Methyl isothiocyanate

Repeated dose toxicity: dermal

Administrative data

Endpoint:

short-term repeated dose toxicity: dermal

Type of information:

experimental study

Adequacy of study:

other information

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

other: This 30-day dermal toxicity study in the rat is unacceptable-guideline and does not satisfy the guideline requirement for a 30-day dermal toxicity study (OECD 411) in rat. Individual animal data for all the parameters are not available

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1975

Report date:

1975

Reference 2

Reference Type:

study report

Title:

Unnamed

Year:

1986

Reference 3

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

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Subacute (31-day) dermal toxicity of MITC to the rat.

GLP compliance:

no

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:

Test article name : MITC
Source: no data
Purity: no data

Test animals

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Zentralinstitut für Versuchstierkunde, Hannover
- Age at study initiation: no data
- Weight at study initiation: 140-243 g
- Fasting period before study: no data
- Housing: under conventional conditions in Makrolon cages type II with perforated bottom (one rat per cage)
- Diet (e.g. ad libitum): a standard diet (Altromin R), ad libitum
- Water (e.g. ad libitum): not precised, ad libitum
- Acclimation period: no data

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21-25°C
- Humidity (%): 40-65%
- Air changes (per hr): yes, but not precised
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Type of coverage:

occlusive

Vehicle:

other: sesame oil

Details on exposure:

TEST SITE
- Area of exposure: dorsal skin surface of 20-30 cm²
- % coverage: no data
- Type of wrap if used: a sprayer tarped with a mull bandage

REMOVAL OF TEST SUBSTANCE : with a soft pulp ("kleenex")
- Washing (if done): no
- Time after start of exposure: 5 hours

TEST MATERIAL
- Amount(s) applied (volume or weight with unit): 5 ml/kg

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

31 days

Frequency of treatment:

5 hours/day, 7 days/week

Doses / concentrations

Remarks:

Doses / Concentrations:
1, 10 and 100 mg/kg bw
Basis:
nominal per unit body weight

No. of animals per sex per dose:

10 animals/sexe/dose

Control animals:

yes, concurrent vehicle

Details on study design:

no data

Positive control:

no data

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes, every day
DETAILED CLINICAL OBSERVATIONS: Yes
DERMAL IRRITATION : Yes
BODY WEIGHT: Yes, once a week
FOOD CONSUMPTION: yes, on 24 days (determined by weighed the portion left every 2 to 3 days)
WATER CONSUMPTION: yes, on 17 days (determined by weighed the portion left every 3 to 4 days)
OPHTHALMOSCOPIC EXAMINATION: no

HAEMATOLOGY: Yes
- Time schedule for collection of blood: in weeks -2, 2 and 4.
- Anaesthetic used for blood collection: No data
- Animals fasted: No data
- How many animals: all
- Parameters examined : hemoglobin concentration, hematocrit value, erythrocyte count, leucocyte count, differential blood count, thrombocyte count.

CLINICAL CHEMISTRY: Yes
- Animals fasted: No data
- How many animals: all
- Parameters examined : in the blood = fasting glucose determination (weeks -2, 2 and 4).
In the serum = GPT, AP (weeks -2, 2, 4), COH (weeks -1, 2, 4, 5), Blood urea nitrogen concentration total cholestrol level (weeks -2, 2, 4), total albumin and serum albumin electrophoresis (weeks -2, 2, 4).
In the plasma and erythocytes : cholinesterase activity (weeks -1,2,3,4).
In the brain = Determination of cholinesterase activity (week 5) in 5 males and females per group.

URINALYSIS: Yes
- Time schedule for collection of urine: weeks -2, -1, 2 and 4.
- Metabolism cages used for collection of urine: No data
- Animals fasted: No data
- Parameters examined : pH-value, specific weight, albumin, glucose, acetone, blood, urobilinogen and sediment.
LDH determined in the 24 hours urine during weeks -1, 2, 4 and 5 in 5 males annd 5 females of each group.

NEUROBEHAVIOURAL EXAMINATION: No
OTHERS : bone marrow analysis : Count of nucleated cells per mg of bone marrow and establishment of myelogram in week 5.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes (liver, kidney, adrenals, heart, pancreas and others).

Other examinations:

ORGAN WEIGHT : liver, kidney, heart, ovary, adrenals, thyroid gland, testicles, brain.

Statistics:

Further detailed results are compiled in the protocos giving individual values or findings. Values significantly differeing from those obtained for the controls are marked * for p>0.01 and ** for p<0.01 in the tables.

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Dermal irritation:

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):

effects observed, treatment-related

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

effects observed, treatment-related

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not specified

Details on results:

CLINICAL SIGNS AND MORTALITY
After the application of 100 mg/kg one male animal does on day 26.
After having received 1 mg/kg all test animals showed yellowish desquamation at surface areas of the treated skin the 14th and the 17th day of treatment. After dosing 10 mg/kg of MITC all animals revealed, between day 5 and 18, slight erythema of the treated skin and particularly in males between day 6 and 8, a light scaling. In the 100 mg/kg group considerable signs of pain were noted in all animals during exposure. Beginning with day 5 desquamation, formation of fissures and surface necroses at the treated skin areas were noted, which were somewhat more pronounced in males. With advanced treatment necroses were still increased. The necrotized parts were cast off between day 15 and 26. The process passed on to the subcutis.

BODY WEIGHT AND WEIGHT GAIN
After 100 mg/kg the male had lost weight between weeks 1and 5 whereas females, in comparison with the controls revealed reduced weight gains (see table 1).

FOOD CONSUMPTION
In comparison with the untreated controls, food consumption, between weeks 1 and 5, was only decreased in male test animals after dosing 10 mg/kg bw MITC and 100 mg/kg bw.

WATER CONSUMPTION
Between weeks 1 and 5, females consumed more water after 100 mg/kg bw.

HAEMATOLOGY
There was no evidence of substance-induced modifications.

CLINICAL CHEMISTRY
After having received 100 mg/kg, one animal showed slight increase in the LDH of the serum in week 4, and two males in week 5. Appeared from electrophoresis the total beta-globulins were increased in week 4 after 1, 10, and 100 mg/kg, albumin were decreased (See table 5).
In female test animals the cholinesterase activity in the plasma was distinctly inhibited in weeks 2 and 4 after 100 mg (See table 6) and in week 4 after 1 mg/kg.

URINALYSIS
During week 4, an increased LDH excretion was recorded in the 24h urine of males dosed 100 mg MITC/kg. After 10 and 100 mg, increased values were found in one female each.

ORGANS WEIGHT : Substance-induced modifications were not ascertained.

GROSS PATHOLOGY : In all animals extended skin necroses were noted at and near the application on site after 100 mg/kg. Subtance-induced modifications were not traced in the one decedent (male) either.

HISTOLOGICAL EXAMINATIONS : The surface at the application site treated with 100 mg MITC/kg showed extended necroses and sclerosis of the adjacent fatty and connective tissues. Further 7 animals (1 male, 6 females) revealed a minimal reactive hyperplasia of the epithelium of the adjacent areas. In one animal (male) of the same dose group a medium atrophy of the lymphatic spleen tissues was noted. As this is an uncharacteristic individual finding it is considered as being not substance-related.

OTHER FINDINGS :
-Bone-marrow examinations : A distinct increase of immature erythropoiesis after 10 and 100 mg/kg in all animals and after 1 mg/kg in females only was seen (See table 2). Contrary to this, the absolute number of erythropoiesis cells was increase in males only after 10 mg/kg. The relative number of semi-mature neutrophilic granulocytopoiesis was also increase in all animals after 100 mg/kg MITC (See table 3) whereas the reticular cells of the bone marrow were clearly reduces. After having received 100 mg/kg bw all animals showed a reduction in the absolute cell numer of the eosinophilic granulocytopoiesis (see table 4). The relative cell number of eosinophilic granulocytopoiesis also showed a decreasing tendency in the same dose dose which however was not statistically significant.

Effect levels

1

Dose descriptor:

NOAEL

Remarks:

systemic toxicity

Effect level:

1 mg/kg bw/day

Sex:

male/female

2

Dose descriptor:

LOAEL

Remarks:

systemic toxicity

Effect level:

10 mg/kg bw/day

Sex:

male/female

Basis for effect level:

other: decreased serum albumin and increased globulin values in addition to increased liver weights. Irritation at all doses

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

Dermal application of 1 and 10 mg/kg of MITC (0.2 resp. 2.0 mg/ml) already results in a slight irritating effect at the application site. 100 mg (20 mg/ml) cause severe dermal necroses, resulting in a number of "indirect substance-related effects" (e.g. reduced food consumption, weight loss, diminution of eosinophilic granulocytopoiesis). These findings tend to indicate that the contact of the skin with oily solutions of methyl isothiocyanate at a concentration of > 2.0 mg/ml may be dangerous.

Executive summary:

In a 30-day dermal toxicity study, MITC (95.5%) was applied dermally for a 5 hour daily exposure to 4 groups of 10 rats/sex/dose 7 days a week at 0, 1.0, 10.0, and 100 mg/kg/day. Sesame oil was used as the vehicle. The 100 mg/kg/day animals exhibited signs of severe pain by vocalizing, jumping, and reaching for the test site. One high dose male died on day 26 the study from “automutilation” presumably from the severe distress caused by pain from MITC at 100 mg/kg/day. Dermal irritation was noted at all treatment levels. At 1 mg/kg/day, yellow colored desquamation. At 10 mg/kg/day, light-colored desquamation combined with erythema were noted. The affect of dermal exposure to the 100 mg/kg/day dose of MITC is severe erythema and necroses accompanied sclerosis of the adjacent fatty and connective tissues. Seven rats in the highest dose group exhibited minimal reactive epidermal hyperplasia of the area adjacent to application. Animals in the highest group At the highest dose group, body weight gain was statistically decreased (p<0.01) compared to control (-50% for females, males lost 4 g over the study). A decrease in food consumption and and increase in water consumption were observed in males of the 100 mg/kg/day groups (p< 0.01; -17% and +20%, respectively) There were no treatment related effects observed in hematological parameters or in the bone marrow. At 10 and 100 mg/kg/day, dose-related increases in globulin with comparable decreases in albumin were observed in male and female rats. Blood glucose was increased significantly at 100 mg/kg/day.

A significant (p < 0.01) increase in relative liver weights of the mid dose females and the absolute and relative liver weights of the high dose females was reported. Male relative liver weights were increased significantly (p< 0.01) at the high dose. The systemic LOAEL is 10.0 mg/kg/day, based on decreased serum albumin and increased globulin values in addition to increased liver weights. The systemic

NOAEL is 1.0 mg/kg/day.