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Dieren en planten

Water en land

Mens en Milieu

Pesticides   Organotin compounds   

Organotin compounds

Organotin compounds are carbon compounds containing the toxic component tin. It is used in anti-fouling paints. In the early 1980s, many abnormalities in benthic (bottom) animals were found in the heavily motored areas of the North Sea. The development of male sexual characteristics in female whelks was particularly apparent. French fishermen found lots of deformed oysters in this same period. Such deformities were also found in yacht harbours, where the link was laid for the first time to tributyltin in anti-fouling paint. Since 2003, the use of tin-holding paints is forbidden worldwide on the hulls of ships. As of 2008, no ships will be allowed to have this kind of paint on the underwater surface of the hull.

  • Amount in harbours
    TBT in the harbour environment, Ecomare

    In 1990, the European Community prohibited the use of tin-holding anti-fouling paint for ships shorter that 25 meters long. The graph shows that the levels of toxic tin compounds in harbour water has declined tremendously since then. However, measurements made in organisms (mussels, shrimp, various species of fish) show that this kind of material remains in the environment for a very long time. In 2003 in the North Sea, the maximum allowable concentration of TBT in the water and bottom was exceeded 10 to 150 times. The paint agent is no longer applied at ship wharves in the Netherlands, as shown from controls in 2004.

  • TBT, presence in the sea environment

    Tributyltin will last for two to five years on the hull of a ship. In this period, TBT slowly leaks out of the paint and into the water. According to the Central Bureau for Statistics, around 85 tons of tributyltin leached into the North Sea in 1985. Its usage has not yet decreased. The largest concentrations are still found in the vicinity of the shipping routes and in the harbours. Leached TBT in water will eventually be found in sludge. In some samples, the concentration of tin compounds in sludge amounts to around 400 times the allowed value.
    When TBT ends up in the water, the material is degraded within several weeks to a less poisonous di- or monobutyltin. Its degradation in the sea bottom is much slower. Depending upon the oxygen level, the degradation or the material can take many months to years.

  • Toxicity

    Environmental toxicologist Wieke Tas received her doctor's degree in December 1993 from the State University of Utrecht in the Netherlands. She did her research in the effects of organotin compounds in fish. In a laboratory, she exposed guppies to organotin compounds. The fish ingested the material quickly, however excreted it slowly, so that it accumulated in their bodies. The fish all died by a concentration one hundred times lower than the deadly concentrations of PCBs. Flounder experiences lower resistance when exposed to TBT. Being a benthic inhabitant, the species is very sensitive to TBT.
    For several years, the notion had been growing by researchers that the toxic agent makes large snails sterile in many parts of the North Sea and was probably leading to the disappearance of the whelk in the Dutch coastal area. In other parts of the world, more and more evidence was evolving that sensitive oysters and snails were receding. With oysters, their shell became thicker when they were exposed to TBT, indicating a disturbance in the animal's calcium production.
    Studies at the Royal Dutch Institute for Sea Research (NIOZ) on Texel confirmed that bodily changes in whelks occurred due to the use of tributyltin. Female whelks obtain a penis-like growth, a phenonmenon known as imposex. It is a direct effect from the use of TBT. Imposex is irreversible, even when the snails have been placed in TBT-free waters.

  • Banned as of 2008

    The International Maritime Organization (IMO) already implemented a ban in 1990 on the use of TBT for ships and yachts smaller than 25 meters. From investigations by the environmental inspection, a number of years after the ban, TBT is indeed rarely applied on pleasure boats. Larger ships were first excluded from this ban because one assumed that the low concentrations of TBT in the open sea were not dangerous.
    Since 2003, TBT is no longer allowed to be applied to any ship and in 2008, no sea-going ships are permitted to have any TBT-holding paint on its hull.