fouling before the chemicals oozed to the surface of the panel (Figure 

 7). The fouling was transient, however, and died off when the toxic 

 creosote mixture reached the surface. The same panel was still essen- 

 tially free of fouling organisms (Figure 8) after it had been in the 

 ocean for 4 years. Other panels made from aggregates impregnated with a 

 mixture of creosote and TBTO at the 250-ml-per-liter level were also 

 essentially free of fouling growth after 3 or more years of exposure in 

 the ocean at Port Hueneme (Figure 9). A panel treated with 100% creosote 

 was covered by a light growth of fouling organisms at the end of 3 years 

 (Figure 10) . 



The smoother side of panels made from aggregates impregnated with 

 mixtures of creosote containing TBTO at the 100-ml-per- liter level 

 (Systems 7, 9, and 10) were also relatively free of fouling organisms 

 (Figure 11). The rough side of the same panels was frequently covered 

 by a light growth of fouling organisms (Figure 12). This phenomenon 

 occurred frequently among the toxic concrete panels. One possible 

 explanation is that the toxic creosote mixture might have come through 

 the smooth surface more readily than through the rough one. Also, the 

 smooth side was the bottom side of the panel and during the setting of 

 the concrete the toxic mixture might have tended to concentrate at the 

 bottom of the mold. 



One of the special panels made with smooth tops and bottoms was 

 exposed in the ocean at Port Hueneme for 2 years. The aggregates from 

 which the panel was made were impregnated with a mixture of creosote, 

 TBTO at a level of 100-ml-per-liter , and other toxic chemicals (System 

 10). Except for a scant growth of brown algae, the panel was free of 

 fouling growth (Figure 13). 



Concrete panels made from aggregates impregnated with mixtures of 

 copper naphthenate and either a volatile solvent or creosote (Figure 14) 

 were covered by as heavy a fouling growth as the control panels contain- 

 ing no toxic chemicals. Coatings of either an epoxy compound or rubber 

 containing TBTO at the 100-ml-per-liter level also failed to prevent or 

 retard the accumulation of fouling organisms when exposed in the ocean 

 for 3 or more years. 



Summary of Antifouling Tests. Salient features of the antifouling 

 tests on concrete impregnated with various chemical mixtures are summa- 

 rized in Table 4. Mixtures of creosote and tributyltin oxide (TBTO) 

 were the most effective of the antifouling mixtures. Malachite green, 

 copper naphthenate, and quaternary ammonium compounds were ineffective. 

 Comparisons of the fouling on panels exposed at the undersea station at 

 depths of 600 and 120 feet and at near-surface exposure sites at Port 

 Hueneme, Point Mugu, and Guantanamo Bay, disclosed that as expected, 

 fouling is heaviest near the surface of the ocean. No comparisons were 

 made of the relationship of compressive strength and antifouling properties. 



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