An expert panel of 21 scientists concluded that the discovery of new BTX-group toxin producing algae and the apparent trend towards expansion of algal bloom distribution, suggested that BTX-group toxins could emerge in shellfish or fish in Europe. They are limited at present to the Gulf of Mexico, the US east coast and the New Zealand Hauraki Gulf region.
There are currently no European regulatory limits for BTX-group toxins for shellfish or fish in Europe, said the CONTAM panel. It added there was evidence of one of BTX group forming DNA adducts – which “raises concern about its potential carcinogenicity and consequential long term effects”.
The experts said that more information of these marine biotoxins was needed in order to develop valid screening methods. An overall lack of information meant they were unable to assess the risk associated with BTX-group toxins in shellfish and fish that may reach the European market.
Characteristics
Brevetoxins are mainly produced by a dinoflagellate Karenia brevis and are lipid-soluble cyclic polyether compounds.
BTX-group toxins are metabolized in shellfish and fish and several metabolites of BTX-group toxins have been characterised. Consumers of contaminated shellfish and fish are thus primarily exposed to BTX-group toxin metabolites rather than parent algal BTX-group toxins.
A number of the toxins have been identified – with BTX-2 (type B) reported as being the most abundant kind in K. brevis. BTX-1 (type A) and BTX-2 are considered to be the parent toxins from which other BTX-group toxins derive. They are metabolized in shellfish and fish and several metabolites of BTX-group toxins have been characterised. Exposure is normally to BTX-group toxin metabolites rather than parent algal BTX-group toxins.
BTX-group toxins cause neurologic (neurotoxic) shellfish poisoning (NSP) – with symptoms - including nausea, vomiting, diarrhoea, parasthesia, cramps – occurring within 30 minutes to 3 hours of consumption and last for a few days. NSP appears to be.
Current knowledge
The EFSA panel ruled out establishing a tolerable daily intake (TDI) at present as no long term studies on BTX-group toxins in experimental animals currently exist. Because of the “acute toxicity” of the BTX group, the panel said an acute reference dose (ARfD) should be established but again added that a lack of data meant this was not possible.
Testing
The mouse bioassay (MBA) has traditionally been used to detect BTX-group toxins in shellfish – but the panel dismissed this method as inappropriate. Concerns were raised both in terms of its accuracy and animal welfare issues.
Alternative detection procedures such as in vitro and immunoassays were proposed. EFSA said that while like the MBA, they do not provide information on toxin profiles, “they could be further developed to be applied as screening methods for BTX-group toxins”
The panel also suggested liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods to allow for specific detection of individual BTX-group toxins. They would be of value for their quantification in shellfish and fish, added the scientists.
EFSA also noted that none of the current methods of analysis to determine BTX-group toxins in shellfish and fish has been formally validated in interlaboratory studies. The experts said certified reference materials for toxicologically relevant BTX-group toxins need to be provided to allow further method development and interlaboratory validation.