engleski

Persistence of butyltin (BuT) compounds in the contaminated sediments from the Croatian Adriatic coast

Since the biocidal properties of tributyltin (TBT) were discovered in the late 1950s, it found a wide application as an active biocide in the antifouling paints, and was directly introduced into the marine environment by this way. After it was established that TBT, acting as an endocrine disruptor, causes imposex and other adverse biological effects (already at levels of 1-2 ng L-1 ) it became clear that it is one of the most toxic anthropogenic compounds ever purposely introduced into the marine environment. TBT is included in the European list of priority pollutants and its use in antifouling paints was finally banned in 2008 in all European countries, including Croatia. However, first data on butyltin concentrations in marine samples (seawater and mussels) from the Croatian Adriatic coast performed in 2009 and 2010 showed widespread pollution of the coastal area with butyltin compounds and suggested that TBT-based antifouling paints were still in use in Croatia (Furdek et al., 2011). Once introduced into the water column, TBT is subjected to microbial and photolytic degradation to less toxic dibutyltin (DBT) and monobutyltin (MBT) compounds, and finally to non toxic inorganic tin. All these compounds readily adsorb to settling particles and accumulate in the bottom sediment where their degradation continues, but at significantly slower rate. Due to their persistence in sediments and continuous release back into the water column, butyltins can cause problems long after their input. The aim of this work is to present data on the distribution of butyltin compounds in sediment cores sampled at 26 polluted locations (marinas and ports) along the Croatian Adriatic coast and to study the factors that influence distribution and persistence of butyltin compounds in these sediments. The results showed that tributyltin pollution is present at all investigated locations with total BuT concentrations ranging from 80 to 55000 ng(Sn)g-1, comprising 15 to 80 % of TBT. Butyltin degradation index [BDI=(MBT+DBT)/TBT] varied from 0.5 – 2 in the surface sediment and from 0.5 – 8 in the deeper sediment layers. The depth profiles of BDI and of BuT concentration showed very different patterns with depth, suggesting different degradation rates of BuT compounds in sediments from different locations. For better understanding of these unequal depth distributions we studied the influence of sediment characteristics (particle size distribution, specific surface area and organic carbon content) on the persistence of TBT in sediments. The assumption that sediment characteristics could affect TBT degradation in sediments was based on the results of our previous experiments which suggested that desorption from sediments into the porewater has a crucial role in BuT degradation in sediments, as the degradation of TBT and DBT in porewater was found to be a fast process, with the half-lives of t1/2= 8.9 days-1 and 2.9 - 9.1 days-1, respectively. References: Furdek, M., Vahčić, M., Sčančar, J., Milačić, R., Kniewald, G., Mikac, N., 2012. Organotin compounds in seawater and mussels Mytilus galloprovincialis along the Croatian Adriatic coast. Marine Pollution Bulletin 64, 189-199.

Organotin compounds; tributyl tin; isotopically enriched tracers; degradation; sediment; porewater

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