Choline hydroxide

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH
Please refer also to Read Across Statement attached in Section 13

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
In this read-across approach choline chloride data is used to fill data gaps for choline hydroxide, in accordance with Regulation No 1907/2006 (REACH), Annex XI. The basis for this read-across approach is the “Read-Across Assessment Framework” (RAAF) (ECHA 2017). The read-across hypothesis for the analogue approach is that choline hydroxide and choline chloride exhibit a similar (eco)toxicological profile. This is due to the fact that both choline salts as quaternary alkylammonium salts dissociate readily into the respective ions when getting into contact with water and the choline cation is what is left to be considered (US EPA, 2010). Thus, the different choline salts are used to for hazard assessment. According to the RAAF this approach is covered by scenario 1: “(Bio)transformation to common compound(s)”.
“This scenario covers the analogue approach for which the read-across hypothesis is based on (bio) transformation to common compound(s). For the REACH information requirement under consideration, the property investigated in a study conducted with one source substance is used to predict the properties that would be observed in a study with the target substance if it were to be conducted. Similar properties or absence of effect are predicted. The predicted property may be similar or based on a worst-case approach.” (ECHA 2017).

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Source chemical:
2-hydroxy-N,N,N-trimethylethanaminium chloride
Molecular formula: C5H14ClNO
SMILES: [Cl-].C[N+](C)(C)CCO
CAS: 67-48-1
Purity: not specified

Target chemical:
Choline hydroxide
Molecular formula: C5H15NO2
SMILES: [OH-].C[N+](C)(C)CCO
CAS: 123-41-1
Purity: 96 %

3. ANALOGUE APPROACH JUSTIFICATION
Upon contact with water, choline hydroxide is expected to dissociate into the cationic form (choline) and the anionic form (hydroxide ions); the hydroxy moiety dissociates and essentially ceases to exist upon mixing with water in preparation for application and in the body. The latter will be even skipped because both choline hydroxide and choline chloride are only distributed as aqueous solution, i.a. due to their hygroscopic properties. The choline cation is what is left to be considered (US EPA, 2010). Due to the structural similarities, i.e. the identical organic cation, which contains a positively charged nitrogen, and small, negatively charged inorganic anion (for choline base: Hydroxide), this is a reasonable and scientifically expectable conclusion, which allow one to draw the generalized conclusion, that Choline salts in general dissociate readily in water into the corresponding positively charged quaternary hydroxyl alkylammonium ion and the negatively charged inorganic anion (OECD SIDS, 2004). The choline cation therefore, is the moiety of interest. Based on the fact that in the environment and in biological fluids the same compounds are formed from the source and the target substances, the same (eco)toxicological profile of choline hydroxide and choline chloride is expected. Therefore, the read-across approach is justified. Thus, the available studies for the source substance choline chloride were used to fill data gaps for choline hydroxide for several environmental and toxicological endpoints.

Reason / purpose for cross-reference:

read-across source

Duration of test (contact time):

ca. 5 d

Preliminary study:

No details are reported.

Test performance:

No details are reported.

Parameter:

% degradation (O2 consumption)

Value:

> 75

Sampling time:

5 d

Details on results:

The percentage of degradation was calculated by dividing BOD5 by ThOD.

1280 mg/g divided by 1710 mg/g amounts to 75 % of degradation.

Parameter:

BOD5

Value:

> 1 066 - < 1 400 other: mg/L

Parameter:

COD

Value:

> 321 - < 322 mg O2/g test mat.

Results with reference substance:

Not applicable.

Table 1. Test results

	BOD [mg/L]	TOC [mg/L]	COD [mg/L]	Initial weight [mg/L]	Oxygen consumption
stock solution	1305	338	322	1022.5	0
				1003.7 (COD)
	BOD [mg/L]	TOC [mg/L]	COD [mg/L]	ThOD [mg/g]	% Degradation based on ThOD
test material	1276	331	321	1430 - 1710	75-89
	Remarks	COD was repeatedly determined; no appropriate reference value

Table 2. BOD5 determination

		Oxygen content [mg/L]			Biochemical Oxygen Demand
Dilution [mL] p	Flask No.	Beginning	End	Consumption [mg/L] Z- ZV	single value 1000/p x (Z-ZV)	Mean value
2	118	9.6
	348		6.9	2.7	1350
	145		6.8	2.8	1400
3	257	9.5
	315		5.9	3.6	1200
	535		5.7	3.8	1270	1305
4.5	494	9.5
	194		4.7	4.8	1066
	538		4.6	4.9	1090
Remarks
Laboratory No.	2567
TOC [mg/L]	338
BOD5 [mg/L]	1305
COD [mg/L]	322
Initial weight [g/L]	1.0225
Initial weight [g/L] for COD	1.0027

Validity criteria fulfilled:

yes

Remarks:

Basic scientifical principles are fulfilled.

Interpretation of results:

readily biodegradable

Conclusions:

Within 5 days, a degradation of 75 % was determined for choline chloride under the given test conditions. Therefore, the substance is considered as readily biodegradable. The study was conducted without GLP compliance and the study report is not well documented. However, the experimental procedure can be considered as valid. Nevertheless, choline is a naturally occurring compound and a strong biodegradation potential for the test substance can be foreseen.

Executive summary:

Choline chloride was found to be readily biodegradable based upon an experiment conducted according to H5 (Bestimmung des biochemischen Sauerstoffbedarfs) published in "Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung, 3. Auflage, 11. Lieferung, Weinheim (1982)" (BASF AG, 1984). Thereby, the biodegradation of the test material was calculated by dividing the measured BOD5 by the calculated ThOD resulting in 75 - 90 % biodegradation within 5 days. The COD determined according to DIN 38 409 (part 43) was not considered as suitable reference value. Based on the fact that in the environment and in biological fluids the same compounds are formed from the source and the target substances, the choline moiety is the considered fraction of the source substance. Thus, this conclusion can also be drawn for the target substance choline hydroxide.

Description of key information

RA_CAS 67-48-1_Readily biodegradability_DIN 38 409 part 43/H5 (Determination of BOD): 75 % degradation within 5 days - readily biodegradable 

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater

Additional information

Choline hydroxide was not investigated experimentally for its potential to biodegrade. A valid experimental result for the read-across substance Choline chloride (CAS 67-48-1) is available concluding that the substance is readily biodegradable. Based on the structural similarities and substance characteristics of both, the same result can be presumed for the target substance. For justification and further details of this procedure, please refer to the separate read-across statement by Chemservice S.A., 2013. In general, choline is a naturally occurring compound and the potential to readily biodegrade can be foreseen for both substances. The available experiment, which was conducted with Choline chloride, was performed according to DIN 38409 (Part 43) and H5 (Detection of biochemical oxygen demand, BOD) published in "Deutsche Einheitsverfahren zur Wasser-, Abwasser- und Schlammuntersuchung, 3. Auflage, 11. Lieferung, Weinheim (1982)" (BASF AG, 1984). Biodegradability was calculated by dividing the measured BOD5 by the calculated ThOD. Thereby, Choline chloride attained 75 - 90 % degradation within 5 days.