MEPS 218:203-212 (2001)  -  doi:10.3354/meps218203

ABSTRACT: Between July 1998 and January 1999, levels of imposex (superimposition of male characters upon females) and organotin bioaccumulation (tributyltin, TBT; dibutyltin; monobutyltin; triphenyltin) were measured in the gastropod Nassarius (Hinia) reticulatus (L.) at 15 localities in NW Spain. Sampling sites were scattered along 5 rías (rivers), 3 with large commercial harbours, 2 mainly given over to fishing activity. Both imposex and organotin concentrations showed that the rías with large commercial harbours were polluted with TBT to an extent similar to or even higher than contaminated areas in other parts of Europe, even when the data on the latter had been recorded before restrictions on the use of TBT laden paints. However, rías lacking large vessel traffic also displayed substantial contamination, indicating that TBT pollution was not confined to the vicinity of the large trading ports. The masculinization of the gonadial section of the oviduct was graded in various stages (i.e. degree of convolution resembling the male seminal vesicle). This anomaly affected a substantial proportion of females (26.5%). It was most prevalent in females displaying advanced imposex, suggesting that after exposure to high TBT pollution, imposex is not constrained to the pallial gonoduct. The average degree of convolution (average oviduct stage, AOS) increased with TBT bioaccumulation up to levels above 2000 ng Sn g^-1 tissue. AOS appears to be a better index for ranking severely polluted sites than customarily applied indices (relative penis length index, RPLI, and vas deferens sequence index, VDSI). A relatively large fraction (4 to 26%) of females suffering from advanced imposex bore masses of aborted egg capsules at all locations within 2 rías highly polluted with TBT. Such a high frequency of functionally sterile females is unparalleled in the scientific literature; N. reticulatus has been previously grouped with other gastropod species in which imposex does not causes sterilization. While still lacking an explanation for the mechanism leading to sterilization, logic indicates that imposex might be the cause. Imposex in N. reticulatus is a useful bioindicator of TBT in polluted areas, where its indicator ability may be enhanced by assessing the degree of masculinization of the gonadial oviduct. The presence of functionally sterile females at highly polluted sites suggests that TBT induced imposex may sterilize female N. reticulatus.

KEY WORDS: Organotin · Imposex · Nassarius reticulatus · Sterile females · NW Spain