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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Data are available for the read-across substance TAME. TAME is characterised as “inherently biodegradable, not fulfilling criteria” for non-adapted sewage sludge, for adapted sludge TAME can be characterised as "readily biodegradable"

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

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 in water 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. Thus, TAME is not readily biodegradable in the aquatic environment according to the standardised aerobic ready-biodegradation tests. As no test results from standard inherent test systems for aquatic biodegradation are available, conclusions are made according to the non-standard tests (e. g. Jensen and Arvin, 1990).

However, certain adapted micro-organisms are capable of degrading MTBE (e. g. Kharoune et al., 2002). Thus, a well adapted industrial STP plant is able to degrade the substance. High degradation rates have been observed in non-standard tests using special types of inoculum, pure cultures and mixed cultures (e. g. Cowan and Park; Hernandez-Perez et al., 2001; 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 aquatic aerobic environment. However, the non-standard test data available indicate that TAME degradation might not fulfil the test criteria (OECD 302). Therefore, in the further assessment the substance is assumed to be “inherently biodegradable, not fulfilling criteria” for professional and consumer releases and on the regional scale.

There is good evidence for ready biodegradability when sewage sludge has become adapted to the substance. Such conditions will apply where there are continuous releases of TAME to a STP, such as for large production and processing sites. Thus, the substance can be assumed to be readily biodegradable in such cases. Therefore the characterisation of biodegradability in such STPs is set at “readily biodegradable” and the Monod kinetics are used for the degradation of TAME in the STP instead of the more simplified first-order kinetics as it can be assumed that the STPS at industrial site are carrying adapted sludge only.