SPECIAL REPORTS 

 Chemicals Toxic to the Red-Tide Organism 

 Kenneth T. Marvin and Raphael R. Proctor 



The current project was started in March 1959 to find a chemical 

 means of controlling intense plankton blooms and thus preventing the damag- 

 ing effects of the red-tide organism, Gymnodinium breve. Previous control 

 attempts have been made by applying copper in both solution and powdered 

 form (copper sulfate) to affected areas. Large-scale experiments employ- 

 ing tons of material dennonstrated, however, that although copper can give 

 temporary relief in localized situations, it is neither economically nor chem- 

 ically feasible for large-scale control. Present research involves the screen- 

 ing of nearly 5, 000 primarily organic chemicals in a search for a material 

 with which the desired degree of control would be feasible. 



Preliminary tests evaluated all chemicals as toxicants for G.breve. 

 These tests, which were covered in last year's laboratory report, permitted 

 separation of those materials toxic at concentration levels of 0. 04 p. p. m. 

 (parts per million) or less from those that were not. The latter group was 

 discarded. 



This year we decided that to be economically suitable, a potential 

 control material must be toxic to G. breve at a concentration of 0.01 p. p.m. 

 or less. We therefore separated the ". 01" chemicals from the ". 04" group. 

 The procedure involved was similar to that covered in the previous report. 

 Each chemical in the ". 04" group was retested three times at five concentra- 

 tions ranging from 0.04 to 0.0004 p. p.m. Two that were toxic at 0.0004 p. p.m. 

 were further tested at 0.0001 p. p.m. In this manner, 32 compounds toxic at 

 0.01 p. p.m. or less were separated from the ".04" group. 



Current activity centers on determining the selectivity of the ". 01" 

 group. The material being sought must be toxic to G. breve, but at the same 

 time have no harmful effect, either directly or indirectly, on commercially 

 important species. Our approach to the problem considers short-term effects 

 only. Any control material recommended as a result of this study should 

 therefore be used cautiously until long-term effects are ascertained. 



The study consists of observing the effects of chemicals in the ".01" 

 group on the young of various species of marine life found in Galveston Bay 

 and Gulf coast waters. Each chemical is tested at five concentrations rang- 

 ing from 0.01 to 1.0 p. p.m. Tests are conducted in 10-liter, all-glass 

 aquaria, each of which contains 10 specimens of the organism being tested in 

 8 liters of treated water from our recirculating sea-water system. All chem- 

 icals are initially prepared in an alcohol solution, hence alcohol as well as 

 untreated-sea-water controls are included with every trial run. 



One -tenth (0. 10) p. p.m. was arbitrarily selected as the threshold 

 level. Any chemical that kills 50 percent or more of any test organism at or 

 below this level within the 24-hour test period is rejected. Thus far, all but 



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