Evaluation of Bioavailable Tributyltin in the Sediment–Porewater System of Industrialized Korean Bays Using Ex Situ Passive Sampling and Partitioning Models

Despite the complete ban on tributyltin (TBT), its ecological risk to benthic organisms remains a concern in coastal areas. To overcome limitations of partition coefficient-based prediction models in estimating bioavailable concentrations, this study developed, for the first time, an ex situ method using a low-density polyethylene (LDPE) passive sampler to measure the freely dissolved concentration (Cfree) of TBT in sediment porewater. The equilibrium between LDPE and porewater was reached within 96 h. The total sedimentary concentrations (Cs) and Cfree of TBT in three industrialized bays in Korea were measured together, ranging from 26.2 to 931 ng of Sn/g of dw and 6.20 to 1363 ng of Sn/L, respectively. Shipbuilding and repair activities were identified as major sources of TBT, and sediments remain secondary sources of porewater contamination over a decade after regulations. As TBT does not exhibit strong adsorption to black carbon, the two-carbon model could not effectively reduce uncertainty compared to the equilibrium partitioning (EqP) method. Comparisons with environmental threshold values indicated a high ecological risk for benthic organisms near contaminated hotspots. These findings underscore the high applicability of LDPE-based ex situ methods as reliable tools for monitoring freely dissolved TBT in sedimentary environments, as they effectively minimize the influence of complex sediment characteristics.