Biomarkers of brevetoxin exposure and composite toxin levels in hard clam (Mercenaria sp.) exposed to Karenia brevis blooms

•ELISA response in hard clams is largely by brevetoxin metabolites.•Identified biomarkers of brevetoxin exposure and composite toxins in hard clams.•High correlation of LCMS and ELISA results of Karenia brevis exposed hard clams.

Brevetoxins in clams (Mercenaria sp.) exposed to recurring blooms of Karenia brevis in Sarasota Bay, FL, were studied over a three-year period. Brevetoxin profiles in toxic clams were generated by ELISA and LC-MS. Several brevetoxin metabolites, as identified by LC-MS, were major contributors to the composite brevetoxin response of ELISA. These were S-desoxyBTX-B2 (m/z 1018), BTX-B2 (m/z 1034), BTX-B5 (m/z 911), open A-ring BTX-B5 (m/z 929), and BTX-B1 (m/z 1018). Summed values of these metabolites were highly correlated (R2 = 0.9) with composite B-type brevetoxin measurements by ELISA. S-desoxyBTX-B2, BTX-B2, and BTX-B1 were the most persistent and detectable in shellfish for several months after dissipation of blooms. These metabolites were selected as LC-MS biomarkers of brevetoxin exposure and reflective of composite B-type brevetoxins in hard clam. ELISA and LC-MS values were moderately correlated with toxicity of the shellfish by mouse bioassay. ELISA and LC-MS methods offer rapid screening and confirmatory determination of brevetoxins, respectively, as well as toxicity assessment in clams exposed to K. brevis blooms.