Tributyltin contamination and its impact on Nucella lapillus populations

Abstract

SynopsisCommon dogwhelks (Nucella lapillus) show a characteristic response to exposure to tributyltin compounds. Females develop male sexual characteristics, a phenomenon termed imposex. Dogwhelks have been collected for assesment of imposex from sites throughout Sullom Voe and Yell Sound in 1987, 1990 and 1991.Results of the 1991 survey have indicated that dogwhelks were completely absent from the terminal area, on the promontory of Calback Ness. The degree of imposex was highest in the population from Kames, the site closest to the terminal. Juveniles were completely absent from this site. Incidence of imposex was high in populations throughout the Voe and 91% of the females examined from within the Voe were reproductively unviable due to blockage of their reproductive tracts with vas deferens tissue. Outside the Voe, in the well flushed waters of Yell Sound, imposex was much lower, but only fell to levels associated with populations from areas distant from tributyltin (TBT) contamination in the two most northerly sites surveyed.Results of the survey have indicated that activities associated with the oil terminal are the source of TBT contamination to the area, and that contamination arising from the terminal operations has not only affected dogwhelks in Sullom Voe, but populations throughout Yell Sound.Comparison of the imposex levels from 1987 and 1990 data indicates that the reproductive capacity of females has progressively declined and that populations within the Voe are gradually being eliminated. Forty-six percent of females sampled from populations within the Voe were sterile in 1987, compared to 65% in 1990, and 91% in 1991. In 1987, both adult and juvenile dogwhelks were present in the jetty area, although 94.5% of the females were sterile. In 1990, juveniles were absent from this area, and all females were sterile. No dogwhelks were found in the terminal area during the 1991 survey and, at Kames, the next closest site, juveniles were absent.