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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