The remediation of tributyltin-contaminated dredgins and waters

Abstract

Tributyltin (TBT) is a pollutant, mainly introduced to the environment as a marine anti-fouling agent. The aim of this work was to assess and develop sustainable and cost-effective remediation technologies for TBT-contaminated dredged materials. For this purpose, analytical methods were developed for sediments and sediment leachates.
For the sediments, a triple extraction followed by derivatisation and measurement by gas chromatography with pulsed flame photometric detection was employed, avoiding the lengthy concentration step of the organic layer. The TBT detection limit of ca 0.04 mg Sn/kg in sediment was below the suggested limit of 0.1 mg/kg for sea disposal of TBT-contaminated dredgings (OSPAR Commission). For the leachates, derivatisation and extraction into hexane was used. Also, a new procedure, with the potential for automation, was developed for the simultaneous analysis of multiple water samples, based on in situ extraction and derivatisation on C18 solid phase extraction cartridges. No legislative limits existed for TBT in leachates, therefore the detection limits of ca 6-10 ng Sn/L achieved were regarded satisfactory, as they were below or similar to the EQS for coastal and estuarine waters or freshwaters (2-20 ng/L TBT). A pilot investigation was carried out on a dockyard to evaluate the use of X-Ray fluorescence as a screening method for the presence of TBT in sediments. Due to tin contamination such a technique was not suitable for the site examined.
Incineration was found to remove TBT but it would incur very high costs. Ultrasonic destruction was not effective enough, even on TBT-spiked water solutions. Carbon products, pure clays, organically modified clays, zero valent iron, fly ash and cements were screened for their abilities to prevent TBT leaching, using a leaching test. The best performer was a powdered activated carbon product which, even mixed with cement that increases the leaching of TBT, delivered a TBT-free (< 5 ng Sn/L) leaching test result 33 days after the mixing. The result showed that this technique could provide a solution for the immobilisation of TBT in contaminated dredgings by mixing this relatively low-cost, multi-purpose and inert additive, with or without cement according to the site specific requirements.

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