Bioaccumulation and depuration of brevetoxins in the eastern oyster (Crassostrea virginica) and the northern quahog (= hard clam, Mercenaria mercenaria)

The eastern oyster (Crassostrea virginica) and northern quahog (= hard clam, Mercenaria mercenaria) are two species of economic and ecological significance in east coast waters of the United States and the Gulf of Mexico. Commercial industries for these species, especially within the state of Florida, are significant. The current study was undertaken to build upon the already established body of knowledge surrounding effects of the toxic dinoflagellate Karenia brevis on shellfish, to provide an understanding of the kinetics of brevetoxins within shellfish tissues, and to provide an estimate of brevetoxin retention times in these shellfish after a bloom event. Individual clams and oysters were exposed to the toxic dinoflagellate, K. brevis at a bloom concentration of 5 × 105 cells·L−1 for eight days and then transferred to filtered water for depuration. Individuals were sampled periodically to determine depuration rates. Concentrations of brevetoxins (and/or their metabolites measured as PbTx-3 equivalent) in tissues were determined using an Enzyme Linked Immunosorbent Assay (ELISA). After five days of exposure, brevetoxin levels in tissues of both species reached concentrations well above the regulatory limit of 800 ng g−1 (Pb-TX3 equivalent). Averaged concentration of brevetoxins in clams was 1000 ng g−1, while the oysters averaged 1986 ng g−1. After two weeks of depuration, tissue concentrations in both species were below regulatory levels with clams averaging ∼204 ng g−1 and oysters averaging ∼437 ng g−1. Toxins (or their metabolities) remained detectable in both clams (139 days) and oysters (82 days) for the duration of the experiment. ► We looked at the uptake and depuration of brevetoxins in clams and oysters. ► Oysters and clams accumulated brevetoxins within 3 days. ► Toxin concentrations were below regulatory levels after two weeks of depuration. ► Low levels of brevetoxins were present in shellfish tissues even after 4 months. ► Oysters were more sensitive to brevetoxins than clams.