QUASIMEME laboratory performance study of the biological effects of tributyltin (imposes and intersex) on two marine gastropod molluscs

The disruption of the endocrine systems of gastropod molluscs and consequen tial physiological changes (imposex and intersex) are used as biomarkers fo r environmental contamination by tributyltin compounds. The first internati onal laboratory performance study on the determination of imposer and inter sex in neogastropod molluscs, Nucella lapillus and Littorina littorea has b een undertaken by the QUASIMEME (Quality Assurance of Information for Marin e Environmental Monitoring in Europe) project. Samples of live gastropods w ere distributed and participants were asked to record shell height and sex, together with penis length and vas deferens sequence stage (VDS) in Nucell a or the intersex stage (IS) and prostate length in Littorina. Calculations were made of vas deferens sequence index (VDSI) and the relative penis siz e index (RPSI) in Nucella and of intersex stage index (ISI) and the average female prostate length (FPrL) in Littorina. Thirteen (87%) of the 15 parti cipating laboratories returned data. The remaining two laboratories asked t o participate in later exercises. For Nucella, seven laboratories reported sex ratios significantly different from the reference laboratory data. Diff erences in penis length measurements between laboratories were largely rand om, although there were indications of systematic errors affecting the data from three laboratories. Seven laboratories reported satisfactory data (Z- score \Z\ < 2)for VDSI. The inclusion of a high proportion of sub-adults in the Nucella samples may have made separation of the sexes more difficult t han in mature adults. The sub-adults will have had smaller pene than mature adults in the same population, and therefore any errors (random or systema tic) in the measurement of penis length or observation of reproductive orga ns would have a potentially greater impact on the final reported values of the summary imposer indices. The Littorina sample did not show a high degre e of intersex (ISI = 0.41). The laboratories could determine the sex of Lit torina reliably and only one laboratory reported data significantly differe nt from the reference laboratory. All except two laboratories reported sati sfactory data for ISI.