Here’s the abstract

ABSTRACT
Aims To perform a wastewater-based analysis to explore the impact of newly legalized retail cannabis sales on its use and to determine if this approach could estimate the siz e of the legal market place, which began 1 August 2014 in the study area. Design Laboratory study of raw wastewater samples collected and analyzed over the 3-year period from 2014 to 2016. Setting and Participants Samples obtained from the two wastewater treatment plants that serviced a municipal- ity of 200 000 people in the state of Washington, USA. Measurements Quantitative analysis of 24-hour composite in- uent samples for the metabolite of the active ingredient in cannabis, 11-nor-9-Carboxy-Δ9-tetrahydrocannabinol (THCCOOH) were performed by liquid chromatography coupled to mass spectrometry. Findings Wastewater estimates for THC-COOH increased by 9% per quarter, suggesting a doubling in cannabis consumption from 1 December 2013 to 31 December 2016. State-sold THC increased at nearly 70% per quarter, while stores operated from 1 August 2014 to 31 December 2016. Estimating the proportion of the total cannabis market supplied by state-regulated cannabis from these data is not currently achievable.
ConclusionAwastewater-basedmeasureofcannabisconsumptionsuggestsasignicantincreaseinconsumptionin

Washington,USAfollowinglegalization,andthatlegalsalesappeartohavedisplaceda largeportionoftheillicitmarket