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Toxicity of clay flocculation of the toxic dinoflagellate, Karenia brevis, to estuarine invertebrates and fish
Lewis, M A., D D. Dantin, R M. Greene, C C. Walker, AND J C. Kurtz. Toxicity of clay flocculation of the toxic dinoflagellate, Karenia brevis, to estuarine invertebrates and fish. Harmful Algae 2(4):235-246, (2003).
The benthic environmental effects of proposed control procedures for red tide events are relatively unknown but important to understand. The objective of this study was to determine the laboratory-derived toxicities of a clay flocculation technique proposed for the Florida red tide dinoflagellate, Karenia brevis using four estuarine test species. Phosphatic clay in mixture with three concentrations (0.5, 5.0 and 50.0 mg/l of a chemical coagulant (polyaluminum hydroxy chloride) was not acutely or chronically toxic in most cases to benthic infaunal and epibenthic macroinvertebrates (Leptocheirus plumulosus, Amplesica abidita, Palemonetes pugio) and larval fish (Cyprinodon variegatus). K. brevis alone (density range = 3880 to 5060 cells/ml; brevetoxin range = 19.8 to 140.7 ?g/l was very toxic to juvenile C. variegatus and, to a lesser extent, L. plumulosus. The addition of clay and coagulant did not usually mitigate this toxicity. The aggregates of clay, coagulant and K. brevis cells when settled over a natural sediment, with few exceptions, were as toxic as the red tide organism alone. This suggests that the use of this control procedure will not increase nor decrease toxicity to benthic organisms attributable to an untreated Florida red tide. Validation of this conclusion, however, is needed since it is based on laboratory-derived, single species toxicity data using media collected from a simulated red tide event. The determination of the environmental effects on indigenous biota in near-coastal areas during a natural red tide event, prior to and after treatment with clay flocculation, would provide needed perspective for a more realistic hazard assessment.