Direct entry of tributyltin (TBT) into the aquatic environment is primarily due to its use in antifouling paints on boats, which gives rise to contamination of waters and sediments of marinas, lakes, and coastal areas. To date, there is a lack of knowledge on other organotin sources and on the contamination of other environmental compartments. Inputs from wastewater and sewage sludge as well as from landfills are not well known. As the consumption of TBT and other organotins increases, these compounds are of growing importance in wastewater and sewage sludge. This chapter reviews speciation and contamination of wastewater and sludge, and describes the fate of organotins in a treatment plant. Organotins were determined by capillary gas chromatography with flame photometric detection after extraction and derivatization. In untreated wastewater of the city of Zurich, Switzerland, substantial concentrations of butyltins were determined. Phenyltins, dioctyltin, and tricyclohexyltin were not detected. Average values on six sampling days were 245 ng l-1 monobutyltin (MBT), 523 ng l-1 dibutyltin (DBT), and 157 ng l-1 TBT. The mean daily load of organotin was 122 g. Partitioning in wastewater showed that ~90% of the butyltins was associated with suspended solids in the influent, and then the percentage dropped at each successive stage of the treatment process. As a consequence, these compounds are removed from raw wastewater by sedimentation in the primary clarifier. Aerobic digestion did not lead to a significant elimination from wastewater, and anaerobic digestion was not very effective in reducing organotins in sludge; hence, substantial organotin levels were determined in digested sludge. Average concentrations were 0.78 mg kg-1 MBT, 0.98 mg kg-1 DBT, and 0.99 mg kg-1 TBT (dry weight). Organotins are therefore efficiently removed from wastewater (elimination 90%), but they become enriched in sewage sludge (daily load 59 g d-1). Sludge is disposed of in landfills and at sea and is used in agriculture as a soil amendment to a large extent, giving a transfer path into the aquatic and terrestrial environment unrecognized thus far. Mono-, di-, and tributyltin residues have also been determined in the leachate of a landfill where the total butyltin concentration was 373 ng l-1. The environmental input from landfills, however, is not as important as that from untreated wastewater and sewage sludge.
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- Organotins in Municipal Wastewater and Sewage Sludge
- Springer Netherlands
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