Screening of benzodiazepines in thirty European rivers

Pharmaceuticals as environmental contaminants have received a lot of interest over the past decade but, for several pharmaceuticals, relatively little is known about their occurrence in European surface waters. Benzodiazepines, a class of pharmaceuticals with anxiolytic properties, have received interest due to their behavioral modifying effect on exposed biota. In this study, our results show the presence of one or more benzodiazepine(s) in 86% of the analyzed surface water samples (n = 138) from 30 rivers, representing seven larger European catchments. Of the 13 benzodiazepines included in the study, we detected 9, which together showed median and mean concentrations (of the results above limit of quantification) of 5.4 and 9.6 ng L^-1, respectively. Four benzodiazepines (oxazepam, temazepam, clobazam, and bromazepam) were the most commonly detected. In particular, oxazepam had the highest frequency of detection (85%) and a maximum concentration of 61 ng L^-1. Temazepam and clobazam were found in 26% (maximum concentration of 39 ng L^-1) and 14% (maximum concentration of 11 ng L^-1) of the samples analyzed, respectively. Finally, bromazepam was found only in Germany and in 16 out of total 138 samples (12%), with a maximum concentration of 320 ng L^-1. This study clearly shows that benzodiazepines are common micro-contaminants of the largest European river systems at ng L^-1 levels. Although these concentrations are more than a magnitude lower than those reported to have effective effects on exposed biota, environmental effects cannot be excluded considering the possibility of additive and sub-lethal effects.