Hydrogen sulphide

Toxicity to reproduction

Administrative data

Endpoint:

screening for reproductive / developmental toxicity

Remarks:

based on test type (migrated information)

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Comparable to guideline study

Cross-reference

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2000

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 421 (Reproduction / Developmental Toxicity Screening Test)

Principles of method if other than guideline:

The purpose of this study was to evaluate whether repeated exposure of male and female CD rats to H2S atmospheres resulted in reproductive or developmental toxicity. This portion of the study was performed, to the extent possible, in compliance with the OECD test guideline 421. Another goal of the present investigation was to determine whether repeated exposure to H2S during the perinatal period of development resulted in neurotoxicity in the offspring.

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Hydrogen sulphide

EC Number:

231-977-3

EC Name:

Hydrogen sulphide

Cas Number:

7783-06-4

Molecular formula:

H2S

IUPAC Name:

hydrogen sulfide

Test material form:

other: gas

Details on test material:

Gas cylinders containing 5% (50,000 ppm) H2S in nitro¬gen were purchased from Holox Gases (Cary, NC)

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 Laboratories, Inc. (Raleigh, NC)
- Age at study initiation: 8 week
- Weight at study initiation: no data
- Fasting period before study: no
- Housing: singly housed (exccpt during mating
- Diet: NIH-07 rodent chow ad libitum
- Water: Deionized, filtered tap water ad libitum
- Acclimation period: approximately 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18.5-21.5
- Humidity (%): 40-70
- Air changes (per hr): no data
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

inhalation: gas

Type of inhalation exposure (if applicable):

whole body

Vehicle:

clean air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Hazelton H1000 stainless steel and glass inhalation 1-m3 exposure chambers
- Method of holding animals in test chamber: individual stainless steel inhalation cage for F0 male and F0 females until GD 19. The dams with litters were exposed on PND 5-18 using individual 4.9-liter glass exposure cylinders
- Source and rate of air: no data
- Method of conditioning air: no data
- System of generating atmospheres: Hydrogen sulfide was metered through mass flow controllers and mixed with the chamber air supply to provide the desired target H2S concentrations.
- Temperature, humidity, pressure in air chamber: 22.0 to 23.5°C; 41 to 46%
- Air flow rate: approximately 200-250 l/min in the 1-m3 chamber and 2.8-4.1 I/min in the cylinder
- Air change rate: 12-15 air changes per hour in the 1-m3 chamber and approximately 35 to 50 air changes per hour in the cylinder
- Method of particle size determination: not appropriate
- Treatment of exhaust air: no data

TEST ATMOSPHERE
- Brief description of analytical method used: Chamber and cylinder exposure atmospheres were measured with a calibrated gas chromatograph equipped with a dame photometric detector and a GS-Q (30-m X 0.53-µm) column
- Samples taken from breathing zone: yes

Details on mating procedure:

- M/F ratio per cage: (1:1) with no change in mating partners
- Length of cohabitation: Each female was placed into the male's home cage in the afternoon after each daily H2S exposure and then removed the next morning prior to the start of exposure.
- Proof of pregnancy: presence of sperm or copulation plugs in the vaginal tract referred to as day 0 of pregnancy
- Further matings after two unsuccessful attempts: no

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

see above

Duration of treatment / exposure:

2 weeks prior to breeding, during 2-week mating period, then from gestation day 0-19. No exposures occurred through the remainder of gestation and during the period of parturition (gestation day (GD) 20 through postnatal day (PND) 4. Dams and pups were concurrently daily exposed starting on PND5 through PND18

Frequency of treatment:

6 hr/day, 7 days/week

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
0, 10, 30, or 80 ppm (0, 14, 42, or 111 mg/m3)
Basis:
other: target conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
10.0 ± 0.6, 30.1 ± 0.8, and 79. 5 ± 2.4 ppm
Basis:
analytical conc.

No. of animals per sex per dose:

12

Control animals:

yes, sham-exposed

Examinations

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: before and after each daily H2S exposure

DETAILED CLINICAL OBSERVATIONS: No

BODY WEIGHT: Yes
The body weights of the Fo male rats were determined weekly throughout the study. The body weights of the Fo female rats were recorded in the same manner until confirmation of mating. Presumed pregnant females were weighed on GD 0, 7, 14, and 20. Dams producing litters and their pups were weighed individually on PND 0, 4, 7, 14, and 21. After weaning on PND 21, pup body weights were collected twice weekly throughout the remainder of the study.

FOOD CONSUMPTION :
Feed consumption for F0 males was recorded weekly throughout the study except during the period of cohabitation. Feed consumption measurements were made weekly for ail F0 female rats throughout the prehreed treatment periods. During pregnancy, feed consumption of F0 females was recorded for GD 0-7, 7-14, and 14-20. Maternal feed consomption was also measured for PND 0-4, 4-7, 7-14, and 14-21.

WATER CONSUMPTION : No

Sperm parameters (parental animals):

At necropsy, the right testis from each F0 male rat was frozen at approximately -20°C for subsequent enumeration of testicular homogenization-resistant spermatid heads. The right cauda epididymis was immediately removed and weighed, and seminal fluid from the cauda was assessed for sperm number, motility (percentage motile and percentage nonmotile) and morphology

Litter observations:

DEVELOPMENTAL LANDRNARKS:
All pups were counted, sexed, examined for external anomalies, and individually weighed on PND 0. Each pup was monitored for the appearance of developmental land-marks beginning on PND 1 (pinnae detachment), PND 4 (surface righting), PND 7 (incisor eruption and negative geotaxis), and PND 12 (eyelid separation). Each female pup was observed for vaginal patency starting on PND 27. Each FI male was observed for preputial separation starting on PND 35.

BEHAVIORAT TESTING
Motor activity:
Motor activity was measured in the same animal (one male and one female from each litter) before the 6-h H2S exposure on PND 13 and 17 and on PND 21 and 60 ± 2. Spontaneous motor activity was measured during ten 6-min intervals for a total of 60 min using an automated cage rack photobeam activity system.
Passive avoidance:
Passive avoidance with a step-through to darkness para¬digm including one training and one retention trial was used to assess short-term learning and memory [271. Passive avoidance was evaluated for one male and female from each litter on PND 22 - 1 and on PND 62 ± 3. Naive animals were tested on PND 21, whereas the PND 62 ± 3 animals had been previously tested for FOB.
Functional observation battery (FOB):
An FOB was performed on one male and one female from each litter on PND 60 ±: 2 using methods described by Moser et al. (1988)..
Acoustic startle:
Acoustic startle was assessed using a microcomputer-controlled automated test system. Acoustic startle was assessed for one male and one female from each litter on PND 21 and 62 ± 3.

Postmortem examinations (parental animals):

SACRIFICE
At the end of the exposure regimen, adult F0 rats were weighed, euthanized with CO,, and exsanguinated.
The nulliparous adult females (n = 11) and adult males (n = 48) were necropsied the day after their last day of exposure. The post-parturient adult females (n = 37) were necropsied the day of or the day after their pups were weaned.

GROSS NECROPSY
A complete necropsy was then performed with special emphasis on the reproductive and accessory sex organs.

ORGAN WEIGHT
Brain, liver, kidney, adrenal gland, spleen, ovaries with oviducts, uterus, cervix, vagina, seminal vesicles with coagulating gland, prostate, testis and the head, body, and cauda of the left epididymis

HISTOPATHOLOGY / ORGAN WEIGHTS
ovaries with oviducts, uterus, cervix, vagina, seminal vesicles with coagulating gland, prostate, testis and the head, body, and cauda of the left epididymis, major structures and mucosae (squamous, respiratory, transitional, and olfactory) of the nasal cavity

Postmortem examinations (offspring):

Neuropathology in F1 rats was evaluated (one rat/sex/litter) in weanling (PND 23 ± 2) rats tested for passive avoidancc and in adult offspring (PND 61 ± 2) rats tested for motor activity.
The brain, spinal cord, and sciatic nerve with its main branches were exposed, grossly exam¬ined, and immersed in perfusion fixative at 4°C for at least 24 h. Brains were then removed, weighed, and measured. Cross-sections of the brain were collected for neuroanatomic pathology at the following sites: forebrain, caudate nucleus, center of the cerebrum, center of the midbrain, cer¬ebellum and pons, and medulla oblongata.

The remaining F1 rat pups (n = 144) were weighed on PND 63 ± 3, euthanized with CO2, and exsanguinated and had a complete necropsy performed. The following organs were weighed: adrenal glands, hrain, heart, kidneys, liver, lungs, ovaries with oviducts, spleen, and testes.

Results and discussion

Results: P0 (first parental generation)

General toxicity (P0)

Clinical signs:

no effects observed

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Other effects:

not examined

Reproductive function / performance (P0)

Reproductive function: oestrous cycle:

not examined

Reproductive function: sperm measures:

no effects observed

Reproductive performance:

no effects observed

Details on results (P0)

CLINICAL SIGNS AND MORTALITY (PARENTAL ANIMALS)
There were no deaths and no adverse physical signs observed in F0 male or female rats during the study.

BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS)
Although not statistically significant, both male and female F0 rats exposed to 80 ppm H2S also demonstrated a small (approximately 5-6%) decrease in body weight following H2S exposure. This approximately 5% decrease in F0 male body weight was persistent throughout the course of the 10-week exposure period.

A statistically significant decrease in feed consumption was observed in F0 male rats from the 80-ppm H2S exposure group during the first week of exposure. Parental male rat feed consumption (mean ± SD) during this initial 1-week period was 198 ± 18.1 and 170.6 ± 14.7 g, for the control and 80-ppm exposure groups, respectively. F0 female rats from the 30 and 80 ppm H2S treatment groups also had lower feed consumption during the first week of exposure (prebreed); however, this difference was not statistically significant. For example, F0 female rat feed consumptions (mean ± SD) during this initial 1-week period were 141 ± 9.4 and 124 ± 8.2 g, for the control and 80-ppm exposure groups, respectively. Decreased feed consumption did not persist beyond this initial prebreed exposure period (data not shown).

REPRODUCTIVE FUNCTION: ESTROUS CYCLE (PARENTAL ANIMALS)
No data

REPRODUCTIVE FUNCTION: SPERM MEASURES (PARENTAL ANIMALS)
Exposure of F0 males to H2S neither affected sperm production nor morphology. A large percentage of abnormal sperm was observed in two F0, rats from the 30-and 80-ppm exposure groups. Abnormal sperm accounted for 29 and 73% of all sperm analyzed from the 30- and 80-ppm exposed rats, respectively.

REPRODUCTIVE PERFORMANCE (PARENTAL ANIMALS)
There were no statistically significant effects on the reproductive performance of the F0 rats as assessed by the mating index, fertility index, postimplantation loss per litter, or number of late resorptions or still births. In addition, the number of females with live pups, litter size, average length of gestation, and the average number of implants per pregnant female were also unaffected.

ORGAN WEIGHTS (PARENTAL ANIMALS)
The only statistically significant difference from control in either absolute or relative F0 rat organ weights was a decrease in the absolute and relative weight of the adrenal glands of male F0 rats from the 10 and 80 ppm H2S exposure groups and a decrease in the relative weight of the ovaries from female rats exposed to 10 ppm H2S.

GROSS PATHOLOGY (PARENTAL ANIMALS)
No data.

HISTOPATHOLOGY (PARENTAL ANIMALS)
Subchronic exposure of male Fo rats to H2S was associated with mild to marked sensory neuron loss and basal cell hyperplasia in the olfactory mucosa living the dorsal medial meatus and the dorsal medial region of the ethmoid recess. This lesion has been described in detail by Brenneman et al., 2000.
Due to the lack of toxicologically relevant lesions in other body systems, microscopic examination of F0 male and female rats was limited to the reproductive tracts in the control and high exposure groups. In addition, F0 males in the 10- and 30-ppm and F0 females in the 80 ppm exposure groups that were not reproductively successful or that had gross observations made in the reproductive tract were also evaluated histologically. Statistical comparison of the control and high-exposure male groups showed no significant difference from control in the incidences of the histological diagnoses found.
However, there were a few histologie diagnoses with a higher incidence in the 80-ppm treatment male group when compared to male control rats. Most of thcse diagnoses were related to seminiferous tubular degeneration (including intratubular sperm stasis, tubular mineralization, sperm granulomas, and multinucleated giant cells), and associated changes in the epididymis (degenerate sperm forms in lumen, aspermia, and oligospermia). One case each of epididymal sperm granulomas and unilateral necrosis of the cauda were detected only in the high exposure group (n =12 rats).
Although not statistically significant, lymphoid interstitial infiltrate in the ventral prostate was observed more frequently in the 80-ppm male treatment group (5 of 12) when compared to control animals (3 of 12).
Statistical comparison of the control and high-exposure female groups showed no significant difference from control in the incidences of histological diagnoses found. One female rat each in both the 10-ppm and the 30-ppm exposure groups had ovarian cysts. Ovaries of one rat in the 80-ppm group contained only a few corpora lutea, which were regressing, and a relatively large number of tertiary follicles. This rat, as well as one other in the 30-ppm exposure group, also had squamous metaplasia of the endometrium localized to the uterus.

Effect levels (P0)

Dose descriptor:

NOAEC

Remarks:

reproductive toxicity

Effect level:

>= 80 ppm

Sex:

male/female

Basis for effect level:

other: = 111 mg/m3

Results: F1 generation

General toxicity (F1)

Clinical signs:

not specified

Mortality / viability:

not specified

Body weight and weight changes:

no effects observed

Sexual maturation:

no effects observed

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings:

no effects observed

Details on results (F1)

VIABILITY (OFFSPRING)
No data.

CLINICAL SIGNS (OFFSPRING)
No data.

BODY WEIGHT (OFFSPRING)
No statistically significant difference in pup body weight gain was observed in H,S-exposed pups of either sex during lactation or the remainder of the postnatal period.

PUP DEVELOPMENT
There were no statistically signiticant differences among groups in pup development as assessed by the onset of pinnae detachment, incisor eruption, negative geotaxis, eyelid separation, vaginal patency, or balano-preputial separation. In addition, the ability to surface right on postnatal day 4 was equivalent across all treatment groups.

ORGAN WEIGHTS (OFFSPRING)
No statistically significant changes in mean organ weights were observed in PND 63 ± 3 male and female F1 when compared to control animals.

GROSS PATHOLOGY (OFFSPRING)
No statistically significant increase in structural malformations was observed in this study. Malformations, however. were only observed in newborn pups from dams that were exposed to H2S (Table 2). Malformations noted at birth included kinked tail, agenesis of the tail, anophthalmia, small rear legs and body, frontal bone defects, hypognathia, and a skin lesion characterized by detachment of the skin and dermis (Table 2). Umbilical hemia was noted on PND 4 in one male pup from one litter exposed to 10 ppm H2S. The histologie appearance of the skin lesion re¬sembled epidermolysis bullosa, a family of inherited or acquired mechanobullous diseases in which minor trauma causes the formation of cutaneous blisters. This skin lesion was observed in seven individuals from one litter that contained 14 pups. No dose-response relationship was observed for any external alteration, because malformations were observed in litters from all treatment groups.
No relevant gross abnormalities were observed at necropsy in the brain, spinal cord, or peripheral nerves of any pup examined after neuroperfusion.

HISTOPATHOLOGY (OFFSPRING)
Microscopy examination of H&E-stained brain sections at six levels from pups in the control and high dose groups failed to demonstrate any relevant histological abnormalities.

BEHAVIORAL EFFECTS
Statistically significant changes in motor activity were observed during the preweaning and postweaning period only in animals exposed to 10 ppm H2S. In the PND 17 open-field motor activity test, there was an increase in overall motor activity and during two time intervals in male pups exposed to 10 ppm H2S. This effect was not treatment related because no dose-response relationship was observed for this end point, and it was only present at one time point in one gender. Exposure to H2S did not affect the ontogeny of motor activity in rats when compared to control animals. A statistically significant gender-related effect on overall motor activity was observed during the PND 17 and PND 60 ± 2 test sessions. Female rats displayed a higher amount of motor activity during the PND 17 and PND 60 ± 2 test sessions when compared to male rats. No statistically significant treatment-related effects on overall motor activity were observed during the PND 13, PND 21, or PND 60 1 2 motor activity test sessions.
Male rats had a significantly increased acoustic response amplitude to both pulse (p < 0.0001) and prepulse (p = 0.0147) trials on PND 62 ± 3 when compared to female rats. Hydrogen sulfide treatment was not associated with any statistically significant alteration in the magnitude of the startle response following prepulse or pulse stimulation. Hydrogen sulfide exposure likewise did not affect the latency of the acoustic startle response following either prepulse or pulse stimulation
There were no statistically significant differences between rats of either sex among treatment groups in initial crossover time measured on the first day of testing on either PND 22 ± 1 or on PND 62 ± 3. There were also no statistically significant differences among groups for the ability to complete the passive avoidance task.
No statistically significant differences in FOB assessments were observed in H2S-exposed rats.

Effect levels (F1)

Dose descriptor:

NOAEC

Remarks:

developmental toxicity

Generation:

F1

Effect level:

>= 80 ppm

Sex:

male/female

Basis for effect level:

other: = 111 mg/m3

Overall reproductive toxicity

Reproductive effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

Groups of 12 male and 12 female Sprague-Dawley rats were exposed to hydrogen sulfide at 0, 10, 30, or 80 ppm 6 h/day, 7 days/week for 2 weeks before breeding. Exposures continued during a 2-week mating period and then on GD 0-19. Exposure of the dams and pups (eight rats per litter after culling) resumed from PND 5 to PND 18. Adult male rats were exposed on 70 consecutive days.
Offspring were evaluated on the basis of motor activity, passive avoidance, a functional observational battery, acoustic startle response, and neuropathology. There were no deaths and no treatment-related adverse clinical signs in parental males or females. There were no significant effects on reproductive performance of the parental rats as assessed by the number of females with live pups, average gestation length, and average number of implants per pregnant female. No treatment-related effects in pups were noted in growth, development, or behavioral tests. No effect on fertility and no other effects were noted at any concentration. The results of this study suggests that H2S is neither a reproductive toxicant nor a behavioral developmental neurotoxicant in the rat.

Therefore the NOAEC for the reproductive and developmental toxicity was 80 ppm (111 mg/m3).

But following exposure to 30 and 80 ppm H2S, a significant increase in nasal lesions, such as olfactory neuron loss and basal cell hyperplasia, was observed.
The no-observed adverse effect level in this study was 10 ppm.

Executive summary:

Virgin male and female Sprague-Dawley rats (12/sex/group) were exposed to 0, 10, 30, or 80 ppm (0, 14, 42, or 111 mg/m3) H₂S 6 hr/day, 7 days/week for two weeks prior to breeding. Exposure continued during a 2-week mating period and throughout gestational days 0-19 (GD 0-19). Evidence of copulation (vaginal plug or sperm in vaginal lavage fluid) during the 2-week mating period was considered GD 0. On postnatal day (PND) 4, litters were randomly reduced to 4 animals per sex when possible. Remaining pups were euthanized and discarded without being examined. Dams and pups were then exposed PND 5-18. Nonpregnant adult females were exposed for an additional 23-24 days following the 2-week breeding period. Adult males were exposed to H₂S for 70 consecutive days.

Clinical examinations were performed on all animals before and after each exposure. The body weights of the F0males and females were determined weekly throughout the study, except that female body weights were not determined weekly once evidence of mating was present. Presumed pregnant females were weighed on GD 0, 7, 14, and 20, and dams were weighed on PND 0, 4, 7, 14, and 21. Feed consumption was determined weekly in F0males and prebreeding females. Feed consumption in presumed pregnant females was recorded for GD 0-7, 7-14, and 14-20. Dam feed consumption was recorded for PND 0-4, 4-7, 7-14, and 14-21. At the end of exposure, adult rats were euthanized and a complete necropsy was performed with emphasis on reproductive and accessory sex organs. Post-parturient animals were necropsied the day of or the day after weaning. At necropsy, the right testis from each F0male was examined for sperm number, production, motility, and morphology.

No deaths or adverse clinical signs were observed in F0males and females for any exposure group. There was a statistically significant decrease in feed consumption in male rats exposed to 80 ppm (111 mg/m3) H₂S during the first week of the study. There was a small, but not statistically significant, decrease in body weight (5-6%) observed in F0males and females exposed to 80 ppm (111 mg/m3) H₂S that was present throughout entire exposure period. The only significant difference in organ weights was an increase in absolute and relative adrenal gland weights observed in F0males exposed to 10 ppm (14 mg/m3) and 80 ppm (111 mg/m3) but not in the mid-dose of H₂S and a decrease in the relative ovary weight of females in the 10 ppm (14 mg/m3) exposure group.

There were no statistically significant effects on reproductive performance (mating index, fertility index, postimplantation loss per litter, and number of late resorptions or stillbirths) in F0animals. Also, the number of live pups, litter size, average length of gestation, and average number of implants per female were not affected. There were no statistically significant effects on sperm production or morphology noted in F0males; however, a large percentage of abnormal sperm was observed in one F0male from both the 30 (42 mg/m3) and 80 ppm (111 mg/m3) exposure groups (29 and 73%, respectively). In comparing high-exposure and control animals, there were a few histologic diagnoses with a higher incidence in the high-exposure group, including: testicular tubular degeneration, intratubular sperm stasis, tubular mineralization, sperm granulomas, and multinucleated giant cells, degenerate sperm forms in the lumen, aspermia, and oligospermia. While the incidence of testicular tubular degeneration in high-exposures was higher (42%) than the controls (17%), statistical significance was not achieved. One incidence each of sperm granuloma and unilateral necrosis of the cauda was present in the 80 ppm (111 mg/m3) exposure group. Notable histological findings in females included one each of ovarian cysts and squamous metaplasia of the endometrium in the 10 ppm (14 mg/m3) and 30 ppm (42 mg/m3) exposure groups. The olfactory neuron loss and basal cell hyperplasia observed in the male rats in this study are reported elsewhere (Brenneman et al., 2000). The assignment of any effect level for reproductive toxicity is problematic since the study considered only 12 rats/sex/group and the study also lacked any statistical significance in either function or histopathology related to reproduction endpoints. In summary, the reproductive segment of this study did not demonstrate reproductive toxicity in either male or female rats following relatively high H₂S exposure of 80 ppm (111 mg/m3) under repeated conditions (up to 70 days for males).

With regards to developmental effects from H₂S exposure, there were no statistically significant increases in structural malformations. Observed malformations included kinked tail, agenesis of the tail, anophthalmia, small rear legs and body, frontal bone defects, hypognathia, and skin lesion characterized by detachment of the skin and dermis. However, none of these effects was dose-related. There were no significant differences in pup weight gain or development (pinnae detachment, surface righting, incisor eruption and negative geotaxis, vaginal patency, preputial separation, and eyelid separation). Surface righting was also equivalent across exposure groups. There were no treatment-related effects on motor activity, acoustic startle response, passive avoidance observed, or FOB. Terminal body and organ weights in all exposure groups were comparable to controls. Although a wide variety of gross observations were noted, they were not considered treatment-related by the investigators. Microscopic examination of six levels of the brain from pups from the control and high-dose group failed to demonstrate any histologic abnormalities.

Therefore the NOAEC for the reproductive and developmental toxicity was 80 ppm (111 mg/m3).

In the histopathologic examination a significant increase in nasal lesions, such as olfactory neuron loss and basal cell hyperplasia, were observed following exposure to 30 and 80 ppm H2S.

The distribution pattern in the nose was multifocal, bilaterally symetrical, and had a characteristic rostrocaudal distribution. The results of this study suggests that H2S is neither a reproductive toxicant nor a behavioral developmental neurotoxicant in the rat. But following exposure to 30 and 80 ppm H2S, a significant increase in nasal lesions, such as olfactory neuron loss and basal cell hyperplasia, was observed. The no-observed adverse effect level was 10 ppm.