Psychotherapeutic drugs in lake sediment : Accumulation and persistence of benzodiazepines in the sediment of Lake Ekoln

Benzodiazepines are the most commonly prescribed group of psychotherapeutic pharmaceuticals on a global scale and have been on the market since the 1960s. Benzodiazepines remain in the aqueous effluent from sewage treatment plants and have been found in natural aquatic environments. The aim of this study was to investigate if there is benzodiazepines in natural sediment from Lake Ekoln situated downstream River Fyris in Uppsala, where previous studies have detected high concentrations in the water. The study tested following hypotheses: (1) benzodiazepines are accumulating in sediments; and (2) breakdown of benzodiazepines is slow in sediment resulting in them being preserved in sediments that are several years/decades old. An extraction method for sediment was developed followed by liquid chromatography-tandem mass spectrometry for analysis of oxazepam, alprazolam, clonazepam, flunitrazepam, diazepam and prazepam. All investigated benzodiazepines occurred in the sediment of Lake Ekoln; hence, in line with hypothesis 1, benzodiazepines are accumulating in natural sediments. Further, all benzodiazepines were found in the upper 10 cm of the sediment and oxazepam, clonazepam and diazepam was found at depth below 20 cm, corresponding to an age of more than 20 years indicating that benzodiazepines resists degradation processes in sediment and are persistent for decades as predicted by hypothesis 2. To my knowledge this is the first study demonstrating that benzodiazepines are accumulated and preserved in natural sediments