Fate of Selected Pharmaceuticals in Soil and Irrigation Water.

Pharmaceuticals are useful tools to prevent and treat human and animal diseases. Following administration, a significant fraction of pharmaceuticals is excreted unaltered into feces and urine and may enter the water ecosystem and soil through irrigation with recycled water. The primary concern with introducing pharmaceuticals in water and soil is the spread of pharmaceutical resistance genes. Understanding major factors influencing their environmental fate is consequently needed to reduce contamination and to set-up bioremediation technologies.

A series of laboratory studies were carried out to investigate the fate of selected pharmaceuticals in soil and irrigation water . The study included two veterinary antimicrobials, sulfamethazine and sulfachloropyridine, and the antiviral drug Tamiflu. In addition, a new and eco-friendly strategy for removing Tamiflu from waste water is proposed.

Average half-lives of sulfamethazine and sulfachloropyridine in two contrasting soils were 18.6 and 21.3 days, respectively. Presence of liquid swine slurry (5% v/w) decreased their persistence in soil. The lower persistence of the two sulfonamides in liquid swine slurry-amended soil was likely due to higher microbial activity, as compared to unamended soil, and/or to the greater bioavailability of the sulfonamides to degrading microorganisms, as estimated by sorption isotherms. DNA fingerprinting of the soil microbial community showed that concentrations of the two veterinary pharmaceuticals up to 100 mg g^-1 had no effect soil microorganisms.

Experiments conducted with irrigation water and water from different aquatic ecosystems showed that the antiviral drug Tamiflu has the potential to persist in the aquatic ecosystem. Approximately 65% of the initial amount remained in water at the end of the 36-day incubation period. Presence of sediments resulted in reduced Tamiflu persistence. The application of a new patent pending microbial formulation showed that the three pharmaceuticals can be rapidly removed from waste water thus permitting the use of pharmaceutical-free water for irrigation purposes.