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Boston Harbor Fish and Shellfish

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 of contaminants.


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 (FDA) guidelines.

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.


PAH levels in mussels have decreased and PCBs, pesticides are well within guidelines.

For this study, mussels from relatively clean areas in Gloucester and Sandwich were put in cages and placed on moorings for one to two months at the Inner Harbor near the New England Aquarium, and Deer Island Flats. Upon retrieval, the mussels were analyzed for lead, mercury, PCBs, PAHs, DDT, and ten other pesticides. PAHs in mussels have decreased since the early 1990s.


Lobster meat shows little contamination, but the tomalley (hepatopancreas) exceeds FDA guidelines for PCBs.

Parts per billion, wet weight
Actual range of annual averages FDA Limit
PCBs 10.8 - 39.8 2,000
DDT 0.7 - 6.0 5,000
Mercury 70 - 280 1,000

MWRA checks lobsters caught near Deer Island for external signs of disease, and tests the tail and claw meat for mercury, PCBs, DDT, and other pesticides. The hepatopancreas is tested for the same contaminants plus lead, cadmium, copper, nickel, silver, zinc, chromium, and PAHs. The levels of contaminants in lobster meat are well below the FDA limit for human consumption.

PCB concentrations in lobster hepatopancreas increased annually since 1993. Industrial PCBs are potential carcinogens and were phased out of production beginning in 1971. Although PCB levels are extremely low in MWRA discharges, PCBs break down very slowly and are therefore very persistent in the environment and marine sediments. This finding confirms existing consumer advisories against eating lobster tomalley.


Blue mussels being retrieved for bioaccumulation testing
(See larger image)

PCBs in lobster hepatopancreas (tomalley), 1992-2000. From 1993-1999 there was an upward trend in PCB levels in lobster caught in the harbor.

One possible explanation for the PCB trend is that as sewage solids reduced in the harbor, lobster started foraging more in the Inner Harbor and Dorchester Bay, where there are more pollutants. Another possibility is that, in later years, sampling for lobster was later in the year, so lobsters were exposed to PCBs longer.