| 6.
|
COMMUNITY CONCERNS (GENERAL)
II – ELECTRIC AND MAGNETIC FIELDS: NATIVE FLORA
AND FUNA.
FARM ANIMALS AND PLANTS
|
| 6.1 |
The Biological Effects on
Animals
|
| |
6.1.1
|
As has been seen in Chapter 5 above,
experiments to discover whether electromagnetic fields have
any biological effects have been conducted with live animals
and on animal tissues and have shown that the fields can cause
biological changes in animals as well as in humans. However,
it has not been established that the effects are harmful.
|
| 6.2 |
Farm Animals
|
| |
6.2.1 |
A number of experiments have been conducted in
the field with a view to discovering whether exposure to the
electric fields or the magnetic fields created by transmission
lines affects the health, behaviour or reproductive performance
of livestock.
|
| |
6.2.2
|
During the period 1977-1979 Amstutz and Miller
made a study of eleven livestock farms traversed by a 765 kV
transmission line, to determine if the fields created by the
line had any detectable effect on farm animals. Various types
of livestock were kept on the farms, viz, beef cattle, dairy
cattle, sheep, hogs and horses. The report(1) found that neither
the health, the behaviour nor the performance of any of these
livestock was affected by the electric or magnetic fields created
by the line.
|
| |
6.2.3 |
A study conducted by Williams and Bieler (2)
over six years of 55 dairy farms located near 765 kV lines in
Ohio fond that the lines had no apparent effect on milk production
or on the health of cattle.
|
| |
6.2.4 |
The effect of electromagnetic fields on the fertility
of cattle has been extensively studied in Sweden. A study by
Algers and Hultgren(3) of cows exposed for 120 days to 4 kV
lines with an average electric field of 4 kV and an average
magnetic field of 20 mG found that the exposure did not influence
the number of inseminations per pregnancy, the overall conception
rate or foetal viability. This confirmed the result of an earlier
study(4) which showed, contrary to the concern expressed by
some farmers who attributed detrimental effects on animal reproduction
to the presence of the lines, that the exposure did not cause
decreased fertility.
|
| |
6.2.5 |
An experiment in Iowa by Mahmoud and Zimmerman(5)
in which pigs were grown in pens housed under a 345 kV line
showed that the fields from the line had no negative effects
on the performance, behaviour or carcass quality of the pigs.
|
| |
6.2.6 |
These and other studies(6) Strongly support the
view that the electric fields and the magnetic fields created
by transmission lines do not affect the health or reproductive
capacity of livestock.
|
| 6.3 |
Native Fauua
|
| |
6.3.1 |
The clearing of the easement area under transmission
lines may have some effect on native fauna and the lines themselves
may present a hazard to birds. These matters are discussed in
Chapter 7.
|
| |
6.3.2 |
The results of the studies of farm animals would
suggest that the fields created by the lines do not have any
harmful effect on the health or behaviour of native fauna. Such
research as has been done appears to support this view(7). Further,
it would appear probable that most native fauna would be less
likely than farm animals to be exposed to the fields created
by transmission lines. In the United States at least some birds
often use transmission line towers for perching and nesting.
A study of hawks nesting on 500 kV and 230 kV lines showed that
they produced the same number of young hawks nesting in trees
and cliffs(8).
|
| 6.4 |
Bees
|
| |
6.4.1 |
It is clear that the electric fields created
by transmission lines do affect the health and mortality of
honey bees inside wooden hives(9). The most likely explanation
for this is that the bees receive small, but frequent, shocks
from the currents induced in the hives. If a hive is placed
near transmission lines, this adverse effect can be mitigated
by screening the hive. No-one who made a sub-mission to the
Inquiry suggested that he or she wished to keep hives on or
near to a transmission line easement and the adverse effect
of the lines on bees in hives does not appear to create any
practical problems.
|
| 6.5 |
Plants
|
| |
6.5.1 |
Studies of plants growing near transmission lines
have shown that some crops suffer leaf damage caused by corona;
when the electric field becomes sufficiently strong, the field
produces heat which dries the tips of the leaves. This occurs
when the leaves have sharp, pointed tips rather than when the
leaves are rounded. The same thing occurs when trees are allowed
to grow too close to a transmission line. Leaf damage of this
kind reduces the growth and height of trees but does not affect
the growth of crops or other low-growing vegetation(10). In
New South Wales, the steps taken to prevent danger from arising
on transmission line easements involves a restriction on the
height of trees growing on transmission line easements.
|
| |
6.5.2 |
A study by Dr Marino and others in 1983(11) reported
that a 5 kV/m field seemed to reduce the rate of germination
of sunflower seeds, but the effect was observed in only four
out of eleven replicates of the study.
|
| |
6.5.3 |
Research in Tennessee(12) suggested that corn
grown beneath a 500 kV line showed lower yields than corn which
was shielded from the field, but other crops (cotton, soy beans
and clover) and trees showed no effects. The researches concluded
that data for the corn study were insufficient to reach definite
conclusions and the further investigation was warranted. A brief
report published by Parsch and Norman on a study of crop growth
near a 500 kV transmission line in Arkansas(13) showed no differences
in yields of rice and soy beans between crops growing under
a line and crops growing away from the line, but showed a reduced
cotton yield under the line. The authors could not determine
whether the effect was related to electric or magnetic fields
or to inefficient spraying with agricultural chemicals of crops
near the line.
|
| |
6.5.4 |
A number of field studies in Indiana(14) of crops
growing near 765 kV lines, and long-term research in Oregon(15)
on crops growing near a 1200 kV prototype line, showed that
exposure to the lines had no effect on the growth or germination
of a number of varieties of plants, except for a reduction in
the growth of trees affected by corona.
|
| |
6.5.5 |
Research in Japan(16) has found that exposure
to a 7.7 kV/m field had no effect on the growth of wheat.
|
| |
6.5.6 |
A study of pasture grasses(17) has shown that
growth of grasses beneath a 1200 kV prototype line was not inhibited.
|
| |
6.5.7 |
The studies lead to the clear conclusion that,
from a practical point of view, transmission lines have no effect
on crops, although they would have an effect on trees allowed
to grow too close to them. There would seem to be no reason
to reach any different conclusion in relation to native flora.
|
| 6.6 |
Conclusion
|
| |
6.6.1 |
Bees in hives under or near to transmission lines
are adversely affected by shocks created by currents induced
by the lines, but the effect can be mitigated by shielding.
|
|
6.6.2 |
The magnetic fields created by power lines do
not affect the health or reproductive capacity of farm animals
or present a danger to native fauna.
|
| |
6.6.3 |
The growth of trees which are close to a transmission
line may be reduced by the effect of corona. In any case, the
height of trees on a transmission line easement will be restricted
when this is necessary in the interest of safety. Any loss which
this causes to the landowner should be included in the compensation
paid for the acquisition of the easement. This matter is further
discussed in Chapter 16.
|
| |
6.6.4 |
From a practical point of view, the electric
fields created by transmission lines have no adverse effect
on crops, pasture grasses or native flora, other than trees,
growing under or near to the lines. |
