Abstract
The potent and heat-stable toxin, tetrodotoxin (TTX), well known to accumulate in pufferfish from tropical and subtropical regions, causes potentially fatal food poisoning. The recent discovery of TTX in bivalve shellfish from temperate seas, including those surrounding the United Kingdom (UK), has raised concerns over food safety. The de novo origin of TTX appears unclear, although several bacterial genera including Vibrio, have been implicated. Significant knowledge gaps exist on the prevalence, risk to public and factors that affect TTX accumulation in shellfish. This study used a holistic approach to investigate various aspects of TTX accumulation in British shellfish. Prevalence and seasonality were assessed in a large systematic screening study using > 3,500 samples collected from around the British coast, while a single field site in southern England was used to assess TTX production against a range of environmental and biological factors. The influencing role of sea surface temperature (SST) on the accumulation of TTX in June and July was apparent in both screening and field studies, where satellite-derived temperature data were used for the first time. Neither phytoplankton nor bacteria could be identified as the biological source of TTX in Pacific oysters, however the preferential accumulation of TTX in their digestive glands pointed at trophic transfer. TTX prevalence in British shellfish in 2016 was 1.1%, indicating on overall low risk to the shellfish consumer. However, TTX-positive bivalves were almost exclusively recovered from shallow intertidal environments in southern England with large annual SST variability and sustained daily mean SST above 16 °C. Although a pattern in seasonal and spatial distribution of TTX could be observed, aiding the identification of higher-risk locations, variable TTX levels above the proposed regulatory limit and the potential future geographical expansion of TTX due to global warming, should not be underestimated.