Sea temperature influences accumulation of tetrodotoxin in British bivalve shellfish

Tetrodotoxin (TTX), a potent neurotoxin mostly associated with pufferfish poisoning, is also found in bivalve shellfish. Recent studies into this emerging food safety threat reported TTX in a few, mainly estuarine, shellfish production areas in some European countries, including the United Kingdom. A pattern in occurrences has started to emerge, however the role of temperature on TTX has not been investigated in detail. Therefore, we conducted a large systematic TTX screening study, encompassing over 3500 bivalve samples collected throughout 2016 from 155 shellfish monitoring sites along the coast of Great Britain. Overall, we found that only 1.1 % of tested samples contained TTX above the reporting limit of 2 μg/kg whole shellfish flesh and these samples all originated from ten shellfish production sites in southern England. Subsequent continuous monitoring of selected areas over a five-year period showed a potential seasonal TTX accumulation in bivalves, starting in June when water temperatures reached around 15 °C. For the first time, satellite-derived data were also applied to investigate temperature differences between sites with and without confirmed presence of TTX in 2016. Although average annual temperatures were similar in both groups, daily mean values were higher in summer and lower in winter at sites where TTX was found. Here, temperature also increased significantly faster during late spring and early summer, the critical period for TTX. Our study supports the hypothesis that temperature is one of the key triggers of events leading to TTX accumulation in European bivalves. However, other factors are also likely to play an important role, including the presence or absence of a de novo biological source, which remains elusive.