What are they?
Shellfish are marine animals that have a shell, including clams, mussels, oysters, and scallops. Crabs, crayfish, lobsters, and shrimp are defined as crustaceans, although they are often also called shellfish.
Shellfish provide food for humans and many other species. Some are found close to shore in tidal flats where people may dig or gather them for personal consumption. Offshore shellfish beds or reefs are more likely to be harvested by commercial fishermen using boats equipped with dredges or tongs.
Why are they a concern?
Shellfish must grow and live in clean water to be safely eaten. Shellfish are “filter feeders,” which means they pump and filter large amounts of water through their bodies every day as they eat. As the water filters through, the shellfish strain out particles for their food. These particles can include harmful chemicals, waste, bacteria, viruses, and marine toxins that can contaminate the shellfish.
Shellfish can become contaminated because of poorly treated sewage from wastewater treatment facility, cesspools, and septic system. Contamination may also come from polluted water runoff from marinas and boats, agricultural runoff, and wildlife waste. Shellfish can be contaminated by marine toxins that are produced by algae blooms. Some marine toxins are dangerous and can cause extremely serious shellfish poisoning and even death in humans who eat contaminated shellfish.
Local and state health departments monitor shellfish for contamination and will ban harvesting in contaminated shellfish beds and coastal areas. Health departments also warn of the increased health risks from eating raw shellfish and may advise cooking shellfish to kill bacteria.
Who is at risk?
People who handle or eat contaminated shellfish are at risk.
What pollutants are of greatest concern?
Some algae produce dangerous toxins that can build up in shellfish. When contaminated shellfish are eaten by people, it can cause:
- Domoic acid poisoning – Exposure to this compound affects the brain, causing seizures and possibly death.
- Paralytic shellfish poisoning – This biotoxin affects the nervous system and paralyzes muscle, sometimes causing death.
- Diarrhetic shellfish poisoning – This illness is marked by intense diarrhea and severe abdominal pains.
Reduce your risk
- Do you eat shellfish?
- Do you go shellfishing?
- Do not eat contaminated shellfish or shellfish harvested from contaminated shellfish beds and coastal areas.
- Make sure all shellfish are sufficiently cooked to kill bacteria.
- Follow local and state health department advisories regarding contaminated shellfish.
- Do not eat shellfish from areas with harmful algal blooms.
National Library of Medicine Resources and Databases
- Water Pollution
Curated links to current consumer health information on the effect of water pollution on human health. These English and Spanish web resources include background information, prevention and risk factors, related issues, specifics, video tutorials, statistics and research, clinical trials, journal articles, relevant agencies, and targeted resources for children and teenagers.
- Foodborne Illness
Curated links to current consumer health information on food-borne illness. These web resources in English and Spanish include background information; diagnosis and tests; prevention and risk factors; related issues; specifics; images; videos and tutorials; games; statistics and research; clinical trials; journal articles; relevant agencies; resources targeted to children, teenagers, and women; and patient handouts.
- Harmful Algal Bloom (HAB)-Associated Illness
(Centers for Disease Control and Prevention)
Information on illnesses associated with harmful algal blooms, including sources of exposure and risk factors, preventing illness and reducing exposure, environmental factors promoting their growth, and links to related resources.