The Portland Moss and Air Quality Study

Project Description

This study set out to test the use of moss as a bio-indicator in an urban setting. Because moss lack roots, they absorb all of their water and nutrients from the atmosphere, inadvertently taking up and storing whatever compounds happen to be in the air. We used samples of moss to test levels of air pollutants. We then took the analysis one step further and developed a fine-scale map of atmospherically-derived cadmium and identified two hotspots near stained-glass manufacturers in Portland. In response to our findings, the Oregon Department of Environmental Quality placed an instrumental monitor 120 m from the larger stained-glass manufacturer in October, 2015. The monthly average atmospheric cadmium concentration was 29.4 ng/m3, which is 49 times higher than Oregon's benchmark of 0.6 ng/m3, and high enough to pose a health risk from even short-term exposure. Both stained-glass manufacturers voluntarily stopped using cadmium after the monitoring results were made public, and the monthly average cadmium levels precipitously dropped to 1.1 ng/m3 for stained-glass manufacturer #1 and 0.67 ng/m3 for stained-glass manufacturer #2. Findings from this study contributed to new pollution controls, reexamination of the regulatory exemptions for the stained-glass industry, and the creation of a new state program, “Cleaner Air Oregon.”

Purpose and Scope

The U.S. Forest Service has been using mosses and lichens as “bioindicators” – living organisms that can help monitor environmental health – since the 1960s. But previous efforts have focused on forest land. We embarked on this novel study to see if we could demonstrate using moss as a bioindicator in an urban setting.

Methods

Using a grid-based random sampling strategy, we collected moss samples at 346 sites across the city. The moss we used is Orthotrichum lyellii, which grows abundantly in Portland. We collected all the samples from December 2-23, 2013, keeping the timeframe narrow to avoid confounding effects. The samples were then processed and analyzed in a laboratory. When our moss sample results came back from the lab, we spatially modeled them to yield a distribution map of cadmium.

Key Findings

Cadmium levels in moss were positively correlated with proximity to two stained-glass manufacturers. The maps showed very high concentrations of cadmium around the two stained-glass manufacturers, neither of which were known to environmental regulators as cadmium emitters.

Urban moss analysis potentially could revolutionize air quality monitoring by serving as an inexpensive screening tool to help cities quickly identify where to place pollution monitoring equipment.

Project Deliverables

Interactive map

• The maps showing the moss-based distribution of the 22 elements can be viewed in an interactive format.
  • The interactive format allows the user to select data layers and view them over various basemaps such as aerial photography or road networks. (User's guide to the interactive map)

(See additional project deliverables in Resources tab.)