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 nanomolar in inland DOM-rich waters. Organic chromium concentrations were positively correlated to both dissolved organic carbon and UV absorbance. Humic substances appear to be important complexing agents in all waters studied. Photolysis experiments indicated that the organo-chromium species were photodegradable, with significant degradation occurring even after short-term exposure to ambient sunlight. Laboratory spike experiments with inorganic chromium standards indicated that the complexation was rapid with the majority of the metal bound within the first 2 h. The existence of organically bound Cr and its photoreactivity may explain some of the inconsistencies regarding chromium chemistry in natural waters and shed new insight into the cycling of this important trace metal in the aquatic environment.