Prada AF, Scott JW, Green L, Hoellein TJ. Microplastics and per- and polyfluoroalkyl substances (PFAS) in landfill-wastewater treatment systems: A field study. Sci Total Environ. 2024 Dec 1;954:176751. doi:10.1016/j.scitotenv.2024.176751. Epub 2024 Oct 6. PMID: 39378946.
The article excerpts and summarizes the research cited above
and the University of Illinois press release.
Since the 1950s plastics have been mass produced in greater
and greater volumes. Global production of plastics was 1.5 million tons/year in
the 1950's and was 370 million tons/year in 2019 (Kumar et al., 2021). It is
estimated that 79 % of all the plastic produced has either been buried in landfills
or becomes fugitive in the environment. Only 9 % of plastic has been recycled
(Geyer et al., 2017). As a result,
plastic pollution, including microplastics the name given for particles smaller
than 5 mm) are now ubiquitous in the environment (Lim, 2021).
Per- and polyfluoroalkyl substances (PFAS) are a class of
synthetic organic chemicals are entirely synthetic. PFAS are used extensively
in aqueous film-forming foams (AFFFs), non-stick coating, paper products,
textiles, and other products because they repel oil and water, resist
temperature extremes, and reduce friction (Paul et al., 2009; Lindstrom et al., 2011).
By design, PFAS are thermally stable, oxidatively recalcitrant, and resist
microbial degradation (Kannan et al., 2001; Kissa, 2001; Parsons et al., 2008)- in other words
they last almost forever. Because of their large-scale use and high stability,
PFAS have spread and are widely detected at low levels in water, soil, and the
atmosphere. (Ahrens et al., 2011; Hamid et al., 2018).
In the last two decades, many PFAS such as perfluorooctane
sulfonate (PFOS) and perfluorooctanoic acid (PFOA) have been ubiquitously
detected in wildlife and humans (Giesy et al., 2010; Nakayama et al., 2019; Remucal, 2019; McDonough et al., 2022).
In animals, PFAS can be immunotoxins, reproductive toxins, developmental
toxins, endocrine disruptors, and possible carcinogens (Lau et al., 2007; Gorrochategui et al., 2014; Grandjean and Clapp, 2015; Jian et al., 2018; Steenland and Winquist, 2021; Panieri et al., 2022).
Microplastics have also been related to health problems as
they could disrupt the gut microbiome, enter organ tissues, cause local
inflammatory and immune responses, and transport other toxic substances (Gruber et al., 2022).
Landfills and wastewater treatment plants (WWTPs) have been
found to be point sources for many emerging contaminants, including
microplastics and PFAS (Michielssen et al., 2016; Stahl et al., 2018; Solo-Gabriele et al., 2020; Sun et al., 2021). Landfill leachate may
contain 102 microplastics per liter (Sun et al., 2021) and PFAS in
concentrations of parts-per-billion (Harrad et al., 2019). WWTP effluent may
contain tens of microplastics per liter (Franco et al.,
2021) and PFAS in concentrations of parts-per-trillion
(Gallen et al.,
2018).
Landfills and WWTPs are
places where plastic materials and PFAS containing material are disposed. However,
those materials do not entirely stay in the landfill and WWTPs. Previous research
suggests most microplastics and PFAS that enter WWTPs are retained in the
biosolids (Harley-Nyang et
al., 2023; Garg et al.,
2023). Biosolids are commonly later used as soil
amendments and thus facilitate the return of contaminants to the environment
when applied to land. Biosolids have also been disposed of in landfills, and
WWTPs are interconnected by the regulatory requirement that landfill leachate must
be treated before it is discharged to surface waters (USEPA, 2000).
Previous studies have examined these systems separately and have
reported concentrations of microplastics and PFAS without further investigation
of how much of the detected concentrations in WWTP influents come from landfill
leachates compared to city sewage.
In the 2024 study cited above, the scientists measured microplastics and PFAS
throughout the linked landfill-WWTP systems, where landfill leachate entered a
WWTP (N = 4 different systems). The objectives of this study
were to:
- Quantify microplastics and 14 of the most common PFAS compounds found in landfill leachate and WWTP influent, effluent, and biosolids
- Perform detailed size measurements of microplastics to calculate microplastic mass, and
- Generate mass balances of microplastics and PFAS to assess their fate.
“We were surprised how high the PFAS levels were in landfill leachate, while the microplastics were lower than expected,” Dr. Andrea Prada
said.
Unfortunately, both microplastics and PFAS accumulate in the
biosolids that settle to the bottom of wastewater treatment plants. These
biosolids must be disposed of in other ways and have been landfilled and land applied
as an agricultural amendment for decades.
Wastewater treatment plants are designed to process
thousands even millions of gallons of wastewater from sanitary (and in older
urban areas storm) sewer systems. That water carries a significant load of
microplastics and PFAS from homes and businesses. While the concentration of
PFAS in water flowing through these systems is lower than that found in
landfill leachate, the massive volume of water coming in from sewers makes the overall
mass of both contaminants higher.
The WWTPs in the study can take in 10,000 gallons of
wastewater per minute but only about 30,000 gallons of landfill leachate per
day. “The problem of microplastics and PFAS in biosolids is not easy to solve,the researchers said. Spreading PFAS and microplastics across cropland is not a good practice,” Dr. John Scott said. “But what else are we to do with it? If we landfill it, we’re just going around and around in the circle of moving it from landfill to wastewater treatment plant and back to the landfill.”
Mankind has created an unholy loop that we need to solve.
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| Photo by Fred Zwicky U of I |
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