V-/EPA
United States
Environmental Protection
Agency
Health Effects Research
Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S1-82-014 Jan. 1983
Project Summary
Effects of 200, 591 and 2450
MHz Microwaves on Cerebral
Energy Metabolism
Aaron P. Sanders and William T. Joines
Earlier work showed that levels of
key biochemicals in the energy pro-
duction system of rat brain are
affected by exposure to 591 MHz
microwave radiation at 13.8 mW/cm2.
The objectives of this study were to
determine whether direct microwaves
affect the biological system, and if
they do, whether they are secondary
to the hyperthermia produced in the
tissue, to establish dose-response
relationships for the effects, and to
investigate different frequencies of
exposure and modulation of the
carrier signal. The fluorescence of
reduced nicotinamide adenine dinu-
cleotide (NADH) in the rat brain was
measured in vivo during exposure to
the microwave radiation, and adeno-
sine triphosphate (ATP) and creatine
phospate (CP) levels were measured
chemically after exposure. An increase
in brain temperature from 35.6 to 39°C
caused no change in NADH fluores-
cence, an 11.8% reduction in the ATP
level and a 28.8% decrease in the CP
level. Microwave exposures at 200
and 591 MHz for 0.5 to 5 minutes at
13.8 mW/cm2 caused no measurable
increase in brain temperature; how-
ever, the maximum NADH fluores-
cence increase was 10% while ATP
levels decreased by as much as 30%.
CP levels decreased by up to 40% at
591 MHz but not at all at 200 MHz.
Similar exposures at 2450 MHz
produced no changes in any of the
parameters measured. These results
indicate frequency specific inhibition
of brain energy metabolism. At 200
MHz, the mitochondria! NADH-to-
ATP production pathway was inhibited.
At 591 MHz both the NADH-to-ATP
and the CP-to-ATP pathways were
inhibited. At 2450 MHz, neither
pathway was affected. The data
support the hypothesis that microwave
radiation directly inhibits mitochondria!
energy production pathways in rat
brain, and that tissue heating is not a
factor.
This Project Summary was developed
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
The question of whether microwave
radiation can cause biological effects
that are independent of tissue hyper-
thermia has been a continuing contro-
versy forseveral years. Whilethe matter
is far from settled, several lines of
evidence indicate a strong possibility of
direct interactions which lead to poten-
tially important biological changes. One
such experiment provided the basis for
this study. Exposure of a rat to 591 MHz
microwave radiation at 138 mW/cm2
produced changes in the levels of three
key brain biochemicals, reduced nico-
tinamide adenine dmucleotide (NADH),
adenosine triphosphate (ATP) and
creatine phosphate (CP) Because the
-------
principal compound, ATP, provides the
energy necessary to drive many biological
functions, any change in the biological
system's capacity to produce this
compound is extremely important.
The objectives of this study were
threefold. The first was to establish
whether or not tissue hyperthermia
plays an obvious role in producing the
biochemical changes. This was ad-
dressed by extensive dosimetry and by
investigation of the effect of temperature
on the in vivo processes. The second
objective was to establish the depen-
dence of the changes on the frequency
of the microwave radiation and on
modulation of the carrier frequency.
Finally, wherever effects were found,
dose-response relationships were de-
veloped.
Summary Text
Most of the microwave exposures
were conducted by placing a rat in a
stripline facing the source of the
radiation. Experiments were conducted
at frequencies of 200, 591, and 2450
MHz. The carrier signal at 591 MHz was
also sinusoidally modulated at several
frequencies between 4 and 32 Hz, and
pulse-modulated at 250 and 500 pulses
per second using 5/usec pulses. Relative
NADH levels were measured during
exposure by uncovering a portion of the
anesthetized rat's brain and placing a
fiberoptic probe adjacent to it through
which NADH fluorescence was mea-
sured by use of a time-sharing fluoro-
meter. Following decapitation of the rat
immediately after exposure, ATP and CP
concentrations in the brain were
determined chemically using established
methods. Temperature controls were
performed by wrapping the anesthetized
rat in a heating blanket to maintain the
desired brain temperature.
Incident microwave fields were mea-
sured at the rat's position inthe stripline
without the rat present. The tissue
absorption of microwave radiation was
measured by the temperature-rise
technique using thermistor probes in
the brains of dead rats.
The relationship of the three bio-
chemicals measured is diagrammed in
Figure 1. NADH oxidation results m
electron flow in the respiratory chain of
the mitochondrion which is coupled to
ATP production. If ATP levels fall below
normal, the CP-CP kinase-ADP-ATP
reaction occurs rapidly to sustain the
ATP pool. The CP pathway maintains
normal levels of ATP until CP levels fall
approximately 40%.
The results of the thermal controls
demonstrated that when the rats were
anesthetized with urethane, the NADH
fluorescence was not affected, and ATP
and CP levels decreased to new steady
state levels as temperature was raised.
A temperature rise from 35.6°C to
39.0°C decreased ATP concentration by
11.8% and CP concentration by 28.8%.
Dose-response curves for NADH
fluorescence in microwave exposed
rats are illustrated in Figure 2, plotted as
a function of the incident field strength.
These data show that at 200 and 591
MHz, the change in NADH fluorescence
increased until exposures of 10-12
mW/cm2 were reached, when the
effect appeared to saturate. Additional
exposures up to 40 mW/cm2 confirmed
Creatme
CP-Kinase
CP+ADP+Pi
-Site 11 —Site /•
NADH
MAD
IVAi
NA
ADP r ADP\ ADP
\r
\ O + Hz Respiratory Chain
Mitochondrion
Interaction of CP, ADP. and
NADH.
Figure 1 .
this saturation level. No change in
NADH fluorescence was found when
the rats were exposed to 2450 MHz. As
can be seen from the conversion
factors in the figure, the energy absorbed
by the rat head per unit time (specific
absorption rate or SAR) varies with
frequency and was actually highest at
2450 MHz where no change was
observed. These results, coupled with
those for the thermal controls, argue
strongly against a tissue hyperthermia
mechanism. If the NADH fluorescence
data are plotted versus the electrical
field strength in the brain tissue, a
threshold of 3-4 volts/meter (V/M) is
obtained at both 200 MHz and 591 MHz.
In Figure 3, typical NADH fluorescence
curves are shown as a function of time
of exposure together with the chemical
data for ATP and CP concentrations
determined after comparable exposure
periods. For 591 MHz exposures, the
changes in ATP concentration appear to
mirror the changes in the NADH
fluorescence. The CP concentrations
changes were always greater than
those for ATP, consistent with the
normal functioning of the CP pathway.
These data indicate an inhibition of the
pathway that uses NADH to produce
ATP, resulting in excess NADH and
insufficient ATP. For 200 MHz exposures,
the relationship of NADH fluorescence
and ATP levels were similar to those of
591 MHz. However, at 200 MHz there
was no decrease in CP concentration,
even though ATP levels have dropped
20
18
16
14
12
10
8
6
200 MHz, Cw
Exposures
'SAft = 0.046 mW
g /mW
cm2
Maximum
Observed^
591 MHz, CW
Exposures
SAR = 0.185 mW
g /mW
,2
cm
Maximum
Observed,
2450 MHz, CW
Exposures
SAR = 0.368 mW
g /mW
Figure 2.
mW/cm2 Surface Power Density
Changes in NADH fluorescence of rat brain vs surface power densities at 200,
591 and 2450 MHz, CW exposures in microstrip system.
-------
significantly. This indicates an inhibi-
tion of both the NADH-to-ATP pathway
and the CP-to-ATP pathway Again, for
exposures at 2450 MHz there was no
statistically significant changes in
NADH fluorescence, ATP levels, or CP
levels, indicating no inhibition of the
system by this frequency. These results
demonstrate a selective frequency-
specific inhibition of the energy produc-
tion system in rat brain.
NADH fluorescence has been mea-
sured for rats exposed to 591 MHz
microwave radiation smusoidally ampli-
tude modulated at frequencies between
4 and 32 Hz. Results for amplitude
modulation frequencies between 16
and 24 Hz were the same as for
unmodulated 591 MHz microwaves At
4-12 Hz and 28-32 Hz, the increase in
NADH fluorescence was about 10%
smaller than for the unmodulated 591
MHz exposures. The significance of this
difference is not known at this time
Rats also have been exposed to pulse
modulated 591 MHz microwave radia-
tion Five microsecond pulses at pulse
repetition rates of 500 and 250 pulses/
sec were employed. The NADH fluores-
cence changes measured at increasing
average incident field strength were
essentially the same as for the un-
modulated 591 MHz exposures.
Conclusions
These data show a frequency-depen-
dent effect of microwave radiation on
energy metabolism in the rat brain.
Under exposure at 591 MHz, the NADH-
to-ATP pathway was inhibited, while at
200 MHz, this pathway, as well as the
CP-to-ATP pathway, was inhibited.
Apparently, at 2450 MHz no inhibition
occurs The threshold for these effects
in terms of field strength in the brain
tissue was 3-4 V/m at both frequencies
This corresponds to a threshold of less
than 005 W/kg in terms of specific
absorption rate. Because of the low
threshold, and because the results are
different from those for thermal controls,
tissue heating is probably not the
causative agent
Many enzymes in the system illust-
rated in Figure 1 (including CP-kmase)
contain a metal atom which is involved
with the enzyme's catalytic action The
metal-enzyme complex normally has a
high dipole moment. The results of this
study are consistent with the hypothesis
that a microwave induced dipole oscilla-
tion disrupts the rigid stereo-specificity
requirements in certain enzymes,
leading to inhibition of the system's
function. These data indicate inhibition
of at least two enzymes in the system.
%NADH
Increase
20
200 MHz 13.8 mW/cm'
cw
I
s^
o
5?
100
90-
80-
70-
60-
50-
C
o
O
;oo
90\
80
70
60
50
Begin Microwaves
51 76
Control
3.41 ±0.09 fjmo/es
9
J L
J
' I
Control
2.50 ±0.03 ymo/es
Mean ± SEM 9
Begin Microwaves
I L
H
591 MHz 13.8 mW/cm2,
cw
1oT~¥j 0°-09 vmoles
J 1 1 L
Control
2.50 ±0.03 /jmo/es
g
2450 MHz 13.8 mW/cm2,
Begin Microwaves
I I
i '
cw
' 8 8 8
Control
4.03 ±0.15 fjmo/es
J L
i i
Control
2.52 ± 0.04 /jmoles
9
0/2345 072345
Exposure Time in Minutes
0 1 2345
Figure 3. Rat brain NADH fluorescence, [CP] and [ATP] at 200. 591 and 2450 MHz, CW.
13.8 mW/cm2 surface power density vs time of exposure.
The results of this study are consistent
with a direct interaction of microwave
radiation with the energy production
system in rat brain, and are not
consistent with a mechanism of tissue
hyperthermia. For these reasons and
because of possible effects on humans,
it is necessary to understand the
mechanism by which the effects are
produced and the relevance to human
exposure.
-------
Aaron P. Sanders and William T. Joines are with Duke University, Durham, NC
27710.
John W. Allis is the EPA Project Officer (see below).
The complete report, entitled "Effects of 200, 591, and 2450 MHz Microwaves
on Cerebral Energy Metabolism," (Order No. PB 83-116 913; Cost: $10.00,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA22161
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
GOVERNMENT PRINTING OFFICE 1983 659O'7/O>
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
------- |