Each chemical is tested for its effect on the young 

 of various species of marine life. 



eight chemicals have been eliminated. (See accompanying table; blank spaces 

 indicate temporary nonavailability of test organisms. ) 



A source of variation over which we have no control and one that 

 could have a profound effect on the results of this project is differential toxic- 

 ity of some chemicals with respect to source of supply. For example, we had 

 to replenish our supply of 3-5-hexadienoic acid, 2-oxo-6 phenyl which, as 

 shown in the accompanying table, is one of the two most toxic materials tested. 

 The new compound, which is supposedly the same as the original, has not 

 proved toxic to G. breve at any of the levels tested. 



Difficulty in finding new sources of supply for some of our materials 

 is also causing concern. For example, our supply of mercury acetate, (2, 3- 

 dimethoxy tetramethylene) bis-, one of the two most toxic materials tested, is 

 exhausted. The original supplier no longer exists, and to date we have been un- 

 able to find a new one. 



Now being planned is a second series of tests through which the chem- 

 icals that have passed the selectivity tests will be rechecked to determine their 

 minimum toxic level for G. breve in relatively large volunnes of culture. Each 

 com.pound will be checked at five concentrations, viz., .01, .003, .001, .0003, 

 and . 0001 p. p.m. in 5 liters of G. breve culture. This will be a 500-fold in- 

 crease in volxime over previous tests and should give an indication, among other 

 things, of the surface -volume effect. 



Mortality estimates will be made after 24, 48, and 72 hours, follow- 

 ing which selectivity tests will be made on important marine species. To min- 

 imize water-quality variables.tests will be made in G. breve media instead of 

 water from the recirculating sea-water system.. Potential control chemicals 

 will also be tested in synthetic sea-water mediunn containing both commercially 

 important species and a sublethal population level of G. breve . 



65 



