Chemical Control 



Kenneth T. Marvin and Raphael R. Proctor, Jr. 



During the past year about 1, 000 organic chemicals have been eval- 

 uated as possible red-tide toxicants. This was a continuation of the screening 

 program started in March 1959 to find a chemical means of controlling the 

 blooming and thus the damage of the red-tide organism, Gymnodinium breve. 

 The work is made possible by the many interested organizations who have sub- 

 mitted samples for evaluation. 



The details of procedure for the first phase of the work are thoroughly 

 covered in last year's report. Briefly, the procedure consists of rapidly eval- 

 uating each chemical and classifying it as toxic or nontoxic. By way of ex- 

 planation, a substance is considered toxic if it kills the red-tide organism with- 

 in Z4 hours at 0.04 p. p.m. During the initial screening, many chemicals pre- 

 cipitate from the water-alcohol phase of the dilution procedure. The reason 

 for this is that during the dilution process the tip of the transfer pipette, for 

 safety reasons, is placed as close to the bottom of the solution flask as pos- 

 sible. Therefore, any undissolved material has a tendency to be picked up and 

 carried through the series of dilutions in an undissolved state, thus resulting 

 in a highrr than desired concentration in the final solution. This increases the 

 apparent toxicity of some of the samples that are not completely soluble in the 

 alcohol- water phase. 



When rechecking compounds in the "toxic" group to determine their 

 minimum effective concentrations, an effort is made to correct this source of 

 error by making all tests in triplicate and reducing the concentration of the 

 initial alcoholic solution from 0. 1% to 0.01%. Furthermore, taller flasks are 

 used for preparing intermediate solutions so that the tip of the transfer pipette 

 can be safely placed about an inch from, instead of on the bottom of the solu- 

 tion flask. This minimizes the possibility of withdrawing undissolved material. 

 We realize that this latter precaution results in a bias having the opposite effect 

 of the one mentioned above. In this case the final concentrations of the com- 

 pounds that did not remain in solution would have a tendency to be lower than 

 desired, and for this reason highly toxic ones could pass our tests undetected. 

 Thus we have a third group, those that might be toxic at the 0. 04 level but 

 whose solubility is such that they are not adaptable to the screening technique 

 employed. It is possible that successful toxicants could come from this group, 

 since compounds of this type would dissolve very slowly, and therefore their 

 possible toxic effects would be more lasting than the more soluble compounds. 

 For this reason we plan to investigate this group later, using somewhat dif- 

 ferent techniques. 



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