Gallium arsenide

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

25.07.1989 to 10.08.1989

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Developmental toxicity study conducted under the US National Toxicology Program (NTP).

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1990

Materials and methods

Test guideline

Guideline:

other: The developmental toxicity study was conducted in compliance with FDA Good Laboratory Practice Regulations (21 CFR, Part 58). In addition, as records from the study were submitted to the NTP Archives, this study was auditied retrospectively.

Principles of method if other than guideline:

The potential for gallium arsenide to cause developmental toxicity was assessed in female mice exposed for 6 hours/day, 7 days/week from day 4 to 17 of gestation.
The developmental toxicity study was conducted in compliance with FDA Good Laboratory Practice Regulations (21 CFR, Part 58). In addition, as records from the developmental toxicity study were submitted to the NTP Archives, this study was auditied retrospectively by an independent quality assurance contractor. Seperate audits covered completeness and accuracy of the pathology data, pathology speciems, final pathology tables, and a draft of this NTP Technical Report. Audit procedures and findings are presented in the reports and are on file at NIEHS. The audit findings were reviewed and assessed by NTP staff, and all comments were resolved or otherwise addressed during the preparation of this Technical Report.

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

gallium arsenide (Mechanically destroyed material not marketed. Particle size is fundamentally different from the coarser particles measured at the workplace.)

IUPAC Name:

gallium arsenide (Mechanically destroyed material not marketed. Particle size is fundamentally different from the coarser particles measured at the workplace.)

Details on test material:

- Name of test material (as cited in study report): gallium arsenide
- Physical state: solid
- Analytical purity: >98%
- Lot/batch No.: M051988
- Storage condition of test material: at room temperature under inert nitrogen atmosphere and protected from direct exposure to light
- Other: gallium arsenide undergoes oxidation in the presence of atmospheric oxygen: however, once a protective oxide surface layer ia formed further oxidation of the material is retarded. The extent of this oxidation was examined by x-ray photoelectron spectroscopy (XPS) during the gallium arsenide repeated dose study. The surface of the test material contained gallium oxide, arsenic trioxide, and gallium arsenide. The molar ratio of gallium oxide to gallium arsenide in the surface oxide layer ranged from approximately 0.24 to 0.30, whereas the molar ratio of arsenic trioxide to gallium arsenide ranged from approximately 0.18 to 0.25. The XPS analysis further indicated that the oxidation observed was confined to a surface layer depth of approximately 50 to 100 A.

Test animals

Species:

mouse

Strain:

CD-1

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories (Raleigh, NC)
- Age at study initiation: 13 weeks old
- Weight at study initiation: 3 weeks after receipt
- Housing: during the quarantine period males and females were housed separately on stainless steel wire racks equipped with automatic waterers
(~10 mice per cage).
- Diet: ad libitum (pelleted NIH-O7 diet) except during exposure period
- Water: ad libitum
- Acclimation period: 4 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23-25
- Humidity (%): 50-60
- Air changes (per hr): 13-15
- Photoperiod: 12 hours dark/light cycle
No further details are given.

Administration / exposure

Route of administration:

inhalation: aerosol

Type of inhalation exposure (if applicable):

whole body

Vehicle:

air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: the study laboratory designed the stainless-steel inhalation exposure chambers so that uniform vapor concentrations could be maintained throughout the chambers when catch pans were in place. The total active mixing volume of each chamber was 1.7 m³.
- System of generating particulates/aerosols: the gallium arsenide aerosol generation and delivery system had five basic components: a flexible-brush dust feed mechanism developed at the study laboratory, a Trost Model GEM-T air-impact mill, a cyclone separator, an aerosol charge neutraliser, and an aerosol distribution system. The flexible-brush dust feed mechanism employed a hopper into which the dry powder was poured. The hopper was reloaded with additional gallium arsenide at regular intervals throughout each day's exposure period. Aerosol passed through the charge neutraliser into the distribution line. At each chamber location, a vacuum pump drew aerosol from the distribution line into the chamber inlet, where the aerosol was further diluted with HEPA-filtered air to the appropriate concentration.
- Temperature, humidity in air chamber: 23-25°C, 55% +/- 15%
- Air change rate: 15 air changes per hour
- Method of particle size determination: cascade impactor samples (Mercer-style 7-stage impactor) were taken once each month from each exposure
chamber during the subchronic study and the stages (glass coverslips lightly sprayed with silicone) were chemically analysed for gallium by ICP-MS or GFAAS. The relative mass collected on each stage was analysed by probit analysis. The overall average MMAD of the aerosol in the developmental toxicity study was 1.1 µm with geometric standard deviation, ranging between 2.0 and 2.1.

TEST ATMOSPHERE
- Brief description of analytical method used: gallium arsenide aerosol concentrations were monitored with real-time aerosol monitors (RAM-1). These devices used a pulsed light-emitting diode in combination with a silicon detector to sense light scattered over a forward angle of 45° to 95° by the particles traversing the sensing volume. The instrument responded to particles in the 0.1 to 20 µm diameter size range.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

see above

Details on mating procedure:

- Impregnation procedure: cohoused
- M/F ratio per cage: one male animal and 2-4 female animals
- Length of cohabitation: 3 consecutive nights
- Proof of pregnancy: vaginal plug referred to as day 0 of pregnancy
- Positively mated females were weighed and randomly assigned to one of the exposure groups using body weight as the blocking variable.
No further details are given.

Duration of treatment / exposure:

6 hours per day, plus T90 (build-up time for the exposure chamber to reach 90% of the target aerosol concentration)

Frequency of treatment:

7 days/week

Duration of test:

Mice were exposed for 14 consecutive days from day 4 to 17 of gestation.

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
10 mg/m³
Basis:
nominal conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
37 mg/m³
Basis:
nominal conc.

Doses / concentrations 3

Remarks:

Doses / Concentrations:
75 mg/m³
Basis:
nominal conc.

No. of animals per sex per dose:

- In total, 368 females and 87 males at study initiation
- Treatment groups: 22-24 female mice per group
- Control group: 23 female mice
- Virgin (test groups): each of the treatment groups (3) included 10 additional virgin females (for comparison)
- Virgin (controls): 10 additional virgin females

Control animals:

yes, concurrent vehicle

other: virgin animals

Details on study design:

Dose selection rationale: the highest target exposure chamber concentration, 75 mg/m³ gallium arsenide, was chosen based on the results of a 2-week range finding study conducted at PNL, and the two lower concentrations were chosen to determine the dose-response relationship of effects (if any) following gallium arsenide inhalation.

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: No data

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: animals were observed twice each day for signs of chemical toxicity, moribundity, and mortality, 7 days per week.

BODY WEIGHT: Yes
- Time schedule for examinations: body weights of mated female mice were acquired on gestational days 0, 4, 6, 9, 12, 15 and 18; virgin mice were weighed on exposure days 1, 3, 6, 9, 12, and at sacrifice.

FOOD CONSUMPTION: No data

WATER CONSUMPTION: No data

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 18
- Organs examined: the maternal liver and kidneys were removed and weighed; the uterus was removed, weighed, and opened.

OTHER:
- Virgins were weighed on the day after their last exposure, killed, and examined for gross tissue abnormalities.
- Liver and kidney weights were obtained and the ovaries were fixed in Bouin's solution.

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of resorptions: Yes
- Number of live or dead implants: Yes

Fetal examinations:

External examinations: Yes
- Live fetuses were weighed and examined for gross defects.

Soft tissue examinations: Yes
- The sex was determined by internal examination of the gonads after a lethal injection of sodium pentobarbital.
- Live fetuses in the uterus of each litter (50%) were examined for visceral defects by dissection of fresh tissue.

Skeletal examinations: Yes
- All fetal carcasses, with and without heads, were prepared for skeletal staining.
- Cartilage as well as ossified bone was visualised by double-staining with alcian blue and alizarin red S.

Head examinations: Yes
- The heads of the fetuses not selected for visceral examination were removed and placed in Bouin's fixative.
- After fixation, the heads were serially sectioned with a razor blade and examined for soft-tissue craniofacial abnormalities.

Statistics:

- Means and standard deviations for animal data were calculated with SAS statistical software on a VAX 11/780 computer.
- Mean fetal body weights, as the mean of litter means, were analysed using the SAS General Linear Models (GLM) Procedure (SAS, 1985) with an analysis of variance (ANOVA) model for unbalanced data.
- Response variables, either body weight or the arc sine transfonmations of proportional incidence data, were analysed against the class variable, "treatment", in a one-way ANOVA model.
- A Tukey's t-test (two-tailed) was used to assess statistically significant differences between control and exposed groups.
- If appropriate, the dose-response relationship was determined by means of an orthogonal trend test on arc sine transformed variablea (Winer 1971).
- The litter was used as the basis for analysis of fetal variables.

Indices:

no details

Historical control data:

no data

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
- Death occurred in 8/10 virgins and 8/42 pregnant females in the 75 mg/m3 group; in the 37 mg/m3 group, 8/10 virgins and 5/22 pregnant females died.
- Dyspnoe was seen in one-half of females at 10 and 37 mg/m3, and in in all females of the 75 mg/m3 group.
- The predominant gross lesion at sacrifice in the 37 and 75 mg/m3 groups was grey and/or mottled lungs; only 2 females of the 10 mg/m3 group showed these changes.
- Maternal body weights and cummulative weight gains were signifcantly (p<0.05) lower in the 37 and 75 mg/m3 groups on GD 9 to 15;
- In addition, females in the 75 mg/m3 group showed significantly (p<0.05) lower body weights by GD 18.
- Adjusted maternal weight gain was significantly (p<0.05) less for the 75 mg/m3 group, and a decreasing trend with increasing exposure concentrations was seen.
- Body weights of virgin females were not affected by treatment.
- Mean uterus weights were significantly (p<0.05) reduced at 75 mg/m3, and there was a trend towards reduction in uteri weights with increasing exposure concentrations.
- The overall pregnancy rate was not affected by treatment; no effects on the number of implantations were seen.
- In the 75 mg/m3 group, the significantly reduced number of corpora lutea was due to the presence of 7 litters with 100% early absorption.
- At 75 mg/m3, the number and percentage of resorptions/litter were significantly (p<0.05) increased and the number of live fetuses/litter was significantly
(p<0.05) reduced.
- An increase of the incidence of early resorptions was significantly (p<0.05) correlated with increasing exposure concentrations.

Effect levels (maternal animals)

1

Dose descriptor:

NOAEC

Effect level:

< 10 mg/m³ air

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

2

Dose descriptor:

NOAEC

Effect level:

< 10 mg/m³ air

Based on:

test mat.

Basis for effect level:

other: developmental toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
- The mean fetal body weights were significantly (p<0.05) reduced in the 37 and 75 mg/m3 exposure groups, and slightly (not statistically significant) in the the 10 mg/m3 group .
- A statistically significant trend (p<0.05) was observed for fetal body weights in relation to increased exposure concentrations.
- Sex ratio was not affected.
- The total number of fetal malformations, the proportion of litters with malformations or the mean incidence of total malformations were not significantly different from control values; however, all values increased with increasing exposure concentrations.
- There were several malformations which were observed in the exposure groups, but not in control animals: cleft palate, encephalocele and several vertebral defects.
- The incidence of vertebral effects (missing or extra vertebrae, fused vertebral arches, misshapen atlases or centra) was significantly (p<0.05) correlated with increasing exposure concentrations.
- In the high dose group (75 mg/m3), the number of fetuses with cleft palate or vertebral defects as well as the number of litters containing fetuses with vertebral defects was significantly (p<0.05) greater than in control animals.
- At 37 and 75 mg/m3, fetal variations (misaligned sternebare, sternebral defects, reduced ossification of sternebrae ) were significantly (p<0.05) higher relative to the control group.
- The incidence of each of the variations as well as the incidence of total variations per litter were significantly (p<0.05) related to increasing exposure concentrations.

Effect levels (fetuses)

1

Dose descriptor:

LOAEL

Effect level:

37 mg/m³ air

Based on:

test mat.

Sex:

not specified

Basis for effect level:

fetal/pup body weight changes

2

Dose descriptor:

NOAEL

Effect level:

75 mg/m³ air

Based on:

test mat.

Sex:

male/female

Basis for effect level:

changes in sex ratio

Fetal abnormalities

Abnormalities:

not specified

Description (incidence and severity):

The total number of fetal malformations, the proportion of litters with malformations or the mean incidence of total malformations were not significantly different from control values; however, all values increased with increasing exposure concentrations.
There were several malformations which were observed in the exposure groups, but not in control animals: cleft palate, encephalocele and several vertebral defects.

Overall developmental toxicity

Developmental effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

A NOAEL for maternal toxicity in mice was not achieved in this study.
A NOAEL for developmental toxicity was not achieved in this study.

Executive summary:

The potential for gallium arsenide to cause developmental toxicity was assessed in CD-1 (Swiss1) mice exposed to 0, 10, 37 or 75 mg/m³ gallium arsenide, 6 hours/day, 7 days/week. Mice were exposed on days 4 -17 of gestation (dg).

The two highest exposure concentrations were maternally lethal to some animals; body weights and body weight gains were reduced in survivors at the two highest concentrations. Mice in the 37 and 75 mg/m³ groups exhibited signs of pulmonary toxicity; minimal pulmonary toxicity was observed in the 10 mg/m³ group. A NOAEC for maternal toxicity in mice was not achieved in this study.

Developmental toxicity in the offspring was evident at all exposure concentrations, and became statistically significant at and above 37 mg/m³, i.e. at concentrations where also significant maternal toxicity was observed. There were signs of embryolethality, fetal growth retardation, significant increases in the incidence of fetal variations (primarily sternebral defects), and a slight, but not statistically significant, increase in the incidence of fetal malformations.

However, the statistical significance of the increase in the incidence of fetal malformations in mice was regarded as questionable. Several malformations were present in exposed groups but not in control animals, and a few of these are relatively rare in mice (encephalocele and missing/misshapen vertebrae). It is also possible, that the observed effects are not specific developmental effects caused by the test item, but instead correlated to the high maternal toxicity at the same doses. In consequence, for mice, a definitive NOAEC is not established.