A Reddit post caused a stir on the Internet this week, claiming that the infamous $ 30 "GamerGirl bathwater" sold by social media star Belle Delphine contained no human DNA – and therefore may not be her bathwater at all . This was immediately criticized and debunked by other Reddit users: shipments of this bathwater had not even been shipped. When the news of the non-scandal hit the offices of The Verge reporters began throwing questions at the science desk, including: "Wait, can you test bath water for DNA?"
"Yes, you can," says forensic biologist Helen Page. Page is a lecturer at Teesside University in the UK and has studied how to get very specific DNA samples from a bath.
It is a serious work. Restoring DNA after a shower or bath can be helpful in investigating a sexual assault, especially if a victim does not want to perform a full forensic examination or is showered after the attack. Page has studied how sperm can be extracted from specially designed mesh objects that fit in shower channels, as well as "bath hair elastics" (also known as sponges, loofahs or stools). She found that you can extract DNA from stitches, from hair ties, and also by simply wiping the walls, floor, and drain of a tub.
Page has shown that it is possible to extract DNA from seeds in bath water, but seeds are very different from other cells. "The structure of a sperm is, as it were, quite resistant to degradation in the same way as other cells," says Page. In the case of dolphins, the most likely DNA source would be skin that could peel off in the tub. Page's research was also conducted under controlled conditions in the laboratory. In the case of "GamerGirl Bathwater," without considering the manufacturing process, it's really impossible to know how much of Dolphin's DNA actually made it into the water.
"It's hard to know how many cells were shed during washing," says Page. She points out that with a light wash of dolphins less skin cells would peel off than with a more thorough wash. "I very much doubt that there will be a lot of DNA in a small bottle of bath water," says Page.
It's also not clear how long DNA would last in the bathwater. The biggest threats to DNA integrity are heat, moisture and bacteria that are abundant in tubs. Soaps and other cleaning products may also play a role in DNA degradation, but there is not enough scientific research to know for sure.