Scientists Put Mussels into Monitoring

The succulent blue mussels so many restaurants serve steamed with a wedge of lemon are being used by Environment Canada scientists in Atlantic region to gauge levels of toxic chemical contaminants in the briny waters of the Gulf of Maine.

Mussels are an ideal indicator species not only because they are abundant and easy to collect, but also because they feed by pumping large volumes of water through their systems, exposing their tissue to contaminants in the process. Because mussels remain fairly stationary over the course of their lives, scientists can determine water quality in a specific area simply by analyzing the concentration of contaminants in the tissue of native mussels.

The Gulf of Maine is one of the most productive ecosystems in the world. Extending from Cape Sable, Nova Scotia, to Cape Cod, Massachusetts, and including the Bay of Fundy and Georges Bank, it supports a vast array of seaweeds, salt marsh grasses, phytoplanktons and marine animals, including many species of commercial importance. Unfortunately, human population growth and land development have dramatically increased the release of atmospheric and effluent pollution into the Gulf's coastal and estuarine environments over the past 50 years. Of particular concern are persistent toxic substances like polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), pesticides, dioxins and furans, and trace metals, because they bioaccumulate in tissue and can magnify to biologically harmful levels in the food chain.

To protect the health of the species in the ecosystem, including the humans who consume its seafood, the Gulf of Maine Council on the Marine Environment established the transboundary Gulfwatch monitoring program. Since 1991, Environment Canada scientists and other members of the Canada/US Gulfwatch Monitoring Committee have headed to the shores of the Gulf each fall to hand-pick some 200 mussels at each sampling site __ most located at the mouths of river watersheds and on coastal drainage systems. Samples are native mussels, but some clean transplants are also collected to evaluate the effects of short-term exposure to the Gulf waters. Five benchmark sites in Nova Scotia, New Brunswick, Maine, New Hampshire and Massachusetts are sampled annually, with the remaining 56 sites sampled once every three years on a rotating schedule.

Results have shown that concentrations of toxic organic contaminants and silver increase from north to south. Lead and chromium concentrations were elevated at sites within Massachusetts, New Hampshire and Maine. Other trace metals show a relatively uniform geographical distribution. Generally, contaminant concentrations were correlated with population density, latitude and distance from known contamination sources.

Very few sites have mussel tissue contaminant concentrations that exceed Canadian or American seafood human health tolerances; however, some have levels that require a more in-depth assessment of human health risk, and several exceed tissue concentrations considered harmful to birds and other wildlife. An examination of changes in data over time indicates that contamination levels at most benchmark sites are either decreasing or show no detectable change.

Government agencies in Canada and the United States use this information for a variety of purposes: to develop environmental management plans and policies, licensing requirements for industrial discharges, and pollution controls; to determine the safety of seafood; and to assess the effects of accidental spills and other specific events on water quality. Shellfish and fish aquaculturists use Gulfwatch data to find clean areas for harvesting and growing facilities.

Graph showing concentrations (2,3,7,8-TCDD TEQs) of PCBs and dioxins/furans found in mussel tissue at Gulf of Maine sites in 1996 and 1997.

Gulfwatch has recently begun collaborating with community-based environmental organizations to address local concerns about other toxic substances, including chemicals used by the aquaculture industry to kill parasites. Researchers hope that as public awareness about the impacts of toxic contamination grows, the use of these and other potentially harmful substances in this prolific ecosystem will decline.

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