MONITORING THE HEALTH OF
FLOUNDER, MUSSEL, AND LOBSTER
Since 1992, MWRA has monitored winter flounder, lobster,
and blue mussel (see monitoring
locations). Flounder and lobster are important biomonitoring
tools because they are commercially important for food, and they
live in close contact with potentially contaminated bottom sediments.
Flounder and lobster for testing are collected near Deer Island.
Mussels feed by filtering particles out of the water, and can
concentrate (bioaccumulate) toxic materials from the water in
their tissues. Mussels are collected from relatively pristine
sites and then transferred to cages which are placed near Deer
Island and in the Inner Harbor for up to 60 days, to permit bioaccumulation
Flounder caught near Deer Island have a much lower
prevalence of liver disease than those caught in the 1980s, and
liver tumors are now rare. Levels of mercury, PCBs, and pesticides
in flounder fillet are well within U.S. Food and Drug Administration
Flounder eat worms and other tiny animals that live
in the sediments, and thus can be exposed to sediment contaminants.
In the mid-1980s, Boston Harbor flounder may have had among the
highest incidence of liver tumors in the northeastern United States.
In more recent years, the flounder caught near Deer
Island have not shown the gross abnormalities, such as fin erosion,
that were observed during the mid-1980s. Of the liver lesions,
a type called centrotubular hydropic vacuolation (CHV)
has been the most common. On average, the rate of CHV is about
two-thirds of the levels found in the 1980s, although this may
be partially explained by the age of the fish: the tested fish
from Boston Harbor have been younger, and younger fish tend to
have lower CHV levels. Liver tumors, which indicate more serious
health effects, have not been observed since 1996.
Liver disease in
winter flounder is a sensitive indicator of pollution effects
on Boston Harbor flounder because the liver can be damaged as
contaminants are metabolized. Other forms of liver disease (not
shown) also have dropped substantially since the late 1980s but
seem to have leveled off over more recent years. (Again these
observations should be interpreted with caution, because of the
younger age of the fish.)
The flounder livers are tested for levels of lead,
mercury, cadmium, copper, nickel, silver, zinc, chromium, PAHs,
PCBs, DDT, and ten other pesticides. In order to test for potential
human health effects, mercury, PCBs, DDT, and seven other pesticides
are also measured in the edible flounder fillets. For many fish
species, consumption advisories because of mercury are a concern.
However, mercury levels in winter flounder have been stable at
about 50-100 parts per billion, well below the U. S. Food and
Drug Administration (FDA) limit of 1,000 parts per billion. Levels
of PCBs and DDT are also well below FDA limits. PCBs, DDT, and
mercury in fillet of flounder caught in the harbor have fluctuated
between years with no clear pattern. All these chemicals have
measured well below the FDA action limits.