[en] The long-term environmental behavior and ultimate fate of ¹²⁹I cannot be inferred with confidence from the well-studied short-lived isotope ¹³¹I. Furthermore ⁹⁹Tc does not resemble iodine in its soil/plant behavior, as has been assumed in the past. Therefore, its long-term behavior and ultimate fate remains uncertain. The quantitative measurement of ¹²⁹I and ⁹⁹Tc in environmental samples is also technically complex and costly. The ¹²⁹I can be measured in a variety of low-level environmental samples using neutron activation procedures. The ⁹⁹Tc still presents difficulties, but a sensitive mass spectrometric approach is under development for environmental application. In aquatic sediment studies, investigations have been directed toward measurement of the physicochemical properties of suspended and bottom sediments of the lower Columbia River watershed and radionuclide (⁹⁹Tc, ¹²⁹I) and trace metal speciation, transport and biological availability as influenced by sediment properties and seasonal and man-induced changes in watershed and river conditions