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Based on the considerations described in the document “Read-across substantiation C5-6 branched alkylmethyl-ethers” (incl. the supporting references Tuppurainen et al., 2007 and Niska et al., 2008), it can be concluded that the available information of TAME can be used to predict the biodegradation of the substance ‘C5-6 branched alkylmethyl-ethers’ with sufficient certainty.

Two closed bottle tests (OECD 301D) with TAME are available (Hazleton Europe, 1995; Slovnaft VÚRUP, a.s., 2005a). The percentage of biodegradation observed is ca. 5% after 7 days in both studies. However, certain adapted micro-organisms are capable of degrading TAME (e.g. Kharoune et al., 2002). These studies show that at least some microbial species are capable to degrade TAME and to use it even as their sole carbon source. It may be concluded that TAME is inherently biodegradable under certain conditions in the aquatic aerobic environment. However, the non-standard test data available indicate that TAME degradation might not fulfil the test criteria (OECD 302) to be classified “inherently biodegradable”. In contrast, adapted sewage sludge is able to rapidly degrade TAME.

Therefore, in the further assessment a distinction will be made between non-adapted municipal STPs which will be classified as “inherently biodegradable, not fulfilling criteria” and adapted industrial STPs where there are continuous releases of TAME which will be classified as “readily biodegradable”. For these adapted STPs the Monod kinetics are used for the degradation of TAME in the STP instead of the more simplified first-order kinetics.

 

In anaerobic, static sediment/water microcosms, TAME does not biodegrade (Suflita and Mormile, 1993; Mormile et al., 1994; Somsamak et al., 2001).

Based on the few studies available it should be concluded that rapid and reliable biodegradation of TAME in soil can not be assumed in any normal environmental conditions indicating very slow degradation in soil (Jensen and Arvin, 1990; Mormile et al., 1994; Zenker et al., 1999). The biodegradability of TAME in soil in aerobic and anaerobic conditions seems to be very slow and favourable conditions for degradation are difficult to attain.

 

The rate constant used in the assessment are:

Degradation in a non-adapted STP

0 d-1

Degradation in an adapted STP

Monod kinetics (default values)

Biodegradation in water

4.62E-03 d-1

Biodegradation in aerated sediment

2.31E-03 d-1

Biodegradation in soil

2.31E-03 d-1