Why is inhalation the most discriminative route of microplastics exposure?

Environmental Science and Pollution Research https://doi.org/10.1007/s11356-022-20653-9 TREND EDITORIAL Why is inhalation the most discriminative route of microplastics exposure? Tariq Mehmood1 · Muhammad Azher Hassan2 · Muhammad Faheem3 · Awais Shakoor4 Received: 15 February 2022 / Accepted: 2 May 2022 © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2022 Abstract Recent research suggests a definite distinction between indoor and outdoor microplastics (MPs). However, knowledge of different MP kinds and relative exposure via inhalation to humans in outdoor and indoor locations is lacking. Notably, MPs formed from various plastic types could have distinct features, and the relative health risk varies by environment. For example, outdoor polyethylene (PE) goods have recently become more popular. These products are generally of poor structure and recycled material, making them more susceptible to decay. Particularly in the outdoor environment, the constant exposure to an open-air environment increases the risk of fragmentation and atmospheric mixing and thus facilitates MP’s availability. Using PE as an example, we aimed to emphasize the importance of explicitly defining exposure intensity and the health risk of each MP type, especially in contrasting situations such as indoor and outdoor. Unchecked and excessive use of these materials can be hazardous, whereas lowering or replacing PE with alternative plastics can significantly reduce potential health hazards. Keywords Atmosphere · Inhalation · Microplastics · Outdoor · Risk exposure Introduction Microplastics concentration in the atmosphere ranged from 0.01 MP to 5650 MP particles m−3 which were found in the West Pacific Ocean (Liu et al. 2019a) and Beijing, China (Li et al. 2020), respectively. In London (United Kingdom) and Beijing (China), MP concentration reached thousands of MP particles m−3 (Levermore et al. 2020; Li et al. 2020), and these studies indicated MPs size in the range of 5–10 µm. Responsible Editor: Philippe Garrigues * Tariq Mehmood 1 College of Ecology and Environment, Hainan University, Haikou 570228, Hainan Province, China 2 Tianjin Key Laboratory of Indoor Air Environmental Quality Control, School of Environmental Science and Engineering, Tianjin University, Tianjin 300072, China 3 Department of Civil Infrastructure and Environment Engineering, Khalifa University of Science and Technology, 127788 Abu Dhabi, United Arab Emirates 4 Department of Environment and Soil Science, University of Lleida, Avinguda Alcalde Rovira Roure 191, 25198 Lleida, Spain Exposure to these MPs from the environment may pose a severe health risk to humans (Goodman et al. 2021). The size and shape of airborne MPs determine their ability to be inhaled and their fate in the human body. Smaller, angular particles, for example, pass through membrane barriers more quickly than those with longer edges or irregular surfaces (Liu et al. 2019b; Mehmood and Peng 2022). Those coarse MPs (size: ≤ 10 µm) that can reach the human respiratory system and deposit in the upper airways or enter the intrathoracic cavity (≤ 10 µm) are called inhalable particles. On the other hand, fine MPs (size: ≤ 10 µm) are called breathable particles and can reach and deposit in the deep lung (gas exchange zone in lungs) (Levermore et al. 2020; Liao et al. 2021). Other factors that mainly dictate MP’s inhalation and corresponding health risk include persistence of MPs in the breathing zone, chemical characteristics, morphology, persistence, and environment (Liu et al. 2019b). Recent data suggest that polyethylene (PE) forms a substantial fraction of total atmospheric MPs in megacities (Mehmood and Peng 2022). On the other hand, a clear difference between indoor and outdoor MPs types and concentration has also been reported (Liao et al. 2021). Albeit, understanding of different MPs types and relative exposure to people in outdoor and indoor environments are limited 13 Vol.:(0123456789) Environmental Science and Pollution Research and restricted to general MPs characteristics. Noticeably, MPs formation from different plastic types may have some separate characteristics as well as the relative health risk could also vary in different environments. Mainly MPs concentration, distribution, and transport are explained by anthropogenic and climatological factors, leaving physicochemical interaction with environmental attributes like ultraviolet (UV) radiation, oxygen, and other pollutants. Likewise, the variability of different MPs and their corresponding levels in contrasting environments such as indoor and outdoor is also unclear. Aspects of MPs health risk assessment based on physical and chemical properties, shape, persistence, and variation in diverse environments are explored in this Editorial. These factors are further elaborated using PE source MPs as an example in the following section. Environmental persistence and health impacts Exposure to MPs can occur through inhalation or ingestion of contaminated soil, dust, and food (Abbasi et al. 2019). Likewise, dry and wet deposition of MPs can contaminate water bodies where fishes and other living organisms can intake them, and these MPs become a part of the food chain (Blettler et al. 2019; Mehmood and Peng 2022). Mucociliary systems usually catch inhaled MPs, but few may remain in the lungs and produce specific metabolic reactions, such as inflammation, especially in people who have poor clearance systems (Gasperi et al. 2018; Wright and Kelly 2017). The constant creation of reactive oxygen species by cell-particle/ fiber contact may result in Flammarion, which leads to cell proliferation and subsequent genotoxicity. Excessive reactive oxygen species generation causes chronic inflammation and lung disease (Greim et al. 2001). In addition, plastic such as PE has been ascribed as carcinogenic (CDC 2020; OSHA 2020). Several studies suggested that atmospheric MPs contain a substantial concentration of PE (Mehmood and Peng 2022). For instance, European Beach, Arenal d’en Castell, Menorca (Levermore et al. 2020), and Hamburg city of Germany (Klein and Fischer 2019) contained PEMPs as the most abundant than other MPs types. At the same time, it ranked second in London (Wright et al. 2020) and 39 major Chinese cities (Liu et al. 2019), and 3rd in the Swiss Alps and Bavaria (Bergmann et al. 2019). Collectively, these investigations revealed that PE could contribute up to 50% of total MPs concentration in the outdoor atmosphere (Mehmood and Peng 2022). Based on the assumption that an adult inhale 15 m 3 of air per day, Liu et al. (2019b) estimated that Shanghai inhabitants are exposed to 21 MPs every day. Noticeably 13 compared to particulate matter, the exposure assessment of MPs determines as item·m−3. Kim et al. (2019) estimated that the intake air volume of an adult is 14.3 m 3 per day. Subsequently, Zhang et al. (2020) reviewed the intake of (...truncated)