Occurrence of tri-n-butyltin-caused imposex in the North Pacific marine snail Nucella lima in Auke Bay,Alaska

Like female dog whelks (Nucella lapillus) in the Atlantic Ocean, females of the Pacific gastropod N. lima respond to low concentrations of tri-n-butyltin (TBT) by growing a penis and vas deferens. This condition, termed imposex, was found to occur in N. lima collected from August 1987 to May 1988 along a TBT pollution gradient associated with a marina in Auke Bay, Alaska. The suite of symptoms characteristic of imposex in N. lima was slightly different than in N. lapillus. Imposex, as measured by relative penis size (RPS) of females to males, increased from 0.0 to 34.27 along this gradient and as measured by vas deferens sequenceindex (VDS) increased similarly from 0.0 to 4.29. Concentrations of TBT in N. lima increased from below detection limits (about 0.010 g Sn g^-1 dry tissue wt) to 0.065 g Sn g^-1 dry tissue wt along the gradient. The gradient was determined by measuring TBT in whole-body tissues of bay mussels (Mytilus edulis). Concentrations of TBT in mussels increased from below detection limits to 0.833 g Sn g^-1 dry tissue wt in mussels from within the marina that was the major local source of TBT. Imposex, tissue TBT burden, and position along a TBT pollution gradient are significantly correlated (P<0.01) in N. lima. TBT was tested as a causative agent for imposex by exposing snails at a distant control site to TBT paint. After 1 mo exposure, 33% of the females grew a penis ranging in size from 0.2 to 0.8 mm. Our results generally corroborate those found for N. lapillus and indicate that imposex in N. lima is caused by environmental TBT exposure. We suggest that the RPS in the genus Nucella may be useful in monitoring TBT in coastal waters worldwide.