Scientists now have the dirt on the rubber ducky: Those cute yellow bath toys are—as some parents have long suspected—a haven for nasty bugs, reports the AP. Swiss and American researchers counted microbes inside the toys and say the murky liquid released when ducks were squeezed contained "potentially pathogenic bacteria" in four out of the five toys studied. Bacteria found included Legionella and Pseudomonas aeruginosa, a bacterium that is "often implicated in hospital-acquired infections," the authors say. The study by the Swiss Federal Institute of Aquatic Science and Technology, ETH Zurich, and the University of Illinois was published Tuesday in the journal Biofilms and Microbiomes. It's billed as one of the first in-depth scientific examinations of its kind. They turned up a strikingly high volume—up to 75 million cells per square 0.15 inch—and variety of bacteria and fungi in the ducks.
Tap water doesn't usually foster the growth of bacteria, but low-quality polymers in the plastic give them the nutrients they need. Bodily fluids like urine and sweat, as well as contaminants and even soap in bathwater, add microbes and nutrients and create balmy brine for bacteria. "We've found very big differences between different bath animals," says lead author Lisa Neu, alluding to other bath toys—like rubber crocodiles—that also were examined. "One of the reasons was the material, because it releases carbon that can serve as food for the bacteria." While certain amounts of bacteria can boost kids' immune systems, they can also lead to eye, ear, and intestinal infections. Among vulnerable users: kids "who may enjoy squirting water from bath toys into their faces." The scientists say using higher-quality polymers to make the ducks could prevent bacterial growth. (Another use for the toys: tracking glaciers.)