Biotoxins and Chemical Testing
ShellMAP undertakes rigorous monitoring of biotoxin and chemical levels, and designs and oversees effective responses to ensure Tasmania’s shellfish industry remains healthy and safe.
Biotoxin News is a weekly update of biotoxin flesh and algal sampling results for commercial bivalve shellfish growing areas in Tasmania.
Read the latest edition:
Please note: Administrative delays may occur posting this newsletter.
Types of Toxins
Filter feeding shellfish take in pollutants from surrounding waters, including biotoxins, which can cause poisoning if the shellfish is then consumed by humans. Shellfish zones must be closed when toxins are found to be above the levels prescribed in the
Australia and New Zealand Food Standards Code.
Significant syndromes when concentrated by shellfish and consumed by humans include:
Paralytic Shellfish Poisoning (Saxitoxins)
Mild Paralytic Shellfish Poisoning (PSP) can cause tingling or numbness around the lips or in fingers and toes, sensations of floating or weightlessness, and gastrointestinal upset (nausea, vomiting, diarrhoea, abdominal pain). Severe PSP can result in functional weakness (impaired grip strength, staggering gait), difficulty breathing and signs of acute respiratory insufficiency such as lips turning blue. In extreme cases PSP can result in respiratory failure and death by asphyxiation.
Diarrhetic Shellfish Poisoning (Okadaic Acid)
Diarrhetic Shellfish Poisoning (DSP) can cause nausea, diarrhoea, vomiting, abdominal pain, and headaches. These symptoms carry additional risk of dehydration, particularly in young children or the elderly.
Amnesic Shellfish Poisoning (Domoic Acid)
Mild Amnesic Shellfish Poisoning (ASP) can cause gastrointestinal upset (nausea, vomiting, diarrhoea, abdominal pain). Severe ASP can cause additional symptoms such as headache, seizures, involuntary, irregular muscle contractions, cognitive impairment and disorientation, anterograde amnesia (inability to lay down new memories following neurological damage), respiratory difficulty and coma.
Vibrio parahaemolyticus is marine bacteria that is linked to the consumption of raw Pacific oysters. Common symptoms include diarrhoea, abdominal pain, nausea, vomiting, fever and headache.
Risk management against vibrio parahaemolyticus can support growers to prevent the spread of foodborne illnesses caused by the bacteria. Growers should take the following steps:
- Hold oysters on lease for at least two tidal cycles after handling.
- Move stock to deeper, cooler water for at least seven days.
- Relay to a lower risk area for at least seven days.
- Harvest early in the morning in warmer months.
- In intertidal areas, harvest as soon as possible after oysters are exposed by the tide.
- Keep oysters cool on boats using shading, air circulation, or sprinkler systems.
- Get stock below 10°C as soon as possible after harvest.
- Maintain cool chain to keep stock below 10°C.
- Make sure delivery is acknowledged on arrival and oysters are places into refrigeration quickly.
- Check temperature of stock on arrival.
- Eat quickly after purchase or place in fridge / on ice.
- Shucked oysters must be stored below 4°C.
- For the elderly / immune compromised, cooking to over 65°C will kill
Biotoxin Management Plan
ShellMAP’s Biotoxin Management Plan outlines the biotoxin sampling, testing and reporting program to ensure shellfish can be safely harvested and can meet market access requirements. The Biotoxin Management Plan is approved by the federal Department of Agriculture Fisheries and Forestry.
Chemical residues may be present in shellfish growing areas where industrial activity is taking place nearby. Residues include heavy metals, organo-chlorines and organo-phosphates.
It also sets Generally Expected Levels for other chemical contaminants with less significant health impacts. Generally Expected Levels are not legally enforceable, but act as a benchmark to measure the contaminant levels in food.
Chemical contaminant surveys show that all commercial shellfish farms in Tasmania comply with FSANZ standards.