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RADIOACTIVITY BACKGROUND in the OPEN SEA and
LAGOONS of the EN/IWETOK PROVING GROUND AREA
1.1
OBJECTIVE
A survey of the EPG was undertaken during the months of April and May 1956 to
determine the radioactivity background prior to the 1956 test series. The program
included radioactivity background studies of the water in the open ocean, the waters
of the lagoons, the sediments on the ocean and lagoon floors, and the biological life
associated with the above areas.
1.2
BACKGROUND
A study of radioactive contamination requires an understanding of the existing background intensities of both naturally occurring and artificially produced radioisotopes.
In an area where physical changes are constantly taking place, it is desirable to make
rapid in situ measurements.
The concentration of trace amounts of isotopes has been observed in marine organ-
isms. Laboratory experiments have shown the uptake and absorption of strontium and
yttrium by brown and green algae, vanadium by tunicates, and zinc and strontium by
fish. During Operation Wigwam, thousandfold concentrations of the fission products
were observed in some organisms, while other organisms from the same water mass
showed little or no uptake of the radioactive isotopes over the same period of time
(Reference 1).
The Japanese survey ships Shunkotsu-Maru during May and June of 1954, the DaifujiMaru during December 1954, and the Kagoshima University training vessel, Keiten-Maru,
during November and December 1954 and January 1955, detected radioactive contamina-~
tion in the Western Pacific and Coral Sea sea water, plankton, and edible fish (Reference
2).
The concentration of radioactivity detected in zooplankton was about 1,000 times, and
in some cases as much as 10,000 times, more than that in the sea water they inhabited.
Hundredfold variations of gross radioactivity were noted from one species to another.
Commercially important tune were found to contain someartificial isotopes. Radiozinc was detected in the viscera of several fish. Zn® apparently was highly concentrated
in certain organs of Katsuwonus pelamis (skipjack tuna) and Parathunnus sibi (big~eyed
tuna). Although Zn®is not a fission product, it has been detected by several investigators (Reference 3).
During March and April 1955, the U.S. Coast Guard cutter Taney on Operation Troll
traversed the Pacific Ocean collecting samples of water and plankton for radioanalysis.
Widespread low-level activity was found to exist in the Pacific Ocean. Water activity