Archive-name: powerlines-cancer-FAQ/part1
Last-modified: 1994/3/25
Version: 2.4

FAQs on Power-Frequency Fields and Cancer (part 1 of 4)

Current version available by anonymous FTP from "rtfm.mit.edu" Directory:
/pub/usenet-by-group/news.answers/powerlines-cancer-FAQ
Files: part1, part2, part3, etc. . . . 

Revision notes:
v2.4 (23-Mar-94): Expanded to four parts.  Added table of contents. 
Expanded and annotated bibliography.  Modified and expanded non-ionizing
bioeffects sections.  Expanded discussion of field reduction techniques. 
Added sections on measurement techniques.  Expanded section on laboratory
studies and broke into multiple parts.  Added short section and references
on reproductive toxicity studies.

Table of Contents:
Part 1
1) Why is there a concern about powerlines 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?
3) Why do different types of EM sources produce different biological
effects?
4) What is difference between EM radiation and EM fields?
5) Do power lines produce EM radiation?
6) How do ionizing EM sources cause biological effects?
7) How do RF, MW, visible light, and IR light sources cause biological
effects?
8) How do the power-frequency EM fields cause biological effects?
9) Do non-ionizing EM sources cause non-thermal as well as thermal effects?
10) What sort of power-frequency magnetic fields are common in residences
and workplaces?
11) Can power-frequency fields in homes and workplaces be reduced?
12) What is known about the relationship between powerline corridors and
cancer rates?
13) How big is the "cancer risk" associated with living next to a
powerline?
14) How close do you have to be to a power line to be considered exposed to
power-frequency magnetic fields?
15) What is known about the relationship between "electrical occupations"
and cancer rates?

Part 2
16) What do laboratory studies tell us about power-frequency fields and
cancer?
    16A) Are power-frequency fields genotoxic? 
    16B) Are power-frequency magnetic fields cancer promoters? 
    16C) Do power-frequency magnetic fields enhance the effects of other
    genotoxic agents?
17) 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?
18) Do power-frequency fields show any effects at all in laboratory
studies?
19) What about the new "Swedish" study showing a link between power lines
and 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?
    20A) Criterion One: How strong is the association between exposure
    to power-frequency fields and the risk of cancer?
    20B) Criterion Two: How consistent are the studies of associations
    between exposure to power-frequency fields and the risk of cancer?
    20C) Criterion Three: Is there a dose-response relationship between
    exposure to power-frequency fields and the risk of cancer?
    20D) Criterion Four: Is there laboratory evidence for an association
    between exposure to power-frequency fields and the risk of cancer?
    20E) Criterion Five: Are there plausible biological mechanisms that
    suggest an association between exposure to power-frequency fields
    and the risk of cancer?
21) If exposure to power-frequency magnetic fields does not explain the
residential and occupations studies which show increased cancer incidence,
what other factors could?
    21A) Could problems with dose assessment affect the validity of the
    epidemiological studies of power lines and cancer?
    21B) Are there other cancer risk factors that could be causing a
    false association between exposure to power-frequency fields and
    cancer?
    21C) Could the epidemiological studies of power lines and cancer be
    biased by the methods used to select control groups?
    21D) Could analysis of the epidemiological studies of power lines
    and cancer be skewed by publication bias?
22) What is the strongest evidence for a connection between power-frequency
fields and cancer?
23) What is the strongest evidence against a connection between
power-frequency fields and cancer?
24) What studies are needed to resolve the cancer-EMF issue?
25) Is there any evidence that power-frequency fields could cause health
effects other than cancer.

Part 3
26) What are some good overview articles?
27) Are there exposure guidelines for power-frequency fields?
28) What effect do powerlines have on property values?
29) What equipment do you need to measure power-frequency magnetic fields?
30) How are power-frequency magnetic fields measured?

Annotated Bibliography
A) Recent Reviews of the Biological and Health Effects of Power-Frequency
Fields
B) Reviews of the Epidemiology of Exposure to Power-Frequency Fields
C) Epidemiology of Residential Exposure to Power-Frequency Fields
D) Epidemiology of Occupational Exposure to Power-Frequency Fields
E) Human Studies Related to Power-Frequency Exposure and Cancer
F) Biophysics and Dosimetry of Power-Frequency Fields

Part 4
G) Laboratory Studies of Power-Frequency Fields and Cancer
H) Laboratory Studies Indirectly Related to Power-Frequency Fields and
Cancer
J) Laboratory Studies of Power-Frequency Fields and Reproductive Toxicity
K) Reviews of Laboratory Studies of Power-Frequency Fields
L) Miscellaneous Studies
M) Regulations and Standards for Ionizing and Non-ionizing EM Sources.

-----

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 (IR),
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) Why do different types of EM sources produce different biological
effects?

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. The well-known biological effects of X-rays
are associated with the ionization of molecules.  At lower frequencies,
such as those characteristic of visible light, RF, and MW, the photons do
not carry enough energy to break chemical bonds.  This portion of the EM
spectrum is termed the non-ionizing portion.  At RF and MW frequencies the
energy of a photon is very much (by a factor of thousands or more) below
those needed to disrupt chemical bonds. For this reason, there is no
analogy between the biological effects of ionizing and nonionizing EM
energy.

Non-ionizing EM sources can still produce biological effects.  One
mechanism is by inducing electrical currents in tissues, which cause
heating by moving ions and water molecules through the viscous medium in
which they exist.  The efficiency with which an EM source can induce
electrical currents, and thus produce heating, depends on the frequency of
the source, and the size and orientation of the object being heated.  At
frequencies below that used for broadcast AM radio, EM sources couple
poorly with the bodies of humans and animals, and thus are very inefficient
at inducing electrical currents and causing heating. 

Thus in terms of potential biological effects the EM spectrum can be
divided into the three portions:
1) The ionizing portion, where direct chemical damage can occur (X-rays,
hard UV).
2) The portion of the non-ionizing spectrum in which the wavelength is
smaller than that of the body, where heating can occur (visible light, IR,
MW and RF).
3) The portion of the non-ionizing spectrum in which the wavelength is much
larger than that of the body, where heating seldom occurs (power
frequencies).

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

When dealing with fields from an EM source it is customary to distinguish
between 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 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 EM 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 an 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 EM theory).  Loss of
energy is a result of resistive heating, not "radiation".  This is in sharp
contrast to RF 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 ELF 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 [M3].

7) How do RF, MW, visible light, and IR light sources cause biological
effects?

A principal mechanism by which RF, MW, visible light, and IR light sources
cause biological effects is by heating (thermal effects).  This 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.  At the
whole-animal level, tissue injury and other thermally-induced effects can
be expected when the amount of power absorbed by the animal is similar to
or exceeds the amount of heat generated by normal body processes.  Some of
these thermal effects are very subtle, and do not represent biological
hazards.
  
It is possible to produce thermal effects even with very low levels of
absorbed power.  One example is the "microwave hearing" phenomenon; these
are auditory sensations that a person experiences when his head is exposed
to pulsed microwaves such as those produced by radar.  The microwave
hearing effects is a thermal effect, but it can be observed at very low
average power levels.

Since thermal effects are produced by heat, not by the electric or magnetic
fields directly, they can be produced by fields at many different
frequencies.  Well-accepted safety standards exist to prevent significant
thermal damage to persons exposed to MW and RFs [M2] and also for persons
exposed to lasers, IR and UV light [M4].

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

The electrical and magnetic fields associated with power-frequency fields
cannot break bonds because the energy per photon is too low.  The magnetic
field intensities to which people are exposed in residential settings and
in the vast majority of occupational settings cannot cause heating because
the induced electrical currents are 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.  If these currents are
sufficiently intense, they can cause heating, nerve excitation and other
effects [F4,K1].  At power frequencies, the body is poorly coupled to
external fields, and the induced currents are usually too small to produce
obvious effects.  Shocks, and other obvious effects usually require that
the body actually touch a conductive objects, allowing current to pass
directly into the body.

It requires a power-frequency magnetic field in excess of 5 Gauss (500
microT, see Question 10 for typical exposures) to induce electrical
currents of a magnitude similar to those that occur naturally in the body. 
Well-accepted safety standards exist to protect persons from exposure to
power-frequency fields that would induce such currents (Question 27).

9) Do non-ionizing EM sources cause non-thermal as well as thermal effects?

One distinction that is often made in discussions of the biological effects
of non-ionizing EM sources is between "nonthermal" and "thermal" effects. 
This refers to the mechanism for the effect, non-thermal effects being a
result of a direct interaction between the field and the organism, and
thermal effects being a result of heating.  Microwave burns are an obvious
thermal effect, and electrical shocks are an obvious nonthermal effect. 
There are many reported biological effects (some of which have not been
reproduced) whose mechanisms are totally unknown, and one should be very
careful about drawing the distinction between "thermal" and "nonthermal"
mechanisms for such effects.

10) 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
(Questions 29 & 30). 

Within the right-of-way (ROW) of a high-voltage (115-765 kV,
115,000-765,000 volt) 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 (12,000 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 [F3] for further details. 

Occupational exposures in excess of 1000 mG (100 microT) have been reported
(e.g., in arc welders and electrical cable splicers).  In "electrical"
occupations typical mean exposures range from 5 to 40 mG (0.5 to 4 microT).
 See Theriault [F3] for further details.

11) 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.

Increasing the height of towers, and thus the height of the conductors
above the ground, will reduce the field intensity at the edge of the ROW. 
The size, spacing and configuration of conductors can be modified to reduce
magnetic fields, but this approach is limited by electrical safety
considerations.  Placing multiple circuits on the same set of towers can
also lower the field intensity at the edge of the ROW, although it
generally requires higher towers.  Replacing lower voltage lines with
higher voltage ones can also lower the magnetic fields.

Burying transmission lines greatly reduces their magnetic fields.  The
reduction occurs because the underground lines use rubber, plastic or oil
for insulation rather than air.  This allows the conductors to be placed
much closer together and allows greater phase cancellation.  However,
placing high voltage lines underground is very expensive, adding costs that
are measured in hundreds of thousands of US dollars per mile.

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

Some studies have shown that children living near certain types of
powerlines (high current distribution lines and transmission lines) have
higher than average rates of leukemia [C1,C6,C10,C17], brain cancers
[C1,C6] and/or overall cancer [C5,C15].  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
[C6,C10,C17].  Several other studies have shown no correlations between
residence near power lines and risks of childhood leukemia
[C3,C5,C7,C8,C9,C14,C15], childhood brain cancer [C5,C8,C14,C15,C17], or
overall childhood cancer [C14,C17].  With one exception [C2] all studies of
correlations between adult cancer and residence near power lines have been
negative [C4,C8,C9,C11,C12,C16].  

13) 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, [C15], 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 [B4] and Doll et al [B5] by inclusion of the new European studies
(Question 19).  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 [E6].

14) 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 cancer incidence.  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, whereas the European
studies have been based strictly on high-voltage transmission lines and/or
transformers.

Field measurements: Several studies have measured power-frequency fields in
the residences [C6,C7,C10,C12,C17].  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.

Proximity to lines: Several studies have used the distance from the power
line corridor to the residence as a measure of power-frequency fields
[C4,C5,C8,C9,C8,C9,C11,C12,C17].  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 two
exception [C5,C17], studies that have used distance from power lines as a
surrogate measure of exposure have shown no significant relationship
between proximity to lines and the incidence of cancer.  The major
exception is a childhood leukemia study [C17] that showed a significant
increase in leukemia incidence for residence within 50 m (150 ft) of
high-voltage transmission lines.  This same study [C12,C17] showed no
elevation of child leukemia risks at 51-100 m (150-300 ft), 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 [C1,C2,C3,C6,C7,C10].  This technique is known as
"wirecoding".  Three studies using wirecodes [C1,C6,C10] have shown a
relationship between childhood cancer and "high-current configuration"
wirecodes.  Two of these studies [C6,C10] failed to show a significant
relationship between exposure and cancer when actual measurements were
made.  Wirecodes are stable over time [F5] and correlate with measured
fields, although the correlation is not very good [F1].  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 power
lines in the past [C12,C14,C15,C17].  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 (Question 19).  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 [C17].  Of course, there is no way to check the accuracy of
the calculated historic fields. 

15) 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 cancer rates.  The original studies [D1,D2 were
only of leukemia.  Some later studies also implicated brain, lymphoma
and/or breast cancer [B1,B2,B3,B4,B5].  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
(Question 13) for the occupational exposure studies are adapted from
Hutchison [B4] and Davis et al [A2].  Again, the confidence intervals
should be viewed as measures of 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:   1.20 (0.9-1.5)   6 studies
all cancer: 1.00 (0.9-1.1)   8 studies

The above relative risks do not take into account more recent studies.  Two
recent European studies [D7,D9] have found excess leukemia in electrical
occupations, but no excess of other types of cancer (Question 19 for
details).  

Two other new occupational exposure studies [D4,D5] shows small but
statistically significant increases in leukemia, but others [D3,D6,D8] do
not.  None of the new studies of electrical occupations show significant
elevation of any types of cancer other than leukemia (specifically brain
cancer or lymphoma)[D5,D7,D8,D9].  Adding these seven new studies raises
the summary RR for leukemia slightly, and lowers the summary RRs for brain
cancer and lymphomas to essentially one.  

End: powerlines-cancer-FAQ/part1


-------------------------------------------------------------------------------
Area # 2120  news.answers           03-25-94 13:03      Message # 8707
From    : John Moulder
To      : ALL                                           
Subj    : Powerlines and Cancer FA

@FROM   :JMOULDER@ITS.MCW.EDU                                         
@SUBJECT:Powerlines and Cancer FAQs (2 of 4)                          
@PACKOUT:03-29-94                                                     
Message-ID: <jmoulder-250394120211@admin-one.radbio.mcw.edu>
Newsgroups: sci.med.physics,sci.answers,news.answers
Organization: Medical College of Wisconsin

Archive-name: powerlines-cancer-FAQ/part2
Last-modified: 1994/3/25
Version: 2.4

FAQs on Power-Frequency Fields and Cancer (part 2 of 4)

16) 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. 

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
chromosomal damage.  

Very few whole-organism exposure studies have been done.  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 [G18] showed that power-frequency magnetic fields did not case
mutations in fruit flies.  Rannug et al [G19] found that power-frequency
magnetic fields did not increase the incidence of skin tumors or leukemia
in mice.  RD Benz et 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 or sister chromatid exchanges, but has never
been published.

A number of published laboratory studies have reported that power-frequency
magnetic fields do not cause DNA strand breaks [G4,G16] chromosome
aberrations [G1,G6,G15], sister chromatid exchanges [G2,G6,G11,G20],
micronuclei formation [G9,G11] or mutations [G3,G15,G17].

Many of the above laboratory studies also examined power-frequency
electrical fields and combination of power-frequency electrical and
magnetic fields [G1,G2,G4,G8,G11,G16].  As with the studies of magnetic
fields alone, the studies of electrical fields and combined fields showed
no evidence of genotoxicity.

There are two positive 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] for no such increase in chromosomal defects in a
similar study.

16B) Are power-frequency magnetic fields cancer promoters? 

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 [L1].  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 that seen for the genotoxin alone, then
that agent is a promoter.

Published studies have shown that power-frequency magnetic fields do not
promote chemically-induced skin cancer [G10,G14,G19] or chemically-induced
liver cancers [G21,G24].  For chemically-induced breast cancer, one study
has shown promotion [G22] and one has not [G23].

16C) Do power-frequency magnetic fields enhance the effects of other
genotoxic agents?
 
There are some other types of studies that are relevant to the carcinogenic
potential of agents, but that are not strictly either genotoxicity or
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 are the cellular equivalent of a promotion study.

Published studies have reported that power-frequency magnetic fields do not
enhance the mutagenic effects of known genotoxins [G3,G9], and do not
inhibit the repair of DNA damage induced by ionizing [G7,G8] or UV [G15]
radiation.

One study [G6] has reported that power-frequency fields can increase the
frequency of sister chromatid exchanges induced by known genotoxins.

17) 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). Most recent studies of the
effects of power-frequency magnetic fields on cancer progression have shown
no effect [G5,G10,H3], but one has reported enhanced progression [G14]. 
Most recent studies of effects of power-frequency magnetic fields on cell
growth have also shown no effect [G1,G11,G16,G20,H2,H7,H8], but some have
shown increased [G6] or decreased [G12] cell growth.  With one possible
exception [H1] 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 [E6,E7].
 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 [K2], but no studies have shown the
type or magnitude of immunosuppression 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 [H6,H7,L2].  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 [H9,H10].  In addition, while there is some evidence
that melatonin has "cancer-preventive" activity against transplanted breast
tumors in rats, there is no evidence that melatonin effects other types of
cancer, or that it has any effect on breast or other cancers in humans.  

18) 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
[H4,H5,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].  

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 [K1,L1].

19) What about the new "Swedish" study showing a link between power lines
and cancer?

There are new residential and occupational studies from Sweden
[C12,C17,D7], Denmark [D9,C15], Finland [C14] and the Netherlands [C16]. 
The published studies are considerably more cautious in their
interpretations of the data than were the unpublished preliminary reports
and the earlier press reports.

The authors of the Scandinavian childhood cancer studies [C14,C15,C17] have
produced a collaborative meta-analysis of their data [B6].  The RRs
(Question 13) from this meta-analysis are shown below in comparison to
meta-analysis of the prior studies [B4,B5]. 
Childhood leukemia, Scandinavian:    2.1 (1.1-4.1)
Childhood leukemia, prior studies:   1.3 (0.8-2.1)
Childhood lymphoma, Scandinavian:    1.0 (0.3-3.7)
Childhood lymphoma, prior studies:   none
Childhood CNS cancer, Scandinavian:  1.5 (0.7-3.2)
Childhood CNS cancer, prior studies: 2.4 (1.7-3.5)
All childhood cancer, Scandinavian:  1.3 (0.9-2.1)
All childhood cancer, prior studies: 1.6 (1.3-1.9)

- Fleychting & Ahlbom [C12,C17].  This is a case-control study of everyone
who lived within 300 meters 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; there is no increased incidence in apartments.  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 [C14].  This is a 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.  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 [C15].  This is 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-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-point.  No
significant increase was found for leukemia or brain cancer incidence for
any cut-point.  A significant increase in lymphoma was found for the 0.10
microT cut-point but not for higher cut-points.

- Guenel et al [D9].  This is a case-control study based on all cancer in
actively employed Danes between '70 and '87 who were 20-64 years old in
'70.  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.  

-Floderus et al [D9].  This is 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.

-Schreiber et al [C16].  This is a 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).  The
total cancer incidence in the exposed group was insignificantly less than
that in the general Dutch population.  No cases of leukemia or brain cancer
were seen in the "exposed" group.  

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
such groups of epidemiological and laboratory studies.  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 (Question 20E).  These criteria are viewed as a whole; no
individual criterion is either necessary or sufficient for concluding that
there is a causal relationship between an exposure and a disease.

Overall, application of the Hill criteria shows that the current evidence
for a connection between power-frequency fields and cancer is quite 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 negative laboratory studies.

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 weak
association.

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
new Swedish study [C17] shows an increased incidence of childhood leukemia
for one measure of exposure, it contradicts prior studies that showed an
increase in brain cancer [B4,B5], and a parallel Danish study [D9] shows an
increase in childhood lymphomas, but not in leukemia.  Many of the studies
are internally inconsistent.  For example, where a new Swedish study [C17]
shows an increase for childhood leukemia, it shows no overall increase in
childhood cancer, implying that the rates of other types of cancer were
decreased.  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 epidemiology.

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-response
relationship.

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 stronger.

Power-frequency fields show little evidence of the type 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.

21) If exposure to power-frequency magnetic fields does not explain the
residential and occupations studies which show increased cancer incidence,
what other factors could?

There are basically four factors that can result in false associations in
epidemiological studies: inadequate dose assessment (Question 21A),
confounders (Question 21B), inappropriate controls (Question 21C), and
publication bias (Question 21D).

21A) Could problems with dose assessment affect the validity of the
epidemiological studies of power lines and cancer?

If power-frequency fields are associated with cancer, we do not know what
aspect of the field is involved.  At a minimum, risk could be related to
the peak field, the average field, or the rate of change of the field.  If
we do not know who is really exposed, and who is not, we will usually (but
not always) underestimate the true risk [C13].

21B) Are there other cancer risk factors that could be causing a false
association between exposure to power-frequency fields and cancer?

Associations between things are not always evidence for causality.  Power
lines (or electrical occupations) might be associated with a cancer risk
other than magnetic fields.  If such an associated cancer risk were
identified it would be called a "confounder" of the epidemiological studies
of power lines and cancer.  An essential part of epidemiological studies is
to identify and eliminate possible confounders.  Many possible confounders
of the powerline studies have been suggested, including PCBs, herbicides,
traffic density, and socioeconomic class.
 
- PCBs: Many transformers contain polychlorinated biphenyls (PCBs) and it
has been suggested that PCB contamination of the power-line corridors might
be the cause of the excess cancer.  This is unlikely.  First, PCB leakage
is rare.  Second, PCB exposure has been linked to lymphomas, not leukemia
or brain cancer.
 
- Herbicides: It has been suggested that herbicides sprayed on the
powerline corridors might be a cause of cancer.  This is an unlikely
explanation, since herbicide spraying would not effect distribution systems
in urban areas (where 3 of 5 positive childhood cancer studies have been
done).
 
- Traffic density: Transmission lines frequently run along major roads, and
the "high current configurations" associated with excess childhood leukemia
in the US studies [C1,C6,C10] are associated with major roads.  It has been
suggested that power lines might be a surrogate for exposure to
cancer-causing substances in traffic exhaust.  This may be a real
confounder, since traffic density has been shown to correlate with
childhood leukemia incidence [E5].  Note that this would explain only the
residential connection, not the occupational connection.

- Socioeconomic class: Socioeconomic class may be an issue in both the
residential and occupational studies, as socioeconomic class is clearly
associated with cancer risk, and "exposed" and "unexposed" groups in many
studies are of different socioeconomic classes [C13].  This is of
particular concern in the US residential exposure studies that are based on
"wirecoding", since the type of wirecodes that are correlated with
childhood cancer are found predominantly in older, poorer neighborhoods,
and/or in neighborhoods with a high proportion of rental housing [C18].

21C) Could the epidemiological studies of power lines and cancer be biased
by the methods used to select control groups?

An inherent problem with many epidemiological studies is the difficulty of
obtaining a "control" group that is identical to the "exposed" group for
all characteristics related to the disease except the exposure.  This is
very difficult to do for diseases such as leukemia and brain cancer where
the risk factors are poorly known.  An additional complication is that
often people must consent to be included in the control arm of a study, and
participation in studies is known to depend on factors (such as
socioeconomic class, race and occupation) that are linked to differences in
cancer rates.  See Jones et al [C18] for an example of how selection bias
could effect a powerline study.

21D) Could analysis of the epidemiological studies of power lines and
cancer be skewed by publication bias?

It is a known that positive studies in many fields are more likely to be
published than negative studies (see Dickersin et al [E3] for examples from
cancer clinical trials).  This can severely bias meta-analysis studies such
as those discussed in Questions 13 and 15.  Such publication bias will
increase apparent risks.  This is a bigger potential problem for the
occupational studies than the residential ones.  It is also a clear problem
for laboratory studies -- it is much easier to publish studies that report
effects than studies that report no effects (such is human nature!).

Several specific examples of publication bias are known in the studies of
electrical occupations and cancer (see Doll et al [B5], page 94).  In their
review Coleman and Beral [B2] report the results of a Canadian study that
found a RR of 2.4 for leukemia in electrical workers.  The British NRPB
review [B5] found that further followup of the Canadian workers showed a
deficiency of leukemia (a RR of 0.6), but that this followup study has
never been published.  This is an anecdotal report, but publication bias,
by its very nature, is usually anecdotal.

22) What is the strongest evidence for a connection between power-frequency
fields and cancer?

The best evidence for a connection between cancer and power-frequency
fields is probably:
a) The four epidemiological studies that show a correlation between
childhood cancer and proximity to high-current wiring [C1,C6,C10,M2], plus
the meta-analysis of the Scandinavian studies [B6].
b) The epidemiological studies that show a significant correlation between
work in electrical occupations and cancer, particularly leukemia and brain
cancer [B1,B2,D7,D9]. 
c) The lab studies that show that power-frequency fields do produce
bioeffects.  The most interesting of the lab studies are probably the ones
showing increased transcription of oncogenes at fields of 1-5 G (100-500
microT) [H4,H5,L1].
d) The one laboratory study that provides evidence that power-frequency
magnetic fields can promote chemically-induced breast cancer [G22].

23) What is the strongest evidence against a connection between
power-frequency fields and cancer?

The best evidence that there is not a connection between cancer and
power-frequency fields is probably:
a) Application of the Hill criteria (Question 20) to the entire body of
epidemiological and laboratory studies.
b) The fact that all studies of genotoxicity, and all but one study of
promotion have been negative (Question 16). 
c) Adairs [F4] biophysical analysis that indicates that "any biological
effects of weak (less than 40 mG, 4 microT) ELF fields on the cellular
level must be found outside of the scope of conventional physics"
d) Jacksons [E8] and Olsens [C15] epidemiological analysis that shows
that childhood and adult leukemia rates have been stable over a period of
time when per capita power consumption has risen dramatically.  

24) What studies are needed to resolve the cancer-EMF issue?

In the epidemiological area, more of the same types of studies are unlikely
to resolve anything.  Studies showing a dose-response relationship between
measured fields and cancer incidence rates would clearly affect thinking,
as would studies identifying confounders in the residential and
occupational studies.  

In the laboratory area, more genotoxicity and promotion studies may not be
very useful.  Exceptions might be in the area of cell transformation, and
promotion of chemically-induced breast cancer. Long-term rodent exposure
studies (the standard test for carcinogenicity) would have a major impact
if they were positive, but if they were negative it would not change very
many minds.  Further studies of some of the known bioeffects would be
useful, but only if they identified mechanisms or if they established the
conditions under which the effects occur (e.g., thresholds, dose-response
relationships, frequency-dependence, optimal wave-forms).

25) Is there any evidence that power-frequency fields could cause health
effects other than cancer.

While this FAQ sheet, and most public concern, has centered around cancer,
there has also been suggestions that there might be a connection between
non-ionizing EM exposure and birth defects.  This concern has focused as
much on video display terminals (VDTs) as on power lines.  Little
epidemiological or laboratory support for a connection between non-ionizing
EM exposure and birth defects has been found. [J1,J2,J4,J5,J6].  Cox et al
[J3] and Chernoff et al [K5] have recently reviewed this field.

End:  powerlines-cancer-FAQ/part2


-------------------------------------------------------------------------------
Area # 2120  news.answers           03-25-94 13:05      Message # 8709
From    : John Moulder
To      : ALL                                           
Subj    : Powerlines and Cancer FA

@FROM   :JMOULDER@ITS.MCW.EDU                                         
@SUBJECT:Powerlines and Cancer FAQs (3 of 4)                          
@PACKOUT:03-29-94                                                     
Message-ID: <jmoulder-250394120431@admin-one.radbio.mcw.edu>
Newsgroups: sci.med.physics,sci.answers,news.answers
Organization: Medical College of Wisconsin

Archive-name: powerlines-cancer-FAQ/part3
Last-modified: 1994/3/25
Version: 2.4

FAQs on Power-Frequency Fields and Cancer (part 3 of 4)

26) What are some good overview articles?

There really no up-to-date reviews of power-frequency fields and human
health.  The reviews by Davis et al [A2], Theriault [F3] and Doll et al
[B5] are good, but were published before many of the important
epidemiological and laboratory studies were available.

27) Are there exposure guidelines for power-frequency fields?

Yes, a number of governmental and professional organizations have developed
exposure guidelines.  These guidelines are based on keeping the body
currents induced by power-frequency EM fields to a level below the
naturally-occurring fields (Question 8).  The most generally relevant are:

- National Radiation Protection Board (UK) [M5]:
  50 Hz electrical field: 12 kV/m 
  60 Hz electrical field: 10 kV/m 
  50 Hz magnetic field: 1.6 mT (16 G)
  60 Hz magnetic field: 1.33 mT (13.3 G)

- American Conference of Governmental Industrial Hygienists [M6]:
  At 60 Hz: 1 mT (10 G); 0.1 mT (1 G) for pacemaker wearers

- International Commission on Non-Ionizing Radiation Protection [M7]
  Magnetic field  
     24 hr general public: 0.1 mT = 1 G      
     Short-term general public: 1 mT = 10 G      
     Occupational continuous: 0.5 mT = 5 G     
     Occupational short-term: 5 mT = 50 G      
  EElectrical field   
     24 hr general public: 5 kV/m     
     Short-term general public: 10 kV/m     
     Occupational continuous: 10 kV/m     
     Occupational short-term: 30 kV/m      

28) What effect do powerlines have on property values?

There is very little hard data on this issue.  There is anecdotal evidence
and on-going litigation (Wall Street Journal, Dec 9, 1993).  There have
been "comparable property" studies, but any studies done prior to about
1991 (when London et al [C10] was published) would be irrelevant.  One
comparable value study has been published recently [L3], and another has
been presented at a meeting [L4]. Neither study shows hard evidence for an
impact of power lines on property values.  However, both studies indicate
that many owners think that there will be an impact, particularly if
concerns about health effects become widespread.

It appears possible that the presence of obvious transmission lines or
substations will adversely affect property values if there has been recent
local publicity about health concerns of property value concerns.  It would
appear less unlikely that the presence of "high current configuration"
distribution lines of the type correlated with childhood cancer in the US
studies [C1,C6,C10] would affect property values, since few people would
recognize their existence. If buyers start requesting magnetic field
measurements, no telling what will happen, particularly since measurements
are difficult to do (Questions 29 & 30), and even more difficult to
interpret (Question 14).

29) What equipment do you need to measure power-frequency magnetic fields?

Power-frequency fields are measured with a calibrated gauss meter.  The
meters used by environmental health professionals are too expensive for
"home" use.

A unit suitable for home use should meet the following criteria:
- A reasonable degree of accuracy and precision, plus/minus 20% seems
reasonable for home use.
- True RMS detection, otherwise readings might be exaggerated if the
waveform is non-sinusoidal. 
- Tailored frequency response, because if the unit is too broadband, higher
frequency fields from VDTs, TVs, etc. may confound the measurements.
- Correct response to overload; if the unit is subjected to a very strong
field, it should peg, not just give random readings. 
- The presence of a strong electrical field should not affect the
magnetic field measurement.
Meters meeting these requirements are quite expensive, $600 would probably
be the bare minimum.  These meters are not suitable for the non-technically
trained.

There is an understandable reluctance to recommend any unit with unknown
characteristics to a person whose technical abilities are also unknown, and
no peer-reviewed articles on inexpensive instruments appear to be
available.  The suggestions that one wind a coil and use headphones or a
high impedance multimeter are misguided.  A clever physicist or engineer
can anticipate and correct for nonlinearities and interferences, but for
the average person, even one technically trained, this is unreasonable.

30) How are power-frequency magnetic fields measured?

Measurements must be done with a calibrated gauss meter (Question 29) in
multiple locations over a substantial period of time, because there are
large variations in fields over space and time. 

Fortunately, the magnetic field is far easier to measure than the
electrical field. This is because the presence of conductive objects
(including the measurer's body) distorts the electrical field and makes
meaningful measurements difficult. Not so for the magnetic field.

It is important for the person who is making the evaluation to understand
the difference between an emission and exposure. This may seem obvious, but
many people, including some very smart physical scientists, stick an
instrument right up to the source and compare that number with an exposure
standard.

If the instrument is not isotropic, measurement technique must compensate
for this.

In the case of power distribution line and transformer fields, the magnetic
fields will probably vary considerably over time, as they are proportional
to the current in the system.  A reasonable characterization needs to be
done over time, with anticipated and actual electricity usage factored in.
It may seem to be as simple as walking in and reading the meter, but it's
not.

------

Annotated Bibliography

A) Recent Reviews of the Biological and Health Effects of Power-Frequency
Fields

A1) Electromagnetic field health effects, Connecticut Academy of Science
and Engineering, Hartford, CT, 1992. 
  "Absolute proof of the occurrence of adverse effects of ELF fields at
prevailing magnitudes cannot be found in the available evidence, and the
same evidence does not permit a judgment that adverse effects could not
occur . . .If adverse health effects from residential magnetic field
exposure exist, they are not likely to make a large contribution. 

A2) JG Davis et al: Health Effects of Low-Frequency Electric and Magnetic
Fields. Oak Ridge Associated Universities, 1992.
  "This review indicates that there is no convincing evidence in the
published literature to support the contention that exposure to extremely
low-frequency electric and magnetic fields generated by sources such as
household appliances, video display terminals, and local power lines are
demonstrable health hazards.

A3) JI Aunon et al: Investigations in power-frequency EMF and its risk to
health: A review of the scientific literature, Universities Consortium on
Electromagnetic Fields, 1992. 
  "the conclusions from this review highlights the absence of health
effects directly related to 60 Hz alternating current EMF on humans."

A4) PA Buffler et al: Health effects of exposure to powerline-frequency
electric and magnetic fields, Public Utility Commission of Texas, Austin,
1992. 
  "no conclusive evidence to suggest that EMF due to electric power
transmission lines poses a human health hazard."
 
A5) JA Dennis et al: Human Health and Exposure to Electromagnetic Radiation
(NRPB-R241), National Radiological Protection Board, Chilton, 1993. 
  "the bulk of the evidence points to there being no effects at levels to
which people are normally exposed".
 
A6) P Guenel & J Lellouch: [Synthesis of the literature on health effects
from very low frequency electric and magnetic fields], National Institute
of Health and Medical Research (INSERM), Paris, 1993. 
  "laboratory studies have never shown any carcinogenic effect [but] the
epidemiological results presently available do not permit exclusion of a
role for magnetic fields in the incidence of leukemia, particularly in
children... The effect of magnetic fields on human health remains a
research problem.  It will only become a public health problem if definite
effects are confirmed."
 
A7) J. Roucayrol: [Report on extremely low-frequency electromagnetic fields
and health]. Bull Acad Nat Med 177:1031-1040, 1993. 
  "There is no conclusive evidence linking EMF to reproductive and
teratogenic effects, and/or that EMF has a role in the initiation,
promotion or progression of certain cancers, even though some data cannot
exclude this possibility. . . reported associations between EMF and certain
pathologies like leukemia and other childhood and adult cancers cannot be
supported by current epidemiological data."

B) Reviews of the Epidemiology of Exposure to Power-Frequency Fields

B1) DA Savitz & EE Calle: Leukemia and occupational exposure to EM fields:
Review of epidemiological studies. J Occup Med 29:47-51, 1987.
  Review of occupational exposures and leukemia, showing a small but
significant excess of leukemia in electrical occupations.

B2) M Coleman & V Beral: A review of epidemiological studies of the health
effects of living near or working with electrical generation and
transmission equipment. Int J Epidem 17:1-13, 1988.
  Review of both occupational and residential studies, including
meta-analysis showing a small but significant excess of leukemia in
electrical occupations.
  
B3) D Trichopoulos, Epidemiological studies of cancer and extremely
low-frequency electric and magnetic field exposures, In: Health effects of
low-frequency electric and magnetic fields, JG Davis et al, editors, Oak
Ridge Assoc Univer, Oak Ridge, pp. V1-V58, 1992.
  Meta-analysis of occupational exposure studies indicating small but
statistically significant relative risks for leukemia and brain cancer.
   
B4) G.B. Hutchison: Cancer and exposure to electric power. Health Environ
Digest 6:1-4, 1992.
  Meta-analysis of residential exposure studies shows a significant excess
for childhood brain cancer, but not for childhood leukemia or lymphoma. 
Analysis also shows an excess of leukemia and brain cancer in electrical
occupations, but no significant excess of lymphoma or overall cancer.

B5) R Doll et al, Electromagnetic Fields and the Risk of Cancer, NRPB,
Chilton, 1992.
  Includes a meta-analysis of the childhood cancer data.  For leukemia, the
analysis shows a significant elevation when wirecodes are used to assess
exposure, but not when distances or measured fields are used.  For brain
cancer, the analysis shows a significant elevation when wirecodes or
distance are used to assess exposure, but not when measured fields are
used.  For all childhood cancer the analysis shows a significant elevation
when wirecodes or measurements are used to assess exposure, but not when
distance is used.

B6) A Ahlbom et al: Electromagnetic fields and childhood cancer. Lancet
343:1295-1296, 1993.
  Pooled analysis of the Scandinavian childhood cancer studies indicates
that if calculated historic power-line fields are used as a measure of
exposure, a small but statistically significant increase is seen in the
incidence of leukemia, but no statistically significant increase is seen in
the incidence of CNS cancer, lymphoma, or overall cancer.

C) Epidemiology of Residential Exposure to Power-Frequency Fields

C1) N Wertheimer & E Leeper: Electrical wiring configurations and childhood
cancer. Am J Epidem 109:273-284, 1979.
  Case-control study of childhood leukemia and brain cancer using type of
powerlines (wirecodes) as an index of exposure.  A significant excess of
leukemia and brain cancer were reported.

C2) N Wertheimer & E Leeper: Adult cancer related to electrical wires near
the home. Int J Epidem 11:345-355, 1982.
  Case-control study of adult cancer.  Significant excess reported for
total cancer and brain cancer, but not for leukemia.
 
C3) JP Fulton et al: Electrical wiring configurations and childhood
leukemia in Rhode Island. Am J Epidem 111:292-296, 1980.
  Case-control study using wire-dose as an index of exposure.  No excess of
child leukemia found.
   
C4) ME McDowall: Mortality of persons resident in the vicinity of
electrical transmission facilities. Br J Cancer 53:271-279, 1986.
  Standard mortality ratio study using proximity to lines as a measure of
exposure.  No excess seen for total cancer or for leukemia in adults.

C5) L Tomenius: 50-Hz electromagnetic environment and the incidence of
childhood tumors in Stockholm County. BEM 7:191-207, 1986.
  Case-control study of childhood cancer using proximity to electrical
equipment as indices of exposure.  Proximity to 200 kV lines was associated
with significant excess of total cancer, but proximity to other types of
electrical equipment carried no significant excess risk.  No significant
excess of leukemia or brain cancer for any index of exposure.

C6) DA Savitz et al: Case-control study of childhood cancer and exposure to
60-Hz magnetic fields. Am J Epidem 128:21-38, 1988.
  Case-control study of childhood leukemia and brain cancer in Denver,
using measurements and wirecodes as indices of exposure.  Possibly
significant excess of leukemia for high-current-configuration wirecodes,
but no excess incidence for measured fields.  Significant excess of brain
cancer for high-current-configuration wirecodes, but no excess incidence
for measured fields.

C7) RK Severson et al: Acute nonlymphocytic leukemia and residential
exposure to power-frequency magnetic fields. Am J Epidem 128:10-20, 1988.
  Case-control study of childhood leukemia in Washington state, using
measurements and wirecodes as indices of exposure.  No excess leukemia for
wirecode or measured fields.
 
C8) MP Coleman et al: Leukemia and residence near electricity transmission
equipment: a case-control study. Br J Cancer 60:793-798, 1989.
  Case-control study of childhood and adult leukemia, using proximity to
powerlines and transformers as an exposure index.  No significant excess of
leukemia was found.
   
C9) A Myers et al: Childhood cancer and overhead powerlines: a case-control
study. Br J Cancer 62:1008-1014, 1990.
  Case-control study of childhood and adult leukemia, using proximity to
powerlines as an exposure index.  No significant excess of leukemia, solid
tumors or all cancer was found.

C10) SJ London et al: Exposure to residential electric and magnetic fields
and risk of childhood leukemia. Am J Epidem 134:923-937, 1991.
  Case-control study of childhood leukemia in Los Angeles, using
measurements and wirecodes as indices of exposure.  Significant excess of
leukemia for high current configuration wirecodes, but no excess risk for
measured fields.

C11) JHAM Youngson et al: A case/control study of adult haema tological
malignancies in relation to overhead powerlines. Br J Cancer 63:977-985,
1991.
  Case-control study of adult leukemia and lymphoma using proximity to
powerlines and estimated fields as measures of exposure.  No significant
excess of cancer found.

C12) M Feychting & A Ahlbom: [Cancer and magnetic fields in persons living
close to high voltage power lines in Sweden]. Lkartidningen 89:4371-4374,
1992.  
  Case-control study of everyone who lived within 1000 feet of high-voltage
powerlines; contains material on adult exposure not in the 1993
publication.  No increased leukemia or brain cancer was found for adults
when exposure was based on measured fields, distance from power lines or
retrospective field calculations.
  
C13) JM Peters et al: Exposure to residential electric and magnetic fields
and risk of childhood leukemia. Rad Res 133:131-132, 1993.
  Discussion of the implications of finding a correlation of cancer with
wire-codes, but not with measured fields.  Possibilities: 
- There is a true etiological association, but there is a methodological
bias in the measurement technique 
- There is a true etiological association, but average and/or spot fields
are not the correct exposure metric 
- Selection bias in the control group 
- A confounder

C14) PJ Verkasalo et al: Risk of cancer in Finnish children living close to
power lines. BMJ 307:895-899, 1993.
  Cohort study of cancer in children in Finland living within 500 m of
high-voltage lines.  Calculated retrospective fields used to define
exposure.  No statistically significant increase in overall cancer
incidence was found.  A significant increase in brain cancer in boys was
due entirely to one exposed boy who developed three brain tumors.  No
significantly increases were found for brain tumors in girls or for
leukemia, lymphomas or "other" tumors in either sex.
 
C15) JH Olsen et al: Residence near high voltage facilities and risk of
cancer in children. BMJ 307:891-895, 1993.
  Case-control study of childhood cancer in Denmark.  Exposure was assessed
on the basis of calculated fields.  No overall increase in cancer was found
when 2.5 mG (0.25 microT) was used define exposure.  After the data were
analyzed, it was found that if 4 mG (0.40 microT) was used as the cut-off
point, there was a statistically significant increase in overall cancer. 
No statistically significant increases in leukemia, lymphoma or brain
cancer were found.
 
C16) GH Schreiber et al: Cancer mortality and residence near electricity
transmission equipment: A retrospective cohort study. Int J Epidem 22:9-15,
1993.
  Study of people living in an urban area in the Netherlands.  People were
considered exposed in they lived within 100 m of transmission equipment. 
Fields in the exposed group were 1-11 mG (0.1-1.1 microT).  An
insignificant decrease in total cancer was found in the exposed group
compared to the general Dutch population.  No leukemia or brain cancer was
seen in the exposed group.

C17) M Feychting & A Ahlbom: Magnetic fields and cancer in children
residing near Swedish high-voltage Power Lines. Am J Epidem 7:467-481,
1993.
  Case-control study of children who lived within 300 m of high-voltage
powerlines.  Exposure assessed by measurements, calculated retrospective
assessments, and distance from lines.  No overall increase in cancer was
found for any measure of exposure.  An increase in leukemia (but not brain
or other cancers) was found in children in one-family homes for fields
calculated to have been 2 mG or above at the time of cancer diagnosis, and
for residence within 50 m of the power line.  No increase in cancer was
found when measured fields were used to estimate exposure.

C18) TL Jones et al: Selection bias from differential residential mobility
as an explanation for associations of wire codes with childhood cancer. J
Clin Epidem 46:545-548; 1993.
  The type of "high current configuration" distribution lines associated
with cancer in the Wertheimer [C1], Savitz [C6] and London [C10] studies
were more common in residential areas that were older, poorer, and which
contained more rental properties.  This could lead to a false association
high current configurations with disease.
  
D) Epidemiology of Occupational Exposure to Power-Frequency Fields

D1) S Milham: Mortality from leukemia in workers exposed to electrical and
magnetic fields. NEJM 307:249, 1982.
  Proportional mortality study of electrical occupations showing a
significant excess incidence of leukemia. 

D2) WE Wright et al: Leukaemia in workers exposed to electrical and
magnetic fields. Lancet 8308 (Vol II):1160-1161, 1982. 
  Proportional incidence study of electrical occupations showing a
significant excess of acute, but not chronic leukemia.
 
D3) S Richardson et al: Occupational risk factors for acute leukaemia: A
case-control study. Int J Epidem 21:1063-1073, 1992. 
  Case-control study of acute leukemia across occupations.  An increase in
leukemia was found for all electrical occupations, but the increase was not
statistically significant.  Significant excesses of leukemia were
associated with benzene, exhaust gasses and pesticides.

D4) JD Bowman et al: Electric and Magnetic Field Exposure, Chemical
Exposure, and Leukemia Risk in "Electrical" Occupations, EPRI, Palo Alto,
1992.  
  Proportional incidence study of leukemia in electrical versus other
occupations.  For all electrical occupations there was a small, but
statistically significant association of leukemia with electrical
occupations.  There was no relationship between the level of exposure and
leukemia.
 
D5) T Tynes et al: Incidence of cancer in Norwegian workers potentially
exposed to electromagnetic fields. Am J Epidem 136:81-88, 1992.
  Cohort study of electrical occupations that showed a statistically
significant excess of leukemia but not of brain cancer.

D6) GM Matanoski et al: Leukemia in telephone linemen. Am J Epidem
137:609-619, 1993. 
  Case-control of telephone company workers, which showed no statistically
significant increase in leukemia in workers exposed to power-frequency
fields.
 
D7) B Floderus et al: Occupational exposure to electromagnetic fields in
relation to leukemia and brain tumors: A case-control study in Sweden.
Cancer Causes Control 4:463-476, 1993.
  Case-control study of leukemia and brain tumors of men in all
occupations.  Exposure calculations were based on the job held longest
during the 10-year period prior to diagnosis.  A statistically significant
increase was found for leukemia, but not for brain cancer.
 
D8) JD Sahl et al: Cohort and nested case-control studies of hematopoietic
cancers and brain cancer among electric utility workers. Epidemiology
4:104-114, 1993.
  Both a cohort and a case-control study of utility workers.  No
significant increase was found for total cancer, leukemia, brain cancer, or
lymphomas.
 
D9) P Guenel et al: Incidence of cancer in persons with occupational
exposure to electromagnetic fields in Denmark. Br J Indust Med 50:758-764,
1993.
  Case-control study based on all cancer in actively employed Danes. No
significant increases were seen for breast cancer, malignant lymphomas or
brain tumors.  Leukemia was elevated among men in the highest exposure
category; women in similar exposure categories showed no increase in any
type of cancer.
  
E) Human Studies Related to Power-Frequency Exposure and Cancer

E1) AB Hill: The environment and disease: Association or causation? Proc
Royal Soc Med 58:295-300, 1965.
  Concise statement of the methods use to assess causation in
epidemiological studies.

E2) M Bauchinger et al: Analysis of structural chromosome changes and SCE
after occupational long-term exposure to electric and magnetic fields from
380 kV-systems. Rad Env Biophys 19:235-238, 1981.
  Lymphocytes from occupationally exposed 50 Hz switchyard workers showed
no increase in the frequencies of chromosome aberrations.

E3) K Dickersin et al: Publication bias and randomized controlled trials.
Cont Clin Trials 8:343-353; 1987.
  A general discussion, with examples, of publication bias

E4) I Nordenson et al: Chromosomal effects in lymphocytes of 400
kV-substation workers.  Rad Env Biophys 27:39-47, 1988.
  Lymphocytes from occupationally exposed 50 Hz switchyard workers showed
an increase in the frequency of chromosome aberrations.
 
E5) DA Savitz & L Feingold: Association of childhood leukemia with
residential traffic density. Scan J Work Environ Health 15:360-363, 1989.
  Analysis of the authors powerline study [C6] using traffic density as the
exposure.  Significant excess risk of leukemia and total cancer associated
with high traffic density.

E6) I Penn: Why do immunosuppressed patients develop cancer? Crit Rev
Oncogen 1:27-52, 1989.
  Review of the relationship between cancer development and immune
suppression

E7) GR Krueger: Abnormal variation of the immune system as related to
cancer. Cancer Growth Prog 4:139-161, 1989.
  Review of the relationship between cancer development and immune
suppression

E8) J.D. Jackson: Are the stray 60-Hz electromagnetic fields associated
with the distribution and use of electric power a significant cause of
cancer? Proc Nat Acad Sci USA 89:3508-3510, 1992.
  Argument that lack of correlation between electric power use and leukemia
rates over time argues against a causal relationship.

F) Biophysics and Dosimetry of Power-Frequency Fields

F1) WT Kaune et al: Residential magnetic and electric fields. BEM
8:315-335, 1987.
  24-hour average measurements correlate poorly with wirecodes.  The
correlation of 0.41, implies that codes account for only 20% of the
variability in average fields.

F2) J Sandweiss: On the cyclotron resonance model of ion transport. BEM
11:203-205, 1990.
  Cyclotron resonance theory inconsistent with basic physical principles
because radius of ion rotation would be about 50 m, and because collisions
would occur much too often for resonance to be achieved.

F3) G Theriault: Cancer risks due to exposure to electromagnetic fields.
Rec. Results Cancer Res. 120:166-180; 1990.
  Good, but dated review. Has good residential and occupational dosimetry
data.

F4) RK Adair: Constraints on biological effects of weak
extremely-low-frequency electromagnetic fields, Phys Rev A 43:1039-1048,
1991.
  Because of the high electrical conductivity of tissues, the coupling of
external electric fields in air to tissues of the body is such that the
effects of the internal fields on cells is smaller than thermal noise.  To
get an effect you need a resonance mechanism, and "such resonances are
shown to be incompatible with cell characteristics. . . hence, any
biological effects of weak ELF fields [less than 500 mG, 50 microT] on the
cellular level must be found outside of the scope of conventional physics".
 Also notes that the current induced by walking in the Earths static field
are greater than those induced by a 4 microT (40 mG) 60-Hz field, and that
any resonance found at 60 Hz would not work at 50 Hz.

F5) T Dovan et al: Repeatability of measurements of residential magnetic
fields and wire codes. BEM 14:145-159, 1993.
  Remeasure of homes that had been included in Savitz study [C6] found that
neither measured fields nor wire codes had not changed significantly over a
five-year period.

End: powerlines-cancer-FAQ/part3
