Phthalates and alternative plasticizers (APs) are widely incorporated in materials to enhance their flexibility and durability. They are found in many everyday products such as flooring, wires and cables, medical equipment, cosmetics, food packaging, children's toys etc. (Pecht et al., 2018; Yang et al., 2020; Qadeer et al., 2022). As these plasticizers are not covalently bonded to the products, they can easily leach out of their source materials into the environment (Mondal et al., 2022). Phthalate plasticizers (including di-(2-ethylhexyl) phthalate (DEHP), di-ethyl phthalate (DEP), dibutyl phthalate (DBP) and butyl-benzyl phthalate (BBzP)) have been considered as hazardous compounds due to numerous reports on toxicological effects, including endocrine disruption, carcinogenicity and developmental defects (Mondal et al., 2022; Hlisníková et al., 2020; Mariana et al., 2016; Howdeshell et al., 2015, Furr et al., 2014). Additionally, they have been associated with type II diabetes, obesity, allergies and asthma and interference with neurological development in children (Benjamin et al., 2017; Lange et al., 2022). These reports raised increasing concerns regarding human health risks due to phthalate exposure, which led to global regulations to limit the use of phthalates in consumer products and decrease human exposure (Monti et al., 2022; Ventrice et al., 2013). DEHP, DBP, DiBP and BBzP have been classified as reproductive toxicants in category 1 B under the Annex VI to the European Classification, Labelling and Packaging (CLP) regulation. This has led to the addition of these phthalates to the list of substances of very high concern (Annex XIV EC, 1907/2006) in the EU, and are therefore subjected to authorization under the Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) regulation. In addition, in July 2020, the restriction of these phthalates in a wide range of products with concentrations greater than or equal to 0.1% in the European Union was implemented (Directive 2011, 2011).

As a result of the efforts to restrict the use of these reproductive toxic phthalates, novel compounds were introduced as substitutes. This class of alternative plasticizers includes chemicals with a phthalate backbone but altered sidechains, such as di-isononyl phthalate (DiNP) and di-isodecyl phthalate (DiDP), and compounds with a non-phthalate backbone including adipates, benzoates, phosphate esters, citrates, sebacates, terephthalates, trimellitates and cyclohexane dicarboxylic acids (i.e. cyclohexane-1,2-dicarboxylic di-isononyl ester (DINCH)) (Qadeer et al., 2022). However, also phthalates in this newer class have been associated with endocrine disruption, leading to their restriction in i.e. children's toys and other consumer products in the European Union (Chen et al., 2014; Glossary, 2023). In this study, DEHP, DEP, DBP and BBzP were grouped as phthalates, while DiNP, DiDP and DINCH were grouped as APs.

Due to the widespread exposure to phthalates and DINCH, their metabolites are frequently analysed in human biomonitoring studies. Pharmacokinetic studies show a fast excretion of these compounds from the human body, with a half-life of less than 24 h (Frederiksen et al., 2007; Wang et al., 2019). Phthalates and DINCH are mainly excreted as conjugated monoesters, and can undergo secondary metabolism, including oxidative transformation, prior to urinary excretion (Frederiksen et al., 2007). The presence of these primary and secondary metabolites in urine has been widely reported in multiple studies to assess human exposure to phthalates and DINCH (Been et al., 2019; Bastiaensen et al., 2020).

Due to the increasing use of newer APs, the number of studies investigating their presence in environmental matrices increased over the recent years (Yang et al., 2020; Qadeer et al., 2022). As we spend most time indoors, the indoor environment has been recognized as an important source of (industrial) chemicals such as plasticizers (Christia et al., 2019). Indoor dust is one of the main sources of human exposure to plasticizers, and multiple studies have reported high phthalates and DINCH levels in indoor dust (Christia et al., 2019; Tao et al., 2022; Promtes et al., 2019). Previous studies have suggested correlations between phthalates concentrations in indoor dust and asthma and allergy symptoms in children (Tao et al., 2022; Ait Bamai et al., 2016; Mattila et al., 2021).

Multiple studies have investigated the occupational exposure to phthalates and, to a smaller extent, APs in the e-waste dismantling sector (Fréry et al., 2020). Zhang et al. (2019) showed significantly higher urinary concentrations of five phthalate metabolites in participants living in e-waste dismantling sites compared to a non-industrial area in Southern China. Moreover, some biomonitoring studies have been performed to study reproductive or endocrine disrupting effects in highly exposed polyvinylchloride workers, suggesting the possible negative health outcomes of exposure to these compounds (Huang et al., 2014; Fong et al., 2015a). However, the studies evaluating exposure to phthalates were mostly located in different parts of Asia, with very few studies addressing occupational exposure in the e-waste sector in Europe (Fréry et al., 2020). Moreover, there is a lack in uniform approaches which could facilitate comparisons between studies, as for now experimental designs still differ largely. Additionally, new phthalates and APs should be included to further assess the human exposure to these compounds in occupational settings (Scheepers et al., 2021).

The primary objectives of this study were (i) to compare the exposure level of phthalates and DINCH of e-waste workers to a control population, to investigate further the differences between pre-shift and post-shift samples, and additionally evaluate if the exposure levels are different amongst e-waste workers performing different tasks and activities, (ii) to investigate the correlations between the concentrations of phthalates and DINCH in urine and the corresponding indoor dust samples from working environments, and (iii) to assess how the daily intake estimated from both internal and external exposure compare with available tolerable daily intake (TDI) adopted by the European Food Safety Authority (EFSA) for use in food contact materials (Silano et al., 2019; Volk and Castle, 2019). Additionally, urinary metabolite concentrations will be compared to human biomonitoring guidance values (HBM-GV) determined by the European Human Biomonitoring Initiative (HBM4EU) for the exposure to phthalates and DINCH in the general population and the occupationally exposed population (Lange et al., 2021).