The U.S. Forest Service researchers had a plan: Collect moss from trees around Portland, study whether it was a living air pollution indicator, then publish their results in a scientific journal.

But after completing their analysis of moss samples from nearly 350 spots citywide, they found something alarming - so alarming they felt compelled to notify environmental regulators right away.

Robert Mangold, station director of the U.S. Forest Service's Pacific Northwest Research Station, said the agency contacted the Oregon Department of Environmental Quality in May 2015 with the results.

They'd found two hotspots where cadmium and arsenic concentrations were unusually high. One was in Southeast Portland; the other sat between Interstate 5 and the Fremont Bridge.

"There was a good level of concern," Mangold said. "We usually don't share these kinds of results until a journal article is out in print. But we had a feeling - not having done a lot of this work - that this was important to get out."

But it would take five months for the Department of Environmental Quality to act. It isn't clear why.

The agency said on Thursday it deployed an air monitor to confirm a suspected source in October. Another three months passed before the results came back and confirmed that cadmium and arsenic were present in volumes that far exceeded state safety targets at a site adjacent to Bullseye Glass, a Southeast Portland manufacturer.

It wasn't until Wednesday that Oregon officials told the public about the problem, drawing a public outcry and concern from nearby residents and parents. Portland Public Schools said it was launching tests of air in five nearby schools in response.

In all, eight months elapsed between the hotspots' discovery and public notification this week, raising questions about why it took the Department of Environmental Quality so long to deploy an air monitor given the alarms sounded by the U.S. Forest Service.

A spokeswoman for the state agency didn't respond to a request for comment. The spokeswoman and two other agency employees had been unable to tell The Oregonian/OregonLive when the Forest Service delivered its findings.

As soon as the findings became public, Bullseye announced it was immediately suspending use of the two metals, used to create colored glass. Advocates and neighbors have asked whether faster notification could've made that happen sooner.

Regulators and advocates have known for a decade that Portland had unexpectedly elevated levels of the two heavy metals, both carcinogens. But it wasn't clear where the pollution was coming from or where it was the worst.

Since the discovery years ago that Portland's air was unexpectedly dirty, the Department of Environmental Quality has been complacent in its investigation of the cause, said Mary Peveto, president of Neighbors for Clean Air, a Northwest Portland nonprofit.

"There's been no urgency that kids are being exposed to a neurological toxic that could affect them for generations," Peveto said. "It's been an academic exercise."

At the levels found, the metals would be expected to cause cancer in one person in every 4,807 people - if they were exposed to the same amount throughout their entire life. The state's goal is for that risk to be one in a million.

Mangold, the Forest Service research director, said he hopes the research's breakthroughs will be applied in other cities including Seattle. Traditional air monitors are expensive and aren't mobile. But moss is easy to get.

"It's omniscient in a wet climate like Portland - we had 350 little vegetation monitors," Mangold said. "The granularity of the information will be much greater. We hope it starts a discussion in different places."

-- Rob Davis

rdavis@oregonian.com

503.294.7657