Chemical Contamination
Chemical
contamination of the marine environment has become widespread as urban
growth and population centers continue to expand within coastal watersheds.
Types of contaminants entering the coastal environment from both point
and non-point sources include suspended solids, organic debris, metals,
synthetic organic compounds, nutrients, and pathogens. The coastal waters
adjacent to the Sanctuary, particularly within Boston and Salem Harbors,
are among the more contaminated coastal environments in North America
for a number of trace metals, PCBs and petroleum hydrocarbons (Pearce,
1990). Contaminant sources include sewage and industrial discharges,
combined sewer overflows, stormwater runoff, ground water inflows, in
place sediments, seeps, and atmospheric deposition (Menzie-Cura, 1991).
Additional chemical and nutrient loads flow into Massachusetts Bay from
the north in the buoyant freshwater plumes associated with the Merrimack
River and several other large river discharges from the southern coast
of Maine (EPA, 1993).
Contaminated
sediments exist at the Massachusetts Bay Disposal Site (MBDS) and the
Industrial Waste Site (Foul Area), both of which lie just outside the
western boundary of the Sanctuary. Analysis of sediment chemistry in
at the MBDS indicate elevated concentrations of copper, lead,
zinc, chromium, total PAH and total PCB relative to samples from outside
the general areas of disposal.(EPA, 1989). Despite the long-term, use
for disposal of contaminated sediments and other debris, (including
unknown amounts of low-level radioactive waste) at these sites, ambient
water quality conditions generally comply with the EPA's chronic water
quality criterion concentrations for most parameters. Mercury was found
to be variable at the site, with elevated concentrations above the chronic
criteria concentration (CCC) of 0.025 ppm and average copper concentrations
were only slightly below the 2.9 ppm CCC (EPA, 1989). Yet despite this
and numerous other sources of contamination, the Bays and waters surrounding
the Sanctuary are not grossly or uniformly polluted, and remain highly
productive habitat for a vast diversity of marine life, including several
species of marine mammals.
There
is a growing body of literature (see sections below) providing evidence
of chemical contamination in the populations of marine mammals which
commonly occur in the Gulf of Maine region, yet due to the highly migratory
nature of most species, it is extremely difficult to determine how and
where certain animals accumulate these contaminants in their bodies.
Given the numerous and diverse sources of chemical loadings to the GOM
and the apparent species/individual dependent nature of effects, it
is likely that direct causative relationships to chemical exposure will
remain illusive until directed research efforts can better describe
the pathways, fate, and induced effects of pollutants on marine mammals
(see Reijnders, 1988). And while there is little empirical data regarding
chemical toxicity in marine mammals from this region, evidence from
around the world is increasingly pointing to chemical pollution as a
contributing cause to viral epizootics and other mass die-offs of marine
mammals (Raloff, 1994, Rik de L. Swart, et. al. 1994, Kuehl, et. al.,
1994).
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