Environmental scientist Amanda Bidwell has joined Soundkeeper for multiple Pint-Sized Science events, sharing the fascinating findings from her master’s degree research, which used moss as a tool for measuring environmental contamination. Below she answers some questions about her research, which revealed important trends in urban pollution. The highest levels of several metals were found in moss near Longfellow Creek, where Soundkeeper has conducted salmon surveys for the past three years to determine why many salmon returning to the creek die before they spawn.
Why study moss? What can it tell us about pollution?
There is a long history of using moss as a bioinidicator of air quality in Europe, dating back to the late 1960s (Rühling and Tyler 1968). Moss, unlike vascular plants, lacks a protective epidermis which allows for the free exchange of solutions and gas across its entire cell surface, similar to a sponge. As an epiphyte, it absorbs all of its nutrients and water from the air. This means if there are elevated levels of heavy metals in an area, moss will absorb wet deposition and trap particulates on its surface. Although the exact period represented by metals in moss tissue is unknown, it likely ranges between several months up to a few years. Most studies that use moss a bioindictors only use the top 2/3 of the moss shoot which represent, at maximum, a three year exposure period. Moss is a inexpensive way to screen urban pollution over a larger area and it provides a snapshot of wet and dry pollution over a short period of time.
The primary objective of my research was to see if moss could be used as an indicator of air quality and pollution in Washington. Given the iconic image of moss-draped forests in the PNW, we were curious as to how these moss communities were responding to varying levels of pollution. We established sites on the Western side of the Olympic Peninsula to act as our “clean sites”, along the I-90 corridor to act as our “intermediate sites”, and sites in Seattle to act as the “polluted sites”.
What are the most common pollutants you found in your research?
We are interested in looking at common heavy metals that are associated with urbanization and the transportation sector (exhaust emissions, diesel fuel/soot, brake and tire attrition, and lubricant degradation). The priority elements of interest include arsenic, cadmium, chromium, copper, iron, manganese, nickel, lead, strontium, titanium and zinc. Six of these (arsenic, chromium, copper, manganese, nickel and lead) are on the EPA’s list of the top 30 hazardous air pollutants that pose the greatest potential human health concerns in urban areas. Several of these elements are also hazardous to aquatic organisms and can bioaccumulate up the foodweb. Roughly half of the copper (66 tons/year) entering Puget Sound originates from brake pad attrition. In 2010 the WA State legislature passed the Better Brake Rule (Chapter 173-901 WAC) that limits the amount of toxic material in brake pads and shoes.
The results from my M.S. research showed moss can used as a comparative index of metal deposition and as a screening tool to assess metal pollution in Western Washington. The highest levels of moss metal concentrations were found in Seattle, followed by sites along the I-90 corridor. The lowest metals levels were observed in moss collected from the Western side of the Olympic peninsula where average daily traffic rates and urbanization influences are the lowest. There was a significant different in metal concentrations observed across these 3 areas (urban, suburban, and rural), meaning each zone was environmentally distinct from the others. The elevated metal concentrations found in moss collected from Seattle sites were significantly correlated with heavier average daily traffic counts compared to the peninsula samples. In Seattle, we observed the highest levels of cadmium, chromium, iron, titanium and zinc in moss collected from the Longfellow Creek Greenspace.
What does this tell us about the impact of people on our environment?
The Puget Sound Regional Council expects our area to grow by around 900,000 people over the next 22 years, which will in turn increase demand for travel throughout the region by 40%. With this region-wide expansion in traffic and congestion there is the opportunity for more heavy metals to enter the environment, which has the potential to negativity impact both terrestrial and aquatic ecosystem health.
What’s the next step for this research?
I am currently working with Seattle Parks & Recreation and Green Seattle Partnership to expand the moss monitoring to 25 parks, greenbelts, and natural areas across Seattle. We are tracking urban pollution to determine the extent and threat it is having on forest health across the city. Field and lab work was completed in early February completed, now I am working on analyzing the results to see what stories lie within the data.
To learn more about WA’s Better Brake Rule and steps you can take to purchase Level A, B or N brakes, visit the Washington Department of Ecology website.
Photos: Amanda Bidwell