Researchers investigating the fate and transport of pharmaceuticals in aquatic environments have previously reported surprisingly low levels of antibiotics in rivers and streams, despite their widespread usage. Because most antibiotics are hydrophobic, many researchers have speculated that the drugs accumulate in sewage sludge and sludge-treated agricultural soils, but until now analytical methods were not available for confirmation.

Alfredo C. Adler and colleagues at the Swiss Federal Institute for Environmental Science and Technology (EAWAG) and the Swiss Federal Institute of Technology–Zürich have developed a method to quantify the two most prescribed human antibiotics in Switzerland, ciprofloxin and norfloxacin, in sewage sludge and sludge-treated soil. They report that fluoroquinolone antibacterial agents persist in sewage sludge and are likely to accumulate in soil when sludge is applied to land as fertilizer.

To obtain high fluoroquinolone recoveries, the researchers used two separate extraction procedures, accelerated solvent extraction and solid-phase extraction. When coupled with a known liquid chromatography fluorescence detection method, they report a limit of quantification of 0.45 and 0.18 milligrams per kilogram (mg/kg) of dry matter for sewage sludge and sludge-treated soils, respectively.

To test the new method, the researchers analyzed both anaerobically treated and untreated sewage sludge from wastewater treatment plants near Zürich. Concentrations of ciprofloxacin and norfloxacin ranged from 1.40 to 2.42 mg/kg of dry matter. The researchers are confident that the new method will transfer to other similar antibiotics and environmental matrixes with little modification. (Anal. Chem. 2002, 74, 5455–5462)