Ubiquitous imposex and organotin bioaccumulation in gastropods Nucella lapillus from Galicia (NW Spain): A possible effect of nearshore shipping

A survey was conducted during the summer of 1996 to assess the expression, extent and impact of imposer (a set of sexual anomalies) in 37 populations of Nucella lapillus spread over the Galician coastline (NW Spain); the bioaccumulation of several organotin (OT) species (monobutyltin, MET; dibutyltin, DBT; tributyltin, TBT; and triphenyltin, TPhT) was also determined in 20 of those samples. While imposer, TBT (from 36 to 974 ng Sn g(-1) dry weight, ppb) and DBT (from 169 to 909 ppb) were detected in every sample examined, MBT (from 65 to 387 ppb) and TPhT (from 39 to 250 ppb) were quantifiable in only 15 and 11 of them, respectively. Imposer was found to have led to frequent female sterilisation in most of the populations of this intertidal gastropod, although none of them is considered to be at risk of extinction. This may be partially due to the observation that these specimens appear more resistant to the sterilising effect of TBT than northern congeners. Fishing and merchant fleets are thought to be the dominant sources of OT pollution within embayments, with pleasure boats being of lesser importance. In addition, the characteristic pattern of OT body residues [i.e. undetectable TPhT and low TBT/(TBT+DBT) ratio] indicates that imposer in several open coast populations may stem from nearshore merchant shipping via the horizontal transport of paint leachates.