"Economic 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

Alexander Leonov

Composition 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 [35].
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 [1].
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 [36].
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 [37]. 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 [36].
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 [44]. 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, 50].
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 [51] 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 [1].
Higher 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 [1]:
  1. alkanes - paraffin (acyclic) saturated hydrocarbons with direct or branched chains of C atoms (40 to 50% of volume);
  2. naphthenes (cycloparaffins) - saturated cyclic and polycyclic compounds in which H atoms may be replaced by alkyl groups (25 to 75%);
  3. 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%);
  4. 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 cracking).
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 [52].
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 [2]. 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 [53] 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.