Dr. MacRae's teaching responsibilities include Introduction to Environmental Engineering at the undergraduate level and Environmental Microbiology. Building on her background in life sciences and microbiology, her research interests focus on the ways that microorganisms affect pollutants. Three areas of particular interest are (1) biodegradation and bioremediation, (2) arsenic cycling in groundwater, and (3) chitin and related products from crustacean waste. She joined the department in May of 1999.
Ph.D.-1997, Environmental Engineering/University of British Columbia
Arsenic in groundwater:
In Bangladesh, Taiwan, Chile and Argentina, devastating health effects have occurred as a result of chronic arsenic poisoning through drinking water. The source of arsenic in these locations is natural, and comes from the geologic materials of the aquifer. Now that the issue has attracted attention, it has become clear that drinking water in many areas, including parts of the United States, contains arsenic above regulatory levels. While correlations with bedrock types have been made, the factors that affect arsenic concentrations and speciation in drinking water are still poorly understood. As(III), the reduced inorganic form, is more mobile and more toxic than As(V), so speciation affects both the concentration and the health implications of arsenic exposure. Microorganisms probably affect As concentrations in groundwater but the magnitude and nature of their participation in the arsenic cycle have not yet been clarified.
Microorganisms can affect the redox chemistry of arsenic compounds in a number of ways. Under reducing conditions, which are usually encountered in groundwater, microorganisms can catalyze the reduction of As(V) to As(III) in energy-generating or detoxification reactions. Other microorganisms may cause the release of adsorbed arsenic through reductive dissolution of Fe(III) and Mn(IV) minerals, which serve as binding sites for arsenic. These transformations result in an increase in soluble arsenic and could contribute to contamination of groundwater.
In my lab, we are trying to learn more about the microorganisms that affect arsenic speciation and mobility in groundwater.
Bacteria from a Maine groundwater sample that gain energy by reducing As(V) to As(III):
Brominated Flame Retardants (BFRs)
In recent years, concerns have been rising about the global presence of brominated flame retardants (BFRs) in all levels of ecosystems. In contrast to the declining levels of polychlorinated biphenyls (PCBs), dioxins and DDT in the environment, levels of BFRs have increased exponentially in the last 30 years as they replaced their chlorinated counterparts in market products. These compounds are highly lipophilic and readily bioaccumulate in the food chain in a manner similar to dioxins and PCBs. Furthermore, their greater tendency for atmospheric transport results in faster and broader global redistribution.
BFRs are used in an increasingly broad range of products and materials. Sources include electronic circuit boards, epoxy resins, phenol resins, polyesters, polyurethane foams, textiles, styrenes polystyrenes, polycarbonate and thermosets. When materials containing these compounds are discarded, they typically enter the solid waste stream. Ingestion by insects and UV breakdown increases the availability of these compounds to other species. Recent studies have shown that combustion of BFRs in the presence of chlorine containing materials, such as during waste incineration, produces brominated/chlorinated dioxins and furans. Washing textiles that contain BFRs may also result in contamination of wastewater and entry of these compounds into the environment in effluent and sludge.
While the toxicity of these compounds has not yet been exhaustively characterized, it is clear that some initiate dioxin-like effects and could disrupt normal thyroid activity. While these hormone effects are less severe than those induced by coplanar PCBs, the environmental concentrations of PBDEs are higher and are rising exponentially in North America.
The potential for negative environmental effects mediated by these compounds is great. Research in my lab is underway to identify important routes of these contaminants to the environment, and to determine their fate in sewage treatment plants and solid residuals.
Other areas of Interest:
Resource Recovery: protein and chitin from crab processing waste
- Use of lactic acid bacterial fermentation to stabilize crab processing waste and separate protein from chitin
- Characterization of protein liquor to assess its use as a feed additive or fertilizer
- Characterization of chitin fraction to assess potential uses
Water and Wastewater Treatment Using Chitin and Chitosan-Based Adsorbents
- Use of chitosan from crab shells for metal biosorption
- Modification of chitosan for improved metal sorption
- Bioavailability and biodegradation of organic pollutants
CIE 231 - Fundamentals of Environmental Engineering
- Basics of ecology and water quality, chemistry and microbiology
- Introduction to pollution prevention and mitigation techniques
CIE 432 - Water and Wastewater Process Design
- Design and elements of water and wastewater treatment plant
CIE 534 - Environmental Microbiology
- Introduction to environmental microbiology for engineering students and others with no biology background
- Importance of microorganisms in nutrient and other chemical cycles, approaches to studying microbial processes in the environment and in environmental media
CIE 598 - Water Pollution
- Introduction to the major causes and effects of water polluti
- Includes mitigation methods
Other courses planned:
- Biological processes in wastewater treatment
- Techniques in environmental engineering (lab course)
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