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Acute Toxicity: inhalation

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Administrative data

Endpoint:
acute toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
2002

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 403 (Acute Inhalation Toxicity)
GLP compliance:
yes
Test type:
acute toxic class method

Test material

Constituent 1
Reference substance name:
Hydrogen sulphide
EC Number:
231-977-3
EC Name:
Hydrogen sulphide
Cas Number:
7783-06-4
IUPAC Name:
hydrogen sulfide
Details on test material:
Hydrogen sulfide was obtained from Praxair Distribution Inc. (Betlehem, PA) at a concentration of 5 % (50 000 ppm) H2S in nitrogen.

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male
Details on test animals or test system and environmental conditions:
Following a 2-week acclimation period, 10 week-old male Sprague–Dawley CD (Crl:CD[SD]BR) rats (Charles River Laboratories, Raleigh, NC) were
assigned to weight-matched exposure groups (n = 5 rats/concentration/time point) for histologic end points and (n = 3 rats/concentration/time
point) for ultrastructural end points. The rats were individually housed in polycarbonate cages (Nalge, Rochester,NY) that contained Alpha-Dri
cagelitter(Shepard Specialty Papers, Kalamazoo, MI) and were secured with stainless-steel wire lids without filter tops. The cages were cleaned
approximately once weekly. The rats were held in biologically clean rooms with HEPA- filtered air, a 12-hourlight-dark cycle, 20,3 °C average
air temperature, and 50 ± 20% relative humidity. Pelleted NIH-07 rodent chow (Zeigler Brothers, Gardners, PA) and deionized-filtered tap water
(Hydro Picosystems, Research Triangle Park, NC) were available ad libitum except during exposures. The study was conducted under federal
guidelines for the care and use of laboratory animals (21) and reviewed by the Institutional Animal Care and Use Committee of the CIIT Centers
for Health Research.

Administration / exposure

Route of administration:
inhalation: gas
Type of inhalation exposure:
nose only
Vehicle:
air
Details on inhalation exposure:
The average temperatures and relative humidities during the 3-hour exposures ranged from 20.6 to 21.1 °C and 42 to 49%, respectively.
Analytical verification of test atmosphere concentrations:
yes
Remarks:
Hydrogen sulfide was obtained from Praxair Distribution, Inc. (Bethlehem,PA) at aconcentration of5% (50,000 ppm) H2S in nitrogen. Exposure concentrations of H2S were generated by metering known amounts of H2S into the air supply of a 52-exposur
Duration of exposure:
>= 1 - <= 5 d
Remarks on duration:
The duration of the exposure was 3 hours for 1 or 5 consecutive days.
Concentrations:
The average analytical concentrations ( ±SD) of H2S for the 3-hour exposures were 0.0 ±0.0, 30.1 ±0.6, 80.4± 1.7, 193 ± 6,
and 395 ± 8 ppm for the 0, 30, 80, 200, and 400 ppm exposure groups, respectively.
No. of animals per sex per dose:
n = 5 male rats/concentration/time point for histologic end points and n = 3 male rats/concentration/time point for ultrastructural end points.
Control animals:
yes
Details on study design:
The rats were held in individual polycarbonate tubes and exposed for 3 hours for 1 or 5 consecutive days to a target concentration of 0, 30, 80, 200, or 400 ppm H2S.

Results and discussion

Effect levels
Sex:
male
Dose descriptor:
other: NOAEL
Effect level:
>= 30
Exp. duration:
5 d
Remarks on result:
other: The exposure duration was from 1 to 5 days. The NOAEL for H2S was 30 ppm.
Gross pathology:
As nasal lesions were not found in rats exposed to 0 or30 ppm at either the1-or 5-day exposure, the NOAEL observed for acute inhalation
exposure to H2S was 30 ppm.

Bilaterally symmetrical, mucosal necrosis was found in the olfactory epithelium lining the dorsal medial meatus in rats exposed for a single 3-hour
period to 80, 200, or 400 ppm H2S (Table1). Following exposure to 80 ppm, only 1 of 5 rats was affected. With exposure to 200 ppm H2S, 3 of 5
rats were affected. Lesions found in 4 of 5 rats exposed to 400 ppm H2S for a single 3-hour period were similar to those seen with exposure to 200 ppm H2S. Five consecutive days of 3-hour H2S exposures resulted in a 100% incidence of olfactory, but no respiratory lesions, at the 80, 200, or
400 ppm exposure levels (Table 1). The amount of surface area affected increased slightly with increasing exposure concentrations.
A regeneration of the olfactory epithelium was observed (partial at 2, complete at 6 weeks), but abnormalities such as small cysts lined by
regenerating olfactory epithelial cells were noted. Respiratory epithelial regeneration was also observed following a single 3-hour exposure to
80, 200, or 400 ppm H2S.

The olfactory mucosa from noses harvested immediately after a single 3-hour exposure to 400 ppm H2S showed severe swelling of mitochondria
in sustentacular cells and olfactory neurons, which progressed to necrosis and cell sloughing at 3 hours postexposure. The sustentacular cells also showed extensive swelling of the endoplasmic reticulum. The dendrites and olfactory vesicles of olfactory receptor neurons were also markedly
swollen and had reduced numbers of cilia.


Other findings:
Cytochrome oxidase immunoreactivity was uniformly distributed in the respiratory epithelium and limited to the apical cytoplasm of respiratory epithelial cells. In the olfactory mucosa, CO immunoreactivity was variably distributed and was also found in the Bowman’s glands and their ducts.

Any other information on results incl. tables

TABLE1.—Nasal lesions in adult male CD rats following a single 3-hour exposure or 5 consecutive daily 3-hour exposures to 80, 200,or 400 ppm H2S.

Nasal lesion

Exposure duration

H2S exposure concentration ppm H2S

Lesion incidence

Site affected

Extent

Olfactory mucosal necrosis

1 d

80

1/5

dorsomedial meatus

localized

 

 

200

3/5

 

 

 

 

400

4/5

 

 

Olfactory mucosal necrosis with early regeneration

5 d

80

5/5

dorsomedial meatus, ethmoid recess

regionally extensive

 

 

200

5/5

 

 

 

 

400

5/5

 

 

Respiratory epithelial regeneration

1 d

80

1/5

lateral wall of ventral meatus

localized

 

 

200

5/5

 

 

 

 

400

5/5

 

 

 

Applicant's summary and conclusion

Interpretation of results:
very toxic
Remarks:
Migrated information CLP: Acute toxicity, category 1 Criteria used for interpretation of results: EU
Conclusions:
In the present study, the character of the acute olfactory lesion (full-thickness necrosis with sloughing) suggests that exposure to H2S
indiscriminately damages most cell types in the olfactory epithelium. This conclusion is supported by ultrastructural lesions including severe
mitochondrial swelling followed by necrosis observed in both sustentacular cells and olfactory neurons immediately following a single 3-hour
exposure to 400 ppm H2S.
Executive summary:

Hydrogensulfide (H2S) is a potent inhibitor of cytochrome oxidase (CO) and is associated with dysosmia and anosmia in humans and nasal lesions in exposed rodents. An improved understanding of the pathogenesis of these lesions is needed to determine their toxicological relevance. 10-week-old male CD rats were exposed to 0, 30, 80, 200, or 400 ppm H2S for 3 hours/day for 1 or 5 days consecutively. The nose was histologically examined 24 hours after H2S exposure, and lesion recovery was assessed at 2 and 6 weeks following the 5-day exposure. A single 3-hour exposure to 80 ppm H2S resulted in regeneration of the respiratory mucosa and full thickness necrosis of the olfactory mucosa localized to the ventral and dorsal meatus, respectively. Repeated exposure to the same concentrations caused necrosis of the olfactory mucosa with early mucosal regeneration that extended from the dorsal medial meatus to the caudal regions of the ethmoid recess. Acute exposure to 400 ppm H2S induced severe mitochondrial swelling in sustentacular cells and olfactory neurons, which progressed to olfactory epithelial necrosis and sloughing. CO immunoreactive cells were more frequently observed in regions of the olfactory mucosa commonly affected by H2S than in regions that were not. These findings demonstrate that acute exposure to 80 ppm H2S resulted in reversible lesions in the respiratory and olfactory mucosae of the CD rat and that CO immunoreactivity may be a susceptibility factor forH2S-induced olfactory toxicity in the rat.

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