Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

The Alkyl Polyglycosides Category contains D-Glucopyranose monomers and oligomers with fatty alcohols C4 to C18 linear or in several cases (C9 to C11) mono-branched. Structural similarities of the category substances are reflected in similar physico-chemical properties and mode of action. Alkyl polyglycosides have a common metabolic fate that involves hydrolysis of the α- and β-glycosidic bond to the fatty alcohol and glucose. Glucose and glucose oligomers enter the carbohydrate metabolic pathway and are catabolised into pyruvate and subsequently to the major extent into acetyl-CoA, which is introduced into the citric acid cycle with the aim to generate reduction equivalents for energy generation in the oxidative phosphorylation. Fatty alcohols, representing the main difference in the structure of different alkyl polyglycosides, are oxidized to the corresponding fatty acid and fed into the physiological pathway of β-oxidation, where they are also oxidised to acetyl-CoA. In addition to its function in the generation of energy by catabolic processes acetyl-CoA can also be used in anabolic processes like lipid synthesis which is important for the storage of energy in form of large high-energy macromolecules.

In accordance with Article 13 (1) of Regulation (EC) No 1907/2006, "information on intrinsic properties of substances may be generated by means other than tests, provided that the conditions set out in Annex XI are met. In particular for human toxicity, environmental fate and eco-toxicity, information shall be generated whenever possible by means other than vertebrate animal tests, which includes the use of information from structurally related substances (grouping or read-across)”.

Therefore, the available experimental data were collected and evaluated according to Annex XI in regard to:

-             Test duration (only tests which cover the expected exposure duration were regarded as suitable)

-             Key parameters of the test (only tests that cover the key parameters were accepted as suitable)

-             Comparability of the test systems

-             The adequacy of the results for C&L

-             The documentation of the test procedures (only in case of good documentation data)

Only data that were judged to cover the requirements specified above were used as adequate data suitable for the category and its members.

In this particular case the similarity of the Alkyl Polyglycosides Category members is justified, in accordance with the specifications listed in Regulation (EC) No 1907/2006 Annex XI, 1.5 Grouping of substances and read across, on basis of scope of variability and overlapping of composition, representative molecular structure, physico-chemical properties, toxicological, ecotoxicological profiles, and supported by various QSAR methods. There is no convincing evidence that any one of these respective chemicals might lie out of the overall profile of this category. The key points that the members share are:

(i)              Common origin: produced from fatty alcohols, reacting with D-glucose in the presence of an acid catalyst.

(ii)             Similar structural features: aliphatic hydrocarbon chain bound to glucose oligomers by alpha or beta glycosidic bond.

(iii)            Similar physico-chemical properties: trend in log Pow based on alkyl chain length and degree of glycosylation; low vapour pressure; water solubility decreasing with the alkyl chain length, starting from very high and high values up to insoluble C16-18; surface active substances fully dissociated in water (exception: C16-18).

(iv)           Common properties for environmental fate & eco-toxicological profile: readily biodegradable, no potential for bioaccumulation, low to moderate adsorption potential, clear trend in aquatic toxicity (increasing toxicity with increasing carbon chain with a maximum at C12-16 and then decreasing), no potential for sediment and soil toxicity.

(v)            Similar metabolic pathways: absorption in the intestine, hydrolysis of theα- andβ-glycosidic bond in intestine and further metabolism of the breakdown products sugar and alcohol. Alkyl polyglycosides withα-glycosidic bond may already be hydrolysed in the saliva by enzymatic activity ofα-amylases.

(vi)          Common levels and mode of human health related effects: The skin and eye irritating properties of the alkyl polyglycosides represent the main factor for effects on human health. The similar toxicokinetic behaviour (hydrolysis of theα- andβ-glycosidic bonds) results in similar cleavage products, which show a low toxicity after acute and repeated oral exposure. Furthermore, all category members are not sensitising, not mutagenic or clastogenic, and have shown no reproduction and developmental toxicity.

 

Similar environmental fate and pathway

The substances of the alkyl polyglycosides category are all readily biodegradable according to OECD criteria, hence they will not be persistent in the environment. In accordance with the Regulation (EC) No 1907/2006, Annex VIII, column 2, studies on the abiotic degradation through hydrolysis do not need to be conducted, since the member substances of the category are readily biodegradable and thus expected to be eliminated through rapid biodegradation in natural environments. Nonetheless, one experimental study is available for the category member D-Glucopyranose, oligomeric, C10-16-alkyl glycosides (CAS 110615-47-9), which was shown to be stable to hydrolysis under environmental conditions.

A potential for bioaccumulation is low as the partition coefficient values (log Pow) are mostly below 3. For substances with log Pow values above 3 (like D-Glucopyranose, oligomeric, C10-16-alkyl glycosides (CAS 110615-47-9) and D-Glucose, reaction products with alcohols C16-18 (even numbered) (excess)), a potential for bioaccumulation in aquatic and terrestrial species could be assumed. However, it is not probable as the substances are readily biodegradable and expected to be rapidly metabolised and eliminated.

Alkyl polyglycosides demonstrate a low to moderate adsorption potential. Most of the category members exhibit a low log Koc ranging from -2.207 to 2.98. It is assumed that these substances will mainly distribute into the water compartment. Reaction products of D-Glucose, n-Butanol and alcohols C10-12 (even numbered), D-Glucopyranose, oligomers, undecyl glycosides and D-Glucose, reaction products with alcohols C16-18 (even numbered) (excess), show a low to high sorption potential based on their log Koc ranging from -2.207 – 3.24, 2.01 – 3.95 and 0.67 and 4.78, respectively. For these substances a partial partitioning to sediment and soil is expected as well as a higher potential of sorption to sewage sludge. However, as all category members of the alkyl polyglycosides are readily biodegradable, they will be eliminated during sewage treatment and are expected to be degraded rapidly in case of reaching the environment.

Abiotic degradation

Abiotic degradation of alkyl polyglycosides via hydrolysis is not a common environmental pathway, due to the chemical structure of the substances. Besides, the testing is not required as the substances are readily biodegradable and thus expected to be eliminated through biodegradation in natural waters. However, one study is available for D-Glucopyranose, oligomeric, C10-16-alkyl glycosides, conducted according to OECD 111. No hydrolysis of the substance could be observed after 5 days incubation at 50 °C. Recovery rate after 5 days was approximately 100% at pH 4, 7 and 9. Thus, the substance can be considered to be hydrolytically stable, which is also assumed for the other category members.

Indirect photolysis is not expected, since all substances are not likely to be present in the atmosphere, due to their low vapour pressure (<1 Pa).

Biodegradation

Ready biodegradability studies are available for all alkyl polyglycosides. Based on the results of screening tests for biodegradation all alkyl polyglycosides are readily biodegradable according to OECD criteria (66 - 114% biodegradation after 28 days), and thus are expected to be rapidly degraded by microorganisms both in aquatic and terrestrial environments. Therefore, in accordance with Regulation (EC) No 1907/2006, Annex IX, Column 2, 9.2.1.2 – 9.2.1.4, further simulation testing for water and sediment or soil biodegradation testing is not required.

Bioaccumulation

Experimental bioaccumulation data are not available for the members of the alkyl polyglycosides category. However, log Pow values (measured, calculated or estimated) as indicators for the bioaccumulation potential are available for all substances and are mostly below 3. Hence, a bioaccumulation potential for these substances can be excluded. Two category member substances, D-Glucopyranose, oligomeric, C10-16-alkyl glycosides (CAS 110615-47-9) and D-Glucose, reaction products with alcohols C16-18 (even numbered) (excess) possess higher log Pow values of 3.88 and 7.72 (worst case assumption of all constituents), respectively. Nevertheless, a potential for bioaccumulation in aquatic and terrestrial species is not anticipated as the substances are readily biodegradable as well as able to be metabolized and therefore expected to be rapidly eliminated.

Alkyl polyglycosides are predicted to be bioavailable via the oral route. They will undergo stepwise hydrolysis into glucose and fatty alcohol, which is further oxidized to the corresponding fatty acid. In the processes of glycolysis and β-oxidation glucose and fatty acids, respectively, are oxidized into acetyl-CoA, which can be incorporated in both the catabolic citric acid cycle and the anabolic pathway of lipid synthesis. Excretion of non-hydrolysed alkyl polyglycosides is assumed to occur mainly via renal elimination, and tissue accumulation can be excluded.

No experimental studies investigating the bioconcentration factors of APGs are available. Generally, it is expected that bioconcentration factors of APGs in the aqueous phase will be due to rapid biodegradation, metabolic processes and low log Pow values, below the level of concern. QSAR calculations of the bioconcentration factors (BCF) of 3 main constituents of D-Glucopyranose, oligomeric, undecyl glycoside are available and resulted to values ranging between 0.8931 and 10.18 L/Kg (BCFBAF v3.01, EPI Suite). These low BCF values (below 2000) predicted for D-Glucopyranose, oligomeric, undecyl glycoside, indicate a low potential for bioaccumulation, encouraging the above described assumption for the APG category.

Adsorption (Log Koc)

Experimental soil or sediment sorption data (Koc values) are available only for one category member (D-Glucopyranose, oligomeric, C10-16-alkyl glycosides (CAS 110615-47-9)) with a resulting log Koc of 1.7 (OECD 121). Additionally, the Koc values for all category members were calculated with KOCWIN v2.00 (estimated based on log Kow and MCI method) using smile notations. Data show a clear trend of increasing adsorption coefficient values with increasing carbon chain length. The determined log Koc values are in a range of -2.207 (D-Glucopyranose, oligomeric, butyl glycoside) to 4.78 (D-Glucose, reaction products with alcohols C16-18 (even numbered) (excess)). Thus, the adsorption potential of alkyl polyglycosides to soil or sediment will be low to moderate, depending on the carbon chain length.

Substances with log Koc values <3 are expected to distribute mainly into the aquatic compartment, in which they will rapidly biodegrade. In contrast, members of the category with log Koc values >3 will mainly target soil and sediment. However, due to their ready biodegradability, they will not persist in the environment.

Table 1: Environmental fate and pathways (*)

ID No.

Substance

CAS No.

Biodegradability

Adsorption/Desorption [log Koc]

# 1

D-Glucopyranose, oligomeric, butyl glycoside

-

ER:

readily biodegradable 114% (28d)

QSAR: -2.207 to 1.15

# 2

D-Glucopyranose, oligomers, hexyl glycosides

-

ER:

readily biodegradable 71% (28d)

QSAR: 0.7 to 1.7

# 3

D-Glucopyranose, oligomeric, heptyl glycoside

1627851-18-6

ER:

readily biodegradable 82.25% (28d)

QSAR: -0.8 to 1.0

# 4

D-Glucopyranose, oligomers, undecyl glycosides

-

ER:

readily biodegradable 85% (28 d)

QSAR: 2.01 to 3.95

# 5

D-Glucopyranose, oligomers, decyl octyl glycosides

68515-73-1

ER:

readily biodegradable 70% (28d)

RA from D-Glucopyranose, oligomeric, C10-16-alkyl glycosides: 1.7

# 6

D-Glucopyranose, oligomers, branched and linear C9-11-alkyl glycosides

157707-87-4

ER:

readily biodegradable 66.9% (28d)

QSAR: -0.31 to 2.98

# 7

Reaction products of D-Glucose, n-Butanol and alcohols C10-12 (even numbered)

-

ER:

readily biodegradable 70-80% (28d)

QSAR: -2.207 to 3.24

# 8

D-Glucopyranose, oligomeric, C10-16-alkyl glycosides

110615-47-9

ER:

readily biodegradable 88% (28d)

ER: 1.7

# 9

D-Glucose, reaction products with alcohols C16-18 (even numbered) (excess)

-

ER:

readily biodegradable 66% (28d)

QSAR: 0.67 to 4.78

# 10

Hexadecan-1-ol (a)

36653-82-4

ER:

readily biodegradable

--

# 11

Octadecan-1-ol (a)

112-92-5

ER:

readily biodegradable

--

 

(*) substances #2, #5 and #8 were registered in 2010, substances #1, #6, #7 and #9 (bold font) were registered in 2013; substance #3 and #4 (bold italics font) are registered or scheduled for registration under Regulation (EC) No 1907/2006 (REACH) in 2014-2016.

(a)Surrogate substances: fatty alcohols. Available data on these substances are used for assessment of environmental properties by read-across on the basis of structural similarity and/or mechanistic reasoning. They are no members of the Alkyl Polyglycosides Category.

D-Glucopyranose, oligomeric, undecyl glycoside has a water solubility of > 1000 g/L, log Koc between 2.01 and 3.95 and a vapour pressure < 0.0000000037. Therefore, the substance will target water as well as partly sediment and soil. However, D-Glucopyranose, oligomeric, undecyl glycoside is readily biodegradable and is therefore not expected to be persistent in the environment. Furthermore, a low potential for bioaccumulation in aquatic and terrestrial species is assumed based on the low log Kow of 2.4, BCFs predicted (0.8931 – 10.18 L/kg), and elimination through common metabolic pathways (for more detail see section toxicokinetics).