Microplastics found in human lungs

Plastic is ubiquitous in social life, and most of the plastic waste is buried in garbage dumps and natural environments. Plastic waste will be broken down into submillimeter fragments, that is, microplastics (Microplastics). The mass production and consumption of plastics in the world, inadequate treatment of plastics, slow degradation of plastics and other reasons lead to the widespread and long-term existence of microplastics in the environment. The potential impact of microplastics on the environment and human health has aroused increasing concern.

Microplastics exist in the air, of different sizes and widely distributed, so they are likely to be inhaled by the human body. Several studies in Shanghai, Paris and London have shown that microplastics have been found in the air of cities. Microplastics are the carriers of pollutants and pathological microorganisms in the environment, and they also contain chemical additives added in the production process. So far, there is no data on the potential adverse effects of microplastics on human health, and their harmful effects on the respiratory system are not clear, but microplastics have been proved to be toxic and harmful to many forms of life in the aquatic environment.

A new study by several scholars at the University of Sao Paulo in Brazil in 2021 found that microplastics are present in human lung tissue obtained by autopsy. In this experiment, lung tissue samples from 20 non-smoking adults were collected. Polymer particles and fibers were observed in 13 of them, and their characteristics, including size, pattern, color and polymer matrix, were identified. All polymer particles are less than 5.5 microns in size and fibers between 8.12 and 16.8 microns in size. The most frequently identified polymers are polyethylene and polypropylene. There is heterogeneity to the respiratory system after inhalation of these pollutants.

The 20 non-smoking adults all underwent autopsies at the death Identification Service of the University of S ã o Paulo, including 7 men and 13 women, aged from 48 to 94, with an average age of 78.5 years. All of them have lived in S ã o Paulo for more than 10 years. All samples were collected from non-smokers, 35% of whom had a smoking history but had not smoked for more than 15 years. One individual had a history of chronic lung disease with unknown duration. Through a questionnaire survey of relatives, the subjects' occupation and underlying disease information were obtained, and the results of autopsy and lung histological examination were reviewed.

Lung tissue collection was carried out from August to October 2019, and the plastic-free method was used throughout the experiment to avoid interference and errors and ensure the reliability of the collected data. All procedures from lung tissue collection to Raman spectroscopy analysis follow the rules recommended by our predecessors (Rochman et al.); all materials are washed with ultra-pure water (Milli-Q water) three times.

Of the 20 dead who were dissected, a total of 31 synthetic polymer particles and fibers and 5 natural polymer particles were found in 13. Of the 31 synthetic polymers, 87.5% are particles (all incomplete), with an average particle size of 3.92 (±0.67) microns, ranging from 1.60 to 5.56 microns; 12.5% are fibers (aspect ratio > 3), while the average fiber length is 11.23 (±1.96) microns, ranging from 8.12 to 16.80 microns. The average diameter of five kinds of natural polymer particles is 3.44 (±1.35) microns, ranging from 1.98 to 5.42 microns. No particles or fibers were found in two lung samples used to verify air microplastic contamination during autopsy and analysis.

Among the microplastics found in the lungs of the deceased, polypropylene was the most common polymer (35.1%), followed by polyethylene (24.3%), cotton (16.2%), polyvinyl chloride and cellulose acetate (5.4%). Polyamide, polyethylene co-polypropylene, polystyrene, polystyrene-polyvinyl chloride and polyurethane (2.7%).

The identification of microplastic particles in this study shows that polypropylene and polyethylene are the most common particles in lung tissue. Both polymers are the most commonly used types of plastics in manufacturing, appearing in areas as diverse as food packaging, auto parts, candy and snack packaging, and bank bills.

Cotton particles were found in 16.2% of the samples. In clothing production, natural fibers are often dyed and coated with chemicals such as flame retardants, which may reduce their biodegradability.

The types of polymers found in the lungs may be related to indoor life, as most people in cities spend more time indoors than outdoors, and the number of fibers in the indoor environment is usually higher than that outside. Dris et al. Experiments in Paris also found that the microplastics in indoor air samples were mainly polypropylene.

The study mainly found polymer particles rather than fibers in lung tissue. The deposition of Chinese and foreign particles in the lungs depends on size, dynamic diameter, charge, density and flow rate. The particles found in the study, ranging in size from 1.60 to 5.58 microns, can indeed reach the bronchoalveoli through inertial collisions and deposits. Whether the fibers can reach the lungs depends on the actual diameter, length and density. Only fibers with a physical diameter of less than 3 microns can reach the alveolar region, which may explain why the number of fibers found in the study is small.

What are the biological effects of microplastics in the lungs from a toxicological point of view, all particles less than 10 microns in diameter have potential biological activities in susceptible individuals. Exposure to nylon villi can lead to interstitial lung disease in workers, but the process and conditions are very different from long-term exposure to degradable microplastics. Microplastic particles can induce local pro-inflammatory response of macrophages or epithelial cells in the human body, and then transport themselves to the pleura or systemic circulatory system.

In addition, fibers larger than 8-10 microns in plastics can induce macrophage activation and the release of many bioactive inflammatory mediators. So far, there is no information in vivo or in vitro to prove that environmentally degraded microplastic particles and fibers are toxic to human lungs, but exposure to the environment seems to promote the internalization of microplastics.

This study is the first to use Raman spectroscopy to identify and identify microplastics in human lung tissue. The study found polymer particles less than 5 microns in diameter in the lungs of the deceased, and fibers in more than half of the subjects' lungs. There are about 0.56 microplastic particles per gram of lung tissue, and the average weight of a group of normal adult lungs is about 840 grams, so there are about 470 particles in one person and two lungs, while men who do light manual work may inhale an average of 272 microplastic particles a day. These data not only confirm that the respiratory system is an exposure path of microplastics, and that the lungs are one of the places where microplastics accumulate in the human body; they also show that a large part of the inhaled microplastic particles remain in the upper respiratory tract.

The limitation of this study is that the number of research samples is limited and the connections or differences between the data can not be clearly judged. It is impossible to determine whether there is any relationship between the number of microplastic particles in the lungs and occupation, and whether there is a difference in the number of microplastics in the lungs of hospitalized and non-hospitalized patients.

Nevertheless, this study confirms the presence of environmental microplastics in human lungs. These particles come from our widely used plastics, such as polypropylene and polyethylene, which are more common than fibers. The potential impact of microplastics on