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Hazardous Substances Thematic Assessment

Executive Summary

Since 1998, including under the NEAES 2010-2020 Strategy, OSPAR’s objective for Hazardous Substances has been “to prevent pollution of the OSPAR Maritime Area by continuously reducing discharges, emissions and losses of hazardous substances, with the ultimate aim to achieve concentrations in the marine environment near background values for naturally occurring substances and close to zero for man-made synthetic substances”. OSPAR also aimed to move towards the cessation of discharges, emissions and losses of hazardous substances by the year 2020.

Concentrations of many of the most serious hazardous substances, such as PCBs, PAHs and organochlorine insecticides, have decreased substantially compared with the 1980s-1990s. Nevertheless, we find that most OSPAR sub-regions (ten out of twelve) have a poor status for hazardous substances in marine animals (fish, mussels and oysters). This is mainly caused by excessive concentrations of mercury and PCB118 (a dioxin-like polychlorinated biphenyl). Moreover, current trends indicate that only one of the sub-regions may improve substantially during the next 10-20 years. For hazardous substances in sediment, the situation is somewhat better, as approximately half of OSPAR’s sub-regions have a good status. Again, mercury is the main culprit. One Region may be expected to go from poor to good environmental status during the next 10-20 years, but no Regions are expected to go from good to poor. The ban on TBT in antifouling paints from 2008, however, seems to have worked, resulting in a general reduction in imposex levels in gastropods to values below the EAC in open waters; TBT levels in coastal areas are, thus, declining, and in some places below the EAC. It should be noted that gastropods are not the most sensitive species, as some fish larvae are hampered in their development at even lower TBT concentrations, so we are on the right track but good status for all waters is still a distant target.

Most OSPAR sub-regions have a poor status for hazardous substances in marine animals (fish, mussels and oysters). © Shutterstock

Most OSPAR sub-regions have a poor status for hazardous substances in marine animals (fish, mussels and oysters). © Shutterstock

For animals at high trophic levels such as predatory whales, even PCBs, which were mostly banned decades ago, are a real threat to survival. © Shutterstock

For animals at high trophic levels such as predatory whales, even PCBs, which were mostly banned decades ago, are a real threat to survival. © Shutterstock

Thus, while society has made considerable progress in reducing many hazardous substances, from high levels in the early 1980s to more moderate levels over the past decade, further progress towards OSPAR's objective of cessation of discharges and emissions is considerably slower. This is because of the high chemical stability of hazardous chemicals and their re-release from marine sediment, which acts as storage for past contamination. This re-release is caused by both natural (e.g., hydrodynamic and biogenic) and anthropogenic processes (e.g., bottom trawling, anchoring, dredging, and dumping operations). Also, there is continued discharge from sources both within and outside the OSPAR area. For animals at high trophic levels such as predatory whales, even PCBs, which were mostly banned decades ago, are a real threat to survival. In recent years, there has also been more focus on emerging contaminants such as PFAS (a large group of fluorinated substances), pharmaceuticals, and chemicals in personal care products (e.g., cosmetics, hygiene products and sunscreens). The diversity of these substances exposes marine organisms to a "cocktail" of chemicals. Owing to the complexity of this issue, there is still quite limited knowledge on the cumulative impact of this mixture of chemicals.

This thematic assessment focuses on the time trends for hazardous substances in the OSPAR CEMP monitoring programme, and the effects of current levels of contaminants. Emerging contaminants have been addressed by the , which represents an important tool in their identification and quantification and should be implemented in all OSPAR Regions as reported elsewhere.

Q1. Identify the problems? Are they the same in all OSPAR regions?

Hazardous substances affect living organisms

Many man-made chemicals enter the North-East Atlantic through land-based and sea-based human activities. Some of them are hazardous for the marine environment. In addition, industrial use of naturally occurring substances such as heavy metals (e.g., mercury and lead) have considerably increased the levels of those metals in the marine environment. Hazardous substances have different effects depending on their type, affecting the health, reproduction or survival of individuals, even up to species-level extinction, and can seriously affect human health through seafood consumption.

Impact across OSPAR Regions

In most parts of the Regions metals, particularly mercury, and the dioxin-like chlorinated pollutant CB 118 are found at above the levels which are expected to have an impact on the marine environment. Local pollution can affect individual Regions, but most substances reach all the Regions through large-scale air- or waterborne transport, both from the countries around the North Sea and through long-range transport from other Regions.

The problem substances and their sources

OSPAR works to identify which substances are hazardous (historical and emerging contaminants) for the marine environment, to prevent, reduce and ultimately eliminate pollution by these substances, and to monitor the effectiveness of the measures for achieving this.

Heavy metals

Heavy metals are naturally occurring substances, but their use in society has led to a significant increase in their concentrations. The heavy metals showing the highest toxicity to humans and animals are mercury, cadmium and lead. They enter the marine environment through several natural processes and human activities, via long-range aerial transport, riverine input, or run-off. Mercury is the most dangerous, as it is transformed into the highly bio-accumulative and poisonous form of methylmercury by anaerobic microbes. As a result, few parts of the Regions present mercury concentrations in organisms that are below the good environmental status threshold. The levels are highest in the North Sea, the English Channel and the Northern Bay of Biscay. Lead and cadmium are also above background levels, but the status of these metals is still considered good.

Leaded fuels, introduced in 1921, were discovered to have huge impact on human health and to increase lead pollution in the atmosphere by a factor of 100. This resulted in the adoption of clean air acts in several countries during the 1990s. In 2021, Algeria was the last country in the world to stop using leaded fuel, ending 100 years of tetraethyllead in fuels. Lead is still an important component in national water distribution, and the input through professional and, especially, recreational fishing is considerable.

Persistent organic pollutants

Many of these pollutants are exclusively man-made; they are not found in nature or produced by natural processes, they are sometimes (extremely) persistent and degrade very slowly by natural processes in the marine environment. Most of these substances have chemical properties that cause them to be excreted very slowly, so that they bioaccumulate in long-lived organisms such as fish. They may have properties that cause biomagnification, meaning that their concentrations become higher in predators than in their prey, so that those concentrations then increase as the substance moves up the food web. Nevertheless, recent findings point to a dilution at low trophic levels because of a high primary production rate occurring too fast to establish equilibrium with lipophilic contaminants (although this does not imply any degradation). Production of many of these pollutants has been banned, at least in Europe, for decades, but they still linger in the environment due to their pervasive use and stability. One example is polychlorinated biphenyls (PCBs), of which 1,2 billion tonnes were produced globally before they were banned in the mid-1980s. This is a typical example of legacy contamination – because the substances are so persistent, they remain present both in the ecosystem and in landfills, harbour sediments and marine dumping sites. Polybrominated diphenyl ethers (PBDEs) have also had widespread usage, for example as flame retardants in textiles, plastics and electronic products, but were banned from 2004 onwards in the European Union. Other compounds are by-products of both industrial and household combustion processes: PAHs (polycyclic aromatic hydrocarbons) are formed in iron mills and other metallurgic industries as well as in oil refineries, but also, and equally importantly, in transport (road, shipping and even air traffic). High concentrations of PAHs may be found near industrial sites, but their airborne release often renders the input diffuse.

PBDEs we widely used as flame retardants in textiles, plastics and electronic products, but were banned from 2004 in the EU. © Shutterstock

PBDEs we widely used as flame retardants in textiles, plastics and electronic products, but were banned from 2004 in the EU. © Shutterstock

Of course, industrial regions like the Southern North Sea exhibit higher contaminant concentrations. Owing to bioaccumulation and biomagnification, species at the top of the food web, like marine mammals, have body burdens likely to produce health consequences.

Organotin compounds

Organotins are biocides, used as plant protection or to prevent biofouling on ships and boats. The best-known substance is tributyltin (TBT), which causes malformations in oyster shells and the development of male characteristics in female marine snails, rendering the most sensitive species sterile. As a result, the dog whelk has become locally extinct in several parts of the OSPAR Maritime Area. The problem is greatest along major shipping lanes and ports. These substances are also toxic to fish larvae and influence a wide variety of marine organisms at very low concentrations.

Q2. What has been done?

OSPAR Maritime Area

Among the earliest international environmental agreements were the Oslo Convention for the Prevention of Marine Pollution by Dumping from Ships and Aircraft, adopted in 1972, and the Paris Convention for the Prevention of Marine Pollution from Land-based Sources, adopted in 1974, which cover what today is the OSPAR Maritime Area. Under the Paris Convention, the signatory countries agreed to eliminate pollution by organohalogen compounds, mercury and cadmium. These agreements formed the basis for what in 1992 became OSPAR.

In total, 65 OSPAR Decisions and Recommendations have been adopted targeting point and diffuse sources of pollution from hazardous substances. Most of these are either fully implemented or have been set aside after being overtaken by measures adopted at national level or within other forums, and are therefore no longer followed by OSPAR. Only one Recommendation, ( concerned with controlling the dispersal of mercury from crematoriums, is still in force, and the status of four others concerning oil facilities, aquaculture, metals in sewage sludge and pesticides was found to be unknown in the latest progress report on the implementation of OSPAR measures (


Historically, many substances have first been restricted or banned at national level, while multi- and bilateral cooperation restrictions and bans at international level have taken years or even decades to be put in place. For instance, France restricted the use of tributyltin (TBT) in 1982 and the Paris Convention adopted a first regional Recommendation addressing the use of TBT in 1987, while the International Convention on the Control of Harmful Anti-fouling Systems on Ships (adopted by most coastal countries banning the presence of TBT on ships’ hulls did not come into force until 26 years later in 2008. In 2000, the EU took the major step of adopting the Water Framework Directive (WFD), under which a list of priority substances was produced in 2001, and of setting Environmental Quality Standards (EQS) for water and biota concentrations under Directive 2008/105/EC. While the WFD is limited to freshwater and near-coastal environments, the Marine Strategy Framework Directive (MSFD, 2008) extends the WFD's concentration thresholds for hazardous substances to the marine environment.   

Major global-level agreements include the Stockholm Convention, ( which forbids or restricts the use of a number of organic persistent chemicals (entered into force 2004), and the Minamata Convention, ( which provides controls over numerous products containing mercury (signed in 2013).

The Paris Convention adopted a first regional Recommendation addressing the use of TBT in 1987. © Shutterstock

The Paris Convention adopted a first regional Recommendation addressing the use of TBT in 1987. © Shutterstock

Within the EU, a proposal to ban 200 PFAS substances was put forward in 2017 by Sweden and Germany, and work is underway to ban the use of PFAS in firefighting foams and a range of other applications (

Q3. Did it work?

Levels of legacy substances have decreased substantially since the onset of OSPAR and EU measures but these decreasing trends have slowed and become less distinct in recent years

The national and regional regulations and initiatives introduced from the 1980s-90s onwards have led to a strong decrease in the concentrations of most legacy hazardous organic and inorganic substances in both sediment and biota, such as insecticides and PCBs. In some "hotspot" locations, concentrations in fish have decreased by a factor of 1 000 since the 1970s. In the last 1-2 decades, the downward trends have been smaller compared with former decades, when decreases were driven by the elimination of large industrial point sources of contamination. Most metals follow the same pattern, but in the more populated OSPAR Regions (Region II and eastern parts of Regions III and IV) increasing trends are being observed in some locations for selected substances like mercury. There is an overall increasing trend for pollution in the Southern North Sea in Region II, whereas no significant improvements have been seen in the Northern North Sea, the English Channel, or the Northern Bay of Biscay, which have poor environmental status.

The OSPAR objective to continuously reduce discharges, emissions and losses has been partially achieved. OSPAR has moved towards the 2020 cessation target. The objective has been partially fulfilled for many legacy contaminants such as PCBs and PBDEs, with many time series showing downward trends and few showing upward trends. However, for heavy metals, there are more upward than downward trends for concentrations in fish and shellfish. For mercury, three times more upward than downward trends are evident in Region II, and this is also the case in all other Regions. Analysis of mercury inputs, however (see:  Inputs of Mercury, Cadmium and Lead via Water and Air to the OSPAR Maritime Area ), shows that those from air and rivers are decreasing, which is also reflected in the decreasing mercury concentrations found in sediment. The generally upward time trends for fish and shellfish could be due to internal release from sediment to water and marine organisms or to a change in the uptake of metals by fish and shellfish owing to higher temperatures. However, it could also be related to a change in the general biological condition at stations. Continuation of the current dependence on coal in Russia, China, and India for power generation, together with increasing risks of forest fires, could imply a risk of increasing atmospheric deposition of mercury in the future, despite the efforts made under the Minamata Convention.

It should be borne in mind that most long-term time series of contamination which are used for assessment, relate to sediment and to relatively short-lived species in the low to middle part of the food web. Long-lived species at the top of the food web, such as marine mammals , still exhibit extremely elevated levels of persistent organic pollutants (POPs) which were banned decades ago, such as organochlorinated pesticides (e.g., DDTs and dieldrin), polybrominated diphenyl ethers (PBDEs) and PCBs. Furthermore, the decrease of PCBs in these species seems to have stalled.

Q4. How does this field affect the overall quality status?

Environmental concentrations are still not near background values for most metals and hazardous substances

Under OSPAR’s NEAES 2010-2020 Strategy, the objective for Hazardous Substances was “to prevent pollution of the OSPAR Maritime Area by continuously reducing discharges, emissions and losses of hazardous substances, with the ultimate aim to achieve concentrations in the marine environment near background values for naturally occurring substances and close to zero for man-made synthetic substances”.

Mercury concentrations are not moving closer to background values for naturally occurring substances, and good environmental status has not been achieved owing to continued (but decreased) atmospheric transport from sources outside the OSPAR Contracting Parties, and possibly to the remobilisation of historically contaminated materials. Therefore, global initiatives to limit atmospheric pollution, as well as land-based remediation measures, are needed in order to achieve the environmental objectives. For many synthetic legacy substances such as PCBs and PBDEs the concentrations are slowly approaching the goal of "close to zero" concentrations, at least for animals low in the food web. However, for animals higher in the food web, it is uncertain whether there is any progress at all at this stage.

Q5. What do we do next?

Preventing pollution is a world-wide task and more knowledge on occurrence and effects is needed

Building on its strategic objectives for 2010-2020, OSPAR has set new strategic objectives for 2020-2030, including the following new operational objectives for this period, as listed in the North-East Atlantic Environment Strategy (NEAES) 2030:

Operational objective S2.01: Identify contaminants of emerging concern and prioritise them for action. One of the main tools used to follow this up has been the COnNECT (CONtaminants of Emerging Concern and Threat) project run by a consortium of Contracting Parties together with the NORMAN network. Here, samples from across the OSPAR area are analysed using methods that can potentially identify risk assessments for thousands of substances, thus highlighting substances that are widespread and that also occur in concentrations that may affect organisms negatively.  In addition, OSPAR has recently developed more robust and holistic models to support future prioritisation listings.

Operational objective S2.02: Further develop and identify marine-relevant assessment criteria. Work needs to be continued to allow assessment of a wider range of substances while enabling Contracting Parties to focus their efforts. In order to be taken seriously by society, the assessment criteria must be credible, and therefore it is important that they are well underpinned by ecotoxicological studies. Such studies should be performed where there is a need for more data. In some cases, such as for PBDEs, the scarcity of proper ecotoxicological data has been pointed out for years. It is highly important that ecotoxicological information on marine organisms be added to admission files of substances in ECHA. The assessment criteria must also be operational for the species commonly used in contaminant monitoring.

Operational objective S2.O3: By 2027, ensure that measures to eliminate discharges, emissions, and losses of hazardous substances are in place to achieve or maintain good environmental status. Consideration must first be given to whether there are unknown sources for the substances with increasing trends and unsatisfactory good environmental status within the Contracting Parties. This is, however, hard to achieve without a comprehensive analysis of the inputs of hazardous substances, which is currently available for only three substances, namely mercury, cadmium and lead. Other analyses of inputs to the environment exist in the scientific literature but do not cover each OSPAR Region comprehensively.

Second, more effective legislation or guidelines for minimising pollution must be introduced. While the production and use of many man-made substances have been banned in Europe, many substances have been replaced by unregulated substances that have similar properties, including toxicity. Such substitution can happen much faster than authorities are able to discover and regulate. One solution is to regulate entire classes of substances, as exemplified by the European Chemicals Agency's proposal to ban all per- and polyfluoroalkyl substances (PFASs) in fire-fighting foams.

Finally, work is required in order to establish worldwide conventions for reducing long-range transport. Many substances spread through the atmosphere, for example mercury (which has a very low boiling point) and PBDEs (which attach to airborne particulates such as dust, soot, smoke, and liquid droplets). In northern latitudes (parts of OSPAR Region I), long-range transport is the dominant input factor, and pollution affects enzyme and immune systems, hormones, reproduction, and the survival of sea birds.

OSPAR Strategic objectives 10, 11 and 12 on climate change. There is substantial evidence that increases in temperature and extreme events may enhance the release, transportation, and mobilisation of both hydrophobic and hydrophilic pollutants in the marine environment. Also, the toxicity of pollutants may increase with increasing temperatures. Climate change also contributes to oxygen depletion (hypoxia and anoxia) in the marine environment, which can increase the uptake of methylmercury in food webs and in several cases has also been found to increase the toxicity of contaminants. Thus, there is a risk that the efforts to combat the spread of hazardous substances will be cancelled out by climate change effects.

Hazardous Substances Assessments


Lead authors: Dag Øystein Hjermann and Martin Mørk Larsen

Supporting authors: Rob Fryer, Rob Berbee, Susana Galante-Oliveira, Mario Milhomens, Johan Näslund, Ane Soerensen, Jon Barber, Koen Parmentier, Lucía Viñas,
Alejandro Iglesias Campos, Eleanor Dening, Barbara Middleton, Lucy Ritchie, Chris Moulton, Julien Favier and Laura De La Torre

Supported by: Working Group on Monitoring and on Trends and Effects of Substances in the Marine Environment (MIME), Hazardous Substances Thematic Assessment Technical Group to develop the Thematic Assessments for the QSR 2023 (TG-HasTA), OSPAR Hazardous Substances and Eutrophication Committee (HASEC), Intersessional Correspondence Group on Ecosystem Assessment Outlook - Cumulative Effects (ICG‑Eco-C), Intersessional Correspondence Group on Economic and Social Analysis (ICG-ESA), Climate Change Expert Group (CCEG) and OSPAR Commission Secretariat


OSPAR, 2023. Hazardous Substances Thematic Assessment. In: OSPAR, 2023: Quality Status Report 2023. OSPAR Commission, London. Available at:

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