The Food Safety Authority (FSAI) is advising consumers against picking and eating shellfish on any area of coastline where it is not commercially harvested, because of the possibility of toxic algae in the water.
The toxins, if ingested can cause symptoms similar to severe food poisoning including vomiting, diarrhoea and headaches.
Any areas of the coast could be affected, even where a health warning had not been issued by the local health authorities, the FSAI has said.
The advice comes after the South Eastern Health Board yesterday warned people not to eat shellfish collected in the Waterford and Wexford coastline due to the presence of poisonous toxins.
A large quantity of the phytoplankton had been discovered off the south-east coast. Bivalve shellfish such as mussels, oysters, clams and scallops feed on the phytoplankton and produce a "neurotoxin", which does not harm the infected shellfish, but can cause potentially serious illness in humans.
A spokesman for the FSAI said that while a high level of the algae had been identified in Wexford and Waterford, it was common in all coastal waters in the summer.
"Toxic phytoplankton are always present in the water but can increase to very high levels during the summer," Mr David Lyons, contracts manager with the FSAI said. In areas where shellfish were commercially collected, they were subject to rigorous "flesh testing" before the company got the go-ahead to harvest. However, in non-commercial waters tests on the levels of toxic phytoplankton were carried out less regularly.
"Sometimes the algae will cause quite dramatic discoloration of the water, from lurid green to a luminous orange, but sometimes you can't see them at all. When shellfish are not collected commercially, eating them is a high-risk activity."
The neurotoxins if ingested can cause nausea, vomiting, diarrhoea, dizziness, tingling in the arms and feet and severe headaches. There have been "anecdotal incidents" of death, Mr Lyons said, but none in Ireland.
While most harmful bacteria can be eliminated through cooking, neurotoxins are "heat stable" and cannot be cooked out.
"Basically if the shellfish are carrying the neurotoxin, there's no way it can be gotten rid of."
Mussels, oysters, scallops and razor clams can all be affected, but periwinkles, crabs and prawns do not feed on the phytoplankton.
Before commercial collectors can harvest shellfish they must have two "clear" samples in a row, tested by the Marine Institute. If one of the samples is not clear, the area is closed immediately for commercial collection and signs are erected warning the public against picking shellfish. Water monitoring is also conducted by the Marine Institute and the Naval Service.
People wishing to collect shellfish in commercial areas should consult the FSAI website www.fsai.ie or the Marine Institute.
