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Learn more about the Division of Environmental Health
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Marine Biotoxin Program
The information below gives a general overview about biotoxins and the Marine Biotoxin Program. Links to specific information on types of biotoxins are available here. For closures, see the links on the sidebar. The goal of the Marine Biotoxin Program is to protect humans from illness and death caused by eating shellfish contaminated with biotoxins. The program encompases both commercially and recreationally harvested molluscan shellfish (those that have a hinged shell such as clams, mussels, oysters, geoduck, and scallops). Biotoxins are poisons that are produced by certain kinds of microscopic algae (a type of phytoplankton) that are naturally present in marine waters, normally in amounts too small to be harmful. However, a combination of warm temperatures, sunlight, and nutrient-rich waters can cause rapid plankton reproduction, or "blooms". These blooms are commonly referred to as harmul algal blooms or "HABs" because of their potential to cause illness. Molluscan shellfish are filter feeders, so anything that's in the surrounding water flows into their system. Algae is a food source for molluscan shellfish, and HABs create an all-you-can-eat scenario for them. Unfortunately, when shellfish eat toxin-producing algae, the toxin remains in their system; large amounts of algae means more toxin can concentrate in their tissue. Biotoxins don't harm shellfish and can accumulate to levels that are lethal to species that feed on shellfish, including humans. We monitor biotoxin levels in molluscan shellfish year-round. Shellfish in both recreational and commercial harvest areas are routinely tested for biotoxins known to be present in Washington marine waters, such as Paralytic Shellfish Poison (PSP, also known as "red tide"), and Amnesic Shellfish Poison (ASP, also known as domoic acid). When toxins are detected at dangerous levels, we close the harvest area. We continue to test the closed area, and when lab results confirm that biotoxin concentrations have dropped again to safe levels, we reopen the area to harvest. When we close an area that is on or near a public beach, we notify the local health department and issue a news release about the closure. We also post the closure information on our web site and include it in our recorded hotline (see side bar on the right) to let recreational harvesters know that shellfish in that area are not safe to eat. Warning signs are placed on the beach. However, they are often vandalized or stolen. Beachgoers should not count on warning signs to let them know if a beach is closed for harvest. When the closure is in an area that is commercially harvested, we contact all licensed companies harvesting in that area and notify them to stop harvesting immediately. We also recall any commercial product on the market that came from the closed area. Biotoxin testing must be done in a lab. All Washington shellfish testing is currently performed at DOH's Public Health Laboratories in Seattle. At this time there is no certified reliable biotoxin test that can be performed outside of a laboratory environment. Biotoxin levels can be very unpredictable. They can rise quickly and remain high for long periods of time, and they can drop just as quickly to safe levels. There are no reliable indicators at this time to suggest when biotoxin levels will increase or decrease, although research is being conducted in this area. Prediction prototypes are currently underway for several regions in the U.S., including Washington State. The National Oceanic and Atmospheric Administration is actively involved in this research. Harmful algal blooms don't always color the water. An area may be experiencing a massive bloom even though the water appears clear. A popular misconception surrounds the term "red tide". This term is commonly associated with PSP toxin, but algal blooms that color the water red are generally harmless to humans. The Woods Hole Oceanographic Institution has a spectacular photo of a non-toxic "red tide". Public Health Significance There is no antidote for biotoxin poisoning. The victim must wait for the toxins to naturally flush from their body. Life support systems such as respirators and oxygen are used in extreme cases to keep the victim alive and stable. See the links below for more information about poison symptoms of specific types of biotoxins. Cooking does not destroy biotoxins. Cooking will kill the toxin-producing algae, but the toxin itself is not affected by cooking and remains in the shellfish tissue. Mussels accumulate toxins more quickly than other types of shellfish and are a good indicator species, alerting us that levels are on the rise. Varnish clams accumulate toxin at higher levels than other species. Their proximity to shallow beaches and fresh water sources (and thus potential pollution) are additional reasons to be especially aware of surrounding conditions when harvesting this species. Varnish clams and butter clams store toxins longer than other species, and can remain toxic for more than a year after a bloom subsides. For this reason an area can be closed to varnish and butter clam harvest but open for other species. Know Before You Dig! A Shellfish Closures Bulletin and a toll-free Shellfish Safety Hotline (1-800-562-5632) lists beaches that are closed to recreational harvest. The closure information is updated whenever changes occur. Always check these resources before harvesting in an area to make sure it is open.
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Diarrhetic Shellfish Poisoning (DSP) - an emerging biotoxin in Washington
The Harmful Algae Page (Woods Hole Oceanographic Institution)
Olympic Region Harmful Algal Blooms Project
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or dark mahogany clam, this species originates from Asia and is considered an invasive species.
Varnish clams concentrate biotoxins at higher levels than other
clams and they hold onto the toxin for longer periods of time. They differ from other molluscs in that they are
bi-modal feeders; they both filter feed and bottom feed, which
may account for the higher toxin levels typically recorded in this
species. This link to the Department of Fish and Wildlife's
web site provides detailed information on the varnish clam; see the section on
