Development and the Environment"
on the Sakhalin Offshore Oil and Gas Fields II
Copyright (C) 1999 by Slavic
Research Center, Hokkaido University.
All rights reserved
Oil and Gas
Development on the Sakhalin Island Shelf: An Assessment of Changes in
the Okhotsk Sea Ecosystem
of Oil in a Marine Environment and Sediment
- At the end of the
1970s, an international project to monitor petroleum pollution was
carried out [33, 34]. Data from visual observations (about 100,000) and
chemical analyses of marine water samples (several thousands) from all
regions of the world's oceans were analyzed. The presence of dissolved
and emulsified oil hydrocarbons in surface waters in concentrations of
up to several µg/l (and in regions of increased petroleum
pollution - up to several mg/l) was revealed everywhere. Many instances
of floating petroleum aggregates and petroleum films (slicks), which
covered 0.5% of surveyed oceanic surfaces, were found .
- Generally, increased concentrations of oil
pollution were found in the bottom sediments of river mouths and
deltas, estuaries, bays, inlets, ports and in regions used for
navigation, extraction and transportation of oil .
- During the last 10
to 15 years, there has been a decrease in the severity of marine
pollution as a result of stricter international rules for the disposal
of oil-containing ship sewage and ballast waters of oil tankers.
However, marine environment pollution by oil products remains a serious
threat. In this environment, highly toxic water-soluble particles of
oil products dispersed as separate "drops" are present.
- According to observations made in 1993 in the
Okhotsk Sea, the average concentration of dissolved aliphatic
hydrocarbons (DAH) and polycyclic aromatic hydrocarbons (PAH) varied in
the range of 15 to 33 µg/l and 5 to 12 ng/l respectively. In
bottom waters, the content of aliphatic hydrocarbons in suspended
substances reached 68% of its total mean value. The background value of
DAH in the Okhotsk Sea was accepted at about 20 µg/l. In the
north-eastern part of the Sakhalin Island Shelf, the mean content of
DAH was 10 times higher (202 µg/l) and in certain cases reached
2172 µg/l owing to local petroleum pollution in the region. The
increased content of oil hydrocarbons in the marine water of this
region is related to natural infiltration from sedimentary rocks.
Structural analysis of the permeating DAH showed their strong
similarity to crude oil in the sediment .
- Mean and maximum
concentrations of oil hydrocarbons in bottom sediments of the
northeastern part of the Sakhalin Island Shelf were 0.08 and 0.18 mg/(g
dry weight) respectively, and these values were higher than in waters
off the Kamchatka Peninsula Shelf and in coastal sediments of the
Pacific Ocean .
The distribution of oil hydrocarbons may vary in regions influenced by
the local inputs of the oil. The content of oil substances in the
surface micro-layer always exceeds (up to 10 times and higher) their
content in the water column. In the surface water micro-layer of the
northeastern part of the Sakhalin Island Shelf, the concentrations of
DAH and PAH were on average 0.574 mg/l and 5032 ng/l respectively .
- The Toxic Influence of Oil
and Its Products on Marine Flora and Fauna
- Oil and its products belong to a group of
toxicants made up of complex structures that have various effects on
living organisms from physiological damage up to cancerous effects. In
the literature on marine toxicology, there are many studies related to
questions on the degree of biological danger from oil pollution ranging
from studies which report an absence of harmful effects (in water with
an oil concentration of approximately several mg/l), to studies which
show damage to the vitality of aquatic organisms even in the presence
of small amounts of dissolved oil hydrocarbons (in the hundredth and
thousandth parts per mg/l) [9, 28,38-43], and oil-spill dispersants
. Different opinions may also be found on the ecological
consequences of oil spills and the influence of low concentrations of
chronic oil pollution on aquatic organisms [35, 45-49]. The reaction of
marine biota (algae, macrophytes, crustaceans, mollusks, benthos, fish)
even to low concentrations of oil hydrocarbons (< 0.001 - 1 mg/l) in
marine water is rather diverse, and on the whole, a decrease in the
population and mortality aquatic organisms has been demonstrated [1,
- One method of
assessing the toxic influence on aquatic organisms is based on the LC50
determination (or a substance concentration causing the death of 50% of
the number of organisms in experiments with a duration of 24 to 96
hours). In the majority of experiments conducted, the values of LC50
for different types of drill solutions were within the range of 10 to
100 g/kg which corresponds to their dilution of 1 to 10%. The exception
is made for drill solutions prepared on the basis of diesel fuel for
which the LC50 value is much lower and can reach the threshold value
0.1 g/kg. This has formed the basis for the limitation (and sometimes
prohibition) in the use of oil-based drill solutions and their gradual
replacement by water-based ones and other solutions (without including
oil and other toxic substances in their structure).
- Some ideas about the LC50 values of dissolved
hydrocarbons for aquatic organisms and the correlation of this
parameter with the size of biota may be found in Fig. 1 and 2:
they show the general tendency of increasing the sensitivity and
vulnerability of small-sized forms of aquatic organisms (including the
embryonic and larval growth stages) to the presence of toxic admixtures
(namely oil hydrocarbons).
- There are a wide
range of toxic and threshold concentrations of dissolved oil (mainly
hydrocarbons) for investigated aquatic organisms (Fig. 3). The increased sensitivity to the
presence of oil is found in the majority of investigated fish  and
invertebrates in the early stages of their growth. The toxic
concentration which causes the destruction of organisms or irreversible
damage to vitally important functions, for caviar (embryo), larvae and
fingerlings of marine animals is usually much lower than for adults and
reaches minimum values of 0.01 to 0.1 mg/l.
- Benthos and demersal forms (including many
kinds of fish living in constant contact with the polluted sediments)
are especially vulnerable. The bottom fish show tumors, mutations and
diseases of cancerous character when the concentration of some DAH in
sediments is in the range of 3 to 5 mg/kg or higher.
- The maximum value
of harmless concentrations of dissolved oil hydrocarbons is about 0.001
mg/l. These concentrations are usually found in waters remote from the
coast, in pelagic regions of oceans and seas, not subject to the
effects of oil pollution.
- Oil concentrations in the 0.001 to 0.01 mg/l
range can be viewed as a zone of reversible threshold effects. These
concentrations are found in relatively clean pelagic and coastal
waters. The possible primary (basically physiological and biochemical)
reaction of biota to similar concentrations is evidence of the presence
of oil hydrocarbons. The permissible content of oil hydrocarbons in
marine water is just in this range .
concentrations of oil products (0.01 to 1 and above 1 mg/l) result in
sublethal and lethal effects. They may be found in bays, estuaries,
port harbors and bays with slow water exchange and increased
concentrations of chronic oil pollution, as well as in areas with
emergency spills of the oil, sewage discharges, etc.
- The ranges of toxic and threshold
concentrations of oil products are shown in Fig.
4 for organisms inhabiting sediments.
- The Composition of Oil Components in a Marine Environment
- From the chemical
point of view, oil is a complex mixture of several thousand
hydrocarbons (basically liquid, accounting for 80 to 90% of the mass)
with a mixture of derivatives containing sulfur (mercaptans,
thiophenes, disulfides, thiophanes and others), nitrogen (homologues of
pyridine, acridine, hydroquinol and others) and oxygen (naphthenic
acids, asphaltites, resins and others). Crude oil also contains water
(up to 10%), dissolved hydrocarbon gases (up to 4%), mineral salts
(mainly, chlorides - up to 4 g/l) and many microelements whose
concentration ratios (more often vanadium and nickel) serve as
additional characteristics regarding the origin and properties of oil.
Four groups of compounds are usually allocated among oil hydrocarbons
- alkanes -
paraffin (acyclic) saturated hydrocarbons with direct or branched
chains of C atoms (40 to 50% of volume);
- naphthenes (cycloparaffins) - saturated cyclic and polycyclic
compounds in which H atoms may be replaced by alkyl groups (25 to 75%);
- arenes - aromatic unsaturated cyclic compounds from the
benzene order where the H atoms may be also replaced by alkyl groups
(usually up to 10 to 20%, rarely up to 35%);
- alkenes (olefins) - unsaturated acyclic hydrocarbons with
direct or branched chains and double connection C=C (the compounds of
this group are not part of crude oil but are the main product of its
- Oil's properties
are exhitibted in their ability to exist in a water environment in
several aggregate states: surface films (slicks); dissolved forms;
emulsions ("oil in water" and "water in oil" type); suspended forms
(black oil aggregates floating on the surface and in water mass, oil
fractions absorbed in particulates); solid and sticky components
settled at the bottom; compounds accumulated in aquatic organisms.
- Long-term observations in the Baltic Sea showed
that 3.6% of the total amount of the oil is in the film state, 0.4% is
adsorbed as rough suspension, 15% is accumulated in bottom sediments,
64% is emulsified, and 17% is found in a dissolved state .
- Oil and oil
products flowing in water rapidly cease to exist in the initial
substrate. Their fate and biological action in water ecosystems are
determined by natural and physiochemical properties, mainly by
volatility (vapor pressure), gravity and solubility in the water.
Almost all components of crude oil and its fractions have a density
less than 1 g/cm3, and the majority of
them may be dissolved to a certain degree. Simultaneously, the
evaporation of easily volatile fractions takes place.
- In conditions of chronic oil pollution,
emulsified oil is frequently the dominant oil fraction. It is
determined by the action of hydrodynamic factors (wind patterns and
others) and by the prevailing method of oil entry and by the presence
of large molecular compounds (promoting self-emulsification).
- The basic mass of
Sakhalin Shelf oil has following characteristics: specific gravity -
0.85 g/sm3 (light); paraffin content -
0.15 to 4% (low-and-mean-paraffin); sulfur content - 0.09 to 0.4%
(low-sulfur); gas content - 100 to 150 m3/t
(completely saturated; free gas has a methane composition; the amount
of condensed gas is 30 to 150 g/m3);
the amount of oil-asphaltic compounds - 1.5 to 6% (low); contents and
ratios of metals (V, Ni, Fe, Mo) vary . As a whole, three groups of
oil on the Sakhalin oil field with different ratios of metals can be
differentiated (Table 5).
- The distinctive properties of oil from the
Sakhalin Island Shelf are important from the environmental viewpoint:
light oil fractions dissolve better in water  and are quickly
assimilated by microorganisms; oil with a low sulfur content should
have a comparatively less aggressive influence on pipeline material
than oil with a high sulfur content.