HYDROPHOBIC C-18 BOUND ORGANIC-COMPLEXES OF CHROMIUM AND THEIR POTENTIAL IMPACT ON THE GEOCHEMISTRY OF CHROMIUM IN NATURAL-WATERS

The complexation of aqueous, inorganic chromium by naturally occurring , relatively hydrophobic dissolved organic matter was investigated in a wide variety of natural waters. Levels of complexed chromium ranged from a few picomolar in open ocean organic-poor waters to several nano molar in inland DOM-rich waters. Organic chromium concentrations were positively correlated to both dissolved organic carbon and UV absorban ce. Humic substances appear to be important complexing agents in all w aters studied. Photolysis experiments indicated that the organo-chromi um species were photodegradable, with significant degradation occurrin g even after short-term exposure to ambient sunlight. Laboratory spike experiments with inorganic chromium standards indicated that the comp lexation was rapid with the majority of the metal bound within the fir st 2 h. The existence of organically bound Cr and its photoreactivity may explain some of the inconsistencies regarding chromium chemistry i n natural waters and shed new insight into the cycling of this importa nt trace metal in the aquatic environment.