Pollution prevention, detection and mitigation in European coastal waters

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Coastal Wiki articles related to Pollution prevention, detection and mitigation are listed in the Category:Coastal and marine pollution.

Pollution is defined as the state of water when it contains a large amount of foreign materials so that it is no longer fit for its intended use, whether it is drinkwater, cold water for the cooling of engines, or clean water for tourism. This topic, which is of utmost importance for the European commission and national governments, covers a broad scope of knowledge including chemical processes of pollutants synthesis, hydraulic transport of compounds, biological impacts on human health or ecosystems, socio-economic consequences of a pollution event and engineering techniques for the mitigation of pollutions. The issue of observing the state of pollution and improving water quality near coastal zones has been addressed in different ways in most coastal countries, through regulations and the organisation of alert and protection systems.

However, in spite of the great efforts which have been made in the past years to reduce the number of accidental pollutions and the impacts of chronic pollutions in coastal zones, one cannot but notice a large step still has to be taken in order to improve the understanding of sources and consequences of pollution and to create better warning procedures and reliable tools to mitigate the impacts of pollution.

The current state (2008) of maritime pollution in Europe and worldwide

Accidental pollution

During the second half of the twentieth century, when economies started to widen across national borders, the amount of trade grew a lot in the world, dragging along the volume of maritime trafic between occidental countries. Governments were neither prepared nor used to face the consequences of such an economic revolution and found themselves unable to deal with the ever growing figures of oil spills and accidental pollutions near their coastlines. Therefore, it was no sooner than the 1970s that the first measures were taken to reduce the number and severity of accidental pollutions, with for instance the United Nations conventions Marpol.

The main source of accidental pollution is oil spills. An overview of their trends and relevance is given in the Coastal Wiki article Overview of oil spills events from 1970 to 2000.

Oil is not the only source of accidental pollution. The sinking of the Ievoli Sun in the Channel Sea in 2000 confirmed the existence of a chemical risk, when the ship went into the waters with its 6000 tonnes load of chemical products, including 4000 tonnes of styrene, 1000 tonnes of trichlorosilane and 1000 tonnes of isopropyl alcohol. It made decision makers notice the importance of preparing adapted responses, using innovative technologies and taking advantage of the experience of other countries.

Chronic pollution

Even if disasters have a huge impact on public opinion due to their depicting in medias, accidental pollutions only stand for a small part of the whole water pollution which is mostly caused by chronic pollutions and waste discharge in coastal waters by chemical industries.

Chemical pollution

Nitrates and phosphates

In many cases, coastal water pollution is caused by the discharge in the nearshore or estuaries of nutrients such as nitrates and phosphates which are used by agriculture and human activities. There are many sources of nutrient runoffs : unsewered urban areas, construction sites, combustion of fossil fuels by traffic, industries and households, see What causes eutrophication?. Other natural processes may be responsible for an increased concentration of nitrates and phosphates in coastal waters : atmospheric deposition of nitrogen on seas, soil erosion. The rate of water renewal plays a critical role in this field, since stagnant water can collect more nutrients than other zones with replenished water supplies.

Nutrient pollution often results in eutrophication. Eutrophication promotes excessive plant growth and favors specific species above others which leads to an excessive amount of aquatic vegetation or phytoplankton in the water and may cause other problems such as a lack of oxygen (hypoxia or anoxia) needed for fish to survive and a limitation of sunlight available to bottom-dwelling organisms. The process may also cause competitive release by making available a normally-limited nutrient which may cause a shift in species composition of ecosystems, see Possible consequences of eutrophication.

Human population are also concerned through economic problems caused by the decrease of resource value of coastal seas with hindered fishing activities and beaches less attractive for tourists.

In Europe, the whole Baltic Sea is affected by eutrophication and nutrient related problems are widespread in esturaries and fjords, see Eutrophication in coastal environments. In the Celtic seas, the phenomenon takes place only in the Irish sea, estuaries and coastal lagoons. In the Mediterranean Sea, eutrophication is more restricted and limited to specific coastal and adjacent offshore areas, especially in the Adriatic, Gulf of Lion and northern Aegean Sea. The main increase in nutrient loads took place during the middle of the 20th century, with a doubling of nitrogen loads from the 1950s to the 1980s and a fourfold increase of phosphorus loads from the 1940s to the 1970s in the Baltic and North Sea regions, and probably similar values in the Mediterranean Sea. Trend analyses in the Baltic and North Sea land-based regions however show a recent decrease in phosphorus loads in the 1990s due to improved sewage treatment and use of phosphate free detergents, but there is no discernible reduction in the nitrogen loads. Generally, nutrient loads are decreasing in all parts of Europe. However, nutrient concentrations do not show a similar trend.

Heavy metals

Heavy metals is a general collective term which applies to the group of metals and metalloids with an atomic density greater than 4 g/cm³. The category includes cadmium, chromium, copper, mercury, lead, zinc, arsenic, boron and the platinum group metals.

Heavy metals in trace amounts are normal constituents of marine organisms and some of them, such as zinc, copper and cobalt, are absolutely essential for normal growth and development. In coastal regions, these metals are normally supplied to the sea in river water. However, at present time, additional quantities of metals are being added to estuaries and coastal regions from industrial effluents, from sewage and atmospheric pollution. At sufficiently high concentrations, those heave metals become toxic to living organisms.

Since heavy metals are basic elements of the periodic classification, they can not be broken down and will persist in the environment. In some specific areas where water flows are concentrated in confined zones like estuaries or lakes, they will even tend to accumulate with time. Many of the heavy metals are toxic to organisms at low concentrations. Effects on the organisms are manifest when the natural regulation mechanism of the body concentration of metals breaks down as a result of either an insufficiency or an excess of metal.

The level of exposition to heavy metals pollution can be estimated through indicators linked to the speed of refreshment of water in a delimited surface, such as residence times, see the Coastal Wiki article Dispersion processes in estuaries.


The largest source of oil pollution in coastal waters is not the numerous disasters happening along the European coasts which only represent 5 % of the total amount of oil spilled in water (6.11 million tonnes in 1973, 2.35 million tonnes in 1990), but the continuous pipelines leaks and runoff, with 61 % of oil coming from river oil pollution and urban runoff and 30 % due to intentional discharges from tankers. Figure 1 shows that chronic sources of oil pollution are relevant compared to accidental disasters and have to be taken into account when elaborating action plans for the mitigation of oil pollution in coastal waters.

Figure 1: Inputs of oil pollution in the marine environment

In this field, a general decrease of total oil pollution is usually observed in the last decades, although this global situation may differ at regional level. This is mainly due to the entry into force of stricter requirements to activities accompanied by oil discharges. In 1981, oil transportation and shipping in general were responsible for discharging about 1.4 million tons of oil products. This amount was reduced to 0.56 million tons in 1990. The reduction mainly occurred as a result of adopting stricter international regulations concerning transportation operations in the sea (International Convention for Prevention of Pollution from Ships and others). The total oil pollution input into the sea during the same period dropped from 3.20 to 2.35 million tons. See alsoOverview of oil spills events from 1970 to 2000.

Persistent organic pollutants

Persistent organic pollutants (POPs) include a wide range of substances: industrial chemicals (such as polychlorinated biphenyls – PCB) and by-products of industrial processes (e.g., hexachlorobenzene – HCB, and dioxins) whose toxic characteristics are unintentional, and others, such as pesticides (e.g., DDT) and herbicides (e.g., lindane – HCH), that are designed to have toxic properties. POPs containing chlorine are referred to as organochlorines.

POPs are of special concern because they persist in the environment for long periods of time, which allows them to be transported large distances from their sources, are often toxic, and have a tendency to bioaccumulate; many POPs biomagnify in food chains.

Biological pollution

Endocrine disruptive compounds

Endocrine disruptive compounds (EDCs) are compounds that may be hormonally active at low concentrations because they are exogenous agents that interfere with the synthesis, secretion, transport, binding, action or elimination of natural hormones in the body that are responsible for the maintenance of homeostasis, reproduction, development and behaviour. EDCs mimick endogenous hormones necessary for the regulation of vital functions in living organisms.

Substances which are potential EDCs are phytoestrogens, synthetically-produced hormones, natural hormones and synthetic industrial compounds such as phtalates, alkylphenols, organochlorine pesticides.

It is quite difficult to characterize the evolution of concentrations of EDCs in coastal waters since they are usually present in very small quantities and may be active at low concentrations. Nevertheless, research should be carried out to improve assessment of different kinds of EDCs, identify the most sensitive areas and characterize the effects of those compounds on human health as well as the interactions between various chemicals. Further details can be found in the Portal on Ecotoxicology and the article Endocrine disrupting compounds in the coastal environment.

Physical pollution

Intrusion of saltwater

Saltwater intrusion is a natural process that occurs in virtually all coastal aquifers, where they are in hydraulic continuity with seawater. It consists in salt water flowing inland in freshwater aquifers. This behaviour is caused by the fact that sea water has a higher density than freshwater. This higher density has the effect that the pressure beneath a column of saltwater is larger than that beneath a column of the same height of freshwater. If these columns were connected at the bottom, then the pressure difference would trigger a flow from the saltwater column to the freshwater column. Pumping of freshwater reduces the water level and water pressure and intensifies the effect, making groundwater unfit for its usual uses : drinking and irrigation. See also Groundwater management in low-lying coastal zones.

As shown on figure 2, the issue of saltwater intrusion is most important in Southern Europe regions, where coastal aquifers are overexploited for the needs of agriculture and the human population living near the sea. Some specific problems are also observed along the Eastern coastlines of Denmark towards the Baltic Sea and, to a smaller extent, in Germany.

Figure 2: Places of saltwater intrusion in Europe (Source : EEA 2000)

Thermal pollution

Thermal pollution results primarily from electric power plants that use large quantities of cooling water and discharge it at temperatures as much as 10 Celsius degrees above that of the surrounding water. The increase in water temperature disrupts the life cycle of many marine organisms and encourages invasion by creatures usually living in warmer waters.

Hot water generally decreases the concentration of dissolved oxygen, thus harming aquatic animals. Thermal pollution may also increase the metabolic rate of poikilotherms organisms, acting as an enzyme and resulting in these organisms consuming more food than usually. Thus an increased temperature may lead to food shortage in coastal ecosystems. It is known that temperature changes of even one or two degrees can cause significant changes in organism metabolism, with an alteration of enzyme metabolism, coagulation of proteins, affecting mortality and reproduction. Furthermore, changes in the environment may also make fishes and aquatic animals migrate to more suitable environment.

Pollution assessment

Observation tools

The detection and measurement of chemical or biological compounds at sea is a quite difficult task, as it is usually expensive to take samples of water to analyse it, and some compounds are present at so low concentrations that there are nearly impossible to observe, even with a sample of water. Other types of chemicals transported at sea mix with water and are rapidly dispersed, or sink to the seafloor because of their higher density and low solubility.

Many tools have been developed and are currently implemented to detect pollution and evaluate water quality in coastal zones. The Coastal Wiki gives examples of local initiatives based on academic research and yielding interesting results in the detection and assessment of maritime pollutions, see the articles Oil spill monitoring, Oil spill pollution impact and recovery, Oil sensitivity mapping and Common biomarkers for the assessment of marine pollution.

Transport and dispersion models

Fast and precise pollution dispersion models can help to predict the fate of contaminated compounds in the nearshore seas and thus, with the help of predictive climate and oceanologic models, to protect coastal populations and ecosystems from the impacts of chemical or biological pollution. A lot of efforts have to be done to improve those models and our understanding of the physical processes behind transport and mixing of pollutants at different temporal and spatial scales. For further details on transport and dispersion models can be found in the Coastal Wiki articles Seawater intrusion and mixing in estuaries and Transport and dispersion of pollutants, nutrients, tracers in mixed nearshore water.

Risk analysis

To protect coastal population from the impacts of marine pollutions, three methods can be applied, simultaneously or successively :

  • prevent the pollution from happening by applying strict regulations on the potentially-dangerous human activities and monitoring the concentration and load of pollutants in high-risk zones such as ship ways and industrial zones ;
  • compensate for the impacts of pollution by limiting the dissemination of pollutants in coastal areas and applying mitigation techniques (cleansing of beaches and nearshore waters, transformation of the pollutant in a less toxic body by addition of a chemical or biological reactive,...) ;
  • flee from the danger by evaluating the level of risk of coastal regions and make human and animal populations retreat in safer areas which have first been prepared to shelter them.

Most of the time, those three aspects are implemented together, although the last one may be not be well accepted by inhabitants of coastal zones who have to leave their home. Nevertheless, after a major pollution event arises which has strong consequences on human population, people become aware of the danger and are willing to settle in safe areas.

Whether it is for the prevention of pollution or for the identification of dangerous areas, a risk analysis is necessary, combining an observation of the actual state of pollutants loads, an evaluation of the neighboring vulnerabilities and an estimation of the socio-economic consequences if an event occurs. This analysis can lead to the drawing of a risks map along the European coastlines which will give decision makers a better understanding of the dangers they have to face in their own regions, helping them identifying priorities in the prevention and mitigation actions.

Environmental risk assessment for pollution of marine activities : this article gives a comprehensive definition of risk assessment in the case of pollution due to marine activities and establishes a framework for the risk evaluation

Case study risk analysis of marine activities in the Belgian part of the North Sea : this case study shows how a full risk analysis can be carried on with the example of the Belgian part of the North sea

Index of vulnerability of littorals to oil pollution : this article gives an easy framework to evaluate the vulnerability of different kind of littorals to oil pollution, with respect to their exposition to swell and tidal waves and their soil composition.

Legal framework and regulations

European level

Since the first issues regarding coastal waters pollution were raised by scientists and local decision makers, the European commission has been dealing with the problem by elaborating recommendations for the member states and publishing directives for the prevention of pollution and the improvement of coastal environment. Two major documents about coastal zones have to be quoted in this framework :

Coastal zones are also indirectly addressed in other European directives :

Regarding dangerous substances discharged into the aquatic environment by industrial plants, EU REACH legislation has introduced a system of stricter limit values, while at the same time leaving member states free to choose the system of quality objectives, with the corresponding obligation to show that these objectives are being complied with. The basic directive 76/464 adopted in 1976, contains a blacklist of 129 substances declared dangerous by virtue of their toxicity and bio-accumulation; it was supplemented in December 1979 by Directive 80/68 on the protection of groundwater against pollution caused by certain dangerous substances. Pursuant to these directives, specific directives were introduced prescribing limit values and quality objectives for the discharge of cadmium, hexachlorocyclohexane (HCH) and mercury.

International level

Most of the European countries have also signed the United Nations convention on the law of the sea (UNCLOS) proposed by the International maritime organisation (IMO) and entered into force in 1994. Its 145th article require member states to cooperate in the field of prevention, reduction and control of pollution to the marine environment, including the coastline. Particular attention must be paid to the need for protection from harmful effects of such activities as drilling, dredging, excavation, disposal of waste, construction and operation or maintenance of pipelines. This includes pollution from land-based sources, seabed activities, dumping, shipping, and atmospheric exchanges.

Various international agreements were also signed at the end of the 20th century to reduce pollution in the worst affected areas. The Bonn agreement deals with the protection of the North Sea against hydrocarbons and other harmful substances. Its main topics are the protection of ecosystems and the prevention of pollution from ships and drilling platforms. The Warsaw convention tries to establish a framework for the conservation of living resources of the Baltic Sea. The Mediterranean sea is also the subject of a number of agreements, dealing with the prevention of pollution caused by dumping from ships.

Specific agreements were signed to solve major issues related to marine pollutions, and are adopted by an increasing number of states in the world. The Convention on the prevention of marine pollution by dumping of wastes and other matter, known as the London Convention of 1972, is the primary international agreement controlling the deliberate dumping of non-ship generated wastes at sea. Since entering into force in 1975, the London Convention has become more restrictive over the years. The Global program of action for the protection of the marine environment from land-based activities was decided in 1995 by the member states and constitutes a practical source of guidance for action which must take place at the national and regional level, aiming to reduce land-based pollution in the nearshore seas. The Internal convention on civil liability for oil pollution damage, which was adopted in 1969 just prior to the first "Fund convention" for compensation of oil pollution damage in 1971, established the IFOP and the first procedure for assisting member states in the compensation of impacts of oil pollution. The Marpol convention was probably one of the most effective in the 1980s and resulted in a dramatic decrease of the number of maritime pollution disasters. Finally, the OPCR convention (International convention on oil pollution preparedness, response, and cooperation) which entered into force in 1995, provides an international framework for a better collaboration between states in the field of prevention, detection and alert of oil pollution incidents and the mitigation and compensation measures. Similar conventions were adopted a few years later and generalised this framework to other pollutants : the International convention on liability and compensation for damage in connection with the carriage of hazardous and noxious substances by sea (1996), the International convention on supplemental compensation for nuclear damage (1997).

A comprehensive list of international agreements as well as national regulations can be found in the Coastal Wiki article North Sea pollution from shipping: legal framework.

Priority issues

Particular care should be taken to improve knowledge and practice in the following unresolved issues :

  • Observation and monitoring of pollution
    • Observation system of priority substances settled by EU
    • Characterisation of pollutants and contaminants
    • Determination of chronic pollution sources
    • Technology for tracking and monitoring of pollutants
  • Management of risk with respect to the ecosystem
    • Integrated assessment of ecological and socio-economic impacts
    • Decision making process to assess sanitary impact
    • Vulnerability indices and sensitivity maps
  • The fate and impacts of pollutants
    • Chemical and physical processes from source to the living organisms
    • Impacts of pollutants on living organisms and ecosystems
    • Pressure on human activities in coastal zones


This section of the Coastal Wiki provides an overview of current and future issues related to maritime pollutions as well as related scientific or policies topics like socio-economic impacts of pollutants in coastal zones, assessment of pollution and methods for risk management and mitigation, and national and European policies dealing with those issues.

Nevertheless, maritime pollution and water quality are highly shifting topics and techniques and policies related to them are in constant evolution, gradually integrating new aspects when major events occur through the world sometimes resulting in human or ecological losses but always involving a progressive awareness of the threats and vulnerabilities and feeding the improvement of mitigation techniques and prevention policies. Therefore this state of the art is only a snapshot at a given time and cannot be regarded as a final document : it has to keep living and being fed with international events and technological news.

Whereas many initiatives were taken during the previous years in the form of international agreements and proved successful by succeeding in decreasing the number and severity of accidental pollutions and reducing the discharge of pollutants in coastal zones, some major issues remain unexplored until today. The chemical and geographical fate of pollutants needs some scientific development as many operational forecasting tools proved inefficient to predict the consequences of a local pollution, even on a short time basis. Moreover, the impacts of pollutants on living organisms need to be better assessed on a long-time scale. As far as the current state is concerned, local research initiatives carried out to assess pollutants loads and impacts in bounded regions have to be merged on a continental scale in a European observatory to benefit from the results of each other. Finally, risk management practices could be improved and their use generalised as a whole component of integrated coastal zone management.