The ocean is, essentially, the world’s largest toilet. Fish poop, whales poop, dolphins poop. Cruise ships dump a billion gallons of man-made sewage into the ocean every year, and rain washes some more fecal matter (from dogs, birds, and people) into storm drains and out to sea.
Despite all that, the water may not be what you have to worry about when you go to the beach, according to a new study in the journal Environmental Science and Technology. Environmental microbiology researchers at the University of Hawaii at Manoa found that common bacteria strains found in feces survived longer in sand than seawater. Which makes the fact that you track home piles of sand in every cranny of your body after a day at the beach awesome.
Bacteria like Clostridium perfringens—one of the most common causes of food poisoning and an indication of the presence of human sewage—decayed slower and were found in higher quantities in beach sand than in seawater. And you don’t have to get sand in your sandwich to come in contact with these poopy bacteria. A previous study found that just digging or being buried in sand increased risk of getting diarrhea.
So maybe wash your hands a few times over the course of your beach outing. And it's probably a bad idea to pair your sand castle building contest with a hot dog eating contest.