Synopsis: In order to answer many of the most important questions regarding mercury in the Great Lakes environment, such as how much mercury is entering the Great Lakes and where this mercury originates, additional monitoring is needed beyond that currently being conducted by federally-run programs. In recent years, highly sophisticated measurement techniques have become available, or are being developed, that can provide answers to many of the pressing questions surrounds where mercury deposition originates and what, if anything, might be done to protect human health and the environment from this pollutant. This study will use advanced techniques to measure mercury in the air and rain at two sites along the coast of southern Lake Michigan to provide the best estimate to date of how much mercury is entering the lake from the atmosphere and what sources are contributing to these mercury loadings.

There is often controversy surrounding estimates of how much mercury is reaching local water bodies from long distances (such as transport of mercury on a global scale) and how much is from nearby sources. Recent research in the Ohio river valley showed that approximately 70% of the mercury measured at that location was from nearly coal-fired power plants. Similar techniques will be used here to identify the primary sources of mercury to southern Lake Michigan and to determine which are local influences and which are from further abroad.

Chemicals Studied: The study will focus on mercury, a substance of high concern within the Great Lakes region due to its high toxicity and tendency to accumulate at high levels within fish. Both the monitoring and modeling approaches used will allow differentiation among the various mercury species commonly found in the atmosphere and in the region’s waters.

Geographic Areas: The study sites will include one near Holland, Michigan and another near Chicago, Illinois. The location of these sites on opposite shores of the southern Lake Michigan basin give an ideal opportunity to examine mercury loadings to this area. In addition to these two sites, four other sites, measuring mercury in precipitation only, are being established in Illinois under a related project and will provide additional information for use in source identification. Mercury deposition to Lake Michigan was measured as a part of the Lake Michigan Mass Balance study in the early 1990’s, but these were prior to the creation of the currently used methods .

Project Duration: Measurements will begin in the fall of 2007 and will continue through the fall of 2008. Project results should be available in 2009.

Methods Used: Precipitation event samples will be collected at each site by an automated sampling system. These wet deposition samples will be analyzed for mercury and trace element concentrations. Additionally, speciated ambient mercury measurements will be taken at two sites to assess elemental and reactive mercury in the gaseous and particulate phases. This ambient data will be used to estimate rates of dry deposition. In addition, the mercury and trace element data will be used to apportion mercury contributions to major source categories using statistical models, such as Positive Matrix Factorization and UNMIX.

Potential Results and Implications: As the first comprehensive effort in more than a decade to estimate the loading of mercury to Lake Michigan, this project represents an important step in gaining the knowledge needed to address this important problem. The methods to be used here will provide for greater accuracy than those used in the past and will allow for more powerful statistical analysis of the results to reveal important patterns and to identify the contributions of various source types. This information can be used by policy makers to determine what actions may be effective in decreasing the amount of mercury depositing to the southern Lake Michigan basin, and to other portions of the Great Lakes region as well.

Project Contact:
Gerald J. Keeler, Ph.D.
University of Michigan
School of Public Health
3003 S. State Street
Ann Arbor, MI 48109-1274
Phone: (734) 936-1836
Email: jkeeler@umich.edu