Scientists have discovered that a significant amount of microplastics and the persistent chemicals known as PFAS circulate through landfills and wastewater treatment facilities, ultimately re-entering the environment.
Researchers examined leachate—liquid waste—from four landfills in Illinois, as well as wastewater treatment plants connected to them, to track the movements of two contaminants: microplastics and PFAS (per- and polyfluoroalkyl substances).
This study revealed a silver lining: landfills effectively hold back most plastic waste, and wastewater treatment facilities manage to filter out 99% of microplastics and a portion of PFAS from the waste they process. However, the downside is that both microplastics and PFAS accumulate in the biosolids that settle at the bottom of these treatment plants, which then require alternative disposal methods.
The findings were published in the journal Science of the Total Environment.
According to the National Biosolids Data Project, which is funded by industry sources, around 70% of biosolids from Illinois wastewater facilities are recycled as fertilizers for agricultural use, while 30% are sent to landfills. This indicates that a major portion of the microplastics and PFAS entering wastewater treatment plants is ultimately released back into the environment, as explained by John Scott, a research scientist at the Illinois Sustainable Technology Center at the University of Illinois Urbana-Champaign, who conducted the study alongside fellow scientist Andres Prada.
“Wastewater treatment plants merely transfer contaminants from one medium to another,” Scott noted.
Each year, several hundred million tons of plastic are manufactured globally, with an estimated 79% ending up in landfills or escaping into the environment. Both microplastics and PFAS, which can interfere with hormonal functions, are now widespread, discovered in soil, water, and even within human bodies.
This research stands out as it quantified the mass of microplastics found in both landfill leachate and the inflows and outflows of wastewater, rather than just counting the number of microplastic particles per volume, which is less reliable as particles can fragment into smaller pieces. The team calculated mass by measuring the total surface area of the plastic particles and applying standard thickness and density measures associated with common microplastic materials like polyethylene and polypropylene.
“Typically, landfills and wastewater treatment facilities are examined in isolation, but they actually function as interconnected systems,” Prada explained. “Regulations mandate that landfills direct their liquid waste to treatment plants.”
Additionally, many previous studies focused exclusively on a single contaminant at a time.
“Our goal was to integrate both systems and provide comprehensive results for both contaminants,” Prada said.
The analysis showed that while landfills effectively retain microplastics, their leachate contains notably high concentrations of PFAS.
“We were taken aback by the elevated PFAS levels found in landfill leachate, while the microplastics concentration was lower than we anticipated,” Prada remarked.
Plastics degrade slowly in landfills due to waste compaction and lack of sunlight after being buried, yet they continue to fragment into smaller particles that will eventually be carried away with leachate, Scott warned.
Wastewater treatment plants are designed to process thousands of gallons of wastewater from sanitary and storm systems, which also contains notable amounts of microplastics and PFAS. The concentration of PFAS in this water is lower than what is found in landfill leachate, but due to the vast volume of water flowing through these systems, the overall load of both contaminants is higher, according to the team.
Wastewater treatment facilities can receive up to 10,000 gallons of wastewater every minute, while they only process approximately 30,000 gallons of landfill leachate daily, Prada added.
Addressing microplastic and PFAS contamination in biosolids poses a complex challenge. Spreading these substances on cropland is not advisable, Scott pointed out. “However, what alternative do we have? If we bury it in landfills, we are simply cycling it back through treatment plants and then to landfills again.”
Treating biosolids prior to disposal is a costly endeavor, Scott mentioned. The preferable solution would be to curb pollution from plastics and PFAS at the source.
“It’s crucial for us to start moving away from these materials and halt their production,” Scott urged. “We need to stop it at the source before the situation worsens.”
This research was supported by the Hazardous Waste Research Fund, managed by the ISTC, part of the Prairie Research Institute at the University of Illinois.
