Testing shellfish toxins

The UK's Food Standards Agency​ has published details of an investigation and audit, carried out by UK scientists which shows discrepancies in current testing methods for shellfish toxins.

Professor Hugh Makin of St Bartholomew's & the Royal London School of Medicine and Dentistry, studied the methods and procedures used by the three laboratories which test shellfish for toxins. Since June 2001, statutory testing of shellfish harvested off the coasts of England, Wales and Northern Ireland has given some atypical responses to the mouse bioassay for diarrhoetic shellfish poisoning (DSP) toxins. It has been unclear whether this was a new toxin or an abberation of the test method used.

In the UK, statutory shellfish testing is carried out by the Centre for Fisheries, Environment and Aquacultural Science (CEFAS) in Weymouth, the Department of Agriculture and Rural Development (DARD) in Northern Ireland and the Fisheries Research Service (FRS) in Scotland. All three laboratories use a DSP method devised by US scientists and based on the mouse bioassay (MBA) test. This has been confirmed by the European Commission as the best method currently available to detects all known toxins.

According to David Byrne. The EU's Health and Consumer Protection Commissioner, results obtained using the MBA take precedence over other methods permitted by EU legislation (Commission Decision 2002/225/EC). However, a standardised international procedure for the application of the test method does not exist, and therefore each laboratory has been operating its own procedures within the same broad framework. The test is designed to detect the following groups of toxic compounds: okadaic acid, dinophysistoxins, yessotoxins, pectenotoxins and azaspiracids. The problem with atypical MBA results has been seen mainly in cockle samples and only rarely in mussel samples.

The full Makin report can be downloaded from the FSA web site, and is accompanied by a further details of investigations to assess whether diethyl ether (DEE) or acetone carry-over during the DSP standard operating procedure is responsible for the atypical response in mice. The Agency's responses to Professor Makin's findings are also available, in tabular format.The solvent carry over report did not show a correlation between the atypical DSP MBA response and DEE and acetone levels, and therefore from data presented in this investigation it was concluded that these solvents were not responsible for the clinical symptoms sometimes observed in mice.

Nevertheless, discrepancies in the numbers and volumes of solvent extractions employed by the three monitoring laboratories were observed and all three laboratories have now agreed to use a standardized procedure.

Makin also found that there were no satisfactory internal quality assurance systems in place for shellfish monitoring protocols, and that certain symptoms seen in the mice were interpreted as a positive result by one of the laboratories, but negative by another. Makin has recommended that the transmission of test results by telephone or orally should be avoided as it leads to errors. Instead, all laboratories should follow a clearly defined procedure in which results are approved by a named certifying scientist, who would scrutinize all the data, including quality control results, before they are released.