1,1-dimethylheptanethiol

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

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

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP study that meets generally accepted scientific standards, well documented and acceptable for assessment

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1985

Report date:

1985

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 412 (Subacute Inhalation Toxicity: 28-Day Study)

Deviations:

yes

Remarks:

2 dose levels, limited haematology, blood chemistry and microscopic examination

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

tert-dodecanethiol (CAS # 25103-58-6)

IUPAC Name:

tert-dodecanethiol (CAS # 25103-58-6)

Details on test material:

Supplier: Phillips Petroleum Company
Test article name: Mercaptan mixture aliphatic, Sulfole 120
Batch : batch no. 444
Purity: no data

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Inc., Portage, MI, USA
- Age at study initiation: 49 days of age
- Weight at study initiation: 252-270 g for males, 162-172 g for females
- Fasting period before study: no
- Housing: individually
- Diet (ad libitum excepted during exposure): Purina certified roden chow #5002
- Water (ad libitum): tap water
- Acclimation period: 14 days

ENVIRONMENTAL CONDITIONS
As per "Guide for the care and Use of Laboratory animals" (DHEW No. NIH 74-23, 1974)

Administration / exposure

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

whole body

Vehicle:

clean air

Remarks on MMAD:

MMAD / GSD: at 100 ppm:
Equivalent aerodynamic diameter (µm) 2.7 +/- 1.64 on week 3 and 3.6 +/- 1.64 on week 5

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: 16 m3 stainless steel and glass chamber
- Method of holding animals in test chamber: individually in suspended stainless steel wire-mesh cages
- Source and rate of air: HVAC system, 2000 L/min
- Method of conditioning air: the air was filtered and the temperature and relative humidity were controlled
- System of generating particulates/aerosols: counter-current vaporization system
- Temperature, humidity, pressure in air chamber: 72-76 °F, 47-57%
- Air flow rate: 2000 L/min
- Air change rate: no data
- Method of particle size determination: Andersen cascade impactor for the 100 ppm group and GC analysis
- Treatment of exhaust air:

TEST ATMOSPHERE
- Brief description of analytical method used: drawing samples of the test atmospheres through sorbent tubes containing XAD-4 resin and analysis with a gas chromatograph equipped with a flame photometric detector
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The actual concentrations of test material were determined by gas chromatograph (GC) each exposure day. Nominal concentrations were also calculated for all exposures. Aerosol particle size determinations were conducted after two and four weeks of exposure for those groups where a significant amount of aerosol was present.

Duration of treatment / exposure:

28 days

Frequency of treatment:

6 hours/day; 5 days/week

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
25 and 100 ppm
Basis:
other: Desired conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
26 ppm and 98 ppm
Basis:
analytical conc.

Doses / concentrations 3

Remarks:

Doses / Concentrations:
42 and 214 ppm
Basis:
nominal conc.

No. of animals per sex per dose:

10

Control animals:

yes, sham-exposed

Details on study design:

- Rationale for animal assignment (if not random): Computerized selection using homogeneity of body weight variances as the criterion for acceptance.
- Dose selection rationale: no data
- Post-exposure recovery period in satellite groups: none

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: All animals were observed for mortality twice daily.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Detailed observations were conducted weekly.

BODY WEIGHT: Yes
- Time schedule for examinations: weekly

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes, weekly

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No

WATER CONSUMPTION: No

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: after 4 weeks of exposure
- Anaesthetic used for blood collection: Yes (identity) / No / No data
- Animals fasted: Yes
- How many animals: all
- Parameters: Hematocrit, hemoglobin concentration, erythrocyte count, mean corpuscular hemoglobin (MCH), mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), leukocyte count (total and differential).

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: after 4 weeks of exposure
- Animals fasted: Yes
- How many animals: all
- Parameters: Aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase, glucose, urea nitrogen, and creatinine.

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes , All surviving animals after 4 weeks.

ORGAN WEIGHTS: heart, lungs and trachea, liver, testis, kidney, brain and ovary.

HISTOPATHOLOGY: Yes
Microscopic examination of formalin-fixed hematoxylin-eosin stained paraffin sections from all animals: adrenal (2), liver (2 lobes), kidney, heart, gonad, lungs (all lobes), trachea (distal and bifurcation), brain and all gross lesions.

Statistics:

Analysis of body weights, clinical laboratory tests and organ weights (absolute and relative both to body and brain weight) will be performed using the methods indicated below.
Parametric analysis was conducted utilizing Bartlett's Chi-Square test for homogeneity of variance followed, where appropriate, by an analysis of variance and then, where appropriate, by Dunnett's -t test. In cases where the data were more amendable to analysis by non-parametric methods, the Conover & Iman Tank transformation method was used. In all cases the level of rejection was at the five (5) percent level.

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 examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
Essentially no signs were observed in the rats for the first three weeks of the study. The only apparently test material-related sign in the rats was the presence of material (described as dark, red or black) around the nose and eyes which was seen more often in the 100 ppm Group animals than in the control and 25 ppm Groups. This sign was observed with significant incidence (3/10 males, 6/10 females) only during week 4.

BODY WEIGHT AND WEIGHT GAIN
The mean body weight for the 100 ppm Group male rats was significantly reduced below that of the controls at weeks 2, 3 and 4. The mean body weights of the female rats from 100 ppm Group tended to be decreased at all weeks, but the differences were not statistically significant.

FOOD CONSUMPTION
Expressed as g/animal/day, the food.consumption of the high level-exposed rats (100 ppm) was significantly decreased below control values of weeks 1, 2 and 3 in the males and weeks 2 and 3 in the females. The values for the 100 ppm Group rats of both sexes also averaged less than the control values at the other weeks of the study, but the differences were not statistically significant. Expressed on a g/kg/day basis, food consumption of the 100 ppm Group animals (male or female) was significantly decreased below control values at weeks 1 and 2, but not 3 and 4.

HAEMATOLOGY
There were no noteworthy haematology differences in the rats.

CLINICAL CHEMISTRY
There were no serum biochemical changes in the rats that were considered to be exposure related. The one statistically significant change (increased creatinine level in the 100 ppm Group males) was considered to be anomalous as the value was written the normal range for male rats of this age.

ORGAN WEIGHTS
Test material exposure-related increases in liver weight were noted at 100 ppm. Since there were no correlative macro- or microscopie liver changes, the increased liver weights in rats cannot be clearly related to the test material exposures.

GROSS PATHOLOGY
There were no clear test article related macroscopic changes observed among rats exposed to either 25 or 100 ppm. An increased incidence of urinary obstruction was observed in females exposed to 100 ppm. The changes were characterized by distention of the ureter and hydronephrosis. There were no calculi reported in either the bladder or the ureter and the bladder was free of other macroscopic changes.

HISTOPATHOLOGY: NON-NEOPLASTIC
Test article related microscopic renal tubular degeneration with regeneration and granular casts were observed in males at both 25 and 100 ppm. The lungs were free of test-article related changes. Hydronephrosis (4 examined) with distention of the ureter(s) (3 examined) was observed in females exposed to 100 ppm. There were no macroscopic calculi observed in either the ureter or the bladder. There were no macroscopic changes in the bladder which therefore remained unexamined microscopically as directed by protocol. The significance of this common spontaneous finding was unclear.
A description of the pertinent findings can be seen below:
Tubular Degeneration:
- Vacuolation and sloughing of tubular epithelial cells primarily in the proximal tubules.
Granular Cast:
- Granular cellular debris occluding the lumen of tubules, usually at the junction of the distal end of the proximal tubule and the beginning of the thin segment of the loop of Henle located near the junction of the inner and outer cortex.
Tubular Regeneration:
- The presence of regenerating epithelium in renal tubules characterized by small basophilie cells with a high nuclear to cytoplasmic ratio. Frequently seen subsequent to tubular degeneration.
The tubular degeneration and regeneration and granular casts seen in male rats exposed to TDM were consistent with "Hydrocarbon Nephropathy". The changes were of trace to mild severity and were invisible macroscopically. However, creatinine was increased significantly in male rats at 100 ppm TDM. Hydronephrosis, observed in females, has been a common spontaneous genetic condition often related to partial obstruction of the ureter(s) either with calculi or by some other more subtle process. In the absence of microscopic examination of the bladder this finding could not be dismissed.
Pertinent but incidental microscopic findings were observed in the lungs and liver. A spontaneous acute pulmonary periarteritis was present in both sexes and in all groups, control and experimental. It was considered to be consistent with an early inflammatory response to viral infection. "Liver masses" and "foci" described macroscopically were focal areas of cell disassociation caused by inadvertent intrahepatic injection of sodium pentobarbital during euthanasia.
Additional microscopic changes were observed in a variety of organs. They were considered to be incidental and usual for rats of this strain and age.

Effect levels

Dose descriptor:

LOAEC

Effect level:

26 ppm (analytical)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: = 215 mg/m3. Kidney changes in female rats.

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

Table 1: PERTINENT ORGAN WEIGHT CHANGES - RATS

Sex	Males			Females
Group	Control	25 ppm	100 ppm	Control	25 ppm	100 ppm
Body Weight (g)	331	327	305	207	206	192
Brain Weight (g)	1.91	1.95	(1.82)	1.82	1.77	(1.72)
Brain/Body Weight (%)	5.82	6.02	6.00	8.83	8.64	9.03
Liver (g)	12.83	13.01	14.34	8.59	9.15	[10.81]
Liver/Body Weight (%)	3.88	3.97	[4.69]	4.15	4.44	[5.60]
Liver/Brain Weight (% x 10-^2)	6.72	6.66	(7.89)	4.74	5.16	[6.30]

( )statistically significant p<0.05

[ ] = statistically significant p<0.01

There were no correlative microscopie findings.

Table 2: PERTINENT MICROSCOPIC CHANGES - RATS

Sex	Males			Females
Group	Control	25 ppm	100 ppm	Control	25 ppm	100 ppm
NUMBER EXAMINED	10	10	10	10	10	10
KIDNEY
Tubular degeneration and regeneration		1	5
Granular casts			4
Hydronephrosis			1		1	4
URETER
Dilatation						3

Applicant's summary and conclusion

Conclusions:

Rats exhibited dark red or black material around eyes and nose in both dose groups. Male rats showed a statistically significant decrease in body weight gain and a corresponding depression in food consumption at the high dose. High dose male rats showed a statistically significant increase in creatinine. Liver weights showed exposure related increase. Since no macroscopic or microscopic changes in rat livers were noted, these weight increases cannot be clearly related to exposure. Male rats  at both concentrations exhibited mild renal tubular degeneration and granular cysts which were consistent with hydrocarbon nephropathy. High dose female rats exhibited hydronephrosis.

Executive summary:

In a 4-week inhalation study (comparable to OECD TG 407), rats exposed to nominal concentrations of 0, 26 (0.22 mg/L) and 98 ppm (0.81 mg/L) (the high concentration was a saturated vapour) t-dodecyl mercaptan for six hours/day, five days/week. Body weight reduction in males (98 ppm; 0.81 mg/L) with a corresponding reduction in food consumption was observed. High-dose males showed an increase in creatinine, and liver weights showed an exposure-related increase. Male rats at both concentrations exhibited mild renal tubular degeneration and granular cysts which were consistent with species-specific hydrocarbon nephropathy. Highdose female rats exhibited hydronephrosis. The LOAEC was 26 ppm (0.22 mg/L).