Designating Seafood a 'Health Concern'

Technical information

Sources: Environmental Defense's health advisories are based on contaminants data aggregated from government and intergovernmental agencies and from peer-reviewed studies in the scientific literature. We do not include data from media reports (e.g. newspapers, magazines and web sites), nongovernmental organizations (NGOs) or industry groups, since these sources may have less rigorous scientific review processes.

Nondetectable Contaminants: When contaminant levels are too low to be detected in a sample, we assume that the value is one-half of the reported detection limit  – a standard assumption in scientific studies concerning seafood contaminants.

Multiple Contaminants: Sometimes fish and shellfish have elevated levels of more than one contaminant. When the contaminants have different health risks – e.g. neurotoxicity for mercury vs. carcinogenicity for PCBs  – we use the average contaminant level that results in the more conservative recommendation. When the contaminants have similar health risks – e.g. carcinogenicity for both PCBs and dioxins – we follow standard scientific practice by adding the risks together and adjusting the consumption recommendation accordingly.

PCB Data: Different techniques are used to measure PCBs -- mixtures of man-made, chlorinated industrial chemicals (also known by the trade name Aroclor) which are no longer manufactured in the United States. There are 209 individual PCBs (called congeners), which were combined into several distinct Aroclor mixtures. Prior to the late 1980s, PCB concentrations in fish were determined by measuring the concentration of the different Aroclor mixtures. This method was relatively inexpensive, but not particularly sensitive. In the late 1980s, a new method for measuring PCB concentrations, congener analysis, became available. This newer method can quantify concentrations of all 209 PCBs at very low levels. Unfortunately, congener analysis is costly, and many state fish advisory programs still rely on less-sensitive Aroclor testing to gather PCB data. Since these two methods produce disparate types of PCB data, we set the following rules:

• We do not use PCB data prior to 1996. Congener analysis became widely available at about this time, resulting in more accurate data.  Moreover, since PCB production was banned in the 1970s, PCB levels in fish continue to gradually decline. Therefore, historical PCB data from the 1970s and 1980s may be higher than data from more recently tested fish.
• When PCB levels are too low to be detected, as occurs in a small percentage of samples, we assign a value of one-half of the detection limit. When one or more Aroclors or congeners are detected, we add the detected concentrations to one-half the detection limit for non-detected mixtures for a composite PCB value. A ‘Health Concern’ designation will not be given to any species for which all or most data points are ‘non-detects’.

Calculating health advisories

Environmental Defense only issues health advisories based on sufficient data:

• Average fish contaminant levels must be based on at least 10 samples (although for many types of seafood our recommendations are based on hundreds or thousands of data points).
• Data must be from more than one geographic location and not solely from heavily contaminated areas. For example, we will not issue an advisory based on data only from Georgia if the species in question is naturally found from Maine to Florida.

Environmental Defense then calculates health advisories using equations from EPA’s “Guidance for assessing chemical contaminant data for use in fish advisories.” These allow us to determine a safe number of meals to eat per month based on body weight, portion size, and average fish contaminant concentrations. See the equations for mercury and PCBs and find out more about EPA's guidance.

Data sources

1. EPA Integrated Risk Information System (http://www.epa.gov/iris/)
2. EPA National Listing of Fish and Wildlife Advisories (http://map1.epa.gov)
3. EPA Office of Water. Guidance for assessing chemical contaminant data for use in fish advisories Volume 2: Risk assessment and fish consumption limits (3rd edition). http://www.epa.gov/ost/fishadvice/volume2/index.html.
4. FDA Center for Food Safety and Applied Nutrition. Seafood Information and Resources. http://www.cfsan.fda.gov/seafood1.html.

Posted: 01-Jan-1900; Updated: 20-Jan-2008