Sorption, plant uptake and metabolism of benzodiazepines

Laura J Carter; Mike Williams; Sheridan Martin; Sara P B Kamaludeen; Rai S Kookana

doi:10.1016/j.scitotenv.2018.01.337

Sorption, plant uptake and metabolism of benzodiazepines

Sci Total Environ. 2018 Jul 1:628-629:18-25. doi: 10.1016/j.scitotenv.2018.01.337. Epub 2018 Feb 13.

Authors

Laura J Carter¹, Mike Williams², Sheridan Martin², Sara P B Kamaludeen³, Rai S Kookana⁴

Affiliations

¹ CSIRO Land and Water, Waite Campus, Adelaide, South Australia 5064, Australia; Environment Department, University of York, York YO10 5NG, UK. Electronic address: laura.carter@york.ac.uk.
² CSIRO Land and Water, Waite Campus, Adelaide, South Australia 5064, Australia.
³ Tamil Nadu Agricultural University, Department of Environmental Science, Coimbatore, Tamil Nadu, India.
⁴ CSIRO Land and Water, Waite Campus, Adelaide, South Australia 5064, Australia; University of Adelaide, Waite Campus, Adelaide, South Australia 5064, Australia.

PMID: 29428856
DOI: 10.1016/j.scitotenv.2018.01.337

Abstract

Reuse of treated wastewater for irrigation of crops is growing in arid and semi-arid regions, whilst increasing amounts of biosolids are being applied to fields to improve agricultural outputs. Due to incomplete removal in the wastewater treatment processes, pharmaceuticals present in treated wastewater and biosolids can contaminate soil systems. Benzodiazepines are a widely used class of pharmaceuticals that are released following wastewater treatment. Benzodiazepines are represented by a class of compounds with a range of physicochemical properties and this study was therefore designed to evaluate the influence of soil properties on the sorption behaviour and subsequent uptake of seven benzodiazepines (chlordiazepoxide, clonazepam, diazepam, flurazepam, oxazepam, temazepam and triazolam) in two plant species. The sorption and desorption behaviour of benzodiazepines was strongly influenced by soil type and hydrophobicity of the chemical. The partitioning behaviour of these chemicals in soil was a key controller of the uptake and accumulation of benzodiazepines by radish (Raphanus sativus) and silverbeet (Beta vulgaris). Benzodiazepines such as oxazepam that were neutral, had low sorption coefficients (K_d) or had pH-adjusted log octanol-water partition coefficients (log D_ow, pH6.3) values close to 2 had the greatest extent of uptake. Conversely, benzodiazepines such as flurazepam that had an ionised functional groups and greater K_d values had comparatively limited accumulation in the selected plant species. Results also revealed active in-plant metabolism of benzodiazepines, potentially analogous to the known metabolic transformation pathway of benzodiazepines in humans. Along with this observed biological transformation of benzodiazepines in exposed plants, previously work has established the widespread presence of the plant signalling molecule γ-amino butyric acid (GABA), which is specifically modulated by benzodiazepines in humans. This highlights the need for further assessment of the potential for biological activity of benzodiazepines following their plant uptake.

Keywords: Metabolism; Pharmaceutical; Radish; Silverbeet; Soil.

MeSH terms

Benzodiazepines / metabolism*
Crops, Agricultural / metabolism*
Humans
Soil
Soil Pollutants / metabolism*
Wastewater

Substances

Soil
Soil Pollutants
Waste Water
Benzodiazepines