Toxic Ship Paint Found in Antarctic Sediment

TOWNSVILLE, Queensland, Australia, May 24, 2004 (ENS) - Australian marine scientists have found the toxic substance tributyltin in Antarctic marine sediment, the first time the anti-fouling chemical has been detected in a polar region. Tributyltin is added to ship paint to repel marine organisms, and the researchers say paint chipping from icebreakers as they ram through thick ice is the most probable cause of the contamination.

Researchers with the Australian Institute of Marine Science (AIMS) warn that high concentrations of tributyltin (TBT) in Antarctica that could harm sensitive polar marine habitats.

The researchers, led by Dr. Nicole Webster of AIMS and New Zealand's University of Canterbury, were investigating pollution in sediment and the effects on microbial communities when they noticed parallels between ship groundings on the Great Barrier Reef and those in Antarctica.

"We surveyed eight sites in McMurdo Sound, one of several Antarctic regions frequented by ice-breakers servicing McMurdo Station and Scott Base, which are major U.S. and New Zealand research stations. TBT was detected in six of the eight sampling sites," said Webster.

AIMS toxicologist Dr. Andrew Negri said, "In some areas, the concentration of TBT was extremely high by world standards and is only exceeded in very busy harbors and at ship grounding sites."

Sediments from two areas at Cape Evans and Turtle Rock that were formerly considered pristine, both contained trace levels of TBT. The scientists say the chemical possibly was transported from the channel that is carved each year to provide access for supply ships to the research stations.

U.S. Coast Guard icebreaker Polar Sea cuts through the sea ice every summer so supply ships can reach McMurdo Station with enough fuel and food to last through the winter season. (Photo courtesy NASA)

The Convention on the Control of Harmful Anti-fouling Systems would impose a complete prohibition on the presence of organotin compounds which act as biocides in anti-fouling systems on ships by January 1, 2008.

"The use of TBT in antifoulant paint is being phased out but is still commonly used on large vessels including some icebreakers because of its effectiveness in reducing algal and barnacle growth on ships hulls," said Dr. Negri.

As antifoulant paints are designed to reduce the fouling of organisms on the hull of ships, scientists fear the potency of TBT could have be deadly for seafloor communities. The shallow marine environment of Antarctica has a diverse range of organisms but is dominated by sponges, sea squirts, soft corals, anemones, and urchins.

"We know that TBT causes sex changes in molluscs, such as marine snails, and this limits their reproductive capacity. Because they feed within the sediments they're particularly susceptible to the uptake of TBT. We're yet to find out how TBT affects Antarctic marine mammals," Dr. Negri said.

Antifouling paints are used to coat the bottoms of ships to prevent sealife such as algae and molluscs attaching themselves to the hull, slowing down the ship and increasing fuel consumption. In the early days of sailing ships, lime, and later arsenic, was used to coat ships' hulls, until the modern chemicals industry developed effective antifouling paints using metallic compounds.

The compounds slowly "leach" into the sea water, killing barnacles and other marine life that have attached to the ship - but studies have shown that these compounds persist in the water, killing sealife, harming the environment and possibly entering the food chain. One of the most effective antifouling paints, developed in the 1960s, contains the organotin tributyltin (TBT), which has been proven to cause deformations in oysters and sex changes in whelks, the IMO states.

U.S. Coast Guard icebreaker Polar Sea approaches McMurdo research station in Antarctica. (Photo courtesy NASA)

Alternatives to TBT paint include coatings based on copper or silicon, which make the surface of the ship slippery so that sealife will be washed off as the ship moves through water.

Anti-fouling systems such as ultrasonic or electrolytic devices to rid ships of clinging marine organisms are in development.

"Even though TBT may be outlawed within four or five years," said Dr. Negri, "the antifoulants that replace TBT may also affect the marine life. We need to ensure that protocols to reduce the stripping of antifoulant paints from ship's hulls during ice operations are developed and enforced," he said.

Scientists expect the TBT sediment contamination to be similar in many areas of the Antarctic where the icebreakers provide access for supply and tourist ships. It is essential that the monitoring be widened to gauge the full extent of the problem, Dr. Negri said. "The contamination is also likely to be a problem in the Arctic where icebreakers work."

Tributyltin may break down very slowly in cold conditions, the AIMS scientists said, but further investigation is needed to establish the true rate of degradation, a more detailed picture of contamination, and the impact of the toxics on Antarctic marine life is required.