"Gibbs Report" on EMFs - chapter 6
This is Chapter 6 of the "Gibbs Report", the chapter that deals with effects on animals and plants.
|COMMUNITY CONCERNS (GENERAL)
II – ELECTRIC AND MAGNETIC FIELDS: NATIVE FLORA AND FAUNA, FARM ANIMALS AND PLANTS
|The Biological Effects on Animals
|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.
|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.
|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.
|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.
|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 400 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.
|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.
|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.
|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.
|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).
|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.
|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.
|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.
|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.
|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.
|Research in Japan(16) has found that exposure to a 7.7 kV/m field had no effect on the growth of wheat.
|A study of pasture grasses(17) has shown that growth of grasses beneath a 1200 kV prototype line was not inhibited.
|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.
|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.
|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.
|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.
|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.