engleski

Distribution and persistence of butyltin compounds (BuT) in coastal sediments from eastern Adriatic (Croatia)

Butyltins (BuTs) have been introduced into the marine environment by the use of tributyltin (TBT) as biocide in antifouling paints since 1960s. However, after it was established that TBT has various toxic effects on the non target organisms, like the appearance of imposex in gastropods at very low levels (1-2 ngL-1), the use of TBT-based antifouling paints has been banned in many countries worldwide, including the whole Europe, while in Croatia they are banned since January 2008. The first measurements of BuT concentrations in seawater and mussels from the Croatian Adriatic coast, sampled during 2009-2010, showed a widespread pollution with TBT, suggesting an ongoing use of those paints, despite restrictions (Furdek et al., 2012). Here we present the first data on BuT concentrations in sediments from the Croatian Adriatic coast collected in the period 2009-2013. In order to elucidate factors influencing the level of BuT pollution, locations with different intensity of maritime activities (marinas, ports and reference sites) were selected for sampling of surface sediments and sediment cores. BuT concentrations in the surface sediments ranged from 5 to 1362 ng(Sn) g-1(d.w.), while contamination levels in marinas and ports were similar and significantly higher than those at reference sites. Extremely high concentrations were found in sediments taken below the service hoists in marinas, where BuT concentration reached the enormous value of 66344 ng(Sn) g-1(d.w.). Obviously, the ban cannot solve the problem of TBT contamination of the marine environment immediately, since contaminated sediments represent its long term source. TBT degradation in sediments occurs in much slower rates than in seawater, thus making TBT very persistent in sediments, from where it may be released back to the water column. Influence of sediment characteristics (grain size and total organic carbon (TOC)) on the TBT degradation efficiency in various contaminated sediments was further studied. TBT degradation efficiency was assessed in 9 sediment cores by determination of TBT and its degradation products with depth (dibutyltin (DBT) and monobutyltin (MBT)), and evaluated using Butyltin Degradation Index, BDI=(MBT+DBT)/TBT. Two types of depth profiles were observed: first, in which efficient degradation was indicated by the decrease of TBT and BuT concentrations with depth with BDI values higher than 1, and second, where weak degradation was indicated by small depth variations of TBT and BuT concentrations and BDI values less than 1. In general, TBT and TOC distributions followed the same depth pattern, while statistically significant correlation was found between TBT and TOC, as well as between BDI and TOC. Grain size distributions did not show significant correlation with other parameters. Therefore, results of this study strongly suggest that organic matter, by controlling TBT adsorption/desorption processes, influences the TBT degradation efficiency and consequently defines its persistence in contaminated sediments, which thus increases in sediments rich in organic matter.

butyltins (BuT) ; tributytin (TBT) ; sediments ; degradation

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