| Summary: | Radioactive chromium-51, a waste byproduct from operation
of nuclear reactors at Hanford, Washington, has been followed down
the Columbia River and into the Pacific Ocean. Chemical factors
influencing the partitioning of ⁵¹Cr between solution and sediment
have been considered.
Chromium-5l, in a hexavalent oxyanion when introduced into the
Columbia River, largely remains in solution in a hexavalent anion
during its passage through the lower river and after its entrance
into the Pacific Ocean.
A minor fraction of Hanford-induced ⁵¹Cr becomes attached
to suspended particles and bottom sediments. Reduction of Cr(VI)
to Cr(III) apparently precedes or accompanies sorption. Iron oxides
appear to be the most important sorption substrate. Sediment
organic matter acts both as a reducing agent, making ⁵¹Cr less
soluble, and as a sorption substrate. Ion exchange on sediment
particles is not important in retention of ⁵¹Cr by Columbia River
sediment.
Chromium-51 is a sensitive and unique tracer for Columbia
River water at sea and has been used to trace the Columbia River
plume up to 525 km away from the mouth of the river.
Dispersion of ⁵¹Cr by the Columbia River system would be
adversely affected by: 1) lowered pH; 2) presence of particulate
organic wastes; 3) increased temperature; 4) increased biological
oxygen demand. These factors would increase the rate of uptake of
⁵¹Cr by sediments and thus increase the steady-state inventory of
⁵¹Cr on the bottom of the river. === Graduation date: 1967
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