RADIONUCLIDES IN PLANKTON AND TUNA
FROM THE CENTRAL PACIFIC
F. G. LOWMAN!
The uptake and retention of radionuclides by
marine organisms are of practical interest to man
insofar as the radionuclides constitute a poten-
tial hazard in his food materials obtained from the
sea.
In addition to the practical considerations,
information may be derived concerning the processes
which control the cycling of stable elements from
sea water through the various levels of food chains.
If the amounts of radionuclides in organisms comprising a food chain are determined at intervais of
time following contamination of the environment,
the interrelations between a trophic level and the
physical environment and with other trophic levels
may be delineated, at least in regard to the movements of mineral components through the system.
Except for the light elements, marine organisms do not discriminate between different isotopes
NeERTS
if the introduced radio-
nuclide has the same chemical and physical form aa
the corresponding stable element, the two are taken
up according to their ratio of abunddnce. However,
radioisotopes do differ from their stable counter-
parts in that they are subject to radioactive decay.
If the biological half-lives of a given ele-
ment, in several organisms comprising a food chain,
are not taken into account, erroneous interpretations may be made, especially if the radioisotope
has a relatively short physical half-life. These
errors may be corrected if the average ratio of
radioactive to stable isotope of an element is determined for each level within the food chain.
The principal factors which control the uptake
and retention of radionuclides by marine organisms
are:
(1) the amount of radionuclide introduced into the sea, (2) the site of introduction inte the
sea in relation to position and depth, (3) the degree of physical dispersion by currents and gravi-
characteristics
of the radioelement, (5) the chemical and physical
forms of non-radioactive materials associated with
the radionuclide, (6) the degree of isotope dilution of the radioelement by the corresponding
stable element (or chemically similar elements) in
sea water, (7) the degree to which the radionuclide
(8) the degree of
selective uptake, and (9) the biological half-life
of the element in the organisms.
Fallout areas near the sites of nuclear weapons tests are of value for investigations of the
fate of radionuclides in the marine environment in
that large amounts of radiomaterials may be introduced into a given area in a short time and at adequate levels to be detected for a relatively iong
time following contamination. Because the fallout
is usually deposited over large areas, most of the
animals collected over a period of time in the area
may be considered to have been exposed to a chronic
rather than to an acute exposure of radioactive
materials.
Present addreaes, Puerto Rico Nuclear Center, Mayaguez,
Puerto Rico,
In the first survey,
measurements were made and samples were collected
time starting less than one hour after detonation
of the nuclear device and extending over a period
INTRODUCTION
is adsorbed to the organisms,
1958; Palumbo et al., 1959).
in a contaminated body of water for an interval of
Seattle, Washington
ty, (4) the chemical and physical
During the nuclear weapons test series in
1958 (Operation HARDTACK I) three oceanographic
surveys were made by members of the Laboratory of
Radiation Biology (Lowman, 1960; Lowman et al.,
Laboratory of Radiation Biology, University of Washington,
of a given element; thus,
MATERIALS AND METHODS
of 48 hours. The samples included plankton and water samples taken at depths to 300 meters.
remaining two surveys included areas which had been
contaminated for more than one week and for an av-
erage time of six weeks, respectively. During the
time of the above described surveys, samples of
tuna (Thunnus spp.), albacore (Thunnus alalunga),
skipjack (Euthynnus
lornis), dolphin (Cor haena
sippurus), barvacuda.(Sphyracna ar enteay-aed
shark caught in the vicentty of the Eniwetok Proving Ground were collected at bor $s-of “landing in
Japan by Dr. Toshiharu Kawabata.“
Samples of the
organs and tissues of tunas comprised the major
part of the collection of more than 1,000 samples.
Wet weights were taken, the samples were dried,
and then sent to the Laboratory of Radiation Biology by Dr. Kawabata.
The samples of sea water, plankton, and fish
were counted for total beta radioactivity and selected samples were subjected to radiochemical
separation and analysis. These techniques and
methods have been described elsewhere (Donaldson
et al., 1956; Kawabata and Held, 1959; Lowman,
19865 Lowman et al., 1957; Palumbo and Lowman,
1958).
RESULTS
In the present paper the ratios of total
radioactivity and the percentage of total radioactivity contributed by individual radionuclides are considered with respect to sea
water and in the food chain composed of plankton, omnivorous fish, and carnivorous fish.
In
most cases the averages of several samples collected within a contaminated area are used in order
to reduce the effect of individual variability, a
factor which has been considered elsewhere (Bonham, 1958; Donaldson et al., 1956; Lowman 1958,
1960; Welander, 1958).
In studies. on the uptake of radioactivity
from sea water by plankton the fractionation of
the radioactivity between the water and plankton
ig usually compared on an equal volume or equal
weight basis and a concentration factor for the
radioactivity by the plankton may thus be derived. However, uptake of radioactivity by plankton from sea water may also be compared on the
basis of the fraction of the total radioactivity
in the water that is accumulated by the contained organiszs.
:
The importance of marine organisms in affecting the movement and distribution of radioactive
contamination in the sea has been emphasized by
several authors (Ketchum, 1957; Lowman, 1958;
Revelle and Shaefer, 1957). In areas of the sea
where relatively large populations of organisms
exist in relation to the total water volume the
organisms may exert an effect of this type
(Ketchum, 1957).
{Scientific names from: List of common and scientific
names of fishes from the United States and Canada, 2nd edition.
Am. Fish. Soc. Spec. Publ. 2.
102 pp.
(1960).
145
DOF ARcCHIV NS