Answers for questions you may not have had

   Here's some answers to questions people have had about domoic acid. Hopefully this answers more questions than it generates.

Below are answers to the questions you posed a few days ago, along with two additional questions that have come up since and associated responses. These responses have been reviewed by California Department of Public Health (CDPH) staff. I hope these answers shed a little light on current information about and processes regarding domoic acid (DA) toxins in California commercial fisheries.

Regards,

Carrie Culver
Aquatic Resources Specialist/Research Scientist
California Sea Grant
Scripps Institution of Oceanography, UC San Diego and
Marine Science Institute, UC Santa Barbara


***********************************************

Responses to Fishing Community Questions

1. Have there been any studies done on if the crab are kept in a closed system, how long it takes them to purge?

Yes, at least one study has been conducted and likely more will be forthcoming (proposal pending;  submitted by California Sea Grant Extension and UCSB, in collaboration with CDPH). For Dungeness crab in a laboratory setting, DA was depurated within 21 days if fed non DA–contaminated food (Lund et al. 1997).

2. How many crab do you actually have to eat to get sick?

This is a difficult question to answer, as it will depend on the levels of DA in the consumed crab, how it is prepared and what parts of the crab are consumed.  Clearly the highest risk of exposure is associated with consuming raw viscera, also known as crab butter, and even raw crab tissue if both contain high DA levels. The process of boiling crab in water reduces the concentration of DA by ~70% (67-71 %) in the crab (Hatfield, et al., 1995; Quilliam, 1991), but steaming, grilling, stir-frying and baking presumably retain higher DA levels as DA is not leached during these food preparation processes.

3. Once the crab are collected, what are the procedures for testing and how long does it really take? 

Crabs first need to be surrounded by gel packs when shipped overnight to the laboratory. Upon receipt the samples are prepared for analysis. This requires cooking the crab and then dissecting the various parts for testing. Crabs from different areas must be cooked separately so as not to cross-contaminate the samples. The viscera is extracted and tested first. If the viscera is above 70 ppm then the body tissue is tested. The preparation of the crab samples takes a ½ - 1 day, depending on the number of different areas the samples are coming from and the number of crabs per area. The laboratory analyses require HPLC techniques, which take approximately 45 minutes per sample. Samples are placed on an autosampler so analyses can be run after hours/overnight to increase throughput.

4. Is 6 crab per port considered a real scientific sample? Should there be more or less collected? Should they all be from the same pot?

This is the California’s standard sample size for testing levels of domoic acid in crabs which is consistent with the protocol used by Washington’s Department of Health and Department of Fish and Wildlife. They must balance the capacity of the lab to process samples with an adequate sample size. California Sea Grant, UCSB and the CDPH have submitted a proposal for obtain funds to better evaluate sample sizes for the different species. Sampling from one or more pots in an area may be better, although since they are moving in from all around it may not matter that much. Keeping samples separated, however, if they are from different locations (e.g., front vs. backside of island; coast vs. offshore) is critical.

5. Has CDPH ever tested spot prawn or any species of shrimp?

The Food and Drug Branch of CDPH is currently working with DFW to coordinate, via fishermen, the collection of spot prawns that will be harvested in areas North of Point Arguello including HMB/SF and Monterey areas. Upon the collection and testing of spot prawns, data on DA levels in this species will be available via the CDPH website. Other species routinely tested for DA include small finfish (anchovy, sardines), and bivalve shellfish (mussels, oysters) and limited data is available for DA levels in spiny lobsters.

6. Are there any other 'certified' labs that can run crab samples so that the FDBL isn't inundated with samples?

Not in CA. There are no labs in CA certified to perform the HPLC method for DA. A commercial lab with a chemistry program could likely spin up this method, but the data could not be used for regulatory purposes.