OIL SPILLAGE INTO WATER—TREATMENT 813
comparison, the Toxicity levels of three dispersant products
developed since the Torrey Canyon, identifi ed as Post Torrey
Canyon, Dispersants D, E, F, are 7500–10,000; 3300–10,000;
and >3300 ppm, respectively. These concentrations are
orders of magnitude greater than the level applied by con-
ventional application in the fi eld.
Other agencies have confi rmed this fi nding. Table
4 illustrates results of a recent study by the Fisheries
Research Board of Canada entitled, “Toxicity Tests withOil Dispersants in Connection with Oil Spill at Chedabucto
Bay N.S.”^36 Again, the large difference in toxicity due to
the surfactant-solvent recipe can be noted in the sum-
mary of results (Table 4). These values represent 4 day
LC 50 values in fresh water to Salmon (Salmo salar L) and
vary from “Toxic” (1–100 ppm) to “Practically non-toxic”
(>10,000 ppm). Over 25 research institutions are known
to have conducted studies on these lower toxicity chemi-
cals. Testing by Dr. Molly Spooner, 37,38 among others, has
encompassed juvenile species, planktonic life and other
very sensitive forms of marine life.
Clearly then, the concern and conclusion that all chemi-
cal dispersants are in themselves inherently toxic is incor-
rect. Some of the most effective emulsifi ers/dispersants
available are those derived from and found in the natural
environment.The Toxic Effects of the Dispersed OilWhen the surface fi lm of oil is dispersed several feet or
more into the water column, it is unfortunately made avail-
able to other forms of marine life in addition to the hydro-
carbonoxidizing bacteria. Necton and other fi ler feeder
many now come into contact with dispersed oil droplets
that they otherwise may have escaped as surface oil. This
is, effect, the “ecological price” for the cited benefi ts of
dispersing oil. There are published data on the acute tox-
icity levels of dispersed oil such as that from the State of
Michigan^39 presented as Table 5. This does indicate an
approximate tolerance level of a thousand ppm or more
for dispersed oil. It can also be noted that the toxicity of
the chemical is refl ected in the toxicity level of 1000 ppm
or so for dispersed oil, however it should be noted that
(1) it is unlikely that fi sh would remain in this inhospitable
environment for 96 hours and (2) the dispersed oil has a
driving force to dilute itself. Of greater concern than these
short term acute effects is the possibility that the fi nely
dispersed oil droplets represent a more subtle contaminant
and may cause long-range detrimental effects. However, it
should also be noted that crude oil is a natural rather than
man-synthesized material. Wheeler North^40 reported after
extensive research into several spill incidents, “Unlike
many of the products man liberates into the environment,
crude oil is a naturally occurring substance. From time to
time it appears on the earth’s crust by natural processes of
exudation.”More Recent Dispersant Research Has Involved
Improvement in EffectivenessThe previous discussion regarding the dispersion mecha-
nism cited the need for mixing energy, W k. This is normally
supplied by means of a work boat applying the chemical.
However, consider the rate by which this work is accom-
plished by the boat’s wake and propeller. A typical work
boat may apply energy to swath 50 ft wide at a speed of
5 knots thereby only mixing 35 acres per hour of ocean.TABLE 3
Development of low toxicity dispersants illustrated by Portmann StudyChemical48 hour LC 50 , ppm brown
shrimp (Crangon Crangon)Torrey Canyon Dispersant “A” 8.8
Torrey Canyon Dispersant “B” 5.8
Torrey Canyon Dispersant “C” 6.6
Post Torrey Canyon Dispersant “D” 7,500–10,000
Post Torrey Canyon Dispersant “E” 3,300–10,000
Post Torrey Canyon Dispersant “F” 3,300
Nonyl Phenol-Ethylene Oxide 89.5TABLE 5
Toxicity of dispersants with and without crude oilChemical 96 hour TLM, ppm Fathead minnow
(Pimephales promelas)Dispersant A 5.6
Dispersant A oil 14.0
Dispersant B 14.0
Dispersant B oil 27.0
Dispersant C 25.0
Dispersant C oil 42.0
Dispersant D 32.0
Dispersant D oil 44.0
Dispersant E 56.0
Dispersant E oil 75.0
Dispersant F 3200
Dispersant F oil 1800 TABLE 4
Summary of Canadian Fish. Res. Bd. evaluation of 10 dispersantsClassification Numbers of dispersants48 hour LC50, ppm
Salmon
(Salmo Salar L)
Toxic 8 1–100
Moderately toxic 1 100–1000
Slightly toxic 0 1000–10,000
Practically non toxic 1 10,000C015_002_r03.indd 813C015_002_r03.indd 813 11/18/2005 10:56:41 AM11/18/2005 10:56:41 AM