Xref: helios.physics.utoronto.ca sci.med.physics:2459 sci.answers:1478 news.answers:27582
From: firstname.lastname@example.org (John Moulder)
Subject: Powerlines & Cancer FAQs 3/6: FAQ 2
Date: Mon, 15 Aug 1994 16:31:50 -0600
Organization: Medical College of Wisconsin
Expires: 12 Sep 1994 00:00:00 GMT
Reply-To: email@example.com (John Moulder)
Summary: Q&As on the connection between powerlines, electrical
occupations and cancer. Discussion of the biophysics of
interactions with EM sources, summaries of the laboratory
and human studies, information on standards, and references.
Keywords: powerlines, magnetic fields, cancer, EMF, non-ionizing
FAQs on Power-Frequency Fields and Cancer (Q&A, Part 2 of 3)
16) Do laboratory studies indicate that power-frequency fields can cause
Carcinogens, agents that cause cancer, can be either genotoxic or
epigenetic (in older terminology these were called initiators and
promoters). Genotoxic agents (genotoxins, initiators) can directly
damage the genetic material of cells. Genotoxins often affect many
types of cells, and may cause more than one kind of cancer. Genotoxins
generally do not have thresholds for their effect; in other words, as
the dose of the genotoxin is lowered the risk gets smaller, but it may
never goes away.
An epigenetic agent is something that increases the probability that a
genotoxin will damage the genetic material of cells or that a genotoxin
will cause cancer. Promoters are a particular kind of epigenetic agent
that increase the cancer risk in animals already exposed to a genotoxic
carcinogen. Epigenetic agents (including promoters) usually affect only
certain types of cells, and may cause only certain types of cancer.
Epigenetic agents generally have thresholds for their effect; in other
words, as the dose of an epigenetic agent is lowered a level is reached
at which there is no risk.
16A) Are power-frequency fields genotoxic?
There are many approaches to measuring genotoxicity. Whole-organism
exposure studies can be used to see whether exposure causes cancer or
causes mutations. Cellular studies can be done to detect DNA or
Very few whole-organism exposure studies have been published (see
Loscher & Mevissen [K6] for summaries of some of the unpublished work).
Bellossi et al [G13] exposed leukemia-prone mice for 5 generations and
found no effect on leukemia rates; however, since the study used 12 and
460 Hz pulsed fields at 60 G (6 mT), the relevance of this to power-
frequency fields is unclear. Otaka et al [G19] showed that power-
frequency magnetic fields did not cause mutations in fruit flies.
Rannug et al [G20] found that power-frequency magnetic fields did not
significantly increase the incidence of skin tumors or leukemia in mice.
Benz et al [G4] conducted a multi-generation mouse exposure study in
1983-1985 as part of the NY State Powerlines Project; this study
reported no increase in mutations rates, fertility, or sister chromatid
exchanges, but has never been published in the peer-reviewed literature.
Published laboratory studies have reported that power-frequency magnetic
fields do not cause DNA strand breaks [G5,G9,G17], chromosome
aberrations [G1,G7,G16], sister chromatid exchanges [G2,G7,G11,G21],
micronuclei formation [G11], or mutations [G3,G16,G18].
Many of the above laboratory studies also examined power-frequency
electrical fields and combination of power-frequency electrical and
magnetic fields [G1,G2,G5,G9,G11,G17]. As with the studies of magnetic
fields alone, the studies of electrical fields and combined fields
showed no evidence of genotoxicity.
There are two published reports of genotoxicity. Khalil & Qassem [G12]
reported that a 10.5 G (1.05 mT) pulsed field caused chromosome
aberrations. Nordenson et al [E4] reported that switchyard workers
exposed to spark discharges had an increased rate of chromosomal
defects, but Bauchinger et al [E2] found no such increase in chromosomal
defects in a similar study.
16B) Are power-frequency magnetic fields cancer promoters?
Epigenetic agents influence the development of cancer without directly
damaging the genetic material. Promoters are a specific class of such
epigenetic agents. In a promotion test, animals are exposed to a known
genotoxin at a dose that will cause cancer in some, but not all animals.
Another set of animals are exposed to the genotoxin, plus another agent.
If the agent plus the genotoxin results in more cancers than that seen
for the genotoxin alone, then that agent is a promoter. It has been
suggested that power-frequency EMFs could promote cancer [L2].
Published studies have reported that power-frequency magnetic fields do
not promote chemically-induced skin cancer [G10,G15,G20,G27,G29] or
chemically-induced liver cancers [G22,G25]. For chemically-induced
breast cancer, two published study have reported promotion [G14,G23],
but two others have not found promotion [G24,G28]. Interpretation of
the breast cancer promotion data is complicated by the fact that one of
the positive studies [G14] has been published only in preliminary form,
and also reports that a static magnetic field of less than the intensity
of the earth's magnetic fields can promote chemically induced-breast
16C) Do power-frequency magnetic fields enhance the effects of other
There are some types of studies that are relevant to the carcinogenic
potential of agents, but that are neither classic genotoxicity nor
promotion tests. The most common of these are cellular studies that test
whether an agent enhances the genotoxic activity of a known genotoxin;
these studies could be regarded as the cellular equivalent of a
Published studies have reported that power-frequency magnetic fields do
not enhance the mutagenic effects of known genotoxins [G3], and do not
inhibit the repair of DNA damage induced by ionizing [G8,G9] or UV [G16]
One study [G7] has reported that power-frequency fields may increase the
frequency of sister chromatid exchanges induced by known genotoxins.
17) Do laboratory studies indicate that power-frequency fields have any
biological effects that might be relevant to cancer?
There are biological effects other than genotoxicity and promotion that
might be related to cancer. In particular, agents that have dramatic
effects of cell growth, on the function of the immune system, or on
hormone balances might contribute to cancer without meeting the classic
definitions of genotoxicity or promotion.
17A) How do laboratory studies of the effects of power-frequency fields
on cell growth relate to the question of cancer risk?
There are substances (called mitogens) that cause non-growing normal
cells to start growing. Some mitogens appear to be carcinogens. There
have been numerous studies of the effects of power-frequency fields on
cell growth (proliferation) and tumor growth (progression). Most recent
studies of the effects of power-frequency magnetic fields on cancer
growth have shown no effect [G6,G10,H3], but one has reported that a 20
G (2 mT) enhanced tumor growth [G15]. Most recent studies of effects of
power-frequency magnetic fields on cell growth have also shown no effect
[G1,G11,G17,G21,H2,H8,H9], but some have shown increased [G7] or
decreased [G12] cell growth after exposure to intense (greater than 10
G, 1 mT) fields. With one controversial exception [H1] there have been
no reported effects on proliferation or progression for fields below
2000 mG (200 microT).
17B) How do laboratory studies of the effects of power-frequency fields
on immune function relate to the question of cancer risk?
In the early 1970¹s there was speculation that damage to the immune
system had a major role in preventing the development of cancer; this
theory was known as the ³immune surveillance hypothesis² [E3,E7].
Subsequent studies have shown that this hypothesis is not generally
valid [E3,E6,E7]. Suppression of the immune system in animals and
humans is associated with increased rates of only certain types of
cancer, particularly lymphomas [E6,E7]. Immune suppression has not been
associated with an excess incidence of leukemia, brain cancer or breast
cancer in either animals or humans [E3,E6,E7].
Some studies have shown that power-frequency fields can have effects on
cells of the immune system [K2], but no studies have shown the type or
magnitude of immune suppression that is associated with an increased
incidence of lymphomas.
17C) How do laboratory studies of the effects of power-frequency fields
on the pineal gland and melatonin relate to the question of cancer risk?
It has also been suggested that power-frequency EM fields might suppress
the production of the hormone melatonin, and that melatonin has "cancer-
preventive" activity [H7,H8,L3]. This is still highly speculative.
There have been a number of reports that electrical fields and static
magnetic fields can affect melatonin production [H7], but studies using
power-frequency magnetic fields have not shown reproducible effects.
Kato et al [H10] reported that exposure to circularly-polarized power-
frequency fields of 10-2500 mG (1-250 microT) caused a small decrease
melatonin production in rats, but that lower-intensity fields [H10] and
vertically- or horizontally-polarized power-frequency fields [H13] had
no effect. Loscher et al [G28] reported that 3-10 mG (0.3-1.0 microT)
power-frequency fields caused a small decrease in melatonin production
in mice, but that this decrease did not lead to promotion of chemically-
induced mammary tumors. Lee et al [H11] reported that exposure to a 500
kV transmission line field (40 mG, 4 microT, 6 kV/m) had no effect on
melatonin levels in sheep.
The second component of the powerline-melatonin-cancer hypothesis, that
a decrease in melatonin levels will lead to an increase in cancer, is
also unproven. While there is some evidence that melatonin has activity
against transplanted and chemically-induced breast tumors in rats, there
is little evidence that melatonin affects other types of cancer in
animals, or that it has any effect on breast or other types of cancer in
18) Do power-frequency fields show any reproducible biological effects
in laboratory studies?
While the laboratory evidence does not suggest a link between power-
frequency magnetic fields and cancer, numerous studies have reported
that these fields do have "bioeffects", particularly at high field
strength [H4,H6,K1,K2]. Power-frequency fields intense enough to induce
electrical currents in excess of those that occur naturally (above 5 G,
500 microT, see Question 8) have shown reproducible effects, including
effects on humans [K1].
18A) Do power-frequency fields of the intensity encountered in
occupational and residential settings show reproducible biological
If a reproducible biological effect is defined as one that has been
reported in the peer-reviewed literature by more than one laboratory,
without contradictory data appearing elsewhere; then there may be no
reproducible effects below about 2 G (200 microT). While there are
reports of effects for fields as low as about 5 mG (0.5 microT), few, if
any, of these reports have been validated.
The lack of validation of the laboratory studies is due to many factors.
First, many reports on the biological effects of power-frequency fields
have never been published in the peer-reviewed literature, and cannot be
scientifically evaluated. Second, no attempts have ever been made to
replicate many of the published reports of biological effects; and one
positive report, standing in isolation, is hard to evaluate. Third,
when attempts have been made to replicate some of the published studies,
these replications have often failed to show the effect [H5,H2,H12].
Lastly, the investigators in this field use a wide variety of biological
systems, endpoints, and exposure conditions, which makes studies
extremely hard to compare and evaluate.
18B) Are there known mechanisms by which power-frequency fields of the
intensity encountered in occupational and residential settings could
cause biological effects?
The known biological mechanisms through which intense (greater than 5 G,
500 microT) power-frequency magnetic fields cause biological effects are
not relevant to fields below about 500 mG (50 microT). The currents
induced in the body by fields of less than 500 mG (50 microT) are
similar to, but much weaker than, the currents that occur naturally
[F2]. The currents induced by a 50 mG (5 microT) are less than those
induced in the body by walking through the Earth¹s static magnetic field
[F2]. Thus, as emphatically pointed out by Adair [F2,F8], if weak
power-frequency magnetic fields do have biological effects, they are not
mediated by induced currents.
It has been suggested that power-frequency magnetic fields could cause
biological effects by acting directly on magnetic biological material
[F3], but analysis of the biophysics indicates that this would require
power-frequency fields of at least 50 mG (5 microT) [F3,F8].
Some of the biophysical constraints on possible mechanisms for
biological effects of weak power-frequency magnetic fields could be
overcome is there were resonance mechanisms that could make cells (or
organisms) uniquely sensitive to power-frequency fields [F1,F8].
Several such resonance mechanisms have been proposed, but none have
survived scientific scrutiny [F1,F8,H5,H2,H12]. There are also severe
incompatibilities between known biophysical characteristics of cells and
the conditions required for such resonances [F8].
Thus if power-frequency fields below 50 mG (5 microT) do actually have
biological effects, the mechanisms must be found, in Adair¹s [F2] words:
³outside the scope of conventional physics².
19) What about the "new epidemiological studies" showing a link between
power frequency fields and cancer?
New studies, particularly epidemiological studies, appear frequently.
When these studies show "positive" effects they generate considerable
media coverage. When they fail to show "positive" effects they are
generally ignored. This section will cover the more recent (1993 and
1994) studies in some detail.
19A) What about the new "Swedish" study showing a link between power
lines and cancer?
There are new residential exposure studies from Sweden [C13,C18],
Denmark [C16], Finland [C15] and the Netherlands [C17]. The published
studies are considerably more cautious in their interpretations of the
data than were the unpublished preliminary reports and the earlier press
The authors of the Scandinavian childhood cancer studies [C15,C16,C18]
have produced a collaborative meta-analysis of their data [B5]. The RRs
(Question 13) from this meta-analysis are shown below in comparison to
meta-analysis of the prior studies [B3,B4].
Childhood leukemia, Scand: 2.1 (1.1-4.1); prior: 1.3 (0.8-2.1)
Childhood lymphoma, Scand: 1.0 (0.3-3.7); prior: none
Childhood CNS cancer, Scand: 1.5 (0.7-3.2); prior: 2.4 (1.7-3.5)
All childhood cancer, Scand: 1.3 (0.9-2.1); prior: 1.6 (1.3-1.9)
- Fleychting & Ahlbom [C13,C18]. A case-control study of everyone who
lived within 300 m (1000 ft) of high-voltage powerlines between '60 and
'85. For children all types of tumors were analyzed; for adults only
leukemia and brain tumors were studied. Exposure was assessed by spot
measurements, calculated retrospective assessments, and distance from
power lines. No increased overall cancer incidence was found in either
children or adults, for any definition of exposure. An increased
incidence of leukemia (but not other cancers) was found in children for
calculated fields over 2 mG (0.2 microT) at the time of diagnosis, and
for residence within 50 m (150 ft) of the power line. The increased
incidence of leukemia is found only in one-family homes. The
retrospective fields calculations do not take into account sources other
the transmission lines. No significant elevation in cancer incidence
was found for measured fields.
- Verkasalo et al [C15]. A cohort study of cancer in children in
Finland living within 500 m (1500 ft) of high-voltage lines. Only
calculated retrospective fields were used to define exposure. The
calculated fields are based only on lines of 110 kV and above, and do
not take into account fields from other sources. Both average fields and
cumulative fields (microT - years) were used as exposure metrics. The
total incidence of childhood cancer was not significantly elevated for
average exposure above 0.20 microT (2 mG), or for cumulative exposure
above 0.50 microT-years (5 mG-years). A significant excess incidence of
brain cancer was found in boys; the excess was due entirely to one
exposed boy who developed three independent brain tumors. No
significant increase in incidence was found for brain tumors in girls or
for leukemia, lymphomas or other cancers in either sex.
- Olsen and Nielson [C16]. A case-control study based on all childhood
leukemia, brain tumors and lymphomas diagnosed in Denmark between '68
and '86. Exposure was assessed on the basis of calculated fields over
the period from conception to diagnosis. No overall increase in cancer
was found when 0.25 microT (2.5 mG) was used as the cut-off point to
define exposure (as specified in the study design). After the data were
analyzed, it was found that the overall incidence of childhood cancer
was significantly elevated if 0.40 microT (4 mG) was used as the cut-off
point. No significant increase was found for leukemia or brain cancer
incidence for any cut-off point. A significant increase in lymphoma was
found for the 0.10 microT cut-off point but not for higher cut-off
-Schreiber et al [C17]. A retrospective cohort study of people in an
urban area in the Netherlands. People were considered exposed if they
lived within 100 meters of transmission equipment (150 kV lines plus a
substation). Fields in the "exposed" group were 1-11 mG (0.1-1.1
microT), fields in the "unexposed" group were 0.2-1.5 mG (0.02-0.15
microT). The total cancer incidence in the ³exposed² group was
insignificantly less than that in the general Dutch population. No
cases of leukemia or brain cancer were seen in the "exposed" group.
19B) What about the new "Swedish" study showing a link between
occupational exposure to power-frequency fields and cancer?
There are new occupational studies from Sweden [D12], Denmark [D14],
Norway [D16], Canada [D15], and the United States [D11,D13]. The
published studies are considerably more cautious in their
interpretations of the data than were the unpublished preliminary
reports and the earlier press reports.
-Floderus et al [D14]. A case-control study of leukemia and brain
tumors in occupationally-exposed men who were 20-64 years of age in '80.
Exposure calculations were based on the job held longest during the 10-
year period prior to diagnosis. Many measurements were taken using a
person whose job was most similar to that of the person in the study.
About two-thirds of the subjects in the study could be assessed in this
manner. A significant elevation in incidence was found for leukemia,
but not for brain cancer.
- Guenel et al [D14]. A case-control study based on all cancer in
employed Danes between '70 and '87. Each occupation-industry
combination was coded on the basis of supposed 50-Hz magnetic field
exposure. No significant increases were seen for breast cancer,
malignant lymphomas or brain tumors. Leukemia incidence was
significantly elevated among men in the highest exposure category; women
in similar exposure categories showed no increase in leukemia.
- Tynes et al [D16]. Case-control study of workers on electrical (16.67
Hz) and non-electrical railroads in Norway. Analysis showed no
significant excess of leukemia or brain cancer, and no significant trend
for either magnetic or electrical fields. On the electrified railroads
fields averaged 19.7 mT (197 mG), and 0.8 kV/m. Cumulative exposures
were as high as 3000 mT-years (30 G-yrs) and 25 kV/m-yrs.
- Theriault et al [D15. Case-control study of electric utility workers
in France and Canada. Exposure to magnetic fields were estimated from
measurements of current exposure of workers performing similar tasks.
No association with magnetic fields was observed for overall cancer or
for any of the other 29 cancer types studied, including melanoma,
overall leukemia, brain cancer or male breast cancer. Workers with
cumulative exposure above 3.1 microT-years (31 mG-years) had a
significantly higher incidence of acute non-lymphocytic and acute
myeloid leukemia, there were no clear dose-response trends.
- Matanoski et al [D11]. Case-control study of telephone company
workers in New York, with exposure defined by job titles plus some
retrospective measurements. The incidence of leukemia was increased,
but not significantly so, in workers with higher exposures to magnetic
fields. The authors interpret their data as showing higher risk with
increasing exposure, but the trend does not appear to be statistically
- Sahl et al [D13]. Cohort plus nested case-control of electrical
utility workers in California. Dosimetry was done on selected workers.
Electricians had the highest exposures, with a time-weighted mean of 30
mG (3 microT). Neither cohort nor case-control analysis showed a
significant excess of total cancer, leukemia, brain cancer or lymphoma.
No significant dose-response trend was found for any cancers.
19C) What about the new studies showing a link between electrical
occupation and breast cancer?
There are some laboratory studies [G14,G23] that suggest that power-
frequency fields might promote chemically-induced breast cancer (see
Question 16B), and a biological mechanism has been proposed that could
explain such a connection (see Question 17C). However, there is
relatively little epidemiological support for such a connection.
McDowall et al [C4] found no excess female breast cancer (and no male
breast cancer at all) in adults living near transmission lines or
substations. Vena et al [C12] found no excess breast cancer in women
who used electric blankets. Tynes & Anderson [D4] and Demers [D5] both
reported a significantly elevated incidence of male breast cancer in
electrical workers. Matanoski et al [D6] and Loomis et al [D7] also
reported an excess incidence of male breast cancer in electrical
workers, but in neither case was the increase statistically significant.
More recently, studies by Theriault et al [D15], Rosenbaum et al [D17]
and Guenel et al [D14] have found no excess breast cancer in electrical
Recently, Loomis et al [D18,D19] reported a significantly elevated
incidence of female breast cancer in occupations with presumed exposure
to power-frequency fields. In occupations with "potential exposure" to
power-frequency fields there was no increased incidence of breast
cancer. The occupations that showed an excess incidence of breast
cancer were ³male-dominated² and the ones that did not were largely
³female-dominated². The authors note that breast cancer mortality is
known to be elevated among women in professional and technical jobs in
general. This elevation is related to the fact that women working in
male-dominated jobs tend to have reproductive histories (for example, no
pregnancies, delayed child-bearing, not breast-feeding) that increase
their risk for breast cancer.
20) What criteria do scientists use to evaluate all the confusing and
contradictory laboratory and epidemiological studies of power-frequency
magnetic fields and cancer?
There are certain widely accepted criteria that are weighed when
assessing epidemiological and laboratory studies of agents that may
pose human health risks. These are often called the "Hill criteria"
[E1]. Under the Hill criteria one examines the strength (Question 20A)
and consistency (Question 20B) of the association between exposure and
risk, the evidence for a dose-response relationship (Question 20C), the
laboratory evidence (Question 20D), and the biological plausibility
The Hill criteria must be applied with caution. First, when employing
the Hill criteria it is necessary to examine the entire published
literature; it is not acceptable to pick out only those reports that
support the existence of a health hazard. Second, it is necessary to
directly review the important source documents; it is not safe to base
judgments solely on academic or regulatory reviews. Third, satisfying
the individual criteria is not a yes-no matter; support for a criterion
can be strong, moderate, weak, or non-existent. Lastly,
the Hill criteria must be viewed as a whole; no individual criterion is
either necessary or sufficient for concluding that there is a causal
relationship between exposure to an agent and a disease.
Overall, application of the Hill criteria shows that the current
evidence for a connection between power-frequency fields and cancer is
weak, because of the weakness and inconsistencies in the epidemiological
studies, combined with the lack of a dose-response relationship in the
human studies, and the largely unsupportive laboratory studies. A
detailed evaluation of the criteria follows.
20A) Criterion One: How strong is the association between exposure to
power-frequency fields and the risk of cancer?
The first Hill criterion is the *strength of the association* between
exposure and risk. That is, is there a clear risk associated with
exposure? A strong association is one with a RR (Question 13) of 5 or
more. Tobacco smoking, for example, shows a RR for lung cancer 10-30
times that of non-smokers.
Most of the positive power-frequency studies have RRs of less than two.
The leukemia studies as a group have RRs of 1.1-1.3, while the brain
cancer studies as a group have RRs of about 1.3-1.5. This is only a
20B) Criterion Two: How consistent are the studies of associations
between exposure to power-frequency fields and the risk of cancer?
The second Hill criterion is the *consistency* of the studies. That is,
do most studies show about the same risk for the same disease? Using
the same smoking example, essentially all studies of smoking and cancer
showed an increased risk for lung and head-and-neck cancers.
Many power-frequency studies show statistically significant risks for
some types of cancers and some types of exposures, but many do not.
Even the positive studies are inconsistent with each other. For
example, while a recent Swedish study [C18] shows an increased incidence
of childhood leukemia for one measure of exposure, it contradicts prior
studies that showed an increase in brain cancer [B3,B4], and a parallel
Danish study [D14] shows an increase in childhood lymphomas, but not in
Many of the studies are internally inconsistent. For example, where a
recent Swedish study [C18] shows an increase for childhood leukemia, it
shows no overall increase in childhood cancer. Since leukemia account
for about one-third of all childhood cancer, this implies that the rates
of other types of cancer were decreased; an examination of the data
indicates that this is true. In summary, few studies show the same
positive result, so that the consistency is weak.
20C) Criterion Three: Is there a dose-response relationship between
exposure to power-frequency fields and the risk of cancer?
The third Hill criterion is the evidence for a *dose-response
relationship*. That is, does risk increase when the exposure increases?
Again, the more a person smokes, the higher the risk of lung cancer.
No published power-frequency exposure study has shown a dose-response
relationship between measured fields and cancer rates, or between
distances from transmission lines and cancer rates. The lack of a
relationship between exposure and increased cancer incidence is a major
reason why most scientists are skeptical about the significance of the
Not all relationships between dose and risk can be described by simple
linear no-threshold dose-response curves where risk is strictly
proportional to risk. There are known examples of dose-response
relationships that have thresholds, that are non-linear, or that have
plateaus. For example, the incidence of cancer induced by ionizing
radiation in rodents rises with dose, but only up to a certain point;
beyond that point the incidence plateaus or even drops. Without an
understanding of the mechanisms connecting dose and effect it is
impossible to predict the shape, let alone the magnitude of the dose-
20D) Criterion Four: Is there laboratory evidence for an association
between exposure to power-frequency fields and the risk of cancer?
The fourth Hill criterion is whether there is *laboratory evidence*
suggesting that there is a risk associated with such exposure?
Epidemiological associations are greatly strengthened when there is
laboratory evidence for a risk. When the US Surgeon General first
stated that smoking caused lung cancer, the laboratory evidence was
ambiguous. It was known that cigarette smoke and tobacco contained
carcinogens, but no one had been able to make lab animals get cancer by
smoking (mostly because it is hard to convince animals to smoke).
Currently the laboratory evidence linking cancer and smoking is much
Power-frequency fields show little evidence of the type of effects on
cells, tissues or animals that point towards their being a cause of
cancer, or to their contributing to cancer (Question 16).
20E) Criterion Five: Are there plausible biological mechanisms that
suggest an association between exposure to power-frequency fields and
the risk of cancer?
The fifth Hill criterion is whether there are *plausible biological
mechanisms* that suggest that there should be a risk? When it is
understood how something causes disease, it is much easier to interpret
ambiguous epidemiology. For smoking, while the direct laboratory
evidence connecting smoking and cancer was weak at the time of the
Surgeon Generals report, the association was highly plausible because
there were known cancer-causing agents in tobacco smoke.
From what is known of power-frequency fields and their effects on
biological systems there is no reason to even suspect that they pose a
risk to people at the exposure levels associated with the generation and
distribution of electricity (see Questions 16,17,18).
Copyright (C) by John Moulder