Impact of diesel exhaust exposure on urinary 1-hydroxypyrene in underground salt and potash workers

Emissions from diesel engines are complex mixtures of diesel particulate matter (DPM) containing elemental and organic carbon and gases such as carbon and nitrogen oxides, among others (IARC, 2014). Diesel engine exhaust (DEE) also contain polycyclic aromatic hydrocarbons (PAH) and several studies have specifically investigated the PAH content of DEE (Corrêa and Arbilla, 2006; Marr et al., 1999). Although PAH profiles in DEE can considerably vary, no significant differences for total PAH concentrations could be detected (Borrás et al., 2009).

DEE is a major contributor to air pollution and global warming (Campbell-Lendrum and Prüss-Ustün, 2019) and has been classified as carcinogenic to humans (Group 1) by the International Agency for Research on Cancer (IARC, 2014). In recent decades, increasingly stringent emission standards have been introduced, especially for road vehicles. Exhaust gas treatment and fuel efficiency have been improved, resulting in lower emissions (Frey, 2018).

DEE poses also an occupational health risk. A review of occupational exposure to DEE found highest exposure concentrations for enclosed underground work sites where heavy equipment is used (e.g. mining and mine maintenance), and lowest when working outdoors or separated from the exposure source (Pronk et al., 2009). A suitable surrogate marker for DEE commonly used for occupational monitoring is elemental carbon in diesel particulate matter (EC-DPM) as it constitutes a large fraction of the particulate mass and can be quantified at low levels (Birch and Cary, 1996). However, external exposure measurements cannot estimate internal workers exposure.

To assess internal exposure to DEE, 1-hydroxypyrene (1-OHP), a metabolite of pyrene, has been commonly used as a surrogate biomarker (Ciarrocca et al., 2014; Hansen et al., 2008; Louro et al., 2022). Reasons include that pyrene has been found in DEE emission. For example, pyrene was the sixth most abundant of the 16 designated high priority PAHs by the US Environmental Protection Agency in a study exploring underground DEE in a Swedish iron ore mine (Gren et al., 2022). In addition, an increase in 1-OHP over the course of a shift was also seen in miners from an Australian goldmine (Du et al., 2019) suggesting that 1-OHP is an appropriate surrogate biomarker to study exposures to DEE and PAH in miners. 1-OHP has also been used in other studies for assessing exposure to PAH thus allowing cross-study evaluation of PAH exposures between different occupational settings rather than settings with DEE exposure alone. For example, the highest 1-OHP concentrations have been previously reported for workers in petrochemical industries (coke-oven workers) and metallurgy workers (Hansen et al., 2008). Less pronounced exposure have been found in firefighters due to their use of high-level personal protective equipment (Hoppe-Jones et al., 2021; Taeger et al., 2023).

Urine concentrations of 1-OHP are also elevated by non-occupational sources of PAH such as tobacco smoking, air pollution, dietary intake, dermal absorption of pharmaceuticals, or contact with contaminated soil (Jongeneelen, 2001). It has been shown that the strongest predictor of urinary 1-OHP excretion in the general population is tobacco smoking (Wilhelm et al., 2008).

To reduce health hazards from DEE in the workplace, an occupational exposure limit (OEL) of 0.05 mg/m³ for EC-DPM was established in Germany in 2017; a transition period has been granted for underground mining (GESTIS Substance Database). As part of this 5-year transition plan to reduce exposure in salt and potash mining, an epidemiological study was conducted to investigate potential health effects within an 8-h shift. First results on selected cardiovascular, inflammatory and respiratory effects of this study have been published recently (Gamrad-Streubel et al., 2022). The aim of this additional analysis was to determine the exposure to PAH using urinary 1-OHP and to study its relationship with DEE in a salt- and potash-mining population commonly exposed to exhausts from large diesel-powered mining equipment and vehicles that are required for underground mining operations.

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