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these effects it has not been possible [o show whether or not a lhreshold dose exists.
However, go as not to underestimate the probability that srch effects will occur, current
radiation protection practise assumes that no threshold dose exists. The Technical Group
adopted this assunpLion in its Report.
Expogures to ionizinq radiation in the South Pacific reqion
Imizinq radiations originate both in sources that occur naturally and in sources created
by human technology. Natural sources of ionizing radiation have been present in the
environrnent since the beginning of the earth's history. They include cosmic rays thal come
from outer pace and natural radionuctides that occur on earth. Barring a nuclear war or
major reactor accidents, natural sources are likely always to be the main environmenlal
contributor to human radiation exposure. Artificial sources of ionizing radiation in the
environment are due almost exclusively to atmospheric nuclear explosions and nuclear electric
power production, the former being by far the most important.
The Technical Group spent a considerable amount of its ef f ort reviewing the
information available on human exposure to sources of ionizing radiation in the environrnent.
Much of that inf ormation is compiled in the most recent report of the United Nations
Scientific CornmiLtee m the Effectg of Atomic Radiation (UNSCEAR, 1982), which derived
global averages for exposure to natural and artificial ionizing radiaLion. In addition the Group
reviewed data relating specifically to the exposures of people Iiving in the South Pacific
Region with the eim of determining how the average exposures to ionizing radiation in the
Region compsre with the global averages.
In the case of natural radiation, the world population as a whole receives an averaqe
annuel effective dose equivalent* of 2OOO microsievert (UNSCEAR, l9B2). This is an average
figurer end there is a large variation from place to place on earth, depending qr a number of
environmental factors, and from person to person, depending m living habi[s, The exposune is
received in a variely of ways: by external exposure to eosmic rays and the radiations emitted
by radioactive elements (potassium, thorium and uranium) in soils, by the consunption of food
containing natural radionuclides, and by the inhalation of radon-222 and other radionuclides
[hat are neturally ptesent in the air. For the South Pacific Region the Technical Group
concluded bhat, on the average, the annual effective dose equivalent from nstunal sources of
ionizing radiation is approximately lmO microsievert, mly half the world average. The
lower-than-average exposures in the Region are the result of several factors: (1) the low
concentrations of radioactive elements in the coralline soils that occur in mueh of the region,
Q) the lower concentrations of radon-222 in the air over the ocean compared with
coneentrations over the continents, and (l) the fact that most people in the region live in
well-ventileted houses and spend much of their time outdoons, thus avoiding exposure to the
elevated levels of radon that often (rcur in indoor air.
Tle Technical Group also concluded that exposure to artificial radionuclides, mainly
the radionuclides formed during past nuclear weapons tests in the atmosphere, is on the
average lower, perhaps two or three times lower, in the South Pacific region than it is for
the world as a whole. This is because most of the population in the Region lives in the
Southern Hemisphere, whereas the greater part of [he fallout from atmospheric testing was
delivered in the Norihern Hemisphere. ln general, the contr!bution to total radiation exposure
due to artificial radionuclides is small and is much less than the variability that exists in
exposure to natural sources of radiat.ion.
Although average doses from both natural and artificial ionizing radiation in the Region
ere albstantially lower Ehan in nnst other parts of the world, there are certain islands in the
Region where populations receive unusually high radiation exposures. Niue Island in the South
Pecifie is a docunented example of en area of unusually high natural nadioactivity (Fieldes et
g[.r t97O; Marsden, L974), and there are data suggesting that part of Guam might also 5E
such an area (Nelson, 1979tr Urusually high levels of artificial radioactivity are found at some
atolls in the Marshall Islands that were contaminated by local fallout from the United States
weapons tests (Robison et al., 1982).
rTfE effective dose equivalent expresses non-uniform doses as
dose which would produce [he same harmful effects. The factons
effective dose equivalen! were assigned by the ICRP (I977).
a uniform whole-body
used in calculating the