Environmental fate of organotin compounds : a chemical and microbiological study
Environmental fate and exposure assessment of triphenyltin and its degradation products in soil has been studied by using both chemical and microbiological methods together. For the chemical method, phenyltin compounds were derivatised by ethylation with NaBEt4 before injection into GC-MS, and analysed under selected ion monitoring (SIM) mode. the extraction recovery of phenyltin components (TPhT and DPhT) in soil was greater than 85%. The detection limits of MPhT, DPhT and TPhT in aqueous solutions were found to be 0.2, 0.2 and 0.3 ng as Sn, respectively which gave the limit of determination for the method as 0.01 μg g-1 for both phenyltins in soils and sediments and butyltin in sediments. The in-situ ethylation was found to be one of the most powerful techniques for organotins in sediments as it is rapid, and reliable and no suppression by any organic content was found. The pH values of test solutions were found to affect the toxicity of phenyltin compounds to microbial biosensors as these factors may influence the hydrophobicity of the compounds. The toxicity order of TPhT, DPhT and MPhT to two luminescent bacterial biosensors was found to be different from that of the Microtox assay. DPhT was found to be the least toxic phenyltin compound to all biosensors while MPhT was found less toxic than TPhT when using lux-marked P. fluorescens, TPhT was found to be more toxic in aqueous solution than in soil extract, while the toxicities of DPhT and MPhT in aqueous and in soil extract were not significantly different. In an experiment that studied the degradation of TPhT acetate and its exposure over a period of 33 weeks, there was no degradation of TPhT in both autoclaved soils observed. The degradation pattern of TPhT was found to be a non-linear regression transformation in both spiked soils with half-life of TPhT as 26 and 20 days in non-sterile soils at 10 and 20 μg g-1, respectively. The toxicity of TPhT mixed with its degradation products has been found to decrease after 8 weeks, this represents only a sole application.