Can microplastics spread disease?

In recent years, there have been a growing number of reports on the potential harm of micro- and nanoplastics to living organisms. Research has increasingly focused on the toxic effects associated with the accumulation of chemical compounds and heavy metals on/near plastic particles and their facilitated transport into living organisms, where they can accumulate, causing inflammation and intestinal dysbiosis, among other things [1]. However, the ability of microplastics to adsorb contaminants can also increase microbial risk.

Studies show that plastispheres, or man-made ecosystems linking plastic waste and the living organisms living on them, are an important link for the spread of antibiotic resistance genes and pathogens. They are becoming a serious threat to public health [2].

Why do microbes interact with plastic?

In early 1972, colonization of diatoms and parasitoid cells was first observed on the surface of plastic fragments – pellets measuring 2.5-5.0 mm – in the western Sargasso Sea. In recent decades, numerous protozoa, algae, fungi, viruses and bacteria have also been confirmed on plastic fragments of various sizes [3, 4].

In an aquatic environment, the attachment of pathogens to microplastic particles is a complex process, but it doesn’t take long at all, as microbes take a few minutes to do so, and a stable layer (in the form of a plastisphere) forms within 6 weeks. When plastics enter the environment, an adsorbed layer of biomolecules and natural organic matter quickly forms on their surface, the so-called eco-crown, which provides the nutrients necessary for microbial growth and allows them to form a biofilm structure[3-5].

Biofilms are communities of diverse microorganisms that act as a shield, enabling them to, among other things, resist adverse environmental conditions and occupy new niches. Microbes use a variety of mechanisms to better cope with environmental stressors (sunlight, antibiotics, disinfectants), including physiological adaptation, physical protection and genetic exchange, among others. Extracellular polymeric substances (biopolymers) secreted by microorganisms play a key role in attracting other organisms (protozoa, invertebrates), while providing space for communication, cooperation and competition among microorganisms [4].

The adhesion of microorganisms to plastics in the environment is influenced by several factors. First of all, hydrophobicity (the tendency to repel water molecules from each other), roughness and porosity of the material. Hydrophobic microplastics provide a solid surface for colonization, as it allows microbes to overcome the forces repelling them from plastics [3, 4].

Immediately after plastic enters the environment, a degradation process is initiated that promotes colonization and increased adsorption of nutrients by microbes. In addition, most bacteria have fimbriae (short, hair-like structures protruding from the cytoplasmic membrane), which can facilitate their attachment. Bacterial filaments can also secrete adhesion proteins that help them attach to surfaces and overcome repulsive forces associated with the substrate. These same properties promote the attachment of pathogenic and non-pathogenic microorganisms to microplastics [4, 5].

Do microplastics “attract” pathogens?

Several studies suggest that some microorganisms, including pathogenic ones, are more prevalent on microplastic particles than on non-plastic surfaces. For example, in various aqueous environments, the abundance of microorganisms from the Hyphomonadaceae and Erythrobacteraceae families was significantly higher on polystyrene and polyethylene than on wood pellets [6]. In addition to bacteria, viruses can also survive on the surface of plastics. Their survival time varies depending on the surface properties and ranges from hours to days. For example, influenza A and B viruses remained infectious much longer on steel and plastic surfaces (24-48h) than on fabric, paper or tissue paper (less than 8-12h).

Some studies also showed higher stability of SARS-CoV-2 virus on plastics and stainless steel (inactivation time of about 72h). Moreover, SARS-CoV-2 RNA persisted on masks and isolation aprons for up to 5-30 days, and the virus remained infectious for 5-7 days [4, 5]. Researchers have also reported specific accumulation of antibiotic resistance genes on microplastic particles, compared to surrounding particles of natural sediments. However, the structures of microorganisms on microplastics have not yet been shown to be more diverse than on other materials [4].

Contaminants such as antibiotics, metal ions or endocrine disruptors are adsorbed on microplastics, but they also accumulate on the surface of the biofilm, forming an important part of the eco-crown, which promotes the selective enrichment of bacteria with new resistance traits. Biofilms thus promote horizontal and vertical gene transfer, thereby contributing to the growth of antibiotic-resistant pathogens. Microplastics, due to their ease of spread, especially in water and air, can transport antibiotic-resistant genes and microorganisms to new, sometimes distant environments, potentially threatening ecosystems and human health. In addition, biofilms slow down the degradation of antibiotics in environments, providing elevated concentrations for longer periods [7-9].

What is the real health risk from microplastic-related pathogens?

The three main routes of exposure to microplastics include the gastrointestinal tract(ingestion), skin and lungs (inhalation). There is still a perception that plastics themselves behave as if they are inert materials, which is not true. Plastics are dynamic systems whose size changes under the influence of organic and inorganic compounds, as well as microorganisms. Determining the potentially harmful dose in the case of microplastics is very difficult, because in real conditions they have different sizes (from a few millimeters to 1 nanometer) and shapes (fines, pellets, fibers, nurdles, etc.).

In addition, microplastics can contain various additives to impart the desired properties to the plastics they build, and interact with a diverse array of contaminants in the environment, enhancing the so-called cocktail effect [10, 11]. These contaminants can vary from location to location. To date, the real risk of bacterial or fungal infection from ingestion of microplastics contaminated with pathogens has not been confirmed [3, 4]. In contrast, contact of damaged skin with microplastics contaminated with antibiotic-resistant microorganisms may contribute to an increased risk of infection. Particular attention should be paid to places that combine the problem of microplastic contamination and the presence of human pathogens, namely beaches, swimming pools and bathing beaches [6].

Studies have also shown that microplastic particles can alter the diversity and activity of intestinal microbes. Continuous exposure to microplastics decreases the number of beneficial gut bacteria and increases the number of pathogenic species, which, for people who suffer from intestinal diseases and problems, can lead to increased symptoms [12]. In studies conducted using a so-called artificial colon (a one-stage fermentation system that simulates the physicochemical and microbiological conditions of an adult) and involving exposure to plastic particles, the abundance of bacteria from the genera Dethiosulfovibrionaceae, Enterobacteriaceae and Desulfovibrionaceae increased. At the same time, a decrease in the abundance of Christensenellaceae and Akkermansiaceae was observed.

Some of the changes in microbial specificity have previously been observed in people suffering from gastrointestinal inflammation and irritable bowel syndrome [12]. Exposure to microplastic particles has altered the profile of volatile organic compounds generated by microorganisms. However, these compounds play an important role in biological interactions between organisms and are increasingly used as biomarkers for various human diseases, including cancer, gastrointestinal and metabolic disorders. The drastic increase in the abundance of indole, 3-methyl or scatol, demonstrated by the researchers, may indicate a potential disruption of the gastrointestinal tract mediated by the microbiota, and following exposure to microplastic particles.

Of course, studies will not fully reflect the real problem. The particles we swallow and inhale come in a variety of shapes and are made of different polymers, making it significantly more difficult to assess their real impact [2, 11, 12]. The studies using the artificial colon model focused on only one type of plastic with a spherical shape. In addition, the researchers analyzed a short study period – only 2 weeks – so we know little about how the human microbiome might change in the long term and whether it can adapt [12].

So there are still many unanswered research questions regarding the effects of microplastics on living organisms. On the other hand, we know that microplastics, even if we excrete them regularly, are not inert to our microbiome, leave a trace in the microbial community, and in extreme cases can be the cause of deterioration of our health.

Dr.-Ing. Edyta Łaskawiec – water and wastewater technologist, scientist at the Zabrze Institute of Fuel and Energy Technology, science popularizer, author of an educational profile on Instagram platform: wastewater_based.doctor. Nominated in the POP SCIENCE Science Popularizer Contest of the Silesian Science Festival Katowice 2024.

In the article, I used, among others:

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[3] J. Jia et al, Biofilm formation on microplastics and interactions with antibiotics, antibiotic resistance genes and pathogens in aquatic environment, Eco-Environment & Health, 2024, https://doi.org/10.1016/j.eehl.2024.05.003.

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[8] D. Hou et al,Assessing the Risks of Potential Bacterial Pathogens Attaching to Different Microplastics during the Summer-Autumn Period in a Mariculture Cage, Microorganisms, 9, 2021, 1909, https://doi.org/10.3390/microorganisms9091909.

[9] M. Junaid et al, Enrichment and dissemination of bacterial pathogens by microplastics in the aquatic environment, Science of The Total Environment, Volume 830, 2022, 154720, https://doi.org/10.1016/j.scitotenv.2022.154720

[10] W. Yang et al, Association between Microorganisms and Microplastics: How Does It Change the Host-Pathogen Interaction and Subsequent Immune Response? International Journal of Molecular Sciences, 24, 4, 2023, 4065, https://doi.org/10.3390/ijms24044065

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