New psychoactive and classic substances in pooled urine samples collected at the Ultra Europe festival in Split, Croatia.

We believe that analysing pooled urine samples for recreational drugs used at mass events can provide useful information about trends in drug use. An opportunity arose with the Ultra Europe music festival, which is attended by more than 150,000 people from over 150 countries every year. We analysed 30 pooled urine samples collected from portable chemical toilets located at or close to the Ultra Europe music festival venue in Split, Croatia in 2016-2018 to detect the presence of classic and new psychoactive substances (NPS). Four urine samples collected in 2016 were from a toilet without added chemicals (otherwise used to kill the smell) while the remaining samples were collected from toilets with added chemicals. Samples were qualitatively analysed with gas chromatography-mass spectrometry (GC/MS) using the full-scan mode. Data were compared with the Wiley mass spectral library of designer drugs and our in-house library containing about 1000 compounds and metabolites. We identified forty-six different substances and metabolites, 26 of which were classic substances/metabolites, mostly from the stimulants group, while 20 were NPS. In the NPS group, most of them were phenethylamines and cathinones. The variety of substances was the highest on the first day of the festival regardless of the year, but 2018 showed a significant drop compared to the previous two years. The results of our study revealed a stable trend of classic drug consumption, while NPS trend changed from one year to another.