4
R. SCOTT RUSSELL
basic concepts. The Recommendations of the International Commission on
Radiological Protection® at once come to mind in this context, but difficulties can arise in applying them to environmental situations. This is not
surprising, as the 1959 Recommendations of ICRP were directedprimarily
to occupational situations, and statements on the exposure of the population
were usually made in less definite terms. Nonetheless, the general intentions
of the Commission are apparent, especially from the addendum to its
Recommendations agreed in 1959.* Referring to the exposure of the population, the Commission then stated:
“The basis for the limits of permissible exposure of the population
to man-made sources of ionising radiation is the dose received by
the various organs of the body and not the MPC values or other
criteria by which the dose is controlled.”
This statement may reasonably be regarded as applying also to persons
living in the neighbourhoodof controlled areas (i.e. Group B (c)), and itis
with them that we are here particularly concerned. This principle has a
number of important implications:
(a) Since the dose received from any one nuclide is determined by the
total radioactivity in the daily intake, the levels in individual components
of diet, or water, are of interest only in so far as they contribute to this
total.
(b) Since the dose delivered by unit intake of different nuclides differs
very widely, measurements of the total alpha, beta or gamma activity have
little value; individual nuclides must be considered.
(c) Since the basic criterion is the tissue dose, and not the radioactivity
per unit weight of individual foods, the significance of dietary contamination
is appropriately assessed in terms of those nuclides and foodstuffs which
are responsible for the highest tissue dose.
Accordingly, if it can be shown that but a few nuclides will always be
responsible for the major exposure in any area and that they will enter the
body mainly in a few foods, attention can be confined to these “critical”
nuclides and foods. The adjective “critical” can conveniently be applied to
them with essentially the same meaning as the phrase “critical organ”. As
will be shown later, the main contribution of food chain studies to the
design of environmental surveys has been the unequivocal identification of
critical nuclides and foods in many circumstances.
In applying these concepts to the evaluation of environmental contamination, the tissue doses with which we are concerned are defined by
ICRP as the dose delivered per year and many authorities agree that the
manner in which it is distributed through the year need not be considered.
A final and equally important question relating to the basis of protection
* See Addendum, p. 10.