Seasonal variations of imposex indices and butyltin concentrations in the rock shell Thais clavigera collected from Hong Kong waters

► Severe imposex occurred in neogastropods at sites with high shipping activities. ► Imposex indices (VDSI and RPSI) positively correlated with tissue burden of TBT. ► VDSI exhibited little seasonal variation, but RPSI was much higher in winter. ► Sampling season should be standardised when using RPSI as a biomarker.