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54 APPENDIX II
stable counterpart in the receiving water m ass, due to differences
in physico-chem ical states, which require time and therefore distance
to resolve.
Ultimately, this approach offers the possibility, at least so far
as food-chain problem s in relation to sea disposal are concerned,
of setting maximum perm issible concentrations for the water. We
are some way yet from being able to attain this objective because
many more data are required on trace element concentrations in
seawater and on their variability in time and space, on the central
problems of relative biological availability, and on the role of
particulate matter and organic com plexes in the cycling of trace
elements and their artificial radionuclides. Indeed, it is appropriate
to sound a note of caution since recent evidence in relation to 55Fe,
60Co and 65Zn, introduced to the marine environment from weapon-test
fall-out, suggests that rather large differences in specific activity
between the water and some elements of the biota can occur.
However, this was foreseen, in the original consideration of this
system , by the Isaacs Committee who allowed a reduction factor
of 10 in permitted concentrations to account for preferential uptake
of such complexed metal radionuclides. Even so, the factors
suggested by the recent findings would need to be m ore of the order
of 1 0 0- 1 0 0 0.
N evertheless, this method does seem to offer perhaps the only
sensible approach to the problem s encountered in assessing the
marine contamination consequences of a project such as the use of
nuclear explosives in the excavation of an A tlantic-Pacific interoceanic
canal. Here, many neutron-induced and fission-product
radionuclides can be shown to be below maximum perm issible
specific activity prior to the time of release, due to very thorough
mixing with stable nuclides from the geological matrix in which the
explosion takes place. Since these will also presumably be in the
same physico-chem ical states after such intimate mixing, their
biological availability and ultimate reconcentration in foods and
humans should be governed by the specific activity model.
The consequences of this system for marine monitoring requirements,
so far as they were considered by the Isaacs Committee at
the time, involved the sampling of all marine foodstuffs and organisms
of com m ercial importance and their analysis for radionuclides and
stable nuclides to provide data on both the curie quantities and the
specific activity. Thus, although only an initial requirement in
that once the validity of the specific activity model for the particular
situation had been demonstrated it could be considerably relaxed,