B16008: Investigation of the efficiency of the lipophilic biotoxin MBA extraction method to remove a model hydrophilic biotoxin (dc-saxitoxin)

Study Duration: June 2005 to October 2005

Contractor: Integrin Advanced Biosystems Ltd

Since June 2001, atypical responses have been observed during the (DSP) assay used within the UK statutory biotoxin monitoring programme. These atypical responses have occurred primarily with cockle samples from England, Wales and Northern Ireland, but also with a small number of mussel samples from England and Wales. It has been proposed that the atypical response may be caused by the unintentional transfer of hydrophilic PSP toxins into the shellfish extracts used for the DSP assay. To investigate this possibility, this research project will measure the degree to which a model PSP toxin (dc-STX) is transferred from shellfish into the extract used for DSP assays.

In this project a blank mussel homogenate will be spiked to contain 40&#181g/100g of dc-Saxitoxin (dc-STX). This spiked sample will then be extracted using different modifications of the UK standard operating procedure for the extraction of lipophilic toxins (UK NRL DSP1). In the unmodified UK SOP an ether extract of the shellfish sample is washed with two x 5ml of water to remove hydrophilic compounds, such as PSP toxins, which includes dc-STX. In this project ether extracts will be washed with 0, 5, 20, 50 or 100ml of water. Additionally, this project will compare the effect of using either 'dry' ether or ether that has been pre-saturated with water, on the transfer of dc-STX into the final extract.

The level of dc-STX remaining in the final extract will be measured using a chemical detection method enzyme-linked immunosorbent assay.

Increasing the backwash volume resulted in declining amounts of dc-STX in the final extract. Omission of the backwash procedure (0ml) resulted in 12% of the dc-STX present in the spiked shellfish sample being carried over into the extract. A backwash of two x 5ml resulted in a carry-over of 1%; 2 x 20ml reduced the carry-over to 0.7%; and 2 x 50ml produced no detectable carry-over of dc-STX. A backwash of 2 x 100 ml produced no detectable carry over in two of the tests, but a carry over of 0.5% in a third test.

The use of ether that had been pre-saturated with water was found to reduce the amount of dc-STX being carried over by around 45%, when compared to the use 'dry' ether.

The results of this study were central in updating the UK standard operating procedure (SOP) for the extraction of lipophilic toxins. The new SOP (UK-NRL LT1 v2) now prescribes the use of pre-saturated ether and the use of 2 x 50ml water for the backwash procedure.

The final report is available from the Agency's Information Centre.

To obtain a copy, please contact the Enquiry Desk, Information Services, Food Standards Agency (tel: 020 7276 8181/8182 or email: infocentre@foodstandards.gsi.gov.uk)

Contact: For any enquiries concerning this research project, please contact the relevant programme contact or email: science@foodstandards.gsi.gov.uk