On the 21st of April a committee meeting was held in Legco (HK law making body) to discuss a new regulation on harmful anti-fouling systems. The legislation seeks to ban the use of organotin such as tributylin (TBT) compounds in paints used on ships which kill any organisms trying to colonize the hulls such as barnacles, worm, mussels, algae and others. Despite a lot of petty squabbling (and personal digs at the previous colonial administrations) it looks hopeful that regulation may eventually make it to a 2nd and 3rd reading in Legco and pass into law.
Tributylin (TBT) is a chemical that was used extensively in anti-fouling paints (bottom paints) on ships to improve efficiency by preventing invertebrates and plants clinging to the hulls. TBT is the most successful anti-fouling agent ever invented and was relatively cheap. It was used extensively for 40 years. But TBT slowly leaches out into the marine environment where it is highly toxic to a wide range of organisms beyond the organisms that it was intended to kill. By poisoning barnacles, algae, and other organisms at the bottom of the food chain, TBT levels are concentrated (biomagnified) up the marine food web and even up to us humans. It also causes developmental problems in marine organisms. One of the most studied organisms are marine snails, such as the Dog whelk (Nucella lapillus) in Europe and America. TBT leads a condition termed ‘imposex’ where female snails are ‘masculinized’ and grow penises. Since fewer fertile females are then available for mating, the population begins to decline, which disturbs the balance of the ecosystem.
Vertebrates such as fish and mammals can become affected by TBT through contact with waters contaminated with TBT and by eating already poisoned seafood. The Japanese rice fish (Oryzias latipes), has been used as a model to test the effects of TBT at different developmental stages of the embryo. Scientists found that as TBT concentration increased the developmental rate decreased and that tail abnormalities occurred as a result. Studies have shown that TBT is harmful to the immune system. Research also shows that TBT reduces resistance to infection in fish which live on the seabed and experience high levels of TBT. These areas tend to have silty sediment like harbours and estuaries (like Hong Kong). Mammals, exposed to TBT through their diet, also suffer. TBT can lead to immunosuppression in sea-otters and dolphins. High levels of TBT were found in the livers of sea otters (Enhydra lutris) and stranded bottlenose dolphins. TBT has also been blamed by hearing experts for causing hearing loss in mammalian top predators such as whales. Because hearing is important for mating and predation in these animals, long-term consequences could be drastic.
How TBT can move up the food chain was shown by one study that found most samples of skipjack tuna tested positive for TBT. Tuna from waters around developing Asian nations had particularly high levels of TBT most likely because the regulation of TBT is not as well enforced in Asia as it is in Europe or the US.
In addition TBT last for a long time in the marine environment. Its half-life in the marine environment is around 25 years. TBT sticks to seabed sediments. But that process is reversible and depends on the pH of the seawater. Studies have shown that 95% of TBT can be released from the sediments back into the aquatic environment. This release makes it difficult to quantify the amount of TBT in an environment, since its concentration in the water is not representative of its availability.
TBT Pollution in Hong Kong
In 1995 a study showed that 3 of the 4 species examined had sign of distorted sex organ development (imposex) and the authors inferred TBT as the cause. Another study in 2000 of 24 species found 5 species with imposex. Again the author inferred TBT as cause. In 2001 a study found the concentration required to cause imposex for one local species was as low as 0.000001 grams per liter.
In the 2004-2012 monitoring, TBT was generally not detected in marine water, river water, sewage effluent or storm water runoff samples by the Environmental Protection Department (EPD). According to the EPD the levels of TBT in Hong Kong marine sediments mostly met Australia‘s sediment quality guideline for the protection of benthic organisms and were generally within the range (falling on the low-side) reported in other Asian countries, such as Japan, Vietnam and Malaysia. The levels of TBT in the biota species were low and largely comparable with the levels for biota in the Pearl River Estuary area.
The Actions of the Hong Kong Government
The production, import and export of TBT paints was already banned in HK. In 1990, the Marine Environment Protection Committee recommended that the Government eliminate the use of TBT-containing antifouling paints on smaller vessels. This was intended to be a temporary restriction until the International Maritime Organization could implement a complete ban of TBT anti-fouling agents for ships, which it did in 2001. The use of TBT in antifouling paint was banned (deregistered) in Hong Kong in 1992. But this new HK regulation seeks to now fully implement the International Convention on the Control of Harmful Anti-Fouling Systems on Ships from 2001 which includes certification requirement for large ships in Hong Kong waters and also extends to Hong Kong registered ships anywhere in the world.
The Convention on the Control of Harmful Anti-Fouling Systems on Ships came about in 2001. Mainland China implemented this Convention in 2011, but Hong Kong (as a major port city) is only now discussing this.
Despite the international bans, TBT will most likely be present in the water column and sediment for up to twenty years because of its long half-life.
Violations of the Ban
Even though its banned by some international agencies, TBT anti-fouling paints are still being used in some countries with poor regulation enforcement, such as countries in the Caribbean.
Note: the new subsidiary legislation (title: Merchant Shipping (Prevention and Control of Pollution) Ordinance (Cap. 413) Merchant Shipping (Control of Harmful Anti-fouling Systems on Ships) Regulation) was published in the Gazette on the 20th of March 2015, introduced into the Legislative Council on 25 March 2015. It was refered for discussion to the subcommittee on Merchant Shipping on the 10th of April 2015. In their report published on the 6th of May 2015 the subcommittee supported the subsidiary legislation. Having cleared the first hurdle.