If you've just built a sand castle on the beach, you might want to rinse your hands before you scarf down that hot dog.
A new study published this week suggests beach sand contains far more E. coli and parasites than beach water does, and could cause gastrointestinal illness.
Researchers with the U.S. Geological Survey conducted experiments with sand collected from a beach on the shore of Lake Michigan near Chicago and found that just a few grains of sand on your fingertips could lead to cases of illness, such as diarrhea.
Four test subjects sanitized their hands, dug through bags of sand for one minute, then immersed their hands in sterilized water. The water was then tested for E. coli levels.
Results suggest that if 1,000 people played with sand for just one minute and ingested what was on their fingertips, 11 of them would develop a gastrointestinal illness. If that same group ingested what was on their entire hand, 33 would fall ill.
But when subjects rinsed their hands with water just once, the level of E. coli dropped by more than 90 per cent.
"I don't think people really think about [hand-washing]when they're on the beach," said Richard Whitman, an ecologist at the U.S. Geological Survey's Great Lakes Science Center and lead author of the study. "Just having their hands rinsed will dramatically reduce their chances of getting sick."
Mr. Whitman said his team wasn't able to track down the exact source of contamination of the sand along the shore, but he floated a few possibilities.
"Some could be from birds, some could be from algae, some could be from a deposition of sewage-laden water," he said.
But Mr. Whitman was certain of one thing: "Even if it's a closed beach, the water's probably cleaner than that sand is."
He said that on average, beach sand contains levels of E. coli 10 to 100 times higher than beach water. "It tends to be dirtiest where kids play."
E. coli levels are lower right at the shoreline because the sand is being washed constantly by the water and is more exposed to sunlight, which kills bacteria, he said. The highest concentration of E. coli is one metre back from the shoreline.
While government health authorities in Canada and the U.S. regularly test water for E. coli and report the level detected to the public, they don't test sand.
Lou D'Alessandro, the manager of the Grey Bruce Health Unit's Safe Water program in southern Ontario, does weekly water tests at Sauble Beach on Lake Huron - one of the longest freshwater beaches in the world. When the E. coli content surpasses a certain level in two consecutive samples, he is required by Ontario's Ministry of Health to close down the beach until another two consecutive samples come back with non-threatening levels of the bacteria.
"I'd love to see [sand tested] but it's not in our protocols right now," he said. "It's difficult to sample, but I'm sure you'd find quite a live zoo of bacteria in there."
Mr. Whitman said beach-goers should be able to figure out how clean the sand is without the aid of a microscope.
"Usually, if the beach looks dirty, it probably is," he said. "Seagulls are a pretty good barometer - they're trash birds, they're scavengers. There'll be a lot of debris, a lot of dirt, vegetation, bird droppings."
Tom Edge, a research scientist at Environment Canada's National Water Research Institute, said studies have shown that E. coli levels in sand vary by beach.
Research suggests the type of sand could make a difference, though.
"Beaches that have a coarse grain don't generally contain as high a level of E. coli. The ones with a more claylike or silty-like sand can have a higher level," he said.
But a coarse-sand beach could still have high levels of E. coli if it's near a sewage treatment plant or other source of contamination, he said.