Spatial and temporal evolution of imposex in dogwhelk Nucella lapillus (L.) populations from North Wales, UK.

Nucella lapillus imposex and organotin tissue contamination were assessed, during 2006, at twenty sites in North Wales, between Anglesey and Shell Island on the Lleyn Peninsula. Vas Deferens Sequence Index (VDSI), Relative Penis Size Index (RPSI) and the percentage of affected females (%I) were used to assess imposex levels which varied between 0.5 and 3.