Organotin contamination of urban dust in Malta

Abstract

In this study, the presence of tributyltin cationic species and its environmental metabolites were determined in settled dust collected mainly from rooftops of school buildings in different parts of Malta. The concentration of the six organotin species BuSn3+, Bu2Sn2+, Bu3Sn+, BuSnMe3, Bu2SnMe2 and Bu3SnMe was determined using an analytical method based on extraction of sizeselected dust fractions with glacial acetic acid followed by a derivatisation/extraction step with sodium tetraethylborate (NaBEt4) and quantitation using gas chromatography with flame photometric detection. The presence of the organotin cationic species tributyltin and its degradation products, monobutyltin and dibutyltin was established in both size fractions of most of the dust samples analysed. TBT concentrations varied from non-detectable to a high of 11,800 ng Sn g1 and there was no statistically significant difference in organotin concentration between the finer (diameter: <125 µm) and the coarser (125 -250 µm) fractions. The presence of the methylbutyl forms was encountered but only occasionally. The levels ofTBT in the urban environment appear to have increased since 2000, the date of an earlier, more limited, survey and TBT seems to have become a ubiquitous contaminant of the urban environment in Malta. We had formulated a previous hypothesis that, in the urban environment, butyltin species arise mainly from particulate residues from TBT-containing antifouling marine paints and are therefore related to shiprepair and boating activities occurring on and around the island. The earlier study from our laboratory had already implicated the ship-repair facilities at Malta Drydocks present in the area of Grand Harbour as an important source ofTBT. This study has confirmed this drydocking facility as a main contributor but it has also identified a number of other probable sources, namely Marsaxlokk bay and possibly also Wied iz-Zurrieq creek, both being popular sites for fishery and leisure boating, as well as the inland municipal solid waste landfill site at Maghtab. The risk to the human population from organotin contamination of urban dust was estimated and, in certain localities, notably in and around the Senglea area, the results suggest cause for concern, especially with respect to effects on sensitive subgroups of the population such as children. Given the imminent international ban on TBT use in marine paints, it is expected that the concentration of TBT in the aquatic and hence the urban environment will decrease in the coming years. Long-term monitoring programmes are required to evaluate progress in this area and further studies are needed in order to adequately assess the health risk to the human population.