Usenet 1994 January/usenetsourcesnewsgroupsinfomagicjanuary1994.iso/answers/powerlines-cancer-FAQ/part1

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From: [e-mail] (John Moulder)
Newsgroups: sci.med.physics,sci.answers,news.answers
Subject: Powerlines and Cancer FAQs (1 of 2)
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Date: 28 Dec 1993 23:43:24 GMT
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Summary: Q&As on the connection between powerlines, electrical occupations
  and cancer.  Includes discussion of the biophysics of interactions with
  electromagnetic sources, summaries of the laboratory and human studies,
  information on standards, and references.
Keywords: powerlines, magnetic fields, cancer, EMF, non-ionizing radiation
Xref: bloom-beacon.mit.edu sci.med.physics:956 sci.answers:766 news.answers:13402

Archive-name:  powerlines-cancer-FAQ/part1
Last-modified: 1993/12/28
Version: 2.2

FAQs on Power-Frequency Fields and Cancer (part 1 of 2)

Notice:  This FAQ sheet may be redistributed as long at remains correctly
attributed.  If it is edited prior to redistribution, please add a note to
that effect.

Revision notes:
v1.9 (19-Dec-93): Sections added on whether powerlines radiate, how close
one has to live to a powerline to be considered exposed, reducing fields,
and on the impact of powerlines on property values.  The sections on
laboratory studies and on arguments pro and con were broken up into
sections. The sections on confounders, and on application of the Hill
criteria were expanded and broken up into sections.  The sections on new
European epidemiological studies and on standards were updated.
v2.2 (28-Dec-94):  Schreiber study and Ahlbom et al meta-analysis added to
Q18.  First version approved for and posted to *.answers newsgroups.
Converted to two parts.

1) Why is there a concern about powerlines and cancer?

Most of the concern about power lines and cancer stems from epidemiological
studies of people living near powerlines, and epidemiological studies of
people working in ╥electrical occupations╙.  Some of these epidemiological
studies appear to show a relationship between exposure to power-frequency
magnetic fields and the incidence of cancer.  Laboratory studies have shown
little evidence of a link between power-frequency fields and cancer.

2) What is the difference between the electromagnetic [EM] energy
associated with power lines and other forms of EM energy such as microwaves
or x-rays?

X-rays, ultraviolet (UV) light, visible light, infrared light, microwaves
(MW), radiowaves (RF), and electromagnetic fields from electrical power
systems are all parts of the EM spectrum.   The parts of the EM spectrum
are characterized by their frequency or wavelength.  The frequency and
wavelength are related, and as the frequency rises the wavelength gets
shorter.  The frequency is the rate at which the EM field changes direction
and is usually given in Hertz (Hz), where one Hz is one cycle per second.

Power-frequency fields in the US vary 60 times per second, so they are 60
Hz fields, and have a wavelength of 3000 miles (5000 km).  Power in most of
the rest of the world is at 50 Hz.  The power-frequency fields are often
referred to as extremely low frequencies or ELF.  Broadcast AM radio has a
frequency of around one million Hz and a wavelength of around 1000 ft (300
m). Microwave ovens have a frequency of about 2.5 billion Hz, and a
wavelength of about 5 inches (12 cm).  X-rays and UV light have frequencies
of millions of billions of Hz, and wavelengths of less than a thousandth of
an inch (10 nm or less).

3)  What differences are there in the biological effects of these different
portions of the EM spectrum?

The interaction of biological material with an EM source depends on the
frequency of the source.  We usually talk about the EM spectrum as though
it produced waves of energy.  This is not strictly correct, because
sometimes EM energy acts like particles rather than waves; this is
particularly true at high frequencies.  This double nature of the EM
spectrum is referred to as "wave-particle duality".  The particle nature of
EM energy is important because it is the energy per particle (or photons,
as these particles are called) that determines what biological effects EM
energy will have.

At the very high frequencies characteristic of UV light and X-rays, EM
particles (photons) have sufficient energy to break chemical bonds.  This
breaking of bonds is termed ionization, and this portion of the EM spectrum
is termed ionizing radiation.  At lower frequencies, such as those
characteristic of visible light, RR and MW, the photons do not carry enough
energy to break chemical bonds; but they do carry enough energy to cause
molecules to vibrate, causing heating (thermal effects).  This portion of
the EM spectrum is termed the thermal, non-ionizing portion.  At
frequencies below those used in commercial broadcast radio (such as the
50/60 Hz frequencies generated in the production and distribution of
electricity), the photons have insufficient energy to cause heating, and
this portion of the EM spectrum is termed the non-thermal, non-ionizing
portion.

4)  What is difference between EM radiation and EM fields?

When dealing with fields from an electromagnetic source it is customary to
distinguish between near fields (which do not transmit energy to infinity
from the source) and radiation (which does).  In general, EM sources
produce both radiant energy (radiation) and non-radiant energy (fields).
Radiated energy exists apart from its source, travels away from the source,
and continues to exist even if the source is turned off.  Non-radiant
energy is not projected away into space, and it ceases to exist when the
energy source is turned off.  When a person or object is more than several
wavelengths from an EM source, a condition called far-field, the radiation
component of the EM source dominates.  When a person or object is less than
one wavelength from an EM source, a condition called near-field, the field
effect dominates, and the electrical and magnetic components are unrelated.


For ionizing frequencies where the wavelengths are less than a thousandth
of an inch (less than 10 nm), human exposure is entirely in the far-field,
and only the radiation from the EM source is relevant to health effects.
For MW and RF, where the wavelengths are in inches to a few thousand feet
(a few cm to a km), human exposure can be in both the near- and the
far-field, so that both field and radiation effects can be relevant.  For
power-frequency fields, where the wavelength is thousands of miles
(thousands of km), human exposure is always in the near-field, and only the
field component is relevant to possible health effects.

5)  Do power lines produce electromagnetic radiation?

The fields associated with transmission lines are purely near-field.  While
the lines theoretically might radiate some energy the efficiency of this is
so low that this effect can for all practical purposes be ignored.  To be
an effective radiation source, and antenna must have a length comparable to
its wavelength.  Power-frequency sources are clearly too short compared to
their wavelength (3000 miles, 5000 km) to be effective radiation sources.

This is not to say that there is no loss of power during transmission.
There are many sources of loss in transmission lines that have nothing to
do with "radiation" (in the sense as it is used in electromagnetic theory).
 Loss of energy is a result of resistive heating, not "radiation".  This is
in sharp contrast to radiofrequency antennas, which "lose" energy to space
by radiation.  Likewise, there are many ways of transmitting energy from
point A to point B that do not involve radiation.  Electrical circuits do
it all the time.

The only ╥practical╙ exception to the statement that power-frequency fields
do not radiate is the use of extremely-low-frequency antennas to broadcast
to submerged submarines.  The US Navy runs a power-frequency antenna in
Northern Wisconsin and the Upper Peninsula of Michigan.  To overcome the
inherent inefficiency of the frequency, the antenna is several hundred
kilometers in length.

6)  How do ionizing EM sources cause biological effects?

Ionizing EM radiation carries sufficient energy per photon to break
chemical bonds.  In particular, ionizing radiation is capable of breaking
bonds in the genetic material of the cell, the DNA.  Severe damage to DNA
can kill cells, resulting in tissue damage or death.  Lesser damage to DNA
can result in permanent changes in the cells which may lead to cancer.  If
these changes occur in reproductive cells, they can lead to inherited
changes, a phenomena called mutation.  All of the known hazards from
exposure to the ionizing portion of the EM spectrum are the result of the
breaking of chemical bonds in DNA.  For frequencies below that of UV light,
DNA damage does not occur because the photons do not have enough energy to
break chemical bonds.   Well-accepted safety standards exist to prevent
significant damage to the genetic material of persons exposed to ionizing
EM radiation.

7)  How do the thermal non-ionizing EM sources cause biological effects?

Visible light, MW, and RF can cause molecules to vibrate, causing heating.
This molecular heating can kill cells.  If enough cells are killed, burns
and other forms of long-term, and possibly permanent tissue damage can
occur.  Cells which are not killed by heating gradually return to normal
after the heating ceases; permanent non-lethal cellular damage is not known
to occur.  All of the known hazards from exposure to the thermal
non-ionizing portion of the EM spectrum are the result of heating.  For
frequencies below about the middle of the AM broadcast spectrum, this
heating does not occur because the photons do not have enough energy to
cause molecular vibrations.  Well-accepted safety standards exist to
prevent significant thermal damage to persons exposed to MW and RFs [45]
and also for persons exposed to lasers and UV light.

The molecular vibration caused by MW is how and why a MW oven works -
exposure of the food to the microwaves causes water molecules to vibrate
and get hot.  MW and RF penetrate and heat best when the size of the object
is close to the wavelength.  For the 2450 MHz (2.45 billion Hz) used in
microwave ovens the wavelength is 5 inches (12 cm), a good match for most
of what we cook.

8)  How do the power-frequency EM fields cause biological effects?

The electrical and magnetic fields associated with power-frequency fields
cannot break bonds or cause molecular heating because the energy per photon
is too low. Thus the known mechanisms through which ionizing radiation, MWs
and RFs effect biological material have no relevance for power-frequency
fields.

The electrical fields associated with the power-frequency fields exist
whenever voltage is present, and regardless of whether current is flowing.
These electrical fields have very little ability to penetrate buildings or
even skin.  The magnetic fields associated with power-frequency fields
exist only when current is flowing.  These magnetic fields are difficult to
shield, and easily penetrate buildings and people.   Because
power-frequency electrical fields do not penetrate, any biological effects
from routine exposure to power-frequency fields must be due to the magnetic
component of the field.

Exposure of people to power-frequency magnetic fields results in the
induction of electrical currents in the body.  These currents are similar
to naturally-occurring currents.  It requires a power-frequency magnetic
field in excess of 5 Gauss (500 microT, see Q9 for typical exposures) to
induce electrical currents of a magnitude similar to those that occur
naturally in the body.   Electrical currents that are above those that
occur naturally in the body can cause noticeable effects, including direct
nerve stimulation.  Well-accepted safety standards exist to protect persons
from exposure to power-frequency fields that would induce such currents
(Q25 for safety standards).

9)  What sort of power-frequency magnetic fields are common in residences
and workplaces?

In the US magnetic fields are commonly measured in Gauss (G) or milliGauss
(mG), where 1,000 mG = 1G.  In the rest of the world, they are measured in
Tesla (T), were 10,000 G equals 1 T (1 G = 100 microT; 1 microT = 10 mG).
Power-frequency fields are measured with a calibrated gauss meter.
Measurements must be done in multiple locations over a substantial period
of time because there are large variations in fields over space and time.

Within the right-of-way (ROW) of a high voltage transmission line, fields
can approach 100 mG (0.1 G, 10 microT).  At the edge of a high-voltage
transmission ROW, the field will be 1-10 mG (0.1-1.0 microT).  Ten meters
from a 12 kV (1200 volt) distribution line fields will be 2-10 mG (0.2-1.0
microT).  Actual fields depend on voltage, design and current.

Fields within residences vary from over 1000 mG (100 microT) a few inches
(cm) from certain appliances to less than 0.2 mG (0.02 microT) in the
center of some rooms.  Appliances that have the highest fields are those
with high currents (e.g., toasters, electric blankets) or high-speed
electric motors (e.g., vacuum cleaners, electric clocks, blenders, power
tools).  Appliance fields decrease very rapidly with distance. See
Theriault [24] for further details.

Occupational exposures in excess of 100 mG (10 microT) have been reported
(e.g., in arc welders and electrical cable splicers).  In ╥electrical╙
occupations mean exposures range from 5 to 40 mG (0.5 to 4 microT).  See
Theriault [24] for further details.

10)  Can power-frequency fields in homes and workplaces be reduced?

There are engineering techniques that can be used to decrease the magnetic
fields produced by power lines, substations, transformers and even
household wiring and appliances.  Once the fields are produced, however,
shielding is very difficult.  Small area can be shielded by the use of Mu
metal, a nickel-iron-copper alloy with ╥high magnetic permeability and low
hysteresis losses╙.  Mu metal shields are very expensive, and limited to
small volumes.

11)  What is known about the relationship between powerline corridors and
cancer rates?

Some studies have shown that children (but not adults) living near certain
types of powerlines (high current distribution lines and transmission
lines) have higher than average rates of leukemia, lymphomas and brain
cancers [1-3, 38, 45].  The correlations are not strong, and none of the
studies have shown dose-response relationships.  When power-frequency
fields are actually measured, the correlation vanishes.  Several other
studies have shown no correlations between residence near power lines and
cancer risk [4-6, 37].

12)  How big is the ╥cancer risk╙ associated with living next to a
powerline?

The excess cancer found in epidemiological studies is usually quantified in
a number called the relative risk (RR).  This is the risk of an ╥exposed╙
person getting cancer divided by the risk of an ╥unexposed╙ person getting
cancer.  Since no one is unexposed to power-frequency fields, the
comparison is actually ╥high exposure╙ versus ╥low exposure╙.  A RR of 1.0
means no effect, a RR of less the 1.0 means a decreased risk in exposed
groups, and a RR of greater than one means an increased risk in exposed
groups.  Relative risks are generally given with 95% confidence intervals.
These 95% confidence intervals are almost never adjusted for multiple
comparisons even when multiple types of cancer and multiple indices of
exposure are studied (see Olsen et al, [38], Fig. 2 for an example of a
multiple comparison adjustment).

An overview of the epidemiology requires that studies be combined using a
technique known as ╥meta-analysis╙.  Meta-analysis is not easy to do, since
the epidemiological studies of residential exposure use a wide variety of
methods for assessing ╥exposure╙.  Meta-analysis also gets out-of-date
rapidly in this field.  The following RRs (called summary RRs in
meta-analysis) for the residential exposure studies are adapted from
Hutchison [7] and Doll et al [39] by inclusion of the new European studies
(Q18).  The confidence intervals should be viewed as measures of the
diversity of the data, rather than as strict tests of the statistical
significance of the data.
   childhood leukemia: 1.5 (0.8 - 3.0)  8 studies
   childhood brain cancer:  1.9 (0.9 - 3.0)  6 studies
   childhood lymphoma: 2.5 (0.3 - 40) 2 studies
   all childhood cancer:  1.5 (0.9 - 2.5)  5 studies
   adult leukemia:  1.1 (0.8-1.6)  3 studies
   adult brain cancer:  0.7 (0.4 - 1.3)  1 study
   all adult cancer:  1.1 (0.9-1.3)  3 studies

As a base-line for comparison, the age-adjusted cancer incidence rate for
adults in the United States is 3 per 1,000 per year for all cancer (that
is, 0.3% of the population gets cancer in a given year),and 1 per 10,000
per year for leukemia [26].

13)  How close do you have to be to a power line to be considered exposed
to power-frequency magnetic fields?

The epidemiological studies that show a relationship between cancer and
powerlines do not provide any consistent guidance as to what distance or
exposure level is associated with increased risk.  The studies have used a
wide variety of techniques to measure exposure, and they differ in the type
of lines that are studied.  The US studies have been based predominantly on
neighborhood distribution lines [1-3], whereas the European studies have
been based strictly on high-voltage transmission lines [4-6, 37, 38, 44,
46].

Field measurements:  Several studies have measured power-frequency fields
in the residences [2, 3, 45].  Both one-time (spot), peak, and 24-hour
average measurement have been made; none of the studies using measured
fields have shown a relationship between exposure and cancer risk.

Proximity to lines:  Several studies have used the distance from the power
line corridor to the residence as a measure of power-frequency fields [4-6,
44, 46].  When something we can measure (distance to the line), is used as
an index of what we really want to measure (the magnetic field), it is
called a surrogate (or proxy) measure.  With one exception, studies that
have used distance from power lines as a surrogate measure of exposure have
shown no significant relationship between proximity to lines and risk of
cancer.  The exception is a childhood leukemia study [46] that showed a RR
of 2.9 (1.0-7.3) for residence within 50 m of high-voltage transmission
lines.  This same study showed no elevation of child leukemia risks at
51-100 m, and no increase in childhood brain cancer, overall childhood
cancer, or any types of adult cancer at any distance.

Wire Codes:  The original US powerline studies used a combination of the
type of wiring (distribution vs transmission, number and thickness of
wires) and the distance from the wiring to the residence as a surrogate
measure of exposure [1-3].  This technique is known as ╥wirecoding╙.  Three
studies using wirecodes [1-3] have shown a relationship between childhood
cancer and ╥high-current configuration╙ wirecodes.  Two of these studies
[2, 3] failed to show a significant relationship between exposure and
cancer when actual measurements were made.  Wirecodes correlate with
measured fields, although the correlation is not very good [47].  The
wirecode scheme was developed for the U.S., and does not appear to be
readily applicable elsewhere.

Calculated Historic Fields:  The recent European studies have used utility
records and maps to calculate what fields would have been produced by
powerlines in the past [37, 38, 44, 46].  Typically, the calculated field
at the time of diagnosis or the average field for a number of years prior
to diagnosis are used as a measure of exposure (Q17).  These calculated
exposures explicitly exclude contributions from other sources such as
distribution lines, household wiring, or appliances.  When the field
calculations are done for contemporary measured fields they correlate
reasonably well [46].  Of course, there is no way to check the accuracy of
the calculated historic fields.

14)  What is known about the relationship between ╥electrical occupations╙
and cancer rates?

Several studies have shown that people who work in electrical occupations
have higher than average leukemia, lymphoma, and brain cancer rates [8-10,
36].  Most of the cautions listed for the residential studies apply here
also: many negative studies, weak correlations, no dose-response
relationships.  Additionally, these studies are mostly based on job titles,
not on measured exposures.

Meta-analysis of the occupational studies is even more difficult than the
residential studies.  First, a variety of epidemiological techniques are
used, and studies using different techniques should not really be combined.
 Second, a wide range of definitions of ╥electrical occupations╙ are used,
and very few studies actually measured exposure.  The following RRs (Q12)
for the occupational exposure studies are adapted from Hutchison [7] and
Davis et al [40].  Again, the confidence intervals should be viewed as
measures diversity rather than as tests of the statistical significance.
leukemia: 1.15 (1.0-1.3)  28 studies
brain: 1.15 (1.0-1.4)  19 studies
lymphoma: 1.2 (0.9-1.5)  6 studies
all cancer:  1.0 (0.9-1.1)  8 studies

The above relative risks do not take into account the recent European
studies (Q18).  Adding these new studies raises the summary RR for leukemia
to about 1.2, and lowers the summary RRs for brain cancer and lymphomas to
essentially one.  Another new study of cancer in the electrical power
industry [30] shows no significant elevation of leukemia, brain cancer or
lymphoma risks.

15)  What do laboratory studies tell us about power-frequency fields and
cancer?

Carcinogens, agents that cause cancer, are generally of two types:
genotoxins and promoters.  Genotoxic agents (often called initiators)
directly damage the genetic material of cells.  Genotoxins usually effect
all types of cells, and may cause many different types 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 never goes away.  A promoter (often called an epigenetic agent) is
something that increases the cancer risk in animals already exposed to a
genotoxic carcinogen.  Promoters usually effect only certain types of
cells, and may cause only certain types of cancer.  Promoters generally
have thresholds for their effect; in other words, as the dose of the
promoter is lowered a level is reached in which there is no risk.

Power-frequency fields show none of the classic signs of being genotoxins -
they do not cause DNA damage or chromosome breaks, and they are not
mutagenic [11-15, 31].  No studies have shown that animals exposed to
power-frequency fields have increased cancer rates.

There are agents (for example, promoters) that influence the development of
cancer without directly damaging the genetic material.  It has been
suggested that power-frequency EMFs could promote cancer [17, 18].   Most
promotion studies of power-frequency fields have been negative [14, 19-21];
but recently there was a positive report of promotion of breast cancer in
rats [32].

16)  How do laboratory studies of the effects of power-frequency fields on
cell growth, immune function, and melatonin relate to the question of
cancer risk?

There are other biological effects that might be related to cancer.  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). Studies of effects on
proliferation and progression have had very mixed results: 75% show no
effect on growth, while the rest are about equally mixed between studies
showing increased growth and studies showing decreased growth [11, 12, 15,
20-22, 33].  With one possible exception [33] there have been no reported
effects on proliferation or progression for fields below 2000 mG (200
microT).

Suppression of the immune system in animals and humans is associated with
increased rates of certain types of cancer, particularly lymphomas [34,
35].  Immune suppression has not been associated with excess leukemia and
brain cancer.  Some studies have shown that power frequency fields can have
effects on cells of the immune system [41), but no studies have shown the
type or magnitude of immunesuppression that is associated with increased
cancer risks.

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 [42, 43].  This is highly speculative.  There
have been some reports that EM fields effect melatonin production, but
studies using power-frequency magnetic fields have not shown reproducible
effects. In addition, while there is evidence that melatonin has
╥cancer-preventive╙ activity against breast cancer in rats, there is no
evidence that melatonin effects other types of cancer, or that it has any
effect on breast cancer in humans.

17)  Do power-frequency fields show any effects at all 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
[16, 17, 41].  Power-frequency fields intense enough to induce electrical
currents in excess of those that occur naturally (above 5 G, 500 microT,
see Q8) have shown reproducible effects, including effects on humans [16].
Below about 2 G (200 microT) there are few published (and replicated)
reports of bioeffects, although there are unreplicated reports of effects
for fields as low as about 200 mG (20 microT). Even among the scientists
who believe that there may be a connection between power-frequency fields
and cancer, there is no consensus as to mechanisms which would connect
these ╥bioeffects╙ with cancer causation [16, 18].

18)  What about the new ╥Swedish╙ study showing a link between power lines
and cancer?

There are new residential and occupational studies from Sweden [46],
Denmark [36, 38], Finland [37] and the Netherlands [44].  Some of the
Swedish studies are still available only as translations of the unpublished
preliminary reports.  The published studies are considerably more cautious
in there interpretations of the data than were the unpublished preliminary
reports and the earlier press reports.

The authors of the Scandnavian childhood cancer studies [37, 38, 46] have
produced a collaborative meta-analysis of their data [51].   The RRs from
this meta-analysis are shown below in comparison to meta-analysis of the
prior studies [7, 39].
Childhood leukemia, Scandanavian:  2.1 (1.1-4.1)
Childhood leukemia, prior studies:  1.3 (0.8-2.1)
Childhood lymphoma, Scandanavian:  1.0 (0.3-3.7)
Childhood lymphoma, prior studies:  none
Childhood CNS cancer, Scandanavian:  1.5 (0.7-3.2)
Childhood CNS cancer, prior studies:  2.4 (1.7-3.5)
All childhood cancer, Scandanavian:  1.3 (0.9-2.1)
All childhood cancer, prior studies:  1.6 (1.3-1.9)

- Fleychting & Ahlbom [Magnetic fields and cancer in people residing near
Swedish high voltage powerlines].   A case-control study of everyone who
lived within 300 meters of high-voltage powerlines between 1960 and 1985.
For children all types of tumors were analyzed, for adults only leukemia
and brain tumors were studied.  The data on childhood cancer has been
published [46].  ╥Exposure╙ was assessed by spot measurements, calculated
retrospective assessments, and distance from powerlines.  No increased
overall cancer risk was found for either children or adults.  An increased
risk for 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 of the powerline.  The increased relative risk of
leukemia is found only in one-family homes; there is no excess risk in
apartments.  The retrospective fields calculations do not take into account
sources other the transmission lines.  No significantly elevated cancer
risks were found for measured fields.

- Verkasalo et al [37].  Study design similar to Fleychting & Ahlbom
(above).  Cohort study of cancer in children in Finland living within 500 m
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 such as
distribution lines, household wiring or appliances. Both average fields and
cumulative fields (microT - years) were used as exposure metrics.  For all
cancers the RR was 1.5 (0.7 - 2.7) for average exposure above 0.20 microT
(2 mG), and 1.4 (0.8 - 2.3) for cumulative exposure above 0.50
microT-years.  A significant excess risk of brain cancer way found in boys,
the excess was due entirely to one exposed boy who developed three
independent brain tumors.  No significantly increased risks were found for
brain tumors in girls or for leukemia, lymphomas or ╥other╙ tumors in
either sex.

- Olsen and Nielson [38].  Case-control study based on all childhood
leukemia, brain tumors and lymphomas diagnosed in Denmark between 1968 and
1986.  ╥Exposure╙ was assessed on the basis of calculated fields over the
period from conception to diagnosis.  No overall increase in cancer risk
was found when 0.25 microT (2.5 mG) was used as the cut-point to define
exposure (as specified in the study design).  After the data were analyzed,
it was found that the risk for all childhood cancer was significantly
elevated if 0.40 microT (4 mG) was used as the cut-point.  For the 0.40
microT cut-point the RR for all cancer (corrected for multiple comparisons)
was 5.6 (1.2 - 30).  No significant increased risk was found for leukemia
or brain cancer for any cut-point.  A significant increase in lymphoma risk
was found for the 0.10 microT cut-point but not for higher cut-points.

- Guenel et al [36].  Case-control study based on all cancer in actively
employed Danes between 1970 and 1987 who were 20-64 years old in 1970.
Each occupation-industry combination was coded on the basis of supposed
50-Hz magnetic field exposure.  No significant increases in risk were seen
for breast cancer, malignant lymphomas or brain tumors.  Leukemia incidence
was elevated among men in the highest ╥exposure╙ category; women in similar
exposure categories showed no excess risk.  For men in the highest
╥exposure╙ category the RR for leukemia was 1.6 (1.2 - 2.2).

-Floderus et al [Occupational exposure to EM fields in relation to leukemia
and brain tumors].  Case-control study of leukemia and brain tumors of men,
20-64 years of age in 1980.  ╥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 significantly elevated risk was found
for leukemia, but not for brain cancer.

-Schreiber et al [44].  Retrospective cohort study of people in an urban
area in the Netherlands.  People were considered exposed in they lived
within 100 m 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).  For all cancers the
RR (╥exposed╙ group vs the general Dutch population) was 0.85 (0.63-1.14).
No cases of leukemia or brain cancer were seen in the ╥exposed╙ group.

End:  powerlines-cancer-FAQ/part1