First detection of β-N-methylamino-L-alanine (BMAA) and its structural isomers (2,4-DAB and AEG) in Japanese shellfish

β-N-methylamino-L-alanine (BMAA) is a non-proteinogenic amino acid produced by certain cyanobacteria and diatoms, and is suspected chronic neurotoxin. Although BMAA and its structural isomers, 2,4-diaminobutyric acid (2,4-DAB) and N-(2-aminoethyl)glycine (AEG), have been found in aquatic food webs in other countries, their presence in Japanese waters and shellfish had not been reported. In this study, we quantified BMAA and its isomers in Japanese shellfish using a non-derivatized LC-MS/MS method. BMAA concentrations in shellfish ranged from below the detection limit to 16.0 µg g−1 dry weight (dw), and tended to be higher in filter-feeding bivalves compared to gastropods. 2,4-DAB was present in all shellfish species (0.0818–13.0 µg g−1 dw), whereas AEG was only detected in some bivalves, with high levels found in Spisula sachalinensis (Schrenck, 1861) (8.55–25.5 µg g−1 dw). BMAA was also detected in particulate organic matter from Tokyo Bay (0.0186 µg L−1), suggesting that suspended microalgae could be a source of exposure for benthic filter feeders. Our results provide the first baseline data of BMAA-related compounds in Japanese shellfish and highlight the need for continued monitoring to evaluate dietary exposure risks.