It turns out the cute, harmless-looking rubber ducky floating around in your bathtub may actually be a Trojan horse for ravenous legions of "potentially pathogenic bacteria."
That's the conclusion of a recent study by a research team from the Swiss Federal Institute of Aquatic Science and Technology, ETH Zurich, and the University of Illinois published this week in the journal N.P.J. Biofilms and Microbiomes, per the New York Times. The researchers wrote they collected "19 real bath toys (e.g., rubber ducks) from five different Swiss households" and then compared them to a control group, eventually concluding that the real bath toys had up to 75 million bacterial cells per square centimeter of interior surface.
According to the Times, Furtwangen University in Germany microbiologist Markus Egert told them, "That's the same density of bacteria you can find in human stool samples. There are probably no other places on earth with such high bacterial densities."
(For comparison, the BBC reports University of Arizona microbiology professor Chuck Gerba says toilet seats - which are much cleaner than the public may imagine — have about 50 faecal bacteria per square inch.)
The study found the the low-quality plastic polymers used to manufacture the ducks release carbon over time, providing an important source of nutrition for bacteria. This is compounded by dirty bath water full of nutrients like "personal care products, but also body fluids like urine and sweat," the researchers wrote, and "both human microbiota and environmental bacteria that are released during bathing." The result is colonies of not just potentially infectious bacteria like Legionella and Pseudomonas aeruginosa, but also fungi, all of which could pose an undetermined risk to ducky users:
... Bath toys are typically used by children, who are potentially sensitive and vulnerable users. Squeezing water with chunks of biofilm into their faces (which is not unexpected behaviour for these users) may result in eye, ear, wound or even gastro-intestinal tract infections. To assess the real extent of this risk, more experimental work with specific focus on hygienic aspects is needed.
Given that one of the recommendations given by the researchers is to boil rubber duckies after use, it may simply be easier to just avoid them entirely. The research team noted that simply cleaning the ducks is not enough, because the surviving bacteria tends to be stronger.
In any case, this makes all those giant rubber ducks sometimes floated out into the rivers of major cities all the more ominous. Spare us, oh avatars of pestilence, for we know not what we have summoned!