ZINC 65 IN EUPHAUSIIDS AS RELATED TO COLUMBIA RIVER WATER OFF TIIE OREGON COAST

Most of the zinc 65 in the northcast Pacific Ocean originates in the Cohunbia River as a result of the Hanford, Washington, nuclear reactor operations. The Colmnbia River is also the principal source of freshwater in the region, so that at certain seasons the pluiiie of the . river is dctcctablc far at sea bccausc of its low salinity. In an effort to dcterminc the fate of the river water at sea, euphausiids from the ocean off Oregon wcrc used as biological monitors. Zn”” content of euphallsiids was mcasurcd by gamma-ray spcctrometry, and relationships bctwcen Zn”” content and salinity distributions over the area were examined. Some correlations were apparent, but deviations occurred. For cxamplc, Zna levels remained fairly high off Oregon cvcn when Columbia River water was not cvidcnt as a low-salinity plume. This indicates that water from the Colmnbia River, which accumulates as a plume off Oregon in the summer, influcnccs the ZN” content in animals in the arca throughout the year, The long half-life of Zn”” in the mixed layer, diurnal migrations of cuphausiids, and seasonal rcvcrsal of currents all may contribute to the maintcnancc of this reservoir of ZnoG in the ocean off the Oregon coast. Outflow of the Columbia River dilutes the surface waters in certain sections of the northeast Pacific Ocean, forming a shallow lens or plume of low-salinity water that overrides more dense oceanic water. In summer, prevailing winds and currents carry this less saline water southward off the Oregon-California coast. In winter, owing to mixing and rcduccd Columbia River outflow, the plume becomes smaller and less distinct and appears to bc driven northw,ard by prevailing winds (Barnes and Paquette 1957; Anderson et al. 1961, 1962; Budinger, Coachman, and Barnes 1963). Water from the Columbia River is used to cool nuclear reactors at Hanford, Washington. The intense neutron flux in the rcactors activates certain trace elements in thl: coolant water. For cxamplc, an estimated 38 curies per day of ZnG5 (245-day half-life) passes Vancouver, Washington, en route to the sea. This leads to an cquilibhrium value of 14,000 c of this isotope in the Pacific Ocean as a result of Hanford activities ( Nelson 1961) . :Zinc 65 has been founcl in sessilc organisms along the Oregon-Washington coast (Watson, Davis, and Hanson 1961)) in marine plankton at some distance from short ( Osterbcrg 1962, 1963), and in marine sediments near the Columbia River (Osterbcrg, Kulm, and Byrne 1963). Zinc 65 in seawater is more difficult to detect because of the low concentrations that exist. It is the affinity 0E marine organisms for zinc that makes them useful monitors of Zn”‘). The constant low-level radioactivity in the Columbia River and the inherent sensitivity of radiotracer tcchniqucs invite an attempt to trace river water at sea by using marine animals which concentrate Zn”” to readily measurable levels. If ZnG5 is a characteristic unique to Columbia River water, and if marine organisms accurately rcflcct the radioactivity of their cnvironmcnt, then Zn”” in animals should be a good indicator of the presence of Columbia River water. This hypothesis is explored, using Ezcphazcsin p&f& as a monitor of Zn”“. Zinc 65 concentration in this abundant macroplankter is compared with salinity distribution in an effort to dclincatc seasonal distributions of Columbia River water in the ocean. WC thank R. W. Perkins of General Electric’s Hanford Laboratories for allowing us to use his equipment, and for his assistance with certain technical aspects of the gammaray spectromctry. WC are indebted to Harriet Van Arsdale, I. Lauren Larsen, Norman Cutshall, and the captain and crew of the RV Aconn for their work in the labo-