What goes around comes around. Scientists say chemicals from trash in our landfills are making their way into our waters via the seagulls’ gastrointestinal tracts. A report on this delightful state of affairs was published in the journal Water Research.

We generally stop thinking about our trash the moment the garbage truck comes to collect it. But it doesn’t just disappear. No, our coffee filters and corn-chip bags head to the landfill, where they sit and sit and sit … unless they get eaten first. Then their nutrients, their nitrogen and phosphorus, disappear into an animal’s gullet and reappear on the other side, sometimes a few days later, sometimes miles away—and sometimes in our lakes, rivers, and streams.

Researchers wondered how much of an impact these trash-picking critters could have. They were especially interested in seagulls, whose poop has previously been shown to carry traces of toxic chemicals from our plastic-filled seas.

The first step was to figure out just how many landfill-mooching seagulls we have. Authors Scott Winton and Mark River of the Duke University Wetland Center used documented seagull sightings in the eBird citizen science database to estimate the number of landfill-living gulls across the entire United States. Their calculations came up with about 1.4 million birds.

"But the actual population is probably greater than 5 million,” Winton said in a statement. “That means the amount of nutrients deposited in the lakes, and the costs of preventing or remediating the problem, could be substantially higher."

The scientists then used that 1.4-million figure to calculate the amount of nitrogen and phosphorus the birds might collectively be dumping.

"The idea that gull feces can be a major water quality problem may sound comical—until you look at data from an individual lake," Winton said, noting the impact on North Carolina's Jordan Lake, home to a 14,000-acre state recreation area and more than 1000 campsites. "In Jordan Lake, for instance, we found that a local flock of 49,000 ring-billed gulls deposit landfill feces containing nearly 1.2 tons of phosphorus into the lake annually."

That phosphorus changes the water's chemical composition and could lead to more algae blooms, which can kill off other organisms in the lake’s ecosystem.

Winton and River suggest that rather than clean our waters after they're polluted, a better approach might be to stop the problem at the source: our trash. They recommend limiting landfill size and covering existing garbage heaps to keep the seagulls from ever finding it.