At least some of the E. coli bacteria closing Great Lakes beaches is growing there naturally and is not the result of sewage spills, gulls or pets.
That's the finding of University of Minnesota research projects reported recently in three scientific journals. They echo a Michigan study reported in the News Tribune one year ago.
It was previously believed that E. coli could come only from the guts of warm-blooded animals, and that, if found in the environment, there must have been a recent source of excrement from one of those animals.
That's why E. coli is used as an indicator for other, more dangerous bacteria that could spread human diseases.
On Tuesday, the Minnesota Pollution Control Agency issued an advisory for the Duluth Boat Club harbor beach at 14th Street on Park Point because of high E. coli levels.
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But if e-coli is naturally occurring in the sand, it may mean the bacteria doesn't represent any real danger in the water, or at least that it doesn't make for a great indicator of elevated risk of disease. The recent studies also found E. coli in soil near streams.
"E. coli comes from several sources and may survive and replicate in sand, sediment, soils and algae in the water,'' said Michael Sadowsky, professor at the University of Minnesota-Twin Cities, in a statement. "This could increase the bacteria counts found on beaches, especially if the counts are taken on windy days when the sediment and algae are churned up. Often it's assumed that E. coli found during beach monitoring is washed into the water from the land or comes from sewage overflows, and we've shown that's not always the case.''
In June 2006, a Central Michigan University report published in the Journal of Great Lakes Research confirmed that E. coli can live and thrive in beach sand without a warm-blooded host.
E. coli is even surviving winter in the sand and is reproducing and expanding in the summer with no new source, the Michigan and Minnesota studies found. It's not clear what the original source of the sand-dwelling bacteria was or even if there was an outside source.
Scientists can determine what animal E. coli comes from based on DNA.
Wind and waves free the bacteria from the sand and bring it in contact with people. Beach monitoring programs then pick it up in water samples and post beaches as closed.
That's happening every summer now along the waterfront of the Duluth-Superior harbor, where E. coli problems are chronic and some waterfront areas remain posted most of the summer for people to stay away.
