Strategic actions for sustainable vessel hull coatings in line with the UN SDGs

2.1 Environmental Impacts of Antifouling Paints

A range of antifouling paints have mainly used toxic materials (called biocides) as the critical content for preventing foulings, which have toxic effects on marine environments. Several studies have identified that antifouling biocides pose a potential environmental risk; for example, owing to the elevated concentration in sediments. In addition, these studies have also emphasized the importance of biological impacts caused by the secondary spread of invasive species into the marine environment [4]. These issues cause changes in the marine food web, thereby resulting in altered productivity patterns that impact ecosystems and human health [5].

2.2 Non-toxic Vessel Hull Coatings: Availability and Properties

Owing to the potential pollution challenge of copper (oxide), there have been continuous discussions for revised (or new) regulations to reduce copper levels or a complete ban. To support this review and consideration, several alternative technological solutions have been developed in recent years. Non-toxic hull coatings are therefore readily and commercially available today; however, they have not been widely adopted, mainly owing to efforts, such as full blast, to build up the new coating system with some skepticisms regarding long-term performance [12], as well as their higher application and material prices than biocide-containing “antifouling” products.

There are generally three types of nontoxic hull coatings: silicone-based, epoxy-based, water-based, and polymer-based coatings. Although the proportion of non-toxic hull coatings remains smaller than biocides containing “‘antifouling,” silicone-based hull and epoxy hull coatings are already commercialized.

As presented in Table 1, regarding epoxy-based and silicone-based non-toxic vessel hull coatings, the major reasons why shipowners and ship operators are reluctant to apply these non-toxic vessel hull coatings are primarily related to the high cost (in both material and application costs) and low fouling control performance of silicone-based and epoxy-based hull coatings, respectively.

Table 1:

General properties of alternative vessel hull coatings

Epoxy-based, polysiloxane-based, and silicone-based vessel hull coatings are usually called “foul-release” coatings and/or “non-toxic” coatings, which are regarded as environmentally friendly antifouling technologies. These technologies have the physical properties of low surface energy and low elastic modulus to achieve antifouling, and they do not dissolve or decompose in seawater. However, existing technology-related issues, such as the mechanical properties and antifouling performance under static conditions, are believed to be the key breakthrough directions for future research [13].

2.3 Regulation for Antifouling: Current and Future

The most distinctive global regulation for antifouling paints is the TBT ban of the “AFS Convention” by the IMO MEPC in 2001. Antifouling paints, using TBT as a biocide, were developed in the early 1960s, and have been widely used globally until 2008, the year the IMO “AFS Convention’ resolution was put into effect.

In the 1980s, several researchers started to emphasize the harmful impact of TBT as a severe toxic substance impacting the marine environment. However, only local prohibitions and regulations were established for small coastal vessels, rather than commercial vessels operating in deep-sea water globally.

In the 1990s, the IMO MEPC continued to study the environmental issues of antifouling paints. In 1990, IMO adopted “an Assembly resolution that called on the MEPC to develop an instrument, legally binding throughout the world, to address the harmful effects of antifouling systems used on ships” [3].

Table 2:

Antifouling major regulation events in IMO

In November 2001, IMO adopted a new International Convention on the Control of Harmful Antifouling Systems on Ships (called “AFS Convention”), prohibiting the use of harmful organotin compounds in antifouling paints used on ships and establishing a mechanism to prevent the potential future use of other harmful substances in antifouling systems [3]. The “AFS Convention” established a global ban on the application of TBT-based antifouling on all vessels after January 1, 2003, including a prohibition of active TBT presence in the paint system after January 2008.

In June 2021, IMO MEPC amended the IMO “AFS Convention” to include controls on the biocide cybutryne (also known under its industry name as Irgarol-1051), which cannot be applied to ships from January 2023 [14].

When IMO discussed the ban on the use of TBT in antifouling systems, their position was that copper (oxide) is far less harmful than TBT [7]. However, because these previous studies were conducted 20 years ago, they need to be reinvestigated with more advanced technologies and insights by new experts.

Considering the background and history, new regulations to ban the use of copper and other biocides in antifouling products should be revisited and developed, which might require a similar process to the TBT ban. Meanwhile, shipowners, naval architects, governments, and port authorities, who can make decisions on antifouling types, should bear sustainable responsibilities for the present and future.

2.4 Economic Importance of Antifouling

According to IMO, “antifouling paints are used to coat the bottoms of ships to prevent sea-life organisms, such as algae and molluscs, from attaching themselves to the hull, which slows down the ship and increases fuel consumption” [3].

From the perspective of shipowners and operators, antifouling is economically very important, as it might be critically influenced by operational efficiency of fuel consumption of vessels, as presented in Table 3.

Table 3:

Fuel consumption reduction by vessel hull coatings

According to the results of the Global Maritime Energy Efficiency Partnership (GloMeep) project driven by IMO, “the coatings will reduce the resistance of the ship hull through water, including the required engine power, thereby reducing fuel consumption.” [15].

This is the area that we should investigate to develop measures to minimize the gap and optimize the solution between economic importance and environmental impact, which could be objectively reviewed from a sustainable perspective.

2.5 The UN SDGs Review for Vessel Hull Coatings

According to the UN website, “the SDGs were adopted by all UN member states in 2015 as a universal call to action to end poverty, i.e., to protect the planet and ensure that all people enjoy peace and prosperity by 2030”. It has a total of 17 goals (with 169 sub-targets), which are closely integrated with each other because any action or outcome from one might affect actions or outcomes in other goals, which should be balanced and harmonized in terms of social, economic, and environment sustainability [16].

As a specialized agency in the UN, the IMO also has a serious responsibility to support the UN SDGs in terms of the safety and security of shipping, as well as the prevention of marine pollution from vessels, given their main commitments “to create a regulatory framework for the shipping industry that is fair and effective, universally adopted and implemented” [17].

This study emphasizes the importance of vessel hull coatings in achieving key topics of the SDGs, which are summarized in Table 4.

Table 4:

UN SDGs in conjunction with vessel hull coatings

SDG 14 – Life Below Water

Among these SDGs related to vessel hull coatings, SDG 14 has a more direct impact on the marine industry. Therefore, IMO has a centralized role for SDG 14, while all SDGs are closely linked to each other.

According to the study by IMO (2017), “the main pollutants of concern with respect to shipping are oil, hazardous and noxious substances and other cargoes capable of causing harm, sewage, garbage, air pollutants, antifouling agents for hull treatment, and transported invasive species.” Based on IMO’s regulatory guidelines, such as its international conventions and codes, these matters have frequently been issued by the global community [19]. The IMO’s global regulatory conventions or resolutions regulate a range of pollution caused by vessels.

Therefore, SDG 14 targets should be reviewed from the IMO perspective to identify tangible actions related to antifouling and biofouling regulations. In June 2018, an IMO regional workshop was held to address the impact of biofouling by ships at Trinidad and Tobago, a port in Spain. According to a recent news article that explains IMO activities, “the workshop, attended by 45 participants from 13 countries, was held based on IMO's technical cooperation fund.” The main agenda of this workshop was centered on how to support the UN SDG 14 target based on the IMO’s existing and future regulations and guidelines [20]. However, there has been no specific discussion regarding the antifouling or biofouling issue in terms of the UN SDG 14.

Sub-targets 14.1 and 14.2 for achieving SDG 14 could be specifically reviewed in relation to the issue of the release of antifouling toxic chemicals and biocides to the ocean (including drydocking and cleaning works as land-based activities). Subtarget 14.2 is also closely related to the transfer of invasive aquatic species by vessels via biofouling.

Table 5:

SDG 14 sub-targets relating biocides into the ocean

In line with sub-targets 14.1 and 14.2 of SDGs, IMO has two regulations directly related to antifouling and biofouling, including invasive aquatic species, as comparably presented in Table 6.

Table 6:

IMO regulations for biofouling, antifouling and invasive species

The “AFS Convention” regulation is mandatory while “Biofouling Management” is based on Resolutions (not mandatory), rather than the Convention regime.

In June 2021, the 76th MEPC decided to ban “cybutyne,” which had been used as a biocide in antifouling paints for a long time. However, given the fact that ‘cybutryne’ has been used by only limited coating companies, this adoption is not enough to pursue the ultimate purpose of SDG 14.

SDG 14 has ten sub-targets that are insufficient with no direct indicators to verify and reduce the negative environmental impact of biocides from antifouling into the ocean. As stated in Resolution MEPC.207(62), although the potential impact of biocides released at the time of hull cleaning is clear, the SDG sub-target 14.2 has already exceeded the target period of 2020 without specific new indicators to prohibit or limit biocides and biofouling management.

SDG 3 – Good Health and Well-being

Given that a lot of foods that humans consume are produced from the oceans, the potential impact of biocides from antifouling products on human health should be considered as a critical subject in terms of SDG 3. More specifically, sub-target 3.9 of SDG 3 also emphasizes the potential health risk from hazardous chemicals.

Table 7:

SDG 3 sub-target relating biocides into the ocean

In line with SDG 3, several countries have already tightened regulations on chemicals such as REACH (Registration, Evaluation, Authorization of Chemicals), and are also tightening regulations on biocide substances used in various industries, via a separate regulation called BPR (Biocidal Product Regulation). South Korea also has the same regulation purposes, which are called K-REACH and K-BPR.

According to K-BPR, “any person who intends to manufacture or import active substance for use in biocidal products must prepare and submit the appropriate data and obtain approval from the Minister of the Environment. The validity of active substance approval is within 10 years in case of biocides for Antifouling products” [21].

Among the 594 biocides listed by K-BPR with grace periods (3–10 years) to obtain approval from the Minister of the Environment, a total of 33 biocides are currently categorized by the use of antifouling products. The required approval dates for the 33 biocides used in vessel hull coatings have been suspended with a grace period of 10 years, which means that these active “substances” must be re-approved before the expiration of the grace period by the end of December 2029. Meanwhile, a grace period of two additional years is given to biocidal “products” that use these active substances, thereby extending the expiration date to the end of December 2031.

Interestingly, the regulatory restriction for these biocides by K-REACH is now more aggressive than K-BPR in terms of timing (see Table 8). Given the public notification of the toxicity level threshold recently stipulated for some active ingredients (selektope and DCOIT), further guidelines on other active ingredients (CPT, ZPT, and copper oxide) will be supposedly announced after a thorough investigation in due course. This means that all major biocides in antifouling products are likely to be re-classified as toxic substances with the clear limitation of mixture weight percentages, which are generally lower than the current ones in their formulations.

Table 8:

Antifouling products’ major biocides status in K-REACH and K-BPR

Regardless of K-REACH or K-BPR, an ultimate ban or strict restriction on biocides would be obvious in the future with just a matter of time. Therefore, more proactive responses from producers, users, and government bodies are required. As previously emphasized in Chapter 2-2, non-toxic vessel hull coatings are already commercialized in the market, where more an active institutional support for the development of high-performing nontoxic vessel hull coatings is required by the government.

SDG 13 – Climate Action

Seeing the description of SDG 13 “Take urgent action to combat climate changes and its impacts,” SDG 13 is currently considered as a priority among all SDGs. However, because international shipping vessels do not operate within the territory of a particular country, it has been difficult to manage carbon emissions per country, although other industries have exhibited the proactive implementation of decarbonization policies and drives for each country. As a specialized agency in the UN, the IMO has made efforts to take this priority, resulting in remarkable regulations that are now closely aligned with the UN SDG 13 “Climate Action.”

In 2018, the IMO adopted an initial strategy to reduce greenhouse gas (GHG) emissions from ships. Levels of ambition include a CO₂ emission reduction of at least 40% by 2030, compared to 2008, and a total GHG emission reduction from shipping by at least 50% in 2050, compared to 2008 [23].

The IMO’s regulatory movement for decarbonization is summarized in Table 9. In general, the target vessel for decarbonization is being expanded from newbuild vessels to existing vessels, and the reduction method is also expanding from the design and technical aspects of the vessel (in EEDI- energy efficiency design index) to operational aspects (in EEXI- energy efficiency existing ship index, and in CII- carbon intensity indicator), and is now pushing for market-based measures (MBM) from an economic perspective.

Table 9:

IMO decarbonization regulation status

In conjunction with the subject of this study, the vessel hull coating has important direct and indirect impacts on these regulations, because it is very closely related to the vessel fuel efficiency (1%–4% reduction in main engine fuel consumption) [15], according to the GloMEEP, which was launched in 2015 by the IMO.

More specifically, for each regulation, although the vessel hull coating element was not directly reflected in the EEDI formula implemented in 2015 (only indirectly reflected in the event of vessel sea trials in verification), it will have a significant and direct impact on the CII, which will be implemented in 2023.

The attained CII can be calculated as the ratio of the total mass CO₂ (M) emitted to the total transport work (W) [24] as follows:

This simple formula of the attained CII could be paraphrased as expressed in (2) to explain how vessel hull coating can directly impact the attained CII, together with the impact on the vessel fuel consumption, such as the low friction vessel hull coating with less fouling, minimized drag resistance and skin friction, and vessel hull cleaning to remove biofoulings.

Contemporary environmental and regulatory considerations have justified the essential requirement to develop new advanced high-performance products, policies, and procedures that will improve the quality of life, health, safety, the environment [6], and economic benefits.

2.6 Conflict between Stakeholders

Although a biocide-free solution for antifouling products is an attractive target as it is environmentally conscious, this issue is in contrast with a majority of commercially available solutions [25]. Regardless of the requirements of new advanced high-performing non-toxic “vessel hull coatings.” there have been disagreements among stakeholders (shipowners, coating companies, governance bodies and non-governmental organizations (NGOs)), who should be aligned in terms of sustainability.

End users – shipowners and operators

In November 2001, IMO adopted “a new International Convention on the Control of Harmful Antifouling Systems on Ships (called AFS Convention), which will prohibit the use of harmful organotin compounds in antifouling paints used on ships and will establish a mechanism to prevent the potential future use of other harmful substances in antifouling systems” [26]. However, most of them believe that the current non-toxic (non-biocidal) coatings require a higher initial cost than normal “antifouling” products. They are reluctant to apply expensive “non-toxic (non-biocidal)” coatings and prefer to use “toxic (biocidal) antifouling” products.

As shown in Table 1, most non-toxic vessel hull coating products “last longer than copper-based antifouling paints” because there is no polishing or depletion mechanism, which means that no full repair is required at every drydocking. Although coating manufacturers claim that non-toxic vessel hull coatings provide the ultimate long-term cost-benefit mainly caused by lowering maintenance and repair costs, several shipowners exhibit a lack of confidence in this area with strong skepticism.

Suppliers - coating companies

Most global coating companies have developed “non-toxic (non-biocidal)” coatings in line with environmental requirements in the future. Some products have been commercially recognized by some shipowners in terms of their fuel efficiency, as well as their green image. However, these coating companies are reluctant to further invest in developing or enhancing this area, because most of their customers, i.e., shipowners, remain reluctant to use non-toxic (non-biocidal) coatings, owing to the high initial cost, and IMO has not seriously and deeply considered banning current toxic (biocidal) antifouling products. A dilemma exists between economic and environmental perspectives among the three dimensions of sustainability.

NGOs / IMO

Several NGOs, together with marine scientists and ecologists, believe that current alternative biocides (instead of TBT) are only slightly less harmful than TBT, which was completely banned in 2008. Some NGOs believe that the current biocidal “antifouling” products should be immediately stopped, given the serious environmental and potential human health problems. They also frequently emphasize this issue as one of the priorities of IMO, with the aim of ending the toxic pollution of “antifouling” products.

Regardless of the NGO’s opinion, the IMO appears not to seriously consider revisiting it or prioritizes it less than other issues such as climate actions, based on their previous position in 2002 that the copper-based (current) biocidal antifouling provides the benefit of less harm to the marine environment after the ban on TBT.

However, this IMO’s old view almost 20 years ago, in relation to biocides currently used in antifouling products, should be revisited in terms of harmful chemicals, biological, and human health hazards with novel technologies and insights, together with various experts and NGOs.

New potential conflict between SDG 13 and 14

The position of each stakeholder on the vessel hull coatings described above is likely to be adjusted as being directly or indirectly impacted by the IMO's new decarbonization regulations, such as EEDI, EEXI, and CII described in Chapter 2-5.

Shipowners should consider all possible factors that can positively impact CII verification annually, which will enter into effect on January 2023. The role of vessel hull coatings could be considered as a potential solution for obtaining better CII levels together with other energy-saving devices. Therefore, although the low-level antifouling products used to be preferred by some shipowners, it is now expected that they will apply higher-performing vessel hull coatings to obtain better CII levels (i.e., more decarbonization in SDG 13 aspect) by maximizing the fuel efficiency of vessels.

The potential concern is that if existing non-toxic vessel hull coatings do not perform sufficiently well with clear cost-benefit for shipowners, between coating investment cost and CII benefits, such administrative incentive and/or preference by their customers, in this case, shipowners are likely to use high-performing toxic (biocidal) antifouling products in SDG 13, rather than shifting to expensive non-toxic vessel hull coatings in SDG 14.

Conversely, although non-toxic vessel hull coatings might contribute to SDG 14 with a negative impact on SDG 13, advanced high-performing non-toxic vessel hull coatings are not developed on time. As explained in Chapter 2-5, K-REACH and K-BPR regulations continue to restrict the use of major biocides. Without better antifouling performance with just no (lower) biocides, although these products can contribute to SDG 14, significant deterioration in SDG 13 could occur in terms of fuel efficiency and decarbonization.

3.1 Enhance Non-Toxic Hull Coatings in SDG 3, 13 and 14

As explained in Chapter 2-2, non-toxic vessel hull coatings, such as silicone-based and epoxy or polysiloxane-based technologies, have been developed and commercialized in the marine coating industry. However, the proportion of non-toxic hull coatings actually being applied in the market remains smaller than that of biocide-containing “antifouling” products.

There are several simple reasons why the market is not yet ready to shift to non-toxic hull coatings instead of current biocidal antifouling products. For non-toxic silicone-based hull coating products, their product features such as high initial cost, application difficulties, and mechanical properties, have been recognized by end-users (shipowners and shipyards) as major barriers in terms of adopting to their vessels in-service and inbuilding.

This study emphasizes the importance of all stakeholders’ efforts. For coating manufactures, they should therefore continue to develop innovative “fuel efficient” hull coatings with non-toxic properties. Although several coating companies have already developed non-toxic vessel hull coating products, as presented in Table 10, a few products have been well recognized by shipowners and maintained in the market with actual track records. Most coating companies focus on biocidal toxic antifouling products rather than non-toxic products with less preference by shipowners.

Table 10:

The UN SDGs in conjunction with vessel hull coatings

To encourage coating companies to continuously develop further enhanced high performing non-toxic hull coatings, the support of other stakeholders (shipowners, IMO, and governments) is essential.

Regarding shipowners or ship operators as end-users of antifouling products, they should evaluate the current existing nontoxic (non-biocidal) hull coatings in terms of “fuel efficiency,” and proactively use these products in line with new decarbonization regulations, such as a CII, which will enter into effect on January 2023. A reason for the reluctant adoption of current nontoxic (non-biocidal) products is related to the high cost of the initial coating in the short term. However, it could eventually be offset if the products provide fuel efficiency in the long term with the benefits of better CII levels, which should be evaluated annually.

Regarding IMO and each nation’s government, because SDG 13 “Climate Action” has been addressed as a priority with full attention, SDG 14 “Life Below Water,” as well as SDG 3 “Good Health and Well-being” should also be objectively prioritized and reviewed in terms of relevant potential environmental and human health impacts caused by biocides used in current antifouling products. This study provides a simple justification for the need for advanced non-toxic vessel hull coatings.

3.2 Improve Vessel Hull Cleaning Methods in SDG 3, 13 and 14

Experienced shipowners and operations are aware that the issue of vessel hull cleaning is an important action in pursuing “fuel efficiency” in vessel operations. In particular, in-water cleaning of the vessel hull would be an immediate and effective action to obtain a better CII level, which is eventually in conjunction with SDG 13 from the IMO perspective. Owing to this regulatory drive from CII, in-water cleaning of the vessel hull is expected to occur more frequently than now for the annual verification of the new regulation CII.

Therefore, under the new operational situation driven by new regulations for SDG 13, the potential high risk of invasive species transfer from vessel hull cleaning should be investigated in line with SDG 3 and 14 with more attention.

This study identified the human health risk with ecological effects in terms of SDG 3 and 14. According to Adel Ali Desher (2018), “the exotic species can destroy the environment and threaten the health and safety of human populations. In any ecosystem, the introduction and spread of exotic species are highly harmful because of the negative and irreversible changes that can result” [26].

However, the open secret is that illegal in-water hull cleanings on vessels have been frequently occurred in several countries. Given the actual situation when vessels are cleaned at or near ports and coastal areas, it can result in not only creating biofouling debris with invasive species, but also in triggering the unnecessary depletion of antifouling coatings with the premature release of biocides that can harm coastal environments in line with SDG 14.

The vessel hull in-water cleaning could have different levels of environmental risk, depending on the types of cleaning machines or vehicles, types of antifouling products, amounts of biocides released, and biocide residue from biofoulings removed.

The methods of vessel hull in-water cleaning, currently applied to large commercial vessels, are dominated by mechanical scrubbing methods, which adopt motor power to rotate the brush and remove biofoulings. These mechanical cleanings are likely to further increase the release of biocides. The other concern is that only a few cleaning machines have specific reclamation functions, which could be a serious issue in terms of minimizing the transfer of invasive aquatic species.

To minimize the unnecessary biocide release caused by in-water cleaning, contactless cleaning methods (such as high water pressure) are strongly recommended, which are also important for minimizing the mechanical damage on non-toxic silicone paint surfaces. Importantly, to minimize the transfer of invasive species when a vessel underwater hull is cleaned by in-water cleaning, shipowners, ship operators, and coating companies must use cleaning equipment or vehicles with reclamation functions, which is also very beneficial in minimizing the biocide residue on biofoulings removed.

The other issue is the less legal binding of regulations for vessel hull cleanings. Although IMO’s resolution “MEPC.207(62)” could be used as a guideline for vessel hull in-water cleaning and maintenance, it has no legal backing and is not mandatory. The right regulation for in-water hull cleaning and its legal bindings would be essential to achieving SDGs 3 and 14, where the IMO’s proper attention and efforts are required.

3.3 Cultivate NGOs Role in SDG 17

The purpose of the SDG 17 “Partnerships for the Goals” is to support the achievement of the SDGs and to harmonize and pursue synergy from all individual SDGs throughout the global partnership for sustainable development. The IMO currently has partnership arrangements with more than 70 NGOs, including major global environmental organizations and bodies [27]. Regardless of the potential hazards in SDG 3 “Good Health and Well-being” and SDG 14 “Life Below Water,” the issue of antifouling products in terms of human health and food chain, owing to “invasive aquatic species” and “biocide” sediment pollution has been relatively less highlighted by current NGOs than other social issues such as SDG 13 “Climate Action.”

Because the previous NGOs played a significant role in identifying the TBT’s dangers to the environment and human health, which eventually led to the ban on the use of TBT in the international convention 20 years ago, current NGOs will have to benchmark the lesson learned from that period, and they need to propose alternative solutions in conjunction with sustainable, nontoxic, high-performance vessel hull coatings, as well as proper in-water vessel hull cleaning methods.