Low biodegradability of fluoxetine HCl, diazepam and their human metabolites in sewage sludge-amended soil
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Background, aim, and scope
The European Union banned disposal of sewage sludge (SS) at sea in Europe in 1998. Since that time, the application rate of SS to land has risen significantly and is set to rise further. Fifty-two percent of SS was disposed to land in the UK in 2000. Land application is, thus, possibly an important transport route for SS-associated organic chemicals into the environment. There are now over 3,000 different pharmaceutical ingredients in use in the EU and many enter sewage systems. Possibly as a result, the last decade has seen an increase in reports of pharmacologically active compounds in the environment (e.g. in watercourses, open ocean and soils). Surprisingly, there is still a significant lack of knowledge of the transport and fate of pharmaceuticals in the environment, particularly in soils. The present project, therefore, investigated the susceptibility to microbial degradation of the selective serotonin re-uptake inhibitor, Prozac® (fluoxetine HCl), and the 1,4-benzodiazepine, Valium® (Diazepam) and their major human metabolites (norfluoxetine HCl, temazepam and oxazepam) in short-term (60 day) bacterial liquid cultures derived from UK SS-amended soil and of fluoxetine HCl in a longer-term (270 day) SS-amended soil culture.
Recently developed extraction techniques, including solid phase extraction, allowed all analytes to be isolated from the biodegradation cultures (aqueous and soil matrices), and subsequently analysed using novel high performance liquid chromatography–electrospray ionization-multistage mass spectrometry (HPLC-ESI-MSn) techniques. Ratio calibration using deuterated internal standards allowed the generation of quantitative data. A simple basified tautomerism experiment was also performed to aid in the identification of a bacterial transformation product. Alongside the biodegradation studies, HPLC-APCI-MSn profiling of bacteriohopanepolyols (BHPs; bacterial membrane marker chemicals) allowed assessment of the microbial community structure in the SS-amended soils.
The pharmaceuticals were found to be resistant to biodegradation in liquid culture studies (60 days), and even after prolonged exposure in SS-amended soil (>200 days; fluoxetine HCl only). Oxazepam was the only 1,4-benzodiazepine studied which underwent biotic transformation (~40%) in liquid culture studies. Evidence to support the theory that the transformation product was a 1,4-benzodiazepine tautomer, is presented. BHP profiles of eight different SS-amended soils suggested that the restricted bacterial community of the soil used as a culture source in these biodegradation studies was typical of SS-amended soils.
The lack of substantial degradation of all target analytes except oxazepam under simulated, but realistic, SS-amended soil conditions indicates their likely persistent nature. Although oxazepam did undergo significant biotic (and abiotic) losses, the metabolite formed under biotic influences was hypothesised to be another bioactive 1,4-benzodiazepine (either 2-enol or 3-enol nordiazepam) which is likely to be resistant to further change. The bacterial communities in SS-amended soils may be unable to degrade such compounds.
Recommendations and perspectives
With such pharmaceuticals as tested here, there is a potential for accumulation within environments such as field soil to which SS is regularly added both as a disposal mechanism and as a fertiliser. When compounds undergo accumulation, the risk of transport to other environmental components becomes more likely. From field soils, these may include potential exposure to flora and fauna and possible bioaccumulation or effects on terrestrial organisms and accumulation in plants, including crops grown on the SS-treated soils. The fate and subsequent impact of many pharmaceuticals within the terrestrial environment is still largely unknown and further research is required before the risks, if any, of SS-associated pharmaceuticals can be fully assessed.
Keywords1 4-benzodiazepines Bacteriohopanepolyol Biodegradation HPLC-ESI-MSn Personal care products (PPCPs) Pharmaceuticals Selective serotonin re-uptake inhibitors (SSRIs) Sewage sludge Solid phase extraction (SPE) Tautomerism
We thank the Biotechnology and Biological Sciences Research Council (BBSRC) and an anonymous pharmaceutical company for providing funding for this work. Thanks also goes to the microbiology team at Becton Dickenson & Co, Roborough, Plymouth, Devon, for kindly sterilising soil samples (γ-irradiation, 25 kGy, 60Co irradiation source). Dr C. Whitby and Dr M. Frenzel from EMERGE, Exeter University, and Mr P. Waines from the University of Plymouth, also deserve thanks for invaluable advice on microbiological techniques. We also thank the Engineering and Physical Sciences Research Council (EPSRC) for funding to MPC and the Science Research Infrastructure Fund (SRIF) from HEFCE for funding the purchase of the Thermo Electron Finnigan LCQ ion trap mass spectrometer (Newcastle).
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