Any object submersed in marine waters for a period of time provides a potential habitat for marine organisms. Many of these organisms attach themselves in a manner which creates maximum turbulence to their surrounding water to maximise feeding opportunities. Unfortunately, when the host body is a vessel, this build up (called hull fouling) causes significant drag and subsequent increased operating costs. Vessel bottoms not protected by anti-fouling systems may gather 150kg of fouling per square metre in less than 6 months at sea. On a large oil tanker with 40,000 square metres of underwater hull surface, this can add up to 6,000 tonnes of fouling. Just a small amount of fouling can lead to increased fuel consumption of up to 40 per cent and increased emissions to air. Effective anti-fouling systems also reduce the risk of introduction of marine pests from infected areas, as they are less likely to be transported on ships hulls. The use of anti-fouling hull coatings has significantly reduced the operating costs for vessels through savings in fuel, less dry docking and reduced maintenance costs.

The concern, however, is in respect to Tributyltin (TBT), the principal toxic ingredient of anti-fouling paints since the mid-1960s. TBT has been found to produce deformities in various shellfish such as oysters and sea snails. TBT anti-fouling paints work by releasing, in a controlled manner, small quantities of TBT, which is toxic to fouling organisms. Whilst TBT dissolved in the water column breaks down into much less harmful products within days, its accumulation in bottom sediments particularly in heavily used areas such as ports, marinas and ship maintenance areas, requires longer periods for breakdown to occur.

International Aspects

In 1990, the Marine Environment Protection Committee of the International Maritime Organisation (IMO) adopted a resolution regarding measures to control the potential adverse impacts associated with the use of TBT compounds in anti-fouling paints. In light of this, in the 1990s most countries around the world introduced a ban on the use of TBT paints for small craft (less than 25 metres) and placed controls on the leaching rate of TBT from the paints. Small craft were targeted first, due to fact that they are usually moored for long periods of time, in large numbers, in calm protected areas that have low water circulation rates. Many countries (including Australia) have also adopted various controls on the repair and dry-docking of TBT coated ships to eliminate contamination associated with discharge from docks after hull cleaning and blasting operations.

In October 2001 the IMO resolved to introduce a global ban on the use of TBT based anti-foulant systems. The objective is to ban the application of TBT paints on ships by 1 January 2003 and a complete prohibition on the presence of TBT paints on ships by 1 January 2008. The 5-year gap allows for ships legally coated with TBT before 1 January 2003 to operate until their next dry-docking for maintenance.

In the past, the call for an outright ban on the use of TBT paints had been rejected for fear of introduction of alternatives of unknown, and possibly more severe, impact. Internationally, research has continued on the development of alternative anti-fouling systems, and whilst some have been developed, none is as effective, durable and lasting as the TBT paints. The issue of suitable alternatives and other potential environmental impacts will need to be considered as the international community moves towards a global ban.

Australian Aspects

Most Australian States have adopted legislation that:

prohibits the use of TBT paints on vessels less than 25 metres in length
limits the leaching rate of TBT paints used on vessels of greater than 25 metres to 4-5 micrograms per square centimetre per day
prohibits the in-water cleaning of hulls (in order to prevent debris and TBT paint flakes accumulating on the seabed)
prohibits the in-water cleaning of hulls (in order to prevent debris and TBT paint flakes accumulating on the seabed)

The Australian and New Zealand Environment and Conservation Council (ANZECC) has published a Code of Practice for Antifouling and In-water Hull Cleaning and Maintenance. This has provided guidance to industry and regulators in applying a consistent approach to the management of these activities.

Western Australian Aspects

Regulations which reflect the above controls on TBT paints have been introduced in WA by the Department of Environmental Protection (DEP). The DEP conducted a formal investigation into the impact of TBT paints on the marine environment, releasing a report titled The Environmental Impact of Organotin Anti-fouling Paints in Western Australia which led to the introduction of legislation in 1991. The DEP also licenses ship maintenance facilities to ensure any toxic residues and discharges from hull cleaning activities are collected and disposed at approved landfill facilities.

Fremantle Port/Harbour Aspects

In 1998 Fremantle Ports introduced a ban on in-water hull cleaning in port waters, consistent with the ANZECC Code of Practice. This complemented the regulatory controls introduced by the DEP and was further enhanced by the closure of the slipways located in Fremantle Inner Harbour.

A recent comprehensive sediment survey conducted by DA Lord & Associates on behalf of the Kwinana Industries determined that 28 of the 31 sites sampled had TBT levels less than the suggested ANZECC screening guideline level of 5 g TBT kg 1. This means there were only 3 locations, typically those associated with extensive hull cleaning operations in the past, with elevated TBT levels at which further investigation for potential environmental impacts should be undertaken. All measured TBT levels were significantly lower than those reported in the Department of Environmental Protections 1996 report Southern Metropolitan Coastal Waters Study, indicating that the controls on TBT use and ship maintenance activities have been very effective in reducing TBT entering the marine environment and that degradation is occurring at a faster rate than accumulation.

Additional work conducted by Fremantle Ports also shows that the elevated levels of TBT in the area of the old slipways in the Inner Harbour have been declining steadily since the slipways were taken out of service.

It is expected that even with considerably increased shipping activities, TBT levels in local sediments will reduce to levels that will not impact on the marine environment due to the fact that:

international and national initiatives to reduce and replace TBT paints are in place
tributyltin degrades naturally over time
controls are now in place to manage the accumulation that has occurred, predominantly in hull cleaning areas

Monitoring within port waters will continue to occur as part of Fremantle Ports Marine Quality Monitoring Program and the Kwinana Industries Council water quality monitoring programs to confirm the downward trend in TBT levels.

Summary

The potential adverse environmental impacts of TBT- based antifouling systems are understood at a local, national and international level. Considerable action has been undertaken to reduce the impact through complementary international guidelines, regulatory controls at a State level and Fremantle Ports restrictions on activities considered to present the greatest threats: for example, use on small craft, hull cleaning and dry dock maintenance facilities. A comprehensive 1999 sediment contamination survey conducted in waters surrounding Fremantle Port has confirmed that TBT levels have declined dramatically since the previous 1996 study and that there are only a few isolated hot spots of concern.

The International Maritime Organisation has resolved to introduce a global ban on the application of TBT in antifouling systems to ships from 1 January 2003 and a complete prohibition on the presence of TBT antifouling systems on ships from 1 January 2008. This, combined with local controls, is expected to result in significant reductions in TBT in the marine environment to levels that will not adversely impact on any aspect of the marine environment.

Suggested References

http://www.imo.org
http://www.ortepa.org
http://www.ea.gov.au/coasts/pollution/antifouling
Australian and New Zealand Environment and Conservation Council (1997) Code of Practice for Antifouling and In-water Hull Cleaning and Maintenance. ISBN: 072 428 0731.
Lord D A and Associates (2001). State of Cockburn Sound. Cockburn Sound Pressure-State-Response.
Environmental Protection Authority (1996). Southern Metropolitan Coastal Waters Study (1991-1994). Final Report. (Department of Environmental Protection, Perth, Western Australia). Report 17.
Environmental Protection Authority of Western Australia The Environmental Impact of Organotin Antifouling Paints in Western Australia. ISBN 0 7309 3520 5

Fremantle Ports contact details:

Tel: (08) 9430 3555 Fax: (08) 9336 1391
Email: mail@fremantleports.com.au
Internet: http://www.fremantleports.com.au

MAY 2002