Comparison of changes in metal toxicity following exposure of water with high dissolved organic carbon content to solar, UV-B and UV-A radiation.
This study examines the effects of natural solar radiation on the metal-binding capacity of dissolved organic matter (DOM). Newington Bog water (35.5 mg L(-1) dissolved organic carbon [DOC]) was irradiated for 20 days under UV-B lamps in the laboratory and under natural solar radiation. In the presence of irradiated DOM, IC(50) (contaminant concentration required to reduce algal growth by 50%) was significantly decreased with UV-B treatment for four metals: Pb, 64%; Cu, 63%; Ni, 35% and Cd, 40%. Solar radiation also significantly decreased IC(50) of Pb (58%) and Cu (49%), DOC concentration (11%), DOM fluorescence (DOMFL, 33%) and DOC-specific UV absorbance. Further experiments on Raisin River water (20.7 mg DOC L(-1)) exposed to 20 days of artificial UV-A and UV-B radiation produced significant decreases in IC(50) for Cu (48%) with UV-A and for Pb (43%) with UV-B. DOC concentration was decreased 20% by UV-B and 24% by UV-A. DOMFL decreased 51.5% in the first 5 days of UV-A exposure, an effect that was not observed with the UV-B treatment. The UV-A treatment decreased UV absorbance more at longer wavelengths and over a broader wavelength band than did the UV-B treatment. Change in toxicity with UV irradiation was inconsistent among the metals tested in this study, indicating that some organic metal-binding ligands were more quickly removed or altered than others. The DOM remaining after irradiation appears to be qualitatively different from the unirradiated DOM. The much greater irradiance of UV-A makes its contribution to the removal and/or alteration of DOM at least as important as the influence of higher energy UV-B.
Winch
Susan
S
Department of Earth Science,University of Ottawa, Ottawa, ON, Canada. swinch@science.uottawa.ca
Lean
David
D
D001681:Biological Assay; D002244:Carbon / Q000737:chemistry*; D056890:Eukaryota / Q000187:drug effects*; D020128:Inhibitory Concentration 50; D019216:Metals, Heavy / Q000032:analysis / Q000633:toxicity*; D009864:Ontario; D009930:Organic Chemicals / Q000032:analysis / Q000528:radiation effects*; D045483:Rivers / Q000737:chemistry / Q000382:microbiology; D012988:Soil Microbiology; D014466:Ultraviolet Rays; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000528:radiation effects*; D018508:Water Purification / Q000379:methods
D019216:Metals, Heavy; D009930:Organic Chemicals; D014874:Water Pollutants, Chemical; D002244:Carbon