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Thursday 01 August 2002

Fluoroquinolones’ fate measured in waste and natural waters

By: Science News

A detailed account of the mass flows of fluoroquinolone antibacterial agents (FQs) in a Swiss watershed, which is posted on the ES&T Web site (10.1021/es0256212), shows they are found at very low concentrations in natural waters.

The study, conducted by Eva Golet, Alfredo Alder, and Walter Giger from the Swiss Federal Institute of Environmental Science and Technology (EAWAG), finds that a large fraction of the FQs entering wastewater plants is removed during treatment, with the remaining FQs in the effluent further reduced as they flow downstream. However, questions remain about the dangers of FQs in biosolids and soil.

FQs represent a very potent class of human and veterinary antibiotics that are often used as the second line of defense when other treatments fail, but concern is growing that frequent use could lead to antibiotic-resistant bacteria. The U.S. Food and Drug Administration’s Center for Veterinary Medicine has proposed banning enrofloxacin, one of the major FQs in the United States, for use in poultry farming because of evidence that shows it contributes to the development of FQ-resistant Campylobacter infections in humans. And in a 2001 discussion paper, the European Agency for the Evaluation of Medicinal Products proposed that an environmental risk assessment be required for human medicinal products that have predicted concentrations in surface water greater than 0.01 micrograms per liter.

Eva Golet and colleagues analyzed raw sewage, treated wastewater effluents, and river water samples at multiple locations in the densely populated Glatt River watershed bordering Zürich for ciprofloxacin and norfloxacin, the most widely consumed FQs in Switzerland. Concentrations of each antibiotic in raw sewage ranged from 255 to 568 nanograms per liter (ng/L), but dropped by 80% during wastewater treatment because of strong sorption of FQs to sewage sludge. The mass balances show that another 48–66% of the remaining FQs were not traceable in the river waters downstream of treatment facilities where the waters enter the River Rhine, as a result of sediment deposition or possibly photolysis.

The Swiss study could well serve as a model for how fate studies of pharmaceuticals should be done, Golet says. Most other studies have relied on grab samples taken from a large area, whereas this study has focused on the fate and transport in a tightly defined region.

The paper also includes a risk assessment, which is based on European Union guidelines, that implies the FQs pose only a low risk of toxicitiy in aquatic environments. However, a second part of the study, to be submitted soon, finds that FQs accumulate in sewage sludge and subsequently persist in soil after biosolids made from that sludge are applied as fertilizer, Golet says. The application of biosolids to agricultural fields has been the subject of controversy in Switzerland for several years. Likewise, a recent report by the U.S. National Research Council on land application of biosolids strongly recommends more detailed research on pharmaceuticals in sewage sludge.

“This is a truly exceptional study”, because it is the first time that a comprehensive mass balance has been determined for a pharmaceutical, says Thomas Ternes of the Institute for Water Research and Water Technology in Wiesbaden, Germany, and one of the first researchers to recognize the environmental hazard of pharmaceuticals. Further research should go toward a broader risk assessment of FQs, including looking at their effects on soil organisms and the generation of antibiotic resistances in bacteria, which could occur at concentrations much below the toxicity level, he emphasizes.

A detailed account of the mass flows of fluoroquinolone antibacterial agents (FQs) in a Swiss watershed, which is posted on the ES&T Web site (10.1021/es0256212), shows they are found at very low concentrations in natural waters. The study, conducted by Eva Golet, Alfredo Alder, and Walter Giger from the Swiss Federal Institute of Environmental Science and Technology (EAWAG), finds that a large fraction of the FQs entering wastewater plants is removed during treatment, with the remaining FQs in the effluent further reduced as they flow downstream. However, questions remain about the dangers of FQs in biosolids and soil.

FQs represent a very potent class of human and veterinary antibiotics that are often used as the second line of defense when other treatments fail, but concern is growing that frequent use could lead to antibiotic-resistant bacteria. The U.S. Food and Drug Administration’s Center for Veterinary Medicine has proposed banning enrofloxacin, one of the major FQs in the United States, for use in poultry farming because of evidence that shows it contributes to the development of FQ-resistant Campylobacter infections in humans. And in a 2001 discussion paper, the European Agency for the Evaluation of Medicinal Products proposed that an environmental risk assessment be required for human medicinal products that have predicted concentrations in surface water greater than 0.01 micrograms per liter.

Eva Golet and colleagues analyzed raw sewage, treated wastewater effluents, and river water samples at multiple locations in the densely populated Glatt River watershed bordering Zürich for ciprofloxacin and norfloxacin, the most widely consumed FQs in Switzerland. Concentrations of each antibiotic in raw sewage ranged from 255 to 568 nanograms per liter (ng/L), but dropped by 80% during wastewater treatment because of strong sorption of FQs to sewage sludge. The mass balances show that another 48–66% of the remaining FQs were not traceable in the river waters downstream of treatment facilities where the waters enter the River Rhine, as a result of sediment deposition or possibly photolysis.

The Swiss study could well serve as a model for how fate studies of pharmaceuticals should be done, Golet says. Most other studies have relied on grab samples taken from a large area, whereas this study has focused on the fate and transport in a tightly defined region.

The paper also includes a risk assessment, which is based on European Union guidelines, that implies the FQs pose only a low risk of toxicitiy in aquatic environments. However, a second part of the study, to be submitted soon, finds that FQs accumulate in sewage sludge and subsequently persist in soil after biosolids made from that sludge are applied as fertilizer, Golet says. The application of biosolids to agricultural fields has been the subject of controversy in Switzerland for several years. Likewise, a recent report by the U.S. National Research Council on land application of biosolids strongly recommends more detailed research on pharmaceuticals in sewage sludge.

“This is a truly exceptional study”, because it is the first time that a comprehensive mass balance has been determined for a pharmaceutical, says Thomas Ternes of the Institute for Water Research and Water Technology in Wiesbaden, Germany, and one of the first researchers to recognize the environmental hazard of pharmaceuticals. Further research should go toward a broader risk assessment of FQs, including looking at their effects on soil organisms and the generation of antibiotic resistances in bacteria, which could occur at concentrations much below the toxicity level, he emphasizes.

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