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EC number: 216-653-1
CAS number: 1634-04-4
There is a complete set of data available for
MTBE, including short-term tests on fish, invertebrates and algae
together with some long-term studies.
There are several acute and chronic guideline
studies available for freshwater and marine fish. For freshwater fish
the most critical effect concentration was a 96-h LC50 value of 672 mg/l
in fathead minnow (Pimephales promelas) (Geiger et al., 1988).
For marine fish the most critical effect concentration was a 96-h LC50
of 574 mg/l in inland silverside (Menidia beryllina) (BenKinney
et al., 1994).
One chronic guideline test is available, an
ELS test with eggs and larvae/fry from fathead minnow (Pimephales
promelas). The 31-d NOEC is 299 mg/l (ENSR, 1999b). A non-guideline
study by Moreels et al. (2000a) on an ELS with eggs from the African
catfish (Clarias gariepinus) is not deemed reliable or relevant
for hazard or risk assessment purposes due to some major deficiencies in
the study. In particular, average exposure concentrations have been
A fish sexual development toxicity assay in
accordance with the OECD 234 guideline is also underway the results of
which will be included in the dossier when available.
Two reliable short term reproduction assays
are available on the toxicity of the test substance to zebrafish (Danio
rerio) and the fathead minnow (Pimephales promelas). Both
studies were performed under GLP conditions and in accordance with test
guidelines OECD 229 and U.S. EPA OPPTS 890.1350.
The purpose of the studies was to investigate
the potential for MTBE to interact with the endocrine system in fish.
For the first study (Wildlife InternationalLtd, 2012) an exceptionally
high exposure concentration of 147 mg/L was included in the study so
that a comparison could be made with a study reported in the literature
by Moreels et al. (2006b). Under usual circumstances, testing according
to OECD 229 and U.S. EPA OPPTS 890.1350 guidelines would not include
such high exposure concentrations.
In zebrafish (Wildlife International Ltd,
2012), a reduction in fecundity was accompanied by a significant
increase in the incidence of oocyte atresia along with a significant
increase in the accumulation of oocyte debris in the oviduct at 147
mg/L; consequently the NOEC for reproduction was determined to be 3.04
mg/L, the next exposure concentration tested. In fathead minnows a NOEC
for reproduction was determined to be 62 mg/L, the highest exposure
The fish endocrine screening studies are
intended to be used for qualitative risk assessment purposes, such as to
determine potential for endocrine interaction and further testing. As
the OECD Fish Toxicity Framework (OECD, 2012) considers that dose
spacing greater than a factor of around 3 should be considered for
qualitative rather than quantitative risk assessment purposes, the NOEC
for fish is considered as 62 mg/L rather than 3.04 mg/L. Considering the
NOEC of 3.04 as not sufficiently precise an indication of toxicity to
fish be relevant for quantitative risk assessment purposes is further
supported by the next exposure concentration of 147 mg/L greatly
exceeding the max. concentration for testing under the OECD 229
guideline of 10 mg/L. The U.S. EPA considers its corresponding OPPTS
890.1350 guideline with a max. concentration for testing of 100 mg/L as
not intended to provide quantitative risk assessment data (U.S. EPA,
There are several acute and chronic guideline
studies available for aquatic invertebrates. For freshwater
invertebrates the most critical effect concentration was a 48-h EC50
value of 472 mg/l inDaphnia magna(Wildlife International Ltd.,
1999c). Results from several studies indicate that the mysid shrimp is
the most sensitive marine species (BenKinney et al., 1994; T. R. Wilbury
Laboratories, Inc., 1994; Rausina et al., 2002), but the results from
the different studies with the mysid shrimp are inconsistent (LC50
values in a range 44 – 200 mg/l). Because no technical reason is
apparent to explain these differences, and since results from the three
studies are less than one order of magnitude apart, the results were
harmonised by a geometric mean. The resultant 96-h LC50 of 106 mg/l for
mysid shrimp (Americamysis bahia) will be used in the assessment.
Two chronic tests are available, for both freshwater and marine species.
The 21-d NOEC in Daphnia magna is 51 mg/l (Wildlife International
Ltd., 1999g) and the 28-d NOEC in mysid shrimp (Americamysis bahia)
is 26 mg/l (Wildlife International Ltd., 1999h).
The test results on algae differ considerably
from each other. The most critical effect concentrations are an IC50 of
491 and an IC20 of 103 mg/l for Pseudokirchnerialla subcapitata (ENSR,
Two studies on the toxicity of MTBE to
micro-organisms have been reported. Both have been performed with Pseudomonas
putida, but they differ in duration and methodology. The most
critical value is an 18-h cell multiplication inhibition EC10 value 710
mg/l (Hüls AG, 1991d).
Studies with sediment and terrestrial
organisms are not available for MTBE. However since it has a low log Kow
(1.06) and relatively high vapor pressure (330 hPa at 25 ˚C), it is
expected that MTBE will partition to the air compartment to a
significant extent. Therefore, direct and indirect exposure of soil and
sediment is not expected as was demonstrated in the exposure assessment.
Data are not available to assess the toxicity
of MTBE to birds. However, there is a large mammalian dataset available
(see Section 5) that indicates MTBE poses a low level of hazard, and as
its log Kow is low (1.06), it
is not expected to bioconcentrate to any significant extent or
accumulate in biota. An assessment of secondary poisoning is therefore
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.
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