Emissions of OTNE (Iso-E-super) – Mass flows in sewage treatment plants

Abstract

The fate and mass flows of OTNE ([1,2,3,4,5,6,7,8-octahydro-2,3,8,8-tetramethylnaphthalen-2yl]ethan-1-one) which is commercialized as Iso-E-Super were studied in three large scale sewage treatment plants (STPs) in detail. The results are compared to 14 smaller ones located in Germany and Switzerland. OTNE inflow concentrations ranged from 4000 to 13 000 ng l⁻¹ while the effluent concentrations ranged from 500 to 6900 ng l⁻¹. It is eliminated from the waste water with 56–64% during waste water treatment. High OTNE concentrations in sewage sludge showed that the elimination was mainly driven by sorption to sludge. This complies with major elimination in the first settling basins (primary settling tanks) while it was removed to a lesser extent in the aeration basin of the activated sludge treatment or in successive biofilters.

The mass flows of OTNE in the influent of the German STPs were between 0.9 and 1.9 g per inhabitant and year. In the annual effluents mass flows of OTNE ranged between 0.2 and 0.8 g per inhabitant which complies with data measured in 13 smaller STPs from Switzerland. The similarity of data suggests that the observed mass flow data might be extrapolated to other European regions.

Introduction

OTNE ([1,2,3,4,5,6,7,8-octahydro-2,3,8,8-tetramethylnaphthalen-2yl] ethan-1-one) (structural formula and mass spectrum given in Fig. 1) has been among the most popular fragrance compounds in the last years. It is commercialized as Iso-E-Super^® with 2500–3000 tonnes annually (Gautschi et al., 2001) while, e.g. HHCB (Galaxolide^®) reaches a volume of about 1500 t/a (Balk and Ford, 1999, OSPAR, 2004). Although the environmental behaviour of fragrance compounds has been discussed for musk compounds such as HHCB, AHTN, musk xylene or musk ketone etc. (Eschke et al., 1994, Eschke et al., 1995, Simonich et al., 2000) little is known on the more fruity or woody smelling synthetic fragrances such as OTNE. Sorption is the main process of elimination of polycyclic musk compounds in sewage treatment though transformation to other compounds may occur, while mineralisation has never been observed (Artola-Garicano et al., 2003, Bester, 2004, Kupper et al., 2006). On the other hand metabolites formed in the treatment process from, e.g., musk xylene and HHCB, are relevant compounds released from sewage treatment plants (STPs). Only a few studies on OTNE, e.g., on volatilisation, fate in sludge and sludge-amended soils are currently available (Aschmann et al., 2001, Simonich et al., 2002, Difrancesco et al., 2004). OTNE was reported to be not readily biodegradable in OECD tests. Concentrations in wastewater were at 3600 ng l⁻¹ in the US and in Europe at 9000 ng l⁻¹. In the USA, the concentrations of OTNE were lower than those of AHTN and HHCB, while in Europe they were equal (Simonich et al., 2002). The contents of OTNE in the effluents ranged from 30 to ∼4000 ng l⁻¹ and the highest amounts were observed in the European samples. In that study the technologies, which are currently applied most, i.e., activated sludge- and mechanical treatment exhibited removal rates of 92% and 29%, respectively. Concentrations of 7–30 mg kg⁻¹ OTNE in dry sludge were determined in sludges from the USA and dissipation half-lives of 30–100 days were observed for OTNE in sludge-amended soils (Difrancesco et al., 2004).

However, OTNE has been on the market as the technical mixture Iso-E-Super^® which was well received by the consumer. The compound which causes most of the (wanted) sensoric effect in this mixture was recently identified to be ((±)-1-[(1R^∗,2R^∗,8aS^∗)-1,2,3,5,6,7,8,8a-octahydro-1,2,8,8-tetramethylnaphthalen-2-yl]ethan-1-one) (Nussbauer et al., 1999). It is a minor component of the technical mixture, but has been synthesized and patented as a pure compound just a few years ago (Nussbauer et al., 1999, Gautschi et al., 2001). Knowledge on the fate of the main constituents of Iso-E-Super^® is thus not only of environmental but also of economic relevance. Therefore the fate of OTNE in wastewater treatment was studied and mass flows in influents and effluents were determined to obtain reliable emission data. This is of high importance in an area were drinking water is produced by soil filtration and underground passage (Andresen and Bester, 2006) from surface water containing 10–30% treated wastewater, such as the river Ruhr (Germany), Thames (England) or Danube (Hungary).