Electromagnetic fields are divided into several categories:
- appliances and power
lines--extremely low frequencies (ELF)
- AM radio transmission--high and
low frequencies (HF and LF)
- TVs and video display
terminals--very low frequencies (VLF)
- TV and FM radio
transmissions--very high frequencies (VHF)
- microwaves--super high frequencies
(SHF)
Recommended safety levels range from 0.5 mG to 2.5 mG as the
maximum exposure -
with 1.0 mG as a preferred standard. Adverse biological
effects have been found at 2.5 mG.
How much are we
exposed?
The amount of exposure is difficult to
determine. Exposure to forces produced by external sources
is generally constant, but the structure of a building
determines how much of the final field strength can be found
inside the building. EMFs produced inside a home can widely
vary depending upon the wiring system and appliance usage.
These variables cloud efforts to determine the relative
importance of local power lines as opposed to the use of
appliances or to internal house wiring.
What are the effects of
exposure?
Most of the research--especially research
focusing on the relationship between exposure to EMFs and
cancer--has focused on public health issues. In most cases,
the findings are difficult to trust because of the
difficulty in controlling the amount of exposure and other
variables, including socioeconomic status, nutrition,
lifestyles, genetics, occupation, and exposure to other
cancer-causing factors. Many study designs lack validity,
which causes further doubt about their value.
Given these limitations and shortcomings, the
research nevertheless does suggest the need for further
investigation of the association between EMFs and some
cancers. These include childhood brain cancer and female
breast cancer. Occupational concerns related to EMFs include
adult brain cancer, adult leukemia, and male breast cancer.
A review of occupational studies examined the
occurrence of malignant melanoma, colon cancer, lung cancer,
bladder cancer, and non-Hodgkin's lymphoma and found
questionable evidence linking those cancers with EMFs or
with working in an "electrical" job.
A number of studies examined the relationship
between parental "electrical" occupation and childhood
central nervous system cancers and found little to suggest a
link. The evidence for adult central nervous system cancers,
male breast cancer, and leukemia is also very weak. Many
respected scientists critique the studies as being flawed.
In spite of limited evidence concerning the
link between EMFs and cancer, a weak connection between the
two appears to exist. Further, valid studies are needed to
determine the specific nature of this link.
Are there any
measurable negative effects?
Currently, the only known measurable negative
effects of EMFs are related to quality-of-life issues. Local
power lines, poles, substations, and high voltage
transmission lines are aesthetically displeasing; a possible
reduction in property values and a deterioration of
community may occur as families choose to relocate to avoid
EMFs. Those who live in areas selected for new EMF
facilities may be resentful and resistant to them being
built..
In woodlands and farmlands, several rare but
easily explained occurrences result from electromagnetic
fields. Damaged conifer needles growing close to power lines
serve much the same function as a lightning rod in
discharging electricity build-up in the air; power lines
sometimes create stray voltage effects that cause constant
low-level electric shock. Decreased milk production in dairy
cows and other minor problems can be avoided by properly
grounding equipment and buildings.
The placement of distribution towers that
produce EMFs into recreational areas and natural areas are
said to have a negative effect, although no quantifiable
data are available and there appears to be no noticeable
decrease in the use of those areas.
Generally, scientists on both sides say they
are dealing at most with rare diseases and an increased risk
that is almost infinitesimal, especially compared with
life's other everyday risks.