In vitro studies of the fate of sulfadimethoxine and ormetoprim in the aquatic environment

These studies showed sulfadimethoxine and ormetoprim to be stable at salinities of 0 and 30 ppt and at pHs of 2, 7, and 12 for a period of 1 year. Sulfadimethoxine was stable at 25 degreesC and 37 degreesC, but showed a marked decrease in concentration at 4 degreesC. Warming of the 4 degreesC sample resulted in a return to original drug levels indicating that the drug had redistributed out of the aquatic phase at the lower temperature, Ormetoprim concentrations were stable at all temperatures evaluated. The concentrations of both sulfadimethoxine and ormetoprim were unaffected by the presence of silica sand, high density poly-ethylene, or poly-vinyl chloride. The presence of bentonite clay caused a reduction in ormetoprim concentrations while sulfadimethoxine was unchanged by this substrate. Acidification of the sample containing the bentonite clay resulted in a return of ormetoprim concentration to original levels. From these studies, it is apparent that the potential environmental half-lives for these drugs must exceed 1 year and are likely to be several years in duration. (C) 2001 Elsevier Science B.V. All rights reserved.