Polycyclic aromatic hydrocarbons (PAHs) are emitted to the environment from pyrogenic and petrogenic sources and, to some extent, from biogenic sources (Wang et al., 2014). Pyrogenic PAHs are mainly generated during the incomplete combustion of organic materials, such as coal, oil, natural gas and wood (Kim et al., 2013). Due to the wide application of combustion processes for heating, transport and in many industrial processes, PAHs are ubiquitous in the environment (Ravindra et al., 2008), which implies an exposure of the general population to these substances by atmospheric pollution via inhalation or consumption of PAH-containing food (Waldman et al., 1991). Higher than average PAH exposure may result from smoking and consumption of grilled and smoked food (Li et al., 2012; St. Helen et al., 2012). Numerous PAHs have been identified as carcinogens or probable carcinogens (IARC, 2010) and several other adverse health outcomes have to be considered as a result of exposure to PAHs such as, for example, reproductive, developmental and immunologic toxicity of PAHs (Danish EPA, 2013; Kim et al., 2013; Vandráček and Machala, 2021). The severe genotoxic and non-genotoxic toxicity as well as the ubiquitous exposure of the population to PAHs has caused significant public health concern and initiated human biomonitoring (HBM) of the PAH exposure in the general population (Becker et al., 2003; Hudson-Hanley et al., 2021). As a first HBM parameter of exposure to PAHs, 1-hydroxypyrene (1-PYR) in urine was established in HBM studies and demonstrated its efficiency as a biomarker in both exposed workers and the general population (Göen et al., 1995; Hansen et al., 2008). Successively, additional HBM parameters have been included in studies of PAH exposure, primarily biomarkers of 2-, 3- and 4-rings PAHs and benzo[a]pyrene (Chetiyanukornkul et al., 2006; Li et al., 2008; Romanoff et al., 2006).

In the pan-European project HBM4EU (European Human Biomonitoring Initiative), several prominent PAH metabolites were considered as priority biomarkers for HBM studies (Louro et al., 2019; Vorkamp et al., 2021). HBM4EU was launched in 2016 as cooperation of 30 countries and European Commission authorities (https://www.hbm4eu.eu) in order to examine the exposure of EU citizens to a variety of chemicals (Vorkamp et al., 2021). The project's aim to harmonise and advance HBM across Europe for a better chemical risk management (Ganzleben et al., 2017) implied the establishment of a network of analytical laboratories which generated comparable data for the analysis of the prioritized human biomarkers in the HBM4EU Aligned Studies (Esteban López et al., 2021). For this purpose, a special Quality Assurance and Quality Control (QA/QC) scheme was designed and implemented in HBM4EU, consisting of several rounds of Inter-laboratory Comparison Investigations (ICIs) and External Quality Assurance Schemes (EQUASs). ICIs were used to compare the results of analytical laboratories applying for the analysis of HBM4EU samples (participating laboratories) among each other, while EQUASs compared the results of the participants to selected expert laboratories having documented experience with chemical analysis in previous HBM studies (Esteban López et al., 2021).

This paper presents the QA/QC programme developed in HBM4EU for thirteen PAH biomarkers in urine (Table 1) focussing on the results obtained, the methods applied and the limits of quantification (LOQs) reported by the participants and experts, but also points out the challenges in the analysis of some PAH biomarkers.