I/.
United States
Environmental Protection
Agency
Health Effects Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S1-87/012 Apr. 1988
&EPA Project Summary
Behavior, Physiology, and
Energy Deposition in Rats
Chronically Exposed to 2450
MHz Radiation
John A. D'Andrea and Om P. Gandhi
This research program was designed
to determine both the specific absorp-
tion rate (SAR) and the behavioral and
physiological consequences of chronic
CW microwave radiation exposure at
2450 MHz in the laboratory rat. Whole-
body average and local SARs at dis-
crete sites within the body of rats and
mice were determined both by model-
ling techniques and experimentally
using several different exposure sys-
tems. The whole-body average SAR
and the distribution of SAR within the
body depends on a variety of factors:
type of exposure system, polarization
of the field, size of the animal, and angle
of radiation incident on the body. Three
experiments were conducted to deter-
mine the effects of chronic exposure
to 2450 MHz microwave radiation on
several measures of rat behiavor and
physiology. Groups of rats were
exposed daily for 90 days to 2450 MHz
radiation at power densities of 0.5
mW/cm2 or 2.5 mW/cm2. Reliable
effects were only observed at a power
density of 2.5 mW/cm2.
This Project Summary was devel-
oped by EPA's Health Effects Research
Laboratory, Research Triangle Park,
NC, to announce key findings of the
research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering
information at back).
Introduction
There has been an ever-growing
increase in the electromagnetic radiation
emanating from communications
sytems, television, radar, food-
processing, industrial and medical
devices. Since 1940, the growth of
sources for such radiation has increased
markedly and is continuing at an ever-
accelerating rate. Concurrent with this
growth in number of sources has been
an increase in the power outputs of such
devices. This situation has resulted in
much concern over possible harmful
biological effects from such radiation in
the radio-frequency and microwave
portions of the electromagnetic spec-
trum. It is well known that microwaves
at very high power densities can cause
adverse biological effects due to the
generation of heat in body tissues.
Unknown, however, are the subtle
physiological, morphological, and behav-
ioral changes due to long-term exposure
at low power densities. This has led to
a controversy in this country over the
significance or even presence of effects
produced by chronic low-level exposures.
Several earlier studies have reported
behavioral and physiolgical changes with
repeated daily exposures to low levels of
microwave radiation. In these studies,
albino rats were given many weeks of
exposure to microwave fields at inten-
sities of 0.5 mW/cm2 or below.
Microwave-exposed rats showed a var-
iety of effects including (1) lowered
threshold for footshock detection, (2)
altered cholinesterase and sulfhydryl
groups in blood, (3) increased 17-
ketosteroid levels in urine, and (4)
retarded learning in an avoidance task.
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In each study the exposure occurred in
an anechoic chamber with the irradiating
antenna placed above rats that were
singly or multiply caged during
irradiation.
This research program was initiated for
two purposes. First, to determine what
factors control the formation of locations
with high levels of energy deposition
(called hotspots) in the rat exposed to
2450 MHz radiation. Both computer
modelling and laboratory measurement
techniques were used to address this
question. Second, to determine the
behavioral and physiological conse-
quence of chronically exposing rats to
CW microwave radiation at 2450 MHz.
The chronic exposure studies were
carried out in a monopole-above-ground
irradiation system that provides for a
more uniform exposure of rats than do
other irradiation systems.
Methods and Material
Both the whole-body averaged SAR,
and the SAR at discrete sites within the
rat body were determined by both ana-
lytical and experimental techniques.
Analytic Procedures
In the analytic approach, a 160-
cubical-cell model of the rat was deve-
loped and a method of moments proce-
dure, employing a pulse function, was
used to obtain a number of solutions for
whole-body averaged SAR and SAR
within each cubical cell for 2450 MHz
microwave exposure. The calculations
were made with the model under several
conditions of exposure and by orienting
the length of the model parallel to: (1)
the electric field vector; (2) the magnetic
field vector; or (3) the direction of wave
propagation. Additional details can be
found in the full report and the computer
programs used are listed in an appendix.
Measurement Procedures
SARs for both the whole-body aver-
ages and values at several discrete
anatomical locations were measured in
rat cadavers exposed to 2450 MHz
microwave radiation in an anaechoic
chamber. Additional experimental
dosimetry experiments were conducted
with both rat and mouse cadavers
exposed in other open and closed expo-
sure systems. SAR distribution was
determined in the cadavers during
exposure to 915 MHz and 2450 MHz
radiation by sampling the temperature
rise at discrete body Icoations with a
microwave compatible temperature
probe. Additional details can be found in
appendices of the full report.
Chronic Microwave Exposures
Three long-term exposures were con-
ducted to determine the effects of 2450
MHz microwave radiation on several
measures of rat behavior and physiology.
In a repeated measures experimental
design, groups of rats were exposed to
2450 MHz radiation at power densities
of 0.5 or 2.5 mW/cm2. Microwave and
sham exposures were given seven hours
per day for 90 days over which time both
behavioral and physiological measures
were repeatedly sampled. Additional
details can be found in appendices of the
full report.
Results and Discussion
Both the specific absorption rate (SAR)
and behavioral and physiological conse-
quences of chronic CW microwave
exposure of 2450 MHz were determined
in the laboratory rat.
Whole-body averaged SAR and SARs
at discrete sites within the body deter-
mined by both analytical and experimen-
tal techniques revealed differences due
to differing exposure conditions. Gener-
ally, the analytical and experimental
determinations of whole-body average
SAR were quantitatively very similar for
exposures in the E-polarization. There
was, however, little agreement between
the analytically and experimentally
determined SAR distributions inside the
rat body. The type of exposure system
and the radiation frequency are impor-
tant determiners for the distribution of
SARs within rat and mouse cadavers.
Distinct SAR patterns were observed in
mice for anechoic chamber exposures
and exposures in rectangular and circu-
lar waveguide systems. Differences of
SAR distributions attributable to method
of exposure were also observed in rats,
but not to the extent found in mice.
Three experiments were conducted to
determine the effects of chronic expo-
sure to 2450 MHz microwave radiation
on several measures of rat behiavor.
During one exposure at 0.5 mW/cm2
decrements in performance in active
avoidance and schedule-controlled lever
pressing forfood were observed. Another
experiment was conducted at 0.5 mW/
cm2 to reevaluate the behavioral effects.
In this experiment the active avoidance
decrement was not observed. Effects
were observed in schedule-controlled
lever pressing for food but were qualit-
atively different from those observed in
the first experiment. It was concluded
that microwave radiation at a field power
density of 0.5 mW/cm2 is below thre-
shold for reliable and reproducible effects
on a wide range of dependent variables.
At a power density of 2.5 mW/cm2,
however, exposed and sham-exposed
rats differed significantly in both the
active avoidance and schedule-
controlled lever pressing tasks. Reliable
differences were also observed for
sensitivity to an electric foot shock. It was
concluded that microwave radiation at a
power density of 2.5 mW/cm2 is above
threshold for reliable and reproducible
effects.
Conclusions and
Recommendations
The whole-body average SAR and the
distribution of SAR within rat and mouse
cadavers depends on a variety of factors:
orientation of the body within the mic-
rowave field, the characteristics of the
exposure system, size of the animal, and
angle of radiation incident to the cadaver.
Points of increased energy absorption,
SAR hotspots, four times largerthan the
whole-body average, were observed in
the esophagus of rat cadavers exposed
to 2450 MHz microwave radiation in the
E- and k-polarizations.
The analytical procedures used to
predict whole-body average SAR were
accurate for a rat model exposed to 2450
MHz radiation in the E-polarization. In
contrast, the analytically predicted SAR
distribution within the rat model was not
in agreement with the experimentally
determined values. Several factors were
thought to account for this discrepancy.
Three chronic exposure experiments
were conducted with rats irradiated daily
for up to 90 days. At a power density
of 0.5 mW/cm2 two minor behavioral
effects were observed: increased varia-
bility among rats performing the active
avoidance task and a decrement on
schedule-controlled lever pressing for
food. During a second experiment con-
ducted at 0.5 mW/cm2, the active
avoidance effect was not observed. In
this experiment, effects were observed
in schedule-controlled lever pressing for
food which were qualitatively different
from those observed in the first exper-
iment. It was concluded that microwave t
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radiation at a field power density of 0.5
mW/cm2 is below threshold for reliable,
reproducible effects on rat behavior. At
a power density of 2.5 mW/cm2, exposed
rats differed from sham-irradiated rats on
both active avoidance and schedule-
controlled lever-pressing tasks. Signifi-
cant differences were also observed for
sensitivity to an electric foot shock. All
of the observed differences between
microwave- and sham-exposed rats
returned to normal values within 60 days
following cessation of treatment. It was
concluded that microwave radiation at a
power density of 2.5 mW/cm2 clearly
results in behavioral effects.
In contrast to previous research in
which reliable behavioral and physiolog-
ical alterations were found for exposures
at 0.5 mW/cm2, reproducible changes
were not observed in this study. How-
ever, the method of exposure in the
earlier studies and in this study were
different. Based on the findings in this
study, the distribution of SARs within
experimental subjects depends to a large
extent on the method of exposure. To
determine whether the SAP distribution
may influence biological measures dur-
ing chronic microwave exposure of rats,
additional experiments comparing sev-
eral methods of exposure are needed.
John A. D'Andrea and Om P. Gandhi are with the University of Utah, Salt
Lake City. UT84112.
Michael I. Gage is the EPA Project Officer (see below).
The complete report, entitled "Behavior, Physiology, and Energy Deposition
in Rats Chronically Exposed to 2450 MHz Radiation," (Order No. PB 88-171
418/AS; Cost: $19.95, 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
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