Prosobranch snails represent almost 50% of all recent molluscs, are ubiquitously distributed, play important roles in various ecosystems and exhibit a variety of reproductive modes and life-cycle-strategies. Many of them attain life spans of several years, which in combination with their limited ability to metabolize organic chemicals, may contribute to the fact that prosobranchs constitute one of the most endangered taxonomic groups in aquatic ecosystems. Although it is not yet known to what extent endocrine disrupting chemicals (EDCs) contribute to this situation, the case of tributyltin (TBT) and its population-level impact on prosobranchs demonstrates the general susceptibility of these invertebrates. The existing evidence for comparable population-level effects in prosobranch snails by other androgens, antiandrogens, and estrogens is critically reviewed. The example of TBT demonstrates the difficulty to prove an endocrine mode of action for a given chemical. Although it is generally accepted that TBT causes imposex and intersex in prosobranch snails as a result of endocrine disruption, the detailed biochemical mechanism is still a matter of debate. The strengths and weaknesses of the five competing hypotheses are discussed, together with previously unpublished data. Finally, the ecological relevance of EDC effects on the population and community level and the application of prosobranchs for the assessment of EDCs are addressed.

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The effects of two suspected endocrine-disrupting chemicals, the xeno-androgens triphenyltin (TPT) and tributyltin (TBT), were investigated in a new whole-sediment biotest with the freshwater mudsnail Potamopyrgus antipodarum (Gastropoda, Prosobranchia). Artificial sediments were spiked with seven concentrations, ranging from 10 to 500 microg nominal TPT-Sn/kg dry weight and TBT-Sn/kg dry weight, respectively. We analyzed the responses of the test species after two, four, and eight weeks exposure. For both compounds, P. antipodarum exhibited a sharp decline in the number of embryos sheltered in its brood pouch in a time- and concentration-dependent manner in comparison to the control sediment. The number of new, still unshelled embryos turned out to be the most sensitive parameter. The lowest-observed-effect concentration (LOEC) was equivalent to the lowest administered concentration (10 microg/kg of each test compound) for most parameters and thus no no-observed-effect concentration (NOEC) could be established. The calculation of effect concentrations (EC10) resulted in even lower values for both substances (EC10 after eight weeks for unshelled embryos: 0.03 microg TPT-Sn/kg, EC10 after four weeks for unshelled embryos: 0.98 microg TBT-Sn/kg). Our results indicate that P. antipodarum is highly sensitive to both endocrine disruptors TPT and TBT at environmentally relevant concentrations.

The effects of suspected endocrine disrupting chemicals on freshwater and marine prosobranch species were analysed in laboratory experiments. In this first publication, the responses of the freshwater snail Marisa cornuarietis and of the marine prosobranch Nucella lapillus to the xeno-estrogenic model compounds bisphenol A (BPA) and octylphenol (OP) are presented at nominal concentration ranges between 1 and 100 micrograms/L. Marisa was exposed during 5 months using adult specimens and in a complete life-cycle test for 12 months. In both experiments, the xeno-estrogens induced a complex syndrome of alterations in female Marisa referred to as "superfemales" at the lowest concentrations. Affected specimens were characterised by the formation of additional female organs, an enlargement of the accessory pallial sex glands, gross malformations of the pallial oviduct section resulting in an increased female mortality, and a massive stimulation of oocyte and spawning mass production. The effects of BPA and OP were comparable at the same nominal concentrations. An exposure to OP resulted in inverted U-type concentration response relationships for egg and spawning mass production. Adult Nucella from the field were tested for three months in the laboratory. As in Marisa, superfemales with enlarged accessory pallial sex glands and an enhancement of oocyte production were observed. No oviduct malformations were found probably due to species differences in the gross anatomical structure of the pallial oviduct. A lower percentage of exposed specimens had ripe sperm stored in their vesicula seminalis and additionally male Nucella exhibited a reduced length of penis and prostate gland when compared to the control. Because statistically significant effects were observed at the lowest nominal test concentrations (1 microgram BPA or OP/L), it can be assumed that even lower concentrations may have a negative impact on the snails. The results show that prosobranchs are sensitive to endocrine disruption at environmentally relevant concentrations and that especially M. cornuarietis is a promising candidate for a future organismic invertebrate model to identify endocrine-mimetic test compounds.