conclusion that they may constitute a public health risk are described below.
Levels in the Environment
The artificial EMF environment of the U.S. is a superimposition of contributions from many
sources having diverse operating characteristics. They include high- and low-power emitters that can be
omnidirectional or directional, and that can operate continuously or intermittently. At high frequencies,
the general EMF background consists predominantly of the AM radio band (0.535-1.604 MHz) and the
FM and TV band (54-806 MHz). About half the U.S. population is exposed to these sources at levels
above 0.005 µW/cm2 at any given moment, and about I% is exposed above 1 µW/cm2 (Fig. 10.1)(1).
The actual number of people exposed above 1 µW/cm2 in any given day, week, or month is
considerably greater because of population mobility.
Fig. 10.1 Population of some U.S. cities exposed to radio and TV signals above (the level considered
safe in the U.S.S.R.). Nationwide, the total population exposed above 1 µW/cm2 at any given time is
about 2 million (1).
EMFs emanating from the electrical power system (60 Hz in the U.S., 50 Hz in Europe and the
U.S.S.R.) constitute most of the artificial low-frequency electromagnetic background. They are
extremely pervasive; except for remote areas such as forests, it is difficult to find places where the
electric and magnetic fields are less than 0.1v/m and 100 µgauss respectively. But even these fields are
several orders of magnitude greater than the naturally present 60-Hz fields. The average man-made
back-ground electric field is probably in the order of 1 v/m (2), and the average background magnetic
field is about 800-900 µgauss (3).
EMFs much greater than the background are found in the vicinity of specific sources. The
power density at various distances from a typical 50,000-watt AM radio station is shown in table 10.2
(4); within a radius of about 3,280 feet, the level does not decrease below 1 µW/cm2. FM radio stations
vary considerably in strength and antenna design, but it has been estimated that 193 of 2750 such
stations in the U.S. could have levels exceeding 1000 µW/cm2 within 200 feet of the antenna (5). In
large urban areas, the elevation necessary for transmission of radio and TV signals is sometimes
ELECTROMAGNETISM & LIFE - 134