PART X — ENVIRONMENTAL CONTAMINANTS 



thus, as they grow they unquestion- 

 ably transfer lumps of petroleum 

 residue to the sea floor by adding 

 weight. It is in all probability this 

 effect and not slight toxicity that 

 accounts for the observation that the 

 largest barnacles attached to oil lumps 

 were 8 millimeters long, whereas bar- 

 nacles attached to pumice reached 11 

 millimeters. 



The existence of floating pumice 

 itself suggests another possibility in 

 the transfer of floating oil to the sea 

 bottom. Floating pieces of pumice on 

 the sea surface are observed to de- 

 crease continually in size as the result 

 of abrasion through wave action. The 

 abraded particles in turn conceivably 

 can be accumulated by (or accumu- 

 late) petroleum particles to the extent 

 that the mixture is heavier than sea 

 water and hence sinks to the bottom. 



Surface Removal Through Bacterial 

 Action — The mechanism for removal 

 at the surface is bacterial oxidation. 

 Horn and his colleagues found oxy- 

 gen consumption of a floating oil lump 

 at 10 centigrade to be about the 

 equivalent of oxidation of 7 x 10 ° 

 g/hr"Vcm" L ' of petroleum. Since a 

 sphere has a surface: volume relation- 

 ship of 3/r, this observation tells us 

 that floating oil with a density of 1.0, 

 if divided into spherical particles of 

 radius 21 x 10 ,; cm, will be com- 

 pletely consumed in one hour at 10° 

 centigrade. One can reasonably ex- 

 pect this value to increase to 42 x 10"° 

 cm at about 18° and to double again 

 at about 26 centigrade. By the same 

 arithmetic, a film of oil 7 x 10"'' centi- 

 meters thick will be consumed in an 

 hour if the bacteria thrive only on 

 one surface at 10° centigrade, but in 

 half this time if they can attack both 

 surfaces at once. 



It may be more illuminating to 

 consider these rates in terms of years 

 (8,765 hours). At 10° centigrade, a 

 layer of oil attacked on only one sur- 

 face will be consumed at the rate of 

 0.6 millimeters per year. This figure 

 may be compared with Emery's 880 

 tons per 78,000 square kilometers in 



a year, which is about 1.1 to 10"'' 

 millimeters per year, or his 135,000 

 tons per year of petroleum-like sub- 

 stances produced by phytoplankton, 

 which is 1.7 to 10"'' millimeters. 



These rate computations allow us 

 to draw several conclusions. One is 

 that the practice of adding emulsi- 

 fiers to floating oil to facilitate its 

 dispersal into small units will also 

 facilitate its natural oxidation as long 

 as the emulsifiers are not bactericidal. 

 Another is that keeping the oil at the 

 sea surface, where ambient tempera- 

 tures are highest, will minimize the 

 time required for its natural oxida- 

 tion. And another is that oil will be 

 more persistent in polar latitudes than 

 in temperate or tropical latitudes. 

 Still another is that both "natural" 

 accumulations of petroleum compo- 

 nents in marine sediments and pro- 

 duction of similar compounds by 

 phytoplankton take place at rates 

 much below the "natural" ability of 

 the systems at the sea surface to 

 oxidize floating oil residues. 



Inasmuch as bacteria form an im- 

 portant food source for the ciliary and 

 mucus feeders in the marine plank- 

 ton, then, and since observation 

 shows that bacterial growth is en- 

 hanced in the presence of the combi- 

 nation of solid surface and source of 

 fixed carbon offered by floating oil 

 lumps, it seems inconsistent to refer to 

 their presence as "chronic pollution." 



Additional Sinking Agents — In 

 shallow coastal water, supposing that 

 oil is delivered to the sea surface at 

 a rate greater than that at which it 

 can be naturally oxidized, it seems 

 likely that airborne dust and other 

 solid residues will act as additional 

 agents in increasing the density of 

 floating oil and causing it to sink to 

 the bottom. A layer of tarry residue 

 will then exist on the bottom in such 

 localities, its thickness increasing with 

 time at a rate equal to the rate of 

 delivery of oil minus the rate of oxi- 

 dation in situ. Such layers can indeed 

 be observed on the bottoms of indus- 

 trial harbors. 



Needed Scientific Activity 



Although present knowledge tells 

 us that, at least in some cases, no 

 harmful effects can be attributed to 

 the presence of petroleum on the 

 sea — the sea off southern California, 

 for all its dozens of oil seeps, is one 

 of the more productive fishery areas 

 in the world — it would be a mistake 

 to assume that we already have all 

 the information required to settle the 

 question of whether oil on the sea 

 floor is preferable to oil at the sea 

 surface. For one thing, crude petro- 

 leum varies widely in its chemical 

 makeup. We need, therefore, to ex- 

 amine the relative toxicity of crudes 

 from a variety of sources to marine 

 plants and animals, pelagic and ben- 

 thic. We need also to examine the 

 rate of bacterial oxidation of various 

 crudes and to establish the effect of 

 temperature on these rates. 



We need also to study bottom con- 

 ditions in the vicinity of oil terminals 

 and tidewater oil refineries as com- 

 pared with control areas lacking such 

 industrial activity to determine the 

 extent to which areas of the ocean 

 floor have already undergone the type 

 of modification that has been ob- 

 served in New York's East River — 

 where there is a thick layer of "black- 

 top" in the vicinity of the Brooklyn 

 Navy Yard — and the influence that 

 incorporation of petroleum residues 

 into bottom sediments has had on the 

 benthic biota. And we need to map 

 the various areas of the continental 

 shelves and slopes of the world, down 

 to the depth below which bottom 

 conditions are without influence on 

 fisheries, and to evaluate their pro- 

 ductivity in terms of current fishing 

 operations. 



At depths greater than about 750 

 meters, the sinking method of oil dis- 

 persal can presumably be used with- 

 out fear of harmful effects. Over 

 lesser depths, where important de- 

 mersal fisheries exist, only laboratory 

 studies of the effect of sunken oil 

 on the biota can provide pollution- 



362 



