E. coli pathogens have already proven that they have a stubborn ability to survive in the human digestive system. Now, new research from the U.S. Department of Agriculture (USDA) shows that they’re also hardy enough to live for months in underwater sediments, sometimes even overwintering in streambeds.
USDA soil scientist Yakov Pachepsky, PhD, and colleagues at the Agricultural Research Service (ARS) Environmental Microbial and Food Safety Laboratory collected three years of data on stream flow, weather, and E. coli levels in a stream in Pennsylvania. They then plugged that information into the Soil and Water Assessment Tool (SWAT), a model that predicts how farming practices affect water quality on watershed scale. Their results suggested that E. coli can survive much longer in underwater sediments than in the water column itself. (Findings from their research have been published in several journals over the past few months, including the June 2011 online edition of. Critical Reviews in Environmental Science and Technology, Vol. 41, issue 12
The particular strains that they analyzed were of the non-pathogenic variety, like most E. coli strains, but there’s no reason why more toxic versions shouldn’t have the same hardiness, Dr. Pachepsky said. And that may have serious implications for food safety.
“Irrigation water has been implicated in carrying pathogens. If the bacteria linger on leafy greens, or any kind of produce, they can enter the leaves, and it’s very hard to disinfect,” he said. “If this is the case, and improper storage may create additional conditions for multiplication, then we have outbreaks. So the microbiological quality of irrigation water is of primary importance, and our research shows that we may not be able to rely on sampling water alone to determine that.”
Dr. Pachepsky’s group was able to detect contamination in the sediment as far as 800 meters away from an original “hot spot.” “That tells us that contamination in one spot can be felt very far downstream, at least half a mile,” he said.
Irrigation systems are shifting more and more from ground water to surface water, in which the contamination of sediment poses a potential issue, Dr. Pachepsky said. “In some places, ground water is depleted and in others, it’s too expensive to get, so surface water is coming more and more into play, and it always has sediments at the bottom,” he said.