Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

The Indicator

Mercury, DDT, and polychlorinated biphenyls (PCBs) are the chemical contaminants of most concern with respect to the human health impacts of the consumption of seafood. Many fish consumption advisories have been issued for because of high concentrations of these compounds. This indicator would report the concentration of DDT, PCBs, and mercury in the edible portion of fish and shellfish. The edible portion is preferred for this indicator because whole-body analyses can overstate the level of risk, as some contaminants concentrate in portions that are not eaten.

The Data Gap

The Food and Drug Administration (FDA), Environmental Protection Agency (EPA), and state governments have a variety of monitoring and reporting programs in place; however, these programs do not provide the basis for national reporting on contaminant concentrations.

The FDA has the power to conduct wharf examinations and collect and analyze fish and shellfish samples for a wide variety of defects including chemical contaminants, decomposition, radionuclides, various microbial pathogens, food and color additives, drugs, filth, and marine toxins such as paralytic shellfish poison and domoic acid. When necessary the FDA has the authority to detain or remove any imported or domestic product from interstate commerce that fails to meet standards. Though these powers are broad, they are not used in a manner that provides periodic national reporting on chemical contamination.

The FDA works with state regulators when commercial fish, caught and sold locally, are found to contain methyl mercury levels exceeding 1 part per million (ppm). The agency also checks imported fish at ports and refuses entry if methyl mercury levels exceed the FDA limit. There is no FDA reporting program based on these inspections, however.

With the cooperation of state, county, regional, and country officials, the FDA has a Pesticide Residue Monitoring program whose emphasis is on the raw agricultural product but also includes some seafood products. In its 1999 Total Diet Study (TDS; http://vm.cfsan.fda.gov/~comm/tds-toc.html), sometimes called the Market Basket Study, the FDA determined intake levels of various pesticide residues, contaminants, and nutrients in foods, in representative diets of specific age-sex groups in the United States. In the 1999 and subsequent studies, a total of 267 different foods were represented in the 26 market baskets analyzed. Of those 267 foods, only seven involved seafood. While this program might provide estimates of consumption of various contaminants in the American diet, it does not provide a consistent means of tracking contaminant concentrations in fish from U.S. waters.

EPA has provided a national guidance manual (www.epa.gov/ost/fish/guidance.html) to states for developing consumption advisories and contaminant monitoring programs, but does not directly conduct such monitoring. The manual, which is not binding upon states, was designed to promote consistency in sampling and analysis methods, risk assessment methods, decision-making procedures, and approaches for communicating risks to the public. In addition, both EPA and FDA have issued action levels for concentration of various contaminants, and states may choose between them when deciding whether to issue fish consumption advisories.

EPA maintains a Listing of Fish and Wildlife Advisories (http://fish.rti.org). This database describes state-, tribal-, and federally issued fish consumption advisories. Information in the database is provided voluntarily by the states and may not include the actual concentration data used to determine an advisory need. Since advisories may be based on different levels in different states; it is not even possible to use this database to determine how many cases exceeded a certain level.

From 1990 to 1995, EPA published the National Survey of Mercury Concentrations in Fish (www.epa.gov/ost/fish/mercurydata.html). In addition to the fact that this survey was discontinued, several factors contribute to the variability of the current database. States collect data for purposes other than mercury analyses, and not all sampling strategies are based on a random sample. For example, data collected for the purpose of annual water-quality monitoring may not produce the same results as a site-specific study of fish tissue mercury concentrations. States use different techniques to sample fish. The sampling techniques used by each state influence sample size, fish size, and fish type. States do not adhere to the same standards for assimilating a composite sample. The absence of a standardized method for grouping fish may result in grouping different species of fish into composites, which can affect both the representativeness of the sample and the results of analyses. States use various analytical procedures to measure the concentration of total mercury in fish. Variations among analytical equipment, use of different protocols and procedures, and different levels of laboratory staff experience can all bias the assessment of mercury concentrations in fish. In addition, mercury analyses reported on a wet weight basis cannot be directly compared to concentrations reported on a dry weight basis.