A Comparison of Assay Techniques for the Analysis of Diarrhetic Shellfish Poisoning Toxins in Shellfish

Abstract

Algal biotoxins were determined on a weekly basis through the summers of 2009 and 2010 on mussel (Mytilus edulis) samples taken from three sites in Killary Harbour, a fjord located on the west coast of Ireland. Chemical (LC-MS), immunoassay (ELISA) and enzymatic (Protein Phosphatase, PP2A) methods were used to analyse algal diarrhetic shellfish poisoning (DSP) toxins in methanol extracts from these samples. Results were compared to test the applicability of the non-chemical methods as alternative rapid testing techniques, which were applied on both hydrolysed and non-hydrolysed samples. Results were also compared with mouse bioassay data from the Irish national monitoring programme. Results from 2009 showed a significant DSP event in July, with toxin concentrations reaching 1.2–1.4 μg (g whole flesh)⁻¹. All methods were capable of detecting this event, which lasted for 3–4 weeks during which harvesting was closed, caused by an influx of a Dinophysis spp. population into the fjord. Examination of integrated (0–10 m) water samples showed Dinophysis cell counts as high as 2,400 cells · l⁻¹. These Dinophysis and toxin levels were never reached during the summer of 2010, when LC-MS results showed that DSP toxin levels rose above the EU maximum permissible level of 0.16 μg g⁻¹ in only one sample, co-inciding with Dinophysis cell counts of 300 cells · l⁻¹. Results using immunoassay on non-hydrolysed samples were broadly similar to the LC-MS data, while the results for the hydrolysed samples were found to be highly variable and often significantly elevated compared with the non-hydrolysed sample LC-MS results. This variability was significantly reduced using the phosphatase assay, which gave results more compatible with the LC-MS data set. The applicability of using non-chemical methods, particularly in geographically remote areas as methods for screening shellfish quality, is discussed.