Oxypurinol - A novel marker for wastewater contamination of the aquatic environment.

The anti-gout agent allopurinol is one of the most prescribed pharmaceuticals in Germany and is widely metabolized into oxypurinol (80%) as well as the corresponding riboside conjugates (10%) within the human body. To investigate the occurrence of allopurinol and oxypurinol in the urban water cycle an analytical method was developed based on solid phase extraction (SPE) and subsequent liquid chromatography electrospray-ionization tandem mass spectrometry (LC-MS/MS). In raw wastewater concentration levels of oxypurinol ranged up to 26.6 μg L(-1), whereas allopurinol was not detected at all. In wastewater treatment plant (WWTP) effluents, concentrations of allopurinol were <LOQ, whereas oxypurinol concentrations ranged from 2.3 μg L(-1) to 21.7 μg L(-1). Elevated concentrations of oxypurinol in biologically treated wastewater originate from the transformation of allopurinol as well as the cleavage of allopurinol-9-riboside, which was confirmed by laboratory experiments with activated sludge taken from a municipal WWTP. Further tracking of oxypurinol in the urban water cycle revealed its presence in rivers and streams (up to 22.6 μg L(-1)), groundwater (up to 0.38 μg L(-1)) as well as in finished drinking water (up to 0.30 μg L(-1)). Due to the high biological stability and the almost ubiquitous presence in the urban water cycle at elevated concentrations, oxypurinol might be used as marker for domestic wastewater in the environment. This was confirmed by correlation analysis to other wastewater markers with strong correlations of the concentrations of oxypurinol and carbamazepine (r(2) = 0.89) as well as of oxypurinol and primidone (r(2) = 0.82).