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Monday, July 28, 2014

E. coli can’t live free or die in our rivers; N.H. standards are unusually strict

David Brooks

New Hampshire, it is fair to say, is not known for imposing overly strict environmental standards – “Live Free or Die,” and all that.

But when it comes to E. coli bacteria in our swimming water, New Hampshire is actually very strict – maybe the strictest country in the land. ...

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New Hampshire, it is fair to say, is not known for imposing overly strict environmental standards – “Live Free or Die,” and all that.

But when it comes to E. coli bacteria in our swimming water, New Hampshire is actually very strict – maybe the strictest country in the land.

State law RSA 485-A:8 sets a maximum of 88 colonies per 100 milliliters of water for a sample in “designated beach areas” in Class A waters. That’s well below the strictest federal EPA limit of 235 colonies used by most other states, even persnickety Massachusetts.

Why are we so strict?

“I’ve asked that question, and I’ve had to rely on anecdotal stories,” said Sonya Carlson, who as beach program manager for the Department of Environmental Services thinks about E. coli bacteria in swimming water all the time.

This topic demonstrates, by the way, the complexity of public health.

In the physical sciences, you usually can pin down an exact value at which something happens by limiting variables, and objects are often interchangeable. Every electron is exactly the same.

In public health, every patient and every circumstance is a little different, variables are almost infinite, and exact values rarely exist. There’s no cut-off figure for E. coli concentration at which water becomes “healthy” or “unhealthy.”

“At some point, we all agree it’s bad; we just don’t agree as to where,” Carlson said.

Argh! Give me physics any day.

Anyway, the 235 level was established by the EPA in a 1986 protocol, as part of a burst of studies done after we realized the extent of health problems associated with E. coli.

Actually, the problem is a specific strain of the bacteria called E. coli O157:H7.

There are plenty of strains of E. coli living in mammal intestines that do no harm, or even do good. This strain is the black sheep of the family.

Its weird name designates the antigens on its surface: In this case, the 157th type of somatic antigen, which for some reason is abbreviated as “O,” and the seventh type of another antigen that is known merely as “H,” as if it was one of James Bond’s higher-ups.

Antigens are proteins that trigger an immune response in the host, such as a human being who swallows the bacteria accidentally. In humans, the immune response triggered by E. coli O157:H7 can include vomiting and bloody diarrhea (hope you’re not reading this at breakfast). Not good.

The EPA did various studies and determined that the 235 count in a single sample was associated with a risk factor of 8 people per 1,000 getting sick, which was determined to be acceptable. (They also settled on a figure of 126 as a geometric mean from five samples taken within 30 days.)

“Apparently, somebody on the committee doing these rules” for New Hampshire “decided that eight people per thousand is too many and said, ‘Let’s do it at four people,’ ” Carlson said.

Because the risk is measured on a logarithmic scale, not a linear one, cutting the risk in half corresponds to a multiple-sample bacteria count of 88, a number that became enshrined in state law.

The Merrimack River has had very low E. coli numbers for years. That reflects the huge improvements that Manchester and Nashua have made to their wastewater treatment systems in recent decades.

The highest bacteria counts in the region are found in slower-moving parts of the Souhegan River – basically the lower half, from Wilton to Merrimack – especially after heavy rains, when lots of waste material is washed into the river. Slower-moving parts of river tend to be swimming spots, such as the bend around Souhegan High School in Amherst.

The most public result of all these measurements occurs at Watson Park in Merrimack, probably the most used swimming area on these two rivers.

The Souhegan Watershed Association posts a flag based on its measurements: a blue flag when the most recent count is below 88 colonies per 100 milliliters, yellow flag when it’s up to 126 colonies and a red flag when it’s above 126. When the count hits 406 colonies, the SWA recommends that the beach be closed, as does the EPA.

Just to add to the confusion, Carlson says the EPA is considering changing its limits, although no details have been decided. The subject sometimes gets tossed around at DES.

“We have had discussions: Should it be higher, should it be lower? But they’re just discussions,” she said.

GraniteGeek appears Mondays in The Telegraph. David Brooks can be reached at 594-6531 or dbrooks@nashuatelegraph.com. Follow Brooks on Twitter @granitegeek