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Hot on the Trail of Hazardous Waste

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Hot on the Trail of Hazardous Waste

Sept. 4, 2014
Engineers with the Superfund Research Program are extracting vital data on hazardous waste at landfills and mining sites.

UA engineers and researchers from disparate disciplines are collaborating to combat an exquisitely complicated -- but fundamentally important -- problem: environmental contaminants and their risks to public health.

Hailing from five colleges in addition to Engineering – Pharmacy, Medicine, Public Health, Science, and Agriculture and Life Sciences – and seven departments, the researchers are participating in the National Institute of Environmental Health Sciences UA Superfund Research Program, or UA SRP. The UA, which has nine ongoing SRP projects, is one of 18 participating universities and has received $14 million from NIEHS for the current funding cycle (2010-2015), and a total of $70 million from the agency to date.

The College of Engineering has been a key player in the multidisciplinary and highly competitive research program, themed “Hazardous Waste Risk and Remediation in the Southwest,” since it began 25 years ago.

In two of the UA SRP projects, engineers are studying arsenic and other environmental contaminants at hazardous waste sites and working with colleagues to develop risk-assessment and remediation strategies.

“We have the only Superfund Research Program located in the desert Southwest, which is the perfect natural laboratory for studying arsenic,” said Jim Field, chair of chemical and environmental engineering, who is among the investigators on the project.

Arsenic Activity at Landfills

One project is examining decomposition of arsenic at waste sites, particularly landfills.

Since the Environmental Protection Agency in 2001 revised its rule for acceptable levels of arsenic in drinking water from 50 to 10 parts per billion, cities and counties have dumped millions of pounds of arsenic-bearing solid waste in landfills.

“A common strategy for disposal of arsenic removed from drinking water has been to send iron-based sorbent waste to landfills,” said Eduardo Sáez, professor of chemical and environmental engineering, and a core member of the research team for the last decade. “But landfills have complex chemical and environmental conditions containing microorganisms and other agents that can alter arsenic’s fate. Often, that fate is to be released back into the environment.”

Because arsenic in the aqueous phase poses the greatest potential threat to human and environmental health, successful cleanup requires understanding how arsenic interacts with other media and rendering it insoluble. Thus, the researchers are examining the mechanisms and pathways for arsenic’s association with iron and sulfur solids and developing intervention approaches that use biological and biogeochemical mineral retention processes to minimize arsenic’s release from solid waste.

Airborne Arsenic at Mining Sites

The second arsenic project involves analyzing aerosols, or airborne particulate matter, associated with mining activity, such as wind-blown dust from mine tailings, and its role in transporting metal contaminants from mining operations. Data collected is being used to develop a high-resolution computational fluid model to predict dust emissions from mine tailings.

Spent ore is deposited in mine tailings that are susceptible to wind erosion. In dry regions soil dust accounts for most airborne particles. Dust generated by mining activity may contain toxic metals, including arsenic, lead, copper, chromium, cadmium and zinc. The dust particles mobilize the metals, which may then accumulate in soil, water, vegetation and air. Humans are exposed to metal-laden dust primarily through inhalation; children are also exposed by ingesting contaminated soil.

Sáez and researchers in the atmospheric sciences department are collecting ambient aerosol particles near the Iron King Mine and Humboldt Smelter Superfund site in northern Arizona and around the ASARCO copper smelter, an aging but active mining operation in Southern Arizona.

The researchers have confirmed that the mine tailings at the Iron King site are a source of arsenic and lead contamination in nearby soils and are working with scientists in the soil, water and environmental science department to evaluate the role of vegetation cover in reducing transport of contaminated dust from the site.

When Toxic Dust Meets Moisture

While Sáez focuses on dry dust particles, Armin Sorooshian, an assistant professor of chemical engineering, is most interested in how dust reacts when it encounters moisture. He is mining data from the research of these and other scientists to illuminate how dust particles behave and transform in the environment -- particularly the humid environment.

Sorooshian is a pioneer in research on hygroscopicity, an aerosol property that governs the ability of a particle to swell or shrink when exposed to humidity. He has discovered that particulate emissions from hazardous waste sites, such as the Humbolt copper smelter, can swell when exposed to humid conditions.

“This is the first time, to my knowledge, that the size-resolved hygroscopicity of airborne contaminants has been studied at a hazardous waste site,” he said. “It is a very difficult measurement and requires a custom-built instrument.”

The human respiratory tract is an extremely humid environment, where humidity may top 90 percent. Sorooshian and colleagues have discovered that the composition of particles governs changes in their size upon inhalation.

“Our work is providing crucial information for predicting where these chemically complex particles deposit when we breathe them.”