Risk assessment of the Scottish monitoring programme for the marine biotoxins in shellfish harvested from classified production areas

The aim of this study was to assess the Scottish inshore monitoring programme for biotoxins in shellfish from classified production areas in Scotland. This programme, conducted by Food Standards Scotland (FSS), aims to determine the prevalence of paralytic shellfish toxin (PST) (responsible for paralytic shellfish poisoning (PSP)), domoic acid (DA) (responsible for amnesic shellfish poisoning (ASP)), and lipophilic toxins (LTs) (some of which are responsible for diarrhetic shellfish poisoning (DSP)). These are produced by certain types of phytoplankton (marine algae).

A multidisciplinary approach was applied in this study, including statistical modelling, knowledge of biotoxins and biotoxin producing phytoplankton, as well as understanding of the industry and legislative requirements in this area. Biotoxin results for mussels (29,154 samples), Pacific oysters (5,526 samples), cockles (1,223 samples), razors (1,105 samples) and surf clams (344 samples) were used in together with phytoplankton data.

Analyses of the data from 2001 to 2015 revealed that:

• there was a very apparent seasonality in the exceedence of the set threshold (both phytoplankton counts and mussel-toxin concentration) for mussels, exceedances were higherduring the period spring to autumn.
• DA levels in shellfish were generally very low, only 3 samples out of 15,377 exceeded the maximum permitted level.
• PSP toxins above maximum permitted level were most frequently detected in surf clams (1.6%) and mussels (1%), followed by razors (0.5%), cockles (0.4%) and Pacific oysters (0.1%)
• LTs above maximum permitted level were most frequently detected in surf clams (7.9%) and mussels (7.6%), followed by Pacific oysters (2.1%), and razors (0.6%). For cockles only 1 out of 940 samples exceed the maximum permitted levels

Using combination of the findings from the risk assessment of the current biotoxin monitoring scheme, biotoxin prevalence estimated by the statistical modelling and the maximum biotoxin levels observed in the data, the researchers were able to propose revisions to monitoring frequencies. In general, the proposed frequencies for testing are specific to shellfish species, biotoxin, location and time of the year.

FSS will use findings from this study to inform a review of the current biotoxin monitoring scheme.