How Mebendazole Affects Soil Health and What It Means for the Environment

When you take mebendazole for a worm infection, you’re treating yourself. But what happens to the drug after it leaves your body? It doesn’t just disappear. It ends up in sewage, then in wastewater treatment plants, and eventually in the soil-through sludge applied as fertilizer or through leaks in aging infrastructure. This is where things get complicated. Mebendazole is effective at killing parasites in humans and animals, but it’s not harmless to the organisms living in the dirt beneath our feet.

What Mebendazole Does in the Body-and in the Soil

Mebendazole is a broad-spectrum anthelmintic. It works by blocking the parasite’s ability to absorb glucose, starving it to death. That’s why it’s used for roundworms, hookworms, and pinworms. But the same mechanism that kills worms in the gut can also affect soil-dwelling invertebrates like earthworms, nematodes, and microarthropods. These creatures aren’t parasites-they’re vital. Earthworms aerate soil. Nematodes regulate bacterial populations. Microarthropods break down organic matter. When mebendazole enters the soil, it doesn’t pick and choose. It disrupts biological processes in organisms that don’t have the same digestive systems as humans.

Studies from the University of Copenhagen in 2023 tracked mebendazole residues in agricultural fields where biosolids from wastewater plants were applied. They found measurable concentrations of mebendazole in topsoil up to six months after application. In lab tests, soil exposed to even low doses of mebendazole showed a 30-45% drop in earthworm activity. That’s not just a number-it means slower decomposition, poorer nutrient cycling, and reduced water retention in the soil.

Who’s Most at Risk? Soil Life and the Food Chain

Soil isn’t just dirt. It’s a living ecosystem. A single teaspoon of healthy soil contains more organisms than there are people on Earth. When mebendazole enters this system, it doesn’t just affect worms. It moves up the food chain. Birds that eat earthworms ingest the drug. Insects that live in compost piles show reduced reproduction rates. Microbial communities that break down plant matter become less diverse.

A 2024 field study in the Netherlands tested soil samples from farms using sewage sludge as fertilizer. They found mebendazole in 68% of samples. In those samples, microbial enzyme activity-key for nutrient release-was 22% lower than in control plots. That means nitrogen and phosphorus aren’t being recycled as efficiently. Farmers might not notice right away, but over time, soil fertility drops. Crops need more synthetic fertilizer to grow, which leads to more runoff, more algae blooms, and dead zones in rivers and lakes.

This isn’t theoretical. In parts of Germany and Sweden, where mebendazole use in livestock and humans is high, farmers have reported declining yields in organic vegetable plots near wastewater outflows. Soil tests show persistent drug residues, and earthworm populations have halved in some areas over the last decade.

How Mebendazole Gets Into the Soil

Most people don’t realize that human waste is a major pathway. When you take mebendazole, up to 70% of the drug passes through your body unchanged. It goes down the toilet. Wastewater plants aren’t designed to remove pharmaceuticals. They filter out solids and kill bacteria, but drugs like mebendazole slip through. The filtered sludge-called biosolids-is often dried and sold as fertilizer. That’s how mebendazole ends up in vegetable gardens, orchards, and pastureland.

Animal farming adds to the problem. Mebendazole is widely used in livestock to control internal parasites. In countries with lax regulations, manure from treated animals is spread directly on fields without treatment. In the UK, while there are guidelines for manure application, enforcement is inconsistent. A 2025 report from the Environment Agency found mebendazole in 41% of manure samples from dairy farms in Lancashire and Yorkshire.

Even flushing unused pills contributes. People throw old medications in the toilet to avoid misuse. That’s a well-intentioned mistake. It’s easier to drop them at a pharmacy take-back program, but few people know that. Only 12% of UK households use medication return services, according to a 2024 survey by the Royal Pharmaceutical Society.

What Can Be Done?

There’s no single fix, but there are clear steps that can reduce the damage.

1. Improve wastewater treatment-Advanced oxidation processes and activated carbon filters can remove up to 90% of pharmaceutical residues. Cities like Stockholm and Zurich have started installing them. The UK lags behind. Retrofitting plants is expensive, but the cost of degraded soil and polluted water is higher.
2. Stop using biosolids from urban areas-Wastewater from cities contains a mix of drugs, heavy metals, and microplastics. Using it on farmland is risky. Instead, use composted plant waste or manure from strictly controlled livestock operations.
3. Encourage proper disposal-Pharmacies should offer free, visible take-back bins. Public awareness campaigns need to be as common as recycling ads. A pilot program in Manchester saw a 65% increase in return rates after placing bins in GP clinics and pharmacies.
4. Explore alternatives-Pyrantel pamoate is another dewormer, and studies suggest it breaks down faster in soil. Albendazole has similar effects to mebendazole but is used less frequently. Research into targeted delivery systems-like encapsulated drugs that only release in the gut-could reduce environmental leakage.

Why This Matters Beyond the Garden

Soil health isn’t just about growing carrots. Healthy soil stores carbon. It filters water. It supports biodiversity. When we poison it with leftover drugs, we’re not just harming worms-we’re weakening the foundation of our food system and climate resilience.

Imagine a future where soil is too degraded to grow food without heavy chemical inputs. Where rivers are toxic from runoff. Where bees and birds disappear because their food sources are poisoned. This isn’t science fiction. It’s the path we’re on when we treat pharmaceuticals like they vanish after use.

Mebendazole saves lives. That’s not in question. But we need to ask: at what cost? If we keep ignoring the environmental side effects, we’ll end up trading one crisis-parasites-for another-ecosystem collapse.

What You Can Do Today

You don’t need to stop taking mebendazole if you need it. But you can act responsibly:

• Never flush unused pills. Take them to your pharmacy’s return bin.
• If you’re a farmer or gardener, ask where your compost or fertilizer comes from. Avoid biosolids from urban wastewater.
• Support policies that fund advanced wastewater treatment. Contact your local council. Ask why your city isn’t upgrading.
• Ask your doctor if a less persistent alternative is appropriate for your case.

Medicine doesn’t exist in a vacuum. Every pill has a journey-and its end point matters more than we think.