E. coll In medium preexposed to sunlight, 19 x 10 ^per ml. 

 E. coll In medium protected from sunlight, 14x10 per ml. 



DISCUSSION OF RESULTS 



Numerous investigators have studied the effects of seawater, sunlight, 

 pressure, or ocean exposure on the survival of sewage bacteria. So many 

 of their results are conflicting [3] that no attempt is made to compare 

 the results of the study reported here with the results obtained by 

 other investigators. 



E. coll cells gradually died off in filtered autoclaved seawater. 

 Apparently they died from lack of nutrients rather than from any harm 

 caused by the sea salts, because they flourished and multiplied rapidly 

 in seawater containing added nutrients such as tryptlc soy broth or 

 human feces. It appears that the filtered seawater contained insufficient 

 nutrients for the microorganisms to multiply. The BACT-CHEK discs 

 themselves may have contained some nutrients because the discs produced 

 cultures with a hundredfold greater ^ coll population when they were 

 Incubated in test tubes of water for 24 hours than when incubated for 2 

 hours. 



In both experiments performed at sea, the counts for samples 

 exposed at 1,000 feet tended to be higher than the counts for samples 

 exposed at 200 feet. The differences were not great, however, and were 

 surely within the range of possible experimental error. In both experiments 

 striking differences were noted in the counts on the samples exposed at 

 200 or 1,000 feet and those exposed near the surface. Unless protected 

 from light, the bacteria died very rapidly at the surface. There were 

 no great differences in the mortality rates of E^ coll in filtered 

 seawater maintained in the laboratory at room temperature, in the 

 refrigerator, or in the ocean at depths of 200 or 1,000 feet. In all 

 Instances, there were probably Insufficient nutrients; and the bacteria 

 died off at rates which would leave few or none living in 1 or 2 weeks. 



Survival times might have varied more had the media contained more 

 nutrients. It is likely that the populations of bacteria would have 

 Increased initially. The nutrients would probably have been used up 

 more rapidly at some temperatures than at others, and the subsequent 

 decline in numbers might then have been more markedly Influenced by 

 temperature. 



Since the E^ coll in this experiment were enclosed in dialyzer bags, 

 it is possible that the bacteria would die even more rapidly if 

 discharged directly into the ocean. It seems unlikely that they would 

 have survived for a longer period of time, unless they were protected in some 

 manner, such as inside a grease ball or inside a fecal mass. 



During the summer in temperate latitudes, and year around in lower 

 latitudes, near-shore surface waters circulate and mix as a layer. 

 Water below the thermocline, which develops in these waters at depths of 

 100 feet or so, mixes only slightly with the water above the thermocline 



