Can Biochar Help Remove Microplastics from Soil?

The interns were there because Pig’s Eye is one of several Twin Cities sites that Emilie Snell-Rood – associate professor, co-lead of the MSP Urban Long Term Ecological Research program and an IonE affiliate – is studying along with postdoctoral researcher Lindsey Kemmerling and community partner Urban Roots, the nonprofit running the internship program. Their research investigates microplastic pollution in urban agriculture and is supported by an Institute on the Environment Impact Goals grant.

As the group walked, Erin Bjork, a natural resources technician with Saint Paul Parks and Recreation, shared that beneath a layer of clean soil lies the remains of more than a decade’s worth of trash. 

Pig’s Eye once served as the state’s largest unpermitted dump until it was shut down in 1972. After its closure, the site was used to dispose of wastewater treatment sludge and incinerator ash until the mid-1980s, before eventually being designated a Superfund site.

Remediation efforts have been attempted throughout the years, but environmental concerns like microplastic pollution remain. That lingering contamination makes Pig’s Eye an ideal outdoor classroom – and a test site. 

Inspired by conversations with Urban Roots partners about rising concerns over microplastics in human bloodstreams and brains – and curiosity about how those particles appear in urban soils – Snell-Rood applied for an IonE Impact Goals grant to launch early-stage research while deepening her partnership with the nonprofit. 

IonE’s Impact Goals funding gave Snell-Rood’s lab the flexibility to break into this new field. “We wouldn’t have been competitive for federal funding yet because microplastics were so new to us,” says Snell-Rood.

Since 2023, the funding has allowed Snell-Rood’s team to begin microplastic research and support the Summer Deep Dive program – paying stipends for youth, covering supplies, and providing Urban Roots staff with resources to weave research into summer programming.

David Woods, the Urban Roots conservation program director, said that after over 25 years of food and environmental youth programming at Urban Roots, this funding has allowed them to “say yes to a lot more.”

Alongside youth engagement, Snell-Rood’s lab has been investigating how microplastics are affecting the urban garden ecosystem, and ways to remediate those pollutants.

A primary focus of the microplastic research is testing whether biochar – a charcoal-like material made from plant or wood waste – can help trap plastic particles in soil and limit their movement. By comparing garden plots with biochar added to those without, the team hopes to see if the additive can both improve soil health and reduce exposure to emerging pollutants.

So far, preliminary analysis has found “soils from the biochar additions have less microplastics hanging out in them after the biochar addition,” says Snell-Rood. They are still studying whether this trend will hold up and if it differs depending on the type of microplastic.

The team has also found that pollinators show relatively low vulnerability to microplastics. In an experiment adding microplastics to the diets of caterpillars, the team found that the insects “mostly seem to just be pooping them out,” says Snell-Rood with a laugh.

Although the research is still underway, Snell-Rood says one of the biggest surprises has been “just how diverse the plastic bits are in these soil samples.”

Even so, Snell-Rood emphasizes the importance of perspective, noting that in terms of microplastic exposure “it’s still better to garden in urban soils than to spend 24 hours a day inside.” Maybe not at Pig’s Eye itself – but in most places, getting outside, planting something new, and caring for the land still brings more healing than harm.
 

Molly Stroh is the Communications & Editorial Fellow at the Institute on the Environment.