Outline of PAJ Study Program on Self-cleanup mechanism ofOcean for Spilt Oil

Yoshkuni YakabeChemicals Inspection & Testing Institute, Japan

1. Introduction

The oil spilt in ocean is evaporated, dissolved and emulsified in sea water and lead tomousse as it spreads and drifts on sea surface at the early stage of oil spill. A part ofthese spilt oil is recovered by skimming operation, but the remainder is dispersed inocean or is drifted ashore. The remaining oil in ocean is supposed to be cleaned up fromocean in a long time by biotic and abiotic degradation with marine microorganism,light and oxygen. The rate of each of these cleanup processes has been estimated fromthe field study on the spilt oil.
PAJ started the study program on Self-cleanup mechanism of ocean for spilt oil at
1994 in the purpose to elucidate the self-cleanup mechanism of ocean for the spilt oilfrom more systematic investigations on various processes participating in the cleanupof the spilt oil in ocean and to propose more effective method utilizing the naturalcleanup function to clean up the spilt oil. In this presentation, the overview of thestudy is shown.

2. Methodology

Various processes are participated in the cleanup of the spilt oil in ocean. It isimportant in elucidation of the self-cleanup mechanism of ocean for the spilt oil tomake clear how and to what extent each process contribute to the cleanup of the spilt
oil in ocean and what affect it. In the study they are examined separately by thelaboratory experiment of each process. However the results of the laboratory1experiments are not necessarily applied directly to natural phenomena because manyfactors affecting these processes come into play simultaneously in natural ocean.
Hence the field study is carried out in order to verify the results of the laboratory
experiments and to recognize the cleanup mechanism of ocean for the spilt oil from theviewpoint of each process participating in the cleanup by relating the results of thelaboratory experiments to those of the field study.

3. Outlines of each study

The laboratory experiment is separately conducted with each of environmental
distribution, bioaccumulation, biodegradation and abiotic degradation of crude oil. In
the field study, the analyses of residual oil and biota on seashore are carried out. Theoutline of each study is as follows:(1) Study on environmental distribution of spilt oil

The spilt oil is distributed among water, air and oil phases according to its physicochemical property of the oil at early stage of oil spill as it spreads and drifts on sea
surface. Subsequently a part of the oil drift ashore and adsorbed to bottom sediment on
seashore. These processes are thought to be strongly affected by natural conditions
such as wind,wave and nature of the bottom sediment. In the study, the rate andextent of the distribution among water, oil and air phases is measured by thelaboratory

experiment in which crude oil or crude oil/oil dispersant mixture is put on

surface of artificial sea water with generating small wave to evaluate thecontribution of the process to cleanup of spilt oil.

2(2) Bioaccumulation

The spilt oil dissolved or emulsified. in sea water is accumulated in sea organism andsubsequently it apparently seems to elminate from sea as the spilt oil is cleaned up
from ocean. Therefore the bioaccumulation is used as an indicator to monitor theextent of cleanup of the spilt oil. There are two routes of uptake of chemical substanceorganism in general;i.e. ,direct uptake through gill and uptake from diet. In this study,
the rate and extent of the uptake and elimination of the spilt oil by fishes andshellfishes are investigated. In addition, the conducted a test concerning to smell ofpolluted fishes in order to examine the acceptability as a marine product.

(3) Biodegradation

Biodegradation is most important process to clean up the spilt oil dispersed in ocean
or drifted ashore in long time. In this study, the laboratory experiments are conductedwith weathered crude oil using natural sea water or natural sea water/costal bottom
sediment mixture as testing sample to evaluate the rate and extent of biodegradationof spilt oil in sea water or drifted ashore, respectively. We conducted two categories oftests. One is to measure the "Ultimate" decomposition of oil, which is the stateachieved to transform the oil to carbon dioxide and water. And other is to measure thedegree of degradation by various crude oil sources. The aim of those measurmants is toclearize the effect of dispersant towards the rate of cleanup of spilt oil through testing
various wheathered crude oil/mixture of weathered crude oil and dispersant,withvarious sea water.

(4) Abiotic degradation

The abiotic degradation in long term by sunlight and oxygen is the another important
process of the cleanup of spilt oil. The contribution of these process to the cleanup of3

the spilt oil is examined by laboratory experiment.

(5) Field study

In the field study, the residual oil and biota in the oh-polluted site and the nonpolluted reference site(as a blank)are analyzed andcompared between bothsites to verify the results from the laboratory experiments andto get more reliable mechanism of the cleanup for the spilt oil in ocean andfurthermore to evaluate the rate and extent of the cleanup at the site of oil pollution.

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