Generally, the TBTO and TBTO/creosote caused necrosis, followed eventually 
by cellular disassociation. This effect is similar morphologically to 
that of elevated temperature (Ref 14). Methoxychlor caused abnormalities 
in developing body parts. After 32 hours, death occurred in all cases 
where toxicant was present. The development of larvae in pails which 
contained the duplicate set of controls continued normally for 7 days, 
after which the experiment was terminated. 
DISCUSSION 
Cost of Materials 
Toxicant cost varies greatly from one system to another. Because 
an OTEC plant will use a large amount of concrete, the cost of the 
material chosen as an antifoulant will be a major consideration. A 
comparison of the raw material cost of the various toxicants employed in 
this investigation is given below in 1979 dollars: 
Treatment Cost 
TBTO ($/1b) 6E55) 
Creosote ($/1b) 0.10 
Cu,0 ($/1b) 1.30 
Methoxychlor ($/1b) 1.40 
TPTH ($/1b) 8.16 
Nofoul rubber, 0.08 in.-thick ($/ft?) 4.85 
Organotin polymer ($/gal) 50.00 
One of the better toxicant systems employs 60% TBTO and 40% creosote 
impregnated into aggregate. Because of the high cost of TBTO relative 
to creosote, concrete containing a higher ratio of creosote to TBTO 
should be considered. It is worth noting that 100% TBTO is a less 
effective antifoulant than the TBTO/creosote mixture employed. The 
immediate conclusion is that the creosote provides antifouling properties 
not present in TBTO alone. It has been observed, however, that concrete 
specimens prepared with TBTO/creosote and left in a fog room for a few 
months become covered with a layer of toxicant that has oozed from the 
concrete. This phenomenon is not observed in specimens prepared using 
TBTO alone. It may be that the creosote acts as a vehicle for the TBTO, 
allowing it to move more readily through the concrete to the surface 
where it is effective as an antifoulant. This phenomenon is considered 
of great importance (Ref 15). If this is the case, other solvents may 
be even more effective. 
The cost of toxicant in concrete prepared using only TBTO at 8%, 
based on the weight of the other constituents, is $65/ft?. When TBTO/ 
creosote is used at 60/40, the cost is $40/ft?. This is significant 
both from the standpoint of reducing cost and from the standpoint of 
better antifouling properties. Further dilution of TBTO by creosote 
10 
