Brevetoxin Metabolites: Emerging Toxins in French Shellfish Determined by LC-MS/MS and ELISA

In France, as part of the monitoring program for the emergence of marine toxins in shellfish (EMERGTOX), brevetoxins (BTX-2, BTX-3) were first detected in shellfish from Corsica (Mediterranean Sea) in 2018. The complex metabolic transformation of brevetoxins in shellfish, coupled with the limited availability of analytical standards for most metabolites, complicates the accurate evaluation of contamination levels. To address this challenge, two complementary analytical approaches were implemented to quantify brevetoxin metabolites in shellfish samples collected from 2018 to 2023: (i) a targeted LC-MS/MS method specially developed for brevetoxins; and (ii) an ELISA capable of detecting metabolites for which no reference standards are available. Of the 11 brevetoxin metabolites targeted, 4 were quantified by LC-MS/MS: BTX-2, BTX-3, BTX-B5, and S-deoxy-BTX-B2 (including its isomers). The ELISA consistently detected brevetoxins in all Corsican samples previously confirmed positive by LC-MS/MS, with concentrations systematically exceeding those measured by LC-MS/MS. This overestimation may result from antibody cross-reactivity and from the presence of unidentified brevetoxin metabolites not detected by LC-MS/MS. Regardless of the analytical method used, the highest concentration detected exceeded the current French guideline value for brevetoxins in shellfish. To ensure consumer protection, a two-step monitoring strategy is proposed: initial screening via ELISA to estimate brevetoxin contamination, followed by confirmatory LC-MS/MS analysis to identify and quantify the specific metabolites.