For Alum, Support From Scientists, Despite Unknown Effects On Mercury

By: Brian Kehrl
Published: 06/25/10

Alum has long been used to improve water quality, but the chemical compound has emerged over the last decade as an increasingly common tool to combat nutrient pollution in ponds on Cape Cod.

It was used in 2001 on Ashumet Pond in Mashpee and Falmouth and on Long Pond in Brewster and Harwich in 2007. It has been approved for use this year in Mystic Lake in Barnstable. The Mashpee Conservation Commission next month will hear a new propos al to use it again in Ashumet Pond. It is now under consideration for Santuit Pond.

Alum is generally regarded as a safe, effective, and relatively cheap way to decrease phosphorous, control algal blooms, and increase the clarity of the water.

But there has been no published scientific research into the connection between alum, the common name for the chemical aluminum sulfate, and the generation of a particularly toxic form of mercury, which several scientists said this week leaves a gap in their understanding of alum’s effects on human health.

“There is a lot of interest in this topic, but I haven’t seen the connection made in the general lake management community,” said Marc W. Beutel, an assistant professor of civil and environmental engineering at Washington State who is beginning a formal study on the issue this summer. “But it is an unknown what alum does to mercury cycling. It might help. Or it might hurt.”

David P. Krabbenhoft, a research scientist specializing in mercury with the United States Geologic Survey Water Science Center in Wisconsin, said, “I don’t believe there is a report we could go and look at to answer that question.”

At issue with alum is the sulfate it contains, which allows mercury already deposited in the water to be changed into methyl mercury, the most toxic form of mercury and one that can easily enter organisms in the food chain. Scientists have documented in detail the connection between sulfates and methyl mercury, dating back to the early 1990s, in research that had sweeping implications for regulating power plant emissions.

The scientists said that beyond the lack of specific research on the issue, it is difficult to even predict what effect alum might have on mercury production. There is a “humped relationship” between sulfate levels and methyl mercury, where not enough sulfate will limit methyl mercury generation, a middle amount will promote it, and rich levels of sulfates will again limit it, according to Dr. Krabbenhoft.

“If it is just your average lake, I believe you would reduce the amount of methyl mercury. But I don’t know,” he said. “I wouldn’t bet my mortgage on it, but I would maybe bet one month’s installment on my mortgage.”

He said the connection would likely be different in different water bodies.

Dr. Krabbenhoft said his interest in the issue is such that he would perform the laboratory analyses to determine mercury levels. “It is not cheap, but I will run them for free,” he said. “I’d love to do it.”

“We have known about this mercury thing for a good 20 years now. I am surprised that no one has put one and one together to ask that question,” he said. “Let’s see what happens. So next time we have this come up, we won’t have this black hole of a response.”

On balance, the scientists agreed with the conventional lake manager’s wisdom that alum is a safe and effective tool.

“It has been used really successfully out here in Washington State,” Dr. Beutel said. “It is a pretty safe material, if it is applied properly.”

It is also an issue that does not often come up in the debate about whether to use alum. The recent draft report on Santuit Pond by the consulting firm AECOM, for example, makes no mention of mercury in a section describing the pros and cons of alum and other treatment possibilities available to the town to address the high phosphorous levels and algal blooms in the pond.

Alum is meant to bind to phosphorous in the water, making it unavailable to algae, and create a layer on the bottom of ponds that prevents the release of additional phosphorous from the sediment. Phosphorous is a nutrient, commonly found in fertilizers, road runoff, and wastewater treated by septic systems, that promotes algal growth. It performs a similar function in freshwater as nitrogen does in salt water.

A massive 2004 state report on treatment possibilities, “The Practical Guide to Lake Management in Massachusetts: A Companion to the Final Generic Environmental Impact Report on Eutrophication and Aquatic Plant Management in Massachusetts,” also does not mention mercury in connection with alum.

A position statement by the North American Lake Management Society on the efficacy and safety of alum comes down in favor of the chemical treatment and makes no mention of methyl mercury. The statement acknowledges concerns that aluminum might be a cause of Alzheimer’s disease, but says these concerns are misplaced because the aluminum in alum is in a different form than the more toxic “free” alum.

When Brewster and Harwich were considering whether to pursue an alum treatment for Long Pond, the issue of mercury did not come up, according to Karen Malkus, a science educator who helped organize the Friends of Long Pond.

Ms. Malkus, who said she opposed the alum treatment for different reasons, particularly its effects on mollusks and other invertebrates, said she only learned about the possible connection during a “Ponds in Peril” workshop after the alum treatment had been approved.

However, a study that was referenced during that workshop, a key scientific report from 1992 linking sulfates to the generation of methyl mercury, has been making its way around Mashpee through the Friends of Santuit Pond.

The subject came up during a field trip of Santuit Friends members and representatives from the Mashpee Wampanoag Tribal Council Department of Environment and Natural Resources last month to a small pond in Harwich, where a water circulation device was installed instead of an alum treatment.

Allen Waxman, a member of the Friends group, asked a Harwich resident who is overseeing the circulator, Joseph P. Seidel, whether the issue had come up during the deliberation of treatment options for Skinequit Pond.

Mr. Seidel said it had not, but residents were wary of people adding large quantities of a chemical to an ecosystem. “I think it was concern about unintended consequences. Just like this issue [with mercury], I suppose,” he said.

However, mercury was considered during the first alum treatment of Ashumet Pond, in 2001, according to Jonathan S. Davis, remediation program manager for the Air Force Center for Engineering and the Environment, which is tasked with cleaning up portions of the pollution at the Massachusetts Military Reservation.

But he said Ashumet already had a problem with methyl mercury—evidenced by a state Department of Public Health advisory limiting the number of fish individuals should eat from the pond each month.

The federal Environmental Protection Agency also considers Ashumet Pond an “impaired water body” due to high mercury content.

Another source is already adding sulfates to the water, Mr. Davis said, allowing bacteria to turn mercury into methyl mercury, so they determined that adding more sulfates with alum would not be an issue.

He said methyl mercury levels were tested, with limited samples before and after treatment, and no substantial difference was found.

Mr. Davis said AFCEE has not yet determined whether the mercury issue has been put to rest and so will not be addressed in the current proposal for Ashumet Pond.

“We haven’t decided yet. We are still putting together our plans, and if we go to conservation and it is brought up, we will do something like we did last time,” he said, adding that it is always better to take samples and have evidence to back up a claim than it is to avoid sampling and then lack evidence. “You can spend a lot more money trying to justify why you didn’t do the samples rather than just doing them in the first place. The mercury may go that way, too.”

For Santuit Pond, however, there is no state public health mercury warning, and the EPA lists the pond as impaired for nutrients and noxious weeds, but not mercury.

Cynthia C. Gilmour, the lead author on the 1992 paper linking sulfates to methyl mercury and now a research scientist with the Smithsonian Environmental Research Center specializing in sulfate-reducing bacteria, said the critical question is whether an alum treatment will change the sulfate levels in the pond to a point where it promotes the methylization of mercury. Natural resource managers involved in permitting or applying alum need to be sure to avoid the “sweet spot” of sulfate levels where methyl mercury is generated, she said.

Dr. Gilmour said ponds near the ocean and ponds with high levels of phosphorous tend to have higher levels of sulfates.

Elizabeth A. Henry, a research scientist with the consulting firm Exponent and a co-author with Dr. Gilmour on the 1992 paper, said the effects of alum are also difficult to predict because methyl mercury is generated when oxygen in the water reaches low levels, a condition that alum treatments are meant to prevent.

“It is hard to say definitively that there is an issue or there isn’t an issue. But alum treatments are meant to move the lake away from the conditions that would create methyl mercury production,” she said.

Dr. Henry said if she lived near a phosphorous-polluted pond, she would likely support using alum to improve water quality. It would take years to generate enough scientific research to prove that the connection between sulfates and methyl mercury is not a concern for alum applications, she said.

“I guess I would support it and then do monitoring. To be able to do a scientific study to definitively prove that it is not going to cause a problem would delay a solution for years,” she said. “But there are a lot of reasons why you might not want to do an alum treatment. One reason clearly is that it is a Band-Aid solution to what is likely an ongoing phosphorous release problem in the watershed.”

Alum may address the symptoms of too much phosphorous, she said, but it does not address the source of the ailment.

Dr. Beutel said if he were advising a friend who lived near a pond that was to be treated with alum, he would emphasize finding a contractor that is familiar with alum and has a good track record with successful applications. “It has to be done right,” he said, citing problems that can arise if the acidity and other aspects of the water chemistry shift, due to faulty application.

He said he would also suggest looking into different chemicals that have similar effects on phosphorous. “Maybe it costs a little more, but maybe that extra cost is worth it,” he said.