Toxic chemicals generated through
human
activities have entered and
continue to enter Casco Bay and its watershed via multiple routes
including outfall pipes, industrial smokestacks, internal combustion
engines, stormwater runoff, oil spills, and atmospheric deposition.
While most of these sources are local, deposition from polluted air
masses via rainfall, gases, and particles, is contributing toxic
chemicals from both local and distant sources. As a result of past and
ongoing activities both here in Maine and in other parts of the United
States, toxic chemicals are found throughout Casco Bay and its
watershed.
Levels of Toxic Chemicals
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.
Ecological Effects
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.
Some Good News
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.
