Oil Spill Incidents and Application of DispersantsHiroshi Tokuda
Ex Professor of the University of Tokyo

It is said that the first large scale application of dispersants was at the Torrey
Canyon Incident, which happened to run aground and released crude oil, as a cargo, of93,000 kl at the Scilly Island off Cornwall Peninsula, UK, in March 1967. Dispersantswere adopted for both floating oil slick on the sea and coastline for cleaning. The latter
application gave a serious affection to marine organisms in shallow waters. This
information generated a rumor that dispersants are deadly poisonous, and scattered toin our country. As a result, many people, especially people who belongs to fishery got apotential rejection towards dispersants. The application of different kind of chemicals,
namely dispersants and precipitants, made a misleading that every chemicals to use foroil spill made sediments containing oils and reached to the seabed, though thefunctional mechanism of those two chemicals is completely different. And
unfortunately enough, many people in the country believed that misleading.
The first application of dispersants to oil spill incident in Japan was at the Juliana
Incident, which happened to occur off Niigata Port in November 1971. The volume ofspilt oil, Oman crude, after wreckage, was estimated to be 7,200 kiloliters. At that time
period, there was no firm application procedures of dispersants to cope with spilt oil,nor regulatory arrangement for dispersants regarding to the toxicity for marineorganisms. A procedure undertaken was to directly drop 5 gallon-cans(18 literscapacity) with their lids open, from helicopter, upon the oil slicks on the sea. As a result,observed many empty cans scattered on the shoreline of the spill site. Though it washard to know what was the brand of despersant actually applied, some products in themarket contained 100% pure aromatic hydrocarbons as the solvent, so that they could
kill phytoplankton even at the concentration of several ppm by its high toxicity formarine organisms.

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In 1973, a regulatory arrangement so called " Model approval and registration
system , in which specified limitation for toxicity against marine organisms, degree ofbiodegradation, degree of emulsification etc., was enacted. Then we were able to getreasonably safe and indicating performance. With implementation of this system as aturning point, dispersants manufacturers made efforts for developing low toxicproducts. Thus, dispersants manufacturers in Japan became the ones indicating lowest
toxicity in the world. However, though those dispersants did satisfy the criteria set for
the regulation, emulsifying efficiency was getting decreased. Actually, thosedispersants did not well perform even if sprayed exceeding a deemed proper amount of20〜25%; this means, if sprayed amount is in the range of deemed one or less thandeemed proper amount, slicks can not be cleaned off.
On the other hand, there also seemed to be problems on the application procedure of
the despersants against to the oil slicks. Generally speaking, to get deemed
performance, many dispersant products should be sprayed directly on to the oil slicks,
while other approach, for example, application of diluted dispersant mixture with sea
water do not indicate effective dispersion. Regardless of such characteristics of thedispersant products, procedures applied for operations were spraying sea watersolution of the dispersants to the slicks with pick-up nozzle and applied mechanicalagitation. Those dispersants mentioned above, have been called conventional type" inthis country. After that, so called concentrate type" products which are rich indispersant and less in solvent have been developed and put into market. However, sincethese were also required mechanical agitation after spraying, it would be the same
category of the conventional type ones.
The above mentioned dispersants can emulsify and disperse spilt oil on the sea
surface very effectively when its kinematic viscosity is below 2,000 cSt. The more
kinematic viscosity is, the less the effect is. 4,000 cSt is considered the limit for being
emulsified and dispersed. However, heavy fuel oil is most likely to be spilt in theincidents around Japan. In Japan, the efficiency of dispersants has been decided byusing Fuel Oil B as the testing oil by law(mentioned above as "Model approval andregistration system" ), 50 the products effective for more viscous oil have not beendeveloped. Moreover, Fuel Oil B has been little demanded recently and is not producedanymore. Due to the situation mentioned above, there was an urgent need to develop
dispersants that are also effective to highly viscous oil. Last November, D-1128, the2dispersants for highly viscous oil were developed in Japan for the first time. These
dispersants were confirmed to be able to fully emulsify and disperse spilt oil in thelaboratory test only when agitating is done after being sprayed. Adequate spraying rate
was equal to 5% or less to the oil amount in case of its kinematic viscosity of below
10,000 cSt. Similarly 6% for 10,000 cSt, 5% for 50,000 cSt, and 10% for 100,000 cSt.
When the Nakhodka incident occurred in the Sea of Japan this January, thesedispersants for highly viscous oil were applied as a test. The properties* of spilt oil wereas follows: specific gravity of 0.959 at 20℃ kinematic viscosity of 137.5 cSt at 50℃ and10,000〜15,000cSt at 10〜8℃ (estimated), and pour point of -17℃. It was confirmedthat the dispersants for highly viscous oil were very effective when spilt oil containedlittle water. However since oil slick gradually absorbed water to change to oilmass(mousse like oil) which had 70% of water content and 10℃ of pour point, thedispersants were no longer effective. The reasons are considered as follows: fine waterparticles in the oil mass prevented the dispersants from penetrating and sprayeddispersants can not directly get to the oil mass because their specific gravity become
closer to that of seawater, which covers the surface of oil. From now on, I hope these
problems will be solved and efforts for improving performance will be made.
To response spilt oil off the coast quickly, it is necessary to spray dispersants to oil
slick from aircraft. To accomplish this, the dispersants are required to change oil slick
to fine particles and disperse them into seawater without agitating. This characteristic
is called "Self-mixing." For this purpose, the dispersants contain the amphiphilic
solvents that are mixable with water and oil. However, due to high toxicity of thesolvent for marine organisms, the dispersants are more toxic for them thanconventional type ones. Since the amount necessary to be effective is less than one fifthof that of conventional type ones, it is possible to approve the use of the dispersants forsprayring from aircraft as long as the usage is limited in the offshore, even thoughthose are more toxic than conventional type ones. In Japan, development of much lower
toxic dispersants for aerial spraying is under way.

* Note by the translator : There are several figures for the properties of the spilt oil
by different sources. However, official figure has not been issued as of July 1, 1997.

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(Reference)① Comparison of specifications for fuel oil② JIS Specification for fuel oil