Hydrobiologia 378: 215–225, 1998. R. M. O’Riordan, G. M. Burnell, M. S. Davies & N. F. Ramsay (eds), Aspects of Littorinid Biology. © 1998 Kluwer Academic Publishers. Printed in Belgium. 215 Toxico-kinetic and -dynamic aspects of TBT-induced imposex in Hydrobia ulvae compared with intersex in Littorina littorea (Gastropoda, Prosobranchia) U. Schulte-Oehlmann 1 , J. Oehlmann 1 , B. Bauer 2 , P. Fioroni 2 & U.-S. Leffler 1 1 Internationales Hochschulinstitut Zittau, Lehrstuhl für Umweltverfahrenstechnik, Markt 23, D-02763 Zittau, Germany 2 Universität Münster, Institut für Spezielle Zoologie und Vergleichende Embryologie, Hüfferstr. 1, D-48149 Münster, Germany Key words: Hydrobia ulvae, Littorina littorea, imposex, intersex, reproductive failure, TBT biomonitoring Abstract A short description of the imposex condition in Hydrobia ulvae is presented. In this species four different imposex stages with two types of development were identified. In laboratory experiments the mud snail accumulates TBT in a time and concentration-dependent manner. Increasing biological indices e.g. VDSI (vas deferens sequence index), female penis length (FPL) and the imposex incidence are significantly correlated with increasing TBT body burden. The percentage of sterile females depends on the TBT contamination of sediments. An interspecific comparison of the mud snail H. ulvae and the periwinkle Littorina littorea elucidates that the mud snail is the more sensitive species at lower environmental TBT concentrations. Introduction The colonisation of underwater surfaces (fouling) by epizoa (e.g. Phycophyta, Anthozoa, Hydroidea, Bi- valvia, Bryozoa, Cirripedia, Ascidiaceae) leads to an increase in frictional resistance of merchant ships and other boats. Consequently this results in a steep rise in fuel consumption. Antifouling paints or biocides were developed to prevent organisms from settlement. Their mode of operation is largely based on the continuous emission of extremely toxic substances e.g. copper, tributyltin (TBT) and further organic compounds used as cotoxicants. TBT compounds belong to the most toxic xenobiotics ever produced and released into the environment (Müller et al., 1989; Stewart et al., 1992). Their use is not restricted to the marine an- tifouling sector; organotins are furthermore applied in the preservation and conservation of outdoor facil- ities. The biocide is added to a variety of materials (e.g. textiles, dispersion paints, PVC etc.). Therefore leaching is also responsible for an increasing TBT contamination of freshwater resources (Kalbfus et al., 1991; Schebek et al., 1991; Oehlmann et al., 1996c; Schulte-Oehlmann et al., 1996b). TBT is known to produce a variety of malformations in aquatic ani- mals. One of them is termed imposex (occurrence of male parts in addition to the female genital sys- tem in dioecious prosobranchs), another one intersex (disturbance of the congruity between gonad and gen- ital tract in the periwinkle Littorina littorea). Both phenomena describe gradual morphological reactions which correlate with an increasing TBT exposure and originate from the androgenic activity of the bio- cide (Oehlmann & Bettin, 1996). Until now imposex and intersex of prosobranch species are the only sub- stance specific effect-monitoring tools known to assess the degree of TBT pollution of the aquatic environ- ment. Both phenomena have already been used in several TBT surveys in different countries (e.g. Ger- many, Ireland, Great Britain, France and The Nether- lands) to determine the actual TBT contamination of coastal ecosystems (Bryan et al., 1986; Gibbs et al.,