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Biodegradation in water - screening tests

For the assessment of the biodegradability of MDIPA-Esterquat C16-18 and C18 unsatd. 3 studies are available, two studies according to OECD guideline 301 B, and one study according to OECD guideline 301 F.

 

In both studies according to OECD Guideline 301 B MDIPA-Esterquat C16-18 and C18 unsatd. was readily biodegradable, but did not fulfil the 10-day window criterion.

Although the 10-day window criterion is not fulfilled, the test substance can be regarded as readily biodegradable as it is a UVCB substance representing a complex multi-constituent substance with structurally similar constituents:

1.according to the REACH Guidance on information requirements and chemical safety assessment, Chapter R.7b: Endpoint specific guidance “These pass levels have to be reached in a 10-day window within the 28-day period of the test. The 10-day window does not apply to TG 301 C or if the test substance represents a mixture of homologous compounds e.g. technical surfactants."

2. according to CLP 7th ATP, 4.1.2.9.5.: "These levels of biodegradation must be achieved within 10 days of the start of degradation which point is taken as the time when 10 % of the substance has been degraded, unless the substance is identified as an UVCB or as a complex, multi-constituent substance with structurally similar constituents. In this case, and where there is sufficient justification, the 10-day window condition may be waived and the pass level applied at 28 days."

 

In the biodegradation study according to OECD guideline 301 F MDIPA-Esterquat C16-18 and C18 unsatd. was readily biodegradable and fulfilled the 10-day window criterion.

 

The closely related source substance MDEA-Esterquat C16-18 and C18 unsatd. proved to be readily biodegradable (>60% biodegradation after 28 d) in a study conducted in accordance with the OECD Guideline 301 B..

 

Biodegradation in water (simulation tests)

According to Annex IX 9.2.1.2. and 9.2.1.4 Column 2, a study on biodegradation in water and sediment does not need to be conducted as the substance is readily biodegradable.

 

Nevertheless, data on biodegradation in water are available with the closely related source substance MDEA Esterquat C16 -18 and C18 unsatd., showing biodegradation under environmental conditions (details are given in the respective sections).

 

Biodegradation in soil

According to Annex IX 9.2.1.3. Column 2, a study on biodegradation in soil does not need to be conducted as the substance is readily biodegradable.

 

Justification for read-across

Hypothesis for the analogue approach

This read-across is based on the hypothesis that source and target substances have similar ecotoxicological properties because they share structural similarities with common functional groups: quaternary amines, esters, and fatty acid chains with comparable length and degree of saturation. Furthermore, they are expected to hydrolyse to a comparable product (amine backbone) and common products (long chain fatty acids). This prediction is supported by biodegradation data on the substances themselves.

 

1. Substance Identity

The target substance MDIPA-Esterquat C16-18 and C18 unsatd. is a UVCB substance composed of diesters of mainly saturated C16 and C18 fatty acids with MDIPA (Methyldiisopropanol amine) as amine backbone.

The source substance MDEA-Esterquat C16-18 and C18 unsatd. is a UVCB substance composed of diesters of mainly saturated C16 and C18 fatty acids with MDEA (Methyldiethanol amine) as amine backbone (Table 1, Figure 1).

In the target and source substances, the amine function is further methylated resulting in a quaternary amine.

 

Table 1: Substance identities

 

Source substance

Target substance

MDEA-Esterquat C16-18 and C18 unsatd.

MDIPA-Esterquat C16-18 and C18 unsatd.

CAS number

1079184-43-2

NA

EC number

620-174-7

941-174-6

Chain length distribution

<C16: <7%

C16, 16‘, 17: 26-35%

C18: 42-52%

C18‘: 15-20%

C18‘‘, 18‘‘‘: </= 1.5%

>C18: </= 2%

< C16: <= 6%

C16 - < C18: 20-65%

C18: 4-60%

C18 unsatd.: 10-43%

> C18: <= 5%

Amine

MDEA

MDIPA

Anion

Chloride

Methyl sulphate

 

Figure 1: Structures of source substance (MDEA-Esterquat C16-18 and C18 unsatd.) and target substance (MDIPA-Esterquat C16-18 and C18 unsatd.), see attachment

 

2. Analogue approach justification

The read-across hypothesis is based on structural similarity of the target and the source substance as well as on similar physico-chemical properties and similar results in the available biodegradation screening tests.

The respective reliable data (RL 1 or 2) are summarised in the table below; robust study summaries are included in the Technical Dossier in the respective sections.

Ecotoxicological data are summarised in the data matrix.

 

2.1 Structural similarity

a. Structural similarity and functional groups

The target substance, MDIPA-Esterquat C16-18 and C18 unsatd., consists of an amine backbone (MDIPA = Methyldiisopropanolamine) esterified with long chain fatty acids C16, C18 and C18 unsaturated. The main reaction product is the dialkylester compound, besides that, small amounts of the monoalkylester may also be formed. The amine function is quaternised with two methyl groups. The counter ion is Methosulfate.

 

The source substance, MDEA-Esterquat C16-18 and C18 unsatd., consists of an amine backbone (MDEA = Methyldiethanolamine) esterified with long chain fatty acids C16, C18 and C18 unsaturated. The main reaction product is the dialkylester compound, besides that, small amounts of the monoalkylester may also be formed. The amine function is quaternised with two methyl groups. The counter ion is Chloride.

 

The source and the target substances share structural similarities with common functional groups (quaternary amines), esters, and fatty acid chains with comparable length and degree of saturation. The amine backbones based on MDEA and MDIPA, respectively, differ only by one methyl group in each chain. All functional groups are identical.

 

b. Common breakdown products

The ester bonds can be potentially hydrolysed, which would result in free fatty acids and Dimethyl-DEA (DEA = Diethanolamine) and Dimethyl-DIPA (DIPA = Diisopropanolamine), respectively. The fatty acids are expected to enter normal metabolic pathways and are therefore indistinguishable from fatty acids from other (natural) sources.

 

c. Differences

Chloride is an essential ion present in all organisms; excess chloride is excreted (see common textbooks on biology / biochemistry). Methyl sulphate is metabolised to Sulphate and Carbon dioxide, and these are excreted via the urine and released by the lungs, respectively. The anions Chloride and Methyl sulphate are not expected to have any influence on toxicity or reactivity.

The methyl side chain of Dimethyl-DIPA, which is not present in Dimethyl-DEA, is not expected to enhance reactivity, which is supported by a similar ecotoxicological profile of the source and the target substance.

 

3. Physicochemical properties, environmental fate

Table 2: Physicochemical properties and environmental fate

Endpoints

Source substance

Target substance

MDEA-Esterquat C16-18 and C18 unsatd.

 

MDIPA-Esterquat C16-18 and C18 unsatd.

 

Molecular weight

697 g/mol


ca. 761 g/mol


Physical state at 20°C / 1013 hPa

solid (waxy)


solid (waxy)


Melting point

OECD Guideline 102; RL1; GLP

54°C

OECD Guideline 102; RL1; GLP

36°C

Boiling point

OECD Guideline 103; RL1; GLP

No boiling point up to 250°C

OECD Guideline 103; RL1; GLP

Decomposition at > 250°C

 

Surface tension

OECD Guideline 115; RL2, GLP

68.3 mN/m - not in line with the expected surface active behaviour of the substance

OECD Guideline 115; RL2, GLP

 

72 mN/m

at 20°C - not in line with the expected surface active behaviour of the substance

Water solubility

ASTM International E 1148 – 02, GLP, RL1

17.6 mg/L at 19.7°C

 

ASTM International E 1148 – 02; RL1, GLP

 

1.01 mg/L at 20°C

ASTM International E 1148 – 02, RL1; ISO17025

 

7.4 mg/L at 20±0.3°C

ASTM International E 1148 – 02, RL1; ISO17025

 

1.9 mg/L at 20±0.3°C

Log Kow

Determination technically not feasible due to the surface-active properties;read-across from DODMAC

 

3.8

Calculation based on Koc

 

 

 

4.43

Vapour pressure

Measurement is technically not feasible due to the substance properties; estimation

7.33E-18 Pa at 25°C

OECD Guideline 104, GLP; RL1

 

 

< 8.4E-07 Pa at 20°C

Biodegradation

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test), RL 2, GLP

 

readily biodegradable

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test) / OECD Guideline 301 F (Manometric Respirometry Test), RL 1, GLP

 

readily biodegradable

Biodegradation in water and sediment: simulation tests

OECD Guideline 303A, RL2; GLP

 

water: >99% removal on average during the 3 weeks removal period

No data, read-across

Draft OECD Guideline 314 (Simulation tests to assess the biodegradability of chemicals discharged in wastewate), RL2; no GLP

 

half life for mineralization: 18 – 24 hr

Hydrolysis as function of pH

No data (readily biodegradable)

OECD guideline 111; RL1, GLP

 

pH4:

t½= > 30 days at 20°C

t½= 53 days at 25°C

t½= 4.5 days at 50°C

t½= 1.8 days at 60°C

pH7:

t½= > 30 days at 20°C

t½= 25 days at 25°C

t½= 3.4 days at 50°C

t½= 1.7 days at 60°C

pH9:

t½= 84 days at 20°C

t½= 49 days at 25°C

t½= 4.2 days at 50°C

t½= 1.9 days at 60°C

 

Adsorption / Desorption

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method); RL 1, GLP

 

for sludges: log Koc = 2.92

for soils: log Koc = 5.69

total: log Koc = 4.30

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method); RL 1, GLP

 

for sludges: log Koc = 1.90,

for soils: log Koc = 4.89,

total: log Koc = 3.69

 

The molecular weights of the target and source substances are in a comparable range. Both substances are waxy solids with slightly different melting points (54°C vs. 36°C) which most probably results from minor structural differences (the methyl side chain of the Dimethyl-DIPA headgroup in the target substance, which is not present in the Dimethyl-DEA head-group in the source substance).

Experimental data on log Kow are not available for the source substance MDEA-Esterquat C16-18 and C18 unsatd. A read-across approach from the structurally similar substance DODMAC (Dimethyldioctadecyl ammonium chloride) was applied, resulting in a log Kow of 3.8. For the target substance MDIPA-Esterquat C16-18 and C18 unsatd. the log Kow of 4.43 was calculated based on the available Koc (organic carbon normalised adsorption coefficient).

Both substances have a very low vapour pressure. The differences in order of magnitude most probably result from the differences of the applied methods (measurement vs. estimation by calculation).

The results from the studies on surface tension with the source substance MDEA-Esterquat C16-18 and C18 unsatd. as well as the target substance MDIPA-Esterquat C16-18 and C18 unsatd. werenot in line with the expected surface tension behaviour of the test substances. Cationic surfactants carrying two C16/C18 alkyl chains, such as MDEA-Esterquat C16-18 and C18 unsatd. or MDIPA-Esterquat C16-18 and C18 unsatd., are designed to possess surface active properties and typically exhibit surface tension values as low as 27 mN/m. However, at temperatures of 20°C, the inner-molecular mobility of the fatty acid C-chains is hindered. Corresponding to this hinderance, on the one hand, the time to reach solubilisation equilibrium is long and on the other hand, there is a tendency to form vesicles. This can be seen i.e. at the test on hydrolysis with low correlation rates for pseudo-first order curve determination for 20°C but high correlation rates at 50 and 60°C.The result obtained with the source substance MDIPA Esterquat C18 unsatd. of 37.5 mN/m at 20°C was in the expected range for substances with this structure.

There are, however, differences in water solubility. Water solubility was determined by measurement of turbidityinstead of analytical determination of concentration, since no suitable method was available to remove undissolved test substance. The standard tests for this endpoint are intended for single substances and are not appropriate for these complex substances. It is stated in the OECD guideline 105 (1995) that:“The water solubility of a substance can be considerably affected by the presence of impurities. This guideline addresses the determination of the solubility in water of essentially pure substances […]”. Although impurities are per definition not present in UVCB substances, the complex and variable composition of the target and source substances may nevertheless influence the outcome in a similar manner.

Due to differences in the methodological approach the results for the water solubility measurement are not directly comparable between MDEA- and MDIPA-Esterquats. For the source substance MDEA-Esterquat C16-18 and C18 unsatd. the solubility of the test substance in water is considered equal to the intercept with the x-axis. Whereas for MDIPA-Esterquat C16-18 and C18 unsatd. a baseline turbidity was calculated, and the intercept with this baseline wasconsidered to represent the water solubility.

Both substances were readily biodegradable. The log Koc was in a comparable range for both substances.

 

4. Comparison of data from environmental fate endpoints

4.1 Environmental fate data of the target and source substances

As described above biodegradation screening data obtained with the target substance MDIPA-Esterquat C16-18 and C18 unsatd. are similar to the source substance MDEA-Esterquat C16-18 and C18 unsatd.

 

5. Quality of the experimental data of the analogues:

All available studies have been conducted according to or are comparable with OECD guidelines and thus have been assigned a reliability of 1 or 2 as documented in the data matrix.

 

6. Conclusion

Adequate and reliable scientific information indicates that the source substance MDEA-Esterquat C16-18 and C18 unsatd. and the target substance MDIPA-Esterquat C16-18 and C18 unsatd. have similar environmental fate profiles. Both substances are readily biodegradable and show a similar adsorption/desorption behaviour.

The structural similarities between the source and the target substance and the expected similarities of their breakdown products as presented above further support the read-across hypothesis.

Therefore, based on the available data, it can be concluded that the results of the biodegradation simulation tests in water obtained with the source substance are likely to predict the properties of the target substance.