Toxins in Casco Bay: Stubborn pollution remains
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By Lori Valigra
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ILLUSTRATION: U.S. ENVIRONMENTAL PROTECTION AGENCY
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The first compendium of toxic chemicals in the sediment, water, air, and biological organisms in and around Casco Bay in southern Maine reveals both good and bad news. Anti-pollution efforts seem to be paying off in terms of lower levels of many toxic pollutants, but fish, seals, and other wildlife are storing some pollutants long term, indicating the pollutants still are making their way up the food chain.
“The good news is that regulatory efforts are starting to work. But the bad news is that many toxic pollutants are persistent, and if they have the ability to biomagnify [build up through successive trophic levels], they can have a long-range impact,” Karen Young, director of the Casco Bay Estuary Partnership (CBEP) said at a seminar in Portland, Maine, this spring. The partnership issued a report, Toxic Pollution in Casco Bay, at the event. “While we are seeing evidence of serious adverse impacts to wildlife and the accumulation of toxic chemicals in fish and other species, there also is signigicant progress being made on reducing the volume of toxics that are entering the bay,”Young said. The 89-page report http://www.cascobay.usm.maine.edu/toxicsreport07.html is the first of its kind to compile all the toxics information available for Casco Bay to get a sense of the impact to the bay.
Mercury levels dropping
David Evers, director of the BioDiversity Research Institute http://www.briloon.org/ and adjunct professor at the University of Southern Maine in Portland, said mercury levels are decreasing in New England, but levels in lakes generally are four times higher than those in the open ocean. Animals such as the kingfish and eagles breed and eat in estuaries, lakes, and coastal zones. “So it makes sense to monitor fresh water for mercury as well,” he said. In the ocean, one great indicator of mercury levels is the Leach's-Storm petrel, a small, reclusive seabird that eats shrimp at the edge of the continental shelf.
Mercury gets into the water from smokestacks and coal-burning plants that discharge it into the atmosphere. It subsequently comes down into the forests, lakes, and oceans. The CBEP report noted that the widespread distribution of toxic chemicals suggests that atmospheric deposition plays a major role in the delivery of toxic chemicals to the watershed and directly to the bay.
Harbor seals also serve as sentinels for mercury and persistent organic pollutants (see related story on Susan Shaw, p. 12). The seals store pollutants in their fat, where it remains for long periods and could pose a health risk, especially among seal pups.
Health impacts
But relating the toxic pollution to health risks in people and mammals is challenging. “For people and marine mammals, there are bigger questions that remain unanswerable,” said Susan Shaw, a marine toxicologist and director of the Marine Environmental Research Institute http://www.meriresearch.org/ in Blue Hill, Maine. “Are current U.S. body burdens of neurotoxic (toxic to the nervous system) and cancer-causing chemicals responsible for the increase in childhood cancers? Brain cancers? Reproductive cancers (breast, prostate), endometriosis? Or attention deficit disorder?” she asked. “Are the extremely high body burdens of chemical mixtures triggering the recurring disease outbreaks and mass mortalities that we are seeing in our harbor seals? Over the years it takes many studies to build a body of evidence, and it is the weight of the evidence that is important.”
The report concludes that human activities have caused toxic chemicals to enter Casco Bay and its watershed, and both heavy metals and organic contaminants have accumulated in the sediments of the bay and in many cases, the tissues of aquatic organisms. The levels of toxic chemicals in the waters and sediments of the bay are below the levels that would cause negative biological effects throughout most of Casco Bay. The exceptions are elevated levels of PAHs (polycyclic aromatic hydrocarbons) in sediments in some inner parts of the bay and the levels of PCBs (polychlorinated biphenyls) and some metals, including mercury, in the Fore River separating Portland and South Portland.
While low levels of toxic contaminants are in most parts of the bay, the chemicals are becoming concentrated in the tissues of organisms, including predatory aquatic organisms, through biomagnification and bioaccumulation. Blue mussels, an indicator organism for the Maine Department of Environmental Protection, CBEP, and the Gulf of Maine Council on the Marine Environment, show elevated levels of metals, including lead, plus PCBs and PAHs at some sites with an industrial history such as in harbors, commercial ports, at the mouths of river watersheds, and in areas adjacent to population centers.
However, there is some hope as the levels of mercury, PCBs, dioxins, and many pesticides entering the environment have declined greatly over the past two decades. For more information visit http://www.cascobayestuary.org.
Lori Valigra is editor of the Gulf of Maine Times.
© 2007 The Gulf of Maine Times