The Fate and Transport of the Antimicrobials Sulfadimethoxine and Ormetoprim in the Environment

Abstract

Over the past decade, there have been increasing concerns regarding antimicrobial contaminants in the environment. To date, there exists limited research regarding the fate of these compounds in the environment once discharged in human and animal waste. The fate and transport of two antimicrobials, sulfadimethoxine (SDM) and ormetoprim (OMP), was investigated in two soils and sand using several series of batch sorption equilibrium experiments as well as miscible displacement column studies. Because OMP and SDM are often administered in combination, their sorption and mobility was investigated in combination as co-solutes as well as individually as single solutes.

Results from multiple experiments indicate relative mobility and subsequent low sorption of these compounds in soils and sand. OMP illustrated a greater tendency to bind to soil than SDM and was quite retarded in column studies. Although OMP illustrated a fairly significant retardation; the compound was readily released from the soil and transported with the mobile water. Overall, sorption of both antimicrobials increased in soils and sand as the organic matter, clay content, and cation exchange capacity increased. Batch sorption experiments suggested an enhanced sorption of OMP when in combination with SDM; however, this was not observed in the column studies. Additionally, sorption results from batch and column experiments were inconsistent, leading to the notion of rate-limited sorption during antimicrobial transport. The results from these experiments confirm the potential threat to surface and groundwater by SDM and OMP. Because these compounds will be mobile in the environment, further research investigating their possible environmental impacts and developing management practices to reduce these impacts is necessary.