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On November 3, 2015, the California Department of Public Health (CDPH) instructed consumers to avoid eating Rock and Dungeness crab caught off the California coastline, because of "dangerous" levels of domoic acid found in the animals (CDPH, 2015). Domoic acid is a naturally occurring neurotoxin produced by algae that can bioaccumulate in shellfish and can be harmful to humans who eat the contaminated food (WDFW, 2015). Symptoms of domoic acid poisoning in humans, which can occur within 30 minutes to 24 hours after eating the contaminated seafood, include nausea, abdominal cramps, vomiting, seizures, permanent memory loss, and possible death (CDPH, 2015). According to the data presented in EPA's AcTOR database, domoic acid is dose-responsive in humans, with no effect at 0.2-0.3 mg/kg, mild (gastrointestinal) symptoms at 0.9-1.9 mg/kg, and most serious symptoms at 1.9 – 4.2 mg/kg (EPA, 2015).

Algae blooms off the Pacific coast are not uncommon, but this year's bloom is unusually large and persistent, because of particularly warm ocean water temperatures (Sommer, 2015). According to the CDPH, "the conditions that support the growth of this [algae] are impossible to predict, and it is unknown when the levels found in crab will subside" (CDPH, 2015). Currently, California's action level for domoic acid in crabs is 30 ppm in viscera and 20 ppm in meat (CDPH, 2015). Samples from at least 72 crabs were taken and the data indicates that a "significant percent of samples exceeded one or both of these criteria", with one rock crab sample as high as 190 ppm and numerous other samples exceeding 100 ppm (OEHHA, 2015). According to the Office of Environmental Health Hazard Assessment (OEHHA), "consumption of Dungeness and rock crabs is likely to pose a significant human health risk as a result of high levels of domoic acid" (OEHHA, 2015).

Based on a simple dose calculation, if a 160 lb person (73 kg) consumed a pound of crab meat during a meal (0.45 kg) that contained 190 ppm of domoic acid, their domoic acid dose would be approximately 1.2 mg/kg. Similarly, if a 120 lb person (54 kg) or 215 lb person (98 kg) consumed this same amount of crab, their domoic acid doses would be approximately 1.6 mg/kg and 0.87 mg/kg, respectively. As referenced above, these doses of domoic acid can cause gastrointestinal symptoms. These results are based on a simple dose calculation, using the 10th, 50th, and 90th percentile weights for males and females over 20 years of age, and do not account for sensitive populations or pharmacokinetics parameters, such as absorption and distribution (EPA, 2011).

There was a previous outbreak in 1987 that involved mussels with domoic acid concentrations ranging between 31 to 128 mg/100 g, or 310 to 1280 ppm (EPA, 2015). The ingested dose by symptomatic patients was estimated to be between 60 and 290 mg domoic acid per person, which correspond to 0.8 to 4 mg/kg doses, which can cause serious symptoms according to the dose-response data described above. Three people died from eating contaminated shellfish, and hundreds of others reported symptoms (EPA, 2015). Currently, there is no antidote for domoic acid poisoning, but supportive and symptomatic treatment is available.

As of November 6, 2015, the California Department of Fish and Wildlife has delayed the opening day for commercial Dungeness crab fishing, which was scheduled to open November 15, and closed the commercial rock crab fishery, which is open year-round (CDFW, 2015).

References :

CDFW (California Department of Fish and Wildlife). 2015. "Commercial Dungeness Crab Season Opener Delayed and Commerical Rock Crab Season Closed." November 6, 2015. Sacramento, CA: California Department of Fish and Wildlife. Retrieved from: https://cdfgnews.wordpress.com/2015/11/06/commercial-dungeness-crab-season-opener-delayed-and-commercial-rock-crab-season-closed/

CDPH (California Dept. of Public Health). 2015. "CDPH issues warning about Dungeness and Rock crabs caught in waters along the Central and Northern California coast." November 3, 2015. Sacramento, CA: California Dept. of Public Health. Retrieved from: https://www.cdph.ca.gov/Pages/NR15-082.aspx

EPA (Environmental Protection Agency). 2011. Exposure Factors Handbook, 2011 Edition. Washington, D.C.: National Center for Environmental Assessment, Office of Research and Development.

EPA (Environmental Protection Agency). 2015. Chemical summary: Domoic acid (14277-97-5). Retrieved on November 12, 2015, from EPA Aggregated Computational Toxicology Resource (ACToR) database, at: http://actor.epa.gov/actor/GenericChemical?casrn=14277-97-5

OEHHA (Office of Environmental Health Hazard Assessment). 2015. "Memorandum: Domoic Acid Threat to Public Health". November 3, 2015. Sacramento, CA: California Office of Environmental Health Hazard Assessment. Retrieved from: http://www.oehha.ca.gov/fish/pdf/110415domoicaciddungenesscrab.pdf

Sommer, L. 2015. "Why is an algae bloom closing crag season in California?" San Francisco, CA: KQED Science. November 5, 2015. Retrieved from: http://ww2.kqed.org/science/2015/11/05/why-is-an-algae-bloom-closing-crab-season-in-california/

Todd, E. C. 1993. "Domoic acid and amnesic shellfish poisoning-a review". Journal of Food Protection, 56(1), 69-83.

WDFW (Washington Dept. of Fish and Wildlife). 2015. "Domoic acid – A major concern to Washington State's shellfish lovers." Olympia, WA: Washington Dept. of Fish and Wildlife. Retrieved from: http://wdfw.wa.gov/fishing/shellfish/razorclams/domoic_acid.html