Determination of Antibiotics in the Swedish Environment with Emphasis on Sewage Treatment Plants
Methods were developed for determining levels in environmental samples of twelve antibiotics that are commonly used in human medicine: trimethoprim and substances from the following groups: fluoroquinolones, sulfonamides, penicillins, cephalosporines, nitroimidazoles, tetracyclines and macrolides. These substances were extracted from liquid and solid samples by solid phase extraction and ultrasonic-assisted liquid/solid extraction, respectively. Liquid chromatography tandem mass spectrometry was then used to separate and quantify them, and internal standards were added to improve the accuracy and precision of the determinations. Extraction yields from aqueous and solid phases were in the ranges 50 - 100% and 14 - 100%, respectively. Concentrations and mass flows of antibiotic substances were determined in a hospital effluent and in the raw sewage water, final effluent, and sludge from five sewage treatment plants (STPs) scattered across Sweden. High levels (in the µg/L range) of ciprofloxacin (a fluoroquinolone) and metronidazole (a nitroimidazole), were found in the hospital effluent. The screening study of the five sewage treatment plants revealed that norfloxacin, ofloxacin, ciprofloxacin, and doxycycline were frequently present in the raw sewage water, final effluent and sludge. Trimethoprim and sulfamethoxazole were not detected in the sludge, but these substances were present in the final effluents at concentrations close to those of the raw sewage water. In the aqueous phase, these six antibiotics were present in the ng/L range and in the solid phase, norfloxacin, ofloxacin, ciprofloxacin, and doxycycline were present in the low mg/kg range. The behaviour of the antibiotic substances during sewage water treatment was also investigated in one of the STPs. The two fluoroquinolones, norfloxacin and ciprofloxacin, sorbed to sludge, and less than 5% of the total amounts that entered the STP were found in the final effluent. In sludge, the corresponding figure was 70%. Results from a process in which digested dewatered sludge was treated with heat (producing pellets) indicated that approximately 50% of the two fluoroquinolones had been degraded. Trimethoprim did not sorb to sludge and 100% of its total amount was found in the final effluent. Theoretical calculations of concentrations and mass flows correlated well with quantitative results for the antibiotics that were frequently detected, but not for the others. In order to increase the accuracy of the calculations, the stability and phase distribution of the antibiotics should be considered. The effects of antibiotics present in the environment are currently unknown. Results of test protocols to assess their toxicity are often irrelevant, and there have been few tests in which organisms have been chronically exposed to biologically active substances at low concentrations. In addition, these tests have not addressed the immense potential of antibiotics in the environment to induce the development of resistant strains of bacteria and to maintain populations of resistant strains. Further studies of the occurrence, fate, and, effects of antibiotic substances in the environment are required.
Source Type:Doctoral Dissertation
Keywords:NATURAL SCIENCES; Chemistry; Environmental chemistry; antibiotics; environment; sewage treatment plants; antibiotika; miljö; avloppsreningsverk
Date of Publication:01/01/2006