Environ. Sci. Technol. 2009, 43, 8587–8592
Photochemical Fate of Sulfadimethoxine in Aquaculture Waters JENNIFER J. GUERARD,† Y U - P I N G C H I N , * ,† H E A T H M A S H , ‡ A N D CHRISTOPHER M. HADAD§ School of Earth Sciences and Environmental Sciences Graduate Program, The Ohio State University, 125 S. Oval Mall, Columbus Ohio 43210. U.S. Environmental Protection Agency, NRMRL/WSWRD/TTEB, 26 W. Martin Luther King Dr. Cincinnati Ohio 45268, and Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus Ohio 43210
Received July 9, 2009. Revised manuscript received September 18, 2009. Accepted September 18, 2009.
Sulfadimethoxine (SDM) is an antibiotic often used in combination with ormetoprim to prevent the spread of disease in freshwater aquaculture. It is known to undergo photochemical degradation in natural sunlit surface waters, but the role of dissolved organic matter (DOM) in this process is poorly understood. Our results show that water from a eutrophic catfish pond at the Mississippi State University Delta Research and Extension Center facility in Stoneville, MS facilitates the rapid phototransformation of SDM. In contrast, water from a nearby stream (Deer Creek) whose DOM is derived from allochthonous precursors does not enhance SDM photodegradation. We attribute these disparate results to DOM composition, whereby dissolved organic matter originating from highly eutrophic water bodies is a better SDM photosensitizer. Experiments conducted concurrently using respective autochthonous (Pony Lake, Antarctica) and allochthonous (Suwannee River) derived fulvic acids corroborate these findings. Scavenging experiments and experiments conducted anoxically show that the main indirect photodegradation pathway occurs by triplet excited-state DOM oxidation. Finally, transformation products assayed by mass spectrometry reveal the same major SDM photoproducts in the presence and absence of dissolved organic matter.
Introduction The high density of catfish in aquaculture ponds makes the spread of disease a real and costly concern, and antibiotics are crucial to ensure the survival of fish. Sulfadimethoxine (SDM) is used in freshwater aquaculture as an antibiotic in a mixture with ormetoprim called Romet 30 to prevent the spread of disease in these environments. Catfish ponds are unique relative to natural water bodies due to their design, as they tend to be shallow and lack both shade and a transitory littoral zone. A large portion of the pond’s surface is exposed to sunlight making them ideally suited for photoreactions. * Corresponding author phone: (614) 292-7637. fax: (614)292-7688; e-mail:
[email protected]. † School of Earth Sciences and Environmental Sciences Graduate Program, The Ohio State University. ‡ U.S. Environmental Protection Agency. § Department of Chemistry, The Ohio State University. 10.1021/es9020537 CCC: $40.75
Published on Web 10/19/2009
2009 American Chemical Society
Conversely, their highly eutrophic nature limits sunlight penetration in the water column. Sulfadimethoxine absorbs light in the UV region rendering it susceptible to direct and possibly indirect photodegradation in the presence of photosensitizers such as dissolved organic matter (DOM) (1). In seawater where DOM levels are low (
