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EC number: 201-535-4
CAS number: 84-51-5
Endogenous Oxygen Depletion
In the OECD guidelines it was stated that the endogenous oxygen
depletion should not exceed 0.6 mg O2/L. In this study the endogenous
oxygen depletion at day 28 is 0.95. To the opinion of the study director
this phenomena does not influence the test results. Also in the update
of the EEC guidelines it is stated that the oxygen depletion should not
exceed 1.5 mg O2/L after 28 days.
The results are mean values of duplicate bottles.
O2 depletion (mg O2/L)
Sampling time (days)
Measured values of the oxygen content in the test bottles, expressed
as mg O2/L
Mineral salt solution+inoculum
The biodegradability of 2-ethylanthraquinone was determined by the
method described in OECD TG 301D, adapted for poorly soluble substances.
A test with the reference compound sodium acetate showed that the
activity of the inoculum was sufficient. The compound
bis(2-ethylhexyl)phthalate (BEF) was used in this study as a reference
compound which is poorly soluble in water, comparable with the
2-ethylanthraquinone and of which the biodegradability is known. The
biodegradability of BEF found in this study (42% in 28 days) is not in
contradiction with literature.
2-ethylanthraquinone was applied coated on silicagel. More than 80% is
degraded within 28 days and it can be concluded that
2-ethylanthraquinone can be classified as biodegradable. In the
guidelines it is stated that a compound may be classified as readily
biodegradable if the level of 60% degradation is reached within 10 days
after the biodegradation reached 10%. According to this criterion the
compounds may not be classified as readily biodegradable. The substance
can therefore be classified as well biodegradable but failing the 10-day
The test substance 2-ethylanthraquinone is regarded to be biodegradable
but failing the 10-day window.
Two studies on the ready biodegradability in water and one study
on the inherent biodegradability in water are available. In the ready
biodegradability study conducted by Thus and van der Laan-Straathof
(1991), the test substance was coated on silicagel. Under these
conditions 81% biodegradation with no lag-phase was observed after 28
days, but the test item failed the 10-day window criterion. Matla and
Blom (1991) performed a Sturm test and reported that
2-ethylanthraquinone was not biodegradable under the test conditions. On
the website of the National Institute of Technology and Evaluation
(NITE), the result of an inherent biodegradation test is published which
indicates that no biodegradation was observed within 2 weeks.
The difference in the results of the biodegradation tests is probably
caused by the way the test compound was applied. Due to the relatively
low water solubility of the test item (0.245 mg/L) the mode of
application is likely to influence the resulting its bioavailability to
Thus and van der Laan-Straathof performed the only study with
application of the test item coated on silicagel, in this way making the
substance in the best possible way available to the microorganisms. This
eventually leads to a fair estimate of the biodegradability of the test
item, and thus to reliable study results.
In contrast, Matla and Blom weighed the powdered compound directly
into the incubation bottles and then added the inoculum (no stirring of
the mixture). As 10 and 20 mg/L test substance was directly applied to
the flasks, i.e. at levels way above the water solubility, only a
fraction of the test item was getting dissolved. As only the dissolved
part of the test item can get subject to biodegradation, and the by far
biggest portion of the test item remained undissolved in the system, the
measured biodegradability is expected to get underestimated by far,
eventually making the study unreliable.
On the NITE website the method of application is not reported,
however it seems appropriate to assume that the test item has directly
been applied (30 mg/L), eventually making the study unreliable for the
same reasons as mentioned above for the Matla and Blom study.
Taking the above considerations into account, the study performed by
Thus and van der Laan-Straathof is regarded as the most reliable one. On
this basis the substance is considered to be biodegradable but failing
the 10-day window.
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