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'''Figure 3''' - Categories of HNS behaviour and the physicochemical characteristics (density , vapour pressure  and solubility ) on which the categorisation is based. The density is specified as 1023 kg/m3; this might vary in different locations depending on the salinity. Source: EMSA (2007).  
'''Figure 3''' - Categories of HNS behaviour and the physicochemical characteristics (density, vapour pressure  and solubility ) on which the categorisation is based. The density is specified as 1023 kg/m<sup>3</sup>; this might vary in different locations depending on the salinity. Source: EMSA (2007).  
'''Density''' - ρ (substance) = mass/volume. Gives an indication of the likelihood that a substance will float or sink (average density of seawater: ρ = 1.025 g/cm3);  
'''Density''' - ρ (substance) = mass/volume. Gives an indication of the likelihood that a substance will float or sink (average density of seawater: ρ = 1.025 g/cm3);  

Revision as of 00:25, 24 November 2017

Copyright Cedre.jpg

The sections below address the hazardous chemicals transported by sea, the chemical spill incidents, the definition of Hazardous and Noxious Substances (HNS) and the risks associated with HNS (e.g. the behaviour of chemicals in the marine environment). A brief introduction to the advantage of classifying chemicals according to the behaviour on preparedness and response to chemical spills is also provided.

1. Hazardous chemicals transported by sea

Society is highly dependent upon chemicals for myriad applications within health care, pharmaceuticals, household goods and products, water sanitation, energy, agriculture, food preservation and transportation. Therefore, chemicals are undoubtedly essential and contribute substantially to society.

Maritime shipping is a highly efficient option for global transportation of chemicals to society. However, chemicals carried by maritime shipping (e.g. through tankers, container ships and bulk carriers) can have the potential to cause harm to human health and the environment (if spilled). These chemicals can essentially be classified into 2 categories (OPRC-HNS Protocol):

  • Oil i.e. petroleum hydrocarbons;
  • Hazardous and noxious substances (HNS) i.e. anything hazardous other than oil.

This course will focus on HNS

Source ITOPF (2014a).png

Maritime transport of HNS

The world maritime transport of HNS has grown considerably in the last few decades, including transportation to, from and within European waters, due to the continuous development of the chemical industry, the need to supply raw materials to this industry and transport high volumes of products from the industries to the customers.

Data indicate that approximately 90% of European Union external trade is transported by sea with estimates indicating:

  • up to 50,000 HNS carried by sea;
  • around 2000 HNS carried on a regular basis.

Furthermore, the International Maritime Organization (IMO) estimated over 200 million tonnes of chemicals traded annually by tankers.

Source International Tanker Owners Pollution Federation 2014a.png

PROBLEM: The constant growth in the volume of chemicals that are transported by sea increases the RISK OF ACCIDENTAL SPILLS.

2. Chemical spill incidents

Maritime chemical incidents vary in their nature and type, but typical examples include fires and explosions, leakages, spillages, and airborne releases. These incidents may be either accidental or deliberate. Additionally, incidents may occur and finish very rapidly whilst others may last for long periods. Their effects may be localised or may extent over very large areas.

It has been observed that chemical spills occur at a much lower frequency than oil spills. Therefore, the probability of shipping incidents involving HNS to occur is considered low because of the high safety standards. However, it does in fact exist as recent ship incidents involving chemicals have shown. Records from European Maritime Safety Agency (EMSA) revealed that around 100 maritime incidents involving HNS happened in European waters between 1987 and 2006. According to Cedre, ship-source HNS incidents over 10 m3 (around the world) reached the number of 126 in the period from 1998 to 2013.

Source ITOPF 2014a.png


1988 - The tanker Anna Broere sank in the Netherlands and released 200 t of acrylonitrile (a toxic, flammable and explosive substance; giving off toxic fumes in case of fire; DE: Dissolver/Evaporator). In this incident:

  • The boat had to be cut in two after lightering its cargo.
  • About half of the acrylonitrile cargo was recovered.
  • The other half had leaked out and rather quickly dispersed into the sea.
  • This incident caused damage to the marine biota, but with significantly less impact than anticipated presumably because a large quantity evaporated and hence was no longer bioavailable for aquatic organisms.

2000 - The tanker Ievoli Sun sank in the English Channel and released 3998 t of styrene (a synthetic chemical considered as a marine pollutant, toxic, relatively insoluble (310 mg/L) and with a lower density than seawater (specific gravity 0.91 vs. 1.04); FE: Floater/Evaporator). After this incident:

  • The entire cargo of styrene was pumped out.
  • However, IFREMER detected styrene in the gills and the tissues of crabs in the vicinity of the wreck, since leakage was detected by a French Navy submersible drone.
  • Initial visual surface observation showed a slick and styrene vapours were detected at a nearby Island (Alderney).
  • High intensity currents resulted in significant dilution or spreading of styrene in seawater.
  • The possibility of chronic effects was considered to be minimal due to the behaviour of styrene following release from the vessel.

The following figure shows other cases of HNS spills (and their localisation) between 2005 and 2014:

Source ITOPF2014 HNS spills.png
Source ITOPF2014a HNS spills (2).png

Information on HNS incidents has been compiled in an online database hosted at CIIMAR. For more information on this database please consult the Unit 4.2 - Integration of online databases in preparedness & response. Other database of spill incidents and threats in water around the world was also produced by Cedre .

Incidents from maritime spills can potentially be devastating and can have a variety of adverse impacts. For more information on human health and/or environmental/ecological impacts resulting from chemical incidents, consult the Unit 2 - Environmental Impacts.

3. Definition of Hazardous and Noxious Substances (HNS)

Not all chemicals transported by sea are considered hazardous but those that are have been termed “hazardous and noxious substances” (HNS) (8 million +).

Hazardous and noxious substance (HNS) (OPRC-HNS Protocol, 2000 - definition) - any 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.


The HNS Convention (2010) (HNS Convention (2010)) describes HNS as a substance identified in one or more lists of the International Maritime Organization's (IMO) Conventions and Codes. Some examples of these conventions and codes can be found in table 1.

Table 1 - Examples of IMO Conventions and Codes providing HNS lists. Source: ITOPF (2014b, d).

IMO Conventions and codes.png

According to table 1, the HNS (gas, liquid or solid) may be carried in bulk or as packaged goods.

The Conventions and Codes listed above are designed to ensure the safe transport of all types of chemicals.

Therefore, HNS INCLUDE (according to the HNS Convention) ...

  • All liquefied gases in bulk (e.g. liquefied natural gas (LNG), liquefied petroleum gas (LPG), ammonia, ethylene, propylene, ethane);
  • Bulk liquids if there are potential safety, pollution or explosion hazards:
    • organic chemicals (e.g. styrene, xylenes, methanol);
    • inorganic chemicals (e.g. acids such as sulphuric or phosphoric acids, caustic soda);
    • persistent and non-persistent oils of petroleum origin;
    • vegetable and animal oils and fats (e.g. palm oil, soybean oil and tallow).
  • Bulk solids such as fertilizers, sodium and potassium nitrates, sulphur, some types of fishmeal;
  • Packaged dangerous, harmful and hazardous material.

Note: By their definition HNS can be a multitude of chemicals ranging from gases and solvents to vegetable oils and metals.

More examples of HNS can be found in the following document:


  • Radioactive materials;
  • Most inert bulk solids (e.g. alumina, iron ore, cement, grain, etc.);
  • Oil damages already covered under CLC, FUND conventions.


If the chemical concerned:

  • has a low biodegradation rate or high persistence;
  • has a high bioaccumulation rate;
  • is classed as toxic / flammable / explosive / corrosive or reactive;


It is likely to be considered as HNS (radioactive and infectious substances are outside the scope of the HNS regime).


The definition of an HNS as defined by the OPRC-HNS Protocol 2000 differs widely from the definition of an HNS under the International Convention on Liability and Compensation for Damage in Connection with the Carriage of Hazardous and Noxious Substances (HNS) by sea (also known as the HNS Convention).

The answer to the question "What are chemical" can also be found in ITOPF (2004b) (pages 2-3; see the document in the Reference list).

4. Risks associated with HNS

Two factors essentially govern the hazards posed by a HNS carried at sea, namely:

  • Its physical behaviour in the environment.
  • Its harmful properties (e.g. toxicity, flammability, persistence, reactivity, corrosivity, explosivity).

Note: Information on HNS hazards (Flammability, Explosivity, Oxidising hazard, Toxicity, Corrosive hazard, Irritant/Harmful, Environmental hazard, Reactivity) can be found in ITOPF (2004b) (pages 5-8; see the document in the Reference list).

Harmful properties of chemicals carried at sea can be obtained from different reference sources (e.g. GESAMP, OECD, TOXNET, WHO IPCS). These properties can have an impact on safety, environmental assets and socioeconomic activity. However, it is the physical fate of the HNS once it is released into the wider environment which determines if these properties will have an impact.

Note: Characteristics of HNS can also be found in a number of databases including:

The fate of HNS material is the behaviour of the material once released into the wider environment. This is determined by the physical properties of density, volatility, and solubility of the released substance. Thus, these parameters determine the hazard(s) presented by the substance (toxicity, flammability, reactivity, explosivity, corrosivity, etc.).

Note: The behaviour of HNS spilled into the sea also depends on the local marine environmental conditions.

Hazardous profile of HNS

According to IMO regulations, any packaged cargo transported at sea which poses a threat to people, other living organisms, property or the environment should be listed on the manifest as “Dangerous Goods” and should display the appropriate hazard labels, for example as per the International Maritime Dangerous Goods (IMDG) code or the UN Globally Harmonised System (GHS). Additionally, any packaged cargo that represents a threat to the marine environment (haz. to env. in figure 1) should also display an “Aquatic Hazard” label (Figure 1).

Hazardous profile HNS ITOPF, 2014a.png

Figure 1 – Hazardous profile of HNS - UN Globally Harmonized System (GHS) of Classification (Source: ITOPF, 2014a).

4.1. Behaviour of chemicals in the marine environment

While most oils are immiscible with seawater and float on the sea surface, HNS chemicals are considered a threat because exhibit a wider range of behaviours once released into the environmental compartments and toxicities to marine organisms.

Note: The HNS that have bioaccumulation potential, moderate to high toxicity, properties of persistence and/or long term carcinogenic effects represent the highest hazard to the marine environment after a spill.

The Standard European Behaviour Classification (SEBC) System has been developed in order to classify chemicals according to their physicochemical behaviours when spilled into the sea. The main principle of the system is the characterization of spilled chemicals as gases (G), evaporators (E), floaters (F), dissolvers (D), sinkers (S) and the various combinations of these (GD, ED, FE, FED, FD, DE and SD) (Figures 2, 3 and 4).

SEBC ITOPF 2014b.png

Figure 2 - Diagrammatic representation of the Standard European Behaviour Classification (Source: ITOPF, 2014b).

In the Bonn Agreement Counter Pollution Manual (Chapter 26: Hazardous Material), the behaviour of HNS once released was grouped as shown in Figure 3.

Categories HNS EMAS 2007.png

Figure 3 - Categories of HNS behaviour and the physicochemical characteristics (density, vapour pressure and solubility ) on which the categorisation is based. The density is specified as 1023 kg/m3; this might vary in different locations depending on the salinity. Source: EMSA (2007).

Density - ρ (substance) = mass/volume. Gives an indication of the likelihood that a substance will float or sink (average density of seawater: ρ = 1.025 g/cm3);

Vapour pressure - Describes the likelihood that a substance will evaporate to form a vapour. The higher the vapour pressure, the more a substance tends to evaporate (Slow evaporator VP > 300 Pa, fast evaporator VP > 3 KPa).

Solubility - The ability of a solid, liquid or gas to dissolve in a liquid (usually given for freshwater).

As we can see in figures 2, 3 and 4 and also in table 1, the substances can have more than one physical fate in the marine environment (e.g. dissolver/evaporator, floater/dissolver). In detail, the types of physical fate (behaviour) for solids, liquids, and gas can be defined under the following groups:

  • EVAPORATORS (E) - substances with a high vapour pressure (>3k Pa) and low solubility (<1%). The vapour cloud formed behaves the same way as that of a GAS (G). Such a liquid substance is also termed a “fast evaporator”.
  • FLOATERS (F) - substances which do not significantly evaporate (<0.3 kPa) and dissolve (<0.1%).
  • DISSOLVERS (D) - substances which dissolve in water (>5%) and do not rapidly evaporate. The degree of solubility of the dissolvers and the turbulence in the water column will determine whether toxic concentrations in the water column will occur.

Note: When the density of a chemical is lower than that of seawater, the parameters of vapour pressure and solubility allow to differentiate between evaporators (volatile liquids), floaters (non-volatile liquids) and dissolvers.

  • SINKERS (S) - comprises all products which are denser than seawater and that are not soluble (solubility <0.1%).
  • GD - chemicals that evaporate immediately and dissolve.
  • ED - liquids which rapidly form a vapour substance (>3 kPa) and dissolve in water (>1%). Although dissolving, such substances may form flammable vapours over the water surface.
  • FE and FED - floating substances which slowly evaporate (0.3-3 kPa), but FE does not dissolve (<0.1%) and FED does (0.1-5%). For FED, the extent of solubility will determine whether toxic concentrations might occur in water. FED will completely disappear in time.
  • FD - floating substances which do not significantly evaporate (<0.3 kPa) but slowly dissolve in water (0.1-5%).
  • DE - substances which dissolve in water (>5%) and rapidly evaporate (>10 kPa).
  • SD - substances which sink and then dissolve with a solubility >0.1%.

The fate of HNS in the environment after a spill is illustrated in the next figure:

HNS fate CEDRE.png

Source: Cedre; Removed from Liebert T (2013).

Some examples of HNS with different behaviours (when released in the environment) can be found in table 1 and figure 4.

Table 1 - Refined grouping of HNS behaviour categories once released in the marine environment. Source: HELCOM Manual on Cooperation in Response to Marine Pollution; EMSA (2007).

Source HELCOM Manual on Cooperation in Response to Marine Pollution; EMSA (2007)..png

Source Cedre; Removed from Liebert T (2013)..png

Figure 4 - Examples and different behaviour classes of HNS. Source: Cedre; Removed from Liebert T (2013).

Recently, GESAMP (2014) added an additional behaviour class by combining floating properties with high viscosity in order to predict longer lasting or persistent slicks. These substances (e.g. Decanoic acid, 1-dodecanol, nonylphenol) are rated as ‘Fp’ (persistent floater).

More information on behaviour of chemicals in the marine environment can be found in ITOPF(2014b) (pages 3-6; see the document in the Reference list) and also in the following document (pages 54-61):

5. Advantage of classifying chemicals according to the behaviour on preparedness and response to chemical spills

There is growing international awareness of the need for safe and effective contingency arrangements for responding to chemical spills. However, HNS preparedness and response is less well defined (and not as straightforward) than that for oil spills due to the great complexity and variety of chemicals transported by sea (their behaviour once spilt, different properties, hazards such as toxicity, etc.). Furthermore, it is known that the consequence of a chemical spill can be more wide reaching than that of oil.

Note: The answer to the question “Are HNS spills more dangerous than oil spills?” can be found HERE (ITOPF page) (also consult the appendix).

Anemona exercise 1.JPG

Anemona exercise 2.jpg

Classifying the chemicals, whether gases, liquids or solids, according to the behaviour exhibited when released into the marine environment, is a useful tool when developing a response strategy. This leads to a need for a relatively low number of generally applicable response options in a spill event. Additionally, based on information on the short-term behaviour of the spilled compound, it is possible to define a detection and monitoring plan well adapted to the geographical location, particular sea and atmospheric conditions, hydrodynamics, and characteristics of the water column and sea bottom compartments. Therefore, it is important to understand the behaviour of HNS spilled in order to decide the most effective response method and also recognise the health and safety implications.

Grouping HNS substances has the advantage of focusing attention on those aspects of the release that relate to potential impact and problems of response.

Anemona exercise 3.jpg


Bonn Agreement (2017). Bonn agreement counter pollution manual. Available at: http://www.bonnagreement.org/manuals (accessed March 30, 2017).

Cedre (2009). Review of chemical spills at sea and lessons learnt. INTERSPILL 2009 Conference White Paper Technical Appendix. Marseille, France (40 pp.).

Cunha I, Neuparth T, Moreira S, Santos MM, Reis-Henriques MA (2014). Management of contaminated marine marketable resources after oil and HNS spills in Europe. Journal of Environmental Management 135: 36-44.

Cunha I, Moreira S, Santos MM (2015). Review on hazardous and noxious substances (HNS) involved in marine spill incidents - an online database. Journal of Hazardous Materials 285: 509–516.

Cunha I, Oliveira H, Neuparth T, Torres T, Santos M (2016). Fate, behaviour and weathering of priority HNS in the marine environment: an online tool. Marine Pollution Bulletin 111 (1-2): 330-8.

EMSA (2007). European Maritime Safety Agency. Action Plan for HNS Pollution Preparedness and Response. Available at: http://www.emsa.europa.eu/hns-pollution/123-hns-pollution/260-action-plan-for-hns-pollution-preparedness-and-response.html (accessed March 16, 2017).

GESAMP (IMO/FAO/UNESCO-IOC/WMO/WHO/IAEA/UN/UNEP Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection) (2014). Revised GESAMP Hazard Evaluation Procedure for Chemical Substances Carried by Ships, 2nd edition. Rep. Stud. GESAMP No. 64, 126 pp.

HASREP (2005). Response to harmful substances spilt at sea. Prepared by the Alliance of Maritime Regional Influences in Europe (AMRIE) Centre de Documentation, de Recherche et d'Expérimentations Sur Les Pollutions Accidentelles Des Eaux. (CEDRE) and TNO Built Environment and Geosciences, The Netherlands (38 pp.).

IMO (International Maritime Organisation) (2000). Protocol on Preparedness, Response and Co-operation to Pollution Incidents by Hazardous and Noxious Substances (OPRC-HNS Protocol). Available at: http://www.imo.org/en/About/Conventions/ListOfConventions/Pages/Protocol-on-Preparedness,-Response-and-Co-operation-to-pollution-Incidents-by-Hazardous-and-Noxious-Substances-(OPRC-HNS-Pr.aspx (accessed March 9, 2017).

IMO/UNEP (2003). Regional Information System, Part D, Operational Guides and Technical Documents, Section 11, Practical Guide to Marine Chemical Spills, REMPEC (Regional Marine Pollution Emergency Response Centre for the Mediterranean Sea).

International Oil Pollution Compensation FUND 1992 (2005). Guide to the implementation of the HNS Convention. 27 pp.

ITOPF (2014a). Session 1 - Overview of Hazardous and Noxious Substances. Available at: http://www.hnsconvention.org/fileadmin/IOPC_Upload/hns/files/1%20Overview%20of%20HNS-Risk%20and%20Incidents%202014_ITOPF.pdf (accessed March 21, 2017)

ITOPF (2014b). Response to marine chemical incidents. Technical Information paper n.º 17. Available at: file:///D:/Desktop/TIP17ResponsetoMarineChemicalIncidents%20(2).pdf (accessed February 15, 2017).

ITOPF (2014c). Chemical Fate and Effects. Available at: http://www.itopf.com/knowledge-resources/documents-guides/hazardous-and-noxious-substances-hns/chemical-fate-and-effects/ (accessed March 3, 2017).

ITOPF (2014d). Hazardous and Noxious Substances (HNS). Available at: http://www.itopf.com/knowledge-resources/documents-guides/hazardous-and-noxious-substances-hns/ (accessed February 14, 2017).

Liebert T (2013). Claims procedures for HNS: How they might work. Available at: http://www.hnsconvention.org/fileadmin/IOPC_Upload/hns/files/Claims.pdf (accessed February 23, 2017)

MARINER (2016). Mariner project. Available at: http://mariner-project.eu/about#objectives (accessed March 23, 2017)

Neuparth T, Moreira S, Santos MM, Reis-Henriques MA (2011). Hazardous and noxious substances (HNS) in the marine environment: prioritizing HNS that pose major risk in a European context. Marine Pollution Bulletin 62: 21–28.

Neuparth T, Capela R, Rey-Salgueiro L, Moreira SM, Santos MM, Reis-Henriques MA (2013). Simulation of a hazardous and noxious substances (HNS) spill in the marine environment: lethal and sublethal effects of acrylonitrile to the European seabass. Chemosphere 93: 978–985.

Solé M, Lima D, Reis-Henriques MA, Santos MM (2008a). Stress biomarkers in juvenile Senegal sole, Solea senegalensis, exposed to the water-accommodated fraction of the “prestige” fuel oil. Bulletin of Environmental Contamination and Toxicology 80: 19–23.

Solé M, Lobera G, Lima D, Reis-Henriques MA, Santos MM (2008b). Esterases activities and lipid peroxidation levels in muscle tissue of the shanny Lipophrys pholis along several sites from the Portuguese coast. Marine Pollution Bulletin 56: 999–1007.