Isooctyl mercaptoacetate

Repeated dose toxicity: oral

Administrative data

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

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

Adequacy of study:

other information

Study period:

From December 7, 2004 to September 2, 2005

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Meets generally accepted scientific standards, well documented

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2005

Report date:

2005

Materials and methods

Test guideline

Qualifier:

no guideline required

Principles of method if other than guideline:

The objective of the study was to determine dosage levels of substance to be evaluated in a reproductive/developmental toxicity screening study in rats.
Therefore, when compared to relevant OECD Guidelines for repeated short-term studies (OECD 407), it suffers limitations, as haematology, clinical chemistry, histopathology and neurobehavioural examinations were not conducted.

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

2-ethylhexyl mercaptoacetate

EC Number:

231-626-4

EC Name:

2-ethylhexyl mercaptoacetate

Cas Number:

7659-86-1

Molecular formula:

C10H20O2S

IUPAC Name:

2-ethylhexyl sulfanylacetate

Details on test material:

- Name of test material (as cited in study report): 2-ethylhexyl mercaptoacetate (EHMA)
- Physical state: colorless liquid
- Stability under test conditions: considered stable
- Storage condition of test material: stored at room temperature under nitrogen

Test animals

Species:

rat

Strain:

other: Crl:CD (SD)

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, North Carolina
- Age at study initiation:
Male: 59 days
Female: 82 days
- Weight at study initiation:
Males: 253.9 - 285.0 g
Females: 242.5 - 272.5 g
- Fasting period before study: not reported
- Housing: individually
- Diet: rodent diet ad libitum
- Water: filtered tap water ad libitum
- Acclimation period: 7 days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20.7 - 23.0
- Humidity (%): 22.8 - 56.1
- Air changes (per hr): approximately 28
- Photoperiod (hrs dark / hrs light): not reported


IN-LIFE DATES: From: January 4 To: January 18, 2005

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS: weekly


VEHICLE
- Justification for use and choice of vehicle (if other than water): no
- Amount of vehicle (if gavage): 4 mL/kg
- Purity: 100%

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Duplicate samples (1 mL each) from top, middle and bottom strata of the pre-initiation formulations prepared at concentrations bracketing those used in the study (1 and 50 mg/mL) were used for homogeneity and concentration determinations. Duplicate samples (1 mL each) for concentration analysis were collected from the middle stratum of the first preparation of each dosing formulation (including the control group).

Duration of treatment / exposure:

14 Days

Frequency of treatment:

daily

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 10, 50 & 150 mg/kg bw/d
Basis:
other: nominal in gavage solution

No. of animals per sex per dose:

5

Control animals:

yes, concurrent no treatment

Details on study design:

- Post-exposure period: none
- Dose selection rationale: Results of the 7-day study of 1992

Positive control:

No

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: No data


DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: twice daily


BODY WEIGHT: Yes
- Time schedule for examinations: daily


FOOD CONSUMPTION : Yes
- Time schedule for examinations: daily


OPHTHALMOSCOPIC EXAMINATION: No


HAEMATOLOGY: No


CLINICAL CHEMISTRY: No


URINALYSIS: No


NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
Gross necropsies were conducted on the 150 mg/kg/day female found dead and all other surviving animals on study day 14. Animals were euthanized by carbon dioxide inhalation at the scheduled necropsy. The necropsies included, but were not limited to, examination of the external surface, all orifices, and the cranial, thoracic, abdominal and pelvic cavities, including contents. Tissues were not retained, and the carcasses were discarded. (See Table 1 for details on organ weights examination)

Statistics:

Mean body weight, body weight change, food consumption (of each interval) and organ weight data were subjected to a parametric one-way analysis of variance (ANOVA) (Snedecor and Cochran, 1980) to determine intergroup differences. If the ANOVA revealed statistically significant (p<0.05) intergroup variance, Dunnett's test (Dunnett, 1964) was used to compare the test article-treated groups to the control group.

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Food efficiency:

not specified

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

not examined

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
One female in the 150 mg/kg/day group was found dead on study day 2. This female had clear material around the mouth noted on study day 1 approximately 1 hour following dose administration and lost 28.6 g during study days 0-1. This female was internally normal. The death of this female was considered test article-related due to effects on mean body weight seen in the other 150 mg/kg/day females and the mortalities seen at 200 mg/kg/day in the previous 7 day toxicity study (See study: Worell (1992)/Oral 7 day repeated 03). All other animals survived to their scheduled necropsy.

Decreased defecation was noted in three of the 150 mg/kg/day females; noted for one female during study days 2-4 and the other two females during study days 8-11. This finding was not noted in the 150 mg/kg/day males. Clear material around the mouth was observed in four males and in the four surviving females in the 150 mg/kg/day group approximately 1 hour after dose administration. This finding was noted in the majority of these animals as early as study day 2 and continued throughout the remainder of the study. Other clinical findings noted at the daily examinations or approximately 1 hour following dosing including hair loss on various body surfaces, lacrimation, swollen eyelids, clear material on the forelimbs and salivation, occurred primarily in single animals in the 150 mg/kg/day group and therefore were not considered to be test article-related.


BODY WEIGHT AND WEIGHT GAIN
When the overall treatment period (study days 0-14) was evaluated, mean male and female body weight gains in the 150 mg/kglday group were slightly lower (not statistically significant) than the respective control groups.
In this group, in both males and females, lower mean body weight gains were observed for the first-week period of the study. In males, the difference was statistically significant during study days 4-5 (p<0.01) and in females during study days 1-2 and 4-5 (p<0.05).
For the second-week period of the study, mean body weight gains in the 150 mg/kg/day group male and females were generally similar to the control group values.

Mean male and female body weights in the 150 mg/kg/day group were similar to the control group from study days 0 through 4.
However, from study days 5 through 12, mean male and female body weights were 5.1% to 9.2% and 6.0% to 11.9% lower than the control group values, respectively.
By the end of the study (study days 13 and 14), mean male and female body weights in the 150 mg/kglday group were similar to the control group.
The only statistically significant (p<0.05) differences noted were lower mean female body weights during study days 5, 8 and 9.

Mean body weights and body weight changes in the 10 and 50 mglkg/day male and female groups were similar to the respective control group values. Differences were slight and not statistically significant; no dose-dependent trends were evident.


FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study)
Mean male food consumption in the 10, 50 and 150 mg/kg/day groups was generally similar to the control group throughout the study (days 0-14). The only statistically significant (p<0.05 or p<0.01) differences noted in any intervals for the male animals on study were increased food consumption in the 150 mg/kg/day group males during study days 10-11 and 12-13.

With the exception of study days 3-4, mean female food consumption in the 150 mg/kg/day group females was lower than the control group from the start of dose administration through study days 10-11; the differences were statistically significant (p<0.05) during study days 2-3 and 4-5. Because of the increases in food consumption during the last 3 days of treatment, mean food consumption in this group was similar to that in the control group when the entire treatment period (study days 0-14) was evaluated.
Food consumption in the 10 and 50 mg/kg/day female groups was similar to that in the control group. The only statistically significant (p<0.05) differences from the control group values were transient increases in the 10 mg/kg/day group females (study days 3-4 and 11-12).


ORGAN WEIGHTS
Mean absolute and relative (to final body weight) liver weights were increased by 14.3% (absolute) in the 50 mg/kg/day males as well as by 25.4 and 25.7% (absolute) in the 150 mg/kg/day male and female groups compared to control group values, respectively. The differences from the control group values for mean relative liver weights at 150 mg/kg/day were statistically significant (p<0.01).
Mean absolute and relative kidney weights were increased by 9.0 and 12.0% (absolute) in the 50 and 150 mg/kg/day males compared to control group values.
Slightly decreased mean absolute and relative thymus and thyroid/parathyroid weights were noted in the 150 mglkg/day group males (14.3 and 16.5% absolute, respectively) and females (17.8 and 23.1% absolute, respectively) compared to the control group values; the difference in mean relative thyroid/parathyroid weight in the males was statistically significant (p<0.05).
No other test article-related effects were noted on organ weights for the 50 and 150 mg/kg/day groups.

No test article-related effects on mean absolute and relative organ weights were observed in the 10 mg/kg/day group males and females. A statistically significant (p<0.05) decrease in mean absolute brain weight was noted in the 10 mg/kg/day group females; this decrease did not occur in a dose-related manner and is not considered to be treatment-related.


GROSS PATHOLOGY
One female from the 150 mg/kg/day group was found dead on study day 2. This female was internally normal. All other animals survived to their scheduled necropsy.
At the scheduled necropsy on study day 14, one male in the control group had white contents in the pericardium and one male in the 50 mg/kg/day group had a dilated renal pelvis. No other gross pathology findings were noted in males or females.

Effect levels

1

Dose descriptor:

NOAEL

Effect level:

50 mg/kg bw/day (nominal)

Sex:

male/female

2

Dose descriptor:

LOAEL

Effect level:

150 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: Death of one female and clinical signs associated

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

Table 2 Mean Body Weights changes (g) – Most relevant changes

Exposure Group	Control	10 mg/kg/d	50 mg/kg/d	150 mg/kg/d
Males
Day 4-5	9.2 +/- 3.2	5.4 +/- 3.2	4.9 +/- 2.2	-6.6 +/- 13.4**
Females
Day 7-14	11.7 +/- 6.9	8.7 +/- 4.3	7.6 +/- 6.4	23.8 +/- 4.3*

*Statistically significant difference from the control group (p0.05) using Dunnett’s test.

**Statistically significant difference from the control group (p0.01) using Dunnett’s test.

Table 3 Food consumption (g/animal/d) – Most relevant changes

Exposure Group	Control	10 mg/kg/d	50 mg/kg/d	150 mg/kg/d
Females
Day 0-7	16.0 +/- 2.2	18.0 +/- 2.0	16.8 +/- 0.8	12.5 +/- 2.7*

*Statistically significant difference from the control group (p0.05) using Dunnett’s test.

Table 4 Organ Weights (g) – Most relevant changes

Exposure Group	Control	43 mg/kg/d	84 mg/kg/d	170 mg/kg/d
Males
Absolute organ Weight (g)
Liver	14.6 +/- 1.69	15.0 +/- 2.53	16.7 +/- 1.78	18.3 +/- 3.14
Kidney	3.01 +/- 0.30	3.03 +/- 0.20	3.28 +/- 0.34	3.37 +/- 0.59
Relative organ Weight (g) to bodyweight
Liver	4.10 +/- 0.21	4.27 +/- 0.47	4.62 +/- 0.45	5.31 +/- 0.52*
Kidney	0.84 +/- 0.07	0.87 +/- 0.05	0.91 +/- 0.11	0.98 +/- 0.09
Thyroids/para	0.007 +/- 0.0	0.007 +/- 0.0	0.006 +/- 0.0015	0.007 +/- 0.0005
Females
Absolute organ Weight (g)
Liver	11.2 +/- 2.07	11.5 +/- 1.76	10.1 +/- 1.16	14.0 +/- 1.41
Brain	1.88 +/- 0.09	1.77 +/- 0.03*	1.90 +/- 0.05	1.83 +/- 0.06
Relative organ Weight (g) to bodyweight
Liver	4.01 +/- 0.50	4.19 +/- 0.58	3.64 +/- 0.42	5.26 +/- 0.56**

*Statistically significant difference from control group (p0.05) using Dunnett’s test.

**Statistically significant difference from control group (p0.01) using Dunnett’s test.

Applicant's summary and conclusion

Conclusions:

In this limited 14-day repeated dose toxicity study by gavage in rats, as it was designed to select dose to be used in a screening reproduction toxicity study, the NOAEL should be derived at 50 mg/kg bw/d, based on the death of a female at 150 mg/kg bw/d and associated clinical findings observed at this level.

Executive summary:

The objective of the study was to determine dosage levels of 2-ethylhexyl mercaptoacetate to be evaluated in a reproductive/developmental toxicity screening study in rats.

2-ethylhexyl mercaptoacetate, in the vehicle, corn oil, was administered orally by gavage to three groups of five Crl:CD (SD) rats/sex/dose once daily for 14 days. Dosage levels were 10, 50 and 150 mg/kg/day administered at a dosage volume of 4 mL/kg. A concurrent control group composed of five animals/sex received the vehicle on a comparable regimen. All animals were observed twice daily for mortality and moribundity. Clinical observations, body weights and food consumption were recorded daily. On study day 14, each surviving animal was subjected to a gross necropsy and selected organs were weighed.

One female in the 150 mg/kg/day group was found dead on study day 2. Decreased defecation was observed in three females in the 150 mg/kg/day group.

Body weight losses and associated slight decrease in feed consumption were observed in the 150 mg/kg/day group males and females during the first week of dose administration. Nevertheless, when the overall treatment period (study days 0-14) was evaluated, mean male and female body weight gains in the 150 mg/kg/day groups were found to be only slightly lower (not statistically significant) than the respective control groups.

Increased absolute and relative (to final body weight) liver weights were observed in the 50 mg/kg/day (males) and the 150 mg/kg/day (males and females) groups. Absolute and relative kidney weights were increased in the 50 and 150 mg/kg/day males compared to control group values. Absolute and relative thymus gland and thyroid/parathyroid gland weights in the 150 mg/kg/day males and females were slightly reduced compared to the control animals.

Based on the results of this study, dosage levels of 10, 50 and 150 mg/kg/day were selected for a reproduction/developmental toxicity screening study of 2-ethlyhexyl mercaptoacetate administered orally by gavage to rats.

The NOAEL of this 14-day study in rats should be derived at 50 mg/kg bw/d, based on the death of a female at 150 mg/kg bw/d and associated clinical findings observed at this level. As increases in kidney and liver weight observed in animals dosed at 50 mg/kg bw/d were not found to be statistically significant and because of the absence of gross pathology findings at this dose, these effects should be considered as not toxicologically relevant.