Nickel-63 in Marine and Terrestrial Biota, Soil, and Sediment
Abstract. A previously unreported radionuclide, nickel-63 (half-life, 92 years),
produced in the testing of nuclear devices, was measured in biological and environmental samples from areas of the Pacific Ocean and the eastern seaboard
of the United States. The concentrations of nickel-63 are low (maximum of 163
those of 3H and*!4C. Compared to
other radionuclides produced in weapons testing, the radiological hazard
from ®Ni is much less and therefore
was of little concern in the evaluation
of the effects of radioactivity on biota.
disintegrations per minute per gram of dry weight), but this radionuclide may be
The specificity of the required analysis
and the lesser hazard probably account
for the fact that measurements of the
concentrations of “Ni in the environment have not been made until now.
that stable nickel in these materials
However, the use of radioisotopes, both
artificial and natural, as tracers of
oceanic currents and water mixing (3)
prompted us to look for @Ni since (i)
a useful tracer of oceanic processes because of its long half-life and long residence
time in the ocean.
A review of the concentrations of
radionuclides measured in biota of the
Pacific Proving Ground during testing
of thermonuclear devices indicated that
the production of measurable quantities
of the radionuclide “Ni was probable.
The large amounts of ®5Fe, Zn, 57Co,
58Co, and ®Co reported by Lowman
(7) resulted largely from nuclear interactions in the structural material used
in and around the device. We concluded
would yield “Ni through the (n,y) activation process. The cross section for
this reaction is large (15 barns).
Detection of “Ni by other than
specific radiochemical separation and
liquid scintillation counting is doubtful.
The radionuclide decays by the emis-
sion of a beta particle (100 percent)
whose maximum energy is only 67 kev
(2), an energy intermediate between
Table 1. Concentration of nickel-63 in environmental samples. Errors given are the 95 percent
confidence levels (2 o) of the count rate measurements.
.
Location
Date of
collection
Sample
Concentration
of nickel-63
(disintegrations per
minute per gram
of dry weight)
Belle Islet
Belle Islet
Belle [Islet
Elugelab Islet
Engebi Islet
Aaraanbiru Islet
Engebi Islet
Eniwetok Atoll
Soil
May 1954
Clam kidney*
August 1964
Clam kidney”
August 1964
Crater sediment
August 1964
Soil
August 1958
Clam kidneyt
September 1958
Ciam kidneyt
August 1964
8.2 +02
158.0 + 2.6
67.8 + 1.6
96 +02
75 + 2
41.2 + 6
11.4 + 6
Bokonejien Islet
Namu Islet
Bokororyuru Islet
Bikini Atoll
Crater sediment
May 1967
Soil
August 1964
Clam kidneyt
August 1964
80.0 + 1.0
9.8 +0.2
163.0 + 3.5
Kabelle Islet
Kabelle Islet
Rongelap Atoll
Soil (0-0.6 cm)
September 1961
Soil (0.6-1.3 cm)
September 1961
Christmas Island
Clam kidneyt
April 1962
Penrhyn Atoll
Clam kidney*
April 1962
44°38'N,125°20°W
44°38'N,125°20'W
44°38'N,125°20'W
47°39N,173°OS W
50°30/N,167°OW
30°N,140°W
Northeast Pacific Ocean
Chaetognaths§
February 1964
Chaetognaths
February 1964
Chaetognaths
April 1964
Chaetognaths
June 1964
Squid ||
‘October 1965
Squid ||
August 1966
Squid4
July 1965
Amchitka Island
Amchitka Island
-~Lichen#
Lichen
Aleutian Islands
October 1965
October 1965
Eastern seaboard
Composite shellfish
August 1963
* Tridacna crocea.
t Tridacna sp.
tTridacna gigas.
§ Sagitta elegans.
sp.
{ Stenoteuthis bartrami.
# Principally Cladonia pacificia.
3.1
0.5
+ 0,2
= .06
91+
.14
424 14
93 .80
2.3 +1.0
40 +30
45 + 2.4
0.19 + 0.08
13 08
38+ 24
A8+
35
.04
.04
02+
.002
|] OQnychoteurhis
the residence time of nickel in the
ocean is 1.8 X 104 years; (ii) nickel is
a constituent of ferromanganese minerals, comprising some 0.4 percent (by
weight) (4); and (iii) Ni has a radioactive half-life of 92 years and is thus
a more useful long-term tracer than
other radionuclides of the transition
elements which have been found in the
oceans but which have half-lives of a
few years or less.
We separated nickel from biological
and environmental samples and other
elements by precipitation and solvent
extraction. Before dissolution of the
samples in concentrated nitric and perchloric acids, 6 mg of stable nickel
were added to each sample to serve as
both a carrier and a yield determinant.
Nickel was concentrated from the digest by precipitation of nickel 1,2-cycloheptanedione dioxime from acid solu-
tion (5). The precipitate was collected
by filtration, removed from the filter
by dissolution in 844 HNO,, and oxidized with perchloric acid to destroy
the organic matter; the nickel was con-
centrated again by a second precipitation with heptoxime. After dissolution
and oxidation of the second precipitate,
Ni(OH). was precipitated by the addition of NaOH. The precipitate was dissolved in 6N HCl, and the resultant
solution was extracted with 10 ml of a
solution of 10 percent Alamine-336 in
xylene. The phases were separated by
centrifugation, the organic layer was
decanted, and the nickel was again pre-
cipitated as the hydroxide. The hydroxide precipitate was prepared for liquid
scintillation counting (Packard Instrument liquid scintillation spectrometer
model 3375) by dissolution in 0.5
a ane TIVES