2-methylpropyl-(R)-2-hydroxypropanoate

Endpoint summary

Description of key information

Isobutyl-R-lactate is not acutely toxic via any route of administration.

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records

Reference

Endpoint:

acute toxicity: oral

Type of information:

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

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Publication, wich meets generally accepted scientific standards. Isobutanol used as read-across partner to isobutyl-R-lactate, since being the primary metabolite.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 401 (Acute Oral Toxicity)

Deviations:

no

GLP compliance:

no

Test type:

standard acute method

Limit test:

no

Species:

rat

Strain:

other: Carworth-Wistar

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: own colony (Mellon Institute of Industrial Research, University of Pittsburgh
- Weight at study initiation: 90 to 120 g
- Fasting period before study: no
- Diet (e.g. ad libitum): ad libitum, Rockland rat diet complete
- Water (e.g. ad libitum): ad libitum

Route of administration:

oral: gavage

Vehicle:

not specified

Doses:

No data

No. of animals per sex per dose:

5 males

Control animals:

no

Details on study design:

Single dose oral toxicity for rats is estimated by intubation of dosages in a logarithmic series to groups of five male rats. Fourteen days after dosing, mortality is considered complete.

Statistics:

The most probable LD50 value and its fiducial range are estimated by the method of Thompson.

Sex:

male

Dose descriptor:

LD50

Effect level:

2 460 mg/kg bw

Based on:

test mat.

95% CL:

>= 1.6 - <= 3.78

Interpretation of results:

not classified

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

In an acute oral toxicity study in rats the LD50 of isobutanol was estimated to be 2460 mg/kg bw.

Executive summary:

In an acute oral toxicity study equivalent to OECD test guideline 401, 5 male Carworth-Wistar rats were given a single oral dose of isobutanol. The animals were observed for 14 days after the single exposure. The oral LD₅₀ reported in this study is 2460 mg/kg bw.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Acute toxicity: via inhalation route

Link to relevant study records

Reference

Endpoint:

acute toxicity: inhalation

Type of information:

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

Adequacy of study:

key study

Study period:

1992-06-02 to 1992-07-29

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP guideline study. Isobutyl-S-lactate used as read-across partner.

Qualifier:

according to guideline

Guideline:

OECD Guideline 403 (Acute Inhalation Toxicity)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test type:

acute toxic class method

Limit test:

yes

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Wistar rats, Crl:WI(WU)BR
- Age at study initiation: 10-11 weeks (5-6 when delivered + 35 days acclimatisation)
- Weight at study initiation: Mean weight of male rats 278 g and female rats 174 g.
- Housing: The animals were housed in an animal room, 5 per cage.
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 35 days
- Fasting: during exposure the animals were deprived of food and water
ENVIRONMENTAL CONDITIONS
Due to technical problems, no check for temperature and humidity was conducted in the period of 14 to 18 May 1992.
- Temperature (°C): 21.0 to 24.0
- Humidity (%): 34 to 71, the relative humidity was between 70 and 83 % at one day and up to 92 % during short periods due to cleaning activities.
- Air changes (per hr): 10
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

nose only

Vehicle:

air

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Inhalation-chamber from ADG Developments LTD.
- Exposure chamber volume: 60 L
- Method of holding animals in test chamber: Plastic animal holder (Battelle)
- Source and rate of air: Compressed with a mean air flow through the test chamber of 37.6 L/min (2.3 m³/h)
- System of generating particulates/aerosols: Atomizer (DR 011, Lechler)
- Method of particle size determination: 11-stage cascade impactor
- Temperature and humidity in air chamber: Temperature and relative humidity has been monitored with a digital thermohygro-monitor (type DAL-02, Novasina AG) and recorded 7 times during the exposure at regular intervals. Temperature was held at 21.7 ± 0.1 °C and relative humidity was below 1 %.

TEST ATMOSPHERE
- Brief description of analytical method used: The actual concentration of 2-methyl-propyl-(S)-lactate in the test atmosphere was determined once each hour by means of gas chromatographic analysis (Vega). The concentration of the test substance in the test atmosphere has been validated once an hour. Therefore, 10 L test atmosphere was passed at 2 L/min through acetone in an impinger, kept at 4 °C. Filled up to 50 ml in a volumetric flask, the sample was then tested using GC. To determine the concentration of 2-methyl-propyl-(S)-lactate in the test atmosphere samples, the peak area of the 2-methyl-propyl-(S)-lactate peak was compared with that of a standard solution containing 105.3 mg 2-methyl-propyl-(S)-lactate in 100 ml acetone, corresponding to a concentration level of 10.53 g 2-methyl-propyl-(S)- lactate per m³ air. The nominal concentration of 2-methyl-propyl-(S)-lactate was determined by dividing the total amount of test material used by the total volume of air passed through the exposure device. Particle size distribution measurement was carried out once using an 11-stage cascade impactor.

Analytical verification of test atmosphere concentrations:

yes

Remarks:

Once per hour via gas chromatography

Duration of exposure:

4 h

Concentrations:

Target concentrations: 5 g/m³

No. of animals per sex per dose:

5

Control animals:

no

Details on study design:

- Duration of observation period following administration: 14 days
- Frequency of observations: Before, during and shortly after exposure, as well as once a day during the observation period.
- Body weight: Before exposure and at day 7 and 14
- Necropsy of survivors performed: Yes

Statistics:

N.A.

Preliminary study:

N.A.

Sex:

male/female

Dose descriptor:

LC50

Effect level:

> 6 160 mg/m³ air (analytical)

Based on:

test mat.

Exp. duration:

4 h

Mortality:

No mortalities occurred.

Clinical signs:

other: During exposure, the breathing patterns of all tested rats changed. Those changes have mostly been a visually noticable decrease in breathing frequency accompanied by signs of post-inspiratory apnoea. In one male and one female rat, the decrease in breath

Body weight:

Normal body weight gain was observed in eight out of ten rats during the observation period. One female rat showed weight loss during the first week, another female rat showed only marginal body weight gain during the second week of observation.

Gross pathology:

No abnormalities were found at necropsy.

Other findings:

Analytical results:
The actual concentrations measured during the exposure to 2-methyl-propyl-(S)-lactate are given in Table 1. The mean actual concentration (and standard deviation) were 6.16 (0.23) g/m³ (Table 1). The nominal concentration was 9.4 g/m³.
Particle size distribution:
The particle size distribution is given in Table 2. The particle size measurement showed that ca. 86 % of the particles had an aerodynamic diameter between 2.4 and 4.2 µm.

Table 1: Actual concentration of 2-methyl-propyl-(S)-lactate in the test atmosphere
Sampling time	Sample no.	Peak area (counts)	Average peak area (counts)	Concentration (g/m³)	Total (g/m³)
Standard solution		795223	792991
		738862
		834753
		803124
9.57	*1-1	164577	162449	1.08	5.91
		160321
	1-2	723596	728293	4.83
		732990
10.57	*2-1	148205	144104	0.96	6.37
		140002
	2-2	819073	815944	5.41
		812815
11.57	*3-1	133891	139593	0.93	6.03
		145295
	3-2	757717	769336	5.10
		780954
12.57	*4-2	124018	125003	0.83	6.30
		125987
	4-2	846954	827766	5.50
		808577
Mean					6.16
SD					0.23

*= content of sampling tube

SD= standard deviation

Table 2: Aerodynamic particle size distribution of 2-methyl-propyl-(S)-lactate test atmosphere
Aerodynamic diameter (µm)		Distribution in % of total mass
< 1.0		0
1.0		0
1.4		0
1.8		0
2.4		5
2.8		20
3.1		18
3.4		11
3.8		27
4.2		5
> 4.2		14

Interpretation of results:

practically nontoxic

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

In conclusion, the acute inhalation toxicity of 2-methyl-propyl-(S)-lactate, as determined in a study according to OECD guideline 403, exceeds an LC50 (4 h) of 6.16 g/m³.

Executive summary:

In an acute inhalation toxicity study according to OECD guideline 403, groups of young adult Wistar rats (5/sex) were exposed at a limit concentration of  6.16 g/m³ via the inhalation route (nose only) to 2-methyl-propyl-(S)-lactate (99.7% purity) in compressed air for 4 hours. After exposure, the animals were observed for a period of 14 days. No mortality or distinct clinical signs were observed after treatment. Macroscopic examination of the animals at the end of the observation period did not reveal any treatment-related gross changes. As no mortality occurred during the 14-day observation period, the inhalation LC₅₀ of 2-methyl-propyl-(S)-lactate is considered to exceed 6.16 g/m³ in male and female rats.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Acute toxicity: via dermal route

Link to relevant study records

Reference

Endpoint:

acute toxicity: dermal

Type of information:

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

Adequacy of study:

key study

Study period:

1994-06-16 to 1994-09-22

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP guideline study. n-Propyl lactate used as read-across partner.

Qualifier:

according to guideline

Guideline:

OECD Guideline 402 (Acute Dermal Toxicity)

Version / remarks:

, adopted February 1987

Deviations:

no

GLP compliance:

yes

Test type:

standard acute method

Limit test:

yes

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Wiga, Sulzfeld, Germany
- Age at study initiation: 5-6 weeks
- Weight at study initiation: males: 358 to 402 g, female: 210 to 241 g
- Fasting period before study: No
- Housing: In stainless steel cages with wire-screen bottom and front, 5 animals per cage; during dermal exposure the animals were housed individually
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: 65 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 3 °C
- Humidity (%): 52.5-92.5 (upper limit higher than the intended 70 %, because of meterological circumstances or because of wet cleaning of the animals room; the 92.5 % peak occured for ca one hour at most)
- Air changes (per hr): 10
- Photoperiod (hrs dark/hrs light): 12/12

Type of coverage:

occlusive

Vehicle:

unchanged (no vehicle)

Details on dermal exposure:

TEST SITE
- Area of exposure: 20cm²
- % coverage: 10 % of the total body surface
- Type of wrap if used: exposed area was covered by plastic foil, which was fixed by adhesive tape and the entire trunk of the rat was wrapped with an impervious material

REMOVAL OF TEST SUBSTANCE
- Washing (if done): the skin was rinsed with lukewarm water
- Time after start of exposure: 24 hours

TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 2 mL/kg bw
- Concentration (if solution): 99.5 %
- Constant volume or concentration used: Yes

Duration of exposure:

24 hours

Doses:

2000 mg/kg body weight

No. of animals per sex per dose:

5

Control animals:

not required

Details on study design:

- Duration of observation period following administration: 14 days
- Frequency of clinical observations: within 1 h and 4 h after the start of dosing, and subsequently at least once daily throughout an observation period
- Frequency of weighing: on day 0, 3, 7 and 14
- Necropsy of survivors performed: On day 14 of the study, all animals were killed with carbon dioxide and examined for external changes. Next the abdomen and the thorax of each animal was opened and examined for gross pathological changes.

Statistics:

N.A.

Sex:

male/female

Dose descriptor:

LD50

Effect level:

> 2 000 mg/kg bw

Based on:

test mat.

Mortality:

No mortality occured.

Clinical signs:

other: Apart from encrustation of the nose on day 1 and day 3 no clinical symptoms were observed.

Gross pathology:

Macroscopic examination of the animals at the end of the observation period did not reveal any treatment-related gross alterations.

Other findings:

Dermal reactions:
After treatment with the test substance, only slight encrustation was observed in two males and one female on day 1 of the study.

Table 1: Acute dermal toxicity of n-propyl lactate in rats
Animal no.	Dose applied (mL)*	Body weights (g) recorded on day				Mortality -/+
		0	3	7	14
Males:
52	0.7	358	348	359	363	-
54	0.8	385	380	391	399	-
56	0.8	402	395	401	416	-
58	0.8	392	380	394	401	-
60	0.7	360	350	355	369	-
	mean	379	371	380	390
	sem**	9	9	10	10
Females:
51	0.4	215	212	219	225	-
53	0.5	227	222	219	224	-
55	0.4	210	218	218	221	-
57	0.5	241	233	236	249	-
59	0.4	217	203	205	209	-
	mean	222	218	219	226
	sem**	5	5	5	7

*= dose of 2 mL per kg body weight of the undiluted test substance

**= standard error of the mean

Interpretation of results:

practically nontoxic

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

In conclusion, since no mortality occurred in an acute dermal toxicity study, the dermal LD 50 of n-propyl lactate is considered to exceed 2000 mg/kg bw, both in males and females

Executive summary:

In an acute dermal toxicity study according to OECD guideline 402, groups of Wistar rats (5/sex) were dermally applied a dose of 2000 mg/kg bw of n-propyl lactate (99.5% purity).

The animals were observed for 14 days after the single exposure. No mortalities occured after treatment with the test substance at 2000 mg/kg bw. Therefore, the dermal LD₅₀ value is greater than 2000 mg/kg body weight, both in male and female rats. n-Propyl lactate is used as read-across partner to isobutyl-R-lactate.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Additional information

No acute oral toxicity data are available for the target substance isobutyl-R-lactate. However, available data on 2-etyhlhexyl lactate, isopropyl-S-lactate, n-butyl-(S)-lactate, and isobutanol (being the primary metabolite of isobutyl-R-lactate) were used in a read-across approach for acute oral toxicity. In these studies, performed according to or similar to OECD guideline 401, the reported LD₅₀ values exceed the limit dose of 2000 mg/kg bw for any of the test substances. Based on structural similarity, representing lactate esters with alkyl moieties of similar length, both linear and branched, the three source substances 2-ethylhexyl lactate, isopropyl-S-lactate and n-butyl-S-lactate are considered to be suitable read-across partners. Due to the rapid enzymatically driven hydrolysis of isobutyl-R-lactate into isobutanol and lactic acid, the toxicology of isobutyl-R-lactate can be understood in terms of the toxicology of isobutanol and lactic acid. Thus, available data from the degradation product isobutanol (source substance) is considered a suitable read-across partner. Therefore, it is concluded that the oral LD₅₀ is greater than 2000 mg/kg bw also for the target substance, i.e. isobutyl-R-lactate is not acutely toxic upon oral administration.

An acute inhalation toxicity test in rats was conducted on isobutyl-S-lactate according to OECD guideline 403. None of the rats exposed to isobutyl-S-lactate aerosol at a measured concentration of 6.16 g/m³ for 4 hours died within the 14 days observation period. Therefore, the LC₅₀ of the test substance is greater than 6.16 g/m³ (> 6.16 mg/L). Isobutyl-S-lactate is a suitable read-across partner as this substance is an enantiomer of the target substance isobutyl-R-lactate. In conclusion, isobutyl-R-lactate is not considered to be acutely toxic via the inhalation route.

n-Propyl lactate was tested for acute dermal toxicity in accordance with OECD guideline 402. Since no mortality occurred the dermal LD₅₀ of n-propyl lactate is exceeds 2000 mg/kg body weight, both in males and females. This study on one potential read-across partner alone would not be sufficient for fulfilling the endpoint of acute dermal toxicity. However, since sufficient data are available allowing conclusions on acute oral and inhalation toxicity, the dermal route is not mandatory.

Justification for selection of acute toxicity – oral endpoint
Available data on 2-etyhlhexyl lactate, isopropyl-S-lactate, n-butyl-S-lactate, and isobutanol (as the primary metabolite of isobutyl-R-lactate) were used in a read-across and weight-of-evidence approach for acute oral toxicity. In these studies, performed according to or similar to the OECD guideline 401, the presented LD50 values exceed the limit dose of 2000 mg/kg bw for any of the test substances. This is extrapolated to isobutyl-R-lactate by read-across.

Justification for selection of acute toxicity – inhalation endpoint
GLP guideline study on a substance used for read-across. In an acute inhalation toxicity test in rats no mortality occurred after exposure to isobutyl-S-lactate. Therefore, the LC50 of the test substance is greater than 6.16 g/m³ (> 6.16 mg/L). This is extrapolated to isobutyl-R-lactate by read-across.

Justification for selection of acute toxicity – dermal endpoint
GLP guideline study on a substance used for read-across. n-Propyl lactate was tested for acute dermal toxicity in accordance with OECD guideline 402. Since no mortality occurred the dermal LD50 of n-propyl lactate exceeds 2000 mg/kg body weight. This is extrapolated to isobutyl-R-lactate by read-across.

Justification for classification or non-classification

Based on the available data on suitable read-across partners isobutyl-R-lactate does not warrant classification for acute toxicity. The LD₅₀ values for the dermal and oral route are above the limit dose of 2000 mg/kg bw of Regulation (EC) No 1272/2008. The LC₅₀ value for the inhalation route (administered as aerosol) was greater than 6.16 mg/L, which is above the limit value for classification of dusts and mists specified in Regulation (EC) No 1272/2008.