Italy: tetrodotoxins in bivalve molluscs, first detection in the northern Adriatic

Tetrodotoxins, a potent neurotoxic class of toxins with potentially fatal effects if ingested by humans, were found in significant amounts in some mussel samples taken in May 2017 and May 2018 from the Marano lagoon (Italy), according to laboratory analyses conducted by the Experimental Zooprophylactic Institute of the Venezie (IZSVe). These poisons have never been found in bivalve mollusks from the Adriatic Sea's northern region before. Tetrodotoxin-positive mussels were found in samples taken from that geographic region as part of official monitoring programs in 2017 and 2018. The researchers discovered an accumulation of tetrodotoxins equivalent to 541 g/kg in 2017 samples and 216 g/kg in 2018 samples, the greatest quantity of these compounds ever recorded in European bivalve mollusks. In the mussels tested in 2017, the presence of tetrodotoxins at a concentration of 413 g/kg was further verified using Liquid Chromatography combined with High Resolution Mass Spectrometry.    

Since 2018, the area affected by the discovery of positive samples has been forbidden to collect bivalve molluscs and has been exclusively used as an experimental study area, where further investigations are still being carried out on the effect of seasonality and the origin of tetrodotoxins. To better understand this phenomenon, the researchers of the IZSVe are continuing to monitor molluscs in the lagoon areas of the Upper Adriatic through a Current Research project funded by the Ministry of Health. The study is still in progress, but from the first data collected it seems to emerge that the period of contamination is limited to late spring.    

In the past, the presence of tetrodotoxins in aquatic creatures was not thought to pose a serious danger to European consumers. This threat has just recently been recognized by academics and authorities. Nevertheless, tetrodotoxin poisoning has been prevalent in Japan, Taiwan, and Bangladesh, among other Southeast Asian nations where these fish are commonly eaten. In the European Union and in many other countries around the world, however, the trade of tetrodontids for food purposes is prohibited.