Gerry E. Studds Stellwagen Bank National Marine Sanctuary
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Contaminants in Organisms' Tissues

Determination of whether contaminant body burdens in Stellwagen Bank species are at levels high enough to elicit adverse effects on the organisms' health is currently impossible, because of the lack of data on contaminant body burdens. As noted earlier, the concentrations of contaminants in the water column are generally below current Water Quality Criteria, and therefore should not have direct toxicological impacts on organisms on the Bank. Nevertheless, low water contaminant levels do not preclude the possibility that contaminants may be taken up slowly, and stored in animal tissues over time. While there is a wealth of information on inshore species (e.g. mussels, winter flounder, lobsters), only a few studies have examined species from the Bank.

Gilbert et al. (1976), for example, sampled polychaetes from three stations on the western edge of Stellwagen Bank, as well as stations in Stellwagen Basin, Massachusetts Bay and coastal stations near the mouth of Boston Harbor. They compared metal concentrations in whole body composites of Nepthys sp. (including N. bucera, N. ciliata, N. incisa, N. longesetosa, and N. picta). Concentrations of most metals were 2 to 15 times higher in the coastal samples than in the samples from Stellwagen Bank (cadmium, lead and zinc were about the same; chromium was 15 times higher inshore; copper, 14 times higher; mercury, 2 times; nickel, 10 times). Gilbert also noted a distinctly higher concentration of both Cr and Pb in the northern part of Massachusetts Bay (including the northern portion of Stellwagen Bank), and hypothesized that this was due to influx of these metals from the Merrimack River. Comparisons of Nepthys sp. metals concentrations with sediment metal levels did not reveal much in the way of significant correlations. Nepthys sp. from the MBDS were reexamined more recently and analyzed for metals, PAHs and PCBs (U.S. COE, 1988, 1990; U.S. EPA, 1989). In all cases, however, it is not known if these elevated metal concentrations in the polychaetes are adversely effecting their health.

Boehm et al. (1984) collected American dab (Hippoglosoides plattessoides) from two stations close to Stellwagen Bank, one at the very edge of Stellwagen Basin (MB-6) and one just off the southern edge of the Basin (MB-10). Tissue fillets were analyzed for PCBs and PAHs. Both PCB and PAH concentrations were low, and were similar to values found in other offshore samples of dab and winter flounder.

Contaminants have been analyzed in several other species as well. Boehm et al. (1984) analyzed PAHs in Jonah crabs (Cancer borealis) and winter flounder (Pleuronectes americanus). Samples of the bivalve Astarte sp., the shrimp Pandalus borealis, and the deep sea scallop Placopecten magellanicus taken from the MBDS have been analyzed for metals, PAH and PCB (U.S. COE, 1988b; U.S. EPA 1989). In addition, P. magellanicus were collected from Pigeon Hill (a rocky knoll 42 nautical miles to the northeast of the tip of Stellwagen Bank) in 1989, 1990 and 1991 and analyzed for metals (cadmium, copper, chromium and zinc; National Undersea Research Center, Groton Connecticut, unpublished data). Due to the isolation of this site, and its subjection to the same circulation patterns as the northern tip of Stellwagen Bank, the analytical results should be applicable to Stellwagen Bank. Preliminary results indicate that metal concentrations in these scallops are representative of relatively clean sites. In all the cases cited above, however, it is not known whether the slightly elevated contaminant levels are having an impact on the health of any of the organisms.

Although the limited data that are currently available confirm our suspicions that contaminant levels in Stellwagen Bank's other species should be low, the expectation that some contaminants (e.g. mercury and lead) may be present at higher levels is based simply on the comparison of total metal concentrations in the water column from near-shore and offshore sites. Although metal concentrations in near-shore waters are relatively high compared to offshore sites, there is considerably more organic matter in the water from inshore waters. Since several metals, including mercury and lead, readily complex with organic matter, the concentrations of biologically available metal is lowered. In offshore waters, less organic matter is present to complex the metals that are present. Thus, while total metal concentrations in offshore waters are lower than in inshore waters, the concentration of biologically available metal could theoretically be greater. This possibility may explain why Wallace et al. (1993) measured higher lead concentrations in the livers of winter flounder from Georges Bank than from fish collected in inshore waters (Broad Sound). Alternatively, flounder that are chronically exposed to elevated concentrations of contaminants may have an enhanced ability to "metabolize" some contaminants compared to offshore specimens which are exposed to much lower concentrations of contaminants. In either event, it will be important to sample directly the species present at Stellwagen Bank, and document tissue body burdens of contaminants, in order to compare concentration levels found inshore. In this way, we can attempt to asses the probability that adverse impacts might occur.

In conclusion, few studies have measured contaminant concentrations in Stellwagen Bank organisms. In the few cases where analyses have been conducted on species from the Bank or adjacent areas, concentrations of contaminants appear to be the same or only slightly elevated compared to clean control sites. At present, it is not possible to determine whether these slightly elevated contaminant concentrations are adversely effecting the health of the organisms on Stellwagen Bank. However, since a number of studies on species closer to shore have shown much higher levels of contaminant body burdens (metals, PAHs, PCBs, pesticides) than the species sampled from Stellwagen Bank, and yet a measurable adverse impact on organism health has only been demonstrated for the most contaminated sites (e.g. Boston Harbor, Salem Harbor, New Bedford Harbor, etc.; Massachusetts EOEA, 1995, in preparation), it is unlikely that the low levels of contaminants measured in Stellwagen Bank species are having adverse effects on organisms' health.

 

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