Worm Food

Cheerful earthworms going about their business, churning up the soil, recycling nutrients—it all sounds good, until you learn that the worms might be recycling more than soil, and that their equanimity might be courtesy of Prozac.

Scientists have known for several years that PPCPs—the pharmaceuticals and personal care products that make their way into wastewater—are not completely removed in sewage treatment plants. Residue is discharged as “treated” wastewater into places such as San Francisco Bay, where no one knows its potential impacts. Just recently, scientists also began examining whether the pharma residue might be present in biosolids, the nutrient-rich sludge left after treatment. Roughly half of the many thousands of dry tons of treated sludge is applied as fertilizer to crop-growing soils in the United States every year.

In a recent study, US Geological Survey scientists found that a potpourri of household disinfectants, pharmaceuticals, synthetic fragrances, and plasticizers often is present in biosolids—and in concentrations tens to thousands of times higher than in treated liquid waste. On a hunch, they collected earthworms from agricultural fields in the Midwest and western United States. “It wasn’t a huge intellectual insight on our part,” says USGS’ Ed Furlong, one of the study’s scientists. “Earthworms aren’t migratory—they’re in the soil, they reflect what’s happening locally. They’re the primary consumers of organic material in soil. We thought that if these compounds persist for any length of time in the soil, the earthworm would be a good candidate to study.”

The worms proved fruitful. The researchers detected 31 compounds, among them household disinfectants, fragrances, caffeine, and Prozac, in the worms’ tissues, in concentrations ranging from 100s to 1,000s of micrograms per kilogram (parts per billion). Furlong stresses that these concentrations are very low, and he doesn’t want people to be alarmed. But he does think that the results point to the need for research—and for solutions. “You have to remember that wastewater treatment systems were never designed to remove all of these compounds,” says Furlong. “Yet they’ve been very successful at managing nutrients, pathogens, and carbon loads as new issues have arisen. This is the way it works—scientists identify the questions, and the wastewater community looks for answers. We’re still coming up with the questions.”

Here’s one—if these chemicals are in worms, what about robins? “It might be a good idea to look at the primary consumers of earthworms and see if they are taking it up,” says Furlong.

For now, his team is investigating whether any of these same compounds are found in the plants that grow in the biosolid-enriched soil—plants that are food for livestock and humans. Furlong agrees that the discovery of Prozac in earthworms illustrates the closed nature of our loop: there really is no “away” anywhere, no matter how much flushing or filling we do. “We’ve always known that the system is broader than ‘flush and gone.’ But this is a way for people to recognize that their choices in what they use and what we as a society use are going to be reflected in the waste stream—and end up in the watershed.”

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