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EC number: 203-911-3
CAS number: 111-82-0
Members of the SCAE Me category are expected to have low bioaccumulation potential.
5.3.1 Aquatic bioaccumulation- SCAE Me category
No experimental data evaluating the bioaccumulation potential of the
SCAE Me category members are available. All substances within the SCAE
Me category have log Kow values above 3, suggesting potential to
bioaccumulate in biota, with the exception of methyl octanoate (CAS No.
106-70-7). The log Kow value estimated for this substance is 2.3 and
therefore, according to Regulation (EC) No. 1907/2006, Annex IX, Column
2, 9.3.2, this substance can be considered to have low bioaccumulation
potential (log Kow ≤ 3). Regarding the rest of the SCAE Me category
members, the information gathered on environmental behaviour and
metabolism in combination with the QSAR-estimated BCF values provide
enough evidence (in accordance to the REACh Regulation (EC) No
1907/2006, Annex XI General rules for adaptation of the standard testing
regime set out in Annexes VII to X, 1.2, to cover the data requirements
of Regulation (EC) No. 1907/2006, Annex IX) to state that these
substances are likely to show low bioaccumulation potential as well.
Intrinsic properties and fate
All substances included in the SCAE Me category are readily
biodegradable. According to the Guidance on information requirements and
chemical safety assessment, Chapter R.7b, readily biodegradable
substances can be expected to undergo rapid and ultimate degradation in
most environments, including biological Sewage Treatment Plants
(STPs)(ECHA, 2008). Therefore, after passing through conventional STPs,
only low concentrations of these substances are likely to be (if at all)
released into the environment.
Once available in the water phase, the estimated log Koc values (< 3,
KOCWIN v2.00) of methyl hexanoate (C6 FA, CAS No. 106-70-7) and methyl
octanoate (C8 FA, CAS No. 111-11-5) indicate low adsorption potential of
these substances to sediment and organic particles, and therefore, they
will be available for uptake by aquatic organisms such as fish mainly
via water. Nevertheless, since the reported log Kow values for these two
substances are 2.3 and 3.3 (CAS No. 106-70-7 and CAS No. 111-11-5), a
low degree of actual bioaccumulation in aquatic organisms can be
expected. According to the Guidance on information requirements and
chemical safety assessment, Chapter R.11, organic substances with a log
Kow value below 4.5 are assumed to not exceed the B criterion (due to an
insufficient affinity for lipids)(ECHA, 2008).
On the other hand, the remaining substances in the SCAE Me category have
log Kow values > 4 and log Koc values > 3. The Guidance on information
requirements and chemical safety assessment, Chapter R7.B (ECHA, 2008)
states that once insoluble chemicals enter a standard STP, they will be
extensively removed in the primary settling tank and fat trap and thus,
only limited amounts will get in contact with activated sludge
organisms. Nevertheless, once this contact takes place, these substances
are expected to be removed from the water column to a significant degree
by adsorption to sewage sludge (Guidance on information requirements and
chemical safety assessment, Chapter R.7a, (ECHA, 2008)) and the rest
will be extensively biodegraded (due to ready biodegradability). Thus,
discharged concentrations of these substances into the aqueous
compartment are likely to be very low. Should the substances be released
into the water phase, due to their hydrophobicity and expected high
adsorption potential, they will tend to bind to sediment and other
particulate organic matter, and therefore, the actual dissolved fraction
available to fish via water will be reduced (Mackay and Fraser, 2000).
Thus, the main route of exposure for aquatic organisms such as fish will
be via food ingestion or contact with suspended solids.
Additional information on the bioaccumulation of SCAE Me in fish species
is available. Estimated bioconcentration (BCF) and bioaccumulation (BAF)
values were calculated for all substances using the BCFBAF v3.01 program
(Estimation Programs Interface Suite™ for Microsoft® Windows v 4.10., US
EPA), including biotransformation rates (Arnot-Gobas method). In the
case of the UVCB substances, the calculations were performed on the main
fatty acid components, as representative structures for each UVCB. All
SCAE Me substances (or at least their main FA components) are within the
applicability domain of the QSAR model (log Kow 0.31-8.70) and
therefore, provide valid supporting information to be considered in the
overall bioaccumulation assessment of these substances.
Within the category, BCF values tend to increase with increasing fatty
acid C-chain lengths from C6 (10 L/kg) up to C14 (201 L/kg), to decrease
again at longer C-chain lengths (C16, 95.6 L/kg and C18, BCF 23.3-29
L/kg), with the exception of the C18 unsaturated fatty acid component,
with a BCF of 117.8 L/kg. On the other hand, BAF values increase as the
fatty acid C-chain length increases, ranging from 10 L/kg (C6) up to 500
L/kg (C18 unsaturated).
The difference in the pattern for BCF and BAF values across the category
can be explained by the exposure route(s) considered for the estimation:
BCF calculations reflect the bioaccumulation potential after uptake via
water, whereas the BAF gives an indication of the bioaccumulation when
all exposure routes (water, food, etc.) are taken into account.
The obtained results indicate that the members of the SCAE Me category
are likely to show low (shorter C-chain lengths) to moderate (longer
C-chain lengths) bioaccumulation potential. According to Regulation (EC)
No. 1907/2006, Annex XIII, 1.1.2, a substance only fulfils the
bioaccumulation criterion (B) when BCF values are > 2000. Even though
this condition is preferred to be confirmed with experimental data, in
this case the estimated QSAR-based BCFs provide sufficient reliable
evidence which suggests that the SCAE Me category members will not be
Biotransformation and metabolism
After lipid content, the degree of biotransformation seems to be the
most relevant factor regarding the bioaccumulation of organic chemicals
in aquatic organisms (Katagi, 2010). Biotransformation consists in the
conversion of a specific substance into another/others (metabolites) by
means of enzyme-catalyzed processes (ed. van Leeuwen and Hermens, 1995).
Carboxylesterases are a group of ubiquitous and low substrate specific
enzymes, involved in the metabolism of ester compounds in both
vertebrate and invertebrate species, including fish (Leinweber, 1987;
Barron et al., 1999). Fatty acid methyl esters are hydrolysed to the
corresponding alcohol (methanol) and fatty acid by esterases (Fukami and
Yokoi, 2012). Particularly in fish rapid metabolism rates of two methyl
esters (haloxyfop methyl ester and fluroxypyr methylheptyl ester) have
been observed in vitro (fish liver homogenates) with half-lives of 5 and
1 minute respectively (Murphy and Lutenske, 1990; Cowan-Elsberry et al.,
2008). Furthermore, in vivo studies conducted with esters, including a
methyl ester (according to OECD 305) resulted in experimental fish BCFs
ranging from 1 to 70, even when the log Kow values of these substances
are above 3, indicating once again rapid metabolism (Rodger and
Stalling, 1972; Barron et al., 1989; Barron et al., 1990).
According to the Guidance on information requirements and chemical
safety assessment, Chapter R.7c (ECHA, 2008), even though ready
biodegradability does not per se preclude bioaccumulation potential,
generally (depending on exposure and uptake rates) ready biodegradable
substances are likely to be rapidly metabolised, and therefore,
concentrations stored in aquatic organisms will tend to be low.
Regarding the biotransformation products of SCAE Me(s), methanol will
partially tend to evaporate from water surfaces (Henry's Law Constant of
4.55x10-6 atm m3/mole (Gaffney et al., 1987)) or stay in the water phase
(low adsorption potential to sediment and organic particles according to
a Koc of 2.75 (Schuurmann et al, 2006)), in which rapid biodegradation
is expected to occur (92% biodegradation in 14 days; NITE, Japan, 2012).
Therefore, its bioavailability to aquatic organisms will be generally
Methanol is a naturally occurring compound in living organisms. It is
known to be metabolised and further excreted in the form of CO2 and H2O
in several species such as mammals. The log Kow value of this substance
(-0.77, Hansch et al., 1995) indicates that bioaccumulation in biota is
not expected. In fish (Leuciscus idus), this was confirmed by a
test in which a measured BCF < 10 was obtained for methanol (Freitag et
On the other hand, fatty acids are naturally occurring components in
living organisms (mammals, aquatic organisms, earthworms, plants, etc.),
which are known to be metabolised quickly and participate in ubiquitous
standard physiological processes (e. g. citric acid cycle, sugar
synthesis and lipid synthesis)(Hochachka et al., 1977; Jump, 2002). In
fish species, fatty acids are the most important energy source resulting
in the release of acetyl CoA and NADH (through β-oxidation) and
eventually, via the tricarboxylic cycle, the production of metabolic
energy in the form of ATP. This fatty acid-catabolism pathway is the
predominant source of energy related to growth, reproduction and
development from egg to adult fish (Tocher, 2003). A similar metabolic
pathway is observed in mammals (see section 7.1.1 Basic toxicokinetics).
The substances included in the SCAE Me category are not expected to be
bioaccumulative. Due to their readily biodegradable nature, extensive
degradation of these substances in conventional STPs will take place and
only low concentrations are expected to be released (if at all) into the
environment. Once present in the aquatic compartment, further
biodegradation will occur and, depending on their log Kow, water
solubility and adsorption potential, the SCAE Me(s) will be bioavailable
to aquatic organisms such as fish mainly via water or on the other hand
via feed and contact with suspended organic particles. After uptake by
fish species, extensive and fast biotransformation of the SCAE Me(s) by
carboxylesterases into fatty acids and methanol is expected. Fatty acids
will be further used by these organisms as their main source of energy
throughout all the different life stages (early development, growth,
reproduction,etc.). Rapid metabolism of analogue ester compounds
(involving hydrolysis into fatty acids and methanol) in fish has been
observed in vitro, with half-lives in fish liver homogenates below 6
minutes. In vivo fish tests reported BCF values ranging from 1 to 70 for
similar ester substances, supporting the argument that rapid metabolism
takes place even when log Kow values are above the trigger value of 3.
The supporting BCF/BAF values estimated with the BCFBAF v3.01 program
also indicate that these substances will not be bioaccumulative (all
well below 2000).
The information above provides strong evidence supporting the statement
that rapid metabolism and low bioaccumulation potential can be expected
for the members of the SCAE Me category (detailed information on the
results of a more extensive literature search can be found as an
A detailed reference list is provided in the technical dossier (see
IUCLID, section 13) and within CSR.
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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