By Kim Smiley

Residents and officials are struggling to find a path forward after toxic heavy metals were unexpectedly found in samples of moss in Portland, Oregon. According to the U.S. Forest Service, the moss was sampled as part of an exploratory study to measure air pollution in Portland.  The objective of the study was to determine if moss could be used as a “bio-indicator” of hydrocarbons and heavy metals in air in an urban environment.  Researchers were caught off guard when the samples showed hot spots of relatively high heavy metal levels, including chromium, arsenic, and cadmium (which can cause cancer and kidney malfunction).  Portland officials and residents are working to determine the full extent of the problem and how it should be addressed.

So where did the heavy metals come from?  And how is it that officials weren’t already aware of the potential issue of heavy metals in the environment? The investigation into this issue is still ongoing, but an initial Cause Map can be built to document what is known at this time.  A Cause Map is built by asking “why” questions and visually laying out all the causes that contributed to the problem.  (Click on “Download the PDF” to view the initial Cause Map.)

Officials are still working to verify where the heavy metals are coming from, but early speculation is that nearby stained-glass manufacturers are the likely source.  Heavy metals are used during the glass manufacturing process to create colors. For example, cadmium is used to make red, yellow and orange glass and chromium is used to make green and blue glass. The hot spots where heavy metals were detected surround two stained-glass manufacturers, but there are other industrial facilities nearby that may have played a role as well.  There are still a lot of unknowns about the actual emissions emitted from the glass factories because no testing has been done up to this point.  Testing was not required by federal regulations because of the relatively small size of the factories.  If the heavy metals did in fact originate from the glass factories, many hard questions about the adequacy of current emissions regulations and testing requirements will need to be answered.

Part of the difficulty of this issue is understanding exactly what the impacts from the potential exposure to heavy metals might be.  Since the levels of heavy metals detected so far are considered below the threshold of “acute”,  investigators are still working to determine what the potential long-term health impacts might be.

A long-term benefit of this mess is the validation that moss can be used as an indicator of urban air quality.  Moss has been used as an “bio-indicator” for air quality since the 1960s in rural environments, but this the first attempt to sample moss to learn about air quality in an urban setting.  As moss is plentiful and testing it is relatively inexpensive, this technique may dramatically improve testing methods used in urban environments.

Both glass companies have voluntarily suspended working with chromium, cadmium and arsenic in response to a request by the Oregon Department of Environmental Quality.  The DEQ has also begun additional air monitoring and begun sampling soil in the impacted areas to determine the scope of the contamination. As officials gain a better understanding of what is causing the issue and what the long-term impacts are, they will be able to develop solutions to reduce the risk of similar problems occurring in the future.