CHROMIUM SPECIATION AND DISTRIBUTION IN THE GREAT-LAKES

A technique is described for selectively measuring the forms of chromi um in freshwater samples, with detection limits of 21 ng L(-1) for Cr( III), 4 ng L(-1) for Cr(VI), and 8 ng L(-1) for colloidal/organic Cr. Recovery of the Cr(VI) and Cr(III) spikes were consistently >90%, but only about 70% for the added organic Cr. When the method was applied t o samples from Lake Ontario, it was found that Cr(VI) made up 75-85% o f the dissolved Cr and that Cr(III) was consistently below the analyti cal detection limit. About 10% of the dissolved Cr was in the colloida l/organic form. Average concentrations of total dissolved Cr in the ep ilimnetic waters were found to be 69 ng L(-1) in Lake Superior, 136 ng L(-1) in Lake Erie, and 351 ng L(-1) in Lake Ontario. The increasing concentration of Cr down the Great Lakes watershed reflects the conser vative geochemical behavior of Cr(VI) and the increasing input of Cr f rom industrial and municipal sources.