Life on earth evolved amid constant exposure to ionizing[3] radiation,
from the earth itself and from space, known as background radiation.
Therefore environmental studies must be conducted in relation to, and
with understanding of, background radioactivity.
[Illustration: _This Pacific Ocean coconut crab, member of a family that
usually sticks to tide-covered beaches, depends on coconut trees for its
food._]
Of some 340 kinds of atoms that have been found in nature, about 70 are
radioactive. Three families of radioactive isotopes[4]—the uranium,
thorium, and actinium series—produce a large proportion of the natural
radiation. Other radionuclides[5] occur singly, rather than in families,
and some of them, such as potassium-40 and carbon-14, are major
contributors of natural radioactivity. Traces of natural radioactivity
can be found, in fact, in all substances on earth.
When man began experimenting with atomic fusion and fission, he placed
in his environment—across vast landscapes, in the oceans, and in the
atmosphere—measurable additional amounts of radioactivity. These
additions were composed of the longer-lived members of some 200 kinds of
atomic radiation. Although the additions constituted but a fraction of
the background burden, they represented the first alteration of the
radiological balance that had existed since the early ages of the
planet. Thus it became necessary to determine what the impact of such a
change might be. In the process of inquiry, these ideas emerged:
1. The addition of man-made radioactivity presents the possibility of
delayed or cumulative effects. Long-term studies, geared to the
assessment of biological effects from extremely low radioactivity, are
essential.
2. The addition of radioactivity makes possible broad-gauged studies
to trace the movement and concentration of radionuclides in the
environment. These studies, in turn, can disclose new information on
biological complexes and mechanisms.
[Illustration: _A flying atmospheric physics laboratory studying
concentration of radionuclides over an Atomic Energy Commission
laboratory. Instrument pod under wing samples air to provide a visual
record of radioactivity._]
[Illustration: _Transferring a sample of water taken from the depths of
the Columbia River for radiochemical analysis in a laboratory._]
The quantities of low-level long-lived radioactivity already released
into our environment will provide materials for future studies covering
decades. Further, because radioisotopes are chemically similar to
nonradioactive forms, observation of their biological fate will provide
clues to the transport, concentration, dilution, or elimination of many
other kinds of man-made toxic agents and contaminants of the
environment.