Interim report of the HELCOM CORESET project

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3.8 Tributyltin (TBT) and the imposex index
General information
Authors: Rita Poikane, Jakob Strand and Martin M. Larsen
Acknowledged persons:
Anders Bignert, Elin Boalt, Anna Brzozowska, Galina Garnaga,
Michael Haarich, Jenny Hedman, Ulrike Kamman, Thomas
Lang, Kari Lehtonen, Jaakko Mannio, Rolf Schneider, Doris
Schiedek, Joanna Szlinder-Richert, Tamara Zalewska
General properties
Tributyltin compounds (TBT-ion CAS No. 688-73-3 (36643-28-4)) belong to organometallic compound
(OTC) class. Usually triorgancompounds used as biocide – antifoulant paints, agricultural pesticides, molluscicides
and wood preservative. TBT compounds are hydrophobic and associate strongly to particles in
natural waters and ultimately are deposited in the sediments. Adsorption to organic rich particles (soils and
sediments) is stronger than to particles (soils and sediments) of mineral origin. Degradation (photodegradation
or biodegradation) of TBTs in environment occurs due to dealkylation and depends on aerobic condition.
Degradation of TBT under anaerobic condition may last long time. Half-life of TBTs in natural waters
may range from a few days to several weeks but in soils and sediments one to few years. TBTs accumulate
in individual organisms – often stronger in benthic organisms than in fi sh. TBT and triphenyltin accumulate
in the food web, but a large variance in accumulation potential has been found between species, even
within the same trophic level. This is probably due to different abilities to degradate TBT or triphenyltins
between the species.
Main impacts on the environment and human health
TBT compounds are very toxic to aquatic organisms especially to benthic organisms. As a consequence of
toxic effects is shell deformation, endocrine disruption and impaired larval recruitment as well as immunosuppression.
TBTs cause endocrine disruption and different types of malformation of the genital system for
certain marine and freshwater bivalve and gastropods species at very low concentrations. The process is
known as „imposex“ and „intersex“. For human health high levels of TBT are potential risk to cause endocrine
disruption. Several OTCs have negative toxic effects: immumosuppresive, neurotoxicity, hepatoxicity,
renal and dermal toxicity, teratogenic and carcinogenic effects.
The ecological relevance of imposex and intersex development in marine snails is high because of the links
to reproductive disorders. In severe stages, reproductive failure in female snails occurs as they are getting
sterile. For instance, sterile female of the red whelk Neptunea antiqua has been found in the Inner Danish
waters (Strand 2009).
Effects of sterile females on population structures have been shown in other studies of TBT contaminated
areas.
The HELCOM thematic assessment of hazardous substances (HELCOM 2010) showed that the thresholds
for fi sh (15 μg kg -1 ww), mussels (30 μg kg -1 dw) and sediment (2 μg kg -1 dw) were exceeded all over the
Baltic Sea.
Status of a compound on international priority lists and other policy relevance
The recent environmental issues surrounding tributyltin have been increasing environmental pressures on
all butyltin compounds and other OTCs in general.
TBT is a substance, which is identifi ed on the priority list of the HELCOM Baltic Sea Action Plan.