Recently, prosobranch snails have been recommended as promising candidates for test organisms for the assessment of endocrine active chemicals. Three prosobranch snail species, the freshwater mudsnail Potamopyrgus antipodarum, the freshwater ramshorn snail Marisa cornuarietis, and the marine netted whelk Nassarius reticulatus are portrayed and their respective biotests are presented together with results of laboratory experiments and biological effect monitoring surveys in the field. All characterized species are highly sensitive toward xeno-androgens [triphenyltin (TPT), tributyltin (TBT), methyltestosterone (MT) and fenarimol (FEN)], and xeno-estrogens [bisphenol A (BPA), octylphenol (OP), ethinylestradiol], and show effects at environmentally relevant, rather low concentrations in laboratory experiments. For exposure to the xeno-androgen TPT, EC(10) values range between 15.9 and 29.0 ng as Sn/L (sediment 0.03 mug as Sn/kg), for TBT, EC(10) values are found between 3.42 and 37.8 ng as Sn/L (sediment 2.98 microg as Sn/kg) and effect concentrations for FEN are calculated as 18.6 ng/L (EC(10)) and 0.19 microg/kg (EC(50) sediment; EC(10) not calculable). Exposure to xeno-estrogens yielded EC(10 )values of 13.9 ng/L (0.19 microg/kg) for BPA, a NOEC of <1 microg/L (EC(10) of 0.004 microg/kg) for OP and a NOEC of 1 ng/l (EC(10) sediment of 2.2 microg/kg) for ethinylestradiol. Responses to androgens comprised the development of imposex and the reduction of fertility or embryo production, effects of estrogens included the stimulation of egg production and embryo production, and the increased weight of glands. Also, biological effect monitoring studies with P. antipodarum and N. reticulatus in several rivers or estuarine areas revealed the capacity of the biotests to detect an androgenic or estrogenic potential of sediment samples. A comparison of the three test species with regard to sensitivity and practical aspects in routine application favors the freshwater mudsnail P. antipodarum for a standardized procedure, and this reproduction test will be introduced into the OECD guideline program for standardization in the near future.

: The ramshorn snail Marisa cornuarietis (L., 1767) exhibits imposex (occurrence of male parts in addition to the female genital duct) under the influence of TBT (tributyltin) in laboratory experiments and accumulates this biocide in a time-and concentration-dependent manner. A comparison of BCF (bioconcentration factors) demonstrates that this limnic species accumulates more TBT than marine species. Evidence is given that TBT causes hormonal disorders which are responsible for imposex development. The testosterone/oestradiol quotient reflects the imposex development which can be described by a classification scheme differentiating four stages in Marisa cornuarietis. In the background of the constantly increasing organotin concentration in the limnic environment Marisa cornuarietis could be a well-suited bioindicator for TBT pollution. No other limnic species with a lower threshold concentration for measurable TBT effects is reported within the literature.

Tributyltin (TBT) compounds, some of the most toxic xenobiotics, produce a variety of pathological 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 (Mollusca: Gastropoda). Examples are the imposex phenomenon in marine and freshwater species, the intersex reaction in littorinids and the reduction of female sexual 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 biosynthesis 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.

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