Fresenius J Anal Chem (1996) 354: 540 — 545  Springer-Verlag 1996 LECTURE J. Oehlmann · E. Stroben · U. Schulte-Oehlmann B. Bauer · P. Fioroni · B. Markert Tributyltin biomonitoring using prosobranchs as sentinel organisms Received: 16 June 1995/Accepted: 5 August 1995 Abstract Tributyltin (TBT) compounds, some of the most toxic xenobiotics, produce a variety of pathologi- cal reactions in animals. A reliable biomonitoring method to assess the degree of environmental TBT pollution has been described based on investigations of virilization phenomena in prosobranch snails (Mol- lusca: Gastropoda). Examples are the imposex phe- nomenon in marine and freshwater species, the intersex reaction in littorinids and the reduction of female sex- ual glands and offspring numbers in further species resulting mainly in a sterilization of females. The degree of imposex or intersex in populations is determined by different biomonitoring indices which allow to assess the TBT pollution of the environment at low costs with high precision. The effectiveness of TBT legislations is analysed by extensive surveys in France and Ireland indicating that there is still a continuing threat to sensitive marine organisms. TBT disturbs the biosynth- esis of steroid hormones on the level of estrogen biosynthesis. The observed virilization phenomena seem due to an inhibition of the cytochrome P-450 dependent aromatase by this organotin compound. Introduction Tributyltin (TBT) compounds used as biocides in anti- fouling paints and in various other formulations are known to produce a variety of malformations in aqua- tic animals with molluscs as one of the most TBT- sensitive groups of invertebrates (for review [1, 2]). As J. Oehlmann ( ) · B. Markert International Graduate School Zittau, Chair of Environmental High Technology, Markt 23, D-02763 Zittau, Germany E. Stroben · U. Schulte-Oehlmann · B. Bauer · P. Fioroni Institute for Special Zoology and Comparative Embryology, Uni- versity of Mu  nster, Hu  fferstrasse 1, D-48149 Mu  nster, Germany the impact of TBT on nontarget organisms became apparent in the early 1980s, France was the first Euro- pean country to draw up regulations to control TBT emission and banned the use of TBT antifoulings on small boats (length (25 m) in 1982. But up to now the TBT pollution of coastal waters in many regions is still high and further controls are necessary [3, 4]. Because the analysis of organotin compounds in environmental samples is rather difficult, time consuming and expen- sive, a biomonitoring system based on easily detectable morphological parameters would give useful results. The imposex phenomenon of prosobranchs, i.e. the formation of a penis and/or vas deferens on females of gonochoristic species, has been successfully used as a biomonitoring system to assess TBT pollution in the marine environment [2, 3, 5—8]. But the established European imposex species for TBT biomonitoring (e.g. Nucella lapillus, Hinia reticulata, Ocenebra erinacea) are absent on the German North Sea coast or can only be found in restricted areas. The periwinkle ¸ittorina lit- torea is the only prosobranch which is very common and can be sampled in sufficient numbers. In this spe- cies TBT induces intersex, i.e. pathological alterations in the female genital system. The potential of the inter- sex phenomenon in ¸. littorea for TBT biomonitoring is evaluated. In contrast to the situation in the marine environment where a sufficient number of biomonitor- ing species for the quantification of TBT contamination is available there is a lack of biomonitoring species in freshwater environments in spite of the fact that here increasing organotin pollution is a cause for concern [9, 10]. Imposex development in the ramshorn snail Marisa cornuarietis and reduction of embryo numbers in the brood pouch of Potamopyrgus antipodarum are described as first approaches for a TBT biomonitoring in limnic ecosystems. Although imposex has been known since years the detailed biochemical mechanisms of its induction have remained obscure. The clearing up of these mechanisms can help to answer the question whether or not the