This research examines the effects of mixtures of synthetic surfactants (C
14EO
14, C
18F
1EO
14, Tween80, C
14FA and Oleyl EO
20) on red-tide causing organisms and red sea bream. Surfactant (1 to 50 ppm) was added to media containing
Chattonella marina or
Heterocapsa circularisquama and examined every 30 minutes for swimming, immobile, and lysed cells for a total of 2 hours. The lowest concentration to immobolize or lyse the cells (LC
50, 2h) was calculated. The LC
50 (24h) of surfactants was also calculated for the ichthytoxicity of red sea bream juveniles. The LC
50 (2h) of C
14EO
14, C
18F
1E0
14 and Tween80 for
C. marina was 1, 5 and 20 ppm, respectively; and for C
14FA and Oleyl EO
20, it was 30 ppm. Conversely with respect to
H. circularisquama, approximately 30% of the cells showed sings of deformation at concentration of 50 ppm, Ichthyotoxicity (LC
50, 24h) for Tween80 was the strongest at 55 ppm, the other surfactants were ichthyotoxic from 125 to 150 ppm.
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