Since January, 26 more clean-up workers at Yellowknife's Giant Mine have shown elevated levels of arsenic. That's in addition to the 31 workers last winter.

Workers are tested weekly. Their arsenic levels are considered elevated if they rise above 35 parts per billion, or 35 micrograms of arsenic per litre of urine.

Giant Mine cleanup workers

Clean-up workers wear protective gear at Giant Mine in 2013. Since January 2014, 26 more clean-up workers at Yellowknife's Giant Mine have shown elevated levels of arsenic, in addition to the 31 workers last winter. (CBC)

Stephen Moss, vice-president of Prevention Services with the Workers Compensation and Safety Commission, which has been monitoring the workers exposure, says the only data on the effects of arsenic on human health have to do with levels of about 500 parts per million.

"There's a lot of things about arsenic that you'd think after 60 or 70 years of arsenic in and around the community we'd understand better, but we really don't," he said.

Moss says workers were removed from the site for a week and monitored until their levels returned to normal.

Last winter, clean-up of the mine`s roaster was temporarily halted when 31 workers showed elevated levels of arsenic.

In January, the WSCC and the federal government came up with new guidelines for workers. They included more education on how to use safety equipment and better inspections of workers' safety suits.

But Moss says there's a lot of other possible sources for arsenic exposure such as smoking, and food.

"We don't have the ability to differentiate where they got the arsenic from," he said. "We're hearing a lot about rice. We were actually advised that some types of granola bars with rice syrup can have it."

A emailed statement from the office of Aboriginal Affairs and Northern Development minister Bernard Valcourt said operating procedures are the responsibility of the contractor and that government "supports the company to ensure the health and safety of the workers." 

"Strong operating procedures are in place, including consistent monitoring and working with an industrial hygienist," the statement said. "We will continue working with our partners to ensure the safety of the workers."