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Pacific Northwest Research Station

 
 
 
 
Pacific Northwest Research Station
333 SW First Ave.
Portland, OR 97204

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Cadmium and the Portland Moss and Air Quality Study

Moss is common in Portland, Oregon. Credit: Sarah Jovan.In brief

Initiated in 2013, the Portland Moss and Air Quality Study set out to learn if moss might be a useful “bioindicator” for assessing exposure to polycyclic aromatic hydrocarbons in Portland, Oregon. The study evolved when laboratory analyses of the moss samples revealed surprising hotspots of high concentrations of heavy metals and other elements known to cause human health problems.  To learn more, the scientists started with cadmium, a top concern of the Oregon Department of Environmental Quality (DEQ). Placement of an air monitor near one hotspot measured cadmium and arsenic at levels that greatly exceeded health benchmarks.

 

The cadmium portion of the moss study revealed that moss is an effective bioindicator of cadmium levels in the air. This finding had immediate impact: DEQ and the Oregon Health Authority held public meetings to alert residents and businesses of the situation. The two sources of the cadmium and arsenic stopped emitting those pollutants, and a new state program, “Cleaner Air Oregon,” was created to overhaul the state’s industrial air toxics regulatory standards.

 

The connection between moss and air pollution

Moss has been used to detect air pollution in forests since the 1960s. Moss doesn’t have roots; it’s like a sponge, absorbing moisture and nutrients from the air, as well as contaminants. These contaminants are stored in the moss tissues, making them a living record of pollution levels in the surrounding environment. Because some species of moss are very sensitive to air pollution, they are indicators of good or bad air quality. If certain sensitive species are declining, it’s an indication that the air quality is declining.

 

Moss in urban forests—indicators of localized emissions

What can we learn from forests in urban areas, home to 80 percent of the U.S. population? Over the past decade, the PNW Research Station has spent more time studying the trees that grow in cities. In 2013, Forest Service scientists began investigating the ability of urban forests to mitigate air pollution. They wondered if moss might be a useful bioindicator for assessing exposure to polycyclic aromatic hydrocarbons in Portland, Oregon. These compounds are potent environmental toxins linked to health problems such as heart disease and cancer. These toxins are found in car and truck exhaust, other fossil-fuel emissions, and wood smoke.

 

How were the moss samples collected?

 

Sample plots. Credit Sarah Jovan.
Click here
for a larger map

Using a grid-based random sampling strategy, the scientists set out in a minivan armed with a ladder and collection equipment. They gathered 346 samples of Lyell's orthotrichum (Orthotrichum lyellii), a moss species that grows abundantly on the trunks and branches of hardwood trees across Portland.

 

The samples were collected during December 2-23, 2013, keeping the time frame narrow to avoid confounding effects. The samples were then processed and analyzed in a laboratory.


The moss samples had to be meticulously cleaned and prepped. Credit: Sarah Jovan.
The moss samples had to be meticulously cleaned and prepped. Credit: Sarah Jovan


 

Unprepped moss. The raw sample contains dirt, insects and other debris that needs to be cleaned out before the moss can be analyzed. Credit: Sarah Jovan.

Unprepped moss. The raw sample contains dirt, insects and other debris that needs to be cleaned out before the moss can be analyzed. Credit: Sarah Jovan.

 

Cleaned moss. The raw sample contains dirt, insects and other debris that needs to be cleaned out before the moss can be analyzed. Credit: Sarah Jovan.

Cleaned moss.


Expanding the study

For this study, the scientists collected moss samples around Portland using methods that took into account the complex urban setting. As the study developed, they decided to have the moss samples tested for heavy metals as well as polycyclic aromatic hydrocarbons. Other organizations involved in the study included Drexel University, Portland State University, and the Oregon Department of Environmental Quality (DEQ).

 

After analyzing the polycyclic aromatic hydrocarbons, the science team turned to the lab results for 22 elements including heavy metals. The scientists started with cadmium, a top concern of the DEQ because a 2011 DEQ study found discrepancies between predicted and observed concentrations of the metal at Portland’s one permanent air-quality monitoring site. Cadmium, which is used primarily in nickel-cadmium battery manufacturing, electroplating, and stained-glass production, is linked to health problems such as kidney disease and cancer.

 

When the scientists looked at the lab results for cadmium, levels in some of the moss samples seemed very high compared to some of the other samples. In fact, the distribution of the cadmium data revealed two major hotspots centered around the two largest stained-glass manufacturers in Portland.

The science team also took a closer look at concentrations of arsenic and selenium in the moss samples. These two elements are co-emitted with cadmium during some industrial processes such as stained-glass manufacturing. Including these secondary elements at this stage of the analysis helped the team more definitively identify one of the stained-glass manufacturers as the source of one cadmium hotspot.

But what exactly did that mean for moss as a bioindicator? Do high levels of cadmium in moss mean there are high levels of cadmium in the air? Past research suggested a correlation, but the strength of the relationship was unknown.


Data from air quality monitor validates moss data

To know if the high cadmium levels measured in moss surpassed state benchmarks and potentially posed health risks, the scientists needed to compare moss data with cadmium levels measured in the air.  In October 2015, DEQ placed an air quality monitor near the largest cadmium hotspot indicated by the moss samples and gathered data for about a month. This DEQ air quality monitor revealed that cadmium and arsenic emissions were 49 and 159 times higher than state benchmarks, respectively. Meanwhile, the scientists collected 25 additional moss samples in the vicinity to bolster the moss dataset.

By using data from the DEQ monitor from October and three other monitors in use for other projects, the scientists found there was a strong correlation between high levels of cadmium in the moss and high levels of cadmium in the air. Although moss and air cadmium could only be compared at four sites, these preliminary results suggest that moss may be a very accurate bioindicator of atmospheric cadmium.

 

Working on two fronts: public outreach and scientific publication

While the research team was sharing these preliminary results with partners, residents at community meetings, and reporters, the team was also working to have the cadmium findings from this innovative study published in a scientific journal. Publishing is an important part of the scientific process. To be published, the findings and the methods used for the statistical modeling and spatial analysis must be reviewed and validated by other scientists. Upon publication, these methods become a scientifically defensible technique that can be used in other parts of the country or world to protect public health.

 

 

For the greater good

  • 2013 moss samples 22 elements (cvs, xlsx)

The raw data for pollutant concentrations in the moss samples is available. Others can use the data and the team’s cadmium modeling techniques or their own approaches to explore possible sources of metals in Portland’s moss.


 

 


 

PNW News Release

 

Study Team:

Geoffrey Donovan, U.S. Forest Service
Sarah Jovan, U.S. Forest Service
Demetrios Gatziolis, U.S. Forest Service
Igor Burstyn, Drexel University
Yvonne Michaels, Drexel University
Michael Amacher, Scientist Emeritus (U.S. Forest Service)

Vicente Monleon, U.S. Forest Service

 

Additional help from:

Wes Hoyer, Portland State University

 

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More information:

 

Additional inquiries about the moss study:

 

pnwinquiry@fs.fed.us

 

For questions not related to the moss study:

 

Oregon DEQ is the lead agency for monitoring and providing data about the affected area, concentrations and types of pollutants, and exploring mitigation efforts with industrial sources.

 

Oregon Health Authority is the lead agency for questions and information about potential health effects, health and medical assessment recommendations, and other health specific questions.

 

 

US Forest Service - Pacific Northwest Research Station
Last Modified: Thursday,09June2016 at15:44:18CDT


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