AFS Convention 2001: Anti-Fouling Systems on Ships, TBT ban + cybutryne

The AFS Convention 2001 (International Convention on the Control of Harmful Anti-Fouling Systems on Ships) was adopted in London on 5 October 2001 and entered into force on 17 September 2008. It prohibits two categories of hull biocide: organotin compounds (principally TBT), banned from application from 1 January 2003 and from presence from 17 September 2008; and cybutryne (Irgarol 1051), banned from new application from 1 January 2023 under Resolution MEPC.331(76), with existing coatings to be removed or sealed at the next scheduled anti-fouling system renewal but no later than 60 months from the last cybutryne application. Ships of 400 GT and above on international voyages require an IAFS Certificate; ships of 24 metres or more but under 400 GT require an AFS Statement.

Background: 1990s TBT-imposex research + IMO action

The path to the AFS Convention 2001 begins with the organotin biocide revolution of the 1960s and 1970s. Tributyltin (TBT) compounds, principally tributyltin oxide (TBTO) and tributyltin fluoride, were introduced to commercial marine antifouling formulations in the late 1960s by paint manufacturers including International Paint in the United Kingdom, Hempel in Denmark, Jotun in Norway, Sigma Coatings in the Netherlands, and several Japanese manufacturers including Chugoku Marine Paints and Nippon Paint. The breakthrough product class was the self-polishing copolymer (SPC) TBT paint, in which TBT moieties are chemically bonded to an acrylic copolymer backbone and released through controlled hydrolysis at the seawater interface. The SPC mechanism produced predictable biocide release rates over 36 to 60 months between drydocking, vastly outperforming the earlier copper-based and rosin-based formulations and rapidly capturing approximately 70 to 80 percent of the global commercial-shipping antifouling market by the mid-1980s.

The first ecological warning signs emerged from Arcachon Bay in south-west France between 1976 and 1982. The Arcachon oyster fishery, a major French shellfish industry producing approximately 12,000 to 18,000 tonnes annually of Pacific oyster (Crassostrea gigas), suffered abrupt and severe production declines from 1976, with cumulative output falling by approximately 50 to 70 percent by 1981. French researchers at IFREMER (Institut Français de Recherche pour l’Exploitation de la Mer) led by Claude Alzieu and colleagues identified TBT contamination as the proximate cause through a series of papers published between 1981 and 1986, documenting shell-thickening abnormalities (chambering) in adult oysters, complete reproductive failure, and TBT residues in oyster tissue at concentrations correlated with proximity to recreational and commercial harbours where TBT-painted hulls were accumulating biocide release.

In parallel, English researchers led by Peter Gibbs and Geoffrey Bryan at the Plymouth Marine Laboratory documented from 1979 onwards a striking pathology in the dogwhelk Nucella lapillus, a common rocky-shore predatory gastropod across northern European coasts. The pathology, named imposex by Smith in 1971 and characterised in detail by Gibbs and Bryan from 1986, comprises the imposition of male sexual organs (penis and vas deferens) on female dogwhelks, with progressive severity along a six-stage scale. At advanced stages, the developing vas deferens occludes the female genital pore and prevents egg-capsule release, causing reproductive failure and population collapse. Gibbs and Bryan documented imposex along the entire south coast of England with severity correlated with proximity to harbours, marinas and shipping channels, and reproduced the pathology experimentally with TBT exposures at parts-per-trillion concentrations, extraordinarily low for any chemical contaminant.

The American shellfish-industry impact emerged from Maine between 1986 and 1990. The Maine eastern oyster (Crassostrea virginica) and softshell clam (Mya arenaria) fisheries documented mortality, reproductive failure and population decline at sites with elevated TBT contamination, leading to a 1990 closure of several Maine shellfish flats and a parallel set of state-level TBT restrictions adopted in Maine, Massachusetts, Maryland, Virginia and California through the late 1980s. The United States Organotin Antifouling Paint Control Act of 1988 (Public Law 100-333) prohibited TBT antifouling on vessels less than 25 metres in length and on aluminium hulls, restricted release rates on larger vessels to no more than 4 micrograms per square centimetre per day, and required state-level monitoring and enforcement. The 1988 Act became the international template for the staged restriction approach subsequently elaborated through the IMO process.

The United Kingdom banned TBT antifouling on small craft (less than 25 metres) and on shellfish farming structures in 1987 through the Control of Pollution (Antifouling Paints and Treatments of Wood) Regulations, with similar measures adopted by France, the Netherlands, Germany, Norway, Sweden and Australia between 1987 and 1991. The Marine Environment Protection Committee of the IMO began discussion of a global TBT regime in 1990, with the first formal proposal tabled at MEPC 30 by Norway and Sweden. The MEPC discussion gathered momentum through the early 1990s, supported by the OSPAR Commission, the Helsinki Commission, and increasingly by the United States, the European Community, Japan and the major flag states. The IMO Assembly Resolution A.895(21) of 1999 called on member states to phase out TBT antifouling by 1 January 2003 with complete prohibition by 1 January 2008, anticipating the legally binding instrument that became AFS 2001.

2001 London signing + 2008 entry into force

The International Convention on the Control of Harmful Anti-Fouling Systems on Ships was adopted at a diplomatic conference held at IMO headquarters in London on 1 to 5 October 2001, with the formal signing on 5 October 2001. The conference was attended by approximately 70 IMO member states, observer organisations including the European Commission, OSPAR, HELCOM, the Cartagena Convention Secretariat, IUCN, WWF and BirdLife International, and industry observers including BIMCO, INTERTANKO, INTERCARGO, the International Chamber of Shipping, and the major paint and coatings industry associations.

The convention text comprises 21 Articles plus four Annexes. The Articles cover the operational scope (Article 3, application to ships entitled to fly the flag of a Party engaged in international voyages of 400 GT and above), survey and certification (Article 5), inspection and detection of violations (Article 11), violations and penalties (Article 12), entry into force conditions (Article 17, requiring ratification by 25 states representing 25 percent of world merchant shipping tonnage), amendment procedure (Article 16) and standard final clauses. Annex 1 lists the controls on harmful anti-fouling systems with substance-specific entries; Annex 2 sets out survey and certification requirements; Annex 3 contains sampling requirements for verifying compliance; Annex 4 prescribes the AFS Statement form for ships not subject to the IAFS Certificate.

The entry-into-force conditions under Article 17 required ratification by at least 25 states representing at least 25 percent of world merchant shipping gross tonnage. The 25-state threshold was reached relatively quickly through the mid-2000s, but the gross-tonnage threshold proved harder to reach. Panama, the world’s largest ship registry by gross tonnage, deposited its instrument of acceptance on 17 September 2007, providing the final tonnage required to meet the Article 17 threshold. Under the standard 12-month delay from threshold-met to entry-into-force, the convention entered into force on 17 September 2008.

By the entry-into-force date, ratifications covered approximately 80 percent of world merchant shipping tonnage. Subsequent ratifications have brought coverage to approximately 96 percent of world tonnage as of 2026, including all major flag states and most coastal states with active shipping activity. Notable non-Party states include several smaller jurisdictions and a small set of geographically isolated states, but the practical reach of the convention through port-state control captures essentially all internationally trading vessels regardless of flag.

Convention scope: ships ≥400 GT international voyages

Article 3 of the AFS Convention sets out the operational scope, applying to:

(a) ships entitled to fly the flag of a Party;

(b) ships not entitled to fly the flag of a Party but operating under the authority of a Party; and

(c) ships not entitled to fly the flag of a Party and not operating under the authority of a Party but engaged in international voyages and entering a port, shipyard or offshore terminal of a Party.

The substantive controls apply to all ships in scope, but the survey and certification regime distinguishes between vessels by size class. Ships of 400 gross tonnage and above engaged in international voyages must hold an International Anti-Fouling System Certificate (IAFS Certificate) issued under Annex 2, supported by an Anti-Fouling System Record. Ships of 24 metres or more in length but less than 400 GT engaged in international voyages must carry an AFS Statement signed by the owner or authorised agent in the Annex 4 format. Ships of less than 24 metres in length are not subject to the survey and certification regime under the convention but remain subject to the substantive prohibitions through national law (where the flag state has implemented the convention into national law) and through coastal-state environmental regulation in territorial waters.

The 400 GT threshold reflects the IMO standard threshold for international ship survey and certification regimes, used also in MARPOL, SOLAS and STCW. The 24-metre threshold reflects the practical extent to which smaller vessels engage in international voyages and the operational practicality of administering the AFS Statement regime to that size class.

The convention scope explicitly includes fixed and floating platforms, floating storage units (FSUs) and floating production storage and offtake units (FPSOs), recognising that these structures use anti-fouling coatings on submerged components and pose the same potential for harmful biocide release as conventional ships. Warships, naval auxiliaries and government-owned ships engaged in non-commercial service are exempt under Article 3, although Parties are obliged to ensure such vessels operate consistently with the convention “as far as is reasonable and practicable.”

TBT ban: 2003 application + 2008 presence

The TBT ban under AFS Convention 2001 applies in two distinct temporal stages, codified in the original Annex 1 Group 1:

Stage 1, application ban from 1 January 2003. From this date, no Party shall permit the application or re-application of organotin compounds acting as biocides in anti-fouling systems on ships in scope of the convention. The application ban does not require removal of TBT systems already on hulls; rather, it prohibits new application from 1 January 2003 onwards.

Stage 2, presence ban from 17 September 2008. From this date (the convention entry-into-force date), ships shall either not bear organotin compounds acting as biocides in anti-fouling systems on their hulls or external surfaces, or shall bear a coating that forms a barrier to such compounds leaching from the underlying non-compliant anti-fouling system.

The two-stage architecture provided operational accommodation for the existing fleet at the convention’s adoption. Vessels with TBT systems applied before 1 January 2003 could continue to operate without immediate removal, but on the next drydock or by the 2008 deadline (whichever came first) they had to either remove the TBT system entirely (by abrasive blasting, hydroblasting, or chemical stripping) or apply a sealing tie coat that forms a barrier preventing TBT leaching from the underlying coating.

The sealing-coat approach captured a substantial share of the practical compliance pathway between 2003 and 2008. Approved sealing tie coats, typically two-component epoxy or modified epoxy formulations applied at 100 to 200 micrometres dry-film thickness, were validated by the major coatings manufacturers and approved by classification societies for the purpose. The practical advantage of sealing over removal was the avoidance of the substantial cost, drydock time and waste-disposal complexity associated with full TBT removal, particularly the regulatory complexity of TBT-contaminated abrasive blast media disposal under regional hazardous-waste regimes.

By the 17 September 2008 deadline, classification society surveys recorded compliance rates in excess of 95 percent across the international fleet, with the residual non-compliance principally on smaller and older vessels operating in regional trades. Port State Control authorities under the Paris MoU, the Tokyo MoU, the Caribbean MoU and other regional MoU regimes implemented systematic AFS inspection campaigns from 2008 onwards, capturing the residual non-compliance through deficiency notation, detention, and remedial-action requirements.

Annex 1 Group 1: organotin TBT

Annex 1 of the AFS Convention is the core regulatory instrument, listing the controlled substances and the specific control measures applicable to each. Group 1 of Annex 1, as originally adopted in 2001 and entered into force in 2008, contains the entry on organotin compounds acting as biocides:

Substance: Organotin compounds which act as biocides in anti-fouling systems.

Control measures: Ships shall not apply or re-apply such compounds (from 1 January 2003) and shall not bear such compounds on their hulls or external parts (from 17 September 2008), or shall bear a coating that forms a barrier to such compounds leaching from the underlying non-compliant anti-fouling system.

Application: All ships in scope of the convention.

Effective date: 1 January 2003 (application) / 17 September 2008 (presence).

The “organotin compounds acting as biocides” formulation captures TBT and its principal commercial variants (tributyltin oxide (TBTO), tributyltin fluoride, tributyltin chloride, tributyltin acetate and the various tributyltin-acrylate copolymers) as well as related organotin compounds including some triphenyltin (TPhT) formulations marketed as antifouling agents in earlier decades. The “acting as biocides” qualifier is important: it excludes organotin compounds used as PVC stabilisers, polyurethane catalysts or in other non-biocidal applications, capturing only those compounds whose function in the anti-fouling system is the killing or repulsion of fouling organisms.

The substance-specific approach, with each prohibited substance listed in a discrete Annex 1 entry with its own control measures and effective dates, is a deliberate architectural choice. It allows the convention to be amended substance-by-substance through the Article 16 amendment procedure as new evidence emerges, without re-opening the broader convention text. This architecture proved its value in 2021 when Resolution MEPC.331(76) added cybutryne as the second prohibited substance under a new Annex 1 entry, parallel in structure to the 2001 organotin entry.

Annex 1 Group 2: cybutryne (Irgarol 1051), MEPC.331(76) 2023

Cybutryne, also known commercially as Irgarol 1051, is a triazine-class booster biocide developed by Ciba-Geigy (later Ciba Specialty Chemicals, subsequently acquired by BASF) and introduced to the antifouling market in the late 1980s as a complement to copper-based primary biocides. Cybutryne acts by inhibiting photosystem II in the chloroplasts of fouling algae, providing strong control against the green and brown microalgal slimes that form the early stages of biofouling on hulls and that copper alone cannot adequately control. Cybutryne was incorporated into a substantial fraction of copper-based antifouling formulations marketed between approximately 1990 and 2010.

The ecological concerns about cybutryne emerged from European coastal monitoring programmes from the mid-1990s. Researchers in the United Kingdom, Sweden, Germany and the Netherlands documented cybutryne residues in coastal sediments, water column and biota at concentrations approaching or exceeding biological-effects thresholds, particularly in the vicinity of marinas and harbours. Cybutryne is highly persistent in marine sediments (half-life of 100 to 500 days under typical conditions) and bioaccumulates in marine organisms with measured bioconcentration factors of 100 to 1,000 in fish and shellfish. Toxicity testing demonstrated No Observed Effect Concentrations (NOEC) in microalgae below 0.1 micrograms per litre, with documented effects on diatom assemblages, seagrass photosynthesis (notably in Zostera marina eelgrass beds), and coral symbiotic zooxanthellae.

The United Kingdom, the Netherlands and Denmark banned cybutryne in pleasure-craft antifouling between 2000 and 2008 under their respective biocide regulations. The European Union Biocidal Products Regulation 528/2012 progressively withdrew cybutryne approvals from European antifouling products through the 2010s, with the final deadline for EU approvals expiring in 2017.

The IMO process began with proposals at MEPC and at the PPR Sub-Committee from 2017 onwards, sponsored by Norway, Sweden, Finland, the European Union member states and the United Kingdom. The proposal worked through PPR 5, PPR 6, PPR 7 and PPR 8 between 2017 and 2021, with technical evaluation conducted by the Technical Group on Anti-Fouling Systems including representatives of flag states, coastal states, the IUCN, OSPAR, HELCOM and the coatings industry. The proposal was approved at PPR 7 in February 2020, circulated to MEPC 75 (November 2020) for approval in principle, and adopted as Resolution MEPC.331(76) at MEPC 76 in June 2021.

The amendment added a new Annex 1 entry for cybutryne with control measures structurally parallel to the 2001 organotin entry but with a different compliance-deadline architecture. Where the original TBT ban imposed a fixed presence-ban date (17 September 2008), the cybutryne entry requires removal or sealing at the next scheduled anti-fouling system renewal after 1 January 2023, but no later than 60 months following the last application of a cybutryne-containing system. The rolling 60-month window reflects the fleet-wide reality that cybutryne was still being applied through 2022, meaning the “last application” date varies by vessel, and a single fixed cutoff date would generate unnecessary early drydock costs for ships that applied cybutryne late in the 2022 window.

Cybutryne removal/sealing: rolling 60-month deadline from last application

The cybutryne removal or sealing obligation under MEPC.331(76) is the most operationally consequential AFS-related deadline of the 2020s decade for the global commercial fleet. Unlike the TBT regime, which imposed a single fixed presence-ban date of 17 September 2008, the cybutryne obligation uses a vessel-specific rolling deadline: ships bearing cybutryne in an existing coating must remove or seal it at the next scheduled renewal of the anti-fouling system after 1 January 2023, but no later than 60 months following the last application of a cybutryne-containing system to that ship.

A vessel that last applied a cybutryne-containing coating in January 2021 must therefore comply no later than January 2026. A vessel whose last cybutryne application was in June 2022 has until June 2027 at the outside. The practical effect for the bulk of the fleet, which drydocks on 5-year cycles, is compliance by approximately 2026 to 2028 depending on individual drydock history.

Vessels with cybutryne in their existing antifouling system (typically the 2010 to 2022 generation of copper-cybutryne SPC formulations applied at the most recent drydock prior to 1 January 2023) must, on the next drydock or by the 60-month cap (whichever comes first):

Option 1: Full removal. Strip the existing cybutryne-containing antifouling by abrasive blasting, ultra-high-pressure hydroblasting (typically 30,000 to 40,000 psi), or chemical stripping. Apply an approved cybutryne-free anti-fouling system in the new drydock cycle.

Option 2: Sealing tie coat. Apply an approved sealing tie coat (typically a two-component epoxy at 100 to 200 micrometres dry-film thickness) over the cybutryne-containing system, then apply an approved cybutryne-free antifouling top-coat. The sealing-coat approach is operationally less expensive and faster than full removal.

For the 2024 to 2028 drydock window (the vessel-specific rolling compliance period for most of the fleet), shipyards in China, South Korea, Singapore, the Middle East, Turkey, Croatia, Poland, Germany and the Netherlands have reported strong demand for cybutryne removal and sealing services. Paint manufacturers including Hempel, Jotun, AkzoNobel (International brand), NIPPON Paint, Chugoku Marine Paints and PPG provide approved sealing-coat product lines and full-system retrofits. Classification societies including DNV, Lloyd’s Register, ABS, Bureau Veritas, NK, RINA, Korean Register, CCS, RS and IRS have issued unified survey guidance for cybutryne compliance verification coordinated with the vessel-specific 60-month cap.

Port State Control implementation mirrors the 2008 TBT enforcement pattern. PSC inspectors verify the IAFS Certificate, the AFS Record entries documenting when cybutryne was last applied, and whether the vessel is still within or beyond its 60-month window. Sample collection under Annex 3 sampling guidelines may be conducted in cases of suspected non-compliance.

Annex 2 Survey + Certification

Annex 2 of the AFS Convention sets out the survey and certification regime. The International Anti-Fouling System Certificate (IAFS Certificate) is issued by the flag administration or by a recognised organisation (RO) acting on behalf of the flag administration, and is required for all ships of 400 gross tonnage and above engaged in international voyages.

Initial survey is conducted before the certificate is first issued, verifying that the anti-fouling system applied to the ship complies with Annex 1 substance prohibitions. The initial survey is typically conducted at the shipyard following the application of the anti-fouling system as part of the new-build delivery process or following the first post-2008 (or post-2023) drydock for retrofit cases.

Additional survey is required after any change or replacement of the anti-fouling system, verifying that the new system complies with Annex 1 prohibitions. The additional survey is typically conducted at each subsequent drydock when the anti-fouling system is renewed.

The IAFS Certificate is a lifetime certificate that does not require periodic renewal in the manner of the SOLAS Safety Construction Certificate or the MARPOL IOPP Certificate. The certificate remains valid for the life of the anti-fouling system unless: the anti-fouling system is changed, in which case an additional survey and updated certificate are required; or the certificate is invalidated by a change in flag, by a substantive non-compliance finding, or by an amendment to the Annex 1 prohibitions that affects the existing system.

The Anti-Fouling System Record is appended to the IAFS Certificate and contains technical detail of the applied system: the manufacturer, product name, application date, location of application (shipyard, port, dry dock), the surface area treated, the dry-film thickness, the curing time and conditions, and the technical statement of compliance with Annex 1. Where a sealing tie coat has been applied over a previously non-compliant system, the Record documents the sealing-coat application as well as the underlying coating.

The Recognised Organisations acting on behalf of flag administrations are predominantly the IACS classification societies (DNV, Lloyd’s Register, ABS, Bureau Veritas, NK, RINA, Korean Register, CCS, RS and IRS), which collectively cover approximately 90 percent of world tonnage. Several non-IACS classification societies and dedicated flag-state survey organisations also act as ROs for specific flag administrations.

Annex 3 Sampling guidelines

Annex 3 of the AFS Convention sets out sampling guidelines for the verification of anti-fouling system compliance through chemical analysis. The sampling guidelines are operationally important for port state control verification and for dispute resolution between flag and coastal states.

The sampling protocol covers:

Sample collection. A sample of the anti-fouling coating is collected from the underwater hull at three or more representative locations, typically near the bow, midships and stern, at depths between approximately 0.5 and 2.0 metres below the waterline. The sample is collected by scraping a defined area (typically 25 to 100 square centimetres) of the coating with a clean stainless-steel blade and transferring the scraped material to a pre-cleaned sample container.

Sample preservation. The sample is sealed in an inert container, labelled with the ship name, IMO number, sampling location, sampling date and the name of the sampling officer, and stored cool (typically below 10 degrees Celsius) prior to transport to the analytical laboratory.

Chain of custody. The sample chain of custody is documented from collection through transport to laboratory analysis, providing the legal-evidentiary basis for any subsequent enforcement action.

Analytical methods. The laboratory analysis follows internationally recognised methods, typically gas chromatography-mass spectrometry (GC-MS) for organotin compounds and liquid chromatography-mass spectrometry (LC-MS) for cybutryne and related triazine compounds. Detection limits are typically in the parts-per-billion range for the dry coating matrix.

Quality assurance. The analytical protocol includes positive and negative control samples, certified reference materials where available, and inter-laboratory comparison exercises coordinated through the IMO and the OSPAR / HELCOM monitoring networks.

The sampling guidelines are not in themselves binding on Parties but provide a recognised operational standard. Several flag and coastal states have adopted the Annex 3 protocol directly into national law and PSC procedures.

Annex 4 AFS Statement format

Annex 4 of the AFS Convention prescribes the AFS Statement form for ships of 24 metres or more in length but less than 400 gross tonnage engaged in international voyages. The AFS Statement is a simpler instrument than the IAFS Certificate, designed for the operational reality that smaller vessels typically do not engage with classification society surveys at the frequency required for the full IAFS regime.

The AFS Statement is signed by the owner or authorised agent of the ship (rather than by the flag administration or a recognised organisation), and contains:

• the ship’s identification (name, IMO number where applicable, registration number, flag, gross tonnage, length);
• the manufacturer, product name and application date of the anti-fouling system;
• a declaration that the anti-fouling system complies with Annex 1 of the convention;
• the surface area treated and the dry-film thickness applied;
• the signature of the owner or authorised agent and the date.

The AFS Statement must be available on board the ship at all times and must be presented to port-state-control inspectors on demand. Where the anti-fouling system is changed, a new AFS Statement is signed and dated and the previous Statement is retained for record.

The AFS Record kept on board with the AFS Statement documents the supporting technical detail: the supplier’s data sheets, the application records (including dates, weather conditions, surface preparation methods, primer and tie coat applications, and final coat thickness measurements), the receipts and invoices for the coating products, and any compliance certificates issued by the manufacturer or the flag-state administration.

AFS Certificate (≥400 GT international voyages)

The International Anti-Fouling System Certificate (IAFS Certificate) for ships of 400 GT and above engaged in international voyages is the principal compliance document under the AFS Convention. The certificate is issued in the standard IMO bilingual format (English plus the flag-state language) and contains:

• the ship’s particulars: name, distinctive number or letters, port of registry, gross tonnage, IMO number, type of ship;
• the issuing administration or recognised organisation;
• a statement that the ship has been surveyed in accordance with Annex 4 (sic; Annex 2 of the convention sets out the survey requirements; the Certificate references the relevant Annex);
• a statement that the survey shows the anti-fouling system on the ship complies with Annex 1;
• the date of the initial survey or the additional survey;
• the date of issue of the certificate;
• the signature of the issuing officer and the seal of the administration or RO.

The Record of Anti-Fouling Systems appended to the certificate contains the technical detail of the applied anti-fouling system as described in the Annex 2 section above. The Record is updated on each additional survey when the anti-fouling system is changed.

The IAFS Certificate is checked routinely by port state control inspectors as part of the standard SOLAS-MARPOL-AFS-BWM inspection package. Inspection deficiency codes under the Tokyo MoU include 18801 for AFS Convention deficiencies, with sub-codes for missing certificate, expired or invalid certificate, inconsistency between certificate and Record, and visible non-compliance (including visible TBT contamination on the hull).

Imposex in Nucella lapillus + Arcachon Bay 1982 decline

The two case studies that drove the 2001 IMO action were the Arcachon Bay oyster decline from 1982 and the imposex epidemic in Nucella lapillus dogwhelks documented through the 1980s in northern European coastal waters.

Arcachon Bay in south-west France is a tidal lagoon of approximately 174 square kilometres covering an extensive intertidal flats system suitable for Pacific oyster (Crassostrea gigas) cultivation. Pacific oyster was introduced commercially to Arcachon from 1971 onwards as the dominant cultivated species after the collapse of the native flat oyster (Ostrea edulis) stocks from the 1920s onwards. The Arcachon oyster industry through the 1970s produced approximately 12,000 to 18,000 tonnes annually, valued at several hundred million francs and supporting approximately 350 oyster-farming enterprises.

From 1976 onwards, Arcachon producers documented progressive abnormalities in oyster growth and reproduction. Adult oysters showed shell chambering (the formation of fluid-filled cavities between the inner and outer shell layers) and shell thickening abnormalities. Reproductive output declined sharply, with spat collection from the natural spatfall declining by approximately 60 to 80 percent compared to the 1970s baseline. By 1981 the industry was in severe distress.

The IFREMER team led by Claude Alzieu identified TBT from antifouling paints on the recreational and commercial vessels using the bay as the proximate cause. Tissue analyses showed TBT residues in oyster tissue at concentrations of 1 to 3 micrograms per gram (parts per million) wet weight, with corresponding water-column concentrations in the range of 50 to 500 nanograms per litre. Experimental TBT exposure of Pacific oysters reproduced the chambering and reproductive failure pathology, providing the causal link.

The French government banned TBT antifouling on vessels less than 25 metres from 1982, the first national TBT restriction worldwide. The Arcachon oyster industry recovered through the 1980s and 1990s as TBT residues declined, although secondary stressors including the 2008 to 2012 Ostreid herpesvirus outbreaks subsequently affected the recovered industry.

The dogwhelk imposex case is biologically more striking. Nucella lapillus is a common rocky-shore predatory gastropod across the cool-temperate north-Atlantic coasts, ranging from northern Portugal through France, Britain, Ireland, Scandinavia, Iceland and the eastern North American coast. Imposex was first reported in dogwhelks in the late 1960s but characterised in detail by Peter Gibbs, Geoffrey Bryan and Peter Burt at the Plymouth Marine Laboratory from 1986 onwards. Their Vas Deferens Sequence (VDS) staging scheme, with six stages from VDS 0 (normal female) to VDS 6 (sterile female with occluded genital pore), became the standard imposex assessment tool used globally.

Gibbs, Bryan and colleagues documented imposex along the entire south coast of England, with severity correlated with proximity to harbours, marinas and shipping channels. Dogwhelk populations were locally extirpated at sites with the highest TBT exposure, including some south-coast estuaries and several Channel Islands sites. The pathology was reproduced experimentally with TBT exposures at parts-per-trillion concentrations (1 to 10 nanograms per litre), among the lowest concentrations at which any chemical contaminant had been shown to produce population-level reproductive failure.

The OSPAR Commission incorporated dogwhelk imposex monitoring into the Coordinated Environmental Monitoring Programme (CEMP) from the 1990s, with annual VDS surveys conducted at coastal stations across the OSPAR maritime area. Post-2003 and post-2008 CEMP data showed clear progressive recovery of dogwhelk populations and decline in imposex severity, providing one of the strongest empirical demonstrations of the AFS Convention TBT ban’s ecological success.

Maine 1990 shellfish closure historical context

The Maine 1990 shellfish closure provided the principal United States case study for TBT regulation and the operational predicate for the 1988 federal Organotin Antifouling Paint Control Act.

Maine has a substantial intertidal softshell clam (Mya arenaria) fishery and an eastern oyster (Crassostrea virginica) fishery in selected estuarine habitat. Through the late 1980s, Maine Department of Marine Resources monitoring documented elevated TBT in sediments and shellfish tissue at sites adjacent to recreational marinas and commercial harbours, with concentrations exceeding human-health and shellfish-population thresholds at several sites. Shellfish mortality, reproductive failure and growth abnormalities were documented at the affected sites.

The 1990 closure of selected Maine shellfish flats by the state Department of Marine Resources was part of a broader regional response that included parallel restrictions in Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Maryland, Virginia, North Carolina and California. The federal Organotin Antifouling Paint Control Act of 1988 (Public Law 100-333, signed by President Reagan on 16 June 1988) prohibited TBT antifouling on vessels less than 25 metres in length, prohibited TBT antifouling on aluminium hulls of any size, restricted release rates on larger vessels to no more than 4 micrograms per square centimetre per day, and required state-level monitoring and enforcement. The 1988 Act was implemented through US EPA regulations promulgated in 1989 and 1990.

The Maine experience and the broader US 1988 Act became the international template for the subsequent IMO process. The 25-metre threshold, the aluminium-hull prohibition, the release-rate limit on larger vessels and the staged compliance approach all influenced the structure of the IMO process leading to AFS Convention 2001. Maine, Massachusetts and other affected US states maintain TBT monitoring programmes through the 2020s, providing a long-term time series documenting the ecological recovery following the 1988 federal Act and the 2008 IMO presence ban.

Alternative 1: Cuprous oxide (Cu2O) ~70% market share

The dominant TBT alternative since the 2003 / 2008 transition has been cuprous oxide (Cu2O), a copper(I) oxide pigment incorporated into self-polishing, ablative and hydrating antifouling paint matrices as the primary biocide. Cu2O acts by slow release of cuprous ions (Cu+) at the seawater interface, providing broad-spectrum biocidal action against barnacles, mussels, tubeworms, bryozoans and many algal species.

The market dominance of Cu2O reflects several operational advantages. The chemistry is well-understood from approximately 100 years of commercial use, predating the TBT era. The release mechanisms in modern self-polishing copolymer (SPC) and self-polishing hydrolysing (SPH) matrices provide predictable 36 to 60 month service intervals. The cost is substantially lower than the booster biocide and silicone alternatives. Regulatory approval pathways under the EU BPR, the US EPA FIFRA, the Korean ABL Act and the IMO AFS Convention are well-established. Disposal of Cu2O-containing coating residues is regulatory-tractable under standard hazardous-waste regimes.

The commercial Cu2O antifouling product range includes flagship products from each major manufacturer: AkzoNobel International (Intersmooth, Interspeed, Intercept), Hempel (Globic, Olympic), Jotun (SeaQuantum, SeaForce), NIPPON Paint (EcoLoFlex, A-LF-Sea), Chugoku Marine Paints (Sea Grandprix, Sea Premier), PPG (Sigmaglide, Sigmaplane, Nexeon), and Sherwin-Williams Sea-Voyage. Typical formulations contain 30 to 50 percent Cu2O by weight in the dry coating, with copper content giving 30 to 40 percent metallic copper equivalent.

The principal limitations of Cu2O coatings are: insufficient control of microalgal slimes (the early-stage soft fouling), requiring booster biocides; potential ecotoxicity in semi-enclosed coastal waters with high vessel density (notably documented for the Mediterranean and Baltic enclosed seas); progressively tightening EU BPR copper-emission limits in coastal waters of EU member states; and the intrinsic constraint that copper is itself a regulated environmental contaminant in many jurisdictions.

Alternative 2: Booster biocides (zinc/copper pyrithione, DCOIT)

The booster biocide category includes substances added to copper-based antifouling formulations to control the microalgal slime that copper alone does not adequately suppress. The principal booster biocides in commercial use post-2008 include:

Zinc pyrithione (ZnPT), also known as zinc 2-mercaptopyridine N-oxide. ZnPT is a chelating biocide effective against algal slimes and microbial biofilms, used at 1 to 3 percent in copper antifouling formulations. ZnPT degrades relatively rapidly in seawater (half-life of hours to days under typical sunlit conditions) through photolysis of the pyridine ring, producing the more environmentally tractable degradation products. The rapid degradation is the principal regulatory advantage of ZnPT relative to more persistent boosters.

Copper pyrithione (CuPT), the copper analogue of ZnPT. CuPT provides similar booster biocidal action with somewhat different degradation kinetics. CuPT and ZnPT are used interchangeably or in combination in many commercial formulations.

DCOIT, also known as 4,5-dichloro-2-octyl-2H-isothiazol-3-one or commercial name Sea-Nine 211 developed by Rohm and Haas (subsequently Dow Chemical). DCOIT is an isothiazolinone-class biocide effective against bacteria, fungi and algae. The marine half-life is approximately 1 hour under typical sunlit seawater conditions, providing very rapid degradation and minimal persistence. DCOIT is approved under the EU BPR and the US EPA FIFRA for marine antifouling use.

Diuron, a urea-class herbicide used as a booster biocide in some pre-2010 formulations but progressively withdrawn from EU BPR approval through the 2010s on persistence and ecotoxicity grounds. Diuron use in marine antifouling has substantially declined post-2015.

Tralopyril, a pyrrole-class biocide developed and marketed by Janssen Pharmaceutica as Econea, used as a copper-free or copper-supplementary booster biocide in some 2010s and 2020s formulations.

Medetomidine (commercial name Selektope), strictly a non-biocidal repellent rather than a booster biocide, but functioning operationally in a similar role in some formulations. Medetomidine is treated separately in the dedicated section below.

The booster biocides are subject to ongoing regulatory review under the EU BPR, the US EPA FIFRA, the Korean ABL Act and increasingly under IMO PPR Sub-Committee consideration. The 2024 PPR review of additional booster biocide candidates for potential AFS Annex 1 listing reflects the continuing concern about persistence, bioaccumulation and chronic ecotoxicity of some booster biocides in coastal waters with high vessel density.

Alternative 3: Silicone foul-release (Hempel, Jotun, International)

Silicone foul-release coatings are a fundamentally different antifouling approach from biocidal coatings. Rather than killing or repelling fouling organisms with biocides, foul-release coatings provide a low-surface-energy, hydrophobic surface to which fouling organisms have weak adhesion, allowing them to be sloughed off by hydrodynamic shear during vessel transit. The silicone (polydimethylsiloxane, PDMS) matrix provides the low-surface-energy property, with formulations typically incorporating modifying additives to optimise the surface energy, the surface roughness, the durability and the hydrodynamic-shear sensitivity.

The commercial silicone foul-release product range includes the major flagship products: AkzoNobel International Intersleek 700, 900, 1100SR; Hempel Hempasil X3; Jotun SeaQuantum X200, SeaLion; NIPPON Paint LF-Sea; Chugoku Marine Paints CMP Bioclean DX; and PPG Sigmaglide 1290 (the latter two being silicone-hybrid rather than pure silicone formulations).

The operational characteristics of silicone foul-release coatings include:

Service life of 60 months or more between drydocking, exceeding typical Cu2O service intervals.

Hydrodynamic performance benefit of approximately 5 to 10 percent fuel-consumption reduction relative to Cu2O coatings on equivalent vessel and trade profile, reflecting the lower hull surface roughness and the absence of biocide-release-driven micro-erosion.

Activation speed requirement of approximately 12 to 15 knots, below which the hydrodynamic shear is insufficient to slough off settled fouling. Vessels in slow-steaming or extended port-stay operation may experience accelerated fouling on silicone foul-release coatings, partially offsetting the operational advantages.

Higher initial cost of approximately 2 to 3 times the per-square-metre cost of Cu2O coatings, partially offset over the longer service interval.

Compatibility constraint with the substrate. Silicone foul-release coatings require specific tie-coat application and rigorous surface preparation, with poorer tolerance for substrate contamination and surface defects than Cu2O coatings.

Repair complexity. In-service damage to silicone foul-release coatings is more difficult to repair than Cu2O damage, often requiring substantial drydock-time investment for remediation.

The silicone foul-release market share has grown progressively from approximately 5 percent in 2010 to approximately 15 to 20 percent by 2025, with strongest penetration in the container, tanker and large bulk carrier segments where the fuel-saving benefit accrues over high vessel utilisation.

Alternative 4: Hydrogel + amphiphilic coatings

Hydrogel coatings and amphiphilic coatings are the next-generation foul-release technologies developed and commercialised through the 2010s and 2020s. Hydrogel coatings incorporate hydrophilic polymer chains (typically based on polyethylene glycol, polyacrylamide or zwitterionic polymers) that retain a thin water-bound layer at the surface, presenting a fouling-resistant interface to settling organisms. Amphiphilic coatings combine hydrophilic and hydrophobic domains at the surface to disrupt fouling-organism settlement and adhesion.

The commercial hydrogel and amphiphilic product range includes NIPPON Paint LF-Sea (a silicone-hydrogel hybrid), AkzoNobel International Intersleek 1100SR (an amphiphilic silicone-hydrogel hybrid marketed since 2017), and Hempel Hempaguard (a silicone-hydrogel hybrid first commercialised in 2013 and refined through subsequent product generations). The product class continues to evolve through the 2020s with increasing penetration of the next-generation amphiphilic formulations.

The operational characteristics improve on the silicone foul-release base line:

Lower activation speed of approximately 8 to 10 knots, broadening the operational range to slower-steaming vessels.

Better static-fouling resistance during port stays, partially mitigating the silicone foul-release weakness in extended port operations.

Comparable or better fuel performance to silicone foul-release coatings.

Service life of 60 months or more, comparable to silicone foul-release.

The hydrogel and amphiphilic coatings are increasingly seen as the operational successor to both Cu2O biocide coatings and to first-generation silicone foul-release coatings, with growing penetration through the 2020s expected to continue.

Alternative 5: Selektope (medetomidine), IMO-approved 2018

Selektope is the commercial name for medetomidine, an alpha-2 adrenergic receptor agonist developed originally as a veterinary sedative and subsequently identified as a potent non-biocidal barnacle repellent. Medetomidine acts on the octopamine receptor in barnacle larvae (cyprids), inducing rapid kicking-leg behaviour that prevents settlement on the treated surface. The mechanism is non-lethal: barnacle larvae exposed to medetomidine simply fail to settle, resuming normal behaviour when the exposure ends.

Selektope was developed and commercialised by I-Tech AB (Sweden) from approximately 2010, with European Biocidal Products Regulation (BPR) approval secured in 2016 and IMO AFS Convention review and clearance completed in 2018 confirming compatibility with the convention’s substantive prohibitions and survey regime. Selektope is incorporated at very low concentrations (typically 0.1 percent by weight in the dry coating) into copper-based or alternative antifouling formulations from licensed manufacturers including Chugoku Marine Paints and NIPPON Paint.

The operational advantages of Selektope-incorporating coatings include:

Service life of 60 months or more.

Strong barnacle settlement prevention even in tropical, equatorial and high-fouling-pressure waters where conventional coatings struggle.

Non-biocidal mechanism provides regulatory durability under tightening biocide regulations.

Compatibility with reduced-copper formulations, supporting copper-emission reduction in sensitive coastal waters.

The principal limitations are: relatively high cost premium per square metre relative to standard Cu2O coatings; concentration on the barnacle target with less complete control of other fouling organisms (mussels, tubeworms, algae); limited long-term operational track record relative to the established Cu2O and silicone foul-release coatings; and limited number of approved formulations and licensed manufacturers as of 2026.

The Selektope case demonstrates the IMO AFS Convention’s flexibility to accommodate non-biocidal antifouling technologies that fall outside the conventional biocide regulatory framework, providing a pathway for further innovation in low-impact antifouling chemistry.

Service life: Cu-based 36-60 mo, silicone 60+ mo

The service life of an antifouling system is the operational interval between successive applications, typically aligned with the vessel drydocking schedule. Service life is a critical economic and regulatory parameter, driving the total-cost-of-ownership comparison between alternative antifouling technologies.

For copper-based (Cu2O) coatings, the typical service life is 36 to 60 months. Service life within the range depends on:

• the specific product formulation, with self-polishing copolymer (SPC) and self-polishing hydrolysing (SPH) matrices providing longer service intervals than pure ablative or rosin-based formulations;
• the trading area, with tropical and equatorial trades imposing higher fouling pressure and shortening service life relative to temperate trades;
• the operating profile, with continuous high-utilisation operation (typical container, tanker, large bulker trades) supporting longer service life than intermittent or extended-stay operations;
• the dry-film thickness applied at the previous drydock, with thicker initial application supporting longer service intervals.

For silicone foul-release coatings including hydrogel and amphiphilic variants, the typical service life is 60 months or more, with leading products marketed for 90 months and for full intermediate-survey-cycle compatibility.

For Selektope-incorporating coatings, the typical service life is 60 months or more, comparable to the silicone foul-release range.

The service life parameter feeds directly into the drydock-interval planning of the operator. Most international commercial vessels operate on a 5-year or 7.5-year intermediate-survey-cycle drydock schedule under the IACS Unified Requirements and the SOLAS / MARPOL surveys regime. Antifouling service life of 60 months aligns with the 5-year cycle, supporting single-application-per-cycle planning. Service life shorter than 60 months requires either an intermediate antifouling top-coat between drydocks (operationally complex and expensive), or accepting accelerated fouling-related fuel-consumption penalty in the latter half of the cycle.

EU Biocidal Products Regulation 528/2012

The European Union Biocidal Products Regulation 528/2012, replacing the earlier Biocidal Products Directive 98/8/EC, provides the principal European regulatory framework for biocidal active substances and biocidal products including marine antifouling. The BPR is administered by the European Chemicals Agency (ECHA) in Helsinki, with implementing decisions taken by the European Commission in consultation with the Standing Committee on Biocidal Products of EU member states.

Under the BPR, marine antifouling products fall under Product Type 21 (PT21), antifouling products. Each biocidal active substance must be approved at EU level following dossier review by ECHA and a designated rapporteur member state, with approval typically granted for a 10-year period subject to renewal. Once an active substance is approved, individual antifouling products containing the active substance must obtain product authorisation at the member-state level, with mutual recognition mechanisms supporting cross-border product approval.

The active substances currently approved or under review for PT21 marine antifouling include:

• Cuprous oxide (Cu2O): approved with restrictions on coastal-water emission limits in some member states;
• Copper thiocyanate: approved as alternative copper source;
• Zinc pyrithione (ZnPT): approved with use-condition restrictions;
• Copper pyrithione (CuPT): approved with use-condition restrictions;
• DCOIT (Sea-Nine 211): approved;
• Tralopyril (Econea): approved;
• Medetomidine (Selektope): approved 2016;
• Cybutryne (Irgarol 1051): approval expired 2017, withdrawal from market complete by 2023;
• Diuron: approval not renewed, withdrawn from market.

The 2024 BPR update is in train through the 2024-2026 EU regulatory cycle, addressing several refinements: tightened coastal-water emission limits for copper-based products; updated risk assessment methodology for booster biocides; harmonised treatment of foul-release coatings under the BPR scope; and integration with the IMO AFS Convention amendments including the 2023 cybutryne addition.

The BPR creates an operational interaction with the IMO AFS Convention. Substances banned under the AFS Convention (TBT and now cybutryne) are also de-facto banned under the BPR through withdrawal of EU approval. The BPR can additionally restrict substances not yet listed under the AFS Convention, providing a forward-looking European regulatory pathway that has historically led the IMO process by 5 to 10 years for several substance classes.

US EPA FIFRA registration

In the United States, marine antifouling biocides are regulated under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), administered by the United States Environmental Protection Agency (EPA). Each active substance must be registered with EPA following dossier review under the FIFRA registration process, with periodic registration review on a 15-year cycle.

The US EPA registration framework for marine antifouling parallels the EU BPR in substantive scope but with operational differences. Registration is at the active-substance level rather than product-by-product, with substantial flexibility for manufacturers to develop product variants under a registered active substance. Use restrictions, label requirements and risk-mitigation measures are specified at registration and refined through the periodic registration review process.

The substances currently registered for marine antifouling under FIFRA include cuprous oxide, copper thiocyanate, zinc pyrithione, copper pyrithione, DCOIT, tralopyril, medetomidine and several others. Cybutryne registration was withdrawn through the 2010s, paralleling the EU BPR withdrawal.

The Organotin Antifouling Paint Control Act of 1988 remains in force as a separate statutory instrument addressing the historical TBT prohibition. The 1988 Act and the FIFRA registration framework operate in parallel for the post-2008 antifouling industry.

The state-level regulatory framework adds further constraints in selected US coastal jurisdictions. California, Washington, Oregon, Maryland and Maine maintain state-level monitoring and restriction programmes for marine antifouling, with copper-emission limits in selected coastal waters and harbour-specific restrictions in some jurisdictions. The Washington state copper-emission programme in Puget Sound and the California Hull Husbandry programme are the most extensive of the state-level frameworks.

Korean ABL Act + national approvals

The Republic of Korea Antifouling System Management Act, often referred to as the Korean ABL Act (from “Anti-fouling Biocide-related Law”), provides the principal Korean regulatory framework for marine antifouling. The Act, enacted in 2015 and subsequently amended, implements the IMO AFS Convention domestically and adds Korean-specific provisions for antifouling product approval, manufacturing controls, application requirements and post-market surveillance.

Under the Korean ABL Act, marine antifouling products are subject to Korean product approval by the Ministry of Oceans and Fisheries, with technical review conducted by designated review bodies. Korean approval is a precondition for sale and use of antifouling products on Korean-flag vessels and for application of antifouling at Korean shipyards.

Other national antifouling regulatory regimes include:

• Japan under the Chemical Substances Control Law and the Industrial Safety and Health Law, with specific marine antifouling provisions administered by the Ministry of the Environment and the Ministry of Health, Labour and Welfare;
• China under the Pesticide Management Regulations and the Environmental Impact Assessment Law, with specific marine antifouling provisions administered by the Ministry of Agriculture and Rural Affairs;
• Australia under the Agricultural and Veterinary Chemicals (Administration) Act and the Industrial Chemicals Act, with the Australian Pesticides and Veterinary Medicines Authority (APVMA) as the principal regulatory body;
• Canada under the Pest Control Products Act administered by the Pest Management Regulatory Agency (PMRA) of Health Canada;
• Norway under the EEA-EFTA implementation of the EU BPR, with Norwegian Environment Agency administration;
• United Kingdom under the post-Brexit GB BPR (essentially mirroring the EU BPR), with Health and Safety Executive administration.

The national approval frameworks create a complex global product-approval matrix for antifouling manufacturers, with major manufacturers maintaining parallel registration dossiers in 5 to 10 jurisdictions for each commercial product line.

WHO + FAO joint review of marine antifoulants

The World Health Organization and the Food and Agriculture Organization jointly review marine antifoulants under the WHO/FAO Joint Meeting on Pesticide Residues (JMPR) and the related Codex Alimentarius processes addressing residues of biocides in food including seafood. The 2008 WHO/FAO joint review provided foundational reference values for TBT residues in seafood, supporting national health-based standards adopted by Codex Alimentarius and by individual food-safety authorities.

The 2024 WHO/FAO update revisits the marine antifoulant residue framework, addressing the cybutryne addition to AFS Annex 1, the broader booster biocide use, and the progressive substitution toward foul-release and non-biocidal alternatives. The update will address residue limits in seafood, dietary exposure assessment, and the implications for shellfish-fishery management in coastal waters with active antifouling-related contamination.

The WHO/FAO process operates in parallel with the IMO AFS Convention but with a distinct food-safety focus. Where the AFS Convention addresses ship-source biocide release as a marine-pollution issue, the WHO/FAO process addresses the consequent residues in human dietary intake. The two frameworks are mutually reinforcing: AFS Convention biocide reductions reduce environmental concentrations and consequently reduce dietary residues, while WHO/FAO health-based residue limits provide an independent endpoint for assessing the AFS Convention’s success.

IMO PPR Sub-Committee handling AFS amendments

The IMO Sub-Committee on Pollution Prevention and Response (PPR) is the technical sub-committee of MEPC that handles AFS Convention amendments and related anti-fouling system technical work. PPR was established in 2014 by the merger of the previous Bulk Liquids and Gases (BLG) Sub-Committee and the Dangerous Goods, Solid Cargoes and Containers (DSC) Sub-Committee with reorganised pollution-related responsibilities.

PPR meets annually in spring (typically February or March) at IMO headquarters in London. The Sub-Committee’s responsibilities include:

• review and development of MARPOL amendments;
• review and development of AFS Convention amendments;
• technical work on chemical pollution response, oil pollution response, hazardous noxious substances response;
• the IBC Code, the IGC Code, and related cargo carriage instruments;
• the GESAMP Hazardous Materials evaluation process;
• the AFS Annex 1 amendment process including the 2021-2023 cybutryne addition.

The cybutryne amendment through MEPC.331(76) was developed at PPR 5 (2018), PPR 6 (2019), PPR 7 (February 2020) and approved at PPR 7 with subsequent submission to MEPC 75 (November 2020) and adoption at MEPC 76 (June 2021). The PPR process for the cybutryne amendment took approximately 4 years from initial proposal to MEPC adoption, with an additional 18 months from adoption to entry into force on 1 January 2023.

Forward-looking PPR work on AFS Convention amendments includes the 2024 PPR review of additional booster biocide candidates and of emerging non-biocidal antifouling technologies including graphene-based and zinc-borate alternatives. The pipeline of potential future Annex 1 additions and of supporting guidance on alternative technologies will be developed through the late 2020s, paralleling the broader regulatory tightening under the EU BPR and other national frameworks.

Relationship to BWM Convention 2004 + biofouling guidance G7

The AFS Convention 2001 sits within a broader IMO regulatory framework addressing vessel-mediated biological impacts, alongside the Ballast Water Management Convention of 2004 and the biofouling guidelines developed by MEPC since 2011.

The BWM Convention addresses the transport of aquatic invasive species in ship ballast water, requiring vessels to install ballast-water management systems and to discharge treated ballast water meeting biological-discharge standards. The BWM Convention entered into force on 8 September 2017 and the implementation experience parallels the AFS Convention path: a multi-year transition period through to 2024, ongoing fleet retrofit through to 2026, and progressive port-state-control enforcement intensifying through the late 2020s.

The Biofouling Guidelines are non-binding IMO guidance documents addressing the prevention and control of vessel hull biofouling as a vector for invasive species transport. The principal instrument is Resolution MEPC.207(62) Guidelines for the control and management of ships’ biofouling to minimize the transfer of invasive aquatic species, adopted in July 2011 and subsequently updated. The 2011 guidelines (often referred to in operational shorthand as “Biofouling G7” although the formal designation is MEPC.207(62)) provide recommended best practice for hull cleaning, antifouling coating selection, biofouling management plans and biofouling record books.

The 2023 MEPC.378(80) revised Biofouling Guidelines strengthened the 2011 framework with: more detailed antifouling coating selection guidance integrating the AFS Convention and BPR requirements; expanded biofouling record book provisions; more detailed in-water cleaning operational guidance; and tighter linkage to the BWM Convention and to coastal-state biofouling regimes including the New Zealand and Australian biofouling regulations.

The interaction between AFS Convention, BWM Convention and Biofouling Guidelines creates an integrated framework for ship-source biological impact management. AFS Convention controls the chemistry of antifouling release; BWM Convention controls the biology of ballast water transport; Biofouling Guidelines control the biological cargo of hull surfaces. The three frameworks together represent the most substantial expansion of marine pollution regulation since MARPOL itself.

GloFouling Partnerships project (2023+)

The GloFouling Partnerships project is an IMO-led initiative implemented in partnership with the United Nations Development Programme (UNDP) and the Global Environment Facility (GEF), building international and developing-country capacity for biofouling management. The project succeeds the earlier GloBallast Partnerships project that supported BWM Convention implementation, and follows the broader IMO/UNDP/GEF capacity-building model.

GloFouling Phase I operated from 2018 to 2023 with funding of approximately USD 7 million, supporting 12 lead partner countries in the Caribbean, the Pacific, southern Africa, west Africa and south-east Asia. Phase II from 2023 onwards expands the partnership to a wider set of lead and observer countries with funding of approximately USD 10 to 15 million committed through 2027.

Project activities include: national biofouling status assessment; national biofouling management strategy development; pilot biofouling management at selected ports; in-water cleaning capacity development; antifouling coating selection technical support; and integration with the broader IMO biofouling guidelines and AFS Convention implementation.

The GloFouling project is a direct operational complement to the AFS Convention’s regulatory framework. Where the AFS Convention prohibits specific harmful biocides, GloFouling provides the developing-country implementation capacity to apply the prohibitions in practice and to build the wider biofouling management infrastructure needed for the BWM Convention and the Biofouling Guidelines.

2024 PPR graphene + zinc-borate alternatives review

The 2024 PPR Sub-Committee review of emerging alternative antifouling technologies addresses the next wave of substitution beyond the established Cu2O / silicone / Selektope set. The review focuses on two principal candidate classes: graphene-based coatings and zinc-borate antifouling.

Graphene-based coatings incorporate graphene oxide (GO), reduced graphene oxide (rGO) or functionalised graphene derivatives into a polymer matrix to provide antifouling, anticorrosion and hydrophobic properties. Several commercial products marketed in the 2020s (notably from Italian, Chinese and Spanish suppliers) claim graphene-based mechanisms, although the antifouling efficacy data are still being accumulated through independent operational testing. The PPR review considers the regulatory pathway for graphene-based coatings under the AFS Convention scope: whether they are inherently outside the convention’s biocide-focused scope (because they are non-biocidal) or whether they should be subject to specific guidance on application, life-cycle and end-of-life management.

Zinc-borate is a copper-free biocide that has been progressively explored as a TBT and copper alternative. Zinc-borate provides moderate biocidal activity with operational characteristics intermediate between conventional copper and the silicone foul-release coatings. Several Asian manufacturers have introduced zinc-borate-based products since approximately 2018 with some commercial uptake.

The 2024 PPR review will inform potential future Annex 1 amendments, but more substantially will produce guidance on the regulatory treatment of non-biocidal and reduced-biocide alternatives under the AFS Convention. The expected outcome is updated technical guidance through the late 2020s, with potential further Annex 1 amendments through the 2030s as additional substance evidence accumulates.

Class society implementation: DNV, LR, ABS, BV, NK, RINA, KR, CCS, RS, IRS

The IACS classification societies (DNV, Lloyd’s Register, ABS, Bureau Veritas, NK, RINA, Korean Register, CCS, RS and IRS) provide the principal Recognised Organisation (RO) function for AFS Convention surveys on behalf of flag administrations. The 10 IACS societies collectively cover approximately 90 percent of world tonnage, with the remaining 10 percent covered by non-IACS classification societies and by direct flag-state surveyors.

The class society AFS implementation includes:

Initial survey of new-build vessels at delivery, verifying that the applied anti-fouling system complies with Annex 1, with appropriate technical documentation from the paint manufacturer and the application yard;

Additional survey at each subsequent drydock when the anti-fouling system is renewed, verifying that the new system complies with Annex 1 and updating the IAFS Certificate Anti-Fouling System Record;

Survey of sealing-coat applications for vessels with previously non-compliant systems (post-2003 TBT cases through 2008, and post-2023 cybutryne cases through the rolling 60-month window), verifying that the sealing-coat application meets the technical requirements for forming a barrier to biocide leaching;

Maintenance of the IACS Unified Requirements addressing AFS Convention implementation, providing harmonised technical interpretation across the 10 societies;

Liaison with the IMO PPR Sub-Committee through the IACS Permanent Representative to IMO and through technical input to IMO instruments and guidance.

The class society AFS implementation interfaces directly with the broader survey programme under SOLAS, MARPOL and the BWM Convention. The harmonised survey scheme provides operational efficiency for vessel operators by combining the AFS, SOLAS, MARPOL and BWM survey activities into integrated drydock-based survey events.

PSC inspection: AFS Certificate + Statement + visible TBT

Port State Control (PSC) inspection of AFS Convention compliance is conducted by national PSC authorities under the regional PSC MoU regimes including the Paris MoU, the Tokyo MoU, the Caribbean MoU, the Mediterranean MoU, the Black Sea MoU, the Indian Ocean MoU, the Riyadh MoU, the West and Central African MoU and the Viña del Mar Agreement. The PSC inspection scope under each MoU follows the harmonised IMO PSC procedures with regional implementation variations.

The AFS PSC inspection includes:

Document inspection. Verification of the IAFS Certificate (for vessels of 400 GT and above) or the AFS Statement (for vessels of 24 metres or more in length but less than 400 GT). Verification that the certificate or statement is current, signed and consistent with the vessel’s operational use of antifouling.

Anti-Fouling System Record review. Verification that the Record entries are consistent with the certificate, that the technical detail of the applied system is documented, and that any sealing-coat applications are properly recorded.

Visible TBT contamination inspection. Where the inspector has reasonable grounds to suspect non-compliance, visual inspection of the underwater hull (typically by ROV, by diver inspection, or at the next drydock occasion) for evidence of TBT-coloured antifouling underneath any subsequent sealing or topcoat application. Visual inspection alone is rarely conclusive, but combined with other evidence may justify sample collection under Annex 3.

Sample collection under Annex 3 sampling guidelines, where reasonable grounds for suspected non-compliance exist. Samples are sent to designated analytical laboratories for GC-MS organotin analysis or LC-MS cybutryne analysis, with results returned typically within 2 to 6 weeks.

Deficiency notation under regional PSC MoU procedures, with deficiency codes recorded in the regional PSC database and shared across MoU member authorities. Deficiencies include missing certificate, expired or invalid certificate, certificate-Record inconsistency, visible non-compliance, and confirmed sample-based non-compliance.

Detention of the vessel where the deficiency rises to the level of clear ground for detention under PSC procedures, typically reserved for confirmed non-compliance through sampling rather than for documentary deficiencies alone.

The PSC implementation has produced documented compliance rates exceeding 99 percent for the TBT regime by the late 2010s, with cybutryne compliance accumulating through the 2023 to 2028 rolling transition window.

Tokyo MoU AFS deficiency code 18801

The Tokyo MoU on Port State Control in the Asia-Pacific region uses deficiency code 18801 as the principal AFS Convention deficiency code, with sub-codes for specific deficiency types. The Tokyo MoU codes are:

• 18801: AFS Convention general deficiency;
• 18802: IAFS Certificate missing or invalid;
• 18803: AFS Statement missing or invalid (for vessels 24 m to less than 400 GT);
• 18804: Anti-Fouling System Record incomplete or inconsistent with certificate;
• 18805: Anti-fouling system non-compliance (TBT or cybutryne presence confirmed by sampling);
• 18806: Visible non-compliance (visible TBT-coloured coating beneath topcoat);
• 18807: AFS-related operational deficiency (record book, application records).

Parallel deficiency codes are used in the Paris MoU (typically with the prefix “13” for the AFS Convention), the Caribbean MoU, the Mediterranean MoU, the Black Sea MoU, the Indian Ocean MoU and the Riyadh MoU. The deficiency codes are harmonised through the IMO PSC framework but with regional MoU coding differences.

The Tokyo MoU AFS deficiency rate has declined from approximately 0.5 to 1.0 percent of inspections in the 2008-2010 period to less than 0.1 percent of inspections in the 2018-2023 period, providing empirical evidence of the convention’s enforcement success. The cybutryne compliance trajectory through the 2023 to 2028 rolling window is expected to follow a similar pattern, with elevated deficiency rates during the early implementation period followed by progressive convergence to baseline.

2020s alternative-coatings market: EcoLoFlex, Globic, Intersleek, SeaQuantum

The 2020s commercial alternative-coatings market is dominated by a handful of flagship product families from the major manufacturers:

NIPPON Paint EcoLoFlex is a hydrophilic-silicone hybrid foul-release coating with strong penetration in the Asian market, particularly on Japanese and Korean newbuilds and on routine drydocking schedules at Asian shipyards. The EcoLoFlex range provides 60-month service life with reduced fuel consumption versus conventional Cu2O coatings.

Hempel Globic is a self-polishing copper-based antifouling product family with multiple variants (Globic 9000, Globic 9500, Globic NCT) addressing different trade profiles and service-life targets. Globic is a flagship product in the Cu2O segment with strong penetration in tanker, bulker and container trades globally.

AkzoNobel International Intersleek product family includes Intersleek 700 (first-generation silicone foul-release), Intersleek 900 (improved silicone foul-release), and Intersleek 1100SR (silicone-hydrogel-amphiphilic hybrid, the flagship 2020s product). Intersleek 1100SR provides 60-month service life with documented 5 to 10 percent fuel-consumption reduction relative to Cu2O baseline.

Jotun SeaQuantum X200 is a silicone foul-release coating with strong newbuild penetration globally. The SeaQuantum range complements Jotun’s SeaForce Cu2O product range, providing the manufacturer’s offering across the full spectrum of biocide-based to non-biocidal antifouling technologies.

Chugoku Marine Paints CMP Sea Premier and Sea Grandprix are flagship Cu2O products with the wider CMP Bioclean DX silicone foul-release product complementing.

PPG Sigmaglide and Sigmaplane include both Cu2O biocide formulations and Sigmaglide silicone foul-release variants.

Sherwin-Williams Sea-Voyage provides Cu2O biocide formulations principally for the North American market with growing international penetration.

The market segment shares as of 2025 are approximately: Cu2O coatings 65 to 70 percent; silicone foul-release and hybrid 20 to 25 percent; copper-pyrithione, zinc-pyrithione and tralopyril boosters within Cu2O formulations 5 to 10 percent; Selektope-incorporating coatings 1 to 2 percent; and emerging hydrogel, amphiphilic and graphene products at the early-adopter scale.

Cost economics: alternative cost premium ~10-30% over TBT (1990s pricing)

The cost economics of the post-TBT antifouling transition have evolved substantially across the 2003-2025 transition period.

At the 2003-2008 transition, the cost premium of TBT alternatives over the established TBT product range was estimated at approximately 10 to 30 percent in 1990s pricing, reflecting the additional formulation cost of high-performance Cu2O and booster biocides relative to the by-then commodity TBT chemistry. The premium was modest in the context of total drydock cost (typically 1 to 3 percent of vessel new-build cost amortised over a 5-year cycle) and was rapidly absorbed into operating-cost baselines.

By the 2010s, the cost differential between Cu2O and the silicone foul-release alternatives became the more operationally relevant comparison. Silicone foul-release coatings command an approximately 2 to 3 times per-square-metre application cost relative to Cu2O coatings, partially offset by the longer 60-month service life relative to the typical 36 to 60-month Cu2O service interval.

The fuel-consumption performance offset for silicone foul-release and hydrogel-amphiphilic coatings provides a substantial economic counter-balance. A 5 to 10 percent fuel-consumption reduction relative to Cu2O baseline, applied to a typical post-Panamax containership consuming 80 to 120 tonnes of fuel per day at sea, produces fuel savings of 4 to 12 tonnes per day or approximately USD 2,000 to 7,000 per day at typical 2020s VLSFO prices. Over a 60-month service interval at typical 75 to 80 percent at-sea utilisation, the cumulative fuel saving exceeds USD 1 to 3 million per vessel, comfortably outweighing the higher application cost of silicone foul-release coatings.

The IMO EEXI (Energy Efficiency Existing Ship Index), CII (Carbon Intensity Indicator) and EU ETS (European Union Emissions Trading System) regulatory frameworks adopted from 2023 onwards add a further economic dimension. Lower fuel consumption translates directly into lower CO2 emissions, lower CII rating, and lower EU ETS allowance cost. For vessels operating with substantial European-trade exposure, the EU ETS cost saving alone can be USD 50,000 to 200,000 per vessel-year for a typical large vessel, providing substantial additional economic incentive for fuel-efficient antifouling selection.

Fuel + hydrodynamic-performance offset

The fuel-consumption offset is the dominant economic driver favouring high-performance antifouling coatings in the 2020s context. The principal mechanisms are:

Hull surface roughness. Smooth coatings present lower frictional resistance to the water flow, reducing the required propulsive power for a given speed. The AS-1 to AS-7 surface-roughness scale developed by Hempel provides a standardised scheme for hull-roughness measurement, with smooth as-applied coatings typically in the AS-2 to AS-3 range and degraded coatings progressing through AS-4 to AS-7 over the service life.

Biofouling penalty. Biofouling accumulation on the hull substantially increases hull frictional resistance, with documented fuel-consumption penalties of 1 to 5 percent for light slime coverage progressing to 20 to 40 percent for heavy macrofouling (barnacles, mussels, tubeworms, weed). High-performance antifouling coatings minimise biofouling accumulation, preserving the hull-roughness-to-fuel performance baseline through the service interval.

Coating ablation profile. Self-polishing copolymer Cu2O coatings ablate progressively over the service life, with the surface roughness increasing through the cycle. Silicone foul-release coatings retain a relatively constant surface profile, providing more consistent hydrodynamic performance throughout the 60-month service interval.

Trim and load optimisation interaction. Hull-coating performance interacts with trim and load optimisation, with the combined fuel-consumption optimisation typically managed through onboard and shore-based hull-performance monitoring systems integrating coating-specific data.

The fuel-consumption offset has driven the progressive penetration of silicone foul-release and amphiphilic coatings through the 2010s and 2020s, with continued growth expected through the 2030s as fuel prices, EU ETS allowances and CII compliance pressures accumulate.

2030 outlook: zero-biocide coatings, regulatory alignment

The 2030 outlook for the AFS Convention and the broader antifouling regulatory framework includes several anticipated developments:

Zero-biocide coatings expansion. Continued penetration of silicone foul-release, hydrogel, amphiphilic and Selektope-incorporating coatings, with combined non-biocide market share potentially reaching 30 to 40 percent of the global market by 2030. The zero-biocide segment growth depends on the trajectory of fuel prices, the EU ETS allowance market, the IMO greenhouse-gas regulatory framework, and the further development of low-activation-speed foul-release technologies suitable for slower-steaming vessels.

Further AFS Annex 1 amendments. The IMO PPR Sub-Committee review of additional booster biocide candidates, of graphene-based and zinc-borate alternatives, and of emerging substances of concern is expected to produce one or more further AFS Annex 1 amendments through the late 2020s and 2030s. The substance-specific architecture of Annex 1 supports incremental amendment without re-opening the broader convention text.

Tightening EU BPR and national approvals. Continued tightening of EU BPR copper-emission limits, of US EPA FIFRA registration review outcomes, and of equivalent national-approval frameworks. The trend favours non-biocidal alternatives and creates regulatory headwinds for copper-based formulations in coastal-water-sensitive jurisdictions.

Integration with greenhouse-gas regulation. Closer integration of antifouling regulation with IMO MEPC greenhouse-gas regulatory frameworks (EEXI, CII, market-based measures) and with the EU ETS, recognising that fuel-efficient antifouling is a substantial GHG-reduction lever.

Biofouling management evolution. Continued evolution of the IMO biofouling guidelines, of New Zealand and Australian biofouling regulations, and of similar emerging coastal-state regimes. The biofouling regulatory dimension increasingly couples with the AFS regulatory dimension.

Capacity-building expansion. Continued expansion of the GloFouling Partnerships project and related developing-country capacity-building initiatives, supporting wider geographic implementation of the AFS Convention and the related biofouling and BWM frameworks.

The combined trajectory points toward a 2030s antifouling regulatory regime substantially tighter than the 2020s baseline, with an increased role for non-biocidal alternatives, tighter biocide-specific controls, and closer integration with the broader maritime decarbonisation and biological-impact frameworks.

Controlled substances: Annex 1 summary table

No further substances had been added to Annex 1 as of June 2026. The IMO PPR Sub-Committee review of additional booster biocide candidates was ongoing through 2024 to 2026, but no resolution proposing a new Annex 1 addition had been adopted at MEPC 80, 81, 82 or 83.

Common compliance errors

Five errors recur in commercial and operational discussion of the AFS Convention.

Conflating adoption with entry into force. The convention was adopted in London on 5 October 2001 but entered into force on 17 September 2008, seven years later. The seven-year gap reflects the time needed to reach the Article 17 tonnage threshold.

Conflating the TBT application ban and presence ban. The 1 January 2003 date prohibited new application of TBT coatings. The 17 September 2008 date prohibited TBT presence (or required a sealing coat). A vessel could continue operating with TBT on its hull between 2003 and 2008, provided the coating was applied before 2003.

Treating the cybutryne deadline as a single fixed date. The cybutryne removal/sealing requirement is not a fixed calendar date. It is vessel-specific: the next scheduled AFS renewal after 1 January 2023, capped at 60 months from the last cybutryne application on that vessel. Operators who treat it as a fixed “2026 deadline” risk being non-compliant earlier if their 60-month cap expires sooner.

Confusing the IAFS Certificate and the AFS Statement. The IAFS Certificate is issued by the flag administration or a recognised organisation for ships of 400 GT and above. The AFS Statement is signed by the owner or authorised agent for ships of 24 metres or more but under 400 GT. They are distinct documents with different signatories and different regulatory weight in a PSC inspection.

Treating cybutryne and Irgarol 1051 as different substances. Irgarol 1051 is the commercial trade name for cybutryne (CAS No. 28159-98-0). The AFS Convention uses the IUPAC name; paint product labels and older regulatory documents may use the trade name. They are the same compound.

See also

• Ballast Water Management Convention
• MARPOL Convention
• MARPOL Annex I
• MARPOL Annex I Regulation 15 oil discharge control
• MARPOL Annex VI Regulation 12 ozone-depleting substances
• MARPOL Annex VI Regulation 14 sulphur cap
• IMO 2020 sulphur cap
• Hong Kong Convention
• Polar Code
• Helsinki Convention 1992
• Barcelona Convention 1976/1995
• OSPAR Convention 1992
• Calculator catalogue

References

References include the IMO Anti-Fouling Systems portal, the International Convention on the Control of Harmful Anti-Fouling Systems on Ships adopted in London on 5 October 2001 and entered into force on 17 September 2008, Resolution MEPC.331(76) adopted at MEPC 76 in June 2021 adding cybutryne to Annex 1 with effect from 1 January 2023, the consolidated AFS Convention text including Annexes 1 to 4 covering controls on harmful anti-fouling systems, survey and certification, sampling guidelines and the AFS Statement form, the IMO GloFouling Partnerships project documentation through the IMO-UNDP-GEF programme, the European Chemicals Agency Biocidal Products Regulation 528/2012 framework, the United States Environmental Protection Agency pesticide registration framework under FIFRA, the Tokyo MoU and Paris MoU port-state-control inspection materials addressing AFS Convention deficiency codes including 18801, the International Antifouling Coatings Association industry materials, the IASPIS European antifouling and surface protection industry suppliers documentation, the IACS International Association of Classification Societies survey and certification implementation, the historical TBT-imposex research literature including the IFREMER Arcachon Bay studies of Claude Alzieu and colleagues from 1981 onwards and the Plymouth Marine Laboratory studies of Peter Gibbs, Geoffrey Bryan and colleagues on Nucella lapillus dogwhelks from 1986 onwards, and the United States Organotin Antifouling Paint Control Act of 1988 and consequential state-level monitoring programmes in Maine, California, Washington, Maryland and other affected coastal states. Full citation links appear in the frontmatter.

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