Sources, Distribution and Fate of Mercury at Contaminated Sites in Penobscot Bay, Maine

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Coastal Ecosystem and Public Health


Henri Gaudette University of New Hampshire Co-Principal Investigator
Stephen Jones N.H. Sea Grant Principal Investigator

Students Involved:

Jordana Langlois UNH - Department of Earth Sciences
Nathan Horton UNH - Department of Biological Sciences
Acksone Soumpholphakdy UNH - Department of Natural Resources & the Environment
Debra Lambert UNH - Department of Biological Sciences
Stephanie Getchell UNH - Department of Earth Sciences

Mercury contamination is a high profile, significant environmental problem throughout the U.S., especially in the Northeast. Continued atmospheric deposition and discharges from point sources make this persistent problem even more critical in the region, especially in aquatic ecosystems. More information is becoming known about the extent and concentration of mercury in marine environments, but little is known about the fate, transformation, bioavailability and effects of mercury relative to estuarine and marine organisms. In particular, little information is available on the fraction of mercury that is bioavailable in marine and estuarine environments. The ability to assess impacts on biota by measuring bioexposure in indigenous organisms can be complicated at some contaminated sites, and the proposed approach of using highly adaptable bacterial communities as one measure of bioavailability and biological response to mercury is a potentially useful approach worthy of evaluation.

The intent of the project is to determine the extent of contamination and availability of mercury to organisms in aquatic environments near suspected mercury sources. The areal and subsurface distribution of mercury will be measured at two sites, one in a low salinity tidal river next to an industrial point source and the other in a small, active fishing harbor on the Atlantic Ocean with sediments contaminated from unknown sources. The potential for bacterial transformation of ionic mercury to volatile elemental and organic forms, and the degree of resistance in bacteria will be determined using samples from the most contaminated sediment areas at both sites. The bioexposure of blue mussels to mercury will also be determined at the harbor site.

Development and application of this unique combination of approaches will help environmental management and public health agencies assess the significance of trace metal contamination. The project is timely in that it coincides with ongoing and new related research projects on mercury in estuarine environments in New Hampshire, and ongoing analysis of the extent of mercury contamination throughout Penobscot Bay by the principal investigators. The results should also provide needed fate and contamination information that compliments other ongoing studies on mercury in Penobscot Bay.


The overall goal of the project is to determine the extent and impacts of mercury contamination at two sites at extreme ends of the Penobscot River watershed. The specific objectives are to:

1) Determine distribution of Hg contamination in surface sediments in Stonington Harbor and the associated dredge dump site

2) Establish the historical chronology of mercury deposition and burial at both sites via analysis of sediment cores

3) Determine Hg bioavailability at both sites by assessing mercury volatilization rates and degree of bacterial Hg resistance

4) Determine Hg bioexposure at Stonington Harbor sites using transplanted mussels.


Experiments will be carried out at various UNH labs and at two sites in Penobscot Bay and River. Surface sediments and cores will be sampled and mercury concentrations will be measured to determine the distribution and historical deposition of mercury at the two sites.

Long- and short-term bioexposure of blue mussels to mercury will be determined at the oceanic site; bacterial resistance to mercury and detoxification processes will be measured from water and sediment samples at both sites. The project will provide useful information on mercury bioavailability.


The project relates particularly to Sea Grant priorities on determination of existing levels of sediment pollutants, estimating the assimilative capacity of the marine environment, relating pollutant concentrations to ecosystem degradation, effects of dredging, and the impacts of coastal development ecosystem health. The project addresses mercury pollution, which is an important national issue. Mercury pollution is probably the number one environmental quality issue in the Gulf of Maine, and there are acute problems on the Maine coast, particularly in Penobscot Bay.

Success in meeting project objectives
The actual research conducted compared to what was proposed in the 4 project objectives differed as a result of a number of factors (see below). The details of project activities relative to meeting objectives provide a basis for future research.
Work on Objective 1 was a complete success. The data provide a comprehensive assessment of Hg in surficial sediments throughout Stonington Harbor, with detailed data around the dredge and disposal sites.
The results of work on Objective 2 were somewhat limited in that Hg concentrations were determined with depth in sediment cores taken at all study sites from the Penobscot River marshes, but the geochronology was not determined. This happened as a result of the unavailability of equipment to one of the PIs as a result of his moving his lab, then he retired. The Hg concentration data provided some high quality profile information that would greatly benefit from supporting geochronology data to pinpoint times when Hg discharges were elevated and causing the most exposure, as well as the longevity of impact from the HoltraChem pollution. No undisturbed cores at Stonington Harbor were found.
Work on Objective 3 was extensive and focused on Hg resistance in indigenous bacteria. There was extensive effort put into adapting published protocols to sediment bacteria, and the end results somewhat met expectations.
For Objective 4, transplanted mussels were not used to assess bioexposure in Stonington Harbor. This decision was made based on the results of a review of the Gulf of Maine Gulfwatch program that was published after the proposal was written. The review recommended discontinuing use of transplanted mussels in the way described in the original proposal, based on 5 years of results from the Gulfwatch program. Another reason was the relatively low levels of Hg detected in sediments around Stonington Harbor. We concluded that our efforts may not be well-spent if we tried to discern differences in uptake of Hg from sites with contaminated compared to uncontaminated sediments, in light of the Gulfwatch results. Instead, Hg concentrations in indigenous mussels were measured at various sites around the harbor to provide a spatial assessment of bioexposure to potentially elevated levels of Hg near the dredge and disposal sites.
New Research Directions and Modifications to the Research Plan
New directions pursued during the project included analysis of sediments collected as part of a previous project from the whole Penobscot Bay for Hg. The samples had been previously analyzed only for a suite of metals that did not include Hg. This enabled a more comprehensive assessment of the distribution of Hg in the whole region and in between the two study sites. Other new directions included work on bacterial Hg resistance from some sites in the Great Bay Estuary of New Hampshire. This work served as a basis for testing the method and for comparison with the HoltraChem site. We also decided to enhance our study of bioexposure to Hg near the HoltraChem site by including analysis of Spartina alterniflora from nearby salt marshes. Combined with sediment core work in the same marshes, we were able to determine how present day and historical Hg in sediments affects Hg concentrations in marsh plants. Clostridium perfringens concentrations were also measured in sediment samples to determine the presence and distribution of sewage contamination to help assess the significance of different potential sources of Hg pollution.
We decided not to pursue transplanting of mussels in the Stonington area for two reasons. The first is that this approach is more complicated than initially realized and can be difficult to interpret results without a vast amount of controls. These conclusions are based on some recent analyses of Gulfwatch results and accompanying discussions amongst Gulfwatch experts. The second reason is the relatively low levels of Hg detected in sediments around Stonington Harbor. We concluded that effort may not be well-spent if we tried to discern differences in uptake of Hg from sites with contaminated compared to uncontaminated sediments, in light of the Gulfwatch results. The final reason was that the delay in sediment analysis results would have made it difficult to complete the transplant experiment and then all analyses prior to the end of the project.


Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant


  • Getchell, S. (2002). The spatial and temporal distribution of Cu, Pb, Zn, and Cd in marine sediments of Boothbay, Maine. Master's Thesis, University of New Hampshire.