Understanding the influence of dissolved organic matter on the photochemical fate of the antibiotics sulfadimethoxine and ormetoprim

Titel:	Understanding the influence of dissolved organic matter on the photochemical fate of the antibiotics sulfadimethoxine and ormetoprim
Kategorie:	Diverses
Datum:	16. Sept. 2009, 09:00 Uhr -
Ort:	Eawag Dübendorf
	FC E-71
Referenten:	Jennifer Guerard, PhD, Environmental Sciences, The Ohio State University
Download:	als Kalender-Eintrag

Sulfadimethoxine (SDM) and ormetoprim (OMP) are antibiotics often used in combination in a medicated feed to prevent the spread of disease in freshwater aquaculture.  While these compounds are known to undergo photochemical degradation in natural sunlit surface waters, the role of dissolved organic matter (DOM) in this process is not well understood.  Our results show that SDM photodegradation is rapid in water from a eutrophic catfish pond at the USDA facility in Stoneville, Mississippi, while no enhancement of photodegradation was seen in a nearby stream (Deer Creek). 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 microbially (Pony Lake, Antarctica) and terrestrially (Suwannee River) derived fulvic acids corroborate these findings.  Scavenging experiments and experiments conducted anoxically corroborates that the main indirect photodegradation pathway occurs by triplet excited-state DOM oxidation.  Finally, photo-derivatives assayed by mass spectrometry reveal the same major SDM photoproducts in the presence and absence of DOM.  OMP was observed to degrade by different mechanisms than SDM, and was found to be reactive to hydroxyl radical.  The role of singlet oxygen was also investigated.   Fulvic acids from both the catfish pond waters and Deer Creek were isolated and characterized.  While these waters are located in very close proximity to each other, their fulvic isolates show characteristics similar to IHSS reference samples as end members of the DOM source spectrum (microbial v. terrestrial).   Overall, the DOM source composition can play a significant role in the photochemical fate of these compounds in aquatic systems.