Maine made headlines in April as the nation’s first state to ban the spreading of sludge and sludge-based compost. Supporters of the law recognized an urgent need — in the Act’s language — “to prevent further contamination of the soils and waters of the State with so-called forever chemicals.”
Few who endorsed that measure realized they were scoring a twofer. By restricting the spread of per- and polyfluoroalkyl substances (PFAS), enduring synthetical chemicals linked to many health risks, Maine unwittingly reduced the threat from another insidious contaminant threatening ecosystems and food safety: microplastics.
Here’s to inadvertent foresight. The sludge-spreading ban is a critical first step in a long-term effort needed to address ubiquitous microplastic pollution.
Filtering out problematic microplastics and then broadcasting them
Microplastics (under 5 mm in size) come in two flavors: primary ones released directly in manufacturing or use of plastics (like the microbeads found in some cleansers and paints), and secondary ones from plastic degradation.
A steady stream of these secondary microplastics — much of them synthetic clothing fibers and tire wear particles — enter wastewater. Most treatment plants do an impressive job removing microplastics, often filtering out more than 90 percent, but the smallest nanoplastics still remain in effluent water.
That filtration success means that microplastics accumulate in wastewater sludge; one study found a single treatment plant had plastic residuals roughly equal to 20,000-plus credit cards each month.
Maine’s sludge-spreading ban takes effect later this summer, but for decades countless microplastics in sludge have been spread on farm fields and sold as compost—here and across the U.S. Roughly half of the nation’s sewage sludge is still land-applied, and the U.S. Environmental Protection Agency (EPA) continues to promote its “beneficial use” as an agricultural fertilizer.
The EPA has not calculated the volume of microplastics this practice introduces into soil ecosystems. An international team of researchers ballparked that figure at between 44,000 and 300,000 tons each year for the U.S., noting that could mean the annual load of microplastics to farmland exceeds the total accumulated load of 93,000 to 236,000 tons in the global oceans. Another study estimated that the annual release of plastics to land is four to 23 times greater than the release to oceans.
Beyond that sludge load to farm soils, microplastics literally rain down from the sky, adding to residues from the plethora of plastics used in agricultural production. Pesticide and fertilizer manufacturers also encapsulate products in plastic coatings, giving primary microplastics a direct means of entering soils and food webs.
Microplastics deposited on farmland, primarily polyester fibers and polyethylene fragments, readily migrate to waterways and adjoining areas, further spreading contamination. Plowing can also redistribute microplastics, according to a recent study that found elevated concentrations of plastics in soils 34 years after the last sludge application.
Maine’s ban on spreading sludge will reduce further build-up of microplastics in farm soils, but the effects of past contamination could extend for decades to come.
Infiltrating food webs
Research on the impacts of microplastics in ecosystems is still nascent and no standardized method exists yet for assessing their presence in soil.
But there’s growing scientific evidence that microplastics in soil could jeopardize both food security and food safety. There’s also growing concern that microplastics could interfere with the soil’s capacity to sequester carbon, reducing its capacity to combat the effects of rising greenhouse gas emissions.
Early studies suggest that microplastics can decrease crop biomass, block soil pores, reduce microbial activity and harm earthworm populations and other soil organisms. Student researchers at the University of Maine recently found — in samples taken for an unrelated experiment — that microplastics were in a fifth of the snails and slugs and more than half of the livestock feces.
Microplastics carry with them more than the chemicals used in plastic production, like bisphenols, phthalates and flame retardants. They also attract heavy metals and toxic compounds that adhere to their surface, making them potential vectors aiding uptake of contaminants into tissue.
Researchers at the Illinois Sustainable Technology Center found that — in contrast to laboratory settings — PFAS are especially likely to stick to microplastics in environments with inorganic and organic matter — such as soil or lake water.
Like “forever chemicals,” microplastics bioaccumulate in plant and animal tissue, and become more concentrated moving up the food web. They’ve already shown up in fruits and vegetables, beverages, honey, seafood and packaged poultry.
Researchers reported this spring that they found microplastics in human blood, and while the implications of that remain unclear, findings from lab animal studies are not encouraging. Microplastics appear to cause metabolic disruptions, accumulate in organs, and damage cells.
Getting a strategy
In coming years, microplastic contamination and its health impacts could become far worse, since global plastic production is projected to double by 2040. While the new ban on sludge-spreading will limit further pollution, Maine needs to address historic contamination and the ongoing generation of microplastics.
California has led the way with a recently released statewide microplastics strategy. Its strategy focuses primarily on marine environments, though, so Maine — as with PFAS — will need to pioneer efforts to protect farmlands and terrestrial food webs.
Maine has already enacted a ban on microbeads in personal care products and over-the-counter drugs, a law that took effect in 2019. To further limit the spread of primary microplastics, the Legislature should expand that ban to cover all intentionally added microplastics, including plastic coatings used in pesticides and fertilizers.
As more states take action to limit the spread of microplastic pollution, they may gain the collective clout to seek reforms in the industries most responsible for generating microplastics, like manufacturers of synthetic textiles and tires.
Maine has not begun to test for microplastics in sludge but the Department of Environmental Protection is in the process of testing 700-plus permitted sludge-spreading sites for PFAS contamination. Ironically, testing for microplastics at some of these sites might help identify where sludge was actually distributed, according to two Cornell University engineers.
Emerging confrontation with the ubiquity of systemic pollutants
Researchers and waste industry professionals often label microplastics “contaminants of emerging concern” as if we’d just now noticed the downsides to a material that has been around since “Bakelite” plastic hit the market in 1907. EPA uses the term, too, even as it admits that “microplastics have been identified as a potential environmental concern since the 1970s.”
PFAS, too, often get called “emerging contaminants” although they’ve been in production since the 1940s, with their health risks known to the manufacturing corporations like DuPont and 3M since the 1960s.
It’s time to drop the bureaucratic euphemisms and confront what really is emerging: a vast and costly environmental health problem in which persistent, irretrievable contaminants are tainting food webs across the globe.