Organotins in settled dust around Malta and Gozo with special reference to outdoor dust

Abstract

In this study, the presence and levels of organotin cationic species mainly; BuSn3+, Bu2Sn2+, Bu3Sn+, BuSnMe3, Bu2SnMe2, PhSn3+, Bll4Sn and Sn4+ were analyzed from samples of settled urban dust in the Maltese Islands. Forty-one samples, thirty-two in Malta and nine in Gozo, were gathered from roof tops, balconies and terraces of houses using a broom and a dustpan. Two dust fractions, namely of diameters <125µm and 125-250µm, were analyzed by means of ultrasound assisted leaching in acid, based on the method established by Carpinteiro et al., derivatization with sodium tetraethylborate (NaBE4) and quantification by Gas Chromatography (GC) equipped with a flame photometric detector (FPD). The levels of MBT, DBT and TBT, obtained from both dust fractions, were lower than those obtained by Decelis in 2005. Concentrations varied from below the detection limit up to 4183ng Sn g-1 dw as TBT in Marsaxlokk in the finer fraction (<125µm). This relatively high concentration of TBT is attributed to the extensive boating activities that occur all year round in this village. Senglea dust also showed high levels of TBT (1549 ng Sn g-1dw ), mainly due to the presence of Malta Shipyards at which blasting is carried out on an industrial scale. The higher concentration of TBT in the fine fraction of dust over the coarser fraction is a statistically significant observation. Both MBT and DBT are considered to be present as the degradation products of TBT, however, their abundant presence in indoor dust (data obtained from a parallel study to this one by Cortis) suggests the possibility of other sources by which MBT and DBT can find themselves in the environment. There is a significant correlation between DBT + TBT concentrations and the spatial setting of collection, i.e. indoor and outdoor dust, implying that when high DBT and TBT concentrations are found in outdoor dust, it is likely that high concentrations of DBT and TBT are also found in indoor dust in that particular site, outdoor dust usually having higher concentrations. Dispersion of organotin laden dust by wind in the Maltese Islands is a major issue since it distributes these ubiquitous contaminants in places that do not appear to have an obvious source. The lower organotin concentrations obtained in the present study show that the ban implemented in these last few years, taking strict actions from January 2008, is showing positive results. Hence the expected decrease mentioned in a previous study (Decelis, 2009) has apparently materialized. Still, the problem should not be overlooked since the mode of degradation in settled dust is totally different from that observed in marine sediments which are probably much more complex systems than the ones under study here. Consequently the need for more research on distribution patterns of organotins is still of utmost importance.