Reaction mass of 2-methyldecan-1-al and undecanal

Ecotoxicological Summary

Additional information

Justification of Read Across

According to the general information provided in section 1.2 (composition), the substance n-/iso undecanal represents a mixture of the linear n-undecanal and the branched isomer, 2-methyl-decanal. The purity is >92%. The relative proportion of these two isomers may vary as described in section 1.2:

Isomer (name, synonyms)	CAS- No.	Concentration range
n-undecanal undecanal undecan-1-al	112-44-7	≥59 -≤70 %
Iso-undecanal 2-methyldecanal 2-methyldecan-1-al	19009-56-4	≥25 -≤36 %

 

Studies are not only available on the substance n-/iso undecanal as defined above, but also on closely related substances, namely

1. n-undecanal itself,
2. iso-undecanal itself, and
3. n-/iso undecanal with relative proportions of the isomers that differ from the specification tabulated above.

Results from studies on these test substances may be read across to the registered n-/iso undecanal for the following reasons.

Structure and physico-chemical data

The sole structural difference between the two isomers is that one has a linear carbon chain whereas the iso-form bears a 2-methyl group. Hence, the molecular weights are identical and the physico-chemical properties are very similar. The chemical reactivity is determined by the aldehyde group that is present in both isomers, i.e. there is no difference in this respect.

Predicted ecotoxicological data

Ecological categorization results from the Canadian Domestic Substance List are available at OECD. The data are accessible via eChemportal (link below). Search for the respective CAS-number gives a number of hits. The results of the Canadian Domestic Substance List are directly accessible (link in the line of the source: CCR).

Link: http://www.echemportal.org/echemportal/index?pageID=0&request_locale=en

 

The data below represent an extract of the Canadian results for both the n- and the iso- undecanal. As can be seen from the table below, there is virtually no difference between the isomers regarding fate, bioaccumulation, and aquatic toxicity.

 

	n-undecanal	2-methyl-Decanal
CAS #	112-44-7	19009-56-4
Categorisation results
Meets Human Health Categorization Criteria?	No	No
Persistent (P)? Rational for P	No QSAR	No QSAR
Bioaccumulative (B)? Rational for B	No QSAR	No QSAR
Inherently Toxic to Aquatic Organisms (iT)? Rational for iT	Yes QSAR	Yes QSAR
Ecological data supporting decisions
1.    Persistence
Predicted Ultimate degradation half-life (days)	15	15
MITI probability of biodegradation	0.9858	0.9644
TOPKAT probability of biodegradation	1	1
EPI Predicted Atmospheric Oxidation half-life (days)	0.298	0.2976
Bioaccumulation
Log Kow predicted by KowWin	4.25	4.18
Log BCF predicted by BCFWIN	1.576	1.519
Inherent toxicity to aquatic organisms
Pivotal value for iT (mg/l)	0.0448	0.0601
Toxicity to fathead minnow (LC50 in mg/l) as predicted by Topkat v6.1	0.0448	0.0601
Toxicity to fish (LC50 in mg/l) as predicted by Oasis Forecast M v1.10	0.9364	1.916361
Toxicity to fish, daphnia, algae or mysid shrimp (EC50 or LC50 in mg/l) as predicted by Ecosar v0.99g	0.863	0.995
Toxicity to fish (LC50 in mg/l) as predicted by Neutral Organics QSAR in Ecosar v0.99g	0.00969	0.0113

 

Toxicology

The general toxicological profile of saturated aliphatic aldehydes is outlined below. Details can be found in toxicology textbooks [e.g. Eisenbrand G and Metzler M (2002) Toxikologie. WILEY-VCH, 2nd edition].

Acute local effects:the primary effect from inhalation of, or direct contact with, any aldehyde by humans is irritation of the eyes, skin, and respiratory tract. This general finding is attributable to the aldehyde functional group, hence there is no difference between aldehydes in general or n- and iso-undecanal in particular.

Sensitisation:Aldehydes may covalently bind to nucleophiles present in proteins, leading to Schiff bases which are known to be involved in the process of chemical sensitisation. Again, there is no difference between aldehydes in general or n- and iso-undecanal in particular. Appropriate testing is required to determine whether a substance is a weak or strong sensitiser, or whether it lacks sensitising properties. As data on both main constituents of the registered substance are available, those results can be used to assess the sensitization potential of n-/iso-Undecanal.

Metabolism:following absorption, aldehydes may also covalently bind to nucleophiles. The vast majority is, however, expected to be distributed, followed by the enzymatic oxidation catalyzed by aldehyde dehydrogenases to the respective organic acid. Undecanoic acid and 2-methyldecanoic acid then be utilized by degradation in the fatty acid cycle. Alternatively, organic acids may combine with UDP-glucuronic acid to form ester-type glucuronides which are then excreted via urine.

The first step in the fatty acid cycle is the oxidation of the ß-carbon. ß-oxidation requires that the ß-carbon is not substituted. This is the case with both undecanoic acid and 2-methyldecanoic, i.e. it is expected that both acids are easily degraded in the fatty acid cycle. Thus, the two acids behave similarly with respect to utilization in the fatty acid cycle and the excretion as the glucuronide in the urine.

 

Conclusions:

Data on n-undecanal and 2-methyldecanal may be read across because the physico-chemical properties, the environmental fate, the ecotoxicological properties and human health effects including ADME (absorption, distribution, metabolism, excretion) of the two aldehydes are comparable to each other.

Additionally, this finding allows read across results that were obtained with mixtures that contain the two aldehydes in proportions that do not meet the concentration specifications of the registered substance.