Seafood Safety
Commercial seafood in California and the United States is generally considered to be safe. Populations of wild mussels and other shellfish are not harvested for commercial sale. Shellfish growers of mussels, oysters and clams occur in hatcheries where toxin levels are regularly monitored and tested. Commercial producers are required to submit samples to the CDPH laboratories at least once a week and this accounts for two thirds of all samples tested.
Minimizing Risks
Common misconceptions regarding food safety are that sensory perceptions such as look, smell, and taste will indicate whether seafood is toxic. The belief is that cooking seafood to a certain temperature may prevent some food borne illnesses, but unfortunately this has no effect on removing certain toxins from food as many of the toxins are heat-stable and do not break down. Many of the toxins are odorless. Many species of clams, mussels, abalone, geoduck, crabs, lobsters, fish, and other organisms are relatively unaffected by biotoxins.
The California Department of Health advises wild mussels should never be assumed safe for consumption. This includes mussels harvested during and outside of the annual mussel quarantine period. Commercially harvested and distributed seafood are considered safe, but consumers are advised to follow certain preparation methods to lower risks as biotoxins may still be present in levels below the FDA safety thresholds.
What goes relatively unnoticed or ignored are required signs stating the potential dangers of eating certain types of seafood. Certain preparations and types of seafood have active health advisories and warnings to consumers in California. For example, deep frying is discouraged in favor of steaming and boiling. Discarding cooking liquids is recommended as some of the biotoxins can be released from the internal organs of clams, mussels, crabs, lobsters, and other seafood. It is strongly advised that the viscera of Dungeness crabs be discarded and completely removed prior to consumption (Figure 5). Digestive tracts of clams and scallops, which typically appear as dark brown and black regions, where domoic acid is most concentrated are advised to be removed prior to cooking and eating.
Figure 5: Cooked Dungeness crab with viscera, yellow-brown goo and liquid located in the shell. Viscera should be removed and discarded.25
The broths made from shellfish, a common ingredient valued for its flavor, to make soups and sauces are advised to be tossed to help reduce toxin exposure. Traditional preparation of cioppino, an Italian seafood stew originating in San Francisco, and commonly prepared by boiling in clams, mussels, and crabs all in their shells, in the soup broth is no longer advised. Dungeness crabs are considered safe to eat, but viscera, the internal organs where higher levels of toxins concentrate, are advised to be thrown out. However, viscera are considered a delicacy among some Asian cuisines. Most Chinese restaurants will serve deep fried Dungeness crab and include the shell body with viscera. Also, we have many local popular restaurants specializing in Cajun seafood boils and Chinese hot pot restaurants that serve whole Dungeness crabs, clams, mussels, and a variety of seafood cooked in their shells. Rarely, if ever, will you find a warning or be advised to discard the viscera or avoid consuming the flavored broths.
California Sampling and Testing Methods
Sampling of wild populations of shellfish along the California coast occurs and varies. A patchwork of local, state, federal, and Tribal agencies, researchers, private educational organizations, and volunteers collect samples for the CDPH laboratory to test. Volunteers are able to sign up, receive training, and are provided with nets for collecting seawater samples.26 For Dungeness crab, testing occurs primarily between September and January,27 but the number of samples per region depends on the quantity submitted and the results.
The California Department of Public Health lab is in Richmond, California, about an hour north of San Jose and across the bay from San Francisco. In a December 2019 article, the San Francisco Chronicle sought to provide some insight to the testing and sampling methods used by the laboratory and its five laboratory workers to explain how decisions regarding the start, and postponements of fishing seasons are determined.
The procedures for testing levels of domoic acid in Dungeness crab used by the CDPH laboratories are meant to emulate how a consumer would prepare and cook crab in their homes. With each sample, a batch of six crabs are selected and steamed for about 50 minutes. After cooking, the viscera of each crab are separated, and 4 grams are collected. The sample of viscera is then processed, and liquid chromatography machine identifies markers for domoic acid and other toxins.28
If samples indicate levels of domoic acid higher than the FDA designated safety thresholds, the CDPH issues advisories against consumption of Dungeness crab, and possibly other shellfish and seafood in areas where the sample was collected. This can lead to delays or cancellations of commercial fishing seasons. For advisories to be lifted, two consecutive subsequent tests in samples taken at least a week apart in affected areas must show levels of domoic acid and other toxins below the safety threshold.29
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