Behaviour of Organotins in the Coastal Environment

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The use of TBT and TPT as constituents of antifouling compounds, over more than three decades, has left many coastal environments with a longstanding legacy of contamination. Inputs to water should no longer be an acute threat. However, despite recent actions by IMO to ban the use of these compounds, recovery will not be instantaneous and contamination could even increase at some locations where the legislation is ineffective, or where coatings are replaced, or sediments re-mobilised. Partitioning to solids is reversible and hence sediments may act as a persistent sink and secondary source of adsorbed organotins, as well as those residues entrained as paint flakes from boatyards and docks. Estimates of TBT half-times in sediments range from a few months to decades (in anoxic sediments), indicating that this ‘reservoir’ of organotins is likely to remain biologically relevant, and will require management, for a considerable period. For some ports and harbours, appropriate dredging and disposal of TBT-enriched sediments represents an extremely costly option to maintain viability, and it will be important to ensure that further harm to the environment does not ensue from remobilization of these residues. Based on example in the UK, we review here some of the factors which influence long-term partitioning behaviour and persistence of organotions (predominantly TBT)–and the likely timescales for recovery.