Antifouling paints
Definition of antifouling paints:
A marine coating designed to prevent, retard or facilitate removal of fouling organisms from submerged surfaces such as ship hulls, nets, piles and offshore structures.
This is the common definition for antifouling paints, other definitions can be discussed in the article
|
Marine biofouling is the accumulation of aquatic organisms on any surface exposed to the aquatic environment, including ship hulls and offshore installations. Although a naturally occurring process, biofouling is widely recognized as detrimental to the performance and durability of marine infrastructure and equipment. Its impacts include increased hydrodynamic drag and fuel consumption in vessels, clogging of seawater systems, added structural weight, accelerated material degradation, and secondary marine pollution.[1]
Biofouling development begins with the rapid adsorption of dissolved organic molecules onto submerged surfaces, forming a conditioning film. This film promotes the attachment and growth of microorganisms such as bacteria and microalgae, leading to biofilm formation which facilitates the establishment of larvae and macrofouling organisms such as barnacles and mussels, resulting in mature fouling communities.
To mitigate these effects, marine biofouling is commonly controlled through the application of antifouling coatings, many of which contain biocidal active substances. While effective, the release of these biocides into the marine environment raises concerns regarding ecological toxicity.
Contents
Tributyltin
Tributyltin (TBT) was widely used as an effective antifouling biocide from the 1960s onwards. Because of its severe effects on non-target marine organisms, organotin compounds acting as biocides in antifouling systems were prohibited internationally under the IMO Anti-Fouling Systems Convention, which entered into force in 2008.
TBT was also used as a biocide in a range of other applications including refrigeration systems, wood pulp, leather processing, wood preservation processes and textile treatments. Ecotoxicologists discovered already in the 1970s that TBT caused severe effects on many non-target marine organisms. Particularly striking was imposex in female gastropods, in which male sexual characteristics develop and severe cases can result in sterility. TBT also caused growth and reproductive abnormalities in oysters.
TBT typically has a half-life of 1–5 years in well-oxygenated surficial sediments, but TBT accumulated in fine-grained anoxic marine sediments persists over several decades. Despite observations of reduced TBT concentrations in many marine sediments over the recent decades, contaminant hotspots are still prevalent worldwide around shipyards, fishery harbors and marinas[2].
Non-biodegradable antifouling paints
Experiments are also being conducted with nano-antifouling coatings. These coatings can gradually release nanomaterials with antimicrobial properties, such as nanosilver. Their activity results from the release of toxic silver ions and, depending on conditions, direct nanoparticle effects and generation of reactive oxygen species (ROS). However, challenges such as nanoparticle aggregation and uncontrolled release currently limit their broader applicability.[3]
Many modern biocidal antifouling paints use self-polishing copolymer coatings. Embedded copper compounds are often combined with so-called booster biocides, organic biocides added to improve effectiveness against fouling organisms that are insufficiently controlled by copper alone. Seawater reactions gradually remove the outer polymer layer, maintaining a controlled release of incorporated biocides while continuously renewing the coating surface.
Besides dissolved biocides released during service, antifouling coatings also generate paint particles through abrasion, weathering and hull maintenance. Such particles accumulate especially in shipyards, harbors and marinas and can contain high concentrations of copper and other additives that are highly toxic to benthic organisms. They are increasingly recognized as an important source of contamination of harbor sediments.[4][5]
Natural biocidal additives
Natural antimicrobial agents (or synthetic derivatives) can be used instead of non-biodegradable additives. Many marine organisms (e.g. sponges, corals) protect themselves by producing secondary metabolites with biocidal activity. These organic compounds can also serve as antifouling agents and can be chemically synthesized. Several natural organic biocides, such as capsaicin and furanones, are actively investigated. They can be embedded as additives to self-polishing polymeric coatings (epoxy, rosin, acrylic, silicone, polyurethane, and others), provided compatibility with the polymeric matrix. [6] Performance criteria include efficacy, sufficiently rapid environmental degradation, low non-target toxicity, stability within the coating and reasonable production cost. Although polymeric matrices are the essence of the coatings, other constituents, such as solvents or diluents, additives, pigments, crosslinkers, and extenders, are also essential for the coating formulation. Investigations are still ongoing to optimize the performance of these paints.[3]
Low surface-energy coatings
Low surface-energy anti-fouling coatings are a type of marine coating designed to mitigate the effect of biofouling by reducing the adhesion between the coating surface and marine organisms. Silicone oils, specifically linear polydimethylsiloxane products, migrate from within the coating to the surface during a vessel’s journey, creating a smooth oil film. The molecular structure of the coating surface significantly diminishes van der Waals forces, hydrogen bonding, and other physicochemical interactions between the coating and the fouling organisms (such as bacteria, algae, and mollusks), thereby effectively delaying and weakening their attachment.[3] They do not necessarily prevent settlement. Instead, organisms adhere relatively weakly and can be removed by hydrodynamic shear or cleaning. This is why they can be less effective on vessels that travel slowly or remain stationary for long periods.[7]
Silicone foul-release coatings can perform as well as or better than copper coatings under suitable conditions and have substantially lower toxicity, although “biocide-free” should not automatically be equated with completely environmentally benign. Moreover, silicone coatings are susceptible to mechanical damage such as cutting, tearing, and puncturing, which reduces the service life.[7]
Zwitterionic polymer coatings[8] Zwitterionic polymers (also known as polybetaines) are an alternative class of hydrophilic antifouling materials. They form a dense hydration layer underwater, deterring the adhesion of fouling organisms by inhibiting protein adhesion. This is due to their specific chemical structure which has opposite charges in each repeating functional group. Good results were obtained when zwitterions were added to raw lacquer, a natural resin coating with Urushiol as the primary component. However, the costs of producing zwitterionic polymers limit their practical use.[9]
Bioinspired polymer matrices such as hydrogels, slipper liquid-infused porous surface (SLIPS), zwitterionic polymers, and other biodegradable matrices are also considered as candidates for antifouling coatings.[6] The principle of biodegradable coatings lies in the fact that a surface constructed from a biodegradable polymer would gradually decompose by erosion or by enzymatic action in seawater. The attached living organisms or inorganic substances are thereby polished, resulting in a self-renewing surface. Several research groups have developed coatings based on biodegradable polyurethanes with interesting antifouling potential and no persistent negative impact for the marine environment.
Bio-inspired antifouling coatings
An alternative are the biometric anti-fouling coatings that mimic the microstructures observed in many marine animals (e.g. dolphins, sharks and shellfish). The micro- or nano-scale roughness of these surfaces reduces the contact area between water droplets and the solid surface, thereby decreasing the adhesion of fouling organisms. [10] These microstructures disrupt the physical adhesion of marine organisms such as barnacles, algae, and bacteria. Despite their environmental benefits, these low surface energy coatings face limitations due to the complexity of their surface microstructures, limited mechanical strength, and difficulties in repair.
Legal regulations
The regulatory policy for self-polishing coatings is primarily governed by the 2001 International Convention on the Control of Harmful Anti-fouling Systems on Ships (AFS Convention), which explicitly prohibits the use of toxic organotin compounds, such as tributyltin (TBT), as active ingredients in self-polishing anti-fouling coatings. In the European Union, the authorization of antifouling paints is regulated in the Regulation (EU) No 528/2012 Concerning the Making Available on the Market and Use of Biocidal Products[11]. The European Union’s Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) regulation imposes strict requirements for the registration, evaluation, and authorization of chemicals used in self-polishing anti-fouling coatings, to ensure that they do not cause irreversible damage to aquatic ecosystems.
Related articles
- TBT
- TBT and Imposex
- TBT and intersex in periwinkles
- Coastal pollution and impacts
- Endocrine disruption by marine pollutants
References
- ↑ Hadzic, N., Jovanovic, I. and Vladimir, N. 2026. Biofouling of ships and offshore structures: research trends and future pathways. Ocean Engineering 347, 123988
- ↑ Beyer, J., Song, Y., Tollefsen, K.E., Berge, J.A., Tveiten, L., Helland, A. Oxnevad, S and Schoyen, M. 2022. The ecotoxicology of marine tributyltin (TBT) hotspots: A review. Marine Environmental Research 179, 105689
- ↑ 3.0 3.1 3.2 Wu, S., Wu, S., Xing, S., Wang, T., Hou, J., Zhao, Y. and Li, W. 2024. Research Progress of Marine Anti- Fouling Coatings. Coatings 14, 1227
- ↑ Soroldoni, S., Vieira da Silva, S., Braga Castro, I., de Martinez Gaspar Martins, C. and Lopes Leaes Pinho, G. 2020. Antifouling paint particles cause toxicity to benthic organisms: Effect on two species with different feeding modes. Chemosphere 238, 124610
- ↑ Muller-Karanassos, C., Arundel, W., Lindeque, P.K., Vance, T., Turner, A. and Cole, M. 2021. Environmental concentrations of antifouling paint particles are toxic to sediment-dwelling invertebrates. Environ. Poll. 268, 115754
- ↑ 6.0 6.1 Pereira, D., Almeida, J.R., Cidade, H. and Correia-da-Silva, M. 2024. Proof of Concept of Natural and Synthetic Antifouling Agents in Coatings. Mar. Drugs 22, 291
- ↑ 7.0 7.1 Hu, P., Xie, Q., Ma, C. and Zhang, G. 2020. Silicone-Based Fouling-Release Coatings for Marine Antifouling. Langmuir 36: 2170–2183
- ↑ Xu, K., Xie, H., Sun, C., Lin,W., You, Z., Zheng, G., Zheng, X., Xu, Y., Chen, J. and Lin, F. 2023. Sustainable Coating Based on Zwitterionic Functionalized Polyurushiol with Antifouling and Antibacterial Properties. Molecules 28, 8040
- ↑ Murali, S., Agirre, A., Arrizabalaga, J., Rafaniello, I., Schaefer, T. and Tomovska, R. 2024. Zwitterionic stabilized water-borne polymer colloids for antifouling coatings. Reactive and Functional Polymers 196, 105843
- ↑ Król, B., Król, P., Byczynski, L. and Szalanski, P. 2017. Methods of increasing hydrophobicity of polyurethane materials: Important applications of coatings with low surface free energy. Colloid. Polym. Sci. 295: 2309–2321
- ↑ Regulation (EU) No 528/2012 of the European Parliament and of the Council of 22 May 2012 concerning the making available on the market and use of biocidal products https://eur-lex.europa.eu/eli/reg/2012/528/oj/eng#anx_II
Please note that others may also have edited the contents of this article.
|
