A Baseline Survey of Dogwhelk (Nucella Lapillus) Imposex in Eastern Canada (1995) and Interpretation in Terms of Tributyltin (TBT) Contamination

Abstract

Tributyltin (TBT) used in marine antifouling paints causes masculinization, i.e. the development of a penis and vas deferens, in female neogastropod snails. This ‘imposex’ phenomenon is used as a bioindicator of TBT contamination. The occurrence of imposex in the dogwhelk (Nucella lapillus) was surveyed in eastern Canada from the Atlantic seaboard into the St Lawrence estuary for the first time in 1995. Imposex was present at 13 of 34 sites throughout the region, but usually at less than 100% frequency. Seven sites had dogwhelks not affected by imposex. Dogwhelks were absent at 14 harbour sites with seemingly ideal habitat. All females were affected at only two sites: Portuguese Cove, within Halifax Harbour, and north of South Bar in Sydney Harbour. Other harbours where imposex was present included Chester, N.S., Les Méchins, Que., Saint John, N.B., and Arnold's Cove and Come-by-Chance, Nfld. Relative female/male Penis Size Index (RPSI) ranged 0.4–38.5%. These frequencies and RPSI indices are relatively low. TBT concentrations in dogwhelks ranged 1–75 ng g⁻¹ wet wt at sites with imposex and were <11 ng g⁻¹ wet wt or not detected at imposex-free sites. The results support 1994 data from the west coast of Canada which suggest that TBT controls introduced in Canada in 1989 have not yet eliminated the environmental problem. The results provide a databank for future monitoring of the effectiveness of the controls.

Keywords:

• Tributyltin (TBT)
• imposex
• dogwhelks
• Canada