Tributyltin: case study of a chronic contaminant in the coastal environment, Ocean Coast Manage 40: 23-36

As early as 1975, significant and repeated disturbances were observed to occur in the Crassostrea gigas oyster farms of the Arcachon Bay along the French Atlantic Coastline. TBT contamination of the local breeding waters was found to be responsible for failure to reproduce and for anomalies occurring in the shell calcification of adult oysters leading to stunted growth. On 17 January 1982, the French Ministry of the Environment issued a 3 month ban on the sale of marine anti-fouling paints with an organotin compound content exceeding 3%.

The Ministerial ban was subsequently renewed and reinforced and ultimately converted into an enforcement decree transcribing an European Union directive into French law, in October 1992. The ban was the first official action in response to a growing awareness to the TBT-related pollution of some coastal areas and to its unacceptable impact on shellfish farming.

These measures were adopted as soon as the first scientific evidence of a causal relationship was established between tributyltin and oyster shell anomalies. Since then numerous research studies have been conducted on the geochemical behavior of tributyltin, its ecotoxicity and on TBT-related risks presented by antifouling paints. The knowledge gained on this topic since 1982 reveals in particular that:

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TBT is extremely toxic to aquatic organisms in general and to molluscs in particular for which the NOELs are below 1 ng l-1(imposex, calcification anomalies),

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Contamination levels can reach very high values in port areas, and even exceed no effect levels beyond which mollusc reproduction and growth are affected, in estuaries or semi-enclosed areas,

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Contamination of breeding waters has a significant economic impact, jeopardizing the sustainable development of some highly exposed marine activities,

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The ban on TBT use in antifouling paints for crafts under 25 m represents an efficient way of reducing TBT inputs in coastal areas and restoring proper water quality,

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The regulations adopted by many countries to ban or restrict TBT use on ships sailing along the coastline, have prompted manufacturers to develop less toxic paints.

Fifteen years after TBT was first implicated as a major cause of coastal contamination, the issue no longer lies in finding out under which conditions TBT could still be used in antifouling paints, but rather in developing environmentally-harmless formulations. While the ban on TBT-based paints may be justified due to their harmful impact on coastal ecosystems, substitutes based on the release of biocides (copper oxide, pesticides …) also give rise to major concerns. Prevention of marine biofouling is not motivated merely by esthetics: it responds to economic needs and to navigation safety requirements. Protection of the ships while preserving the coastal ecosystems remains a major challenge for future research.