2-ethoxy-2-methylpropane

Biodegradation in water: screening tests

Description of key information

ETBE is characterised as “inherently biodegradable, not fulfilling criteria” for non-adapted sewage sludge, for adapted sludge ETBE can be characterised as "readily biodegradable"

Additional information

ETBE cannot be regarded as readily biodegradable in standard test systems (Fayolle et al., 1998; Slovnaft VÚRUP, a.s., 2005a). However, certain adapted micro-organisms are capable of degrading ETBE (e.g. Cowan and Park, 1996; Steffan et al., 1997; Kharoune et al., 1998, Kharoune et al., 2001; 2002). Therefore, a well adapted industrial STP plant is considered 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. These studies show that at least some microbial species are capable to degrade ETBE and to use it even as their sole carbon source.

It may be concluded that ETBE is inherently biodegradable under certain conditions in aquatic aerobic environment. However, the non-standard test data available indicate that ETBE 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 ETBE 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 ETBE 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.