Course Coordinator

D. DINU

Course:

<<MARINE POLLUTION I>>

Student:

Ana Maria Stan

Marine Spills and Environmental Impact

Marine Spills Fate of Oil Spills

o Weathering Process o Persistence of Oil o Models

Effects of Oil Spills o Environmental Impact o Recovery o Economic Impacts

About Vegetable Oil Spills About HNS

Marine Spills

Recognition of spilt oil at sea or on the shoreline may be the first indication of an oil spill. Depending on the quantity and type of oil involved, a clean-up response may have to be organised for removing the oil and protecting sensitive areas nearby.

The fate of spilt oil depends on a number of factors, such as the amount of oil spilled; its initial physical and chemical characteristics;

the prevailing weather and sea conditions; and whether the oil remains at sea or comes ashore.

Once spilled at sea, the natural tendency for the oil will be to spread, break up and become dissipated over time. This dissipation is a result of a number of chemical and physical processes acting on the spilt oil. These processes are collectively referred to as weathering.    

In considering the fate of spilled oil at sea and potential clean-up and response techniques, the persistence of the oil in the environment should be taken into account.

A variety of models exist which may be used to aid in decision making processes and forecasting the likely locations the oil may strand. Models

2

can be used at a contingency planning stage, allowing stakeholders to envisage a variety of scenarios and their likely outcome, as well as during a real-time spill to aid clean-up and response decisions.

The effect of oil spills can be far reaching, posing both an environmental and economic threat. Recreational activities, local industry, fisheries, and marine life are among the resources that can be adversely affected by oil spills.

The recovery of the environment after a spill depends on a variety of factors such as the type and amount of oil spilled; the biological and physical characteristics of the affected area; time of year and weather conditions, and notably the clean-up and response strategy used. Typical environmental impacts range from toxicity to smothering effects.

Spills of chemicals and other Hazardous and Noxious Substances (HNS) may also present a threat to the environment. The behaviour and fate of spilled HNS will depend on its chemical and physical properties. Its impact will also vary according to local conditions.

 

Fate of Oil Spills

Oil is a general term used to denote petroleum products which mainly consist of hydrocarbons. Crude oils are made up of a wide spectrum of hydrocarbons ranging from very volatile, light materials such as propane and benzene to more complex heavy compounds such as bitumens, asphaltenes, resins and waxes. Refined products such as petrol or fuel oil are composed of smaller and more specific ranges of these hydrocarbons.

Oil, when spilled at sea, will normally break up and be dissipated or scattered into the marine environment over time. This dissipation is a result of a number of chemical and physical processes that change the compounds that make up oil when it is spilled. The processes are collectively known as weathering. Oils weather in different ways. Some of the processes, like natural dispersion of the oil into the water, cause

part of the oil to leave the sea surface, whilst others, like evaporation or the formation of water in oil emulsions, cause the oil that remains on the surface to become more persistent.

The way in which an oil slick breaks up and dissipates depends largely on how persistent the oil is. Light products such as kerosene tend to evaporate and dissipate quickly and naturally and rarely need cleaning-up. These are called non-persistent oils. In contrast, persistent oils, such as many crude oils, break up and dissipate more slowly and usually require a clean-up response. Physical properties such as the density, viscosity and pour point of the oil all affect its behaviour.

3

Dissipation does not occur immediately. The time this takes depends on a series of factors, including the amount and type of oil spilled, the weather conditions and whether the oil stays at sea or is washed ashore. Sometimes, the process is quick and on other occasions it can be slow, especially in sheltered and calm areas of water.

A number of models are available for predicting the trajectory and dispersion of oil spills at sea.  These can serve as a useful guide to understanding how a particular oil is likely to behave and help in assessing the scale of the problem which a spill might generate.

Weathering Process

Most of the weathering processes, such as evaporation, dispersion, dissolution and sedimentation, lead to the disappearance of oil from the surface of the sea, whereas others, particularly the formation of water-in-oil emulsions ("mousse") and the accompanying increase in viscosity, promote its persistence. The speed and relative importance of the processes depend on factors such as the quantity and type of oil, the prevailing weather and sea conditions, and whether the oil remains at sea or is washed ashore. Ultimately, the marine environment assimilates spilled oil through the long-term process of biodegradation.

The eight main processes that cause an oil to weather are described below and summarised in the following diagram.

4

Figure 1: Fate of oil spilled at sea showing the main weathering processes

 Spreading

As soon as oil is spilled, it starts to spread out over the sea surface, initially as a single slick. The speed at which this takes place depends to a great extent upon the viscosity of the oil. Fluid, low viscosity oils spread more quickly than those with a high viscosity. Nevertheless, slicks quickly spread to cover extensive areas of the sea surface. Spreading is rarely uniform and large variations in the thickness of the oil are typical. After a few hours the slick will begin to break up and,

because of winds, wave action and water turbulence, will then form narrow bands or windrows parallel to the wind direction. The rate at which the oil spreads is also determined by the prevailing conditions such as temperature, water currents, tidal streams and wind speeds. The more severe the conditions, the more rapid the spreading and breaking up of the oil.

5

Evaporation

Lighter components of the oil will evaporate to the atmosphere. The amount of evaporation and the speed at which it occurs depend upon the volatility of the oil. An oil with a large percentage of light and volatile compounds will evaporate more than one with a larger amount of heavier compounds. For example, petrol, kerosene and diesel oils, all light products, tend to evaporate almost completely in a few days whilst little evaporation will occur from a heavy fuel oil. In general, in temperate conditions, those components of the oil with a boiling point under 200ºC tend to evaporate within the first 24 hours. Evaporation can increase as the oil spreads, due to the increased surface area of the slick. Rougher seas, high wind speeds and high temperatures also tend to increase the rate of evaporation and the proportion of an oil lost by this process.

Dispersion

Waves and turbulence at the sea surface can cause all or part of a slick to break up into fragments and droplets of varying sizes. These become mixed into the upper levels of the water column. Some of the smaller droplets will remain suspended in the sea water while the larger ones will tend to rise back to the surface, where they may either coalesce with other droplets to reform a slick or spread out to form a very thin film. The oil that remains suspended in the water has a greater surface area than before dispersion occurred. This encourages other natural processes such as dissolution, biodegradation and sedimentation to occur.

The speed at which an oil disperses is largely dependent upon the nature of the oil and the sea state, and occurs most quickly if the oil is light and of low viscosity and if the sea is very rough. These factors led to the complete dispersion of the oil spilled from the BRAER (Shetland Islands, United Kingdom, 1993).

The addition of chemical dispersants can accelerate this process of natural dispersion.

Emulsification

An emulsion is formed when two liquids combine, with one ending up suspended in the other. Emulsification of crude oils refers to the process whereby sea water droplets become suspended in the oil. This occurs by physical mixing promoted by turbulence at the sea surface. The emulsion thus formed is usually very viscous and more persistent than the original oil and is often referred to as chocolate mousse because of its appearance. The formation of these emulsions causes the volume of pollutant to increase between three and four times. This slows and delays other processes which would allow the oil to dissipate.

6

Oils with an asphaltene content greater than 0.5% tend to form stable emulsions which may persist for many months after the initial spill has occurred. Those oils containing a lower percentage of asphaltenes are less likely to form emulsions and are more likely to disperse. Emulsions may separate into oil and water again if heated by sunlight under calm conditions or when stranded on shorelines.

Dissolution

Water soluble compounds in an oil may dissolve into the surrounding water. This depends on the composition and state of the oil, and occurs most quickly when the oil is finely dispersed in the water column. Components that are most soluble in sea water are the light aromatic hydrocarbons compounds such as benzene and toluene. However, these compounds are also those first to be lost through evaporation, a process which is 10 -100 times faster than dissolution. Oil contains only small amounts of these compounds making dissolution one of the less important processes.

Oxidation

Oils react chemically with oxygen either breaking down into soluble products or forming persistent compounds called tars. This process is promoted by sunlight and the extent to which it occurs depends on the type of oil and the form in which it is exposed to sunlight. However, this process is very slow and even in strong sunlight, thin films of oil break down at no more than 0.1% per day. The formation of tars is caused by the oxidation of thick layers of high viscosity oils or emulsions. This process forms an outer protective coating of heavy compounds that results in the increased persistence of the oil as a whole. Tarballs, which are often found on shorelines and have a solid outer crust surrounding a softer, less weathered interior, are a typical example of this process.

Sedimentation/Sinking

Some heavy refined products have densities greater than one and so will sink in fresh or brackish water. However sea water has a density of approximately 1.025 and very few crudes are dense enough or weather sufficiently, so that their residues will sink in the marine environment. Sinking usually occurs due to the adhesion of particles of sediment or organic matter to the oil. Shallow waters are often laden with suspended solids

providing favourable conditions for sedimentation.

Oil stranded on sandy shorelines often becomes mixed with sand and other sediments. If this mixture is subsequently washed off the beach back into the sea it may then sink. In addition, if the oil catches fire after it has

7

been spilled, the residues that sometimes form can be sufficiently dense to sink.

Biodegradation

Sea water contains a range of micro-organisms or microbes that can partially or completely degrade oil to water soluble compounds and eventually to carbon dioxide and water. Many types of microbe exist and each tends to degrade a particular group of compounds in crude oil. However, some compounds in oil are very resistant to attack and may not degrade.

The main factors affecting the efficiency of biodegradation, are the levels of nutrients (nitrogen and phosphorus) in the water, the temperature and the level of oxygen present. As biodegradation requires oxygen, this process can only take place at the oil-water interface since no oxygen is available within the oil itself. The creation of oil droplets, either by natural or chemical dispersion, increases the surface area of the oil and increases the area available for biodegradation to take place.

Combined processes

The processes of spreading, evaporation, dispersion, emulsification and dissolution are most important during the early stages of a spill whilst oxidation, sedimentation and biodegradation are more important later on and determine the ultimate fate of the oil. To understand how different oils change over time whilst at sea, one needs to know how these weathering processes interact. To predict this, some simple models have been developed based on oil type. Oils have been classified into groups roughly according to their density - generally, oils with a lower density will be less persistent. However some apparently light oils can behave more like heavy ones due to the presence of waxes. Although simple models cannot predict the changes an oil undergoes very precisely, they can provide clues about whether an oil is likely to dissipate naturally or whether it will reach the shoreline. This information can be used by spill responders to decide upon the most effective spill response techniques and whether such techniques can be initiated quickly enough.

Persistence of Oil

The concept of persistence in relation to oil spills probably originated after the TORREY CANYON incident in 1967. This is the time when discussions first arose regarding various new measures to protect the marine environment and to manage marine oil spills, particularly in relation to liability and compensation. Generally, persistent oils contain a considerable proportion of heavy fractions or high-boiling material.  They do not dissipate quickly and will therefore pose a potential threat to natural resources when released to the environment.  Such threats are evident in terms of impacts to wildlife, smothering of habitats and oiling of

8

amenity beaches.  In contrast, non-persistent oils are generally of a volatile nature and are composed of lighter hydrocarbon fractions.  When released into the environment they will dissipate rapidly through evaporation. As a result, spills of these oils rarely require a response but when they do, clean-up methods tend to be limited. Impacts from non-persistent oils may include, for example, effects on paint coatings in marinas and harbours and - at high concentrations - acute toxicity to marine organisms.

The international compensation regime for oil spills only applies to spills of “persistent” oil. Whilst this term is not precisely defined in any of the conventions, the International Oil Pollution Compensation Funds (IOPC Funds) have developed guidelines which are widely accepted.  Under these guidelines an oil is considered non-persistent if at the time of shipment at least 50% of the hydrocarbon fractions, by volume, distil at a temperature of 340°C (645°F) and at least 95% of the hydrocarbon fractions, by volume, distil at a temperature of 370°C (700°F) when tested in accordance with the American Society for Testing and Materials (ASTM) Method D86/78 or any subsequent revision thereof.

However, this definition is based on distillation characteristics of oils under standard laboratory conditions. It may not, therefore, fully reflect the behaviour of oil in the environment, where factors such as burial in sediments can lead to the long-term persistence of oils that would normally be defined as non persistent.

Oils which are normally classified as persistent include crude oils, fuel oils, heavy diesel and lubricating oils.  Non-persistent oils include gasoline, light diesel oil and kerosene. 

 

Models

Modelling of the likely fate and behaviour of oil once spilled can follow a number of different approaches. These range from a simple vector calculation, to estimate the probable two–dimensional trajectory of the centre point of a slick, to sophisticated computer models of the movement and distribution of the oil in three dimensions with the concurrent predictions of the change in properties as the oil weathers. The main properties which affect the fate of spilled oil at sea are specific gravity (its density relative to pure water - often expressed as ° API* or API gravity); distillation characteristics (its volatility); viscosity (its resistance to flow); and pour point (the temperature below which it will not flow). In addition the wax and asphaltene content influence the likelihood that the oil will mix with water to form a water-in-oil emulsion. Oils which form stable oil-in-water emulsions persist longer at the water surface.

9

Volume of oil and water-in-oil emulsion remaining on the sea surface, as a percentage of the original volume spilled

The graph above represents a simple empirical model based upon the properties of different oil types. For this purpose, it is convenient to classify the most commonly transported oils into four main groups, roughly according to their specific gravity (see table below). Having classified the oils, the expected rate at which the volume of oil at the sea surface decreases can be estimated. These four groups are shown in the above graph, where account is also taken of the competing process of emulsification which, for most oils, leads to an increase in volume.

Group Density Examples

GroupI less than 0.8 Gasoline, Kerosene

GroupII 0.8 - 0.85 Gas Oil, Abu Dhabi Crude

GroupIII 0.85 - 0.95 Arabian Light Crude, North Sea Crude Oils (e.g Forties)

GroupIV greater than 0.95

Heavy Fuel,Venezuelan Crude Oils

Group I oils (non-persistent) tend to dissipate completely through evaporation within a few hours and do not normally form emulsions. Group II and III oils can lose up to 40% by volume through evaporation but, because of their tendency to form viscous emulsions, there is an initial volume increase as well as a curtailment of natural dispersion, particularly in the case of Group III oils. Group IV oils are very persistent due to their

10

lack of volatile material and high viscosity, which preclude both evaporation and dispersion.

To model the movement of oil, the most important input parameters include the type and quantity of oil spilled, along with the rate of release. Key environmental input data include wind, ocean currents, tides and air and sea temperatures. While this does not sound particularly onerous, one must keep in mind that there are numerous variables associated with each of these parameters and usually this type of information is not readily available. The reliability of a trajectory model will depend on the availability of a detailed hydraulic model from which water movement data can be drawn and these require detailed knowledge of water depths (bathymetry), currents at various depths and tidal streams. Although trajectory models exist where such basic data can be input to generate hydraulic models, this takes considerable time and most are limited to those geographic areas where such hydraulic models already exist.

The other component required to model the transport of oil spilled at sea is wind data. During the period over which the incident is modelled the wind strength and direction is likely to change and can vary at different locations across the spill area as time progresses. As far as possible this information also has to be input to the model although often, average values are used for set time intervals.

It is important to appreciate the assumptions upon which models are based and not to place complete reliance on the results. However, they can serve as a useful guide to understanding how a particular oil is likely to behave and help in assessing the scale of the problem which a spill might present. The principle uses of such models are for planning, training, emergency response, and impact assessment. The suitability of computer modelling for each of these applications differs.

Computer models are widely used for contingency planning where they are particularly helpful for decision makers who need to link their site-specific, pre-identified risks with decisions concerning the locations and make-up of the planned response measures, including equipment, materials and manpower. This can be done by running the model over and over using a range of the most likely scenarios and then observing the predicted oil movement and behaviour. Based on the results, those locations shown to be the most vulnerable can be identified, the logistics of responding to these locations studied and response assets placed accordingly. There is, of course, no guarantee that these resources will be best placed in the event of a spill, but the planners will have made the best judgement based on available information.

Spill response training is another key application for models. The model is used to help course participants feel as if they are involved in a real-life situation, even if they are only taking part in a table-top exercise. Trainers use the models in a variety of ways, but one approach is to run the model at real-time speed for 20-30 minutes so that participants can make some decisions about what measures should be taken and what equipment

11

should be mobilised. Then the model is fast-forwarded to a later period and participants are asked to deal with the updated situation. In this way, an event of 2-3 days can be collapsed down to an hour or so.

The use of computer models in emergency response itself is much more challenging, depending on the particular details of the case, because it requires the timely acquisition of the numerous input parameters. Usually the release occurs immediately after an incident occurs, for example, following a collision. Little will be known about the oil types or the quantities involved. As the incident develops better information will improve the outcome of the model. However, one immediate application is to inform decisions on the scope of initial aerial surveillance flights where the movement of oil may not be immediately obvious, for example, following an instantaneous release of oil at night the oil may have moved a considerable distance from the source.

Perhaps the most controversial application of computer modelling is for damage assessment. Computer modelling in this case is used to show where the oil might have gone as it spread, drifted, dissolved, and evaporated. In the simplest cases, reference is made to, for example, the threshold levels for the contaminants in marine products for safe human consumption. The geographic areas simulated to have been exposed to concentration levels in excess of these standards are assumed to have been impacted. In more sophisticated models, input data for related toxicological studies is used together with ecological sub-models to predict what sort of acute exposure and impact may have been experienced. The trouble with this approach is that the models do not actually show damage, they simply predict it based on a host of simplifying assumptions. Many years of field experience have made it clear that when there is real impact, it can be observed on site. While before-the-fact impact assessment might be a useful planning tool, for example to study the need for specialist wildlife cleaning equipment and expertise, it is no replacement for scientific field work and post–spill surveys.

*°API = (141.5/SG) -131.5

Note: API gravity values increase with decreasing density eg. SG 1 = 10° API & SG 0.8 = 45.4° API

Effects of Oil Spills

Oil spills can have serious effects on marine life, as highlighted by the photos of dead birds which regularly appear in the news after such an event. Such images fuel the perception of widespread and permanent

12

environmental damage after every spill, and an inevitable loss of marine resources with serious economic repercussions. A science-based appraisal of the effects reveals that whilst damage occurs and may be profound at the level of individual organisms, populations are more resilient and natural recovery processes are capable of repairing the damage and returning the system to normal functions. The first stage on the road to recovery is usually a well conducted clean-up operation but in some specific habitats aggressive clean-up methods can cause more harm than good and then it is better to let natural cleaning processes take their course.

Many spill impacts have been documented in the scientific and technical literature, and although not all the effects of oil pollution are completely understood, an indication of the likely scale and duration of damage can usually be deduced from the information available. However, it can be difficult to present a balanced view of the realities of spill effects, given the often highly charged and emotional nature of a spill and its aftermath. The scientific community can become polarised into opposing camps with one side intent on quantifying every aspect of damage, and the other emphasising the capacity of the environment to recover naturally. The simple reality is that sometimes significant damage occurs, sometimes not and the aim of these pages is to draw together what general information is known about spill effects and their longevity.

The marine ecosystem is highly complex and natural fluctuations in species composition, abundance and distribution are a basic feature of its normal function. The extent of damage can therefore be difficult to detect against this background variability. Nevertheless, the key to understanding damage and its importance is whether spill effects result in a downturn in breeding success, productivity, diversity and the overall functioning of the system.

Spills are not the only pressure on marine habitats; chronic urban and industrial contamination or the exploitation of the resources they provide are also serious threats. The following sections consider some of the types of damage caused by oil spills as well as some of the benefits of conducting post-spill studies.

Environmental Impact

The exact nature and duration of any impacts from an oil spill depend on a number of factors. These include the type and amount of oil and its behaviour once spilled; the physical characteristics of the affected area; weather conditions and season; the type and effectiveness of the clean-up response; the biological and economic characteristics of the area and their sensitivity to oil pollution. Typical effects on marine organisms range across a spectrum from toxicity (especially for light oils and products) to smothering (heavier oils and weathered residues). The presence of toxic components does not always cause mortality, but may induce temporary

13

effects like narcosis and tainting of tissues, which usually subside over time. Some typical oil impacts are described below.

Plankton

The importance of plankton in primary productivity of the oceans and as a temporary home for the eggs and larvae of fish, shellfish, sea bed and shoreline organisms is well known, but is there evidence of widespread harm to these functions from spills which subsequently translates into long term damage? Laboratory studies have demonstrated toxic and sub-lethal effects on the plankton caused by oil, and there is little doubt that there is potential for widespread impact. Unfortunately, plankton is extremely difficult to study reliably because they are amongst the most variable of marine communities in space and in time. The presence of oil on open water is also patchy and transient, making it difficult to establish where and when the plankton might have been exposed to the oil. Whilst the possibility of long-term effects can not be excluded, there is no indication that oil-induced losses of eggs and larval stages cause a significant decline in adult populations.

Seabirds

Seabirds are amongst the most vulnerable inhabitants of open waters since they are easily harmed by floating oil. Species that dive for their food or which congregate on the sea surface are particularly at risk. Although oil ingested by birds during attempts to clean themselves by preening may be lethal, the most common cause of death is from drowning, starvation and loss of body heat following fouling of plumage by oil.

Cleaning and rehabilitation after oiling is often attempted, but for many species it is rare for more than a fraction of oiled birds to survive cleaning and rarer still for those that survive to breed successfully after release. Penguins are an exception and are much more resilient than most other birds. When handled properly, the majority are likely to survive the cleaning process and rejoin breeding populations.

Bird mortality occurs during most spills and in some major spills breeding colonies have been seriously depleted. Some species react to colony depletion by laying more eggs, breeding more frequently or younger birds joining the breeding group. These processes can assist recovery, although recovery may take several years and will also depend on other factors like food supply. Whilst it is common for short and medium term loss to occur in populations, there is scant evidence of spills causing long-term harm to populations, or of a spill tipping a marginal colony into permanent decline.

Sea Mammals

14

Whales, dolphins and seals in the open sea do not appear to be particularly at risk from oil spills. Marine mammals such as seals and otters that breed on shorelines are, however, more likely to encounter oil. Species which rely on fur to regulate their body temperature are the most vulnerable since, if the fur becomes matted with oil, the animals may die from hypothermia or overheating, depending on the season.

Shallow Coastal Waters

Spill damage in shallow waters is most often caused by oil becoming mixed into the sea by wave action or by dispersant chemicals used inappropriately. In many circumstances the dilution capacity is sufficient to keep oil concentrations in the water below harmful levels, but in cases where light, toxic products have become dispersed, or in major incidents where heavy wave action has dispersed large volumes of oil close inshore, large kills of marine organisms such as shellfish have occurred. Post-spill studies reveal that recovery has taken place in a relatively short timescale through the processes noted earlier, and impacts are rarely detectable beyond a few years. In one instance, the BRAER spill in Shetland, UK, most of the spilt oil was dispersed naturally by heavy wave action, thus avoiding much of the shoreline contamination normally associated with large oil spills. However, some oil became incorporated into sea bed sediments, causing long-term tainting of some commercial species.

Shorelines

Shorelines, more than any other part of the marine environment, are exposed to the effects of oil as this is where it naturally tends to accumulate. However, many of the animals and plants on the shore are inherently tough since they must be able to tolerate periodic exposure to pounding waves, drying winds, high temperatures, rainfall and other severe stresses. This tolerance also gives many shoreline organisms the

ability to withstand and recover from oil spill effects.

Rocky and sandy shores exposed to wave action and the scouring effects of tidal currents tend to be resilient to the effects of a spill as they usually self-clean quite rapidly. Rocky shores exposed to wave action are often quoted as those which recover most rapidly, and there have been many cases in which this was true. A typical example of impact on this habitat is the temporary loss of a keystone species, the limpet, which is a grazing snail, which leads to a 'bloom' of seaweeds in their absence. Because of

15

the increased availability of their food source, re-colonisation by limpets usually follows rapidly and the normal grazing pattern is re-established.

However, in some circumstances, subtle changes to rocky shore communities can be triggered by a spill, which can subsequently be detected for ten or more years. Although the functioning, diversity and productivity of the ecosystem is restored, the detailed distribution of particular species present may alter. The TORREY CANYON oil spill in 1967 is a case in point. Heavy and inappropriate use of toxic cleaning agents caused massive damage to some shores, and although re-colonisation by most of the dominant organisms was rapid, subtle differences in the distribution of species could be traced over more than twenty years when compared with un-oiled sites. The overall functioning and productivity of these shores seems unimpaired, but it is difficult to be absolutely certain of this because of all the other stresses on the system, including those from tourism and fishing.

Soft sediment shores consisting of fine sands and mud are found in areas which are sheltered from wave action, including estuaries, and tend to be highly biologically productive. They often support large populations of migrating birds, indigenous populations of specialist sediment dwellers and shellfisheries. They also act as nursery areas for some species. Oil can become incorporated in fine sediments through a number of mechanisms. Examples include flocculation with sediment stirred up by storm activity and penetration down worm burrows and open plant stems. If oil does penetrate fine sediments it can persist for many years, increasing the likelihood of longer-term effects. The upper fringe of 'soft' shores is often dominated by saltmarsh which is generally only temporarily harmed by a single oiling. However, damage lasting many years can be inflicted by repeated oil spills or by aggressive clean-up activity, such as trampling or removal of oiled substrate.

In tropical regions, mangrove swamps replace saltmarshes and provide an extremely rich and diverse habitat as well as coastal protection and important nursery areas. The mangrove trees which provide the framework upon which this habitat depends can sometimes be killed depending on the type of oil and the substrate in which the trees are growing. Damage is more likely if oil smothers their breathing roots or if toxic oils penetrate the sediments. Where high mortality of trees occurs, in some cases including trees which are 50 or more years old, natural recovery to a diverse and productive structure can take decades. An important function of both saltmarsh and mangrove habitats is that they provide organic inputs to coastal waters which in turn enrich the communities living there. It is in these marsh and mangrove areas where

16

damage has been recorded that reinstatement measures have real potential to speed up recovery.

Recovery

Natural Recovery

Marine organisms have varying degrees of natural resilience to changes in their habitats. The natural adaptations of populations of animals and plants to cope with environmental stress, combined with their breeding strategies, provide important mechanisms for coping with the daily and seasonal fluctuations in their habitats and for recovering from predation and other stochastic events.

Some natural phenomena can be highly destructive. The short-term power of hurricanes and tsunamis can easily be appreciated, as can the damage they cause. The cyclical El Niño phenomenon has major long-term consequences for marine organisms, seabirds and marine mammals throughout the entire Pacific Ocean. Organisms suffer under such onslaughts, but after what is often severe disruption and widespread mortality, the marine populations re-establish themselves over a period of time and this process constitutes natural recovery.

An important reproductive strategy for many marine organisms is the production of vast numbers of eggs and larvae which are released into the plankton and are widely distributed by currents. This mechanism has evolved to take maximum advantage of available space and resources in marine habitats and to deal with e.g. predation. In some cases, only one or two

individuals in a million actually survive through to adulthood.

A less common reproductive strategy that is generally restricted to long-lived species that do not reach sexual maturity for many years is to produce relatively few, well-developed, offspring. These species are better adapted to stable habitats and environments and as a result, their populations are likely to take much longer to recover from the pressures of localised mortality e.g. the effects of an oil spill.

Whilst there may be considerable debate over what constitutes recovery, there is a widespread acceptance that natural variability in systems makes getting back to the exact pre-spill condition unlikely, and most current definitions of recovery focus on the re-establishment of a community of plants and animals which are characteristic of the habitat and are functioning normally in terms of biodiversity and productivity.

17

Restoration

Removal of bulk oil contamination either through natural processes or a well-conducted clean up operation is the first stage of the recovery and restoration of a damaged environment. Dependent on the scale and nature of the spill, for many marine habitats, the clean up operation is all that is necessary to promote natural recovery, and there is little further that can be done to speed up this process.

However, in some cases, especially in circumstances where habitat recovery would otherwise be relatively slow, the clean up operation can be followed by further measures which help restore a habitat structure. An example of such an approach following an oil spill would be to replant an area of salt marsh or mangrove after the bulk oil contamination has been removed. In this way erosion of the area would be minimised and other forms of biological life would be encouraged to return.

A salt marsh impacted by an oil spill before (left) and after (right) replanting

While it may be possible to help restore damaged vegetation and physical structures, designing meaningful restoration strategies for animals is a much greater challenge. In some cases it may be warranted to protect a natural breeding population at a nearby non-impacted site, for example by predator control, to provide a reservoir from which re-colonisation of the impacted areas can occur. In reality, the complexity of the marine environment means that there are limits to which ecological damage can be repaired by artificial means. In most cases natural recovery is likely to be relatively rapid and will only rarely be outpaced by restoration measures.

Post-spill Studies

The short-term effects of oil spills on many marine species and communities are well known and predictable, but concerns are often raised about possible longer-term ("sub-lethal") population effects. Extensive research and detailed post-spill studies have shown that many components of the marine environment are highly resilient to short-term adverse changes, including oil spills, and as a result even a major oil spill will rarely cause permanent effects.

18

However, in some instances, in order to determine the full extent of the damage and the progress of the recovery, it may be necessary to undertake post-spill studies. The costs of post-spill studies may be admissible for compensation under the international conventions provided they are a direct consequence of a particular spill and are intended to establish the precise nature and extent of environmental damage and habitat recovery. Studies of a general or purely scientific character would not be admissible for compensation.

Studies will not be necessary after all spills and would normally be most appropriate in the case of major incidents where there is evidence of significant environmental damage. Any studies which are considered should be carried out with scientific rigour, objectivity and balance, with the aim of providing reliable and useful information towards assessing pollution damage,

reasonable reinstatement measures and habitat recovery. The scale of such studies should be in proportion to the extent of the contamination and the predictable effects.

Economic Impacts

Contamination of coastal amenity areas is a common feature of many oil spills, leading to interference with recreational activities such as bathing, boating, angling and diving. Hotel and restaurant owners and others who gain their livelihood from the tourist trade can also suffer temporary losses. A return to normal requires an effective clean up programme and the restoration of public confidence.

Industries that rely on seawater for their normal operation can also be adversely affected by oil spills. Power stations and desalination plants which draw large quantities of seawater can be particularly at risk, especially if their water intakes are located close to the sea surface, thereby increasing the possibility of drawing in floating oil. The normal operations of other coastal industries, such as shipyards, ports and harbours, can also be disrupted

by oil spills and clean-up operations.

Fisheries and Mariculture

An oil spill can directly damage the boats and gear used for catching or cultivating marine species. Floating equipment and fixed traps extending

19

above the sea surface are more likely to become contaminated by floating oil, whereas submerged nets, pots, lines and bottom trawls are usually well protected provided they are not lifted through an oily sea surface. However, they may sometimes be affected by dispersed or sunken oil. Less common is mortality of stock, which can be caused by physical contamination or close contact with freshly spilled oil in shallow waters with poor water exchange.

A common cause of economic loss to fishermen is interruption to their activities by the presence of oil or the performance of clean-up operations. Sometimes this results from a precautionary ban on the catching and sale of fish and shellfish from the area, both to maintain market confidence and to protect fishing gear and catches from contamination. Cultivated stocks are more at risk from an oil spill: natural avoidance

mechanisms may be prevented in the case of captive species, and the oiling of cultivation equipment may provide a source for prolonged input of oil components and contamination of the organisms. Cultured seaweed and shellfish are particularly vulnerable in tidal areas where they may become contaminated with oil as the tide drops.

It is almost always necessary to make a thorough investigation of the status of a fishery and alleged effects of a spill, in order to determine the real impacts. This will often require scientifically rigorous sampling and analytical techniques which are capable of documenting the damage and providing proof that any damage observed has been caused by the oil in question. Nevertheless, separating spill effects from other factors which affect fisheries is frequently problematic. Wild stocks of commercial species are in decline in many parts of the world because of over-fishing, industrial pollution, destruction of coastal habitats and other natural factors such as increasing sea temperature. Similarly, mariculture is often ravaged by disease or suffers from the accumulation of its own wastes. Therefore, in order to make the best assessment of damages attributed to contamination by oil it is necessary to make comparisons of post-spill recovery results with the conditions which pre-existed the spill or with control areas outside the affected area.

About Vegetable Oil Spills

The fate, behaviour and environmental impact of spills of vegetable oils in the marine environment are not as widely appreciated as those of mineral oils. Despite this, a spill of vegetable oil can prove to be equally problematic.

• What are Vegetable Oils?• Behaviour and Fate of Vegetable Oils

20

• Impact of Vegetable Oil Spills• Response Techniques

 What are Vegetable Oils ?

Vegetable oils are oil extractions from plants and fruit such as palm nut, sunflower, soybean, coconut, rapeseed, canola, olive, castor and corn. There are a variety of derivatives and degrees of processing. For example, in general terms, crude describes oil that has been generated by extraction with no further processing. “De-gummed” oil describes a more refined product with the resin-like compounds removed whereas the term refined oil applies to those products that have been clarified and any undesirable colour and sediment removed.

Behaviour and Fate of Vegetable Oils

As with mineral oils, vegetable oils can vary significantly and on release to the marine environment will behave differently according to their individual characteristics. These characteristics will depend on factors at the time of cultivation of the feed stock eg climate; the degree of processing; the type and specific nature of the oil, the sea state and weather conditions at the time of  the spill. In many circumstances, the influence of vegetable oil characteristics on the behaviour of the oil in the environment is not well studied or understood. Consequently, the behaviour and fate of specific vegetable oils is somewhat harder to predict than that of mineral oils.

In general, vegetable oils will behave similarly to mineral oils in the initial stage of a spill. To this extent, they will tend to float and spread on the surface of the water. However, vegetable oils tend to be even less soluble in water than mineral oils; they do not undergo dispersion in the water column nor will they evaporate to any extent.

Depending on their pour point (the temperature at which solidification commences) and the sea surface temperature, vegetable oils may form solid lumps when spilled that will float on the water surface. These discrete lumps have little tendency to coalesce as a surface slick. Over time and dependent on the prevailing conditions the product may accumulate sediment and may sink to the sea floor.

Vegetable oils are comprised primarily of triacylglycerols, or fatty acids, which, in their fresh state, may be broken down by marine bacteria. This decomposition contributes to the rancid odours typical of vegetable oil spills.

Vegetable oils will not readily form water-in-oil emulsions but may undergo a process of polymerisation to form rubbery strings and clumps. These deposits are highly impermeable curtailing oxygen diffusion and replenishment, dramatically slowing the degradation process and forming an anoxic layer. By this process, vegetable oils, particularly with the incorporation of sediment, may give rise to the formation of very tough and highly persistent deposits.

21

Generalised Summary Of Vegetable Oil Behaviour

• Low aquatic toxicity• Limited solubility in water• Do not evaporate to any significant degree• Generally do not form water-in–oil emulsions (though water may become entrapped in    polymerised lumps)• Do not undergo dispersion in water• Tendency to polymerise• Not amenable to dispersion by oil dispersants

Return to topImpact of Vegetable Oil Spills

Historically, vegetable oils have been considered relatively benign, non-toxic and therefore of limited concern to the environment. However, this generalisation has been demonstrated to be incorrect. Previous experience has shown that both chronic and acute pollution incidents can lead to deleterious effects. This awareness has led to the reclassification of many vegetable oils as category Y (hazardous) products under Annex II of the MARPOL Convention with associated limitations on their carriage.

Spilled palm oil Rock coated with palm oil

A spill from a palm oil production plant in Colombia ©

Elastec

In this incident, skimmers were put to work recovering the oil ©

Elastec

 

(Note, the appearance and characteristics of the oil are dependent on a number of factors, such as

22

the degree of processing, see above)

The primary environmental consequences of spills of vegetable oils are seen in relation to surface dwelling organisms where oil can lead to smothering and suffocation. Examples include oiling of bird plumage and animal fur. However, vegetable oils will also readily form solids which tend to have less smothering impact on surface organisms. A polymerised vegetable oil may form an impermeable barrier on the shoreline with potentially serious environmental and economic consequences.

Unlike mineral oils, the environmental impact associated with ingestion of vegetable oils is low. Whilst experimentation has shown some effects such as reduced growth rates, poor food conversion and liver impairment in fish and bivalves resulting from prolonged ingestion, these effects have been minimal even in cases of heavy contamination. However, vegetable oil spills can have significant effects through oxygen depletion and asphyxiation.

One of the primary concerns with vegetable oils is the uncertainty and lack of knowledge of their degradation and weathering products. Ongoing research suggests for example that the toxicity of products such as canola oil and soybean oil actually increase significantly during aerobic biodegradation. The effects of such a process in a confined, shallow environment could be significant.

Summary of Potential Environmental ImpactsPhysical • Smothering

• Coating fur and feathers• Suffocation through oxygen depletion and smothering• Formation of intractable lumps in sediments• Polymerised oils produce impermeable layers on shore

Chemical/ Biological

• Suffocation through oxygen depletion• Anoxia in sediments and water

Amenity • Rancid odours, particularly during degradation• Fouled shorelines• Blocked water intakes

Response Techniques

With the tendency of some vegetable oils to polymerise and form solid lumps, the most appropriate response technique is that of containment and recovery. Ideally, these floating lumps should be removed from the water surface before they have a chance to accumulate sediment and sink and before they are able to reach the shoreline.

Response techniques applied during previous incidents involving a spill of vegetable oil include the use of conventional boom for containment, combined with a variety of recovery techniques. Skimmers may be used to recover vegetable oils of suitable viscosity. Manual recovery techniques employing scoops, trawls and grabs have proved to be effective in the recovery of solidified vegetable oils. The high viscosity of solidified

23

vegetable oils may preclude certain recovery techniques, for example using pumps. Furthermore, dispersants formulated for use on mineral oils have been shown to have little or no effect on vegetable oils.

About HNS

The volume of chemicals transported by sea is increasing but remains significantly lower than the seaborne trade in oil. In addition recent ITOPF experience shows that spills of bunker fuel from all types of ship are at least as likely to occur as loss of cargo oil from a tanker. Consequently chemical spills occur at a much lower frequency than spills of oil. However, the consequence of a chemical spill can be more wide reaching than that of oil and there is growing international awareness of the need for safe and effective contingency arrangements for chemical spills. The wide variety of chemicals transported, their varying physical and chemical properties, the different ways in which they behave in the environment and the potential for effects on human health mean that response to chemical spills is not as straightforward as for oil.

What are Hazardous and Noxious Substances (HNS)? Human Health Aspects

Effects on Marine Resources

Fate of Chemicals in the Marine Environment

Chemical Response Strategies

 What are Hazardous and Noxious Substances (HNS)?

A Hazardous and Noxious Substance is a term used to describe a substance other than oil which, if introduced into the marine environment is likely to create hazards to human health, to harm living resources and marine life, to damage amenities or to interfere with other legitimate uses of the sea†.

Whether a substance is classed as hazardous or noxious is largely determined by its inclusion in one or more lists found in a number of IMO Conventions and Codes (see Table 1) designed to ensure maritime safety and prevention of pollution. If the chemical transported has one or more of the following properties, it is likely to be considered as a ‘hazardous and noxious substance’. (Radioactive and infectious substances are outside the scope of the HNS regime.)

FlammableExplosive

Toxic

24

Corrosive

Reactive

Table 1: Examples of IMO Conventions and Codes providing HNS lists  

Material Conventions & Codes

Bulk Liquids Chapter 17 of International Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk (IBC Code)

   

Gases Chapter 19 of International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk (IGC Code)

   

Solids in bulk Appendix 9 of Code of Safe Practice for Solid Bulk Cargoes (BC Code) if also covered by IMDG Code in packaged form

   

Packaged goods International Maritime Dangerous Goods Code (IMDG Code)

 

Human Health Aspects

Manufacturers of Hazardous and Noxious Substances typically provide Material Safety Data Sheets (MSDS) which summarise the specific hazards associated with each substance. Over time these will be replaced by Safety Data Sheets (SDS) under the UN Globally Harmonized System of Classification and Labelling of Chemicals (GHS)*. GHS classifies chemicals by the types of hazard they represent and proposes harmonized hazard communication by consistent labelling and safety data sheets. It aims at ensuring that information on physical hazards and toxicity from chemicals is available to enhance the protection of human health and the environment during the handling, transport and use of these chemicals.

MSDS and SDS both follow the same format and provide the following information:

 

1. Identification 9. Physical & chemical properties

2. Hazard(s) identification 10. Stability & reactivity

25

3. Composition/ingredients 11. Toxicological information

4. First-aid measures 12. Ecological information

5. Fire-fighting measures 13. Disposal considerations

6. Accidental release measures 14. Transport information

7. Handling & storage 15. Regulatory information

8. Exposure controls/personal protection

16. Other information 

 Effects on Marine Resources

The effects of a chemical lost into the marine environment depend on a number of factors such as the toxicity of the material, the quantities involved and resulting concentrations in the water column, the length of time biota are exposed to that concentration and the sensitivity of the organisms to the particular chemical. Dilution is brought about by water movement due to tidal flow, ocean currents and turbulent diffusion but even if the concentration is below what would be considered lethal, sub-lethal concentrations can still lead to longer term impacts. Chemically-induced stress can reduce the overall ability of the organism to reproduce, grow, feed or otherwise function normally. The characteristics of some chemicals, particularly metals and some organic compounds, can result in the bio-accumulation of these materials. Sessile marine organisms that filter seawater for food, such as shellfish, are particularly vulnerable to this phenomenon. Bio-magnification may follow if the materials pass up the food chain.      GESAMPThe effects of chemicals on the marine environment have been summarised by GESAMP (the Group of Experts on Scientific Aspects of Marine Environmental Protection www.gesamp.net), an advisory body to the United Nations established in 1969. GESAMP comprises experts, drawn from a wide range of relevant disciplines, but who act in their individual capacity. GESAMP has published a Hazard Evaluation of Substances Transported by Ships for the most commonly transported chemicals. The properties of the chemicals have been evaluated in relation to a number of predefined effects should any of the listed chemicals be spilt at sea:

BioaccumulationBiodegradation

Acute and chronic toxicity on marine organisms

26

Long term health effects on humans

Effects on marine wildlife, and on benthic habitats

Effect on other marine resources

This easily accessible and simple guide provides an important first step in evaluating the severity of a spill.

MARPOL The MARPOL Convention is the main international convention covering prevention of pollution from the shipping industry. Within MARPOL are two annexes that are directly relevant to HNS:

Annex IIMARPOL Annex II contains regulations for bulk liquid cargos that may cause environmental pollution if lost at sea. Within the annex are four categories that are graded depending on the hazard the bulk liquid presents to marine resources, human health and amenities.

Category X – liquid substances which are deemed to present a major hazard  to either marine resources or human health, and therefore justify the prohibition of the discharge into the marine environment. Category Y – liquid substances which are deemed to present a hazard to either marine resources or human health or cause harm to amenities or other uses of the sea and therefore justify a limitation on the quality and quantity of the discharge into the marine environment.

Category Z – liquid substances which are deemed to present a minor hazard to either marine resources or human health and therefore justify less stringent restrictions on the quality and quantity of the discharge into the marine environment.

Category OS – these “other substances” are deemed to fall outside of categories X, Y, and Z and are deemed to present no harm to marine resources, human health, amenities or other uses of the marine environment.

 Annex IIIAnnex III deals with the provisions for the prevention of pollution by harmful substances carried by seas in packaged form. As part of these regulations, any compounds that are environmentally harmful (known as marine pollutants) must be clearly marked and labelled as a ‘marine pollutant” (see Figure 1) to distinguish them from less harmful cargos.

27

Fate of Chemicals in the Marine Environment

Physical BehaviourWhen chemicals are spilt, they behave in a number of different ways. It is important to understand this behaviour, not only so that human health and safety implications are recognised but also to decide on the most effective response.  In simple terms, a substance behaves in one or more of five ways when spilt:

← Dissolve← Evaporate

← Float

← Gas

← Sink

Figure 2: Processes that can act on a chemical spilt into the marine environment

Classifying the substances depending on the properties they exhibit when released into the marine environment is a useful response tool. The ‘fate’

28

of a substance is determined by the properties of volatility, solubility and density and in turn, the nature of the hazard presented by the substance (toxicity, flammability, reactivity, explosive, corrosive, etc). It also defines the most appropriate technique in dealing with it, e.g. it may be possible to contain and recover a chemical classed as a “floater” using a boom.  The classification system covers gases, liquids and solids. HNS showing similar behaviour in water can be grouped together and classified into the following 12 groups on the basis of the five behavioural characteristics – See Table 3. However, it is important to be aware that this system only classifies chemicals according to their major property/properties relevant to spill response and a chemical may also exhibit other properties e.g. Benzene is classed according to its major property (evaporator) but it is also soluble to a certain extent and so this too may need to be considered.

Table 3: the European Classification System for chemicals

Property Group PropertiesG           gas evaporate immediatelyGD        gas/dissolver evaporate immediatelyE           evaporator float, evaporate rapidlyED evaporator/dissolver evaporate rapidly, dissolveFE            floater/evaporator float, evaporateFED      floater/evaporator/dissolver                

      float, evaporate, dissolve

F           floater floatFD        floater/dissolver float, dissolveDE        dissolver/evaporator dissolve rapidly, evaporateD           dissolver dissolve rapidlySD        sinker/dissolver sink, dissolveS           sinker sink

 Chemical Response Strategies

Once the main physical and chemical properties, and hence the behaviour of a spilt substance are known and the likely impacts to human health and marine resources have been taken into account, a suitable response can be considered. A brief summary of potential response techniques for the different groups of chemicals is given below. However, the response strategy eventually implemented will also be largely dependant on the specific circumstances of the incident. Gas & Evaporators- the release of a gas or chemical substance evaporating under the weather conditions prevailing at the time have the potential to generate large vapour clouds that might be toxic or form an explosive mixture with air. As a result, there may be potential health and safety implications for the vessel crew, responders and population nearby.

In order to plan a response, it is important to know how the gas or vapour will behave and the likely trajectory of the hazardous cloud. Relevant

29

computer modeling of the spreading of airborne contaminants is likely to help to forecast the movement and fate of the plume as it disperses. Appropriate safety zones can then be put into place as necessary and the public advised as appropriate.

Issuing advice to the public to remain indoors for a short period may be given by the authorities.  If the chemical is of a flammable nature, then all ignition sources must be eliminated. Techniques such as trying to “knock down” a water-soluble vapour cloud or trying to stop or deflect it using water sprays are other measures that may be available to responders. In such incidents occurring near populations, the fire brigade are likely to have the commanding role in the response.

In any case, responders must wear the appropriate Personal Protective Equipment (PPE) and response / monitoring crafts must be adequately designed should they need to enter the hazardous atmosphere. 

Chemicals that dissolve – A dissolving chemical will form a growing ‘plume’ of decreasing concentration in the water and eventually dilute. It is important to monitor the concentrations in the water to track the movement of the chemical and therefore to predict any hazard that may arise to the environment, fisheries, fresh water intakes, recreational areas, etc. Again, relevant computer models can give useful indications on the likely fate of the substance.

The ability to contain and recover dissolved chemicals is extremely limited. Providing means to accelerate the natural processes of dispersion and dilution may be the only way to respond to such chemicals. Some dissolved chemical plumes may, in theory, be neutralised, oxidised, flocculated or reduced by the application of other chemicals. However, careful assessment of feasibility and expected efficiency in an open environment as well as approval of the relevant authorities is usually required before this response method is employed.

Chemicals that float - Chemicals that float will spread under the effect of gravity to form a slick in a similar way to oil. However, unlike oil they may not be visible on the water. Nevertheless, in some cases remote sensing techniques may be employed to detect and monitor floating materials.

Floating chemicals can be low or high viscosity liquids, or may even be solid. If the spilt chemical has a high vapour pressure it may evaporate quickly and form a gas cloud above the slick. In such cases air quality monitoring is usually undertaken to assess fire, explosion and toxicity risks,.

It may be possible to consider deploying booms to contain and control the movement of substances over the water surface. Skimmers and other oil spill response equipment may also be used to recover the material from the surface of the water. However, it is important to make sure, prior to use, that the spilt chemical will not react with the equipment by taking into account the chemical’s reactivity. Alternatively, emergency

30

responders may have fire-fighting or suppressant foams that can be applied to reduce the evaporation and the risk of fire/explosions.

Again, responders must wear the appropriate Personal Protective Equipment and response / monitoring crafts must be adequately designed should they need to enter a hazardous atmosphere.

Chemicals that sink – Chemicals that sink have the potential to contaminate the seabed, and sometimes to persist in the sediment. The response to sunken chemicals may, therefore, need to consider the recovery of the chemical and any heavily contaminated sediment. Careful attention will also need to be paid to the removal and disposal of these contaminated sediments.

In shallow waters, mechanical dredgers and pump/vacuum devices may be used to recover sunken substances. The use of submersibles and remotely controlled underwater cameras may identify and recover chemicals on the seabed.

 

 Bioaccumulation refers to the build up of a substance within a living organism, or certain tissues of a living organism, due to the rate of uptake of that substance being greater than the rate of elimination by metabolic transfer or excretion. The term tends to be associated with certain lipid-soluble organic chemicals that are not readily metabolised by living organisms such as pesticides (e.g. DDT) and organometallic compounds such as methylmercury and tetra-ethyl lead (TEL).  Biomagnification refers to the sequential build up of a bioaccumulative substance up the food chain through predation.  Typically the highest concentrations of the substance are found within the tissues of the top predators within the food chain.

NB: Bioaccumulation occurs within a trophic (food chain) level. Biomagnification occurs across trophic (food chain) levels.

31