Contaminant pathways in Port Curtis: Final report - OzCoasts

Contaminant pathways in Port Curtis: Final report6: Occurrence of imposexChapter 6 Occurrence of imposex in Port Curtis6.1 IntroductionTributyltin (TBT) is a broad spectrum biocide used to coat the bottom of ships toprevent attachment of marine organisms. Introduced in the 1960s, it is one of themost effective antifouling agents ever developed. However, it became apparent inthe 1970s that leachates of organotin compounds were having deleterious effectson non-target organisms such as gastropods. The extensive use of TBT on alltypes of boats led to the virtual collapse of oyster farming industries in severalcountries during the 1980s. The harmful effects of organotin compounds wererecognised in 1989 by the International Maritime Organisation (IMO), of whichAustralia is a member. In 1990 the IMO recommended a ban on the use of TBTon vessels less than 25 m in length, as well as the elimination of all paints with aleaching rate of more than four µg of TBT per day. In 1999, the IMO adopted aresolution calling for a global ban on the application of all organotin compounds by2003 and a complete prohibition by 2008 (IMO 2002).The issue of elevated butyltin concentrations in Port Curtis was first identifiedduring the early stages of the Port Curtis contaminant risk assessment (Apte et al.2005). Water column TBT concentrations were above the trigger value of 0.006 µgSn/L, although still much lower than concentrations in many world harbours. TBTconcentrations were elevated in 13% of the 56 sediment samples analysed, butagain were low compared to severely polluted harbours in other parts of the world.TBT was also found to have bioaccumulated in resident oysters, mud whelks andmud crabs from Port Curtis, indicating exposure of these organisms.A follow-up study was therefore undertaken to characterise the effects of TBTexposure on marine organisms resident in Port Curtis. An imposex survey of thegastropod Morula marginalba (mulberry whelk) was conducted. Full details of thisstudy may be found in the publications by Andersen and co-workers (Andersen etal. 2004a, b). A summary is given below.6.2 Imposex in marine gastropodsThere have been a number of deleterious impacts of TBT on non-targetorganisms, most notably, the imposex phenomenon in marine gastropods.Imposex is the imposition of male sexual characteristics (notably a penis) onfemale marine snails. Reproductive failure and death of affected females can68