1120 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1957 



Fig. 12 — Test rack being lifted from water at Wrightsville Beach. Heavj^ ac- 

 cumulation of fouling on test rods in water-exposed area stops at point where rods 

 entered the sediment. 



structures and coatings, is referred to the report of the investigations 

 conducted at the Woods Hole Oceanographic Institution during the 

 years 1940 to 1946.^^ The restricted areas beneath fouHng, particularly 

 under the Imses of calcareous organisms such as barnacles, provide ideal 

 cells for l)acterial activity. Conditions of pH and aeration may be mai'k- 

 edly different in these confined areas from those in the surrounding 

 water. Some of the test rods made of polyvinyl chloride plastics contain- 

 ing basic lead stabilizers, illustrate the fact rather dramatically. Ana- 

 erobic, sulfate-reducing bacteria are common marine organisms which 

 release hydrogen sulfide in the process of breaking down organic ma- 

 terial. Under tightly adhering fouling, aerobic bacteria can utilize the 

 free oxygen much more rapidly than it can be replaced by diffusion from 

 the surrounding water. Once the oxygen has been depleted, the anaerobic 

 organisms begin their activity and cause relatively high concentrations 

 of hydrogen sulfide to be built up. The hydrogen sulfide reacts with the 

 basic lead salts used as stabilizers and produces black lead stilfide. The 

 sharp l)()undaries of the different envii'oimiental conditions existing 

 ])('ii(>atli tlu> base of a barnacle on one of the polyvinyl chloride test rods 

 are illustrated in Fig. 13. Here the pattern of the barnacle base has 

 literally been reproduced b.y the sulfiding which occurred under it. The 

 black border and black radiating lines correspond to areas of exception- 



