Marine biotoxins — Seafish

Marine biotoxins

Marine biotoxins can occasionally contaminate some species of seafood, particularly filter feeding species.

It is normal for biotoxin-producing algae to be present in our coastal waters. They are usually at very low concentrations and pose no concern for most people that eat moderate amounts of shellfish. However, when the quantities of algae increase in the marine environment, so too can biotoxin-producing species. The more of these algae the shellfish eat, the more biotoxin they can accumulate. 

These biotoxins are heat tolerant, so are not destroyed by cooking or other processing. Nor are they removed by the purification process often called depuration. It is, therefore, important to ensure that the animals destined for human consumption do not accumulate biotoxins.

As a result, there are specific regulatory limits on the levels permitted in bivalve molluscs, echinoderms, tunicates and gastropods that are placed on the market. The maximum permitted levels are:

Seafood Maximum permitted level

Paralytic shellfish poisoning (PSP)

800 µg saxitoxin/kg (STX)

Amnesic shellfish poisoning (ASP)

20 mg domoic acid/kg (DA)

Diarrheic Shellfish Poisoning (DSP):

okadaic acid (OA), dinophysistoxins (DTXs)

and pectenotoxins (PTXs)

60 µg okadaic acid equivalents/kg 


3.75 mg yessotoxin equivalent/kg


160 µg azaspiracid equivalents/kg


To ensure best practice guidelines are followed Seafish has produced a series of industry guidance notes for fishermen and shellfish farmers: 

We have also created an overview guidance sheet - Safer Shellfish: Biotoxin Monitoring.

UK guidance and information

The Food Standards Agency (FSA) Shellfish Monitoring page provides  links to a variety of information on regulation and monitoring of the shellfish harvesting industry. 

Food Standards Scotland (FSS) has published a toolkit Managing Shellfish Toxin Risks. The guidance demonstrates how food businesses can use available evidence to develop food safety management systems for controlling the risks of biotoxins in line with legislative requirements. The central tenet of the document is the concept of a ‘traffic light’ system which indicates how harvesting actions should be adjusted in response to green, amber and red trigger levels being breached in either phytoplankton or biotoxin results obtained from the official control monitoring programme or tests carried out by businesses themselves. During high risk periods, the application of this system will generally mean increased levels of end product testing by food businesses prior to product being released onto the market.