Using Wastewater to Detect Psychoactive Drug Use at Music Festivals: A Systematic Review

The choice of a suitable sampling approach is a critical component of WBE, especially during high-intensity social events such as music festivals. Two primary sampling methods were utilised: wastewater samples collected from sewage systems and pooled urine samples obtained directly from portable facilities.

Wastewater sampling approaches were employed in 16 out of 23 studies, representing the most common sampling strategy for festival-based substance monitoring. The predominant method was 24 h composite sampling, utilised in 14 studies, which involved automated collection systems that gathered samples at regular intervals throughout the festival period to account for temporal variations (Bijlsma et al., 2020, 2014; Berset et al., 2010; Mackuľak et al., 2019, 2014; Senta et al., 2023; Bade et al., 2024; Benaglia et al., 2020; Brandeburová et al., 2020; Bodík et al., 2016; Gomes et al., 2025; Maasz et al., 2021; Nadarajan et al., 2024; Puljević et al., 2024; Sutlović et al., 2021). Time-proportional sampling was the preferred composite approach, typically collecting smaller volumes at 15 min intervals over 24 h periods (Brandeburová et al., 2020; Mackuľak et al., 2014; Nadarajan et al., 2024; Senta et al., 2023).

Automated sampling devices were extensively used to ensure consistent sample collection under controlled conditions. These systems typically operated in refrigerated environments to preserve sample integrity and prevent degradation of target analytes (Bade et al., 2024; Berset et al., 2010; Bijlsma et al., 2014; Bijlsma et al., 2020; Brandeburová et al., 2020; Devault et al., 2020; Gomes et al., 2025; Lai et al., 2013; Mackuľak et al., 2014; Mackuľak et al., 2019; Puljević et al., 2024). The sampling frequency varied between studies. Several studies took samples every 15 min. Puljević et al. (2024) used a battery-powered sampling device which collected ~0.1 mL subsamples every 10 s into one composite sample over the 24 h.

Grab sampling of wastewater was employed in a limited number of studies, particularly where composite sampling was not feasible due to logistical constraints or when investigating specific temporal patterns (Jiang et al., 2015).

Pooled urine sampling was utilised in 7 studies, offering advantages in terms of higher analyte concentrations and reduced sample dilution compared to wastewater matrices (Bijlsma et al., 2020; Brett et al., 2022; Geuens et al., 2022; Gjerde et al., 2019; Hoegberg et al., 2018; Kinyua et al., 2016; Sutlović et al., 2021). Samples were collected from portable toilets, urinals, and storage tanks using grab sampling techniques. The sampling process typically involved drawing samples from internal storage tanks connected to male urinals or portable toilets using 50 mL syringes (Bijlsma et al., 2020; Kinyua et al., 2016; Sutlović et al., 2021), 50 mL pipettes (Brett et al., 2022), or pumps (Geuens et al., 2022; Hoegberg et al., 2018).

Some studies employed hybrid approaches combining multiple sampling strategies, such as the simultaneous collection of wastewater and pooled urine samples, to maximise detection capabilities and provide complementary data sets (Bijlsma et al., 2020). Berset et al. (2010) extended wastewater monitoring to include supplementary surface water (river and lake water) to assess broader environmental contamination patterns beyond the immediate wastewater treatment infrastructure, demonstrating the downstream fate of drugs detected in festival wastewater across multiple Swiss cities. Additionally, one study incorporated self-reported surveys and oral fluid samples into the data collection to reveal discrepancies in reported vs. actual drug use (Gjerde et al., 2019).

A variety of analytical methods were employed across the included studies to identify and quantify psychoactive substances in wastewater and pooled urine samples (see Table 2). The choice of analytical techniques was primarily driven by three factors: target analyte classes (traditional drugs versus NPS), sample matrix characteristics (wastewater versus pooled urine), and available laboratory infrastructure.

LC-MS/MS emerged as the predominant quantitative approach (16/23 studies), chosen for its established reliability in detecting traditional recreational drugs at trace levels. This preference reflected researchers' confidence in validated methods, with studies that focused on consumption estimation consistently selecting this approach for its quantitative precision. The approach is also the most selective for targeted analysis.

LC-HRMS adoption in five studies specifically addressed NPS detection challenges, recognising that the rapid emergence of novel compounds made targeted approaches insufficient. Researchers chose high-resolution techniques when study objectives included comprehensive screening or when preliminary intelligence suggested significant NPS activity.

Solid-phase extraction (SPE) was employed in 17/23 studies, becoming standard for wastewater analysis to address the highly diluted nature of analytes. However, both Nadarajan et al. (2024) and Berset et al. (2010) demonstrated that direct injection methods could achieve comparable sensitivity for smaller populations and for multi-site wastewater monitoring, respectively, challenging the assumption that SPE was universally necessary. However, this technology is not widely available to other labs. Critical comparative findings shaped subsequent methodological choices. Hoegberg et al. (2018) demonstrated immunoassay inadequacy for pooled urine screening, detecting 77 drugs and metabolites via Ultra-Performance Liquid Chromatography High-Resolution Time-Of-Flight Mass Spectrometry (UPLC-HR-TOF-MS) compared to limited immunoassay detection due to cut-off value differences and cross-reactivity issues.

Evidence-based optimal combinations emerged from comparative studies: SPE + LC-MS/MS provided the gold standard for quantitative analysis of traditional drugs, while SPE + LC-HRMS offered superior capabilities for NPS detection and confirmation. Pooled urine combined with LC-HRMS delivered the highest sensitivity for real-time festival monitoring, though with geographic and demographic limitations. Cost-effectiveness considerations influenced method selection, particularly for studies requiring extensive temporal sampling or multi-site coordination (Kinyua et al., 2016; Bijlsma et al., 2020). However, the direct injection approach demonstrated by Berset et al. (2010) offered advantages for multi-city monitoring programmes.

Wastewater analyses revealed distinct patterns in psychoactive substance consumption at music festivals, with consistent preferences emerging for specific drug categories despite variations in geographical locations, festival types, and analytical methodologies.

MDMA emerged as the most prominently detected substance across multiple festival settings and geographical regions. Lai et al. (2013) documented MDMA loads averaging 240 mg/day/1000 people in 2010 and 190 mg/day/1000 people in 2011 at an Australian music festival. Similarly, Puljević et al. (2024) reported median MDMA consumption estimates of 21,030 mg consumed/d/1000 in 2021 and 12,660 mg consumed/d/1000 in 2022, demonstrating both the substance's popularity and temporal variations between festival years. Mackuľak et al. (2019) observed significant increases in MDMA consumption during festivals in Slovakia and Czech Republic. Berset et al. (2010) documented a festival-related increase in MDMA during the Street Parade in Zurich, with influent concentrations rising from <20 ng/L during baseline weekdays to approximately 100 ng/L during the festival event, representing a >5-fold increase. Bijlsma et al. (2020) reported MDMA as the most prominent substance across six European festivals, while Gomes et al. (2025) detected MDMA consumption ranging from 18 after the event to 613 ng/L during the Carnatal festival in Brazil. The consistency of MDMA detection across diverse analytical approaches, festival types, and international contexts underscores its role as a primary substance of choice at music festivals.

Cannabis, measured through its main metabolite THC-COOH (Tetrahydrocannabinol), represented the second most frequently detected substance category. Bijlsma et al. (2020) documented THC-COOH presence in all pooled urine samples from six European festivals, while Lai et al. (2013) consistently detected cannabis metabolites across all sampling days at an Australian festival, similar to Brett et al. (2022), who identified cannabis derivatives including THC-COOH across multiple New South Wales festivals, and Berset et al. (2010), who documented THC-COOH presence primarily during festival periods. Puljević et al. (2024) reported median cannabis consumption ranging from 3145 to 4234 mg consumed/d/1000 people.

Cocaine consumption, primarily measured through its metabolite BZE, demonstrated variable, but consistent detection patterns. Lai et al. (2013) reported cocaine loads of approximately 3.5 mg/day/1000 people for cocaine, but an average between 37 and 45 mg/day/1000 people for BZE across both festival years. Maasz et al. (2021) reported cocaine detection frequencies of 28% across sampling campaigns. Gomes et al. (2025) documented cocaine concentrations ranging from 760 after the event to 8914 ng/L during the Brazilian Carnatal festival, while Bijlsma et al. (2020) detected cocaine across multiple European festival sites. Brett et al. (2022) found cocaine detection frequencies of varying levels across Australian festivals, indicating substantial use patterns despite generally lower detection frequencies compared to MDMA and cannabis.

Amphetamine and methamphetamine patterns varied significantly across geographical regions, reflecting regional consumption preferences rather than universal festival trends. Mackuľak et al. (2019) identified methamphetamine as historically prevalent in Czech and Slovak populations, resulting in minimal festival-specific consumption changes despite high baseline concentrations. Conversely, amphetamine showed more pronounced festival-associated increases across multiple studies, with Bijlsma et al. (2020) and Brett et al. (2022) documenting detection frequencies that demonstrated clearer temporal relationships with event schedules.

Ketamine demonstrated emerging prominence as a festival-associated substance across multiple international studies. Bijlsma et al. (2020) noted increased ketamine concentrations in 2016 samples compared to previous years, suggesting evolving consumption trends. Puljević et al. (2024) reported substantial ketamine consumption estimates ranging from 15,700 to 18,430 mg consumed/d/1000, while Brett et al. (2022) consistently detected ketamine across multiple Australian festivals. Jiang et al. (2015) documented ketamine as one of the highest-concentration substances detected during their festival study (138,000 ng/L), indicating significant user adoption globally.

NPS appeared with lower frequency and concentrations compared to traditional drugs across all studies. Brandeburová et al. (2020) detected five NPS at concentrations ranging from 0.4 to 8.6 ng/L, primarily synthetic cathinones including mephedrone and methcathinone. Bijlsma et al. (2020) identified 21 different NPS across six European festivals, with synthetic cathinones and phenethylamines being most detected. Bade et al. (2024) successfully identified α-D2PV (Novel synthetic cathinone, part of the broader class of NPS) and its metabolites, demonstrating analytical feasibility while confirming relatively limited prevalence. Brett et al. (2022) detected higher than expected levels of cathinones in wastewater that were not reported by survey respondents, highlighting the utility of wastewater analysis for detecting unexpected adulterants. The low detection frequencies and concentrations suggest that while NPS are present in festival environments, they represent supplementary rather than primary consumption choices.

Prescription and pharmaceutical substances demonstrated consistent background presence across festival samples. Mackuľak et al. (2019) included pharmaceuticals in their screening approach, with little observed increase in tramadol, citalopram, venlafaxine, codeine, and oxazepam, while Bodík et al. (2016) screened for 120+ pharmaceuticals, finding high enough concentrations for only a few (e.g., tramadol, venlafaxine). Jiang et al. (2015) used separate methods for pharmaceuticals and recreational drugs, finding that, out of a total of 13,950 g of emerging substances, 20.8% were analgesics, 5.7% antibiotics, and 2.7% other pharmaceuticals. Puljević et al. (2024) reported detection of substances including benzodiazepines (temazepam, diazepam), opioids (methadone, codeine, tramadol), and stimulants (pseudoephedrine, ephedrine), indication diverse pharmaceutical substance exposure in festival populations.

Polydrug use patterns emerged from multiple validation approaches. Gjerde et al. (2019) employed triangulation approaches combining self-reported data with oral fluid and pooled urine samples to confirm polydrug consumption. Brett et al. (2022) identified substances in wastewater that were not reported in surveys, indicating complex consumption behaviours involving both intended and unintended substance use. These findings align with wastewater detection of multiple substance categories within individual samples, suggesting complex consumption behaviours rather than single-substance preferences.

Several studies revealed distinct patterns of substance use that appeared to correlate with specific music genres and festival types. The most prominent association identified was between EDM events and elevated consumption of MDMA. Gjerde et al. (2019) performed a comparative analysis of three Norwegian festivals and discovered that a markedly higher percentage of participants at the EDM event reported MDMA usage (3.9%) relative to attendees at other music festivals (0.7%). This finding was supported by wastewater analysis data showing elevated MDMA concentrations during EDM events compared to other music genres, where cocaine, THC-COOH, and NPSs prevailed. However, Lai et al. (2013) noted that "MDMA use is not limited to the electronic/techno dance scenes" as these specific music genres were not being represented at the festival that they covered.

Mackuľak et al. (2019) examined wastewater from music festivals across the Czech Republic and Slovakia, covering multiple genres including with over 130,000 active festival attendees. The study demonstrated that MDMA and cocaine were primarily consumed during dance, pop, and multi-genre festivals, while cannabis use showed increases during pop/rock festivals. Notably, metal and country/folk festivals showed no significant changes in drug consumption patterns. The study's comprehensive approach included previous research by Mackuľak et al. (2014) which had identified cocaine and codeine, as well as methamphetamine, as dominant substances at country/folk festivals.

A comprehensive analysis of studies across multiple continents revealed regional variations in drug consumption patterns at music festivals (see Table 3), reflecting distinct geographical differences shaped by historical, socio-economic, and cultural factors.

Central and Eastern European countries exhibited a methamphetamine-dominant pattern rooted in historical factors. Mackuľak et al. (2019) extended their previous analysis across both Slovakia and the Czech Republic, revealing that "the EMCDDA counts Slovakia and the Czech Republic among countries with dominant methamphetamine consumption", rooted in the easy and cheap production of methamphetamine during the Iron Curtain period. Additional studies by Bodík et al. (2016) and Brandeburová et al. (2020) further confirmed this regional pattern in Slovakia, while documenting geographic variations within the country, with highest cocaine concentrations in Bratislava and highest methamphetamine in rural areas. Croatian studies by Sutlović et al. (2021) identified 46 total substances (26 classic drugs plus 20 NPS) from pooled urine samples, while Senta et al. (2023) documented a 30-fold MDMA increase during festivals. Serbia, included in the six-country study by Bijlsma et al. (2020), demonstrated MDMA-centric festival culture with clear dominance over other substances, representing some of the highest festival-associated increases documented globally. Hungarian festival research by Maasz et al. (2021) identified environmental contamination of lake ecosystems with psychoactive substances, including MDMA, cocaine, and others, as well as methamphetamine, keeping in line with the central and eastern European trend.

Western European countries generally exhibited MDMA-dominant festival patterns with notable sub-regional variations. Belgian studies by Bijlsma et al. (2020), Geuens et al. (2022), and Kinyua et al. (2016) revealed MDMA as having the highest concentrations among traditional drugs, with critical safety concerns regarding dangerous cardiac medications (flecainide and amlodipine) detected as cocaine adulterants. Spanish research by Bijlsma et al. (2014, 2020) demonstrated significant MDMA increases during festival periods. Switzerland presented interesting time patterns, with Benaglia et al. (2020) conducting two-year festival monitoring (2014–2015), showing that MDMA and amphetamine increased significantly per capita during festivals while cocaine remained stable, attributed to population-increase effects only. Berset et al. (2010) documented acute drug loading impacts following the 2009 Street Parade in Zurich, revealing dramatic post-event concentration spikes of cocaine, BZE, and amphetamine-like stimulants (amphetamine and MDMA) in influent wastewater compared to reference weekday samples, with the authors noting that heavy rainfall during the event likely diluted samples and actual concentrations would have been even higher under dry conditions. French studies by Devault et al. (2020) found no specific festival effect, a result that they attributed to the public nature and diverse audience of the monitored event. Bijlsma et al. (2020) also included Portugal, revealing cannabis with the highest increase (10-fold) during festival periods. The United Kingdom showed a large-scale in NPS diversity, with Kinyua et al. (2016) documenting 53 different NPS detected. Bijlsma et al. (2020) included the UK in their six-country study, revealing temporal patterns with more NPS detected in 2015 versus 2016, while ketamine concentrations increased significantly in 2016, potentially indicating the country's role as a global pioneer in emerging substance monitoring.

When it comes to Scandinavian countries, Danish research by Hoegberg et al. (2018) stated that ketamine was detected using UPLC-HR-TOF-MS. Norwegian festival drug consumption patterns present conflicting evidence regarding amphetamine-type stimulants. Bijlsma et al. (2020) found that Norway was unique among European countries studied, as amphetamine and methamphetamine levels in pooled urine samples were "only sufficiently high in Norway to allow accurate quantification". However, this finding directly contradicts Gjerde et al. (2019), who conducted individual testing of 651 Norwegian festival attendees and found 0% tested positive for amphetamine. These contradictory findings suggest either methodological differences between pooled versus individual sampling approaches, or potentially different populations/time periods being studied. The most commonly detected substances in Norwegian festivals were cannabis, MDMA, and cocaine, consistent with broader European patterns.

Australian studies consistently demonstrated high MDMA and cannabis combinations, establishing Australia as the first country to apply design of experiments (DOE) optimisation for detection of 71 NPS. Australian research revealed clear festival versus residential differences, with Lai et al. (2013) specifically noting that "MDMA consumption at the festival was substantially higher than in the urban area (4–58 vs. 1–7)", demonstrating the festival-specific elevation effect characteristic of the region.

Taiwanese research by Jiang et al. (2015) focused on environmental monitoring during the Spring Scream Festival, analysing 30 sampling sites, with concentrations of ketamine and MDMA peaking during festival periods, representing a pollution control perspective rather than epidemiological focus.

Gomes et al. (2025)'s study in Brazil revealed a cocaine-dominant pattern, unusual compared to global MDMA dominance at music festivals. Particularly significant was the detection of cocaethylene (COE), where "COE metabolite commonly produced by individuals after the concomitant use of cocaine and alcohol, was detected only in samples collected during the Carnaval", demonstrating region-specific polydrug use patterns combining cultural drinking practices with local drug availability.

Table 4 provides a brief summary of the main findings.

The methodological approaches employed across the included studies reflect both the evolving sophistication of WBE and the unique challenges presented by festival environments. The predominance of 24 h composite wastewater sampling strategies suggests that researchers have prioritised population-level assessment over real-time monitoring capabilities, though this preference may reflect infrastructural constraints rather than optimal research design. Sampling frequency can only be considered in a meaningful way when appropriate sewer infrastructure is in place. In urinals, portable toilet blocks or portaloos, drug residue stability is the decisive factor. Once excreted, the sample remains in the collecting container until the unit is emptied—typically after the event or at night.

The strategic choice between wastewater and pooled urine matrices across studies reveals fundamental trade-offs between analytical sensitivity and population representativeness. While pooled urine sampling approaches (Bijlsma et al., 2020; Brett et al., 2022; Gjerde et al., 2019; Kinyua et al., 2016; Sutlović et al., 2021) offered superior analyte concentrations and reduced dilution effects, enabling enhanced detection of NPS, the demographic limitations of these approaches highlight significant representativeness concerns. The successful detection of 77 drugs and metabolites through UPLC-HR-TOF-MS compared to limited immunoassay detection in pooled urine (Hoegberg et al., 2018) definitively established the inadequacy of simpler screening approaches, influencing subsequent methodological choices across the field.

The analytical evolution from targeted LC-MS/MS approaches toward HRMS techniques (Bade et al., 2024; Bijlsma et al., 2020) reflects the field's adaptive response to rapidly changing recreational drug markets. However, the observation by Kinyua et al. (2016) regarding the lack of commercial standards for most metabolites highlights the challenge in current analytical capabilities that extends beyond instrumental sophistication to encompass broader knowledge gaps in NPS metabolism and excretion patterns.

The widespread adoption of SPE across 17 studies represents methodological standardisation driven by practical necessity rather than theoretical optimisation. However, alternative approaches to traditional SPE protocols have demonstrated viability in specific contexts.

Nadarajan et al. (2024) suggested that direct injection methods can achieve comparable sensitivity and that this might have implications for the scalability and accessibility of festival monitoring programmes, particularly in resource-limited settings where sophisticated sample preparation infrastructure may not be available. However, the frugality of direct injection methods is debatable, as the equipment used for direct injection is cost-prohibitive for most laboratories and requires constant maintenance to maintain sensitivity. SPE manifolds, in contrast, are comparably cheap and can be operated by a person with minimal training. The mass spectrometer, however, requires specialist operators and resources.

The substance detection patterns revealed across festival settings demonstrate both consistent global preferences and profound regional variations that challenge simplistic assumptions about recreational drug use in festival environments. The dominance of MDMA across diverse geographical contexts establishes this substance as a defining characteristic of contemporary festival culture. However, the substantial variations in consumption estimates, ranging from Puljević et al. (2024) with median estimates of 12,660–21,030 mg consumed/d/1000 people to more modest levels in other studies, suggest that festival-specific factors, analytical methodologies, or regional preferences significantly influence detected patterns.

The geographic variations in substance preferences reveal underlying social, economic, and cultural factors that extend far beyond festival characteristics. The observation by Mackuľak et al. (2019) that "the EMCDDA counts Slovakia and the Czech Republic among countries with dominant methamphetamine and cannabis consumptions", rooted in historical methamphetamine production during the Iron Curtain period, demonstrates how political and economic transitions shape contemporary recreational drug markets. Similarly, the cocaine-dominant pattern identified by Gomes et al. (2025) in Brazilian festivals, contrasting sharply with global MDMA predominance, reflects regional drug availability and cultural consumption patterns that transcend festival-specific influences. The unprecedented diversity of NPS detected in UK festivals compared to Belgian and Norwegian events (Bijlsma et al., 2020; Kinyua et al., 2016) suggests that drug market dynamics vary significantly even within relatively homogeneous European contexts, challenging the development of standardised monitoring protocols.

Central and Eastern European methamphetamine dominance, South American cocaine prevalence, Western European MDMA-centricity, and unique and contradicting Scandinavian patterns each reflect distinct historical, economic, and cultural influences on regional drug markets. The detection of region-specific preferences demonstrates that standardised international monitoring protocols may miss critical regional variations. Understanding these geographical differences is essential for developing culturally appropriate, pharmacologically relevant festival safety initiatives and tailored evidence-based harm reduction strategies.

The influence of music genre on substance use patterns represents an additional layer of complexity that intersects with but transcends geographical variations. The strong association between EDM events and MDMA consumption, demonstrated by Gjerde et al. (2019), suggests that musical programming significantly influences drug preferences beyond regional availability patterns. Mackuľak et al. (2019) provided comprehensive evidence of genre-specific consumption patterns, documenting that MDMA and cocaine were primarily consumed during dance, pop, and multi-genre festivals, while cannabis use increased during pop/rock festivals, and notably, metal and country/folk festivals showed no significant changes in drug consumption patterns. However, the observation by Lai et al. (2013) that "MDMA use is not limited to the electronica/techno dance scenes" indicates that while genre associations exist, they may not be deterministic, with festival culture and attendee expectations potentially mediating these relationships. As only some of the analysed studies compared specific music genres or included mixed genres, definitive conclusions regarding the association between music genres and consumed drugs should not be made. Preliminary conclusions may introduce bias, reinforcing misleading associations.

Temporal consumption patterns revealed consistent increases during festival periods compared to baseline measurements across multiple studies. The capacity of large-scale festivals to generate acute loading events on wastewater infrastructure was demonstrated by Berset et al. (2010), by comparing influent samples collected on a reference day with those obtained immediately after the event, which revealed significant concentration spikes, with elevated cocaine, BZE, and amphetamine-like stimulants (amphetamine and MDMA). Critically, the authors noted that heavy rainfall during the event likely diluted these measurements, suggesting that actual substance loads under dry conditions would have been substantially higher. Gomes et al. (2025) demonstrated significant festival-to-baseline ratios for key substances, with MDMA and cocaine showing the most pronounced increases during event periods. Mackuľak et al. (2019) observed similar temporal patterns across seven different festivals with varying musical genres, while Bijlsma et al. (2020) documented consistent day-to-day increases throughout festival periods. These temporal dynamics suggest that festival environments fundamentally alter consumption behaviours, with important implications for harm reduction timing and medical resource allocation strategies.

The application of wastewater monitoring for public health and harm reduction purposes represents one of the most promising yet underdeveloped aspects of festival-based epidemiology. The capacity for population-level, anonymous monitoring demonstrated across studies provides unique opportunities for evidence-based intervention design, yet the translation of analytical findings into effective harm reduction responses remains challenging. Brett et al. (2022) emphasised the potential for wastewater analysis to be "triangulated with complementary data sources currently available in Australia such as police seizures, surveys, medical presentations, information from peer-based harm reduction services and toxicological analyses to feed into public health alerts", highlighting both the integrative potential and current fragmentation of festival surveillance systems.

The detection of dangerous adulterants and NPS through WBE offers critical safety benefits that extend beyond traditional surveillance capabilities. The identification of cardiac medications such as flecainide and amlodipine as cocaine adulterants (Geuens et al., 2022) and the detection of highly toxic substances such as N-ethylpentylone and norfentanyl (Brett et al., 2022) demonstrate the capacity of wastewater monitoring to identify specific health risks that might otherwise remain undetected until clinical presentations occur. However, the temporal lag between sample collection, analysis, and result availability fundamentally limits the utility of current approaches for immediate harm reduction responses during ongoing events.

The pioneering detection of emerging substances, including the world's first identification of kavain (the metabolite of kava) and psilocin (the metabolite of psilocybin or "magic mushrooms") in festival wastewater (Puljević et al., 2024), illustrates the potential for wastewater monitoring to serve as an early warning system for NPS entering recreational drug markets. This capability is particularly valuable given the rapid evolution of NPS markets and the challenges faced by traditional surveillance methods in detecting emerging substances. However, the successful implementation of early warning systems requires sophisticated data interpretation frameworks and rapid communication channels that currently remain underdeveloped across most festival contexts.

The integration of wastewater monitoring with complementary surveillance approaches, as demonstrated by Brett et al. (2022), Gjerde et al. (2019), and Puljević et al. (2024) through triangulation of surveys, oral fluid samples and wastewater/pooled urine data, reveals the potential for comprehensive monitoring systems that overcome individual methodological limitations. The demonstrated capacity for objective, population-level surveillance provides a foundation for evidence-based harm reduction approaches, yet successful implementation depends on addressing current temporal, technological, and coordination limitations through sustained methodological development and stakeholder engagement.

While this review focuses on festival WBE as a public health tool, it is important to acknowledge that the detected substances also pose environmental risks. Studies like Maasz et al. (2021) as well as Aberg et al. (2022) have demonstrated that festivals can transiently contaminate aquatic ecosystems with biologically active compounds that retain pharmacological activity and may adversely affect wildlife.

Understanding acute loading patterns has implications beyond immediate harm reduction, extending to wastewater treatment plant operations and environmental monitoring. The observation by Berset et al. (2010) that sewage treatment plants can be exposed to brief periods of exceptionally high drug concentrations during major festivals raises questions about the capacity of standard treatment processes to handle such acute loads, and whether these events contribute disproportionately to downstream environmental contamination. This infrastructure perspective complements the individual-level harm reduction focus of most festival monitoring studies, highlighting the broader environmental and operational implications of mass gathering substance use.

Stakeholders from all involved groups (e.g., festival goers, festival organisers, musicians, political and cultural representatives, physical and mental health experts, WBE experts and environmental associations) should discuss and develop actionable recommendations for public health surveillance, harm reduction and festival interventions.

The aim of this systematic review was to evaluate and synthesise the existing literature on recreational drug consumption at music festivals based on wastewater analysis. Thus, it had an aim rather than a specific research question.

We restricted the review to wastewater analysis. Therefore, we did not capture many important aspects of substance use at music festivals. Wastewater analysis measures the consumed substances of the group or a subgroup of festival goers, not the drug consumption of one individual. Moreover, as drugs can be contaminated, individuals might believe they are consuming different substances than those detected. To investigate such discrepancies, mixed-method studies including individual qualitative and quantitative interviews as well as individual drug tests could provide valuable contextual insights.

Based on this review, future researchers might develop more specific questions, for example, what the specific differences in drug and alcohol abuse between electronic and folk music festivals are. Such a more specific review should follow the PICO (population, intervention, comparison, outcome) approach to formulate a research question.

We only included studies published in English, German, and Romanian. Publications in other languages might have been missed.

Our literature search was restricted to PubMed, MEDLINE and Embase. The decision was made because these databases focus on biomedical science, medicine, drug research and pharmacology. However, databases focused on psychological research such as APA PsycInfo might contain additional relevant articles.

A primary limitation of this review is that the current literature exhibits significant geographic concentration, with studies predominantly conducted in European countries. Notable gaps exist in coverage from major regions including the United States, Africa, and large portions of Asia and South America. This geographic bias fundamentally limits the global applicability of findings. The concentration of research in higher-income countries with established wastewater infrastructure may not adequately represent patterns in regions with different socioeconomic contexts or emerging festival markets.

Festival events create complex population dynamics that complicate data interpretation. Senta et al. (2023) note that the intake of psychoactive substances seen during the festival week cannot be deemed indicative of permanent residents. This also ties in with the impossibility of determining exact contributor numbers. Kinyua et al. (2016) acknowledge that population fluctuations within festival events cannot be predicted, making accurate normalisation of consumption estimates problematic. Furthermore, wastewater sampling at festivals cannot determine how many people consumed recreational drugs and how many of these had a substance use disorder.

Another pervasive limitation across multiple studies is the systematic demographic bias toward male populations in pooled urine sampling approaches. Hoegberg et al. (2018) explicitly acknowledge that the urinals were designed exclusively for men, as "the design of the urinals did not favor easy use for females". Geuens et al. (2022) explain that technical requirements for sample processing prevent the inclusion of mixed waste, effectively limiting data collection to male urinal users only. This systematic exclusion creates substantial gaps in understanding substance use patterns among female festival attendees and may miss important gender-specific differences in drug preferences, consumption patterns, and associated health risks. However, female underrepresentation and the lack of knowledge on gender differences can be overcome in the future with suitable infrastructure and technical adaptations.

Festival-based sampling presents unique coordination complexities constrained by existing infrastructure and technical limitations that significantly impact study feasibility and introduce potential selection bias. Research groups document the substantial communication requirements between festival organisers, volunteers, and wastewater treatment operators, with success heavily dependent on stakeholder willingness to participate (Bijlsma et al., 2020). Brett et al. (2022) describe how practical constraints related to the number of available facilities and limited sampling windows create additional barriers. These coordination requirements may result in convenience sampling of more cooperative festival organisers rather than representative sampling across diverse festival types, sizes, and management approaches. International research coordination introduces additional bureaucratic complexities, potentially limiting cross-national comparative studies.

Environmental conditions and chemical contamination present ongoing challenges to sample integrity and analytical accuracy. Multiple studies document weather-related interference, with researchers reporting contamination from dilution by non-urine liquids and variable exposure to rain at uncovered sampling sites (Hoegberg et al., 2018; Geuens et al., 2022). Maasz et al. (2021) highlight the difficulty in determining contamination sources, noting the uncertainty about whether detected substances derive from direct festival use or inappropriate wastewater drainage from surrounding areas.

Furthermore, sample integrity during collection and storage presents ongoing analytical accuracy challenges. Kinyua et al. (2016) warn that "there is a chance of missing unstable targets during analysis if sample collection and storage (freezing) are delayed". These storage and stability issues may be particularly problematic in festival settings where immediate laboratory processing is impractical. Additionally, the stability of target molecules might be impacted by contamination of the samples with sanitiser or deodoriser.

Another potentially critical aspect is the limited availability of commercial reference standards for NPSs. Kinyua et al. (2016) highlight that "most metabolites are not available as commercial standards so to be included in targeted methods". Similarly, multiple studies describe the rapidly changing nature of the NPS market as a fundamental constraint when applying standard analytical techniques (Brett et al., 2022; Hoegberg et al., 2018; Nadarajan et al., 2024). This limitation restricts researchers to qualitative identification methods for many substances and prevents accurate quantification of emerging drug classes.

Complex sample matrices present significant analytical challenges across multiple studies. Nadarajan et al. (2024) identify them as one of the primary challenges in LC-MS analysis, finding that "only 75% of tested compounds (53 out of 71 NPS) achieved acceptable matrix effects". The absence of standardised analytical protocols creates significant comparability challenges across studies. Hoegberg et al. (2018) document substantial methodological inconsistencies that exist between the outcomes of bioanalytical tests and drug-screening immunoassays, with the latter yielding both false negative and false positive results. Such variation in detection thresholds and analytical approaches can lead to dramatically different conclusions about substance prevalence and may compromise meta-analytical approaches.

Pooled sampling approaches are another potential confounder, with both Bijlsma et al. (2020) and Kinyua et al. (2016) acknowledging that pooled urine data represents a momentary capture of substance use rather than comprehensive temporal patterns. This limitation prevents researchers from capturing dynamic consumption patterns throughout festival events and may miss important variations in substance use intensity, timing, and sequential polydrug use patterns.

In addition, the absence of historical baseline data complicates trend identification and context interpretation. Gomes et al. (2025) recommend comparing metabolite ratio values from suspected dumping events with historical data from the same location, while noting that their study represents the first wastewater monitoring research conducted in Natal. The general absence of longitudinal data limits researchers' ability to distinguish festival-specific consumption patterns from broader temporal trends in substance use.

Differential excretion profiles across substance classes create interpretation challenges for temporal analysis. Bijlsma et al. (2020) note that substances exhibit varying excretion rates; for instance, cannabis has significantly prolonged excretion rates compared to drugs such as MDMA. Gjerde et al. (2019) highlight additional complexity related to extensive metabolism of many NPS, which results in predominantly metabolite detection with minimal parent drug concentrations in urine samples. These pharmacokinetic differences mean that detection patterns may not accurately reflect contemporaneous consumption patterns, potentially leading to misinterpretation of substance use timing and relative consumption intensities.

Another point to consider is the rate of drug clearance from the body. During a festival event spanning less than a day, there is a high chance that drugs used during the festival may only be metabolised and excreted after the event, at a different site. It is also possible that drugs excreted at the site were consumed well prior to the event. Drug loads in wastewater from festivals should therefore be interpreted with caution.

Wastewater analysis uses pooled specimens and can only provide a positive test of a drug or the concentration of a drug within the whole sample, not for the individual person. This method is unable to ascertain the proportion of festival goers who consume a substance. A small subgroup of festival visitors or even a single visitor can influence the overall result. Thus, data derived from wastewater analysis at music festivals, as well as secondary research studies based on such analyses, must take this methodological shortcoming into account to avoid conclusions about individual festival participants or the totality of festival goers.

Methodological heterogeneity across studies creates substantial challenges for evidence synthesis and meta-analysis. Bijlsma et al. (2020) caution that data interpretation between different festivals and countries requires careful consideration due to variations in festival characteristics, populations, timeframes, sample matrices, and collection methods. This methodological heterogeneity fundamentally limits the ability to conduct robust comparative analyses and develop generalisable conclusions.

We already mentioned potential biases regarding epidemiology and gender above. However, the design of the included studies did not involve randomisation, concealment, specific care or treatment. Therefore, selection and performance bias are not relevant for this systematic review. Detection bias is possible, as only pre-selected drugs were measured and most metabolites are not available as commercial standards. Attrition bias or loss to follow-up bias does not apply, because the studies were single-timepoint studies.

Prior to this systematic review, the evidence for assumptions regarding the causes of heterogeneity was scarce. However, given the obtained results, geographic and demographic conditions, the music genre, sampling and analytical methods might be considered as causes of heterogeneity in future cross-sectional, epidemiological and cohort studies using wastewater analysis for psychoactive substances at music festivals. Given the nature of the obtained data, a sensitivity analysis to assess the robustness of the synthesised results was not deemed meaningful.