Safety_Series_041_1975 - gnssn - International Atomic Energy ...

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This publication is no longer valid Please see http://www.ns-iaea.org/standards/ 54 APPENDIX II stable counterpart in the receiving water m ass, due to differences in physico-chem ical states,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,
This publication is no longer valid Please see http://www.ns-iaea.org/standards/ A PPENDIX II 55 the scale of effort is considerably: greater than that involved in the critical pathway approach at the same stage. Ultimately, perhaps, monitoring could be reduced to the sampling and determination of those nuclides at or near maximum specific activity in either the m ajor m aterials or the receiving water m ass, but even then the analytical effort involved would be considerable. The establishment of a satisfactory specific activity model im plies that adequate control can eventually be exercised by demonstrating that the concentrations in the water are below maximum specific activity, but representative sampling of open coastal seawater is a very difficult task and involves the establishment of a sampling network that is extensive in both time and space.
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