Antidepressants and other psychoactive drugs are designed to affect the human brain. But after they enter the water system in excrement or unused drugs flushed down the drain, traces of these compounds can enter the environment in biosolids—the nutrient-rich material left over after wastewater treatment that is used as fertilizer. New research suggests an unexpected mitigation strategy: using wood-rotting fungi that can break down these chemicals before they reach soil, crops, and people.
Conventional wastewater treatment methods are effective at killing pathogens and reducing metals, but they are far less successful at neutralizing complex organic chemicals. This limitation prompted the research team to explore new, low-cost, and sustainable approaches to reducing pharmaceutical contamination before biosolids are applied to croplands.
Key Takeaways
- Two species of white-rot fungi remove most of the psychoactive pharmaceuticals tested-sometimes almost completely-in biosolids.
- The drugs often degraded differently in biosolids than in standard laboratory test liquids, underscoring the importance of evaluating treatments under real-world conditions.
- The broken-down products appear less harmful, suggesting true detoxification rather than redistribution of contaminants.
Researchers in the Johns Hopkins Department of Environmental Health and Engineering, which spans the Bloomberg School of Public Health and the Whiting School of Engineering, have shown that two species of "white-rot" fungi—oyster and turkey tail mushrooms—can degrade a wide range of psychoactive pharmaceuticals commonly found in biosolids. The study demonstrates that these fungi can break down many persistent drug compounds before biosolids are applied to farmland, potentially reducing environmental and public health risks.
The findings were published in ACS Environmental Au.
Biosolids are widely used across the United States as fertilizers and soil conditioners because they are rich in nitrogen, phosphorus, and organic matter.
While some studies have shown that pharmaceuticals can be absorbed by plants grown in biosolids-amended soils or irrigated with wastewater, there is no conclusive evidence that these chemicals reach people who consume those crops.
"Even small concentrations of these compounds can have psychological effects when consumed, which is why they have become contaminants of concern," says Kate Burgener, a PhD student and lead author of the study. "Many of them are also difficult to break down and can persist in the environment, where they may have toxic effects on aquatic life."
The researchers focused on white-rot fungi, a group of fungi known for their ability to decompose lignin—the tough polymer that gives wood its rigidity. Unlike many bacteria, white-rot fungi release powerful enzymes directly into their surroundings. These enzymes are "nonspecific," meaning they can act on a wide range of complex molecules rather than targeting a single compound.
It is their enzymatic flexibility that makes white-rot fungi well-suited for breaking down pharmaceuticals, which are tightly bound to organic matter in biosolids.
The two species—Pleurotus ostreatus (oyster mushroom) and Trametes versicolor (turkey tail)—are among the most studied and most widely available mushroom species. Biosolids from a municipal wastewater treatment plant were spiked with nine psychoactive drugs, including commonly used antidepressants such as citalopram and trazodone. The fungi were then allowed to grow directly on the biosolids for up to 60 days.
To better understand how fungal growth conditions influenced degradation, the researchers conducted parallel experiments in liquid media without biosolids. Using high-resolution mass spectrometry, they measured drug concentrations over time and identified chemical byproducts formed as the fungi broke the compounds down. Some compounds degraded more in the biosolids experiments than in liquid culture.
"While it is promising when liquid fungal culture degrades a compound, it doesn't necessarily mean that's what will happen when you grow the fungi in a polluted environment," says Burgener. "So we decided to test a relevant medium—in this case biosolids—that gets contaminated with psychoactive chemicals with the fungi to see if fungi break down these contaminants before they are spread in the environment."
Both fungal species proved highly effective. Each degraded eight of the nine pharmaceuticals tested, with removal rates ranging from approximately 50% to nearly complete elimination after two months. Pleurotus ostreatus was particularly effective, removing more than 90% of several antidepressants.
Chemical analyses showed that the fungi were not simply trapping the drugs but chemically transforming them. The researchers identified more than 40 products formed as the pharmaceutical molecules were broken apart. Many of these reactions—such as cleavage into smaller molecules or the addition of oxygen—are characteristic of white-rot fungal enzymes.
Using the EPA's Cheminformatics hazard assessment module, the researchers predicted that most of the transformation products would be less toxic than the original drugs, suggesting that fungal treatment may reduce overall hazard rather than replace one contaminant with another.
The findings highlight "mycoaugmentation"—the intentional use of fungi—as a promising strategy for treating biosolids prior to land application. Because white-rot fungi are widespread in nature and can grow on solid materials, they could potentially be integrated into existing biosolids management practices with relatively low energy and infrastructure requirements.
"The fungi represent a promising bioaugmentation strategy on a real-world matrix, not just lab-based liquid culture," Burgener says.
On a personal note, Burgener prefers her mushrooms in the laboratory rather than on her plate.
"I don't find them especially appetizing," she says. "They're good for you, so sometimes if they're doused in butter, I'll eat them."
The study was co-authored by Carsten Prasse, associate professor in the Department of Environmental Health and Engineering. It was supported by a U.S. Environmental Protection Agency National Priorities grant (R840247) and Johns Hopkins University.
