Partitioning of phytocannabinoids between faeces and water - Implications for wastewater-based epidemiology

Evaluating consumption estimates for lipophilic drugs in wastewater has proven to be a challenge. A common fea-ture for these compounds is that they are excreted in faeces and in conjugated form in urine. Limited research with no obvious experimental evidence has been conducted to investigate the degree to which faecal-bound chemical markers contribute towards mass loads in wastewater. Cannabis chemical markers, known as phytocannabinoids, have been suggested in literature to fall into this category. In this study, cannabis users (n = 9) and non-cannabis users (n = 5) were recruited and provided faecal and urine samples after using the substance. The common chem-ical markers of cannabis consumption, 11-nor-9-carboxy-Delta(9)-tetrahydrocannabinol (THC-COOH), 11-hydroxy-Delta(9)- tetrahydrocannabinol (THC-OH), Delta(9)-tetrahydrocannabinol (THC) and cannabidiol (CBD), were investigated. An extraction method was developed for the cannabis chemical markers in faecal matter and urine and analysis was performed by liquid chromatography-mass spectrometry. Participant samples were used to establish adsorption and desorption dissolution kinetics models and to assess the equilibrium between faeces and water for these com-pounds. Equilibration between phases were found to be fast (<5 min). THC-COOH, which is the primary metabolite used in wastewater studies, partitioned-40% in water while the less polar metabolite and CBD remained largely as-sociated with the particulate fraction. Faecal loads of both cannabis users and non-users affected the total measured amounts of cannabinoids in the aqueous phase. The implications for wastewater monitoring of lipophilic substances are discussed. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study evaluated the distribution of cannabis chemical markers in faeces and urine, and their impact on wastewater loads. THC-COOH was found to partition 40% in water, while CBD remained largely associated with the particulate fraction. Faecal loads from cannabis users and non-users affected the total measured amounts of cannabinoids in the aqueous phase.