Chemical Risks Associated with Consumption of Shellfish Harvested on the North Shore of the St. Lawrence River's Lower Estuary

Article excerpt

Shellfish have the capacity to accumulate chemical contaminants found in their biotope and therefore present a potential risk for consumers. This study was conducted to assess the chemical risks associated with consumption of shellfish harvested on the north shore of the St. Lawrence River's lower estuary. A survey was carried out on 162 recreational harvesters, and shellfish were sampled for chemical contaminant analysis. We quantified 10 metals, 22 polycyclic aromatic hydrocarbons (PAHs), 14 polychlorinated biphenyls (PCBs), and 10 chlorinated pesticides. We subsequently evaluated cancer and noncancer risks for four consumption scenarios based on our survey results and published results. Soft-shell clams (Mya arenaria) were by far the most consumed shellfish species. Of the 56 selected contaminants, 36 were detected in the 23 homogenates of soft-shell dam meat. None of the contaminants found in the soft-shell clams were associated with intakes that exceed the main exposure limit recommendations proposed to prevent noncancer effects. However, several limits must be considered before drawing conclusions about the relative safety of shellfish consumption regarding this end point. Furthermore, inorganic arsenic and PCBs were present in sufficient concentrations to lead to cancer risks exceeding the level often considered acceptable for environmental exposure (1 x [10.sup.-4]/to 1 x [10.sup.-6]) in each of the four scenarios, even for the lowest observed scenario of 15 meals of soft-shell clams per year. Key words: cancer risks, chemical, contamination, inorganic arsenic, PCBs, polychlurinated biphenyls, shellfish. Environ Health Perspect 112:883-888 (2004). doi:10.1289/ehp.6847 available via[Online 10 March 2004]


Many residents on the north shore of the St. Lawrence River's lower estuary harvest and eat bivalve shellfish found in this territory. They therefore ingest the various contaminants contained in these organisms. Although the shellfish and shellfish-harvesting areas are regularly inspected in order to detect the presence of toxic algae or microbiologic contamination, the existing monitoring program does not include the characterization of chemical contamination in this region.

Bivalve shellfish are marine invertebrates known to be reliable indicators of the marine environment (Cossa 1989; Goldberg et al. 1978; Ramade 1992). In fact, they present several characteristics of a "bioindicator" organism: sedentariness, capacity to bioaccumulate contaminants without being affected by them, accessibility, and longevity. In addition, the contamination rate of these organisms correlates directly with the biotope contamination level.

Such considerations also make consumption of shellfish potentially dangerous to human health. To better estimate and control such a risk, it has been recommended that a program be set up to estimate shellfish consumption, to identify populations at high risk, and to determine the distribution, nature, and extent of residues in the various marine organisms (Dawe et al. 1991).

The present study was carried out in order to accurately document the shellfish consumption of recreational harvesters of the north shore of the St. Lawrence River's lower estuary. In addition, we analyzed samples of shellfish harvested in this area to determine the nature and levels of the chemical contamination. We also aimed to assess the cancer and noncancer risks associated with consumption of shellfish harvested in this area.

Materials and Methods

Study population. The population studied was the group of recreational shellfish harvesters living on the north shore of the St. Lawrence River's lower estuary. This region extends from Tadoussac to Baie-Trinite and therefore covers 365 km of shoreline. In 2001, close to 48,000 people lived in this area. Recreational shellfish harvesters were met at 18 harvesting areas identified as frequently visited. …