Choline hydroxide

Endpoint summary

Description of key information

Repeated dose toxicity:
- Chronic (72 weeks + 31 weeks post-observation) study oral (feed), rat (Fischer 344) male (similar to OECD guideline 452): NOAEL > 1200 mg/kg bw/day choline chloride (highest / only dose tested), recalculated to 1040 mg/kg bw/day choline hydroxide
- Subchronic (3 – 4 months) study oral (feed and drinking water), rat m/f (similar to OECD Guideline 408): NOAEL = 1300 – 2900 mg/kg bw/day choline chloride, recalculated to 1130 - 2520 mg/kg bw/day choline hydroxide, LOAEL = 3400 – 5000 mg/kg bw/day choline chloride, recalculated to 2950 - 4340 mg/kg bw/day choline hydroxide
- Subacute (28 day) study oral (gavage), intraperitoneal and intranasal, mouse (Balb/c) m/f (GLP, OECD Guideline 407 / no guideline available): NOEL > 200 mg/kg bw/day choline chloride (highest / only dose tested), recalculated to 174 mg/kg bw/day choline hydroxide

Key value for chemical safety assessment

Toxic effect type:

dose-dependent

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The study was performed on the read-across substance Choline chloride similar to OECD 452 with minor deviations and not all details are given. However, the available information is sufficient to consider the results as reliable.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 452 (Chronic Toxicity Studies)

Deviations:

yes

Remarks:

only male rats used

GLP compliance:

not specified

Limit test:

no

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Kingston, NY
- Age at study initiation: no data
- Weight at study initiation: 50 - 60 g
- Fasting period before study: no
- Housing: three per cage in plastic shoebox cages
- Diet (e.g. ad libitum): ad libitum a natural ingredient ground chow (Wayne Laboratory Blox Allied Mills, Inc., Chicago, IL)
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 5 days

Route of administration:

oral: feed

Vehicle:

unchanged (no vehicle)

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:
chow diet was supplemented with 1.0 % Choline chloride

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

five days of non-supplemented chow, i.p. injection of saline (since the choline group served as a control group in a tumor promoting study), five days of non-supplemented chow.
72 weeks of treatment with supplemented chow, followed by 31 weeks post-observation with non-supplemented chow

Frequency of treatment:

continuously, i.e. application via feed which was available ad libitum

Dose / conc.:

1 other: percent (nominal) in diet

Remarks:

Doses / Concentrations: 1%
Basis: nominal in diet

Dose / conc.:

10 000 ppm

Remarks:

calculated from the above mentioned dosage of 1 % in diet

No. of animals per sex per dose:

30 males / dose

Control animals:

yes, plain diet

Details on study design:

- Dose selection rationale: Choline treated rats served as controls in a tumor promoting study on Phenobarbital (PhB) and 1,1 bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT), the levels of Choline chloride was based on previous experiments wherein these levels were shown to inhibit the drop in hepatic S-adenosylmethionine levels due to PhB and DDT
- Rationale for animal assignment (if not random): random
- Rationale for selecting satellite groups: not applicable
- Post-exposure recovery period in satellite groups: not applicable

Positive control:

Due to original study aim (tumor promoting effects), results will be given derived from animals which were initiated with i.p. injection of 200 mg/kg bw of diethylnitrosamine dissolved in sterile normal saline followed by a diet supplemented with 0.05 % 1,1 bis(p-chlorophenyl)-2,2,2-trichloroethane (DDT)

Observations and examinations performed and frequency:

DETAILED CLINICAL OBSERVATIONS: No data, only body weight denoted

BODY WEIGHT: Yes
- Time schedule for examinations: Body weights were taken at weekly intervals for 16 weeks and biweekly thereafter

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No data
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No data

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Not applicable

OTHER: Gross pathology performed

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (see table 1)
HISTOPATHOLOGY: Yes, but no results provided

Other examinations:

Growth and survival

Statistics:

The comparisons between the incidences of tumors in different groups were analysed by Fischer's exact test. The survival data were analysed by the computer program developed by Thomas el al. (Thomas CG, Breslow N and Gart JJ (1977) Trend and homogeneity analyses of proportions and life table data. Computers Biomed. Res., 10, 373-381.). Kaplan-Meier survival curves were derived by using this procedure. Comparison among survival of different experimental groups were made by Cox's test and P value based on the chi-square test from Cox's analysis. The incidences of liver and lung tumors and of leukemias in each group were based upon the number of animals surviving at 1 year since the first instance of each of the tumors occurred between weeks 55 and 60.

Clinical signs:

no effects observed

Description (incidence and severity):

mortality: no difference compared to control animals

Mortality:

no mortality observed

Description (incidence):

mortality: no difference compared to control animals

Body weight and weight changes:

no effects observed

Description (incidence and severity):

no difference compared to control animals

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

Water consumption and compound intake (if drinking water study):

not specified

Ophthalmological findings:

not specified

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

relative liver weight: no difference compared to control animals

Gross pathological findings:

no effects observed

Description (incidence and severity):

performed, but limited data given; Liver and lung tumor formation: no difference compared to control animals

Histopathological findings: non-neoplastic:

not specified

Histopathological findings: neoplastic:

no effects observed

Description (incidence and severity):

Various lung, liver and other tumors, leukemia: no difference compared to control animals

Details on results:

CLINICAL SIGNS AND MORTALITY - no difference compared to control animals

BODY WEIGHT AND WEIGHT GAIN - no difference compared to control animals

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study) no data

FOOD EFFICIENCY no data

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study) not applicable

OPHTHALMOSCOPIC EXAMINATION no data

HAEMATOLOGY no data

CLINICAL CHEMISTRY no data

URINALYSIS no data

NEUROBEHAVIOUR no data

ORGAN WEIGHTS - relative liver weight: no difference compared to control animals

GROSS PATHOLOGY - performed, but limited data given; Liver and lung tumor formation: no difference compared to control animals

HISTOPATHOLOGY: NON-NEOPLASTIC no data

HISTOPATHOLOGY: NEOPLASTIC (if applicable) - various lung, liver and other tumors, leukemia: no difference compared to control animals

HISTORICAL CONTROL DATA (if applicable) controls see table 1

OTHER FINDINGS See table 1

Dose descriptor:

NOAEL

Effect level:

> 10 000 ppm

Based on:

test mat.

Remarks:

Choline chloride

Sex:

male

Basis for effect level:

other: see 'Remark'

Remarks on result:

other: originally reported as 1 % in diet

Dose descriptor:

NOAEL

Effect level:

> 1 200 mg/kg bw/day (nominal)

Based on:

test mat.

Remarks:

Choline chloride

Sex:

male

Basis for effect level:

other: see 'Remark'

Dose descriptor:

NOAEL

Effect level:

> 1 040 mg/kg bw/day (nominal)

Based on:

other: Choline hydroxide, amount recalculated from choline chloride

Sex:

male

Basis for effect level:

other: Basis for effects: overall effects; mortality; body weight; gross pathology; organ weights Recalculated value from NOAEL > 1200 mg/kg bw choline chloride regarding the molecular weight of each compound.

Critical effects observed:

not specified

Table 1: Results – Comparison of rats fed 1% choline chloride in diet to control group (plain diet)

Endpoint		Treatment Group (1 % Choline chloride in diet)	Control Group (plain diet)	Positive Control Group (i.p. 200 mg/kg bw of diethylnitrosamine, 0.05 % DDT in diet)
Survival at week	52	28	28	28
	78	28	28	21
	102	24	23	3
Body weight at week / g	10	258	253	262
	50	406	408	394
Relative liver weight (%)		3.4	3.60	13.42
Number of animals bearing liver tumors	Neoplastic nodules	2	2	1
	Hepatocellular carcinomas	0	1	28
	Cholangiomas + cholangiocarcinomas	0	0	6
	Lung metastases	0	0	13
Number of animals with tumors / extrahepatic lesions	Lung	1	2	4
	Leukemia	2	8	4
	Others	4	7	8

Conclusions:

The present study was classified as reliable with restrictions due to the limited information provided. However, since the available information is sufficient to consider the study as reliable, the results obtained can be used to assess the repeated dose toxicity of choline chloride and hence, choline base. The study duration was 103 weeks, wherein the animals were dosed the first 72 weeks with 1 % Choline chloride (10,000 ppm) in diet. Consequently, considering the total life span of a rat of approx. 1.5 - 2 years, the study duration was chosen long enough to detect all possible effects arising from Choline chloride.

The read-across from choline chloride to choline base is justified because the absorption after oral application is very likely to have remained unchanged, information gained from choline chloride for this endpoint can be used as weight-of-evidence information without modification. This is due to the fact that, if ingested orally, the contact time of the basic solution to the oesophagus is rather short for causing severe chemical burns which will be necessary to enlarge the oral uptake. Once reaching the stomach, the basic pH of the choline base solution will be immediately neutralized by the gastric acid. Only when ingesting large amounts of choline base, the neutralization capacity of the stomach acid will be used up. However, this scenario is unlikely due to expected pain in the oral cavity and pharynx caused by hydroxide. Also, in case it would have been decided to neutralize the test compound in order to avoid diminished food intake due to the undesired taste and pain, chlorous acid would be the recommended one, resulting in choline chloride anyway.
Hence, only effects of the choline cation have to be regarded and the results gained from choline chloride can be used without modifications.

No adverse effects were detected compared to control. In fact, although not statistically significant, Choline chloride treated animals developed less tumors than control animals. Also, no effects were seen regarding body weight gain, and the relative liver weight was also slightly, but not significantly decreased compared to control. This could be due to the fact that Choline chloride, which is also used as a feed additive, is an effective methyl donor, which does not require extensive metabolic pathways, which could possibly lead to additional liver damage due to hazardous degradation products. Hence, it is likely that CC does not only exhibit no adverse effects but also liver-protecting effects. Most likely effects for an increased liver weight can be (non)-neoplastic lesions, fatty liver or scar formation / cirrhosis due to necrosis already on only single cellular level, and also an increased requirement of metabolic enzymes. These effects are diminished by an additional gavage of Choline chloride. Furthermore, the positive control (i.p. 200 mg/kg bw of diethylnitrosamine, 0.05% DDT in diet) led to a decreased body weight and increased relative liver weight and tumor formation compared to control, which is an additional reason why the study, and so the results, can be considered as valid.
So, taking further into account the average food consumption of 120 g/kg bw/day of a male rat as given in ECHAs guidance document R.8, and the fact that no adverse effects were denoted compared to control at an average choline chloride (CC) consumption of 1 % in diet (10,000 ppm), the NOAEL was determined to be > 1 % CC in diet, which corresponds to > 1200 mg/kg bw/day (nearly life time duration). This NOAEL can be recalculated for choline hydroxide to 1040 mg/kg bw/day, regarding the molecular weight of each compound.
In conclusion, it can be stated that choline chloride and hence choline base does not induce any adverse effects and can be considered as non-toxic when administered chronically to rats, and no classification, neither as carcinogenic or STOT-RE, is required.

Executive summary:

In a chronic toxicity study equivalent to OECD Guideline 452, the read-across substance choline chloride was administered orally 1 % (10,000 ppm) in feed to male Fischer 344 rats, 30 animals per group, over 72 weeks with 31 weeks post-observation period.

There were no compound-related adverse effects denoted compared to control regarding the observed endpoints, i.e. body weight and body weight gain, relative liver weight, tumor formation in liver and lung, leukemia and other tumors. So the NOAEL is > 1 % Choline chloride (10,000 ppm) in food, based on all observed effects, which corresponds to NOAEL > 1200 mg/kg bw/day choline chloride or a NOAEL > 1040 mg/kg bw/day for choline hydroxide.

This chronic toxicity study in rats is acceptable with restrictions, satisfies the guideline requirements for a chronic oral toxicity study (OECD 452) in rats, and allow to draw the conclusion that Choline chloride and hence choline hydroxide is practically non-toxic.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

1 040 mg/kg bw/day

Study duration:

chronic

Species:

rat

Quality of whole database:

Three equivalently reliable studies assessed with Klimisch 2 are available to cover the endpoint "Repeated Dose Toxicity: oral" on the read-across substance choline chloride, whose results can be transferred without relevant modification to choline hydroxide. Three different study durations are covered, one subacute, one subchronic and one chronic. The former covers the standard information requirements as demanded by REACH Annex IX column 1 No. 8.6.1 (28 days), the latter two ones, which are due to the test duration the more important ones, cover REACH Annex IX column 1 No. 8.6.2 (90 days resp. column 2, chronic). Hence, the available information meets fully the tonnage-driven data requirements of REACH.
Additionally, all available studies revealed equivalent, plausible and consistent results over all three durations, i.e. give all no rise to concern of compound-related toxic effects when applying choline chloride and hence choline hydroxide repeatedly and trigger no classification as STOT-RE.
So, the whole database is of high quality.

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

There are three studies available evaluating the possible hazards of the read-across substance choline chloride by repeated oral application.

 

The read-across from choline chloride to choline hydroxide aka choline base is justified because the absorption after oral application is very likely to have remained unchanged, information gained from choline chloride for this endpoint can be used as weight-of-evidence information without modification. This is due to the fact that, if ingested orally, the contact time of the basic solution to the oesophagus is rather short for causing severe chemical burns which will be necessary to enlarge the oral uptake. Once reaching the stomach, the basic pH of the choline base solution will be immediately neutralized by the gastric acid. Only when ingesting large amounts of choline base, the neutralization capacity of the stomach acid will be used up. However, this scenario is unlikely due to expected pain in the oral cavity and pharynx caused by hydroxide. Also, in case it would have been decided to neutralize the test compound in order to avoid diminished food intake due to the undesired taste and pain, chlorous acid would be the recommended one, resulting in choline chloride anyway. Hence, only effects of the choline cation have to be regarded and the results gained from choline chloride can be used without modifications. Additionally, skin contact may possibly occur when using choline hydroxide.

 

In general, the neutral choline cation is not favoured for absorption, due to:

- Molecular weight: Less than 100 favours dermal uptake. Above 500 the molecule may be too large. With a molecular weight of 104.2 g/mol, absorption in general could be possible, but isn´t, as explained below.

- LogPow: For substances with Log Pow values < 0, poor lipophilicity will limit penetration into the stratum corneum and hence dermal absorption. Values < -1 suggest that a substance is not likely to be sufficiently lipophilic to cross the stratum corneum, therefore dermal absorption is likely to be low. Since choline chloride, which serves as an example for the cation, too, due to its ionic structure, has a logPow of -3.77 at 25 °C, dermal absorption may practically not occur. This is supported by the negative logPow of -2.25 of choline base (Intertek, 2013).

- Water solubility: If water solubility is above 10,000 mg/L and the Log Pow value below 0 the substance may be too hydrophilic to cross the lipid rich environment of the stratum corneum. Dermal uptake for these substances will be low. As stated above, log Pow is below 0, and additionally, water solubility was found to be 325 - 650 g/L (choline chloride, which serves as an example for the cation, or >486 g/L choline hydroxide (Intertek, 2013)), i.e. over 10 g/L. Also here, dermal absorption may practically not occur due to the high hydrophilicity of the compound.

Hence, based on the physico-chemical properties of the choline cation, a dermal absorption is very hindered and so unlikely.

Nevertheless, the absorption will be enhanced due to the corrosive properties of choline base, and so the toxicity via the dermal route should not be disregarded. When applying a corrosive chemical to the skin and not instantaneous removing it, not only single cell membranes will be damaged, but also several layers of the skin. The stratum corneum consists of several layers of dead, cornified keratinocytes (i.e. corneocytes), which are linked by structural proteins forming an effective barrier. A prolonged exposure to hydroxides leads i.a. to the hydrolysis of these proteins, resulting in the disintegration of this barrier and finally severe chemical burns. Once that the stratum corneum is removed or at least made permeable, the primary barrier for hydrophilic compounds is not existent anymore and the free choline cation can easily reach the epidermis and from there be easily distributed mainly unmetabolized via the blood stream. Hence, the poor dermal absorption for the choline cation is not applicable anymore and the estimated absorption rate of 10 % must be adjusted upwards. An estimated absorption of 50 % is considered reasonable, because the absorption is enhanced, but not equal to the bioavailability after an intravenous injection, because it can be expected that not the complete dermal cells will be damaged and a certain barrier function emanates also from the epidermal cells. So, the estimated absorption via the oral route, as already outlined in the subchapter regarding the toxicokinetics of choline hydroxide, equals the absorption via the dermal route, i.e. approx. 50 % percent of the applied compound. Hence, the available information gained from choline chloride via the oral route can be transferred without modifications to choline base (dermal route).

 

The relevant studies are:

a) Chronic study (Shivapurkar et al., 1986):

No adverse effects were detected when applying 1200 mg/kg bw /day Choline chloride (CC), which corresponds to 1040 mg/kg bw/day choline base, compared to control. In fact, although not statistically significant, choline treated animals developed less tumors than control animals. Also, no effects were seen regarding body weight gain, and the relative liver weight was also slightly, but not significantly decreased compared to control. This could be due to the fact that choline, which is also used as a feed additive, is an effective methyl donor, which does not require extensive metabolic pathways, which could possibly lead to additional liver damage due to hazardous degradation products. Hence, it is likely that CC does not only exhibit no adverse effects but also liver-protecting effects.

In conclusion, it can be stated that choline chloride and hence choline base do not induce any adverse effects and can be considered as non-toxic when administered chronically to rats, and no classification, neither as carcinogenic or STOT-RE, is required.

 

b) Subchronic study (Hodge HC, 1945):

With an increasing dose of choline chloride applied either in the feed or drinking water over 3-4 months to rats, the body weight gain decreases at doses ≥ 2.7 % in feed (≙ 1869.2 - 2554.6 mg/kg bw/day) or ≥ 1 % in drinking water (≙ 1337.6 - 2153.8 mg/kg bw/day), as do the organ weights. Nevertheless the relative organ weights remain unchanged. Also, the average food intake and water consumption decreases with an increasing dose of Choline chloride. Hence, it is most likely that the observed effects, i.e. body weights gain, are due to the decreased feed and water consumption because of a possibly undesired taste of the feed or water. So, the required nutrients for growth are not or not fully available to permit body weight gain comparable to control. As a conclusion, the observed effects are not due to intrinsic toxic effects of choline chloride but only a consequence of feed and water refusal due to the taste. This conclusion is furthermore supported by the fact that only the organ weights, but not the relative organ weights were diminished compared to control and also all histopathological examinations were negative or not CC-dose-related. So it is only possible to determine mainly NOELs but not NOAELs since no adverse effects can be detected which are directly attributable to toxic effects of choline chloride.

Additionally, the dose may increase when taking into account the nominal CC percentage in feed or water. Nevertheless, when correcting the dose to the actual feed or water intake to units of mg/kg bw/day, all effects are in the same range of approx. 1300 – 2900 mg/kg bw/day choline chloride, which corresponds to 1130 - 2520 mg/kg bw/day choline hydroxide. Since, as stated above, these effects are not due to intrinsic toxic effects of CC, this value should be considered to be the NOAEL within this study. The only observed exemption is made by the 10 % dose group with CC application via feed. This is the only dose group in which also the relative organ weights deviate from control and deaths occurred during the feed study. Also, the absolute CC intake is markedly increased, compared to the other dose groups, to approx. 3400 – 5000 mg/kg bw/day choline chloride, corresponding to 2950 - 4340 mg/kg bw/day choline hydroxide. Hence, these effects may be considered as directly related to the choline chloride intake and therefore as the LOAEL in the subchronic study.

For choline hydroxide a similar outcome is expected. 

 

c) Subacute study (Mehta et al., 2009):

The results are not only available for oral administration, but also for i.p. and i.n. routes, which broadens the insight in possible effects by choline.

In general, all observed parameters (body weights gain, organ weights, haematological parameters or clinical bio-chemistry parameters) did not deviate from the control groups, when choline chloride was applied at a dose of 200 mg/kg bw/d choline chloride, which corresponds to 174 mg/kg bw/day choline hydroxide. The only observed derogation from control was an elevated creatinine level. Since this is most probably due to the application route, which is not relevant for humans, this effect can be neglected.

So, the NOEL was determined as > 174 mg/kg bw/d choline hydroxide. Since this was the calculated value based on the highest dose tested and there not a single relevant effect was observed, it can probably be much higher, which is supported by a recalculated NOAEL of > 1040 mg/kg bw/day for choline hydroxide (chronic study with Choline chloride, Shivapurkar et al., 1986), and the results on choline chloride do not indicate any need for classification of choline hydroxide.

 

No studies are available for the repeated application via inhalation or dermal route. However, they were not conducted due to animal welfare as they were not considered necessary for human risk assessment:

The oral route is considered to be the most likely one for humans, because the test substance has a very low vapor pressure and a high melting point, so the potential for the generation of inhalable forms is low. Furthermore, the substance is distributed as an aqueous solution, so no dust with inhalable particles will be formed and therefore no acute inhalation test was performed.

Additionally, the study performed by Mehta et al., 2009 (IUCLID chapter 7.5.1) on choline chloride, covers three different applications routes over 28 days including intranasal application, which is the most similar application route to inhalation, as the absorption will be over the trachea and lung, too, and so the compound is objected to the tissue-specific metabolism, e.g. rather via cytochrome P450 1A than CYP 3A4. In this study, no substance-related toxic effects were denoted up to the highest dose tested, i.e. the NOEL by i.n. application is recalculated for choline hydroxide to be > 174 mg/kg bw/day.

As outlined above, the same subacute to chronic values gained from the oral studies on choline chloride can be adapted without relevant modifications to choline hydroxide, dermal route.

 

Even though the physico-chemical properties of Choline hydroxide (molecular weight, LogPow, water solubility) are not in favour a absorption, a dermal absorption might be enhanced as the substance is a skin irritant/corrosive. Such substances damage the skin surface and this might enhance penetration. However, as Choline hydroxide is available as a 45 % aqueous solution, this effect does not have to be evaluated further. 

 

In summary, there are three repeated dose studies on the read-across substance choline chloride with oral application available, all assessed with Klimisch 2. Hence, the results obtained can be used to assess the repeated dose toxicity of choline chloride and hence, choline base. All available studies revealed equivalent, plausible and consistent results over all three durations including a nearly lifetime exposure with an NOAEL > 1200 mg/kg bw choline chloride, corresponding to 1040 mg/kg bw/d choline hydroxide, i.e. all studies give no rise to concern of compound-related toxic effects when applying choline chloride and so choline hydroxide repeatedly and trigger no classification as STOT-RE.

There are no repeated dose toxicity studies available with dermal application or via inhalation. However, these studies are not considered necessary due to exposure or other considerations regarding the unlikeliness of absorption or transferability as stated above.

Consequently, there are no data gaps in repeated dose toxicity. Although no human data is available on the possible hazards of the substance, there is no reason to believe that the observed lack of adverse effects in all studies would not be relevant for humans, as the available animal models are all accepted as a scientifically justified surrogate for human testing. All possible deviations regarding absorption, metabolism or other factors are considered to be negligible when assessing the possible risk for humans with the available animal data.

Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:
Three equally reliable studies on the reliable read across substance choline chloride are available for this endpoint. Hence, the study with the longest test duration was chosen as this is the likeliest study to detect all possible substance-related effects with repeated application, which is the actual purpose of the endpoint.

Justification for selection of repeated dose toxicity inhalation - systemic effects endpoint:
There are no studies available evaluating the possible hazards of Choline hydroxide by repeated inhalation application. However, according to REACH Annex IX column 1, the most appropriate route of administration, having regard to the likely route of human exposure, has to be chosen for repeated dose toxicity testing. In this case, the oral route is considered to be the most likely one for humans, because the test substance has a very low vapor pressure and a high melting point, so the potential for the generation of inhalable forms is low. For this route of  exposure three reliable studies on the reliable read across substance choline chloride are available. Therefore, adequate information is available for the most appropriate route of exposure and no repeated dose testing via inhalation route needs to be performed. 

Justification for selection of repeated dose toxicity inhalation - local effects endpoint:
In general, an inhalation study does not need to be provided due to exposure considerations as laid down above. Also, due to the high pH value of the substance solution, irritant or corrosive effects are expected to occur in the respiratory tract and testing can be omitted.

Justification for selection of repeated dose toxicity dermal - systemic effects endpoint:
There are no studies available evaluating the possible hazards of Choline hydroxide by repeated dermal application. However, according to REACH Annex IX column 1, the most appropriate route of administration, having regard to the likely route of human exposure, has to be chosen for repeated dose toxicity testing. In this case, the oral route is considered to be the most likely one for humans, For this route of  exposure three reliable studies on the reliable read across substance choline chloride are available. Therefore, adequate information is available for the most appropriate route of exposure and no repeated dose testing via the dermal route needs to be performed.

Justification for selection of repeated dose toxicity dermal - local effects endpoint:
Due to the corrosive properties of choline hydroxide, severe chemical burns of the skin can be expected. Following this, no need for additional testing was apparent and hence, further testing must be omitted due to animal welfare.

Justification for classification or non-classification

In a chronic toxicity study on the reliable read across substance choline chloride, the NOAEL was determined to be > 1 % Choline chloride (CC) in diet, which corresponds to > 1200 mg/kg bw/day CC (over nearly life time duration), which corresponds to > 1040 mg/kg bw/day choline hydroxide. No substance-related effects on specific organs were reported.

This is supported by the results of a subchronic study with choline chloride (NOAEL recalculated to choline hydroxide: ca. 1130 - 2520 mg/kg bw/day, LOAEL recalculated to choline hydroxide: ca. 2950 - 4340 mg/kg bw/day) and a subacute study (NOEL recalculated to choline hydroxide: > 174 mg/kg bw/day), without any detectable specific organ toxicity after repeated exposure. Additionally, all mentioned doses for the no effect levels are above the guidance values for classification as STOT-RE Cat. 2, as given in section 3.9.2.9.7 of Regulation 1272/2008/EC. Hence, choline hydroxide does not need to classify choline hydroxide as STOT-RE or carcinogenic.