Encyclopedia of Environmental Science and Engineering, Volume I and II

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RADIATION ECOLOGY

Radiation Ecology or Radioecology is a term that came into

common usage in 1956 to denote that area of the broad field

of ecology concerned with the assessment of radioactivity

in the environment. More specifically, radiation ecology has

come to be recognized as that area of ecology concerned

with radioactive substances, radiation and the environment.

The development and subsequent expansion of nuclear

energy for military and peaceful purposes has been accom-

panied by environmental problems, some of which are typi-

cal of other facets of industrialization and some unique to

atomic energy. The unique problems primarily concern the

fate and ecological effects of radionuclides released into

the environment.

The major environmental problems introduced by the

Atomic Age may be grouped into several areas of scien-

tific and public concern. Underlying each of these is the

worry about the effects of ionizing radiation—on man, his

domesticated plants and animals, and on the environment

and its living components, Fallout from weapons testing,

reactor radioactive waste effluents, radioactive waste dis-

posal, nuclear war, and use of nuclear explosives for major

engineering and related technological projects of large scale

comprise the activities which have concerned society and

which, because of potential impact on the environment and

man, have stimulated the development of radiation ecology.

Understanding the manner in which our ecological systems

(ecosystems) distribute, assimilate, and affect the environ-

mental behavior of radioactive substances, and the effects of

radiations emitted from those substances, are the concern of

the radioecologist.

RADIONUCLIDES OF ECOLOGICAL IMPORTANCE

Radionuclides which are of interest to the ecologist are

listed in Table 1. These radioactive elements represent the

major naturally-occurring and man-made sources of radia-

tion in the environment. Principal sources of exposure from

background (natural) radiation are represented by the ura-

nium, thorium and actinium decay series. Internal exposure

to man results primarily from^40 K,^14 C,^226 Ra, and^228 Ra and

their daughter products that are deposited in the body.

Radionuclides such as^222 Rn and^220 Rn and their daughter

products represents sources of internal radiation exposure to

man from inhalation.

Radionuclides produced by the fissioning of uranium

(fission products) are of the greatest current concern. These

man-made isotopes are not essential to organisms, but they

constitute the major sources of radiation in the environment

whether it be from fallout or waste disposal from reactor

operations. All of these radionuclides may enter ecosystems

where they become part of the flux of systems that are being

circulated within and between systems.

Some of the fission products which are chemically simi-

lar to biologically essential elements are of special inter-

est. They vary greatly in their physical half-life and in the

extent to which they participate in metabolic processes of

living organisms. The most important radionuclides affecting

plants and animals on land are strontium-90, cesium-137, and

iodine-131.

Strontium-90 remains in the environment for a long

time. Its half-life is 28 years. Strontium is chemically similar

to calcium, and it can enter living organisms as a replace-

ment for calcium. In weapons fallout strontium-90 is usually

deposited in the root systems of plants. the amount of^90 Sr

that a plant absorbs from soils depends on several factors,

particularly on the quantity of calcium in the soil, the relative

quantities of calcium and strontium at the depth where the

roots are located, and the ability of the plant to discriminate

between the two elements. The plant is the base for^90 Sr to

enter the human food chain. This chain is a short and simple

one consisting of plants, cows, and man, with cow’s milk

being the chief source of entry into man. There is consider-

able discrimination against the transfer of strontium at each

step in this food chain, but the small amount that is trans-

ported to man tends to concentrate in bone tissue. It remains

there, undergoing radioactive decay and emitting its radia-

tion. Its danger is related to the fact that bone contains blood

forming (erythropoetic) tissue. In sufficient quantities the

radiation can cause leukaemia and bone cancer.

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