Sorption of tributyltin in seawater by municipal solid waste compost

Abstract

The use of municipal solid waste (MSW) compost as a sorbent for tributyltin (TBT) in seawater was investigated. TBT-contaminated seawater, both artificially prepared and that collected from Msida Creek yacht marina (Malta), was allowed to percolate through untreated and water-washed columns of compost and then analysed for organotins using gas chromatography-flame photometric detection. About 90% of dissolved TBT ranging in concentration from about 800 to 8000 ng Sn l À1 was sorbed by treating 500 ml solutions with 100 g untreated compost. On the other hand, no detectable breakthrough of TBT was observed from compost that had previously been washed by water to remove soluble organic matter. Breakthrough of TBT from unwashed compost is thought to be due to formation of complexes between the soluble organic matter in compost and aquated TBT, which renders the organotin more hydrophilic. The use of washed MSW compost as sorbent for the purification of TBT-contaminated waters generated in large quantity during hull-cleaning activities in drydocks is suggested as a mitigatory measure against the impact of TBT on the coastal marine environment.

Adsorption characteristics of tributyltin on municipal solid waste compost

“…The fresh compost was air dried, crushed to pass through a 2.8 mm sieve and thoroughly mixed prior to use. The IR spectrum of the compost was very similar to that for MSW compost from the same composting facility used in a previous study, 7 as well as for a city refuse compost from Yokohama, Japan, 8 and contains the following absorption bands indicative of groups typical of humic materials: aliphatic and aromatic C-H bonds (2900 cm −1 and 900-650 cm −1 respectively), carboxylic (1700-1600, 1500-1400 cm −1 ) and alcoholic and/or phenolic OH groups (3500-3300, 1100-1000 cm −1 ).…”

“…Sodium azide (0.3 g) was also added as a biocide to prevent the degradation of TBT, as reported by Vassallo and Vella: 7 we established experimentally that, at the concentrations employed in this work, azide ions do not interfere with the ethylation of TBT. A small subsample of the compost was taken and used for moisture content determination.…”

“…Although the Grignard derivatization used by Vassallo and Vella 7 was capable of alkylating all TBT in solution, irrespective of whether it was associated with soluble organic matter or not, no data were available on the ethylation efficiency of sodium tetraethylborate in the presence of dissolved organic matter (DOM). This issue was investigated as follows: deionized water and a series of solutions obtained through serial dilution of the DOM extract and having an organic carbon (OC) concentration between 0.0 and 0.6 mg ml −1 were each spiked with 400 ng (as tin) of TBT and TPrT (internal standard), stirred for 15 min and then analysed.…”

“…7 The reduction of DOM in the leachate was monitored by measuring the reduction in UV-visible absorption over the range 200 to 900 nm. The final washed compost was air dried, gently crushed to pass through a 2.8 mm sieve and used throughout this work.…”

“…We have investigated the possibility of cleaning up discharges and contaminants released from dry docks and ship-repair yards by the use of municipal solid waste (MSW) compost, which is a cheap and readily available adsorbent. Preliminary work carried out by Vassallo and Vella 7 has already shown that MSW compost can act as an effective solid-phase sorbent for the removal of TBT in solution. The major objectives of this study were to determine in greater detail the sorption behaviour of TBT onto MSW compost and to give first insights into the equilibrium and kinetic behaviour of this transfer process.…”