Table 1. Comparison of toxic effects between Torrey Canyon era 

 and post-Torrey Canyon dispersants 



96 -h TLm (ppm) 

 Fathead minnow 

 Chemical {Pimephales promelas) 



Product A 6.1 



Product B 9.5 



Product C 5.3 



Product D 13.0 



Product E >10,000 



Clearly then, the statement that all chemical dispersants are in them- 

 selves highly toxic is incorrect. Table 1 does not represent an isolated 

 data point since more than 25 research institutions have conducted studies 

 that have verified the low toxicity of several chemical dispersants developed 

 after the Torrey Canyon incident. 



In addition to concern about the toxicity of the chemical itself, there 

 are also toxicological factors to be considered with regard to the dispersed 

 oil. Where the surface film of oil is dispersed several feet or more into 

 the water column, it is then available to other forms of marine life, in 

 addition to the hydrocarbon-oxidizing bacteria. Studies at Battelle Pacific 

 Northwest Laboratory (1973) have shown that the oil per se is not made more 

 toxic by the presence of the chemical dispersant. The dispersed oil is 

 merely made more available to the test species in lab bioassays; hence, 

 lab tests with chemically dispersed oil will show increased toxicity, compared 

 to oil that has not been chemically treated. 



However, it is important to consider the dilution effect of chemically 

 dispersed oil that is not apparent in the artificial environs of lab bioassays 

 with fixed-volume aquaria. In this regard, one of the most intensively 

 studied oil spills was that accompanying the blowout and fire in March 1972 

 at Chevron's Main Pass Block 41 Platform C in the Gulf of Mexico. A report 

 by McAuliffe et al . (1975) described in detail the effects of the oil spill on the 

 on the surrounding marine community. A total of 65,000 barrels of oil were 

 spilled from the platform, and the major portion of this spill was dispersed 

 by 2,000 barrels of chemical dispersant. Despite the large amount of oil that 

 was spilled, the maximum level of dispersed oil 1 mile (1.6 km) from the 

 platform was only 1 ppm, and there was no shore contamination. Extensive 

 trawl samples showed no alteration in the annual life cycle of commercially 

 important shrimp. Blue crabs were observed throughout the area, and the 

 number of species of fish collected was comparable to that collected during 

 a prior study. 



Of equal significance, because of the extensive activity during the past 

 2 to 3 years, is the effort to improve effectiveness, principally along 

 the lines of minimizing or eliminating mixing energy. This was probably the 

 key limitation to the large-scale application of chemical dispersants. For 

 example, to provide mixing after chemical application during the Torrey Canyon 

 spill, 42 workboats were employed. Despite this fact, a substantial amount 

 of oil still came ashore. 



84 



