Sudbury high school students propose novel method of arsenic cleanup
Two high school students from Sudbury are bringing attention to phytoremediation as a means of cleaning up an arsenicladen tailings site from a past producing gold mine 25 kilometres southwest of the city.
The two girls - Marika Moskalyk and Alex Millar, Grade 11 and 12 students, respectively, at Marymount Academy – won best in fair at the Sudbury Regional Science Fair and a silver medal at the Canada-wide Science Fair in Windsor, Ontario, earlier this year for their research project, Green Gold: Phytoremediation of the Long Lake Gold Mine.
Moskalyk learned about the arsenic problem soon after her family moved to a home on Long Lake in 2011.
“People started asking us where we were getting our water from and if we’d heard about the arsenic in the lake,” she said.
“That really concerned us. We looked into it and learned there was a gold mine at the very end of the lake along with tailings that are highly contaminated with arsenic that have been leaching into the soil and water over the last century.”
The mine was operated by the Canadian Exploration Company from 1908 to 1916 and by Lebel Oro Mines Ltd. from 1937 to 1939 – years before the Ontario Mining Act required mining companies to assume responsibility for mine closure and remediation.
In 2012, sampling by the Ontario Ministry of the Environment found arsenic concentrations in the westernmost part of the lake exceeded drinking water standards and, the following year, announced plans for a three-year clean-up project.
Environmental consultant CH2MHill was hired to perform a site assessment and proposed a remediation plan based on the physical relocation of the tailings and containment by means of a plastic capping.
“The proposed remediation plan was just covering up the issue, not solving it, so we looked into other options,” said Millar.
In their research, the girls learned about the Chinese Brake Fern, a plant species that accumulates arsenic “in their fronds at levels 200 times greater than other plant species.”
Discovered by researchers at the University of Florida, the Chinese Brake Fern has been used in orange groves to take up arsenic contained in pesticides that were used years ago.
The girls also got in touch with Dr. Michael Blaylock of Edenspace Systems Corp. in West Virginia, whose company has exclusive rights from the University of Florida to market the Chinese Brake Fern for phytoremediation. Locally, they received help from Dr. Graeme Spiers and Dr. Peter Beckett of Laurentian University.
The girls acquired 40 plants courtesy of Edenspace, collected approximately 20 kilograms of contaminated soil from the edge of the lake and started a grow-op in the Moskalyk kitchen.
Four different growing media were used: 100 per cent potting soil, a 50:50 mixture, 75 per cent tailings and 100 per cent tailings.
They planted eight ferns for each soil type for a total of 32 four-litre pots and harvested frond samples every eight weeks until March 9, 2014.
The fronds were air dried, sealed, labeled and tested using inductively coupled mass spectrometry at Laurentian University.
“They all accumulated over 1,000 mg/kg of arsenic, which is absolutely huge, but in comparison with the amount of arsenic in the area, it didn’t seem like a lot,” said Moskalyk. “I think they found 32,000 mg/kg of arsenic in one area, but every year we could replant them and it would just be a longer project.”
The ferns growing in the pots with 50:50 mixture of tailings and potting soil were most successful in taking up arsenic. Those planted in pots with higher concentrations of tailings also took up arsenic, but withered noticeably during the six-month experiment.
In a larger scale application of phytoremediation, the leaves would be harvested and disposed of in a hazardous waste area.
The arsenic in the Long Lake tailings is naturally occurring arsenopyrite and part of the mineralogy, explained Steve Reitzel, a project engineer with the Ministry of Northern Development and Mines.
“When the arsenopyrite is exposed to oxygen and water, the pyrite part, which is essentially iron sulphite, breaks down into sulphuric acid, releasing the arsenic.”
Much of the arsenic in the lake is in the form of arsenopyrite and stable as long as it isn’t exposed to oxygen. The problem is with the material that is periodically exposed to the air in the summer when the water level drops and leaves “a tailings beach,” said Reitzel.
With the fluctuations in the water levels, the arsenic is then flushed into the lake. According to Reitzel, phytoremediation has potential in areas with lower levels of arsenic, “but you still have to have a strategy for dealing with the worst of the contamination.”
Several additional studies will be conducted over the next two years to come up with a detailed engineering plan, with actual construction expected to commence in 2017.
The total cost of the cleanup will be between $12 million and $18 million.
The Ministry has also looked at the possibility of reprocessing the tailings to recover their gold content, but “some people say the volumes are not significant enough,” said Reitzel.
“In spite of that, there’s still some interest. MIRARCO is doing some work, and others have expressed interest as well, so we haven’t closed the door on that.”