from 2,920 to 4,000 Angstroms and very intense visible radiation from 

 5,000 to 6,000 Angstroms. The intensity of the ultraviolet radiation in 

 sunlight varies considerably from day-to-day and hour-to-hour. 



The transmission of ultraviolet light in seawater also varies 

 considerably. The concentrations of microorganisms, nitrate ions, 

 sediments, and organic matter all help to determine the transparency of 

 seawater to ultraviolet radiation [10]. As depth increases, the intensity 

 of ultraviolet light decreases. The shorter the wavelength, the greater 

 is the decrease in intensity with depth. In consequence, the average 

 wavelength of sunlight radiation increases with depth of penetration. 



If there were radiations in sunlight with a wavelength of 2,540 

 Angstroms, the most highly germicidal wavelength, they would penetrate 

 no more than 1/2 meter of seawater. Ultraviolet radiation with a wavelength 

 of 2,920 Angstroms, the shortest in sunlight, penetrates no more than 

 approximately 3 meters of seawater [6]. Ultraviolet sunlight with a 

 wavelength of 4,000 Angstroms may penetrate 10 to 20 meters, and visible 

 light may penetrate to a depth of 100 meters [8]. 



The maximum depth at which the detrimental effects of sunlight are 

 great enough to overcome the ability of E. coli cells to resist and 

 multiply has not been precisely determined. Beyond the depth of sunlight 

 penetration, E^ coli cells survived for nearly 2 weeks in seawater 

 containing insufficient nutrients for growth. Whether they would survive 

 for shorter periods when exposed to sunlight radiation penetrating 

 to depths of 10, 25, 50, or 100 feet is not known. This information is 

 part of that needed for a thorough assessment of the hazards of disposing 

 of sewage at sea. 



CONCLUSIONS 



Escherichia coli , the principal bacterial species of sewage, is 

 very sensitive to sunlight. Unless protected inside a grease ball or a 

 fecal mass, microorganisms of this species in sewage discharged near the 

 ocean surface would surely perish within a few days. There would be 

 relatively small differences in the mortality rates of E. coli in sewage 

 discharged at ocean depths of 200 and 1,000 feet. Very little sunlight 

 penetrates to these depths, and sewage bacteria of this species would 

 survive for an estimated week or two. If the sewage were discharged at 

 a depth of 1,000 feet, there would be no danger of contaminating surface 

 waters because the cold deep water does not mix with the warmer surface 

 waters. If the sewage were discharged at a depth of 200 feet, there 

 would probably also be no danger of contaminating surface waters unless 

 the thermocline was deeper than that. . 



10 



