Assessment of TBT and organic booster biocide contamination in seawater from coastal areas of South Korea

•TBT levels still exceed water quality criteria 6 years after a total ban on TBT use.•Diuron and Irgarol 1051 were the common alternative biocides identified in the samples.•Diuron levels recorded greatly exceeded water quality criteria.•Irgarol 1051 levels were marginally lower than the relevant water quality criteria. Seawater samples from major enclosed bays, fishing ports, and harbors of Korea were analyzed to determine levels of tributyltin (TBT) and booster biocides, which are antifouling agents used as alternatives to TBT. TBT levels were in the range of not detected (nd) to 23.9ng Sn/L. Diuron and Irgarol 1051, at concentration ranges of 35–1360ng/L and nd to 14ng/L, respectively, were the most common alternative biocides present in seawater, with the highest concentrations detected in fishing ports. Hot spots were identified where TBT levels exceeded environmental quality targets even 6years after a total ban on its use in Korea. Diuron exceeded the UK environmental quality standard (EQS) value in 73% of the fishing port samples, 64% of the major bays, and 42% of the harbors. Irgarol 1051 levels were marginally below the Dutch and UK EQS values at all sites.