Scientists at the Woods Hole Oceanographic Institution (WHOI) say the current method available to test water quality and accepted by state officials is inherently flawed. The weakness is the long time lag between sampling and test results.
Local health agents and town officials have expressed frustration with the current method used to test beach water quality, and state Department of Public Health regulations that require beaches to stay closed after a spike in bacteria levels, even when follow-up single day samples show the water is safe.
Officials at the U.S. Environmental Protection Agency (EPA), under a court order to come up with a better test, are preparing to introduce a new procedure that could yield test results in about four hours.
Timing is everything
The currently accepted method of testing for enterococci bacteria, an indicator organism that signals the presence of other harmful bacteria, takes a minimum of 24 hours.
“One of the big questions with beach closures is that the system of culturing bacteria has a big time lag,” WHOI graduate student Elizabeth Halliday said. “You don’t know if there was bad bacteria in the water until more than a day after you took the samples.”
Under guidelines established by the EPA, and adopted by Massachusetts and most other coastal states, local health agents collect water samples from beaches. They have six hours to get the samples to a lab, and the lab must begin the tests within two hours of receiving the samples. The test requires overnight incubation of the samples.
So when local health agents get test results, it tells them the water was unhealthy for swimming yesterday, far too late to protect the public from illness. They must then close the beaches, take another sample, and wait another 24 hours. If the single sample is clean, the beach water must still meet another standard called a geometric mean trend, a complex formula that measures the five most recent water samples. Unlike an arithmetic mean, or average, the geometric mean discounts unusually high spikes in water quality, according to public health officials.
Biologists at WHOI are using a new kind of test in research on Provincetown beaches this summer. It identifies genetic markers, or DNA, in the bacteria, and can return results in about four hours. Theoretically, a test taken at 6 am could return results in time for health officials to close a beach that morning, a better scenario for protecting public health.
In response to a lawsuit from the Natural Resources Defense Council, federal courts have ordered the EPA to come up with a better testing procedure. They are moving toward the kind of test used by WHOI scientists in their research. The court has ordered new testing procedures adopted by the end of 2012.
The DNA test has been routinely used in medical settings for some time, but is just now being adapted to environmental testing.
The new method has its drawbacks, scientists say.
“It’s significantly more expensive than the test we use now,” Caitlyn Wittoe, regional beach coordinator for the EPA said.
Health agents test most Island beaches once per week in the summer. Unless they move to daily testing, the new test may not significantly improve their ability to protect public health.
One mystery is why some Island beaches test clean and others test high for bacteria. Suspicion was directed at the Wampanoag Tribe water testing lab in Aquinnah. However, recent control testing of beach water samples by three different labs, including those in Aquinnah and Tisbury, showed the labs are returning accurate results, within a scientifically accepted statistical range of variation.
While the results provided by the new test are provided quicker, the new test does not clear up the mystery of why beaches in relatively undeveloped areas, like Long Point on the south side of Martha’s Vineyard, can suddenly show extremely high levels of bacteria.
In their work on Provincetown beaches, the WHOI scientists have found wide variation in water quality across short distances of shoreline.
“Beaches, even within the same general area, can behave differently,” Rebecca Gast, associate scientist at WHOI said. “It depends on human traffic, paved areas, circulation, the amount of things that accumulate on the beach. It can be really difficult to give a black-and-white answer.”
The WHOI scientists have developed an informative website that explains the science around beach water testing, contamination, and illnesses.
There is also more and more evidence that enterococci, which thrive in warm-blooded animals, can also survive and multiply in beach sand.
EPA environmental biologist Matt Liebman said the current testing method is a matter of probability that may not reflect an ongoing threat to public health.
“Taking 100 millilitres of water [about half a cup] out of a big ocean, you may have gotten some water that’s been contaminated from a boat, or some other storm water discharge, or some other plume that made its way down there.”
Safer, not safe
The standards developed by the EPA do not represent water completely safe for swimming, but an acceptable risk to public health.
The single sample standard for enterococci is 104 colony forming units per 100 millilitres of water (cfu/100ml). The standard for the geometric mean trend is 35 cfu/100ml. At those levels some people will still get sick.
“All the illness rates are based on the geometric mean,” Mr. Liebman said. “That level is the increased risk over non-swimmers. There’s a one to two percent probability you’re going to get sick with some kind of gastrointestinal illness.”
Illnesses associated with contaminated beach water are very difficult to track, according to the scientists. Many people don’t associate sickness with swimming in the ocean. They often blame it on the sun, food poisoning, vacation travel, or toxic plants.
“If the standards are met, and a family of four swims at least once a week, every week in the summer, at least one person would get sick,” Ms. Gast said. “There’s always a risk; it’s just lower, below the standard. Going to the beach when the standards are met is pretty much the same as when you take the bus. You’re exposed to a lot of people and you might get the flu.”
The one bright side of the issue, and one thing on which all the scientists and health officials agree, is that the water off Massachusetts beaches is much safer than it was several decades ago.
“Contamination is so much lower than it used to be,” Ms. Gast said. “They’ve been able to identify some of the major sources, and there are now laws against it. What we’re dealing with now is less definable sources, that we don’t quite know how to deal with.”