Nanoplastics are already a concern because they can be directly ingested by people, but new research points to another possible danger. These small plastic particles can also make it more difficult to control harmful bacteria.
In a study published in water researchVirginia Tech researcher Jingqiu Liao and an international team found that nanoplastics can interact with environmental microorganisms and pose indirect risks to human health, particularly through drinking water systems.
“It is very important to better understand the negative effects of nanoplastics on human health and the negative effects not only on humans but also on the environment, which indirectly affects human health,” said Liao, assistant professor of civil and environmental engineering. “Nanoplastics can better survive antibiotic-resistant pathogens, which can be harmful to the environment and impact public health.”
Nanoplastics could complicate water treatment
Researchers reported that bacteria exposed to nanoplastics may become more resistant to disinfectants. This could cause serious problems for water treatment plants and distribution networks designed to keep drinking water safe.
“When nanoplastics interact with biofilms and the bacteria inside them, they can strengthen the biofilm and make it more resistant to all measures to keep water clean,” said Liao, who is also affiliated with the Global Change Center at the Fralin Institute for Life Sciences.
Jingqiu Liao is an assistant professor of civil and environmental engineering. Photo by Peter Means of Virginia Tech.
Nanoplastics are a smaller category of microplastics. Their size is approximately 1 to 1,000 nanometers and cannot be seen with the naked eye. In this study, researchers investigated how these particles affect biofilm formation in drinking water systems.
How bacterial biofilms form
Biofilms are groups of bacteria that attach to surfaces such as the inner walls of water pipes. Microorganisms produce protective substances around themselves and help protect society from environmental threats.
Biofilms are not necessarily harmful. Depending on the settings, it can help remove unwanted substances. However, within drinking water supply systems, there can be risks as some of the bacteria they contain can cause disease.
This problem is further complicated by bacteriophages, which are viruses that infect bacteria. Until this study, scientists knew little about how nanoplastics affect the relationships between biofilms, bacteria, and these viruses.
“The main process we were particularly interested in was how bacteria and bacteriophages interact as nanoplastics affect the entire biofilm,” said Liao, who is also affiliated with the Fralin Institute for Life Sciences’ Center for Emerging, Zoonoses, and Arthropod-Borne Pathogens.
Research on microorganisms and antibiotic resistance
Liao specializes in microbial ecology and metagenomic analysis. Her previous research investigated how soil contributes to the spread of antibiotic resistance.
She also recently received a Scaling Scholarship Award through the School of Engineering’s Major Grants Initiative for research related to the Nature Communications publication “Different roles of deterministic and stochastic processes in structuring soil bacterial ecotypes across terrestrial ecosystems.”
Nanoplastics trigger multiple bacterial reactions
The researchers studied a biofilm composed of E. coli and Pseudomonas aeruginosa. When the biofilm was exposed to nanoplastics, the bacteria responded in several ways.
Different bacteria “talk” to each other, releasing substances that make the biofilm thicker, heavier, and more protective.
A prophage, a phage that inserts its genome (DNA) into the bacterial host’s genome, is activated. They destroy the bacterial cells they inhabit while producing large numbers of new virus particles.
Bacteria protect themselves from prophages by using DNA or RNA cellular clustered regularly interspaced short palindromic repeats (CRISPR) to target viruses as part of their antiviral defense system.
Diagram of the three reactions of bacteria when nanoplastics come into contact with biofilms. Image courtesy: Jingqiu Liao
Stronger biofilms could threaten water systems
The study found that exposure to nanoplastics increased the physical strength of biofilms, making them more resistant to disinfectants.
The authors conclude that “the increased mechanical strength of biofilms and their resistance to disinfectants highlight potential challenges to water treatment and distribution systems, as nanoplastics can increase the formation of difficult-to-eradicate biofilms on the surfaces of some water treatment and distribution systems.”
These findings suggest that nanoplastics may facilitate the formation of stubborn biofilms on surfaces used for water treatment and delivery, which may be difficult to remove.
further research is needed
Liao said additional research is needed to identify the molecular processes that drive reactions in complex biofilms containing multiple microbial species.
She also noted that particle size may play an important role. Microplastics are larger than nanoplastics and can affect interactions between bacteria and phages in different ways.
“Overall, our findings provide new insights into the interaction of nanoplastics with bacteria-phage dynamics and highlight the increased microbial risks associated with waterborne nanoplastics,” Liao said.
Other researchers participating in the study are:
- Haibo Wang, Associate Professor, Center for Ecological and Environmental Sciences, Chinese Academy of Sciences, Beijing, China
- Hui Chen, Associate Researcher, Center for Ecological and Environmental Sciences, Chinese Academy of Sciences, Beijing, China
- Chujin Ruan, Postdoctoral Researcher in Environmental Microbiology, Swiss Federal Institute of Fisheries Science and Technology, Dübendorf, Switzerland
- Cory Schwartz, Civil and Environmental Engineering and Rice Water Institute Postdoctoral Researcher, Rice University, Texas
- Baoyou Shi, Professor, Center for Ecological and Environmental Sciences, Chinese Academy of Sciences, Beijing, China
- Pedro J. J. Alvarez, Professor of Civil and Environmental Engineering and Rice Water Institute, Rice University, Texas
- Pingfeng Yu, Postdoctoral Researcher, School of Environment and Resource Sciences, Zhejiang University, Hangzhou, China
