Ecotoxicology of Organotin compounds
Organotin and especially butyltin compounds are used for a variety of applications, e.g. as biocides, stabilizers, catalysts and intermediates in chemical syntheses. Tributyltin (TBT) compounds exhibit the greatest toxicity of all organotins and have even been characterized as one of the most toxic groups of xenobiotics ever produced and deliberately introduced into the environment. TBT is not only used as an active biocidal compound in antifouling paints, which are designed to prevent marine and freshwater biota from settlement on ship hulls, harbour and offshore installations, but also as a biocide in wood preservatives, textiles, dispersion paints and agricultural pesticides. Additionally, it occurs as a by-product of mono- (MBT) and dibutyltin (DBT) compounds, which are used as UV stabilizer in many plastics and for other applications. Triphenyltin (TPT) compounds are also used as the active biocide in antifouling paints outside Europe and furthermore as an agricultural fungicide since the early 1960s to combat a range of fungal diseases in various crops, particularly potato blight, leaf spot and powdery mildew on sugar beet, peanuts and celery, other fungi on hop, brown rust on beans, grey moulds on onions, rice blast and coffee leaf rust. Although the use of TBT and TPT was regulated in many countries world-wide from restrictions for certain applications to a total ban, these compounds are still present in the environment.
In the early 1970s the impact of TBT on nontarget organisms became apparent. Among the broad variety of malformations caused by TBT in aquatic animals, molluscs have been found to be an extremely sensitive group of invertebrates and no other pathological condition produced by TBT at relative low concentrations rivals that of the imposex phenomenon in prosobranch gastropods speaking in terms of sensitivity. TBT induces imposex in marine prosobranchs at concentrations as low as 0,5 ng TBT-Sn/L.
Imposex or pseudohermaphroditism describes a virilisation phenomenon on females of gonochoristic prosobranch species. Thereby, females develop male sex organs (e.g. penis and/or vas deferens) additionally to the complete female genital tract. Since 1993, for the littorinid snail Littorina littorea a second virilisation phenomenon, termed intersex, is known. In female specimens affected by intersex the pallial oviduct is transformed of towards a male morphology with a final supplanting of female organs by the corresponding male formations. Imposex and intersex are morphological alterations caused by a chronic exposure to ultra-trace concentrations of TBT. The gradual virilisation can be described and categorised by assessment schemes with 6 stages for imposex and 4 stages for intersex development. In the final stages, imposex- and intersex-affected females are functionally sterilised.
A biological effect monitoring offers the possibility to determine the degree of contamination with organotin compounds in the aquatic environment and especially in coastal waters without using any expensive analytical methods. Furthermore, the biological effect monitoring allows an assessment of the existing TBT pollution on the basis of biological effects. Such results are normally more relevant for the ecosystem than pure analytical data.
Our Department at the Johann Wolfgang Goethe University Frankfurt as well as the Marine Laboratory in Aberdeen are reference institutes for the biological effect monitoring in coastal waters of the Northeastern Atlantic within the scope of the Joint Assessment and Monitoring Programme (JAMP) initiated by the Oslo and Paris Commission (OSPAR) and the International Council for the Exploration of the Sea (ICES). The laboratories are responsible for quality assurance and quality control of the analyses in the participating national labs as well as for the regular training of the scientists and technical staff within the programme. In addition to extensive experiences in training of other laboratories, we can offer expertise for the conduct of biological effect monitoring with more than 20 marine and freshwater snails species as well as in the field of chemical organotin analyses in water samples, sediments and biota. Recently, a specific biotest on TBT-contamination in marine, brackish and freshwater sediments was developed. In cooperation with the lab LimnoMar in Hamburg this test is used for an assessment of TBT-contamination in sediments.