Methyl isothiocyanate

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1987

Report date:

1987

Reference 2

Reference Type:

other: Regulatory review

Title:

4th Revised Toxicology Disciplinary Chapter for: Metam Sodium (PC Code 039003) and Methyl isothiocyanate (MITC, PC Code 068103)

Author:

Lowit A and Facey J

Year:

2005

Bibliographic source:

United States Environmental Protection Agency Washington, D.C. 20460. Office of Prevention Pesticides and Toxic Substances

Report date:

2005

Reference 3

Reference Type:

other: Regulatory review

Title:

Draft Assessment Report (DAR) - public version - Initial risk assessment provided by the rapporteur Member State Belgium for the existing active substance ME TAM-SODIUM

Author:

Anonymous

Year:

2007

Bibliographic source:

Volume 3, Annex B, part 2, B.6

Reference 4

Reference Type:

other: Regulatory review

Title:

Human Studies Review Board: Weight of Evidence Discussion for Methyl isothiocyanate (MITC).

Author:

Lowit A

Year:

2006

Bibliographic source:

United States Environmental Protection Agency Washington, D.C. 20460. Office of Prevention Pesticides and Toxic Substances

Report date:

2006

Reference 5

Reference Type:

other: Regulatory review

Title:

EVALUATION OF METHYL ISOTHIOCYANATE AS A TOXIC AIR CONTAMINANT. Part C—Human Health Assessment

Author:

Rubin AL

Year:

2002

Bibliographic source:

California Environmental Protection Agency, Department of Pesticide Regulation, Sacramento, California, USA

Report date:

2002

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

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

Deviations:

yes

Remarks:

(food consumption was not monitored)

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Methyl isothiocyanate

EC Number:

209-132-5

EC Name:

Methyl isothiocyanate

Cas Number:

556-61-6

Molecular formula:

C2H3NS

IUPAC Name:

isothiocyanatomethane

Details on test material:

- Name of test material (as cited in study report): methyl isothiocyanate

- Substance type: organic
- Physical state: solid/brown crystals
- Analytical purity: 96.9% (98% according Aldrich)
- Impurities (identity and concentrations): no

- Purity test date: not reported
- Lot/batch No.: 6205 MK (supplied by Aldrich)
- Expiration date of the lot/batch: not reported

- Stability under test conditions: was ensured throughout the study (cf. report APE/RF, Jan.24, 1986)
- Storage condition of test material: cool and dry
- Other:
- Code Letters: MITC;
-Test substance No.: 85/231; (Number 85/231-2 was used for exposure);
- Homogeneity: was ensured due to the high degree of purity.

Test animals

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Dr. K. Thomae GmbH, D-7950 Biberach, FRG
- Age at study initiation: 8 weeks
- Weight at study initiation:
Test group 0: 280.2 ± 5.8 (males), 170.0 ±2.4 (females);
Test group 1: 278 ± 13.6 (males), 170.6 ± 6.8 (females);
Test group 2: 274.9 ± 6.0 (males), 171.3 ± 6.9 (females);
Test group 3: 280.2 ± 9.7 (males), 173.2 ± 4.5 (females).
- Fasting period before study: no
- Housing: during the non-exposure period: singly in type D III wire mesh cages supplied by Becker, Castrop-Rauxel, FRG; during the exposure period: singly in wire mesh cages in the inhalation chambers.
- Diet (e.g. ad libitum): during the exposure free period: Kliba Laboratory diet, rat/mouse maintenance Kliba 24-343-4, 10 mm pellets, Klingentalmühle AG, CH-4303 Kaiseraugst, Switzerland; The feed used was from batche: Nos. Ba 33-85 and Ba 34-85.
- Water (e.g. ad libitum): during the exposure free period: tape water ad libitum
- Acclimation period: 4 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20-24
- Humidity (%): 30-70
- Air changes (per hr): not reported
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

other: nitrogen/air

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Inhalation chamber: glass/steel construction) with a volume of about 500 liters.
- Method of holding animals in test chamber: the rats in the test groups were housed singly in wire mesh cages in the inhalation chamber.
- Source and rate of air: supply air about 8000 L/h, Nitrogen/air quantity ratios for the thermostatic water bath were set in average at: 0 L/h (Test group 0), 0.28 L/h (Test group 1), 1.91 L/h (Test group 2) and 7.98 L/h (Test group 3).
- Method of conditioning air: Methyl isothiocyanate was contained within a fritted glass flask placed in a thermostatic water bath. A stream of metered nitrogen took up the vapors and together with a stream of supply air, was introduced into a whole body exposure system (inhalation chamber: glass/steel construction) with a volume of about 500 liters after passing through a thermostatic mixing device arranged upstream. The inhalation system was also connected to an exhaust air system.
- System of generating particulates/aerosols: not applicable
- Temperature, humidity, pressure in air chamber: 22°C, 50% humidity, and a pressure below atmospheric of -2 Pa in chambers 1+2 (Test groups 1+2), and of -5 Pa in chamber 3 (Test group 3) and an excess pressure of 1 or 2 Pa in the chamber 0 (Test group 0).
The temperature and all air flows, as well as the supply air and exhaust air, were continuously measured for all test groups (digital thermometer, rotameter) and recorded 3 times during each exposure.
The pressure in the chambers was measured continuously (inclined-tube manometer) and recorded once daily. The humidity in the chamber was checked twice during each exposure by means of a humidity measuring probe (Vaisala) and was recorded.
- Air flow rate of the sample taken for gas chromatographic analysis: 1.5 L/min
- Air change rate: not reported
- Method of particle size determination: not applicable
- Treatment of exhaust air:
- Test group 0: The exhaust air system was set by about 200 L/h lower as compared to the supply air system (excess pressure) (7800 L/h). This ensured that no laboratory air could reach the control animals.
- Test groups 1-3: The exhaust air system was set by 100 and 300 L/h higher as compared to the supply air system (pressure below atmospheric) (8300 L/h (Test group 1+2) and 8110 L/h (Test group 3)) . This was to ensure that no contamination of the laboratory occurred as the result of possible leakages from the inhalation chambers.

TEST ATMOSPHERE
- Brief description of analytical method used: The concentrations for the test groups were measured after absorption of methyl isothiocyanate in 2-propanol gas chromatographically.
- Samples taken from breathing zone: yes, 6 vapor samples per concentration group were taken from the breathing zones of the animals daily.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Sampling from inhalation chambers and gas chromatographic analysis:
Equipment for vapor sampling:
- Elster experimental gas meter, converted for counting impulses
- Neuberger diaphragm pump
- BASF impulse counter with automatic pump switching
- Absorption set (glass)
- Sampling probe: 4 mm diameter
The flow rate of the sample was 1.5 L/min.

The samples were collected in 2 absorption vessels connected in series with a downstream fritted glass flask, each of which being filled with 15 - 20 ml 2-propanol.
The following sample volumes were drawn from the inhalation chambers: 50 L (Test group 1), 15 L (Test group 2), and 5 L (Test group 3).
0.5 ml internal standard was added to the samples and filled with 2-propanol in 50-ml graduated flasks up to the calibration mark. Then 2 ml of the samples were filled in tubes for the automatic sampler and analyzed. The volume injected was 2.5 µL.
Methyl isothiocyanate quantities were calculated from the corresponding area integral values, which, under conversion of the sample volumes, yielded the methyl isothiocyanate concentrations for test groups 1 - 3.
Concentration measured were: 5.1 ± 0.53, 19.9 ± 1.27, and 100.0 ± 5.33

Duration of treatment / exposure:

4 weeks

Frequency of treatment:

6hr/day, 5d/wk

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
5, 20 and 100 mg/m3
Basis:
nominal conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
1.7, 6.8 and 34 ppm
Basis:
analytical conc.

Doses / concentrations 3

Remarks:

Doses / Concentrations:
5.1, 19.9 and 100 mg/m3
Basis:
analytical conc.

No. of animals per sex per dose:

5 rats/sex/dose

Control animals:

yes

Details on study design:

- Dose selection rationale: 1)The highest concentration should be in a range that would make it possible to recognize any toxic effects (toxic profile of action). Within the frame of a 1-week preliminary study (Proj. No. 3010231/8113) only minimal toxic effects were observed at 30 mg/m³ [body weight gain unaffected; clinicochem. parameters and hematology unaffected; pathologic findings in the lungs: pinhead-sized focuses (activated alveolar epithelium; alveoli filled with macrophages)]. The highest selected concentration was therefore 100 mg/m³.
2) The intermediate concentration was selected in such a way that concentration-response relationships could be recognized. The concentration selected was 20 mg/m³.
3) The low concentration should present a NOEL. The concentration selected was 5 mg/m³.
- Rationale for animal assignment: the animals were randomized on a weight basis (randomization program WTALOC of Instern). Groups of the same weight were obtained.

Positive control:

no

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: several times each working day and once workdaily on exposure free days.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: several times each working day and once workdaily on exposure free days.


BODY WEIGHT: Yes
- Time schedule for examinations: The animals' body weight was checked at the beginning of preflow and of the exposure periods, thereafter once weekly, and at the end of exposure. In general, the weighings were carried out at the same time of day.

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No

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: Yes

WATER CONSUMPTION: No

OPHTHALMOSCOPIC EXAMINATION: No


HAEMATOLOGY: Yes
- Time schedule for collection of blood: in the morning between 07.00 and 12.00 hours
- Anaesthetic used for blood collection: No data
- Animals fasted: No
- How many animals: 5 animals per test group and sex
- Parameters checked in table [1] were examined.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: in the morning between 07.00 and 12.00 hours
- Animals fasted: No
- How many animals: 5 animals per test group and sex
- Parameters checked in table [No.1] were examined.

URINALYSIS: No


NEUROBEHAVIOURAL EXAMINATION: No

OTHER EXAMINATIONS:
- The activities of enzymes:
- glutamate pyruvate transaminase (ALAT);
- alkaline phosphatase (AP);
- glutamate oxalacetate transaminase (AST).
- Clotting analysis: - thromboplastin time (Hepato Quick's test)

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (see table 2)
HISTOPATHOLOGY: Yes (see table 2)

Other examinations:

no data

Statistics:

The data were evaluated statistically using the computer systems of the Department of Toxicology (responsible: Dr. Hoffmann, ZNT) or in the Computer Center of BASF Aktiengesellschaft (responsible: Mr. Helmstadter, ZLI/NI).
Clinical examinations:
For the statistical evaluation of the study means and standard deviations were calculated for the variables (body weight and body weight change) of the animals in each test group, and printed in the form of tables together with the individual values (body weight). Statistical analysis was carried out using the ANOVA test and Dunnett's test.
Blood and plasma examinations: Means and standard errors were calculated and tabulated together with the individual values.
In order to test significances, the individual dose groups were compared with the control group using the t- test.
Pathology: In the statistical evaluation of the study, means and standard deviation (of the individual values) were calculated for the variable (absolute organ weights) of the animals of each test group and were tabulated together with the individual values.
The statistical evaluation was carried out using a t test generalized by WILLIAMS for the simultaneous comparison of several dose groups with a 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):

not examined

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Clinical biochemistry findings:

effects observed, treatment-related

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:

no effects observed

Details on results:

CLINICAL SIGNS AND MORTALITY
No deaths occurred during the study.
Clinical observations at the high dose revealed marked mucous membrane and respiratory tract irritation (reedish nasal discharge, salivation, eye discharge) resulting in a change in breathing pattern and whooping respiration. Intensified cleaning and stretched posture were also noted. As the study progressed, certain signs (ruffled fur and respiratory sounds) ceased being reversible. less severe signs (eyelid closure, somnolence, and ruffled fur) were noted at the mid dose from day 3 onward. However, unlike the high dose animals, mid dose animals began to recover following the completion of each day's dosing. incidence rates for these clinical signs were not reported.

BODY WEIGHT AND WEIGHT GAIN
High dose males suffered a substantial weight loss during the first week (-19.2g, compared to a gain of 23-5g in control males, p<0.01). High dose females gained less weight than control during the first week (1.1g vs. 13.1 in controls), though statistical significance was not etablished. These differences were maintained throughout the study in both sexes. High dose male body weights on days7, 14, 21 and 27 were lower than controls by statistically significant margins. No convincing weight differences were observed at either of the two lower doses in either sex.
There were no measurements of food consumption, making it difficult to determine the reasons for the body weight effects at the high dose.

HAEMATOLOGY
Mid and high dose males exhibited increased numbers of neutrophilic polymorphonuclear granulocytes. The mean concentration in giga/L at increasing doses was 0.43±0.05, 0.48±0.07, 0.69±0.07*, and 1.42±0.18** (*p<0.05, **p<0.01, Student’s t test on logtransformed data [Dunnett’s parametric t test was positive at the high dose only]). Females showed this increase only at the high dose, with mean concentrations in giga/L at increasing doses of 0.52±0.09, 0.52±0.10, 0.55±0.08, and 1.44±0.28**. Overall leukocyte counts were also increased in high dose females (mean concentration in giga/L: 5.19, 4.72, 4.54, 6.73). These changes were considered related to inflammatory processes occurring in the respiratory tract.

CLINICAL CHEMISTRY
Clinical chemistry revealed statistically significant decreases in serum urea (22%), glucose (17%), triglyceride (58%), and albumin (9%) in high dose males. The urea and glucose concentrations in high dose females were likewise statistically depressed (30% and 14% respectively). Total bilirubin concentrations and thromboplastin time (a measure of blood clotting ability) were markedly increased in high dose males (92% and 16% respectively), though not in females. These changes were difficul to ascribe to a particular clinical picture. Smaller changes in urea (-17%), glucose (-5%), bilirubin (+41%), and thromboplastin time (+14%) were also present mid dose males, though these did not achieve statistical significance.

ORGAN WEIGHTS
Organ weight determinations showed statistically significant decreases in liver (18%) and kidney (17%) weights and an increase in lung (70%) weight among high dose males. Females showed only the increase in lung weight (83%).

GROSS PATHOLOGY
Gross pathology showed the lungs of all high dose males and three females to be pale, rigid, and of a puffy consistency.

HISTOPATHOLOGY: NON-NEOPLASTIC
Histopathology revealed an increase in incidence and severity of rhinitis in the nasal cavity at the high dose in both sexes (incidence in males: 2/5, 2/5, 2/5, 5/5; females: 0/5, 3/5, 1/5, 5/5). Other histopathologic findings at the high dose included: metaplasia of the nasal epithelium, tracheal epithelial proliferation and single cell necrosis (all high dose animals), bronchopneumonia and bronchial and bronchiolar epithelial proliferation (5 males, 2 females), and emphysema (3 males, 2 females). One finding, nasal epithelial atrophy, may have been induced at the low dose. This was based on increases in focal atrophy at that dose, and increases in total atrophy. The latter was evident both in the number of animals exhibiting focal + non-focal atrophy and in the fraction of section planes, particularly among females, showing atrophy. The absence of a further increase at the mid dose may be due in part to a process by which focal atrophy at lower doses was replaced by “non-focal” atrophy, considered to be a more general (i.e., diffuse) and potentially more serious lesion, at higher doses. Such a process was very clear at the high dose, where virtually all reported atrophy was non-focal.

Effect levels

1

Dose descriptor:

NOAEC

Remarks:

systemic toxicity

Effect level:

19.9 mg/m³ air (analytical)

Sex:

male/female

Basis for effect level:

other: increased neutrophilic polymorphonuclear granulocytes in the blood of males secondary to the respiratory tract irritation

2

Dose descriptor:

LOAEC

Remarks:

systemic toxicity

Effect level:

100 mg/m³ air (analytical)

Sex:

male/female

Basis for effect level:

other: lower body weight gain

3

Dose descriptor:

NOAEC

Remarks:

extrathoracic (ET) region

Effect level:

19.9 mg/m³ air (analytical)

Sex:

male/female

4

Dose descriptor:

LOAEC

Remarks:

extrathoracic (ET) region

Effect level:

100 mg/m³ air (analytical)

Sex:

male/female

Basis for effect level:

other: pathological changes of the nasal cavity (metaplasia of respiratory epithelium and atrophy of the olfactory epithelium)

5

Dose descriptor:

NOAEC

Remarks:

tracheabronchial (TB) region

Effect level:

19.9 mg/m³ air (analytical)

Sex:

male/female

6

Dose descriptor:

LOAEC

Remarks:

tracheabronchial (TB) region

Effect level:

100 mg/m³ air (analytical)

Sex:

male/female

Basis for effect level:

other: pathological changes (tracheal epithelial proliferation and single cell necrosis, bronchopneumonia and bronchial and bronchiolar epithelial proliferation)

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

Table 3:Mean Body Weights and Body Weight Gains

	Concentration (mg/m^3)
Treatment day	0	5	20	100
	Mean body weights (g)
Males
-7	280.2	278.0	274.9	280.2
0	307.9	311.0	302.9	310.7
7	331.4	335.8	322.3	291.5**
14	350.5	356.6	340.7	288.7**
21	370.8	378.3	358.8	282.6**
27	387.6	394.6	375.7	295.8**
Weight gain (g)
Day 7	23.5	24.7	19.3	-19.2**
Day 14	42.6	45.6	37.8	-22.0**
Day 21	62.9	67.2	55.8	-28.2**
Day 27	79.7	83.6	72.7	-14.9**
Females
-7	170.0	170.6	171.3	173.2
0	184.9	183.4	185.3	184.8
7	198.0	198.9	198.8	185.9
14	206.4	207.0	207.0	195.4
21	209.0	216.0	218.2	201.4
27	220.6	223.7	226.0	207.1
Weight gain (g)
Day 7	13.1	15.5	13.5	1.1
Day 14	21.5	23.6	21.7	10.7
Day 21	24.1	32.6	32.9	16.6
Day 27	35.7	40.3	40.7	22.4

Table 4 :Hematology and Clinical Chemistry

	Concentration (mg/m^3)
Parameter	0	5	20	100
Males
Thromboplastin time (sec)	35.900	36.580	40.780	41.840*
Thrombocytes (10^9/L)	983.6	934.0	1006.4	1034.4
Leucocytes (10^9/L)	7.568	8.106	6.360	7.188
Neutrophilic polymorphonuclear granulocytes (10^9/L)	0.43	0.48	0.69	1.42
Lymphocytes (10^9/L)	6.64	6.93	5.08	5.16
Creatinine (µmol/L)	64.592	61.288	52.583*	55.421
Potassium (mmol/L)	6.303	5.464**	5.823	5.834
Inorganic phosphate (mmol/L)	2.791	2.415**	2.581	2.479
Total bilirubin (mmol/L)	1.302	1.358	1.833	2.501**
Urea (mmol/L)	8.448	7.906	7.019	6.641*
Glucose (mmol/L)	7.802	7.681	7.437	6.493**
Triglycerides (mmol/L)	3.248	2.718	3.139	1.351**
Albumin (g/L)	39.880	40.200	37.900	36.520*
ALT (µkat/L)	1.216	1.100	1.070	1.130
AP (µkat/L)	8.086	8.054	8.074	8.002
Females
Thromboplastin time (sec)	39.980	38.140	35.760	41.140
Thrombocytes (10^9/L)	1012.4	1012.75	1060.8	1065.0
Leucocytes (10^9/L)	5.192	4.722	4.544	6.732**
Neutrophilic polymorphonuclear granulocytes (10^9/L)	0.52	0.52	0.55	1.44
Lymphocytes (10^9/L)	4.23	3.89	3.62	4.60
Creatinine (µmol/L)	62.528	59.507	65.013	53.171
Potassium (mmol/L)	5.778	6.085	5.741	5.427
Inorganic phosphate (mmol/L)	1.997	2.267	2.229	2.178
Total bilirubin (mmol/L)	2.142	1.709	1.724	1.789
Urea (mmol/L)	8.744	8.580	8.107	6.143*
Glucose (mmol/L)	7.094	7.387	7.115	6.079*
Triglycerides (mmol/L)	2.042	2.083	2.079	1.129
Albumin (g/L)	42.040	40.440	41.300	36.950
ALT (µkat/L)	0.872	1.000	0.920	1.104*
AP (µkat/L)	5.318	7.282*	5.940	6.958**

Table 5:Absolute Organ Weights

Body / Organ weights (g)	Concentration (mg/m^3)
	0	5	20	100
Males
Body weight day 27	387.6	394.6	375.7	295.8**
Kidneys	2.328	2.274	2.172	1.944**
Liver	12.028	11.734	10.694	8.882**
Lungs	0.962	1.028	0.930	1.650**
Females
Body weight day 27	220.6	223.7	226.0	207.1
Kidneys	1.414	1.448	1.348	1.366
Liver	6.458	6.506	6.564	6.524
Lungs	0.624	0.706	0.686	1.062*

Table 6:Histopathology

	Concentration (mg/m^3)
Findings	0		5		20		100
	M	F	M	F	M	F	M	F
Lungs
emphysema	0/5^1)	0/5	0/5	0/5	0/5	0/5	3/5	2/5
bronchopneumonia	0/5	0/5	0/5	0/5	0/5	0/5	5/5	2/5
bone metaplasia	1/5	0/5	0/5	1/5	0/2	1/5	3/5	0/5
epithelial proliferation	0/5	0/5	0/5	0/5	0/5	0/5	5/5	2/5
Trachea
inflammation	0/5	0/5	0/5	0/5	0/5	0/5	1/5	1/5
epithelial proliferation	0/5	0/5	0/5	0/5	0/5	0/5	5/5	5/5
single cell necrosis	0/5	0/5	0/5	0/5	0/5	0/5	5/5	5/5
Nasal cavity
rhinitis	2/5	0/5	1/5	2/5	1/5	1/5	5/5	5/5
focal atrophy	1/5	1/5	2/5	3/5	2/5	1/5	1/5	1/5
atrophy	2/5	0/5	1/5	2/5	2/5	2/5	5/5	5/5
metaplasia	0/5	0/5	0/5	0/5	0/5	0/5	3/5	5/5

*:            significantly different from control (p < 0.05);**:  significantly different from control (p < 0.01)

Applicant's summary and conclusion

Conclusions:

Methylisothiocyanate caused nasal epithelial atrophy at the low dose. At the middle dose, this atrophy was seen in addition to clinical signs in both sexes andan increase in neutrophilic polymorphonuclear granulocytes in males. The latter sign, which also occurred in females at the high dose, was considered to reflect an inflammatory process in the lungs. Such a process was clearly evident at the high dose, where increased lung weight and severe histopathologic signs were observed.

Executive summary:

In a 28 day inhalation toxicity study (OECD 421), methyl isothiocyanate [96.9 % a. i. ] was administered to 5/sex/dose of SPF Wistar/Chubb: THOM rats by whole body exposure at analytical concentrations of 0, 5.0, 20, or 100 mg/m3 (measured concentrations 0, 5.1, 19.9 or 100 mg/m3) and (equivalent to concentrations of 0, 1.7, 6.8, and 34 ppm) for 6 hours per day, 5 days/week for a total of 28 days (Klimisch et al., 1987; Rubin, 2002; Lowit and Facey, 2005; Lowit, 2006). All animals survived to study termination. Mid and high dose rats demonstrated clinical signs during exposure from the third exposure period day. No clinical signs were observed in the low dose animals. According to the study report, “During exposure, the animals of test group 2 showed eyelid closure, somnolence, and ruffled fur from the third day of exposure onwards. On the next morning before exposure nothing abnormal was found in the animals. At 20 mg/m3 the animals showed first indications of an irritating effect of the test substance and a slightly deteriorated general state of health. ” Additional clinical signs observed at the high exposure concentration included reddish nasal discharge, salivation, eye discharge, and difficulty in breathing or whooping respiration, and stretched posture. In the high dose rats, although signs recovered between exposures at the beginning of the study, towards the end of the study ruffled fur and respiratory sounds were no longer reversible. Body weight and body weight gain were significantly decreased (p<0.05) at the high dose. Food consumption and feed efficiency were not measured. There were decreases in plasma urea, glucose, triglyceride, and albumin the high dose males. In high dose females, urea and glucose were also decreased. In the males of mid exposure group, there was a decrease in urea concentration in the plasma. At the mid and high exposure concentrations, increase in neutrophilic polymorphonuclear granulocytes in the peripheral blood was observed in males; this was also observed in the high exposure concentration for females. There was increased lung weight at the high exposure concentration. Histopathology revealed an increase in incidence and severity of rhinitis in the nasal cavity at the high exposure concentration in both sexes (incidence in males: 2/5, 2/5, 2/5, 5/5; females: 0/5, 3/5, 1/5, 5/5). Other histopathologic findings at the high exposure concentration included: atrophy of the olfactory epithelium, metaplasia of the nasal respiratory epithelium (3 males in section plane 1 only, 5 females in section planes 1 and, to a lesser extent, section plane 2), tracheal epithelial proliferation and single cell necrosis (all high exposure concentration), bronchopneumonia and bronchial and bronchiolar epithelial proliferation (5 males, 2 females), and emphysema (3 males, 2 females). The systemic LOAEL is 100 mg/m3 (34 ppm), based on effects on the body weight gain. The systemic NOAEL is 19.9 mg/m3 (6.8 ppm ) based on an increase of neutrophilic polymorphonuclear granulocytes in the blood of males, which was not observed the oral OECD 422 and 90-day inhalation studies, and which could be considered as a secondary effect of the respiratory tract inflammation. The LOAEL for effects in the extrathoracic (ET) region is 100 mg/m3 (34 ppm), based on observation of pathological changes of the nasal cavity (metaplasia of respiratory epithelium and atrophy of the olfactory epithelium). The ET NOAEL is 19.9 mg/m3 (6.8 ppm). The LOAEL for effects in the tracheabronchial (TB) region is 100 mg/m3 (34 ppm), based on observation of pathological changes (tracheal epithelial proliferation and single cell necrosis, bronchopneumonia and bronchial and bronchiolar epithelial proliferation). The TB NOAEL is 19.9 mg/m3 (6.8 ppm).