n two surveys made during 1958
uring the period less than 48 hours
3 collected at greater than one week
sar devices. The five samples taken
en subjected to radioactive fallout
jurvey
8 hours
Collett
of the plants.
Marsh Survey.
Survey
6 weeks
> 1 week
|
|
12
0
<1
0
|
3
5
|
2
8
1
0
23
0
6
0
2
0
69
3
0
0
0
2
2
7
0
|
0
5
1.4
0
0
20
0
0
9
ao
3
3
15
14
1
25
24
0
0
<1
1
|
0
0
0
0
0
0
0
|
0
|
|
|
|
2ments comprised 62% of the
eks accounted for 74% of the
(Zr95_-Nb®5 and Ru!°*—Rh®)
ie chemically similar anion or
ronment. Evidence that radioin observations on the uptake
known metabolic function.
[AN et al (19) found a neutron-
che first time. The isotope was
.(~50% of the total activity)
180 miles in diameter. About
ssociated with silica, probably
r samples was contributed by
srial containing the latter radiox filter with a pore size of 0.454.
i later. During the time between
moved 150 miles to the WSW,
ikton samples collected during
igh almost all the radioactivity
{n marine algae the level of W1® was related to the exposed surface area.
Radioactive tungsten is probably removed from organic surfaces in the sea
by exchange with the ions in the water.
The second process of accumulation of radioisotopes by marine organisms
is brought about by filter-feeding planktonic organisms which would accumulate both inorganic particles and microscopic organisms with their adsorbed ions. Some of the radioactivity contributed by the transition radioelements would probably be present in the area in combination with the
hydrated oxides of iron. Also the radioactive anions accumulated by plankton
would be largely associated with the same particles. GOLDBERG (34)
showed that a marine diatom was unable to take up ionic iron in the complexed form but readily assimilated particles of hydrated iron oxide. Thus,
in addition to the concentration of transition elements by the filter-feeding
plankton by direct surface adsorption, a further concentration of these elements
would occur through ingestion by these organisms of particles of hydrated
iron with associated radioelements, particles of organic detritus with adsorbed
radioelements, and contaminated microplankton.
Limited data from both control experiments (15) and field observations (4)
suggest that an important route for uptake of fallout radioisotopes by marine
animals is through the ingestion of particulate matter containing the radioactivity, whether the particles be inorganic or phytoplankton. CHrpman (15)
noted that, in addition to the filter-feeding animals, two species of algae were
also able to concentrate Ce!44 several times over the levels in the water although
the radioisotope was in the particulate form. The uptake of particulate material
may either involve adsorption of the particle on to the organism or the ingestion of the particulate material, which would include both food particles
and non-living particulate detritus.
The fractionation of introduced radioactive materials in the sea between
the macroplankton, microplankton, nannoplankton, non-living particulate
matter and colloidal and soluble fractions is important in the interpretation
of the deposition of radioisotopes in marine organisms or in the bottom of
the sea. In surveys at the Eniwetok Test Site the total activity in the samples
was subdivided into three fractions—-the macroplankton, the microplankton
plus particulate matter greater than 0.45 yx, and the soluble-colloidal material
less than 0.45 4. The macroplankton and some microplankton were collected
by means of half-metre nets of No. 6 mesh, and the nannoplankton plus
inorganic particulate matter was collected by filtering 500 ml of sea-water,
taken at various depths, through a millepore filter with a pore size of 0.45 u.
A portion of the filtrate was then treated with concentrated CaCo, to precipitate practically all the radioelements from the water. The latter fraction
eluded colloidal and soluble material.
Although some microplankton was undoubtedly retained by the filter
123
“AP
ae.
at
?
shoboth
in the water samples was contributed by this radioisotope. Zr°°—Nb** were
present in the plankton.
Although there wasa high initial uptake of W1%5 by the plankton, probably
by surface adsorption, the loss of the isotope was rapid. W1*° also forms
complexes with the surfaces of terrestrial plants and marine algae. In
terrestrial plants it remains complexed to the surfaces of leaves exposed to
almost daily rainfall, and the degree of binding appears to be directly related
to the waxiness of the leaf surface. It was not present in the internal parts
ce
WR