1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione, zinc salt

Acute Toxicity: inhalation

Administrative data

Endpoint:

acute toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

October 2002

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Conducted according to GLP.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2003

Report date:

2003

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.1300 (Acute inhalation toxicity)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test type:

standard acute method

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione, zinc salt

EC Number:

262-872-0

EC Name:

1,3-dihydro-4(or 5)-methyl-2H-benzimidazole-2-thione, zinc salt

Cas Number:

61617-00-3

Molecular formula:

C8H8N2S.1/2Zn

IUPAC Name:

Zinc bis[4(or 5)-methyl-2-thioxo-2,3-dihydrobenzimidazol-1-ide]

Test material form:

solid: particulate/powder

Remarks:

migrated information: powder

Details on test material:

Description: Off-white powder.
Date received: 14 August 2002.
Storage conditions: Room temperature, in the dark.

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

On receipt the animals were randomly allocated to cages. After an acclimation period of at least five days the animals were given a number unique within the study by ear punching and a number written on a color coded cage card. At the start of the study the animals were approximately eight to twelve weeks old and within the weight range of 200g to 350g. The females were nulliparous and non-pregnant.
With the exception of the exposure period, free access to mains drinking water and food was allowed throughout the study.

The environmental controls were set to achieve values of 21 +/- 2 deg C and 55 +/- 15% relative humidity. The rate of air exchange was at least fifteen changes per hour and the lighting was controlled to give twelve hours continuous light and twelve hours darkness. The animals were retained in this accommodation at all times except during the exposure period.

Administration / exposure

Route of administration:

inhalation: dust

Type of inhalation exposure:

nose only

Vehicle:

air

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
A dust atmosphere was produced from the test material using a SAG 410 Solid Aerosol Generator located adjacent to the exposure chamber. The SAG 410 was connected to a metered compressed air supply.
Compressed air was supplied by means of an oil free compressor and passed through a water trap and respiratory quality filters before it was introduced to the SAG 410.
The cylindrical exposure chamber had a volume of approximately 30 litres (dimensions: 28 cm diameter x 50 cm high). The concentration within the chamber was controlled by adjusting the test material feed rate from the SAG 410. The extract from the exposure chamber passed through a 'scrubber' trap and was connected with a high efficiency filter to a metered exhaust system. The chamber was maintained under negative pressure.
Homogeneity of the test atmosphere within the chamber was not specifically determinded during this study. Chambers of the same design (ADG DeveLoments Ltd) have been fully validated and shown to produce evenly distributed atmospheres in the animals' breathing zone with a wide variety of test materials.
Prior to the start of the study, test material atmospheres were generated within the exposure chamber. During this characterization period, test material input rates were varied to achieve the required atmospheric concentrations.

TEST ATMOSPHERE
The temperature and relative humidity inside the exposure chamber were measured by an electronic thermometer/humidity meter located in a vacant port in the animals' breathing zone of the chamber and recorded every thirty minutes throughout the four-hour exposure period.
Oxygen levels within the exposure chamber were measured by an electronic oxygen analyzer located in a sampling port in the animals breathing zone during each exposure period. The test atmosphere was generated to contain at least 19% oxygen.
The actual chamber concentration was measured at regular intervals during the exposure period. The gravimetric method used employed glass fiber filters placed in a filter holder. The holder was temporarily sealed in a vacant port in the exposure chamber in the animals' breathing zone and a suitable, known volume of exposure chamber air was drawn through the filter using a vacuum pump.
Each filter was weighed before and after sampling in order to calculate the weight of collected test material. The difference in the two weights, divided by the volume of atmosphere sampled, gave the actual chamber concentration.
The nominal chamber concentration was calculated by dividing the mass of test material used by the total volume of air passed through the chamber.

PARTICLE SIZE DISTRIBUTION
The particle size of the generated atmosphere inside the exposure chamber was determined three times during the exposure period using a Marple Personal Cascade Impactor. This device consisted of six impactor stages (9.8, 6.0, 3.5, 1.55, 0.93 and 0.52 microM cut points) with stainless steel collection substrates and a backup glass fibre filter, housed in an aluminium sampler. The sampler was temporarily sealed in a sampling port in the animals' breathing zone and a suitable, known volume of exposure chamber air was drawn through it using a vacuum pump.
The collection substrates and backup filter were weighed before and after sampling and the weight of test material, collected at each stage, calculated by difference.
The mean amount for each stage was used to determine the cumulative amount below each cut-off point size. In this way, the proportion (%) of aerosol less than 9.8, 6.0, 3.5, 1.55, 0.93 and 0.52 microM was calculated.
The resulting values were converted to probits and plotted against Log10 cut-point size. From this plot, the Mass Median Aerodynamic Diameter (MMAD) was determined (as the 50% point) and the geometric standard deviation was calculated. In addition the proportion (%) of aerosol less than 4 microM (considered to be the respirable portion) was determined.

Analytical verification of test atmosphere concentrations:

no

Duration of exposure:

4 h

Concentrations:

A target concentration of 2.0 mg/L was used for exposure.

No. of animals per sex per dose:

5

Control animals:

no

Details on study design:

All animals were observed for clinical signs at hourly intervals during exposure, immediately on removal from the restraining tubes at the end of exposure, one hour after termination of exposure and subsequently once daily for fourteen days. Any evidence of overt toxicity was recorded at each observation.

Results and discussion

Effect levels

Sex:

male/female

Dose descriptor:

LC50

Effect level:

> 2.12 mg/L air

Based on:

test mat.

Exp. duration:

4 h

Mortality:

No mortality.

Clinical signs:

other: Signs of hunched posture, pilo-erection and red/brown staining around snout are commonly seen in animals for short periods on removal from the chamber following 4-hour inhalation studies. Wet fur is commonly recorded both during and for a short period aft

Body weight:

Reduced bodyweight gain was noted in one male during week 1 of the study. Normal development was noted during week 2. Four females showed reduced bodyweight gain or a slight bodyweight loss during week 1 and/or 2 of the study but such variations are not uncommon in female rats of this strain or age and are considered not to be significant.

Gross pathology:

No macroscopic abnormalities were detected at necropsy.

Applicant's summary and conclusion

Interpretation of results:

Toxicity Category IV

Remarks:

Migrated information Criteria used for interpretation of results: EU

Conclusions:

No deaths occured in a group of ten rats exposed to a mean achieved atmosphere concentration of 2.12 mg/L. It was therefore considered that the acute inhalation median lethal concentration of ZMB2 in the Sprague-Dawley Crl:CD (SD) IGS BR strain rat, was greater than 2.12 mg/L. In accordance with the CLP Regulation (EC 1272/2008) the substance is classified as Cat IV for acute inhalaiton toxicity.