Oils and petrochemicals
Entry into the marine environment
Whitehead (1983) describes crude oil as a complex
mixture of many compounds comprising mainly compounds
of hydrogen and carbon. The composition of crude
oil is very variable and all types will contain
different quantities of the many different hydrocarbons
together with quantities of sulphur, oxygen, nitrogen
and traces of metals. Crude oil is variously described
as light, medium or heavy, sweet or sour (containing
hydrogen sulphide), paraffinic (light), asphaltic
(heavy) or mixed (aromatic) base oil, dependent
largely on the dominant proportion of hydrocarbons.
The hydrocarbons present in crude oil can range
from aliphatic (straight chain) compounds to more
complex aromatic (containing a benzene ring) and
polynuclear aromatic (containing two or more benzene
rings) compounds. Hydrocarbons can be present in
the full range of physical states from gaseous through
liquids to solids. Heavy crude oils have a greater
proportion of long chain aliphatic hydrocarbons
than light crude oils where short chain aliphatic
compounds predominate. Aromatic compounds predominate
in medium (mixed base) crude oils.
Refining of crude oil produces a range of products,
ranging from lubricating oils and waxes, asphalts
and heavy fuel oils through aviation fuel, diesel
fuel and heating oils to gasoline and liquid petroleum
gases. Other processes can be used to create a wide
range of petrochemicals, including familiar hydrocarbons,
such as propylene, acetylene, benzene, toluene and
GESAMP (1993) estimated that 2.35 million tonnes
of oil per year entered the marine environment from
all sources. At least 15% comes from natural oil
seeps. Anthropogenic sources include chronic discharges
from storage facilities and refineries, discharges
from tankers and other shipping along major routes
and accidental events, such as oil spills and ruptures
of pipelines. Sources also include river-borne discharges,
diffuse discharges from industrialised municipal
areas, offshore oil production (e.g. drilling, transport,
refining and burning of oil and petrochemicals)
and the atmosphere. Locally, an important source
is the exhaust from outboard engines.
Elliott and Griffiths (1987) classify sources of
hydrocarbons to the Forth estuary as petrogenic,
pyrogenic and biogenic (see table below) and this
classification is probably applicable to oils and
petrochemicals in the marine environment.
Petrogenic sources tend to be point sources of
oil and petrochemicals, whereas pyrogenic and biogenic
inputs are considered as diffuse sources .
Sources of oils and petrochemicals or by-products
to coastal waters (from Elliott and Griffiths (1987))
Production waters from oilfields
Tanker ballast water
Storm water discharges
Leisure craft powered by outboard engines
from incomplete burning of fossil fuels/peat/wood
in domestic and industrial plant
and terrestrial inputs
In-situ diagenic production of hydrocarbons
by chemical and microbial processes
In the UK, 14 of the 155 estuaries studied as part
of the Estuaries Review (Davidson et al 1991)
had oil refineries on them in 1989, including the
Forth, Humber, Thames and Mersey. Nineteen of the
155 had import/export jetties and single point moorings
and were therefore at risk from tanker related spillages.
Oil spills in estuaries vary in size and their impact
depends on the amount and type of oil involved.
Elliott and Griffiths (1987) reported six spillages
of heavy oil or diesel in the Forth estuary between
1970 and 1978, with only minor incidents up to 1987.
In 1983, 6,000 tonnes of crude oil were released
in to the Humber estuary at Immingham (the Sivand
oil spill) (NRA, 1993). The Mersey estuary received
150 tonnes of crude oil from a fractured pipeline
in 1989 and in 1996 the >Sea Empress=
released 72,000 tonnes of crude oil in Milford Haven.
Oils and petrochemicals also form part of municipal
discharges as a result of road run-off, domestic
usage and the licensed discharge of small quantities
to sewer. Oils and petrochemicals are therefore
found in sewage and storm water discharges, either
directly into the estuary or into the freshwater
Pyrogenic sources of petrochemicals enter estuaries
either directly or indirectly from atmospheric deposition
and, although this is technically a diffuse source,
deposition is likely to be greater in the footprint
of point sources to the atmosphere, such as coal-fired
power stations. The burning of fossil fuels is a
major source of polynuclear aromatic hydrocarbons
(PAHs) into the environment (see Section B46).
Biogenic sources of hydrocarbons can be generated
in estuaries where sediment deposits accumulate
and microbial and chemical conditions are appropriate.
Recorded levels in the marine
The concentration of oil in the environment and
in the biota is measured in a number of different
ways, including total hydrocarbons, total aliphatic
hydrocarbons, total aromatic hydrocarbons, persistent
oils and grease. The use of these different parameters
hinders spatial comparisons.
Fate and behaviour in the marine
Various reviews on the fate and weathering of petroleum
spills in marine waters have been conducted (Jordan
and Payne 1980; Marine Technology Society 1984;
Lange 1984; Kuiper and van der Brink (1987). The
persistence of oil depends on the type of oil; the
season, the geomorphology of the coast and the degree
of exposure (GESAMP 1993). SEEEC (1998) review the
fate of oil in relation to the Sea Empress oil spill.
Effects on the marine environment
Oil and petrochemicals exert impacts on the environment
through both physical and chemical (toxic) means.
Long-chain aliphatic hydrocarbons are effectively
solids and exert their effects by physical means,
coating surfaces and smothering organisms. Short-chain,
low boiling point compounds, unsaturated compounds
and aromatic hydrocarbons exert their effects by
primarily chemical (toxic) means. The overall impact
of a discharge of oil or petrochemical on the environment
is dependent on the distribution and composition
of the petroleum hydrocarbons, especially their
weathering, persistence and consequently their bioavailability
Effects differ in open waters and in enclosed systems.
In open waters, the action of waves and currents
can decrease concentrations of contaminants rapidly.
In enclosed systems, such as estuaries, the potential
for dispersion is not so great and, on shorelines,
a number of factors determine its persistence: properties
of the oil, porosity of sediments, presence of animal
burrows, wave action and type of vegetation (GESAMP
1993). The table below summarises the vulnerability
of different coastal habitats and ranks them in
order of vulnerability.
Vulnerability index of shores (in order of increasing
sensitivity to oil damage, adapted from Gundlach
and Hayes (1978))
reflection keeps most of the oil offshore. No
swept. Most oil removed by natural processes
grained sand beaches
oil does not penetrate into the sediment, this
facilitates mechanical removal if necessary.
Otherwise, oil may persist for several months.
However, penetration can occur, depending on
water table movements in sediments.
may sink and/or be buried rapidly, making clean-up
difficult. Under moderate to high-energy conditions,
oil will be removed naturally from most of the
compacted tidal flats
oil will not adhere to, nor penetrate into the
compacted tidal flat. Clean-up is usually unnecessary.
sand and gravel beaches
may penetrate the beach rapidly and become buried.
Under moderate to low-energy conditions, oil
may persist for years.
as above. Clean-up should concentrate on high
tide/wash area. A solid asphalt pavement may
form under heavy oil accumulations.
of reduced wave action. Oil may persist for
many years. Clean-up may be necessary although
the sensitivity of the area should be taken
of great biological activity and low wave energy.
A number of interpretations of the >biological activity= are possible.
In this case, it is taken to mean a combination
of high productivity, biomass and possibly bioturbation.
Oil may persist for years. Clean-up is not recommended
unless oil accumulations are heavy. These areas
should receive priority protection by using
booms or oil absorbing materials.
most productive of aquatic environments. Cleaning
of saltmarshes by burning or cutting should
be undertaken only if heavily soiled. Protection
of these environments by booms or absorbing
material should receive first priority.
SEEEC (1998) review the effects of the Sea Empress
oil spill on marine communities.
A number of projects assessing the environmental
impact of the Sea Empress spill was commissioned
by the Sea Empress Environmental Evaluation Committee
- fate of oil
- marine impacts
- shoreline impacts
- maritime vegetation and agriculture
- reviewing the effectiveness of clean-up operations.
A list of all the reports is included within the
SEEEC Report (SEEC 1998).
Toxicity to marine organisms
An exhaustive literature review on the toxicity
of oils and petrochemicals to marine organisms has
not been carried out for the purposes of this profile.
The information provided in this section is taken
from existing review documents (e.g. GESAMP 1993,
Elliott and Griffiths 1987). The most sensitive
groups of organisms have been identified.
Various reviews have been conducted on the toxicity
of petroleum spills on marine ecosystems and populations
(Clark 1982; Geraci and St Aubin 1990), to which
the reader is also referred.
Reproductive, developmental and behavioural processes
are very sensitive to exposure to hydrocarbons.
Generally, early life stages are more sensitive
than adults and many juvenile and adult crustaceans
and echinoderms are more sensitive than juvenile
and adult fish. It is well established that different
oils vary in their toxicities and that acute toxicity
is largely due to components of the water soluble
fractions and dependent upon exact conditions and
duration of exposure to them (GESAMP 1993).
Chronic sublethal effects caused by petroleum hydrocarbons
spilled or discharges into low energy, shallow coastal
waters remain a valid concern.
The major habitats affected are intertidal and
subtidal sediments and to, a lesser extent, the
water column. GESAMP (1993) highlighted low-energy,
marshes and seagrasses as being among the most sensitive
and vulnerable shorelines to oil pollution. Threshold
effects concentration for various species and different
hydrocarbons and their mixtures in water were reported
as low as a few mg l-1.
Elliott and Griffiths (1987) provided a summary
of the biological effects of petrochemical pollution
in the Forth (see table below).
Biological effects of oil and petrochemical pollution
in the Forth (from Elliott and Griffiths 1987)
and floral community changes:
Chronic by discharges
Catastrophic by oil spillages
and changes in the rates of bioaccumulation
toxic effects (near-field and far-field)
effects on fecundity, behaviour, pathobiology
A change in MFO activity induction in fish
Changes in mussel ecophysiology (Scope for
Growth) and sub-cellular structure and functioning
Changes in palatability of benthos and fish
The physical effects arise from the tendency of
oils to coat surfaces, including sediment surfaces,
rocky shores and vegetation. Large deposits are
associated with discharges or spillages of crude
oil where large expanses of intertidal mud and sand
flats, rocky shore and saltmarshes can be covered.
When such deposits are not removed as part of a
spill clean-up, they smother benthic organisms and
prevent feeding by birds and fish. The response
of benthic invertebrate communities is very similar
to the response to organic enrichment and pollution
because the primary effect is to create anoxia in
the sediment by preventing exchange of water between
the sediment surface and the water column.
The toxic effects of crude oil and a range of petrochemicals
have been demonstrated on a range of estuarine invertebrates,
including polychaetes (Reish 1979), decapod crustaceans,
including crabs (Williams and Duke 1979), shrimps
(Couch 1979) and larval decapods (Epifanio 1979),
amphipod crustaceans (Reish and Barnard 1979) and
molluscs (Menzel 1979). While comparisons are difficult
because of the use of different oils and various
ways of preparing oil for testing, a number of laboratory
tests were performed using water soluble fractions
of No. 2 fuel oil and Venezuelan crude. The fuel
oil was generally more toxic.
Studies on the changes in fish and macrocrustacean
community structure in relation to a discharge of
oil and petrochemicals in estuaries are few and
have been hampered by the lack of appropriate fish
community descriptors and the high levels of natural
variability (GESAMP 1993).
Impacts at the fish population level are also difficult
to detect but are unlikely to be great because fish
will avoid localised areas polluted by oil. In enclosed
systems, such as estuaries, extensive pollution
by oil may reduce the holding capacity of the system
for fish such that its value as a nursery or feeding
ground may be reduced.
Lancaster et al (1998) studied the recruitment
of sea bass in relation to the 'Sea Empress'
oil spill in 1996 and concluded that although some
differences were detected between estuaries, they
were unlikely to be more significant than natural
Laboratory and field studies in the 1970s and 1980s
demonstrated acute and chronic effects in adult
fish exposed to waters and sediments contaminated
with high levels of hydrocarbons (GESAMP 1993).
Lethal effects on estuarine crabs, shrimp and lobsters
have been demonstrated (Williams and Duke 1979,
Couch 1979 and Epifanio 1979). Petroleum spills
generally have a low acute toxicity potential for
adult fish but fish kills may occur due to high
exposure to emulsified oil in shallow waters (i.e.
the Braer spill, January 1993, Shetland Isles) (GESAMP
1993). However, the creation of oil water emulsions
requires a high energy system which is unlikely
to occur in many European estuarine systems.
In laboratory studies with a range of fish (rainbow
trout, perch, sea trout, fathead minnow and pike),
the effects of exhaust from a two-stroke outboard
engine were studied. Estimated environmental concentrations
of 0.27 to 1.6 ml
l-1 of exhaust condensate in the wake
of the engine were used in the laboratory experiments
and effects were observed at the subcellular level
(including enzyme activity) and on physiological
functions (carbohydrate metabolism and on the immune
system) (Balk et al 1994).
Marine wildlife (seabirds and mammals) are often
the most conspicuous victims of oil spills. Diving
and surface-dwelling populations of seabirds and
sea otters are known to be vulnerable and sensitive
Following a spill, seabirds may be affected in
a number of ways. Although oil ingested during attempts
to clean plumage may be lethal, the most common
causes of death are from loss of body heat, starvation
and drowning following damage to the plumage by
oil. Plumage is essential to flight, heat insulation
and waterproofing and even small effects on any
of these functions can result in mortality. As well
as external effects, birds can ingest oil when eating
contaminated food. This can cause direct toxicity
and lead to decreased survival, density and fecundity
of bird populations (GESAMP 1993).
Documentation for the field on the effects of oiling
on mammals, especially cetaceans, is scarce (GESAMP
Seals and dolphins are highly mobile animals which
are generally able to avoid any prolonged encounter
with an oil slick. The main threats to these animals
are not so much the reduction in insulation but
internal damage resulting from ingesting contaminated
food. Seals are vulnerable to hydrocarbons and other
chemicals evaporating from the surface of oil. Exposure
to these pollutants causes symptoms which include
irritation to the eyes and lungs and breathing difficulties.
Elliott and Griffiths (1987) demonstrated bioaccumulation
of hydrocarbons by flounder and plaice in the Forth
estuary system and suggested that the primary route
of uptake was via the food.
Biomarker studies have revealed that fish detoxify
bioaccumulated hydrocarbons and the degree to which
this process has been initiated. The induction,
through the cytochrome P-450 pathways, of mixed
function oxidases (MFO) activity has become a biomarker
for hydrocarbon exposure and contamination (Payne
and Fancey 1982, Elliott and Griffiths 1987). Initial
studies in the Forth in 1987 indicated that MFO
activity was greatest closer to the main source
of hydrocarbons to the estuary (Elliott and Griffiths
1987). This response has also been detected in the
Elbe estuary .
Tainting (an odour or flavour foreign to the product)
has occurred in commercial species contaminated
with crude and refined oils. GESAMP (1993) report
studies detecting taints in fish and macro-crustaceans
resulting from exposure from acute incidents, chronic
discharges and in experimental studies. Tainting
from acute incidents involving crude oil has been
reported for mackerel, sea trout, plaice, carp,
mullet, salmon, crab and lobster and involving refined
oils for mackerel, herring, flounder, sea trout,
salmon, haddock, saithe and lobster. Chronic discharges
of refinery wastes have resulted in reported taints
in grey mullet, eel, 'flatfish',
and rainbow trout. Taints have been induced in plaice,
eels, salmon, saithe, cod, trout, shrimp and crab
in experimental studies using a variety of crude
and refined oils.
Experimental studies indicate that taints can be
detected when fish are exposure to concentrations
of oil in water in the range 0.01 to 1 mg l-1.
Alkylbenzenes have been indicated as capable of
causing a taint in fish but this is not the only
class of tainters in crude and refined oils. Fish
can be tainted very rapidly on exposure - within
a few hours at concentrations of oil above 1 mg
l-1 - and have been shown to lose their
taint within 1 to 4 days (experimental study on
cod). However, field studies have indicated fish
were still tainted days or weeks after a spill of
fuel oil (GESAMP 1993).
Potential effects on the interest
features of European marine sites
Potential effects include:
- intertidal habitats are under greatest threat
from the physical effects of oil pollution. The
most vulnerable habitats are sheltered rocky coasts,
intertidal sand and mudflats and saltmarshes;
- subtidal habitats and their associated flora
and fauna may be threatened in high energy coastal
situations where the likelihood of oil/water emulsions
forming is greater;
- seals and dolphins are threatened by the consumption
of contaminated food. An additional hazard for
seals is the inhalation of volatile components
of oil causing eye and lung irritation and breathing
- damage to intertidal habitats used as seal haul-outs
could be significant if the incident occurred
during the breeding season;
- birds are affected by oil through the physical
damage to plumage and by the consumption of contaminated