01/01/2003

Degradation behaviour of antibiotic drugs

German Federal Environment Agency (reserach project FKZ: 298 63 722, 1999-2003)

Sponsor:

German Environmental Agency, Dessau (298 637 22)

Realisation:

Hydrotox GmbH, Stefan Gartiser, Elke Urich

Within the framework project:

Inflow of Antibiotics in the Aquatic Environment - Testing the Biological Degradability and Influence on the Cleaning Efficiency of Municipal Sewage Treatment Plants - Identification of Possible Risk Fields

Institute of Environmental Medicine and Hospital Epidemiology, Prof. Dr. Klaus Kümmerer (Project management)

Project duration:

August 1999 – August 2003

Within the framework project Hydrotox was commissioned to carry out the partial project "Investigation of the aerobic and anaerobic degradability and of the anaerobic inhibition of antibiotics in standardised test systems".

Summary

The investigation of biodegradation of antibiotics must meet special demands due to their bactericidal effects. One aspect of the experimental work was therefore dedicated to the development of suitable test methods.

The following testing methods were applied:

Inherent biodegradability in the CO2/DOC Combination test

Principally, all test methods based only on the decreasing of soluble organic carbon (DOC) as an end point (e.g. Zahn-Wellens test) cannot distinguish between elimination due to biological degradation and elimination due to physical-chemical factors (such as adsorption). The test results are therefore interpreted primarily as “elimination” and not as “biodegradation“. On the other hand, adsorption with subsequent biodegradation is the fundament of the activated sludge treatment process and the adsorbed fraction is not principally prevented from biodegradation.

By a combination of distinct end points (CO2, DOC) the mineralised fraction can be distinguished from the adsorbed fraction. Following ISO 14852 and ISO 9439, this method has been optimized during the project. Benzylpenicillin was determined as being completely mineralised ultimately. Besides, only Amoxicillin was biodegraded to a partial extent and after a lag phase of 14 days (up to 60%). Tetracycline showed a DOC elimination curve typical for biodegradation processes, which was not confirmed by the CO2-evolution. This substance would misleadingly be classified as biodegradable if considering only its DOC-elimination. On the contrary, the DOC-elimination of Nystatin declined due to desorption processes. As measured in parallel controls, some antibiotics caused inhibitory effects which could hinder their biological degradation. All other antibiotics are classified as not inherently biodegradable.

Anaerobic inhibition and biodegradation

ISO standards 13641 (2003) and 11734 (1999) were used for assessing the anaerobic inhibition of 16 antibiotics and the anaerobic biodegradability of 9 antibiotics, respectively. Digestion sludge from a municipal sewage treatment plant (1 g/L d. s.) was used as inoculum in both tests. Most antibiotics showed only moderate inhibition effects after a 7 day incubation period, with EC50 values between 24 mg/L and more than 1000 mg/L (equal to mg/g d.s.). In contrast, Metronidazole was decisively toxic to anaerobic bacteria with an EC50 of 0.7 mg/L. In the anaerobic degradation tests according to ISO standard 11734 (1995), only Benzylpenicillin showed partial ultimate biodegradation after 60 days, and most antibiotics inhibited the digesting sludge in the respective parallel tested inhibition controls.

Further information

The final report (376 pages) will be published in German by the German Environmental Agency. A pdf of the report written in German can be downloaded Leitet Herunterladen der Datei einhere.  

Öffnet internen Link im aktuellen FensterPart of the results have been presented at SEATC conferences and have been published in Chemosphere.

Contact Person

Dr. Stefan Gartiser (Öffnet ein Fenster zum Versenden der E-Mailgartiser(at)hydrotox.de, Tel: +49-(0)761-45512-24)

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