When Will the TBT Go Away? An Integrated Monitoring and Modeling Approach to Anticipate the Future of TBT in the Drammensfjord, Norway

摘要

Background. Despite recent international efforts to ban the use of the antifouling agenttributyltin (TBT), its presence in harbors remains a serious environmental concern. InNorway, official records indicate that no TBT was imported into or produced within thecountry since 2003. Nevertheless, emissions into harbors are still evident. The generalcause of these emissions are largely attributed to TBT contaminated soil, TBT contaminatedsediments, TBT-laden materials from before the ban (paints and PVC materials),and activities such the refurbishing TBT contaminated boats. Being in a post-TBT banera, the question emerges, how long will it take until TBT goes away?Approach. To address this, we developed an extensive TBT monitoring campaign in theDrammensfjord, Norway, from 2008 to 2011. In addition, we established a TBT fatemodel, specifically parameterized for the Drammensfjord that accounts for the gradualdecrease in TBT emissions to the harbor over time. The monitoring results were carefullyintegrated into the model. First, earlier measurements of TBT emissions from 2005 wereused as input, monitoring data from 2008 to 2009 were used to calibrate the model usinga Bayesian Monte Carlo updating approach, and 2010 to 2011 monitoring data were usedto test the model.Results. The result from monitoringof TBT in the sediment indicated astrong decrease in TBT concentrationsince 2005. The higher solubilityof TBT compared to other organiccontaminants means that transfereefrom sediment to overlying watercan explain much of the decrease insediment concentration. The observeddecrease was also well reflectedby the model. However, itmay still take several decades for thisdecrease in TBT concentration toreach concentrations acceptable according to the Norwegian Sediment Quality Guidelines.Uncertainty in model output is a limiting factor in this assessment. Further, potentialmitigation strategies can be put in place to reduce TBT concentrations.