for 22 months
to extremely low-frequency electromag-
netic fields but found no changes in
general health; the major difference
between exposed and control animals
was an increased growth rate in the
exposed monkeys.
Discussion
There is a clear need for basic informa-
tion on the thermoregulatory conse-
quences of long-term low-level exposure
of primates to microwaves, preferably at
different ambient temperatures. This
project summary describes a longitudinal
study of highly trained animals (initially
naive to microwaves) that combined both
physiological and behavioral tests. Fol-
lowing the assessment of baseline levels
of thermoregulatory function, squirrel
monkeys were either sham-exposed or
exposed to 2450-MHz continuous wave
(CW) microwaves, 40 h/wk for 15 weeks.
Power densities were 1 or 5 mW/cm2 at
controlled ambient temperatures of 25,
30 or 35°C. Periodic physiological and
behavioral tests were performed to assess
thermoregulatory function during and
after chronic exposure. The purpose of
this study was to determine:
1. whether this exposure alters the
normally-preferred ambient temper-
ature and the ambient temperature
selected during brief exposures to
microwaves of higher field strength;
2. whether this exposure can produce
"irritability" as measurd by changes
in the pattern of thermoregulatory
responding;
3. whether significant changes occur
in body mass and in standard
hematological parameters;
4. whether this exposure changes the
setpoint for body temperature, al-
ters the normal physiological re-
sponses of heat production and
heat loss in cold, neutral, and warm
environments, or alters vasomotor
activity; and
5. whether ambient temperature and
microwave energy interact syner-
gistically to produce changes in
thermoregulatory function.
This longitudinal study was undertaken
to determine whether or not the normal
thermoregulatory responses of squirrel
monkeys may be altered during and after
chronic exposure (40 h/wk for 15 wk) to
2450-MHz CW microwaves, at power
densities of 0, 1, and 5 mW/cm2, when
ambient temperature is simultaneously
controlled at 25,30 or 35°C. The findings
were largely negative: no changes that
occurred in metabolic heat production,
resting metabolic rate, normal regulated
body temperature, or the microwave
threshold for the alteration of thermo-
regulatory behavior could be ascribed
unequivocally to chronic microwave ex-
posure. Chronic exposure to the 35°C
environment, irrespective of concomitant
microwave exposure, increased sweating
rate and lowered the environmental
temperature selected by most animals.
Significant shifts in mean skin temper-
ature were difficult to interpret because
of variability in baseline data, a difficulty
compounded by the small sample size. No
trends in the data over time indicated a
cumulative influence of microwave ex-
posure on thermoregulatory mechanisms.
Tests of hematological and serum chem-
istry parameters yielded random results
that were of dubious relevance to the
exposure treatments. The most reliable
finding appeared to be a reduction in body
mass of the microwave-exposed animals
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egardless of exposure temperature, an
;ffect that was most pronounced in those
Animals exposed at 5 mW/cm2.
The study was exploratory, in the sense
hat a wide range of chronic exposure
.onditions was examined for possible
hermoregulatory consequences. As a
esult, very few animals constituted each
reatment group, rendering statistical
malysis of the data very difficult. An
ilternative approach would have involved
sxposing larger numbers of animals to
nany fewer exposure conditions. How-
sver, no relevant experimental evidence
jxisted on which to select the "critical"
ixposure conditions. In the belief that
nicrowave exposure in thermoneutral
md warm environments posed a greater
hreat to efficient thermoregulation than
iimilar exposure in the cold, the selected
ixposure conditions had the potential for
leat stress, in the context of the thermo-
egulatory capacity of the squirrel mon-
;ey. Hence, the three ambient temper-
itures at which chronic exposure oc-
:urred were equivalent to the middle and
wo extremes of the thermoneutral zone
)f the species in question. The power
tensities selected were either well below
1 mW/cm2) or near (5 mW/cm2) the
ower limit of those that just provoke
ihanges in thermoregulatory responses
luring acute microwave exposure under
naximally-favorable environmental con-
Jitions. The conditions selected set the
stage most favorably for the manifestation
>f cumulative effects and/or the enhance-
nent of particular response changes to
)ne environmental variable by a second
variable acting synergistically. That most
}f the results were negative or equivocal
•eflects the influence of many factors, all
>f which are detailed in the final report.
f. R. Adair, D. E. Spiers, R. 0. Rawson, B. W. Adams, D. K. Sheldon. P. J. Pivirotto,
and G. M. Akel are with John B. Pierce Foundation Laboratory, New Haven, CT
06519.
Joe A. Elder is the EPA Project Officer (see below).
The complete report, entitled "Thermoregulatory Consequences of Long-Term
Microwave Exposure at Controlled Ambient Temperatures," (Order No. PB
84-236 603; Cost: $11.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Health Effects Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
U.S. GOVERNMENT PRINTING OFFICE; 1984 — 559-016/7842
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