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 express ion, extent and impact of imposer (a set of sexual anomalies) in 37 po pulations of Nucella lapillus spread over the Galician coastline (NW S pain); the bioaccumulation of several organotin (OT) species (monobuty ltin, MET; dibutyltin, DBT; tributyltin, TBT; and triphenyltin, TPhT) was also determined in 20 of those samples. While imposer, TBT (from 3 6 to 974 ng Sn g(-1) dry weight, ppb) and DBT (from 169 to 909 ppb) we re detected in every sample examined, MBT (from 65 to 387 ppb) and TPh T (from 39 to 250 ppb) were quantifiable in only 15 and 11 of them, re spectively. Imposer was found to have led to frequent female sterilisa tion in most of the populations of this intertidal gastropod, although none of them is considered to be at risk of extinction. This may be p artially due to the observation that these specimens appear more resis tant to the sterilising effect of TBT than northern congeners. Fishing and merchant fleets are thought to be the dominant sources of OT poll ution within embayments, with pleasure boats being of lesser importanc e. In addition, the characteristic pattern of OT body residues [i.e. u ndetectable TPhT and low TBT/(TBT+DBT) ratio] indicates that imposer i n several open coast populations may stem from nearshore merchant ship ping via the horizontal transport of paint leachates.