A severely toxic harmful algal bloom involving paralytic shellfish poisoning (PSP) toxins in Washington’s Hood Canal has demonstrated the value of a shellfish toxin test. After more than a decade of research, validation, and technology transfer (moving this method from the research laboratory into routine public health use), public health authorities are using the test developed by NOAA’s NCCOS scientists to protect consumers and recreational shellfish harvesters. The algae bloom produced high concentrations of toxins that cause PSP, a serious illness resulting from eating contaminated shellfish that in extreme cases can cause death. Because cooking does not destroy the toxins, effective monitoring and timely harvest closures are essential to protect public health.
The 2026 event is the most severe toxic bloom associated with paralytic shellfish toxins (PSTs) reported in Hood Canal in over a decade. Toxin concentrations increased rapidly, reaching levels more than a hundred times the federal regulatory limit for safe harvest, prompting emergency closures of commercial and recreational shellfish harvest areas. The rapid increase was largely unexpected because Hood Canal has historically experienced little PSP.
The Washington State Department of Health detected the increase early using NOAA’s receptor binding assay (RBA), a highly sensitive test for paralytic shellfish toxins such as saxitoxin. The RBA can detect toxin concentrations approximately five times lower than the mouse bioassay (a traditional test that measures toxin levels by observing their effects in laboratory mice), providing an early warning as toxin concentrations begin increasing. This allowed state health officials to increase sampling and quickly implement harvest closures before recreational harvesters collected contaminated shellfish or they entered the marketplace. Washington public health scientists believe the earlier detection likely prevented illnesses and greatly reduced the size of a seafood recall, while protecting the state’s shellfish industry and maintaining consumer confidence.
The benefits extend beyond improved public health protection. During the Hood Canal response alone, Washington estimates that using the receptor binding assay eliminated the need for thousands of mice and reduced testing costs by tens of thousands of dollars compared with the traditional mouse bioassay, while providing more timely information to guide management decisions.
NOAA scientists developed, validated, and standardized the receptor binding assay to support its adoption into the U.S. Food and Drug Administration’s (FDA) National Shellfish Sanitation Program (NSSP), and worked with state and Tribal partners to transfer the technology from the research laboratory into operational use. With technical support from NOAA, the Washington State Public Health Laboratories became the first state public health laboratory in the United States to implement the receptor binding assay as an operational regulatory method for shellfish toxin monitoring when the laboratory adopted the method in Fall 2025. The assay now supports decisions to close shellfish harvest areas under the NSSP. Tribal shellfish programs in Alaska have successfully used the NOAA-developed assay for nearly a decade to help inform traditional and subsistence shellfish harvesting, demonstrating its value in protecting coastal communities.
Following Washington’s successful implementation, several other state public health laboratories are preparing to adopt the receptor binding assay for operational shellfish toxin monitoring. NOAA’s continued technology transfer efforts are supporting these laboratories as they implement the method, expanding access to modern shellfish toxin testing across the United States.
NOAA, the Washington State Department of Health, the Sitka Tribe of Alaska, and the Alaska Department of Environmental Conservation are now collaborating on additional validation studies to seek further acceptance under the FDA’s NSSP of the receptor binding assay. While the assay is currently approved for harvest closure decisions, the collaborative project aims to support its use for both harvest closure and reopening decisions across additional shellfish species. Expanding regulatory acceptance would provide state shellfish monitoring programs with a more sensitive and efficient tool for protecting public health while modernizing the nation’s shellfish safety program.
The Hood Canal event illustrates how NOAA research delivers real-world benefits long after a method is initially developed. Investments in innovative analytical tools, rigorous validation, and sustained partnerships with public health agencies are helping communities respond more effectively to harmful algal blooms, protect coastal economies, and ensure the safety of the nation’s seafood supply.
This effort was supported by the NCCOS Prevention, Control, and Mitigation of Harmful Algal Blooms (PCMHAB) project Advancing the Receptor Binding Assay for Multi-Species Monitoring of Paralytic Shellfish Poisoning, led by the Washington State Department of Health. PCMHAB is a peer-reviewed, national, competitive program authorized under the Harmful Algal Bloom and Hypoxia Research and Control Act (33 U.S.C. §§ 4001 et seq.) and the NOAA Authorization Act of 1992.