of Diesel oil and 76 ml. of crude oil, the resultant ratios of water to 

 oil being 1:500 and ltl89 respectively. In one aquarium of each set the 

 oil was left floating on the surface, while in a second one the oil slick 

 was sprinkled with carbonized sand until the oil was completely combined 

 with the sand and settled on the bottom. The third had no oil and served 

 as a control* 



Samples of water, taken at frequent intervals close to the bottcsn, 

 were analyzed for dissolved oxygen and determination made of the pH. No 

 abnormal conditions with respect to these two factors were observed during 

 the tests* 



Jn Hie aquaria in -wAiioh oil was floating on the surface, it was ob- 

 served that after some time •tiie bottom and sides of the aquaria and the 

 shells of the oysters became coated with an oil film. No such film 

 appeared irfien oil and sand mixtures were used, the oil being permanently 

 bound to the carbonized sand. 



In the experiment with Diesel oil (ratio ltl89) the first death 

 occurred on the third day in the aquarium with an oil layer on the surface, 

 and on the fourtii day in the aquarium with oil and sand mixture. By the 

 end of the test on the 13th day, the mortality was 67 percent in the test 

 with oil on the surface against 25 percent in that with the oil treated 

 with carbonized sand (table 19). There was no mortality among the control 

 oysters. The results show theit the toxicity of Diesel oil anchored on the 

 bottom by carbonized sand is scmewhat reduced. At the end of the experiment, 

 all the oysters that survived were removed, washed with tap water, and 

 opened for examination. Their meats had a marked oily odor. 



Experiments with crude oil added in the ratio of lt500 gave similar 



results. In these the first death was observed on the ninth day and the 



mortality was less pronounced, due probably to the smaller quantity of oil 

 used (table 20), 



2« Effect of prolonged exposure to omde oil mixed with carbonized sand 

 in running sea water t 



To observe the effect on oysters, small quantities' of crude oil mixed 

 with carbonized sand were placed on the bottom of tanks of running sea water 

 or introduced into a flowing sea water system* The following tests were 

 performed t 



Fifty adult oysters were placed on the bottom of each of three wooden 

 tanks 28 l/4 x 58 l/2 inches. A depth of eight inches of water was main- 

 tained in each tank by a standpipe* One tank was maintained as control. 

 To the other tank 500 ml. of crude oil were added and oil slick immediately 

 sprinkled with carbonized sand until all the oil had been removed fran the 

 surface and settled on the bottom. Some of the oil and sand mixture was 

 directly on oysters. The third tank contained no oil but received the 

 water that was running over a layer of oil and sand. This was accomplished 



30 



