LABORATORY BIOASSAYS 



Static 96-hr TLm acute bioassays (Standard Methods 1965) were 

 conducted as shown in Figure 7. The in situ transplanting of 

 organisms described above was designed to test the toxicity of the 

 effluent on organisms under natural conditions. Laboratory 

 experiments were performed only as a method of identifying the 

 most toxic constituent in the effluent. 



Initially, acute toxicity was determined for dilutions of the 

 unaltered effluent. Samples of effluent were diluted with ambient 

 water taken upcurrent from Safe Harbor. Ten, 50-liter glass aquaria 

 were set up with various dilutions of the effluent and a natural 

 seawater control. For experiments with echinoids (Lyteohinus varie- 

 gatus) , crabs (Menippe meraenaria) , ascidians {Ascidia nigra), and 

 gorgonians (Pterogorgia anaeps\ ten experimental animals were used 

 per tank (this being the largest number which survived well in the 

 50-liter aquaria). Turtle grass {Thalassia testudinum) was analyzed 

 in a different set-up (see Section IV Methods and Procedures). 



Analysis was complicated by the varying characteristics of the 

 effluent, particularly in regard to copper concentration. The data 

 plotted in Figures 52 through 55 represent resistance to effluent 

 taken after the plant was operating at 80 to 90 percent load for 

 more than 48 consecutive hours. 



These data were plotted as recommended by Standard Methods 12th 

 Edition, 1965 to interpolate 48 and 96-hr TLm's. It is recognized 

 this method has been validly criticized, i.e. (Wilber, 1965) as not 

 representative of effluent toxicity in the natural environment and 

 that it is not statistically sophisticated. The method was used 

 in this study for the express purpose of determining approximate, 

 relative toxicological values to aid in identifying the more 

 deleterious constituents of the effluent. The 48 and 96-hr TLm 

 values given here are not intended to be representative of the 

 toxicity of desalination plant effluents, especially since the 

 toxicity varied greatly during the course of the study due to 

 fluctuations in copper content. 



Ascidia nigra had the least tolerance to the effluent with 50 percent 

 of the test animals dying after a 96-hour exposure to 5.8 percent 

 effluent (Fig. 52). Lyteohinus variegatus showed a similar 

 sensitivity with a 96-nr TLm value for 8.8 percent effluent (Fig. 

 53). Menippe mercenaria had a 96-hr TLm value for twelve percent 

 effluent (Fig. 54). Photosynthetic activity of specimens of Thalassia 

 testudinum was depressed by 50 percent in 24 hour exposure to 12 

 percent effluent (Fig. 55). 



To determine if temperature, salinity, or copper (the three major detri- 

 mental factors identified in the effluent analyses) were responsible for 



126 



