Oral Presentation Society of Environmental Toxicology and Chemistry Australasia 2021

The complexities associated with new psychoactive substances in influent wastewater: the case of 4-ethylmethcathinone (#134)

Richard Bade 1 2 , Vincenzo Abbate 3 , Simon Elliott 3 4 , Ahmed Abdelaziz 1 , Lynn Nguyen 1 , Stephen Trobbiani 5 , Peter Stockham 5 6 , Jason M White 1 , Cobus Gerber 1
  2. Queensland Alliance for Environmental Health Sciences, Woolloongabba, Queensland
  3. King's College London, London, United Kingdom
  4. Elliott Forensic Consulting, Birmingham, United Kingdom
  5. Forensic Science SA, Adelaide, Australia
  6. Flinders University, Adelaide, South Australia, Australia

Influent wastewater is a notoriously difficult matrix in which to detect new psychoactive substances (NPS), due to the multitude of interferences.  For that reason, suspect and non-target methodologies, employing high resolution mass spectrometry are becoming commonplace to facilitate the detection of new and existing compounds. In this work, a suspect screening workflow was followed to identify NPS in influent wastewater samples collected from around Australia.

In one sample, an extracted ion chromatogram of m/z 192.1382 (± 2 mDa) showed a large signal. This was the same accurate mass as two NPS standards present in our method (pentedrone and 4-methylethcathinone), however the retention times did not match. An elemental composition search was made, with [C12H18NO]+ the only suitable formula, indicating it as an isomer of the aforementioned compounds. Moreover, several of the fragment ions were identical between the standards and the ‘unknown’ compound.

To identify this compound, a collaborative non-target analysis was performed. The sample was re-extracted and analysed at two different laboratories with different instruments.  Utilising public mass spectral libraries, vendor libraries and literature data, high confidence was given to an isomeric set of 2-,3-, or 4-ethylmethcathinone. The data (both low energy and high energy fragmentation) were also analysed by experts in high resolution mass spectrometry and toxicology, with similar findings. A retention time prediction method, based on artificial neural networks, was employed to further reduce the uncertainty around the unknown peak. However, it was unable to resolve the isomers. The standards of 2-,3- and 4-ethylmethcathinone were then acquired and investigated. Upon spiking the standards into the extracts, 4-ethylmethcathinone was finally confirmed as the signal, which is the first time this compound has been found in wastewater.  This work shows the complexities involved in identifying new substances in influent wastewater, while emphasizing the need for collaboration to facilitate the process.