Less than 20 miles from Maine’s Acadia National Park, toxic wastes from the abandoned Callahan Mine have been poisoning the Goose Pond estuary for more than four decades, posing a threat to coastal marine life, birds, and humans. In 2001, the open-pit mine was designated a Superfund cleanup site by the U.S. Environmental Protection Agency (EPA).
Professor Celia Chen and her Dartmouth colleagues have been evaluating the extent of the mine’s impact on the local estuarine food web as well as its broader impact beyond the estuary. Based on their studies of the estuary’s waters, sediments, and fish, Chen and her fellow members of Dartmouth’s Toxic Metals Superfund Research Program are providing information that is useful to EPA’s environmental risk assessment and ongoing cleanup efforts. It also contributes to a growing database establishing a baseline for evaluating future actions at the site.
The Goose Pond estuary is an arm of Penobscot Bay, where toxic heavy metals that include copper, zinc, cadmium, and lead seep from old mining residue. The pollution is coming primarily from waste rock removed from the surface to expose the ore and from tailings—the dregs remaining after the metal has been extracted from the ore.
To reach the copper and zinc ore body submerged beneath the estuary, the Callahan Mining Corp. constructed dams at both ends of the pond. This diverted the freshwater that had been flowing into the estuary while creating a downstream barrier to the tidal exchange with Penobscot Bay. Between 1968 and 1972, Callahan dug a 300-foot deep, 1,000-foot wide pit, and excavated 800,000 tons of copper and zinc ore. After mining ceased, the dam at the Penobscot end was opened, tidal flow resumed, and the pit filled with water.
As the only open-pit mine in an estuary system in the United States, the Callahan Mine affords scientists a unique opportunity to study its impact on a sensitive environment. The Dartmouth scientists looked for the presence of toxic metals in Goose Pond’s water, its sediments, and its fish. Beyond the estuary itself, the Dartmouth team considered farther-reaching impacts on the coastal marine food web.
The findings of their study, funded by the National Institute of Environmental Health Sciences, appear in the journal Archives of Environmental Contamination and Toxicology. In discussing the sediments, the authors write, “regionally the site represents a hot spot of copper, zinc, and lead for the Gulf of Maine surpassed only by levels in some areas of Boston Harbor.”
They found that sediment concentrations for all four metals—copper, zinc, cadmium, and lead—were particularly high adjacent to the tailings, and the same was true for metal concentrations in the water near the tailings. The metal concentrations were high in water and fish even though tides are continually flushing the estuary. This provides evidence that the metals are continually seeping from the mine’s waste rock piles and debris, as well as passing upward from the bottom sediments to the overlying water and potentially out into the bay with the flow of the tide.
The toxic metals from the abandoned mine could potentially affect humans through the fish we eat, although fish higher in the food web have not been studied. The Dartmouth scientists focused on the tiny Atlantic killifish because it is an important link in the food chain that leads to our dinner table. The killifish, also known as the mummichog or mud minnow, live in shallow, brackish coastal waters throughout the eastern United States and Canada.
As larger predatory fish like striped bass and tautog travel into Goose Pond from Penobscot Bay, they will feed on resident species such as killifish. The researchers propose that levels of toxic metals in killifish may be high enough to be transferred along the food chain to larger fish that feed on them—fish typically consumed by humans.