The other 18 cages were attached to the nylon line anchored in the 

 ocean. Three each of the opaque and translucent cages were suspended 

 from the line at a depth of only a few feet; three each, at a depth of 

 200 feet; and three each, at a depth of 1,000 feet. One opaque and one 

 translucent cage was removed from each depth at the end of 24, 48, and 

 120 hours. 



The bags were removed from the cages and samples for bacterial 

 counts were obtained by piercing the bags (Figure 9). Figures 10 to 13 

 show the colonies which developed on the field monitor plates for the 

 final or 120-hour samples after the series of dilutions of 10 ml of the 

 contents of the bags. The results of the experiment are summarized in 

 Table 2. 



Sunlight Effect on E. coli in Glass and in Polyethylene 



A comparison was made of the survival of E^ coli exposed to sunlight 

 in containers made of pyrex glass and containers made of polyethylene. 

 The shorter wavelengths of ultraviolet light are less able to penetrate 

 the glass than the plastic containers. 



A culture was prepared by inoculating 1-1/2 liters of autoclaved 

 seawater containing 0.5 gram of ' ' Eugenbroth' ' (a proprietary mixture 

 of nutrients and salts sold by the Division of Bio Quest, Cockeysville, 

 Maryland for preparing bacteriological media with E^^ coli ) . The culture 

 was incubated for 24 hours at 32 C, at which time growth of E. coli was 

 sufficient to cause the medium to be cloudy. One hundred ml of culture 

 was added to each of three small polyethylene bottles and three pyrex 

 glass flasks. The six containers were placed outdoors in the sunlight 

 for 6 hours. During the first 2 hours, the sun was obscured by fog and 

 low-lying clouds. During the next 2 hours the cloud cover disappeared, 

 and the sunlight was very bright for the last 2 hours of the exposure. 

 Periodically, bacterial counts were made of the contents of the 6 flasks. 

 The following values were obtained for the counts per ml: 



Containers 



hr 



2 hr 



6 hr 



Plastic 

 Glass 



24 X 10' 

 24 X 10 



26 X 10" 

 28 X 10 



<10 

 <10 



Effect of Sunlight on Seawater 



An experiment was conducted to ascertain if sunlight altered the 

 chemical composition of seawater in such a way as to make it unsuitable 

 for the growth of ^ coli . Four Erlenmeyer flasks, each containing 100 

 mg of Eugenbroth preparation and 400 ml of seawater, were autoclaved at 

 15 psi for 20 minutes. Two of them were then exposed to sunlight for 

 one complete day and the other two were stored in the dark. All four 

 flasks were then inoculated with 1 -ml portions of a vigorous E. coli 

 culture, and all four were incubated in the dark for 24 hours. Counts 

 of E^ coli were then made, and the following results were obtained: 



