The regular reports of water quality at popular beaches provide a measure of the levels of bacteria typically found in the digestive tract of humans and animals. These bacteria, E. coli and Clostridium, can carry serious diseases, yet most outbreaks lead to skin rashes, stomach upsets and diarrhoea.
In the ocean these bacterial levels decline as they are killed by salt water and UV light. The natural actions of waves and currents also act to dilute the residual bacteria. Scientists, however, have been increasingly reporting that the bacteria are found between 10 and 100 times higher in the sand than in the ocean.
Detailed analysis of the interactions between sand and faecal bacteria has shown that sand provides a temporary home so the bacteria can survive for considerably longer. Sand, even when dry, can provide sufficient moisture just a few millimetres below the surface.
Water quality warnings of beaches affected by faecal contamination may also carry a hidden health risk in the sand. Before choosing a place to throw down the beach towel or set up a game of beach cricket, it’s worth considering the many bacteria hidden in the sand.