Course:EOSC270/2023/The Effect of TBT on Ecosystems Within High Marine Vessel Traffic Areas.

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What is TBT?

A molecule of the tributyltin compound tributyltin chloride.

Tributyltin (TBT) is a class of organotin compounds that contain the group (C4H9)3Sn.[1]

TBT is commonly used industrially in wood preservation, paper making, as a water disinfectant, in agricultural fungicides, in textile production, and as an antifouling agent.[1][2] The reason TBT is used as an antifouling agent is because it is a biocide, inhibiting organismal growth.[1] Because of this inhibition, TBT saw widespread use as a component of ship paints.[1] The ship paints are meant to improve the performance of ships, and increase their durability and longevity, since organisms growing on a ship’s hull can increase drag and wear on the vessel.[1]

However, the biocidal properties of TBT can also lead to negative effects in ecosystems. TBT leaches into water and can cause harmful effects to untargeted organisms, particularly in areas where boat traffic is high, like ports.[1] The leached TBT causes issues for organisms, including disturbing mitochondrial function, as well as impairing organisms’ growth, development, reproduction, and survival.[2] This can lead to a decline in the populations of organisms. Additionally, TBT is a carcinogen, and can bioaccumulate, and its concentration increases the further up the food chain you go.[1][2] This bioaccumulation is most pronounced in organisms with low metabolic conversion rates, and/or high TBT uptake.

Types of Ecosystems affected by TBT?

When TBT enters the water, it eventually sinks to the bottom of the water column and enters the environment's sediment [2]. Thus, chemicals are consumed by mollusks and shellfish when they feed, which causes TBT to accumulate in their bodies[2]. Mollusks and shellfish that have consumed the TBT are then consumed by upper trophic level organisms like fish and marine mammals. This can negatively affect their reproductive systems, weaken their immune system, and can eventually lead to death[2]. Marine ecosystems, like the intertidal and subtidal zones, are vulnerable to TBT not only because of the effects of bioaccumulation, but also due to the amount of time it takes for TBT to degrade and the length of time that ships stay near them in ports[3]. Thus, the concentrations of TBT can be particularly high close to near shore ecosystems, and the pollution via TBT accumulates over time[4]. Additionally, though TBT can impact all organisms, it impacts mollusks and shellfish particularly strongly. Because large populations of these organisms live intertidal zone, they are also disproportionally at risk of TBT contamination.

Measuring TBT concentrations

Accumulation in sediments

Even though TBT has a short residence time in the water column, it can accumulate in sediments as it strongly binds to it. Therefore, there may be a persistent eco-toxicological risk even after the ban of TBT from a given area, due to the slow degradation of TBT in sediments.[5] TBT was detected in sediments deposited over 15 years ago in Auckland, New Zealand.[6] Some studies suggest that under anaerobic conditions in benthic zones, TBT can remain for decades in sediments.[7] This suggests that TBT can have long-lasting, detrimental effects on marine ecosystems, as it has the potential to continuously leach from sediments in marine environments over prolonged periods.

Sediment concentrations in Portugal were measured between April 1999 to May 2000 at 15 stations. About 50 percent of river and coastal sediment samples from the Portuguese coast showed contamination. The direct release of TBT from antifouling paint represents a significant pathway for TBT entering marine environments, as its absorption and partitioning to suspended particulate matter, followed by sedimentation, result in the accumulation of TBT.[8] Additionally, it can be further distributed throughout the local marine environment via re-suspension during storm events and sediment disturbance.[7]

Dredging involves the removal of sediments and debris from marine environments to facilitate safe navigation and vessel berthing, as well as to support new civil engineering projects. In the UK, regulation of dredged sediment falls under the Marine and Coastal Access Act, ensuring that only sediments with acceptable contamination levels, as per predetermined action levels, are disposed of. TBT concentrations have been monitored through data between 2000 and 2018 in the UK, and research suggests that existing action levels are not effective at limiting or managing TBT concentrations. This is because sites with a lower risk of TBT contamination are no longer being screened for TBT prior to disposal, leading to a higher likelihood of exceeding action levels due to the combined total of contamination. Additionally, the sampling sites utilized for contamination monitoring may miss hot spots of TBT, resulting in inaccurate representations of concentration levels.[7] In conjunction with emerging contaminants like nanoparticles, such as nano-sized titanium dioxide, which also have an affinity to bind to sediments, the toxicity of TBT can increase. This increase can result in hatching inhibition and malformations in abalone[9], emphasizing the importance of monitoring and regulating TBT concentrations. The cumulative impact of TBT, coupled with other pollutants, can amplify their adverse effects on marine organisms.

Concentrations near shipyards

The International Maritime Organization (IMO) has repeatedly expressed concern regarding the harmful effects of TBT on marine organisms, and in October 2001, it resolved to introduce a global ban on the use of TBT based antifouling paint. However, high concentrations of TBT remained and were detected around the world in the early 2000s, even after the ban. Concentrations in coastal sediments are primarily related to heavy boat traffic and shipyard activities.[8] The presence of TBT has been influenced by the ship building industry, the volume of shipping, improper cleaning of vessel hulls and poor practice of the disposal of TBT-based paints in dry dock facilities.[7] In Auckland, New Zealand, highest TBT concentrations were measured in sediments near a naval dry dock and close to boat washdown facilities.[6] In addition, the world’s largest shipbuilding industries are in Korea, Japan and China, therefore high concentrations of TBT have been found in Asian coastal environments.[10] Despite regulatory measures being implemented, widespread detection of TBT persists along the Korean coast, with the highest concentrations observed near industrial complexes and large shipyards.[11] The use of TBT has been gradually regulated in Korea since 2000, and it was totally banned in November 2003. Nevertheless, a study published in 2011 revealed extremely high levels of TBT in surface sediment at a station situated in front of a drydock and near the surface runoff outfall of a shipyard. Analysis of sediment cores further substantiated this finding, demonstrating significant positive correlation between TBT contamination and the annual tonnage of ship construction within the shipyard over the past three decades.[12] This reinforces that shipyards are a primary source of TBT contamination.

Marine organisms used to measure concentrations

Since TBT is a hydrophobic molecule, it is readily concentrated in marine organisms. Bivalves such as mussels and oysters are useful for measuring and monitoring TBT due to their high accumulation of organotins, non-mobility and wide distribution.[10] Specifically, mussels (Mytilus galloprovincialis) are good sentinel organisms for monitoring water quality, as they easily accumulate TBT and are widely distributed in rocky shores, including harbours. They also have limited ability to metabolize TBT.[8] Additionally, if no native species are available, mussels can be transplanted from pristine areas to contaminated sites to measure TBT concentrations.[13]

In Portugal, between the period from April 1999 to May 2000, mussels were used to determine TBT concentrations. High concentrations of butyltin compounds, including TBT, were detected in mussels of 6 of the 15 stations, indicating a fairly widespread distribution of TBT in Portuguese coastal waters.[8]

In Korea, the mussel transplantation method was used to evaluate TBT contamination at 7 stations around a large shipyard for 126 days. Despite the complete ban on TBT-based antifouling paints in Korea, mussels still exhibited TBT accumulation following transplantation. This study conducted in 2008 showed significant correlation between TBT concentrations in water and mussels. The findings strongly suggested that although newly constructed ships are no longer painted with TBT-based antifouling paints, residues within nearby shipyard painting facilities may continue to release leachate containing TBT. Consequently, the concentrations detected in these mussels primarily originated from paint leachate.[13] This highlights the importance of continuously monitoring TBT concentrations, as it persists in contaminating waters long after it has been banned.

Challenges of marine life in high traffic areas?

Persisting TBT Concentrations

Despite the banning of TBT coating on ships in many Countries, the compound still leaches from the surrounding environment back into the ocean. This happens through two primary ways, first, reservoirs of TBT have been created in marine sediments and secondly, many small vessels under 25m can still be coated in TBT.

This image demonstrates the compounds that TBT breaks down into (dibutyltin and monobutyltin) and that they bind to sediments on the sea floor. On the right it shows the relative rate of resuspension of the compounds back into the water and that TBT remains within the sediments and leaches into the water very slowly. This is what creates a reservoir of TBT within marine sediments. [14]

The half-life of TBT increases significantly when it is bound to sediments than when it is in overlying waters. In open waters, the half life of TBT is within days, however in sediments on the marine floor, the half life can vary from months to even years. [15] This means that a sort of TBT reservoir has been created from years of heavy TBT use as an antifouling agent on ship hulls up to the end of the 20th century. Now TBT slowly leaks from the sediments into the surrounding waters despite little new input of TBT. This creates a consistent concentration of TBT that marine organisms need to deal with.

Additionally, while Canada has completely banned the use of TBT as an antifouling coating[16], many Countries still allow vessels under 25 meters to coat their hulls with tributyltin. [17] Therefore, the waters in these countries remain to have an input of TBT into their waters and concentrations of the compound can spread to other parts of the ocean before it degrades fully.

Species Dependent Effects

This simple food web of shallow and deep water ecosystems that includes the species most sensitive to TBT concentrations (molluscs and sponges) shows the effect that high TBT concentrations can have on an ecosystem's food web. With most sensitive species found at the bottom of the food chain, there can be profound bottom-up effects of TBT toxicity. [4]

The effect that TBT has on the marine life depends on the specific species of organism being exposed to the compound and their ability to metabolize TBT. Species that are able to metabolize TBT quickly and break it down into DBT and MBT seem to be less affected by TBT concentrations in an ecosystem. However, species that metabolize the compound slowly, have bioaccumulation of the compound within their tissues and it rises to harmful concentrations quickly. [15] A previous study found that sponges, coelenterates, bryozoans and mollusks were the groups most sensitive to TBT exposure. [4] This implies that these species are unable to quickly metabolize TBT. As the compound concentration in their tissues rises, toxicity can develop which looks different depending on the organism. For example, oysters will develop shell thickening and decreased growth while other species will have increased larval mortality and inhibited egg development. [3] This inevitably affects the fitness of these species and can threaten their populations in regions with persistent TBT concentrations.

Additionally, species that can metabolize TBT quickly and break it down into DBT and MBT may not be directly affected. However, changes in the food chain after vulnerable species populations decrease can alter the food source for many resistant species. For example, Mollusca are a source of food for many higher trophic level organisms such as lobsters and small fish, when their populations decrease from TBT toxicity, their predators may struggle to find food. Generally, the species most sensitive to higher concentrations of TBT are found near the bottom of the food chain in an ecosystem. This means that a change in population size of these vulnerable species can cause a ripple effect up the food chain as they support the top half of the food chain.

Imposex

One specific, well studied effect of TBT on Neogastropod populations is called imposex. This is the imposition of male sex characteristics on female snails. This phenomenon has been observed mostly in N. Lapillus and Ocenebra Erinacea for which TBT concentrations of 1 ng/L and 3 ng/L respectively have been found to cause the initiation of imposex. This involves the development of a penis and a vas deferens on female snails. [15]Additionally, the oviduct of N. Lapillus became sterilized at TBT concentrations between 4 ng/L - 10 ng/L [15].

The combination of imposex and oviduct sterilization can create incredibly challenging conditions for Neogastropods to reproduce. With TBT concentrations causing imposex, the male:female ratio of these populations will shift towards to male side and there will be too few female snails to support the population. As the two species of Neogastropod, N. Lapillus and Ocenebra Erinacea are incredibly sensitive to TBT they are rarely found in busy waterways anymore.

Ecosystem restoration and solutions.

Bans and Regulations

On October 5th, 2001, the International Maritime Organization implemented the international convention on the control of harmful anti-fouling systems on ships (AFS) [13]. This convention prohibited the use of TBT and all other organotins in antifouling paint on ship hulls. The convention was put into force on September 17th, 2008 and also works to prevent the future use of other harmful substances in anti-fouling ship hull paint[13].

In correspondence with the convention, participating countries must prohibit the use of TBT in antifouling paint on ships under their authority, as well as all ships that enter their ports, shipyards, and terminals. Out of 195 countries, only 91 participate in this convention[18].

Ships participating in international voyages that are 400 gross tonnage or larger and must obtain an International Anti-Fouling System Certificate and a survey must be executed before the ship can be put into the water and before the certificate can be used[13].

Specifically in Canada, TBT in antifouling paint is prohibited on any Canadian ships whether geographically located in Canada or not[19]. Furthermore, all ships entering Canada must not have TBT antifouling paint on their hulls[19]. For ships that request to transfer onto the Canadian registry of ships, all coatings that include TBT must be removed[19].

Monitoring and Removal

Although the ban of TBT has been implemented for more than a decade, further monitoring is required to ensure that long-term effects are being managed appropriately. Research is currently being done demonstrating that the bans of TBT have been effective in decreasing the concentration of TBT in the water columns and marine sediments, but the effects of TBT are still being seen today. In a study done in a fishing port in Taiwan, measured the concentrations of butyltins in the sediments of the fishing port in 2020[20]. In the water column, the half life of TBT is approximately 6 days to several months[20]. However, the half life of TBT in marine sediments is very slow at 1 to 8.09 years[20]. Overall, the study demonstrated that 80% of the effected sediments that contain TBT can have negative impacts on gastropods that are especially sensitive to TBT and can effect their reproduction[20].

Due to sediments still being contaminated with TBT, remediation methods are currently being researched within the past 3 years. These removal methods would be able to be used on extracted sediments from environments with high TBT concentrations with the goal of reusing these sediments for various applications. Methods include electrochemical oxidation treatments or oxidation reagents[21]. Presently, these methods are being tested on small-scale lab environments. Sediments were retrieved from estuaries and coastal regions that were in close proximity to shipping yards[21]. Fenton's reagent (hydrogen peroxide and ferrous iron) can convert TBT into harmless inorganic compounds that are easier to remove from water[21]. This remediation method was deemed effective as during the study it had the capability to remove 64% of the TBT from the sediment[21]. However, the sediment after the procedure had lower pH and would require other treatments before the sediment can be reused. Electrochemical remediation was suitable in both the water column and marine sediments and was determined that it can remove 58% of TBT from sediments in the experiment and did not require further various treatments, resulting in it being determined to be more suitable as a remediation method[21]. There is currently little research done on removing TBT from sediments while still in the ecosystem.

Innovative alternatives

In terms of the use of alternative antifouling methods that do not involve the use of TBT and other organotins there are various solutions. Presently antifouling paints include metal biocidal agents and fouling release coatings. Some of the most prominent antifouling systems include (tin-free) self-polishing copolymers, (tin-free) conventional paint, and control depletion polymers (CDPs) - copper paint[22]. All have their advantages and disadvantages when it comes to efficacy and life-span and many still include the use of biocides and metals in order to manage biofouling. Another alternative that is currently being researched are nature inspired antifouling methods[23]. There are three main areas of research that are looking to nature for antifouling methods which are natural antifoulants and synthetic analogs, bio-inspired polymeric coatings for marine antifouling, and biomimetic surface topographies[23]. Natural antifoulants look to the antifoulants that marine organisms release to prevent biofouling. Bioinspired polymeric coatings look to Zwitterionic polymers, slippery liquid-infused porous surfaces which are inspired by pitcher plants, DOPA-based coatinfs which are inspired by the proteins used by mussel feet for attachements, and self-polishing copolymers inspired by pilot whale skin. Biomimetic surface topographies mimic the surfaces of marine organisms, plants, and insect wings. All three of these areas have their advantages and disadvantages and are very new research ideas that require further inspection[23]. However, these three areas are inspiring a new hope for environmentally friendly antifouling methods.

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Miguez, Diana; Tarazona, Jose V. (2024). "Organotin compounds". Encyclopedia of Toxicology. 7: 189–194 – via Elsevier.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Antizar-Ladislao, Blanca (2008). "Environmental levels, toxicity and human exposure to tributyltin (TBT)-contaminated marine environment. A review". Environment International. 34: 292–308 – via Elsevier.
  3. ↑ 3.0 3.1 Beyer, Jonny; Song, You; Erik Tollefsen, Knut; Berge, John; Tveiten, Lise; Helland, Aud; Oxnevad, Sigurd; Schoyen, Merete (June 28, 2022). "The ecotoxicology of marine tributyltin (TBT) hotspots: A review". Science Direct. Retrieved April 8, 2024.
  4. ↑ 4.0 4.1 4.2 Henderson, R.S (1985). "Effects of Tributyltin Antifouling Paint Leachates on Pearl Harbor Organisms. Site-Specific Flowthrough Bioassay Tests". Defence Technical Information Center. Retrieved April 8, 2024.
  5. ↑ Ceulemans, M; Slaets, S; Adams, F (July 1998). "Speciation of organotin in environmental sediment samples". Talanta. Volume 46 (Issue 3): Pages 395-405. doi:10.1016/S0039-9140(97)00403-7 – via ScienceDirect. |access-date= requires |url= (help)
  6. ↑ 6.0 6.1 de Mora, S.J.; Stewart, C.; Phillips, D. (January 1995). "Sources and rate of degradation of tri(n-butyl)tin in marine sediments near Auckland, New Zealand". Marine Pollution Bulletin. Volume 30 (Issue 1): Pages 50-57. doi:10.1016/0025-326X(94)00178-C – via ScienceDirect.
  7. ↑ 7.0 7.1 7.2 7.3 Warford, L.; Mason, C.; Lonsdale, J.; Bersuder, P.; Blake, S.; Evans, N.; Thomas, B.; James, D. (March 2022). "A reassessment of TBT action levels for determining the fate of dredged sediments in the United Kingdom". Marine Pollution Bulletin. Volume 176. doi:10.1016/j.marpolbul.2022.113439 – via ScienceDirect.
  8. ↑ 8.0 8.1 8.2 8.3 Díez, Sergi; Lacorte, Sílvia; Viana, Paula; Barceló, Damià; Bayona, Josep M (August 2005). "Survey of organotin compounds in rivers and coastal environments in Portugal 1999–2000". Environmental Pollution. Volume 136 (Issue 3): Pages 525-536. doi:10.1016/j.envpol.2004.12.011 – via ScienceDirect.
  9. ↑ Zhu, Xiaoshan; Zhou, Jin; Cai, Zhonghua (March 2011). "TiO2 nanoparticles in the marine environment: impact on the toxicity of tributyltin to abalone (Haliotis diversicolor supertexta) embryos". Environ. Sci. Technol. doi:10.1021/es103779h – via ScienceDirect.
  10. ↑ 10.0 10.1 Shim, Won Joon; Hong, Sang Hee; Kim, Nam Sook; Yim, Un Hyuk; Li, Donghao; Oh, Jae Ryoung (2005). "Assessment of butyl- and phenyltin pollution in the coastal environment of Korea using mussels and oysters". Marine Pollution Bulletin. Volume 51 (Issues 8–12, 2005): Pages 922-931. Retrieved April 8, 2024 – via ScienceDirect.
  11. ↑ Choi, Minkyu; Choi, Hee-gu; Moon, Hyo-bang; Kim, Gui-young (2009). "Spatial and temporal distribution of tributyltin (TBT) in seawater, sediments and bivalves from coastal areas of Korea during 2001-2005". Environmental Monitoring and Assessment. Volume 151 (Issue 1-4). doi:10.1007/s10661-008-0271-0 – via ProQuest.
  12. ↑ Kim, Nam Sook; Shim, Won Joon; Yim, Un Hyuk; Ha, Sung Yong; An, Joon Geon; Shin, Kyung Hoon (August 2011). "Three decades of TBT contamination in sediments around a large scale shipyard". Journal of Hazardous Materials. Volume 192 (Issue 2): Pages 634-642. Retrieved April 10, 2024 – via ScienceDirect.
  13. ↑ 13.0 13.1 13.2 13.3 13.4 Kim, Nam Sook; Shim, Won Joon; Yim, Un Hyuk; Sung Yong, Ha; Park, Pan Soo (2008). "Assessment of tributyltin contamination in a shipyard area using a mussel transplantation approach". Marine Pollution Bulletin. Volume 57 (Issues 6–12): Pages 883-888. Retrieved April 10, 2024 – via ScienceDirect. Cite error: Invalid <ref> tag; name ":8" defined multiple times with different content
  14. ↑ Furdek Turk, Martina (June 15, 2020). "Simultaneous analysis of butyltins and total tin in sediments as a tool for the assessment of tributyltin behaviour, long-term persistence and historical contamination in the coastal environment". Science Direct. Retrieved April 8, 2024.
  15. ↑ 15.0 15.1 15.2 15.3 Bryan, Geoffrey (1991). "Impact of Low Concentrations of Tributyltin (TBT) on Marine Organisms: A Review".
  16. ↑ "Anti-Fouling Systems". Government of Canada. 2019-07-31. Retrieved April 8, 2024.
  17. ↑ Lah, Katarina (2011). "Tributyltin" (PDF). Archived from the original (PDF) on 2011.
  18. ↑ "International convention on the control of harmful anti-fouling systems on ships". ECOLEX: The gateway to environmental law.
  19. ↑ 19.0 19.1 19.2 "Anti-fouling systems. Transport Canada". Government of Canada. 2019, July 31. Check date values in: |date= (help)
  20. ↑ 20.0 20.1 20.2 20.3 Lee, S.-H. (2022, March 5). "Butyltin Contamination in Fishing Port Sediments after the Ban of Tributyltin Antifouling Paint: A Case of Qianzhen Fishing Port in Taiwan". water. 14(5) – via MDPI. Check date values in: |date= (help)
  21. ↑ 21.0 21.1 21.2 21.3 21.4 Norén, Anna (2022, January 5). "Removal of organotin compounds and metals from Swedish marine sediment using Fenton's reagent and electrochemical treatment". Environmental Science and Pollution Research. 29 – via ProQuest. Check date values in: |date= (help)
  22. ↑ Chambers, L.D. (2006, December 4). "Modern approaches to marine antifouling coatings". Surface and Coatings Technology. 201(6): 3642–3652 – via Elsevier Science Direct. Check date values in: |date= (help)
  23. ↑ 23.0 23.1 23.2 Chen, Liren (2021, April 20). "Biomimetic surface coatings for marine antifouling: Natural antifoulants, synthetic polymers and surface microtopography". Science of The Total Environment. 766 – via Elsevier Science Direct. Check date values in: |date= (help)
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