Use of this information is subject to copyright laws and may require the permission of the owner of the information, as described in the ECHA Legal Notice.
EC number: 216-653-1
CAS number: 1634-04-4
MTBE is resistant to hydrolysis at environmentally relevant pH values as
demonstrated in an OECD guideline, GLP-compliant study. Strong acids can
contribute to the hydrolysis of MTBE but the pH needed for decomposition
is far below that normally detected in natural soil and water (Lyman et
According to existing data, the degradation half-life of MTBE in the air
is 3-6 days depending on environmental conditions (predominantly
OH-radical concentration). Using a degradation rate constant of
2.84E-12cm3/molecule/s and an OH-radical concentration of5E05
radicals/cm3 a half-life of 5.65 days is calculated.
Direct photolysis will not be an important removal process since
aliphatic ethers do not absorb light at wavelengths >290 nm. The
UV-spectrum (max t 289 nm) indicates that direct photolysis in water may
MTBE is not readily biodegradable in the aquatic environment according
to standard aerobic ready-biodegradation tests (Hüls, 1991a; RBM, 1996a;
Slovnaft VÚRUP, a. s., 2005a). However, high degradation rates have been
observed in non-standard tests using special types of inoculum, pure
cultures and mixed cultures (Shell, 1993; Salanitro et al., 1994;
Steffan et al., 1997; Cano et al., 1999; Kharoune et al., 2001; 2002).
These studies show that at least some microbial species are capable of
degrading MTBE and to use it even as their sole carbon source. It may be
considered that MTBE is inherently biodegradable under certain
conditions in the aquatic aerobic environment. However, the non-standard
test data available indicate that MTBE degradation might not fulfil the
test criteria (of OECD 302). In contrast, it also shows that adapted
sewage sludge is able to rapidly degrade MTBE.
It could be assumed that where there are continuous releases of MTBE to
a STP, such as for large production and processing sites, sewage sludge
will have become adapted to the substance and in these cases, the
substance could be considered as readily biodegradable. For
professional and consumer releases and releases on the regional scale,
where adaptation may not occur, the non-standard test data available
indicate that MTBE degradation might not fulfil the test criteria (of
OECD 302), and a slower degradation categorisation as “inherently
biodegradable, not fulfilling criteria” could be considered.
This approach is consistent with the conclusion from the EU Risk
Assessment Report for MTBE, which concludes “MTBE is inherently
biodegradable under certain conditions in aquatic aerobic environment”
(European Commission, 2002).
However, owing to the lack of ready biodegradation seen in the available
standard screening tests, and as mandated by ECHA via a substance
evaluation decision, a conservative approach to the available data means
that the conclusion ‘under test conditions no biodegradation observed’
has been used for exposure assessment purposes.
In anaerobic, static sediment/water microcosms, MTBE does not biodegrade
(Suflita et al., 1993; Mormile et al., 1994). Under mixed
aerobic/anaerobic conditions biodegradation may in some cases be a
significant removal process of MTBE in aerobic sediment (Bradley et al.,
Several studies are available for degradation of MTBE in soil. The
results are conflicting. In a study in which soil was polluted with
gasoline containing MTBE it was shown that aerobic biodegradation was
observed after the spill (Yuan, 2006). This behaviour of MTBE was also
observed by Borden et al. (1997). However, other studies concluded that
rapid and reliable biodegradation of MTBE in soil cannot be assumed
under any normal environmental conditions (both aerobic and anaerobic),
indicating very slow degradation in soil (Yeh and Novak, 1994; Allard et
al., 1996; Reisinger et al., 2000). As the study by Yuan (2006) was
better in design and reporting than the other studies mentioned, the
worst-case half-life of 101.6 days in soil from this study is used in
constants used in the assessment are:
Degradation for hydrolysis
Degradation for photolysis
Degradation in air
Degradation in a non-adapted STP
Degradation in an adapted STP
Monod kinetics (default values)
Biodegradation in water
Biodegradation in aerated sediment
Biodegradation in soil
data support the paramaters used in the modelling, as discussed in
Chapter 9 on Exposure Assessment.
bioconcentration factors (BCF) of 1.5 and 1.4 were reported for Japanese
carp exposed to 10 and 80 mg/l MTBE in a flow-through system at 25 ºC.
Fish exposed for 28 days and then transferred to clean water eliminated
almost all MTBE residues within 3 days (Fujiwara et al., 1984). The BCF
indicate a low potential for bioconcentration. The BCF of 1.5 l/kg is
used in the assessment.
carbon-water partitioning coefficient (Koc) calculated from the
octanol-water partition coefficient (log Kow = 1.06) using the equation
from the Technical Guidance Document (2003) (predominantly hydrophobics)
is 9.1 l/kg (log value = 0.95). This predicted value is used in the
The Henry's Law
constant (H) is calculated as 69.8 Pa m3/mol (log H = 1.84), based on a
vapour pressure of 33 kPa at 25 °C and a water solubility of 42,000 mg/l
at 25 °C in EUSES, this corresponds to a Henry's Law constant of 33.3 Pa
m3/mol at environmental temperature.
The Level I
fugacity model is used to calculate the theoretical distribution of MTBE
between four environmental compartments (air, water, soil, sediment) at
equilibrium in a unit world. The model calculates that 93.9% of MTBE
partitions to the atmosphere.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
Welcome to the ECHA website. This site is not fully supported in Internet Explorer 7 (and earlier versions). Please upgrade your Internet Explorer to a newer version.
Do not show this message again