Survey of tetrodotoxin in commercially available bivalve molluscs in Japan, including first report of detection in oysters in Western Japan

In this study, LC-MS/MS was used to detect tetrodotoxin (TTX) in 47 commercially available bivalve molluscs (fifteen oysters, six clams, nine short-necked clams, three hard clams, three mussels, four corbiculae, and seven scallops) purchased from supermarkets and retail stores in Japan. In addition, eight preserved mussel samples collected from Osaka Bay in 2014–2015 for paralytic shellfish poisoning surveys were examined. TTX was detected in one oyster from western Japan and two scallops from eastern Japan (detection rate: 6.4%), with the highest TTX concentration detected in the oyster (20 µg/kg in the whole weight), followed by the scallops (8.2 and 17.6 µg/kg in the whole weight). These detected concentrations were below the EFSA-recommended threshold for total TTX concentration in bivalve molluscs (44 µg/kg). TTX had previously been detected only in scallops collected from eastern Japan; however, this study is the first to report TTX in oysters from western Japan. By contrast, TTX was not detected in mussels collected from Osaka Bay. This result contradicted a hypothesis that some paralytic-shellfish-toxin-producing plankton might produce TTX, so showed that no relationship exists between such plankton and the TTX content in bivalve molluscs.