Using Moss to Detect Fine-Scaled Deposition of Heavy Metals in Urban Environments

Sarah Jovan1, Geoffrey Donovan2, Demetrios Gatziolis3, Vicente Monleon4 and Michael Amacher5

Mosses are commonly used as bio-indicators of heavy metal deposition to forests. Their application in urban airsheds is relatively rare.  We used moss to develop fine-scaled, city-wide maps for heavy metals in Portland, Oregon, to identify pollution “hotspots” and serve as a screening tool for more effective placement of expensive air quality monitoring instruments. In 2013 we measured twenty-two elements in epiphytic moss sampled on a 1km x1km sampling grid (n = 346). We detected large hotspots of cadmium and arsenic in two neighborhoods associated with stained glass manufacturers. Air instruments deployed by local regulators to moss-detected hotspots measured cadmium concentrations 49 times and arsenic levels 155 times the state health benchmarks. Moss maps also detected a large nickel hotspot near a forge where air instruments later measured concentrations 4 times the health benchmark. In response, the facilities implemented new pollution controls, air quality improved in all three affected neighborhoods, revision of regulations for stained glass furnace emissions are underway, and Oregon’s governor launched an initiative to develop health-based (vs technology-based) regulations for air toxics in the state. The moss maps also indicated a couple dozen smaller hotspots of heavy metals, including lead, chromium, and cobalt, in Portland neighborhoods. Ongoing follow-up work includes: 1) use of moss sampling by local regulators to investigate source and extent of the smaller hotspots, 2) use of lead isotopes to determine origins of higher lead levels observed in moss collected from the inner city, and 3) co-location of air instruments and moss sampling to determine accuracy, timeframe represented, and seasonality of heavy metals in moss.


1U.S. Forest Service Pacific Northwest Research Station,
2U.S. Forest Service Pacific Northwest Research Station,
3U.S. Forest Service Pacific Northwest Research Station,
4U.S. Forest Service Pacific Northwest Research Station,
5US Forest Service, retired,