Imposex in pre-pollution times. Is TBT to blame?

Imposex is known to be induced by TBT at a very low ambient concentration, just a few nanogram per litre, and its development seems dose-dependent. However, the causal, exclusive link between TBT and imposex still need to be assessed in all species where imposex has been reported, becoming one of the most controversial issues of marine biology in the last two decades. In this paper we report evidence of imposex occurrence in gastropods prior to the use of TBT. TBTbased antifoulants first came on to the market in the 1960s but became widely used on ship hulls starting in the mid-1970s. We analyzed 55 museum specimens of Hexaplex trunculus, a Mediterranean neogastropod species known as an exhibitor of imposex. Samples had been collected between 1845 and 1930, 30-115 years before the use of TBT, in several locations of Mediterranean Sea and Atlantic Portuguese coasts. Morphological inspection of specimens revealed anomalous male traits in four females as an incipient penis behind the right ocular tentacle and a bifallic male. Our finding of imposex in specimens that lived before the TBT era challenge the TBT-imposex paradigm and is the clearest demonstration that factors other than TBT could alter the endocrine control of imposex development.