Chromium species in the Columbia River and estuary1

Columbia River and estuary samples were analyzed to determine dissolved Cr species and particulate Cr concentrations. Flocculation and spike experiments were done to elucidate the processes controlling the distribution of Cr. River water contained an average of 3.2 nM dissolved Cr (98% as CrO42−) and 1.8 nM particulate Cr; estuary samples contained an average of 2.4 nM dissolved Cr and 2.8 nM particulate Cr. Dilution plots suggest that CrO42− is conservative in the estuary, while flocculation processes increase the Cr(particulate) and Cr(III) concentrations. Up to 28% of the dissolved Cr in river water could be removed by adsorption onto or flocculation with freshly formed particles. Over 70% of added Cr(III) was removed by adsorption onto particles and container walls within 1 h; CrO42− spikes behaved conservatively.