Shellfish Sample Types
Sample type describes whether a portion of or whole organism is to be analyzed, and whether the sample is composed of an individual specimen or a composite of multiple specimens.
Tissue to be Analyzed
The edible portions of shellfish are analyzed to calculate estimates of contaminant exposures.
| Organism | Edible portions to be analyzed |
|---|---|
|
clam |
all tissue |
|
conch |
muscular part |
|
crab |
abdomen, claws, legs, "mustard" (hepatopancreas) |
|
crayfish |
abdomen, claws |
|
cuttlefish |
tentacles |
|
lobster |
abdomen, claws, legs, tomalley (digestive gland) |
|
mussel |
all tissue |
|
octopus |
tentacles and mantle |
|
oyster |
all tissue |
|
scallop |
adductor muscle, or whole (depending on consumption habits of target audience) |
|
shrimp |
abdomen |
|
squid |
tentacles and mantle |
Some consumers eat the lobster tomalley, crab “mustard” or the whole scallop. These glands or tissues should be considered for separate analysis since they may contain higher concentrations of contaminants. Consumption advisories for these specific glands or tissue types may be necessary to inform target audiences of how they can reduce their exposure to contaminants. For example, the Maine Safe Eating Guidelines states, “there are no known safety considerations when it comes to eating lobster meat, consumers are advised to refrain from eating the tomalley.”
- Lobsters: Some consumers eat the tomalley (digestive gland) of the lobster, which has been shown to contain higher concentrations of contaminants than the claw, leg, or tail meat. Analyze it separately to determine whether contaminant concentrations in the tomalley only, or in the claw, leg, and tail meat are above levels of human health concern. Some jurisdictions recommend against eating the tomalley.
- Crabs: Some consumers eat the “mustard” or hepatopancreas (digestive gland) in crab species, which has been found to contain higher concentrations of contaminants than claw, leg, or body muscle tissue. Analyze it separately to determine whether contaminant concentrations in the hepatopancreas only, or in the claw, leg, and body muscle tissue are above levels of human health concern.
- Scallops: Most consumers eat only the adductor muscle tissue so this should be analyzed separately. Some consumers eat the whole body of the scallop as part of a stew. If this is the consumption habit of a known segment of the target audience, the whole body of the scallop should be analyzed.
Individual Samples
Individual shellfish samples are appropriate when species large in size are collected (e.g., lobster, crabs, conch, some clams) since a single organism can provide sufficient tissue for contaminant analysis. Analyze the extracted meat from the lobster, crab or conch and all the tissue of the clam. Samples should be of legal harvestable size (based on local fishery management regulations), live, intact, and collected at the same time.
The Analytical Methods and Fish Tissue Mass Table can be used to determine whether individual or composite sampling is appropriate for the target species.
An advantage of individual samples is that maximum contaminant tissue concentrations are more discernible. Composite samples result in an averaging of contaminant levels. Field collection may be faster when only individual samples are needed.
Composite Samples
Composite shellfish samples are necessary for smaller target shellfish species (e.g., oysters, mussels, clams, scallops, shrimp, crayfish) to acquire enough tissue for contaminant analyses. Composite samples should be:
- Only one species. Accurate taxonomic identification is essential. Different species can have different contaminant bioaccumulation rates.
- Legal-size or at least be of consumable size if no legal harvest requirements are in effect.
- Live and intact.
- Similar in size so that the smallest individual in a composite is no less than 75% of the total size of the largest individual. Size is used as a surrogate for age, which provides some estimate of the total time the individual organism has been at risk of exposure. Each individual specimen should be measured. Height is a standard measurement of size for oysters, mussels, clams, scallops and other bivalve mollusks. The lateral width of the carapace is a standard size measurement for crabs. The standard measurement of body size for shrimp and crayfish is the length from the rostrum to the tip of the telson. Additional information on Size Class.
- Collected at the same time (i.e., collected as close to the same time as possible but no more than 1 week apart). The timely collection of samples is important so that temporal changes in contaminant concentrations that are associated with the reproduction cycle of the target species are minimized. Individual shellfish may have to be frozen until all organisms to be included in the composite sample are available for delivery to the designated laboratory.
- Collected in sufficient numbers. Three to 50 shellfish may be needed to provide sufficient tissue for contaminant analysis. The same number of individuals should be used in each composite sample, if possible, at each sampling site. This results in a simpler data analysis and more comparable results. When unequal numbers are used, the arithmetic average is no longer unbiased and requires qualification.