USDA/Food Safety Initiative: Characterization of the Cadmium Health Risk, Concentration and Ways to Minimize Cadmium Residues in Shellfish

Purpose or Scope:

This project was designed to study spatial and temporal distribution of cadmium in commercially important west coast molluscan shellfish, evaluate the human health risk to consumers, economic risk to industry and methods to minimize cadmium residues in shellfish products marketed to consumers. Outreach to the industry provided crucial information on geographic regions with high cadmium concentrations and appropriate culture methods, species and husbandry practices that can be utilized to minimize cadmium residues. The results of this research also provided crucial information to USFDA and the Interstate Shellfish Sanitation Conference (ISSC) for inputting into the international Codex deliberations.

Approach:

The overall approach was to: 1) Complete a comprehensive sampling effort of cadmium concentrations in molluscan shellfish throughout U.S. west coast growing areas; 2) define geographic locations, culture methods, shellfish species, harvest times and additional factors that affect cadmium concentrations in an effort to minimize cadmium residues in shellfish products; 3) identify the public health risk of cadmium in shellfish as well as the economic risk to the oyster industry given the proposed 1 μg/g ML standard; 4) conduct a preliminary risk assessment and toxicity modeling based on data collected in this study and validated models and approaches from the literature in order to estimate human health risk from consumption of west coast oysters; and 5) provide outreach and extension services to the shellfish industry, regulatory agencies, high risk consumer groups, and the scientific community.

Progress and Results:

Comprehensive sampling to determine cadmium concentrations in Pacific oysters was conducted along the Pacific west coast. This was followed up with seasonal sampling at selected sites for to assess levels of cadmium and arsenic in oyster tissues, sediments and water samples. The results were analyzed and an in-depth literature review and assessment of the human health risk associated with varying levels of cadmium in oysters and other shellfish was conducted.

Prior to initial sample collection, a Quality Assurance Project Plan was reviewed and accepted by the Washington State Department of Health Office of Environmental Health Assessment. In September, 2004, 123 oyster composites were collected from 41 sites located throughout California, Oregon, Washington and Alaska and tested for cadmium. Integral Consulting, Inc. created GIS maps to graphically illustrate the geographic distribution.

To determine harvest times (seasonality) and additional factors that impact cadmium concentrations, seasonal sampling of oyster tissue, seawater, and sediments was conducted from Winter, 2005 to Fall, 2005 at sites in California (2), Oregon (2), Washington (5) and Alaska (1). Washington sites were selected according to the geographic distribution of tissue cadmium concentrations observed during the initial sampling effort in Fall of 2004. Oyster tissue, seawater and sediment were collected in January, April, July and October to test for tissue metal concentrations (Cd and Zn), total and dissolved metals in seawater (Cd and Zn), seston, total suspended solids, plankton, sediment metal concentrations (Cd and Zn), total organic carbon, and sediment grain size. In addition, oyster seed were distributed to 5 Washington locations in April, 2005 to determine growth rates.

To test the impact of culture method and oyster ploidy on cadmium concentrations in oysters, diploid and triploid seed were placed at 5 Washington sites in adjacent on-bottom bags or offbottom aqua-purses. OSU (Dr. Morrissey and Rasmussen), in cooperation with Goose Point Oyster Company, conducted separate field experiments in Willapa Bay to test the impact of various processing techniques (jarring, cold storage, high pressure processing) on cadmium concentrations.

To measure cadmium concentrations in different species of shellfish, four varieties of oysters, two clam species, mussels and geoduck were harvested and tested in Spring of 2006. Oyster seed was placed at 6 sites (5 in Washington and 1 in Oregon) in April, 2005 and shipped to Dr. Wen Wang at The Hong Kong University of Science & Technology in July and October, 2005. Laboratory experiments were performed to test oysters for cadmium body burdens, subcellular cadmium concentrations, Metallothionein (MT) concentrations, cadmium clearance rates, assimilation efficiencies (for different food types and diatom concentrations), dissolved uptake rates (rate at which oysters take up dissolved metals in seawater) and efflux rates.

Integral Consulting, Inc. completed the human health risk assessment in late-2006 using probabilistic risk assessment methods to evaluate the intake of cadmium via consumption of oysters harvested in the Pacific Northwest. The Health Risk Characterization for Consumption of Cadmium in West Coast Oysters report will be available in early 2008 and contains the following sections: 1) introduction to the issue; 2) evaluation of cadmium in oyster tissue data; 3) exposure scenarios and assumptions selected for use in the risk assessment; 4) toxicity of cadmium and toxicity values associated with this assessment; 5) risk characterization including quantitative estimates of health risks for each scenario evaluated; 6) a review of current domestic and international cadmium intake guidelines; 7) study conclusions and recommendations; and 8) a list of cited references.

Northern Economics, Inc. (NEI) conducted an Economic Impact Study, covering four primary objectives: 1) Survey growers to estimate impact in terms of net production revenues; 2) Estimate economic impact; 3) Run an economic model; and 4) Write a technical memorandum describing model results.

Publications and conference presentations have been conducted to provide outreach and extension services to the shellfish industry, regulatory agencies, tribes and the scientific community. Two peer-reviewed journal articles and a Masters Thesis have been published to date. The reports and presentations listed below can be viewed in PDF format (file sizes are indicated).

Final project report:

Completed publications include:

Completed conference oral presentations include:

Project Partners:

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