Environ Monit Assess (2011) 177:375–384 DOI 10.1007/s10661-010-1640-z Imposex and butyltin concentrations in Bolinus brandaris (Gastropoda: Muricidae) from the northern Tunisian coast Sami Abidli · Youssef Lahbib · Najoua Trigui El Menif Received: 26 January 2010 / Accepted: 29 July 2010 / Published online: 12 August 2010 © Springer Science+Business Media B.V. 2010 Abstract The imposex incidence and butyltin concentration i.e. tributyltin with its di- and mono- substituted metabolites were investigated in the muricid Bolinus brandaris sampled from two sites on the northern Tunisian coast (the Lagoon of Bizerta and the small Gulf of Tunis). Both popu- lations had imposex, with stages of imposex devel- opment varying between VDS 1 and VDS 4.3. All imposex indices (imposex frequency (I %), female penis length, female vas deferens length, vas def- erens sequence index, relative penis length index, and vas deferens length index) were significantly higher in snails from the Bizerta lagoon. Butyltins were detected in the whole tissues of both sexes from the two sites. TBT levels were higher in gastropods collected from the lagoon of Bizerta (12.65 ± 1.48 ng Sn g −1 dw in female and 15.21 ± 1.13 ng Sn g −1 dw in male) than in individuals from the Gulf of Tunis (10.71 ± 1.26 ng Sn g −1 dw in female and 11.65 ± 1.63 ng Sn g −1 dw in male), corroborating the data of imposex analysis. These S. Abidli · Y. Lahbib · N. Trigui El Menif (B ) Faculty of Sciences of Bizerta, Laboratory of Environment Bio-monitoring, University of 7th November at Carthage, 7021 Zarzouna, Bizerta, Tunisia e-mail: elmunif2004@yahoo.fr results confirmed that B. brandaris could be used as a bioindicator species of butyltin pollution in the studied areas. In addition, this study provided baseline data that could serve for long-term mon- itoring of TBT pollution in Tunisia, since legisla- tion to reduce the use of TBT-based antifouling paints has not been introduced yet. Keywords TBT · Gastropod · Bioindicator · Lagoon of Bizerta · Gulf of Tunis Introduction Organotins, like tributyltin (TBT) and its deriv- atives, have been widely used in a variety of consumer and industrial products including agri- cultural pesticides and in antifouling paints for ship hulls, aquaculture facilities, and other struc- tures exposed to marine waters (Terlizzi et al. 2001). TBT is known to cause genital disorder in female marine prosobranch snails at a concen- tration of just a few nanograms per liter (Gibbs and Bryan 1986; Abidli et al. 2009a). This phe- nomenon was called imposex (Smith 1971) as an abbreviation of imposed sexual organs, because male genital organs, such as penis and vas def- erens, are imposed upon female individuals. This abnormality was first reported by Blaber (1970) in British population of the dogwhelk Nucella