Butyltins in indoor dust in homes in Malta

Abstract

In this preliminary study, the presence of tributyltin compounds and its degradation products was investigated in settled house dust collected from 23 houses around the island of Malta. The concentration of six organotin species was analysed namely BuSn3+, Bu2Sn2+, Bu3Sn+, BuSnMe3, Bu2SnMe2 and Bu3SnMe. These species were determined by extracting in glacial acetic acid followed by simultaneous extraction and derivatisation using sodiumtetraethyl borate (NaBEt4). Analysis and quantification was carried out using gas chromatography with flame photometric detection. Ubiquitous contamination by the three main organotin species, MBT, DBT and TBT was present. MBT and DBT were present in all samples. Their concentration was found to be in the range of 7-204 ngSn/g for MBT and 3- 253 ngSn/g for DBT. TBT concentrations ranged from non-detectable to 246 ngSn/g. Methylbutyl tins were also present. The levels of organotins found in this study were not similar to those found in a previous study where outdoor dust was investigated. In the previous study, butyltin contamination arose mainly from emissions related to ship repair and boating activities in which paint particles from TBT-based marine antifouling paints are released into the air and settle on dust. In this study the indoor environment is considered and this is exposed to contaminants mainly coming from leaching and normal wear and tear from household furniture and furnishings that may contain organotins as additives or as stabilisers. The indoor TBT contamination was found only in areas which are in very close proximity to ship repair and boating activities. The other butyltins mainly MBT and DBT were found in all samples and their presence is due to leaching and abrasion from household interiors and not from TBT degradation since TBT is not used as a stabiliser or furniture additive. Human exposure to organotins inside their homes was below the Tolerable Daily Intake (TDI) but it is still a cause for concern since house dust is not the only exposure route of organotins for humans. This particularly applies to children who have a lower TDI. The worst case scenario, for exposure to organotins in house dust, represented by M'Xlokk was calculated and resulted to be 32% of the TDI quoted for children. Levels are expected to decrease once the total ban on organotin- containing products will come into force in 2008. Proper human risk assessments must be performed by constant monitoring of the organotin levels on land and by determining all the likely exposure pathways of humans to organotins.