A full life-cycle (240 days) bioassay using the terrestrial snail, Cantareus aspersus, allowing exposure during embryogenesis and/or the growth and reproduction phases, was used to assess the effects of Bypass®, a glyphosate-based herbicide (GlyBH), on a range of endpoints, including parameters under endocrine control. As a positive control, a mixture (R-A) made of diquat (Reglone®) and nonylphenols (NP, Agral®), known for its endocrine disrupting effects in other organisms, was tested. At environmental concentrations, both pesticides (R-A mixture and GlyBH) enhanced growth but reduced reproduction. The R-A mixture acted mainly on the fecundity through a delay in egg-laying of approximately 20 days and a strongly reduced number of clutches. This latter dysfunction may be caused by a permanent eversion of the penis, suggesting a disrupting effect at the neuro-endocrine level, which prevented normal mating. GlyBH acted on fertility, possibly due to a decrease in the fertilization of eggs laid by adults exposed during their embryonic development. These results, associated with the absence of observed effects on gonad histology of GlyBH exposed snails, suggested that the underlying mechanisms are neuro-endocrine.

Imposex is a disorder caused by organotins, mainly tributyltin, which results in the appearance of male sexual characteristics in females of gastropod mollusks. The main objective of this work was to make a critical analysis of the relationship between imposex and butyltin body burdens in Nucella lapillus and Nassarius reticulatus. Specifically, this study evaluates possible additive effects among butyltins, proposes scales of effects based on robust statistical criteria as alternatives to existing ones and defines the body burdens of TBT in N. lapillus and N. reticulatus corresponding to the assessment classes (ACs) of the Vas Deferens Sequence Index (VDSI) established by OSPAR. Data of organotin body burdens and biological effects was retrieved from the ICES Dataset and from scientific literature. All responses, except the percentage of females displaying Imposex (IMPF) in Nucella lapillus, showed a sigmoidal profile regarding to the body burden of mono- (MBT), di- (DBT) and tributyltin and sum of butyltins (SumBTs). TBT and the SumBTs were better indicators of the VDSI or Relative Penis Size Index/Relative Penis Length Index (RPSI/RPLI) responses than MBT or DBT in most cases. From a statistical point of view, RPSI/RPLI and VDSI were better indicators of contamination by TBT than IMPF, although both RPSI and RPLI showed lower sensitivity than VDSI. The model used for describing the joint effect of butyltins provided a statistically significant fitting to the data assuming a null effect for both MBT and DBT for N. lapillus, and a lower toxic contribution of MBT and DBT with respect to TBT for N. reticulatus. RPSI or RPLI values, equivalent to the ACs for VDSI, were proposed as alternative criteria when measuring moderate to high levels of imposex. TBT concentrations in N. reticulatus and N. lapillus tissues, corresponding to the ACs were calculated and provided valuable information for cross-species comparisons.

Using the vas deferens sequence index (VDSI) and relative penis size index (RPSI) in dogwhelks (Nucella lapillus), imposex levels were assessed at 63 sites within 11 sea inlets during 2010/2011 and compared these with levels gathered since 1987. Sterile females (VDS>5.0) were found at 14 of the 63 sites and 47 sites (75%) met the EcoQO (VDSI<2.0). The absence of imposex in ‘control’ areas on the west coast is due to the lack of vessel paint applications or net dips with TBT being used as an active anti-fouling ingredient. A significant decline was observed following 2005 when comparing VDSI levels which is consistent with the decline of TBT usage. Current levels are consistent with an overall improvement towards achieving Good Environmental Status according to the requirements under the Marine Strategy Framework Directive.

This study investigated butyltin contamination in Hong Kong waters using the rock shell Thais clavigera as a biomonitor. We collected rock shells from nine coastal sites in both winter 2005 and summer 2006 to examine the spatial and seasonal patterns. The relative penis size index (RPSI) and vas deferens sequence index (VDSI) were determined following a standard protocol, while the tissue concentrations of butyltins (i.e., mono-, di- and tri-butyltin) were measured using gas chromatography. The results showed that imposex was particularly severe in T. clavigera collected from Victoria Harbour, Pak Sha Wan and Sai Kung Pier where shipping activities were frequent. Both imposex indices had a positive correlation with tissue concentration of tributyltin in T. clavigera. While VDSI exhibited little seasonal variation, RPSI of winter specimens was significantly higher than that of summer specimens. Thus, sampling season should be standardised when using RPSI as a biomarker.

Imposex is a condition in which females of dioecious marine snails develop rudimentary male characteristics. It is caused by tributyltin (TBT) used as an antifoulant in vessel paints since the late 1960s. Following the 2008 international ban on TBT, a decreasing rate of imposex has been observed worldwide. In Western Australia, imposex surveys of the whelk Thais orbita up to 2011 in the Perth metropolitan area suggested a decreasing trend but a significant recovery has not been confirmed. Collection of T. orbita from 11 sites in 2019 demonstrated a virtually complete recovery from imposex. Although it is generally accepted that male snails are not affected by TBT, the historical data set allowed confirmation that the male penis is of similar size in T. orbita collected at heavily affected sites and at relatively unaffected sites. Similarly, imposexed female snails had similar shell lengths to female snails at non-impacted sites.

Tributyltin (TBT) was a commonly used biocide in anti-fouling paints for marine vessels, however, it had negative impacts on non-target species, including causing imposex in dogwhelks (Nucella lapillus). Since the 1980s, legislation has been introduced to curtail its usage, culminating in a ban by the International Maritime Organisation (IMO) in 2008. In 2004 a national imposex monitoring network was established in Northern Ireland to determine the level and extent of TBT pollution. The level of imposex in N. lapillus was assessed according to the degree of male sexual development in the female using three measures: percentage of imposex-affected females (%I), the relative penis size index (RPSI), and the vas deferens sequence index (VDSI). All sites showed improvement since the initial survey with a reduction in imposex and an improvement in ecological quality under the classification of the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR).

Organotin (OT) based Antifouling Systems (AFS) were globally banned by the AFS Convention since 2008, but the Republic of Cabo Verde did not ratify this Convention, nor did it develop a national legislation to control OT-AFS. Gemophos viverratus imposex and butyltin tissue contamination were assessed around the São Vicente Island (Cabo Verde) in 2019 and compared with the data available from 2012. The vas deferens sequence index (VDSI), the relative penis length (RPL), the percentage of females with imposex (%I) and the percentage of sterilized females (%S) in 2019 ranged from 0 to 4.0, 0–84.4%, 0–100% and 0–5.1%, respectively, whilst TBT reached maximum values of ≈30 ng TBT-Sn g⁻¹ dw in the whelk tissues. These values are very similar to those registered in 2012, which indicates that TBT pollution has not decreased over the years, in contrast to the declining trend observed worldwide.

Thais gradata samples were collected from six locations along the southern shores of Peninsular Malaysia and analyzed for imposex incidence and organotin (butyltins (BTs), including tributyltin, dibutyltin, and monobutyltin, and phenyltins (PTs), including triphenyltin, diphenyltin, and monophenyltin concentrations), in tissue burden. On average, the BT levels were found to be higher than the levels reported a year before for other biota. In contrast, the PT compounds were found to be lower than in the previous report. The present study also classified the morphological expressions of the imposex scheme for this species into seven stages (stage 0 to stage 6) by observing the development of vas deference sequence (VDS) and penis bulk. This latest imposex scheme clearly indicates the mechanism of VDS growth, the structural changes from penis bulk to a penis with flagellum, and from a normal vaginal opening to a swollen vaginal opening. The degree of imposex was assessed using the vas deference sequence index and the percentage of females possessing the imposex characteristics. It was found that locations possessing high imposex levels also tended to show high BT levels in the snail tissue samples. However, correlation analysis did not show a significant relationship among the two parameters. A better result could be obtained if more samples and sampling locations were added in order to prove the hypothesis. The nonsignificant correlation between the shell height and any of the organotin compounds, along with no significant differences between BT levels in female and lower imposex stage samples, suggests that the BT concentration detected was a recent contamination.