Inside the moss mystery: How the organisms helped reveal Portland’s pollution

Surveys of tree moss uncovered contamination that may have led to higher cancer rates.

 

On a drizzly March day, Sarah Jovan pauses to inspect a leafless maple growing through a hole in a downtown Portland sidewalk. She passes a slender hand over the miniature ecosystem colonizing its trunk — chartreuse savannahs that stretch between stands of thick, shaggy moss and lone shrubs of fruticose lichen. “These look stressed,” she says of the latter, noting that the pale green epiphytes seem dull and stunted compared to their brethren in the wild.

That’s where Jovan, a moss and lichen expert at the U.S. Forest Service’s Pacific Northwest Research Station, usually works. But in 2013, she and her colleagues began studying the moss on Portland’s countless urban trees. Their findings rattled the city: The moss revealed that Portland has an air pollution problem.

The news wasn’t a complete shock. The Oregon Department of Environmental Quality (DEQ) has known for years that Portland’s air contains unhealthy levels of heavy metals like cadmium and arsenic, both carcinogens. But a city-wide survey of moss allowed scientists to finally pinpoint a likely source: two art glass producers that use the metals in their manufacturing process.

Sarah Jovan, national lichen advisor to the Forest Inventory and Analysis Program, shows how moss is collected from urban trees to test air quality.
Julia Rosen

Moss grows on a tree in the damp city of Portland.
Julia Rosen

The DEQ confirmed the moss results in October, using conventional air monitoring instruments that detected levels of cadmium and arsenic far above state benchmarks near one of the plants. The early February announcement angered many residents, who thought the department — which is charged with protecting Portland’s air — should have taken action sooner. The director stepped down soon after, citing health issues.

After the revelations surfaced, the glass manufacturers — Bullseye and Uroboros — voluntarily stopped using heavy metals. The DEQ will now require both to install emissions control devices after the EPA determined that the plants do not, in fact, qualify for an exemption that allowed them to operate without such devices in the past. Meanwhile, officials have scrambled to cope with the consequences. So far, follow-up tests of soils and urine from residents near the plants suggest the long-term human health risks are low, although authorities identified a slight increase in bladder cancer rates around Uroboros between 1999 and 2003.

Without moss, though, the issue may never have come to light. Unlike vascular plants, moss and lichen lack roots, so they must extract all the nutrients they need from the air. And because they also lack waxy leaf coatings or other natural barriers to unwanted compounds, they soak up pollution “like a sponge,” Jovan says.

Scientists, who first realized these plants could act as biomonitors in the 1970s, have since used them to study a range of pollutants, from heavy metals to polycyclic aromatic hydrocarbons, which threaten both human and environmental health. In fact, one of the great benefits of moss is that a single sample can yield information about many different contaminants, says Linda Geiser, director of the Forest Service’s Air Resource Management Program. And studying moss is cheap. “It doesn’t require power, and you can just send someone to hike back wherever you want, into the most remote place, to collect information,” Geiser says.

That’s one reason the Forest Service and other agencies have used moss to monitor air quality on public lands. A 2001 study in Alaska, for instance, revealed that dust from mining trucks was dousing fragile tundra plants in the Cape Krusenstern National Monument with heavy metals.

Still, moss has limitations when it comes to gauging threats to human health. The exposure pathways are different: Moss passively absorbs contaminants, while the effects on humans vary depending on whether they are inhaled or ingested. And concentrations in moss can’t be directly translated into concentrations in the air. So it’s not entirely clear what Jovan’s results, on their own, mean for Portland’s residents.

Geoffrey Donovan, Jovan’s colleague, stresses that their moss study wasn’t a replacement for traditional air monitoring, but a way to guide it. In the past, Portland only had one air monitoring station capable of detecting heavy metals, which could not provide regulators with detailed information about individual emitters. So Donovan used a model to turn their 346 moss samples — collected from every square kilometer of the city — into a detailed map of pollution hotspots that helped the DEQ focus its investigations. The cadmium results were recently published in the journal Science of the Total Environment.

The approach, which has been used in European cities, may now gain traction in the U.S. The Environmental Protection Agency plans to review the Portland study to evaluate whether it could use the method to screen for toxic air pollutants.

As cars roll past Jovan’s tree, the tires sucking at the wet pavement, the moss already seems to have melted into the fuzzy green backdrop of Portland life. But the story isn’t over. Despite the state’s reassurances, some locals fear possible health impacts and question whether the DEQ will prevent similar situations in the future. To quell these concerns, Gov. Kate Brown recently established a new state program to strengthen air quality regulation.

Moss may very well play a role in that initiative — precisely because of its ability to detect sources of pollution. That, Jovan says lovingly, “is what we are solving with these delightful little primitive plants.”

Julia Rosen is a freelance reporter based in Portland, Oregon.

High Country News Classifieds
  • ATTORNEY AD
    Criminal Defense, Code Enforcement, Water Rights, Mental Health Defense, Resentencing.
  • LUNATEC HYDRATION SPRAY BOTTLE
    A must for campers and outdoor enthusiasts. Cools, cleans and hydrates with mist, stream and shower patterns. Hundreds of uses.
  • LUNATEC ODOR-FREE DISHCLOTHS
    are a must try. They stay odor-free, dry fast, are durable and don't require machine washing. Try today.
  • PROFESSIONAL GIS SERVICES
    Custom Geospatial Solutions is available for all of your GIS needs. Affordable, flexible and accurate data visualization and analysis for any sized project.
  • FREE RANGE BISON AVAILABLE
    Hard grass raised bison available in east Montana. You harvest or possible deliver quartered carcass to your butcher or cut/wrapped pickup. Contact Crazy Woman Bison...
  • CONSERVATION ASSOCIATE - OKANOGAN LAND TRUST (NORTH CENTRAL WA)
    Do you enjoy rural living, wild places, and the chance to work with many different kinds of people and accomplish big conservation outcomes? Do you...
  • CARDIGAN WELSH CORGIS
    10 adorable, healthy puppies for sale. 4 males and 6 females. DM and PRA clear. Excellent pedigree from champion lineage. One Red Brindle male. The...
  • A CHILDREN'S BOOK FOR THE CLIMATE CRISIS!!
    "Goodnight Fossil Fuels!" is a an engaging, beautiful, factual and somewhat silly picture book by a climate scientist and a climate artist, both based in...
  • DIGITAL ADVOCACY & MEMBERSHIP MANAGER
    The Digital Advocacy & Membership Manager will be responsible for creating and delivering compelling, engaging digital content to Guardians members, email activists, and social media...
  • DIGITAL OUTREACH COORDINATOR, ARIZONA
    Job Title: Digital Outreach Coordinator, Arizona Position Location: Phoenix or Tucson, AZ Status: Salaried Job ID Number: 52198 We are looking for you! We are...
  • DESCHUTES LAND TRUST VOLUNTEER PROGRAM MANAGER
    The Deschutes Land Trust is seeking an experienced Volunteer Program Manager to join its dedicated team! Deschutes Land Trust conserves and cares for the lands...
  • ASSOCIATE DIRECTOR OF DEVELOPMENT
    The Nature Conservancy in Wyoming seeks an experienced fundraiser to join our team. We're looking for a great communicator who is passionate about conservation and...
  • INDIAN COUNTRY FELLOWSHIP
    Western Leaders Network is accepting applications for its paid, part-time, 6-month fellowship. Mentorship, training, and engaging tribal leaders in advancing conservation initiatives and climate policy....
  • MULESHOE RANCH PRESERVE MANAGER
    The Muleshoe Ranch Preserve Manager develops, manages, and advances conservation programs, plans and methods for large-scale geographic areas. The Muleshoe Ranch Cooperative Management Area (MRCMA)...
  • ARTEMIS PROGRAM MANAGER
    Founded in 1936, the National Wildlife Federation (NWF or Federation) is America's largest and most trusted grassroots conservation organization with 52 state/territorial affiliates and more...
  • ASSISTANT OR ASSOCIATE PROFESSOR OF ENVIRONMENTAL HUMANITIES
    Assistant or Associate Professor of Environmental Humanities Whitman College The Environmental Humanities Program at Whitman College seeks candidates for a tenure-track position beginning August 2023...
  • EXECUTIVE DIRECTOR
    High Country Conservation Advocates (HCCA) in Crested Butte, CO is seeking an enthusiastic Executive Director who is passionate about the public lands, natural waters and...
  • ASSOCIATE DIRECTOR OF VOLUNTEER PROGRAMS
    Are you passionate about connecting people to the outdoors? The Pacific Crest Trail Association (PCTA) is looking for someone with volunteer management experience to join...
  • EXECUTIVE DIRECTOR
    The conservation non-profit Invasive Species Action Network seeks an executive director. We are focused on preventing the human-caused spread of invasive species by promoting voluntary...
  • HIGH COUNTRY NEWS EDITORIAL INTERNS
    High Country News, an award-winning magazine covering the communities and environment of the Western United States, is looking for its next cohort of editorial interns....