New insights into when beach sand may become unsafe for digging and other contact

Tomoyuki Shibata and Helena M. Solo-Gabriele explain that disease-causing bacteria from sewage can cause skin infections and gastrointestinal (GI) disorders in people who come into contact with contaminated water. The U.S. Environmental Protection Agency (EPA) has guidelines to determine when microbe levels in water are high enough to pose an unacceptable risk of GI illness for contact with both ocean water and freshwater. Microbes, however, tend to concentrate in higher levels in beach sand -- to the point where one previous study found that the sand on one fingertip, placed in the mouth, had enough germs to cause GI illness. No guidelines exist to determine when contact with beach sand might be too risky for children and others who play in beach sand, digging in it or being buried in the sand. The scientists set out to fill that knowledge gap.

The scientists used millions of computer simulations and measurements of disease-causing microbes at beaches in California and Florida to determine how many bacteria would have to be present in beach sand to exceed the EPA's guideline for water. In doing so, they established "reference levels" for beach sand that correspond to the EPA risk guidelines for water. The focus of children at the beach environment is especially important, due to play behavior at beach sites that would increase a child's exposure, the scientists noted.

The authors acknowledge funding from the National Science Foundation and the National Institute of Environmental Health Sciences.