First U.S. report of shellfish harvesting closures due to confirmed okadaic acid in Texas Gulf coast oysters

Between March 7 and April 12, 2008, several bay systems on the east (Gulf of Mexico) coast of Texas, USA were closed to the harvesting of oysters (Crassostrea virginica) due to the presence of the DSP (Diarrheic Shellfish Poisoning) toxin okadaic acid in excess of the 20 μg/100 g tissue FDA regulatory guidance level. This was the first shellfish harvesting closure due to the confirmed presence of DSP toxins in US history. Light microscopic cell counts were performed on water samples collected from numerous sampling sites along the Texas Gulf coast where shellfish harvesting occurs. Ultra performance liquid chromatography, electrospray ionization, selected reaction monitoring, mass spectrometry (UPLC/ESI/SRM/MS) was used to detect DSP toxins in oysters. The closures were associated with an extensive bloom of the dinoflagellate Dinophysis cf. ovum. Only okadaic acid (OA) and OA acyl esters were found in shellfish tissues (max. OA eq. levels 47 μg/100 g tissue). OA was also confirmed in a bloom water sample. No illnesses were reported associated with this event. DSP toxins now add to a growing list of phycotoxins, which include those responsible for PSP (paralytic shellfish poisoning), NSP (neurotoxic shellfish poisoning), and ASP (amnesic shellfish poisoning) which must now be monitored for in US coastal waters where shellfish are harvested.