Nuclear and isotopic techniques for investigating marine pollution

Seawater is a solution of largely uniform composition which varies in concentration (salinity) from place to place. A quantitative knowledge of vertical mixing is vital if we are to understand the ocean's capacity for assimilating contaminants (introduced from terrestrial sources or as a result of dumping), and as a receptor for ''greenhouse gases''. Now that tritium is no longer convenient as an ocean-scale tracer, the search is continuing for other longer-lived radionuclides which reflect mixing processes. Suitable candidates are krypton-81 (half life 2.1 x 105 years), which is an inert but not very soluble fission product that may reflect air-sea exchange; neptunium-237, mainly introduced as a waste product of nuclear fuel or reprocessing plants but with a very long half-life (2.1 x 106 years); and iodine-129, a fairly conservative fission product with a half life of about 107 years. The problem with using these potential tracers is their low concentration and weak radioactivity. The IAEA's Marine Environment Laboratory (IAEA-MEL) in Monaco is currently investigating new ''non-nuclear'' techniques for measuring some of these tracers using inductively coupled plasma mass spectrometry (ICP-MS). This search may eventually provide oceanographers with new tools to track the pathway and dispersion of contaminants, whether nuclear or non-nuclear, and to model the ocean's capacity for assimilating them. 4 figs