Lebanon — Scientists studying a cluster of ALS, or Lou Gehrig’s disease, around Mascoma Lake are urging people not to make too much of their early findings. They suspect, but have not established, a link between the disease and a toxin produced by cyanobacteria in the lake.

The research has caused concern because Mascoma Lake is not only a place for recreation, but also the city of Lebanon’s source of drinking water.

The researchers at Dartmouth-Hitchcock Medical Center caution that they’re just beginning to study the question, and that they have not actually found the toxin they think is related to ALS in Mascoma Lake. If a cyanobacteria toxin in the water has anything to do with causing ALS in some susceptible people, they were probably exposed to the toxin decades ago, when cyanobacteria bloomed in the lake every year, covering its surface with green scum.

Lebanon water treatment plant supervisor James Angers said that the system was designed to filter out a wide variety of contaminants, and he assured residents that the city’s drinking water is safe.

“We treat for just about anything that can hit the water,” Angers said.

Tracie Caller, a Dartmouth researcher involved in the study, said that merely identifying a cluster of ALS cases near the lake does not necessarily mean that something in lake water causes ALS.

“There could be something else that people around a lake are sharing,” she said.

Paul Raymond, owner of Mascoma Lake Campground in Lebanon, said that people he’s talked to have gotten a different message.

“People are scared to go in the water,” he said.

He said he’d had five people call to cancel reservations at his campground in the past few days.

“We’re taking a hit up here,” he said.

The toxin in question is found within the cells of cyanobacteria, tiny organisms also known as blue-green algae.

Cyanobacteria were thought to be algae until scientists discovered that they are actually a kind of bacterium, according to Jody Connor, chief water pollution biologist with the New Hampshire Department of Environmental Services.

Connor has been collaborating with the Dartmouth researchers studying ALS and cyanobacteria.

Cyanobacteria are commonly found in bodies of water all over the world. Some kinds of cyanobacteria make potent toxins, and are known to pose health hazards for people and pets when large masses of them grow in a lake or pond.

Although the idea of a possible link between cyanobacteria and ALS is recent, it’s well known that cyanobacteria toxins can damage the liver, kidneys and nervous system, and they can also irritate skin.

There have been numerous cases of animals dying from drinking or swimming in water contaminated with cyanobacteria toxins, Connor said.

Connor explained that merely disinfecting water does not remove cyanobacteria toxins. Killing the bacteria, he said, breaks their cell walls, releasing the toxins contained in the cell.

Angers said that Lebanon disinfects drinking water with chlorine as one of the last steps in the treatment process, after any cyanobacteria would have been filtered out.

Water comes into the plant from the Mascoma River, downstream from Mascoma Lake.

It’s treated first with activated carbon powder. The carbon traps many contaminants in the water. Then, another chemical, polyaluminum chloride, is added. This chemical makes fluffy flakes that trap more particles in the water. In two giant tanks, paddles slowly stir the water, allowing particles trapped in the flakes to settle on the bottom. In the next stage, the water is pumped into basins where it slowly filters through layers of sand and anthracite coal. Before going into storage tanks that supply city water pipes, the water is chlorinated to kill any remaining pathogens.

“We get excellent removals through the plant,” Angers said.

He said that cyanobacteria toxins are not among the harmful contaminants for which the Environmental Protection Agency requires drinking water to be tested.

But he said that he does monitor water coming into the treatment plant for bacteria and algae, because some, like cyanobacteria, can make the water smell and taste bad.

He said that the Lebanon plant is not a new design, and that the same basic system has been in place since the 1950s. “This technology has been working for a while,” he said.

Connor said that activated carbon should be able to trap cyanobacteria, and that it’s a good thing that the water is chlorinated at the end of the process.

“There should be very little that would be released because of chlorine,” he said.

The question remains whether a certain kind of cyanobacteria toxin, an amino acid called Bmaa (B-Methylamino-L-alanine), can get through the filtering system.

Bmaa is what the researchers at Dartmouth think might play a part in causing ALS. “The molecule is very small,” said Caller, the Dartmouth researcher. “My guess is that it’s probably not filtered out.”

But Bmaa has not been found in Mascoma Lake yet, and the lake isn’t as full of cyanobacteria as it once was. “Unless you have an active bloom, it’s going to be pretty diluted,” said Dartmouth neurologist Elijah Stommel, who heads up the ALS study at Dartmouth.

“We haven’t had any really bad blooms in Mascoma in the last 10 years,” Connor said.

The state monitors lakes and ponds in New Hampshire for cyanobacteria, and has a system in place for posting warnings if there’s too much of it in the water. Connor said that he does not recall a cyanobacteria warning having been posted for Mascoma Lake in at least the past five years.

Treated sewage flowed into the Mascoma Lake for decades, until environmental regulations ended the practice around 1980, Connor said. The sewage was full of phosphorus, a nutrient that fueled explosions of cyanobacteria growth in the water every summer.

Back then, the state treated the lake with copper sulfate to kill the cyanobacteria.

“At that point, in the ’60s and ’70s, scientists didn’t really know about the toxins that are associated with cyanobacteria,” Connor said. “The copper killed the cells off, but in doing so, the toxins got into the water.”

He said that the researchers think that the cluster of nine ALS cases around Mascoma Lake could be in people who were living there in the 1950s to the 1980s, but not more recently.

“I think for the most part, the lakes are safe,” Connor said. “We’ve come a long way in the last few years.”

Martin Downs can be reached at mdowns@vnews.com or (603) 727-3210.