Skip Navigation
We are currently testing a new website »» Preview Our New Site ««

Food Safety

Shellfish Biotoxin Results

The latest toxin and phytoplankton sampling results, together with more information on shellfish harvesting controls is available on the Food Standards Scotland (Shellfish) website.
Below are summaries of these results using the traffic light system. These are for information only and all results should be checked against those on the Food Standards website.

Shellfish Harvesting

There are a variety of shellfish that are harvested from the Outer Hebrides. The following controls apply to bivalve and marine gastropods, including scallops, mussels, winkles, oysters, razor fish and cockles.

Food Standards Scotland (FSS) sets out the overall policy for the monitoring and classification of shellfish harvesting areas. They manage the programme according to a published E Coli Protocol.

Local sampling officers collect weekly samples from all the commercially harvested shellfish sites in the Outer Hebrides, including bacteriological, toxin and phytoplankton samples.

These samples are required under EU legislation and help ensure that the shellfish harvested from the islands are safe to eat.

Classified Waters

Bivalve and marine gastropods, other than scallops, can only be commercially harvested from waters that are classified in accordance with EU Regulation.  The classification awarded to each area depends on the level of E.coli in the flesh of the mollusc sent for bacteriological sampling over the sampling period.

A summary of the classification system is given below:

Shellfish Classification System
Classification Permitted Levels Outcome  
A ≤230 Less than 230 E. coli/100g flesh May go direct for human consumption if end product standard met.
B 231-4600 Less than 4,600 E. coli/100g flesh (in 90% of samples Must be subject to purification, relaying in Class A area (to meet Category A requirements) or cooked by an approved method.
C 4601-46,000 Less than 46,000 E.coli/100g flesh Must be subject to relaying for a period of at least 2 months or cooked by an approved method.
Above 46,000 E.coli/100g flesh Prohibited. Harvesting not permitted

Only shellfish from Class A waters may go directly for human consumption. 

Information on the classification of shellfish waters around Scotland is available from the Food Standards Scotland website.

Specific information for classified areas in the Outer Hebrides is available below:

More detailed information on Shellfish classification is explained in the Protocol for Classification and Management of E.coli Results document.

Shellfish Registration Document

A shellfish registration document is required to accompany each batch of live shellfish during transportation from the production area to the approved dispatch or purification centre, to ensure traceability of the product.

If you wish to gather shellfish from a classified production area within the Outer Hebrides, you must fill out a request form:

Request Form (PDF, 45K)

All shellfish leaving an approved dispatch or purification centre must be labelled with an identification mark, which includes their unique approval number, before being placed on the market for human consumption.

Shellfish Toxins

There are 3 main types of shellfish biotoxins that affect the shellfish in the Outer Hebrides – Amnesic Shellfish Poisoning (ASP), Diarrhetic Shellfish Poisoning (DSP), and Paralytic Shellfish Poisoning (PSP).  These marine biotoxins are produced by naturally occurring phytoplankton and shellfish can accumulate these toxins in their flesh at levels that are harmful. 

Amnesic Shellfish Poisoning (ASP) is caused by the neurotoxin domoic acid (DA) and its variants. ASP is characterized by gastrointestinal disorders (vomiting, diarrhea, abdominal pain) with higher doses leading to more serious neurological problems (confusion, short-term memory loss, disorientation, seizure, coma), particularly in elderly patients.

Diarrhetic Shellfish Poisoning (DSP) is caused by a group of lipophilic toxins including okadaic acid, and dinophysistoxins (collectively known as DSTs). DSP generally causes mild gastrointestinal disorders which can last from 2-3 days including nausea, vomiting, diarrhoea, and abdominal pain, which can be accompanied by chills, headache, and fever.

Paralytic Shellfish Poisoning (PSP) is caused by a group of water soluble neurotoxins that are collectively referred to as saxitoxins or paralytic shellfish toxins (PSTs). PSP causes neurologic symptoms ranging from a tingling of the lips, mouth, and tongue to numbness, weakness, dizziness, and headache; and in severe cases can lead to respiratory paralysis and death.

Consumption of shellfish which are contaminated with these biotoxins can lead to illness, ranging from sickness and diarrhoea to more serious conditions which could require hospital treatment.

Shellfish Toxin Monitoring Programme

Food Standards Scotland monitors Scotland’s classified harvesting areas for the presence of marine toxin producing phytoplankton in waters and marine biotoxins in shellfish flesh.

This programme identifies when there is an increased risk of shellfish becoming contaminated with biotoxins, and when businesses will need to take appropriate steps to ensure the shellfish they are placing on the market do not contain unsafe levels.

This system adopted is known as the ‘traffic light system’, which is explained in Food Standards Scotland’s Managing Shellfish Toxin Risks guidance document.

When legal limits of biotoxins in shellfish flesh are breached, i.e. results are higher than the ‘red’ trigger value, Food Standards Scotland and the Comhairle take action to ensure the affected areas are closed for harvesting.

The trigger values for amber and red toxic events for each of the biotoxins and their phytoplankton indicators are summarised below:

Trigger values for amber and red toxic events for each of the biotoxins and their phytoplankton indicators
Toxin Regulatory level Amber flesh trigger level Red flesh trigger level Phytoplankton indicator Amber phyto trigger level
Paralytic Shellfish Poisoning (PSP) 800 micrograms/kilogram >RL* 400 µg/kg Alexandrium spp
Greater than or equal to 40 cells/litre of Alexandrium
Amnesic Shellfish Poisoning (ASP) 20 of domoic acid milligrams/kilogram >LOQ 10mg/kg Pseudo-nitzschia spp.
(domoic acid)
Greater than or equal to 150,000 cells/litre
Diarrhetic Shellfish Poisoning (DSP) OA/DTXs/PTXs 160 micrograms of okadaic acid equivalents/kilogram 80 µg/kg 160 µg/kg Dinophysis spp. Prorocentrum lima (okadaic acid, dinophysistoxin);  Greater than or equal to 100 cells/litre
Azaspiracids (AZAs) 160 micrograms of azaspiracid equivalent /kg 80 µg/kg 160 µg/kg Not currently monitored NA
Yessotoxins (YTXs) 3.75 milligrams of yessotoxin equivalent/kilogram 1.8 mg/kg 3.75mg/kg Protoceratium reticulatum and Lingulodinium polyedrum NA

End-Product Testing for Shellfish Toxins

Shellfish growers, harvesters and processors, as food businesses, are placing food on the market and must satisfy the legal requirements that all reasonable measures have been taken to ensure it is safe.

Unlike many of the other hazards associated with food production, biotoxins are largely heat stable, which means that even if the food is cooked the toxins will not be broken down or removed.  The only way to minimise the risk of consumers becoming ill through consumption of contaminated shellfish is to ensure that a product likely to contain unsafe levels of toxins is not placed on the market.

Compliance with Food Standards Scotland’s Managing Shellfish Toxin Risks guidance document will provide processors with the tools required to better manage the risks associated with toxins.  This includes end-product testing of each batch of live bivalve molluscs dispatched from the approved premises during periods of toxic events, i.e. when toxin or phytoplankton levels have crossed their individual ‘amber’ trigger values.

The latest toxin and phytoplankton sampling results, together with more information on shellfish harvesting controls is available on the Food Standards Scotland (Shellfish) website.

Please Contact Us for further information.