Multiyear Wastewater Monitoring of High-Risk Substances Surrounding an Annual Electronic Dance Music Festival, Las Vegas, Nevada, USA, 2023-2025: Surveillance Study.

Background: Prior studies involving music festivals (including on-site surveys, drug checking, and wastewater-based analyses) suggest that recreational substance use is common among festivalgoers, though preferred substances and usage may be region- and event-specific. However, multiyear, event-specific wastewater surveillance data in the United States are limited. Objective: This study aimed to characterize concentrations of high-risk substances (HRS) and their metabolites in wastewater surrounding an annual electronic dance music (EDM) festival in Las Vegas, Nevada, USA. Using a progressive sampling approach over 3 consecutive years (2023-2025), we assessed trends and examined comparisons by sample type, day, and location to inform situational awareness and future public health surveillance efforts and risk mitigation strategies. Methods: Wastewater samples were collected from utility access points at the festival site (2024-2025), off-site in the surrounding community (2023-2024), and at the downstream wastewater treatment plant (WWTP; 2023-2025) during the festival week and weekend. For comparison, samples from a nonfestival weekend were collected off-site and at the WWTP in 2023. Target analytes consisted of 24 parent compounds and metabolites, including stimulants, opioids, and sedatives, which were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) with isotope dilution. Analyte selection prioritized substances associated with overdose risk and with prior festival-related surveillance. Results: Cocaine (and 3 of 4 measured metabolites), methamphetamine, amphetamine, 11-nor-9-carboxy-Δ-9-tetrahydrocannabinol (THC-COOH), and tramadol were detected in 100% of festival weekend samples; 3,4-methylenedioxymethamphetamine (MDMA; ecstasy) was detected (at concentrations of up to nearly 2 mg/L) in all but 1 festival site sample collected prior to the start of the event in 2025. Festival-associated signals were most pronounced for stimulant-related analytes, which were also detected in WWTP and off-site samples during the festival. Compared with nonfestival weeks, MDMA concentrations were approximately 10 to 30 times higher at off-site locations and nearly 100 times higher at the downstream WWTP during the festival. Opioid-related concentrations were comparable at the WWTP and the festival site, although there were notable detections of norfentanyl and relatively high concentrations of tramadol in some festival site samples. MDMA- and cocaine-related analyte concentrations peaked during the final festival days in 2024 and 2025; the 2023 samples highlighted the presence of HRS in local wastewater during nonfestival weekends. Conclusions: Event-focused, multiyear wastewater surveillance detected stimulants and psychoactive substances, opioids, and Δ-9-tetrahydrocannabinol (THC) associated with an annual EDM festival weekend. Findings are consistent with previous wastewater-based studies of music and dance festivals, with MDMA concentrations among the highest reported in similar surveillance efforts. Codetection of opioid- and stimulant-related analytes suggests varied usage preferences, polysubstance use, and/or unintentional adulteration (eg, lacing). These findings demonstrate the value of wastewater monitoring as a complementary, population-level tool to support public health preparedness, harm-reduction strategies, and attendee safety during large-scale events. These data also inform wastewater utilities about expected influent composition during special events, with relevance for treatment operations and water reuse applications.