Both heavy metals and organic contaminants have accumulated in the sediments of the Bay and, in many cases, in the tissues of aquatic organisms. The levels of toxic chemicals found 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 the elevated levels of PAHs found in the sediments in some inner parts of the Bay, and the levels of polychlorinated biphenyls (PCBs) and some metals, including mercury, in the sediments of the Fore River. While low levels of toxic contaminants are found in most parts of the Bay, these chemicals are becoming concentrated in the tissues of organisms through the food chain. Blue mussels show elevated levels of metals including lead and the organic pollutants PCBs and PAHs at some sites in the Bay with an industrial history in harbors, commercial ports, at the mouths of river watersheds and in locations adjacent to population centers.

Elevated concentrations of mercury have been found in predatory species from insect-eating birds to fish-eating birds and mammals. Studies have shown that the mercury levels in Maine’s fish, loons and eagles are among the highest in the country and that the productivity of Maine’s loons and eagles is being impacted by mercury. As top level predators, seals are especially vulnerable to bioaccumulation. Research indicates that seals from southern Maine have elevated body burdens of mercury and the organic chemicals PCBs and DDE (a metabolite of DDT). 

As consumers of fish, humans are also at the top of the food chain and are potentially at risk of health impacts from toxic chemicals. Levels of mercury and some organic chemicals found in freshwater and certain marine fish have led the State of Maine to issue fish consumption advisories and guidelines on safe fish and lobster consumption practices. These are especially important for the most vulnerable consumers, including pregnant women and children.
Despite the clear evidence that toxic chemicals are found throughout Casco Bay and its watershed, impacting both the ecosystem and our ability to safely eat certain fish, there is some good news. The levels of mercury, PCBs, dioxins, and many pesticides entering the environment have declined greatly over the past two decades (see Toxic Pollution in Casco Bay, 2007).  As reported in State of the Bay (CBEP 2005), levels of most heavy metals, pesticides, tributyltin, PCBs and low molecular weight PAHs decreased in the sediments of the Bay between 1991/1994 and 2000/2001.

Continued decreases in the loading of toxic chemicals will require an ongoing commitment from government agencies and the citizens of the Casco Bay watershed to use all of the available tools, including: regulatory enforcement; monitoring and assessment of sources, risks, and impacts; development of new approaches to reduce the use and release of toxic chemicals; and vigorous environmental stewardship at every level.

Click here or on the Current Projects button to the right for examples of the toxics related activities that CBEP and our partner organizations are supporting.