Researchers are pointing to the food safety and public health threat of microplastics in wastewater, which can serve as a vehicle for pathogenic biofilm communities and antibiotics, introducing these hazards to the environment and crops.

Foodborne Pathogens Form Treatment-Resistant Biofilms on Microplastics in Wastewater

The presence of microplastics in wastewater can cause foodborne pathogens to form biofilms that are resistant to treatment, according to a new study published in PLOS One.

The study published in PLOS One, conducted by researchers at the Norwegian University of Life Sciences, aimed to identify pathogens present in wastewater biofilm communities attached to microplastics—also called “plastispheres”—which are known to promote the spread and survival of human pathogens, aiding their introduction to the environment.

For the study, microplastic particles made of polypropylene, polyvinyl chloride, and high-density polyethylene propylene were submerged in raw and treated wastewater sampled from Norway’s largest wastewater treatment plant, on which plastispheres were allowed to form for 14 and 30 days. Pathogens in the plastispheres were isolated and subjected to genetic sequencing, revealing the presence of Listeria monocytogenes, Escherichia coli, norovirus, and adenovirus. Additionally, Klebsiella pneumoniae and Acinetobacter were successfully cultured from raw and untreated wastewater, suggesting that biofilms on microplastics are protective of these pathogens against treatment.

Although the type of microplastic particle did not affect the microbial composition of the plastispheres, it did affect microbial diversity.

The researchers underline the importance of developing proper wastewater treatment protocols and plastic waste management to mitigate the introduction of pathogens into the environment and food chain via microplastic particles in wastewater.

Microplastics in Wastewater as a Vehicle for Pharmaceuticals, Antimicrobial Resistance (AMR)

Treating and recycling wastewater for use in agriculture is not uncommon, and is a practice that is expected to increase to offset drought-induced water shortages, according to the U.S. Department of Agriculture’s Agricultural Research Service (USDA-ARS). The presence of microplastics in wastewater therefore poses a food safety threat, as microplastic particles can serve as a vehicle for harmful contaminants like pharmaceutical chemicals.

When recycled wastewater is introduced to crops, the microplastics within can release pharmaceutical chemicals, which are then taken up by plants.

Not only is the introduction of pharmaceutical chemicals to crops a food safety hazard in itself, but these chemicals can influence microbes present in the environment to develop AMR, contributing to the global public health threat of increasingly drug-resistant pathogens.

ARS researchers are currently working with partners at Clemson University and the University of North Carolina, Greensboro to investigate the interaction of microplastics and antibiotics in agricultural ecosystems by introducing plastic particles and drugs to soils and measuring the subsequent development of AMR.

Like the Norwegian University of Life Science researchers, ARS experts stress that there may be a need to remove microplastics from treated wastewater to avoid public health consequences, especially if microplastics are shown to increase the uptake of antibiotics and other contaminants into food crops.