Biologic monitoring of exposure to particulate matter: the exhaled breath condensate

Introduction. By non-invasively cooling the air exhaled by a subject, it is possible to collect a liquid composed primarily of water and a small amount of fluids from the lining of the airways,1 namely the exhaled breath condensate (EBC). This matrix finds use in various applications, including biomarker identification, inflammation assessment, and early diagnosis in at-risk individuals. Recently, some studies have started measuring the concentration of particulate matter in EBC as a tool for assessing the exposure in occupational and environmental settings. However, they often reach conflicting conclusions, partly due to the wide variability of the analytical techniques used to analyze the particulate matter. Objectives. The main contributions of the literature on the use of EBC as a representative matrix for the assessment of particulate matter exposure in occupational settings will be illustrated. Additionally, a pilot study conducted in an office work environment (i.e., a scenario with low exposure to airborne particles) will be presented, using electron microscopy as the quantitative characterization technique for the particulate matter, representing an element of innovation compared to the existing studies. Methods. The most recent publications in which the EBC is used to estimate the occupational exposure to airborne particles have been identified. For the pilot study, the EBC was sampled from several volunteers at the beginning and end of their work shifts, following the existing recommendations to limit contamination and ensure proper sample handling. Information was also obtained regarding the activities carried out during the work shift. Additionally, respirable particles were collected by sampling every subject breathing zone, via personal samplers, for 4 working hours. Airborne respirable particles and those in the EBC were quantified and morphologically/chemically characterized using scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy. Results and Conclusions. The existing publications highlight the need for further steps before the EBC can be properly positioned as a scientific research and occupational exposure monitoring tool. Indeed, the results of some studies are contradictory and lack information at the level of the individually characterizable particles, making them difficult to interpret. Furthermore, in the available literature, the concentration and type of airborne particles are rarely correlated with those present in EBC: starting from the objective of investigating this relationship through a technique such as electron microscopy, which represents the state of the art in terms of resolution and quality of information obtainable about individual particles, the pilot study presented in this work revealed that EBC is a highly complex matrix, subject to interactions between its liquid component and the various airborne particle species to which the subjects are exposed. Indeed, the particles in the EBC are not a simplistic representation of the airborne particle species, instead they must be interpreted in light of the physicochemical characteristics of the inhaled particles, such as their solubility. Precisely for this reason, the amount and type of the particulate matter found in the EBC samples does not seem to be influenced by the smoking status of some of the participants in the pilot study, confirming what was highlighted by previous studies. The “particle-by-particle” analysis approach developed in this study can be further applied to other occupational exposure scenarios to confirm its validity as a method capable of providing information regarding exposure to other particulate matter forms, such as microplastics and wood dust.