This is a story about sludge, worms, and songbirds, and it starts in your bathroom cabinet.

Photo: Southernpixel via Flickr

When we treat our wastewater to remove “biosolids” — a polite term for our human waste — all sorts of other things end up in the leftover sludge, including the drugs we take and the “personal care products” like lotion, shampoo, makeup, and cologne that we slather on our bodies, which have been absorbed through our skin and then excreted in our waste. The treated wastewater is usually discharged into the local river, and the sludge that’s been removed from it frequently becomes fertilizer for agricultural production.

Researchers at the U.S. Geological Survey have found that the hungry earthworms who feed on this sludge in farm fields contain concentrated levels of our drugs and personal care products in their bodies. In fact, a USGS study published in February found that the compounds bioaccumulate in earthworms, meaning that the worms bear higher levels of these pollutants than the surrounding soil does. The USGS researchers note that worms could become monitoring species to help us determine the relative pollution levels in soil, but state that the pollution in these worms have “unknown effects” for wildlife (read the story in Science News).

“Unknown” maybe in that particular study, but researchers in the U.K. published a disturbing study about a week later that provides some insight into what happens to the polluted worms: Birds eat them.

This particular study examined European starlings in the wild, who like to forage in farm fields where fertilizer from sewage sludge has been applied, because the soil is rich in earthworms and other organisms who are busy feasting on the nutrients in the fertilizer. But they’re also feasting on the contaminants in the fertilizer, and those contaminants have an impact on the foraging birds (story in The New York Times).

The contaminants in sewage sludge can contain hormone-mimicking compounds that act like estrogen in the birds’ bodies. (Following the thread here? Those compounds are the drugs and personal care products that the USGS was examining in the earlier study.)

The U.K. researchers found that the contaminants boosted development in the part of the male birds’ brains that control their songs, making them sing longer and more complex songs. The researchers also found that female starlings preferred the long, complex songs of the contaminated male starlings.

The bad news is … they’re contaminated. The same endocrine-disrupting compounds in the male starlings that made them attractive as mates make them unfit as fathers, because the compounds suppress the birds’ immune systems and make them sick. While that might be good news for American birders who aren’t fond of invasive starlings, it’s rather bad news for birds everywhere who like to eat worms. While that fat earthworm might taste good and improve a male songbird’s chances of attracting a pretty lady bird, it could actually be crippling his chances of producing a healthy brood of babies.

This might seem like just a scientific curiosity if the same kinds of effects hadn’t also been noted in many other species, including fish, reptiles, and amphibians. Sort of makes you think twice about that nice body spray in your bathroom cabinet that’s supposed to make you more attractive to a mate, doesn’t it?