- Researchers investigated the stability of viruses over time when suspended in water containing microplastics.
- They found that viruses can attach to microplastics and remain more stable than in water alone.
- They note that further research is needed to understand how long pathogens can survive by binding to microplastics.
Microplastics are plastic particles that are under 5 millimeters (mm) in size. Once in the environment, they are quickly colonized by microorganisms.
Although wastewater treatment plants remove up to 99% of microplastics from sewage water, sewage water remains one of the main sources by which microplastics enter the environment.
This presents a risk for pathogens from human waste to attach to bacterial colonies known as biofilms on plastics.
Knowing whether or not pathogens that sit in microplastic biofilms remain infectious could aid public health initiatives.
Recently, researchers assessed the stability of viruses when submerged in water containing microplastics.
They found that viruses attached to microplastic biofilms were more stable than when in water alone.
The study appears in Environmental Pollution.
For the study, the researchers tested two types of viruses. One, a bacteriophage — bacteria-eating virus — known as Phi6, had an “envelope” or lipid coat around it similar to the flu virus, while the other — rotavirus strain SA11 (RV)— was “non-enveloped.”
To begin, the researchers grew biofilms on 2 mm polyethylene microplastic pellets by inserting them into flasks containing filtered lake water, unfiltered lake water, or water infused with nutrients to encourage microbial growth for 7–14 days.
Biofilms formed on all three water treatments, although they formed more rapidly among the pellets from the nutrient-based water source.
The biofilm-coated pellets were then inserted in flasks containing 100 milliliters (ml) of fresh lake water and 1 ml of either Phi6 or rotavirus SA11 at concentrations typical to wastewater samples.
To track virus particle numbers, the researchers extracted microplastic samples and 1 ml of water at 3 hours, 24 hours, and 48 hours.
After analyzing the samples, the researchers noted that both Phi6 and RV particles had formed on the microplastics.
While virus stability declined over time, virus inactivation was lower in biofilm-colonized pellets than in water samples.
They additionally noted that RV viruses remained more stable than Phi6 viruses. This, they noted, demonstrates how the interaction between non-enveloped viruses and bacterial cell wall components can increase their infectivity and thermostability.
Dr. Nikolas Stasulli, assistant professor in the Department of Biology and Environmental Science at the University of New Haven, not involved in the study, told Medical News Today, when asked how viruses might remain intact when hitchhiking microplastics in freshwater:
“As the authors note, much of the ability to ‘hitchhike’ on microplastics is because of the layer of biofilm that is formed by bacteria on the microplastics. Once bacteria attach and adhere to the surface of microplastics they can keep recruiting more bacteria through the production of biofilm, which acts like a biological glue that can help keep bacteria in close association with each other.”
“During this process, other, smaller things in the surrounding area — like viruses or chemical compounds — can also become attached to this biofilm. It is widely known that biofilm can protect bacteria encased within it from factors like antibiotics and unfavorable environmental changes — like drying out — so it could be that viruses attached to this biofilm are granted the same type of protection from environmental changes that may inactivate them,” he added.
The study authors conclude that microplastic pollution is a potential pathway for viral dissemination and persistence in the environment.
When asked about the study’s limitations, Dr. Saif Uddin, senior researcher at the Kuwait Institute for Scientific Research, not involved in the study, told MNT that the researchers did not sufficiently account for
He noted that efforts for avoiding cross-contamination are crucial as the highest microbial loads are transferred to microplastics from exhaled air.
He added that the researchers also did not investigate biofilms on dust or sand particles, which take less time to form on these materials than plastics.
Dr. Stasulli moreover noted that these are preliminary findings, and further study is needed. He said that “[m]ore studies will certainly be conducted on a variety of viral human pathogens which will include variables like the route of infection and the infectious dose.”
“Combining future information on viral infectious dose and route of microplastic ingestion, along with the variables discussed in this novel study, will certainly help to establish the impact that viruses on biofilm-coated microplastics can have on human health,” he continued.
Dr. Stasulli added that such research is nevertheless important for public health: “[As] they are microscopic, these microplastic particles contaminated with human pathogens are easily ingested or inhaled by humans. The increased viability time on a surface that can easily enter the human body only increases the potential infection rate from these pathogens.”
Dr. Uddin, however, pointed out that the risk of contracting a virus from microplastics is low compared to other routes of transmission due to generally low microplastic concentrations in water.
To put it in perspective, he noted that levels of microplastics in water typically range from 1–10 parts per cubic meter. Meanwhile, levels of phytoplankton, suspended particulates, and zooplankton range from 1,000–100,000 per cubic meter.