First detection of the gymnodimine A isomer, 13-desmethylspirolide D and pinnatoxin G in mussels from Croatia's southern Adriatic Sea

Cyclic imines (CIs) are lipophilic marine toxins produced by dinoflagellates, that are known for their neurotoxic effects and have raised concern among food regulatory agencies due to insufficient data on their presence. This study is the first to systematically investigate the possible presence of 29 CIs in shellfish from the southern Adriatic Sea in Croatia. Liquid chromatography-tandem mass spectrometry and liquid chromatography-high-resolution mass spectrometry were used to analyse 126 mussel samples. For the first time, 13-desmethylspirolide D (13-desme SPX D), pinnatoxin G (PnTX G) and a gymnodimine (GYM) A isomer were detected in wild and farmed mussels from the region. The highest level of PnTX G was measured in August at 9.77 μg/kg, while 13-desme SPX D reached a maximum value of 3.55 μg/kg in June. In addition, 13-desmethylspirolide C (SPX 1) and GYM A were detected in the majority of samples, with GYM A reaching a maximum value of 39.28 μg/kg in June and SPX 1 reaching a maximum value of 13.79 μg/kg in April. The statistical analysis confirmed a seasonal pattern for GYM A, while SPX 1 showed no seasonality. Furthermore, there was no significant difference in the concentrations of SPX 1 and GYM A between wild and farmed mussels. However, samples collected in the same month during the 2021-2023 monitoring period showed year-to-year variations in their concentrations. Due to the lack of sufficient data, no statistically significant variations could be confirmed for 13-desme SPX D, PnTX G and the GYM A isomer in the period 2021-2023.