M7 AM Metals in the Environment: Chemistry and Fate Issues
Monday, 14 November 2005: 8:00 AM - 11:40 AM in 327-329
(BRO-1117-832713) Photochemical control of copper speciation by dissolved organic matter in Rocky Mountain Streams, Colorado USA.
Brooks, M1, Clements, W1, McKnight, D2, 1 Colorado State University, Fort Collins, CO, USA2 University of Colorado, Boulder, CO, USA
ABSTRACT- We investigated photochemical, source, and seasonal effects on copper (Cu) complexation by dissolved organic matter (DOM). Cu-DOM complexation regulates Cu toxicity by decreasing the activity of the cupric ion ({Cu2+}), the most bioavailable Cu species. Because DOM is photochemically unstable, we analyzed Cu-DOM complexation before and after photooxidation of DOM collected from 3 wetlands and 3 rivers during spring run off and late summer (n = 12 DOM solutions). After irradiation of DOM solutions for 24 h in a solar simulator, (∼4 d of sunlight), we analyzed Cu-DOM complexation during potentiometric titrations of Cu into dissolved organic carbon (DOC) concentrations of 5 mg L-1. Across the range of titrations (7.8×10-8 to 8.7×10-6 
mol Cu L-1), photooxidation of DOM decreased Cu complexation, increasing {Cu2+} by 154% in 10 DOM types. However, in another DOM solution irradiation enhanced Cu complexation and decreased {Cu2+} by 30% but had no net effect on a final DOM solution (8 + 7%, mean + SD). Cu-DOM complexation did not vary between wetland versus riverine sources of DOM before or after irradiation. Similar Cu complexation before irradiation decreased significantly more during photooxidation of spring DOM (-184%) than summer DOM (-144%). Although fluorescence of DOM did not covary with Cu-DOM complexation, the specific ultraviolet absorbance (SUVA; absorbance254 nm per mg DOC) explained 52 to 70% of the variation in Cu complexation regardless of DOM source, season, or extent of photooxidation.
Key words: copper, photochemistry, DOM, bioavailability