Gallium arsenide

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics in vivo

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1993-1995

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP 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:

publication

Title:

Unnamed

Year:

2000

Materials and methods

Objective of study:

other: lung and tissue burden study

Test guideline

Guideline:

other: The 2-year study was conducted in compliance with FDA Good Laboratory Practice Regulations (21 CFR, Part 58). In addition, as records from the 2-year study were submitted to the NTP Archives, this study was auditied retrospectively.

Principles of method if other than guideline:

Tissue burden study: lung, testes, blood and serum from male rats were evaluated. At 1, 2, 4, 6, 12, and 18 months, 5 male rats from the 0, 0.1, and 1.0 mg/m³ groups were evaluated. 4 or 5 male rats from the 0.01 mg/m³ group were evaluated at 2-, 12-, and 18-month time points.
The 2-year study was conducted in compliance with FDA Good Laboratory Practice Regulations (21 CFR, Part 58). In addition, as records from the 2-year 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

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, dark gray to black, fine powder
- Analytical purity: 99,0 % +- 0.2%, with total impurities <119 ppm
- Lot/batch No.: 12956-13
- Stability under test conditions: gallium arsenide was found to be stable for 2 weeks at temperatures up to 60°C when stored protected from light. Stability was monitored by the study laboratory throughout the studies with ICP/AES. No degradation of the bulk chemical was detected.
- Storage condition of test material: The bulk chemical was stored in amber glass bottles with Teflon®-lined caps under a nitrogen headspace at room temperature.
- Mass Median Aerodynamic Particle Diameter: 0.8 - 1.9 µm in the 2-year studies
- Origin: the analytical chemistry laboratory, Midwest Research Institute (Kansas City, MO) obtained gallium arsenide from Johnson Matthey, Inc. (Ward Hill, MA) and prepared the single lot.

Radiolabelling:

no

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Taconic Farms (Germantown, NY)
- Age at study initiation: approx. 6 weeks old (after being quarantined for 14 days)
- Housing: individually; stainless steel wire bottom (Hazzelton System, Inc., Aberdeen, MD), changed weekly
- Diet: ad libitum, except during exposure and urine collection periods; NIH-07 open formula pelleted diet (Zeigler Brothers, Inc., Gardners, PA), changed daily
- Water: ad libitum, softened tap water (Richland municipal supply) via automatic watering system (Edstrom Industries, Waterford, WI),changed weekly
- Acclimation period: 14 days quarantine

ENVIRONMENTAL CONDITIONS
- Temperature (°C): ~23 - 25
- Humidity (%): 55 +/- 15
- Air changes: 15/hour
- Photoperiod: 12 hours dark/light cycle

Administration / exposure

Route of administration:

inhalation: aerosol

Vehicle:

other: 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 vapour 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 aerosol generator consisted of a drum, body, and cap. The drum rotated at 60° increments, with set time intervals between drum rotation. Rotation of the drum was controlled by a compressed-air -driven valve driver (VICI Valco Instument Co., Houston, TX). Output of the generator was regulated by adjusting the rotation cadence. The aerosol passed through the distribution line to the exposure chambers, where it was diuted with filtered air to the proper exposure concentration.

- Method of particle size determination: the particle size distribution in each chamber was determined during pre-study testing and monthly during the 2-year study using a Mercer-style seven-stage impactor. The stages (glass coverslips lightly sprayed with silicone) were analysed by ICP/MS. The relative mass collected on each stage was analysed by probit analysis. The mass median aerodynamic particle diameter and the geometric standard deviation of each set of samples were estimated.

- Chamber aerosol concentrations were monitored with real-time aerosol monitors (RAMs) that used a pulsed-light emitting diode in combination with a silicon detector to sense light scattered over a forward angular range of 45° to 95° by particles traversing the sensing volume. The instrument responds to particles 0.1 to 20 µm in diameter; the geometric diameter of gallium arsenide aerosol approached the minimum of this range. Each RAM was calibrated by correlating the measured voltage with gallium arsenide concentrations determined by analyzing exposure chamber samples collected on fiberglass filters (Teflon-coated Pallflex, Pallflex Corp., Putum, CT). Filter samples were dissolved in nitric acid and analyzed for gallium arsenide using inductively coupled plasma/mass spectroscopy (ICP/MS). RAMs were calibrated twice monthly during the 2-year studies. During the 2-year studies, calibration was verified by ICP/MS analysis of filter samples collected every other day (control chambers) or daily.
- Uniformity of aerosol concentration was evaluated every 3 months. Chamber concentration uniformity was acceptable throughout the studies

Duration and frequency of treatment / exposure:

2 years, 6 hours/day, 5 days /week

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 0.01, 0.1, 1 mg GaAs/m³

No. of animals per sex per dose / concentration:

Month 1, 2, 4, 6, 12, and 18: 5 males (0, 0.1, and 1 mg/m³)
Month 2, 12, and 18: 4 or 5 males (0.01 mg/m3)

Control animals:

yes

Positive control reference chemical:

no

Details on study design:

- Dose selection rationale: in a preceding 90-day study no no-effect level was achieved for the lung.
Based on the increased severities of lung proteinosis and at least a 2-fold increase in lung weights in males and females, exposure concentrations of 10 mg/m³ or greater were considered sufficiently severe to preclude their use in a 2-year study. Because a no-effect level was not achieved for the lung, the lowest exposure concentration for rats in the 2-year stady was set at the lowest concentration that the chamber particle monitor could monitor continuously with accuracy.
Therefore the gallium arsenide exposure concentrations selected for the 2-year inhalation study in rats were 0.01, 0.1 and 1.0 mg/m³.

Details on dosing and sampling:

Lung burden study:
The lungs, testes, blood, and serum from male rats were evaluated at:
Month 1, 2, 4, 6, 12, and 18: 5 males (0, 0.1, and 1 mg/m³)
Month 2, 12, and 18: 4 or 5 males (0.01 mg/m³)

- Method type(s) for identification: atomic absorption spectrometry
- Limits of quantification: 0.20 µg Ga/g lung, 1.45 µg As/g lung
0.005 µg Ga/g blood, 2.68 µg As/g blood
0.042 µg Ga/g serum, 0.086 µg As/g serum
0.051 µg Ga/g testes, 0.126 µg As/g testes

Statistics:

Survival analyses:
- The probability of survival was estimated by the product-limit procedure of Kaplan and Meier (1958).
- Statistical analyses for possible dose-related effects on survival used Cox's (1972) method for testing two groups for equality and Tarone's (1975) life table test to identify dose-related trends. All reported P values for the survival analyses are two sided.

Analysis of neoplasm and non-neoplastic lesion incidences:
- The Poly-k test (Bailer and Portier, 1988; Portier and Bailer, 1989; Piegorsch and Bailer, 1997) was used to assess neoplasm and nonneoplastic lesion prevalence.

Analysis of continuous variables:
- Organ and body weight data, which historically have approximately normal distributions, were analyzed with the parametric multiple comparison procedures of Dunnett (1955) and Williams (1971, 1972).
- Blood and bone marrow hematology, clinical chemistry, urinalysis, spermatid, and epididymal spermatozoal data, were analyzed using the nonparametric multiple comparison methods of Shirley (1977) and Dunn (1964). Jonckheere.s test (Jonckheere, 1954) was used to assess the significance of the dose-related trends and to determine whether a trend-sensitive test (William's or Shirley's test) was more appropriate for pairwise comparisons than a test that does not assume a monotonic dose-related trend (Dunnett.s or Dunn.s test).
- Average severity values were analyzed for significance with the Mann-Whitney U test (Hollander and Wolfe, 1973). Treatment effects were investigated by applying a multivariate analysis of variance (Morrison, 1976) to the transformed data to test for simultaneous equality of measurements across exposure concentrations.

Results and discussion

Toxicokinetic / pharmacokinetic studies

Details on absorption:

Lung weights increased in all male rats exposed to 0.1 or 1 mg/m³ throughout the study when compared to chamber controls and the 0.01 mg/m³ group. In addition, lung weights of these rats continued to increase to a greater extent throughout the study than did lung weights of the chamber controls and the 0.01 mg/m³ group. The percentages of gallium and arsenic in the lung relative to the total lung burden were similar at all exposure concentrations throughout the study because the deposition and clearance rates in the lung for gallium and arsenic were similar within each exposed group.

Lung burden for gallium and arsenic increased with increasing exposure concentration. The lung burdens increased with increasing exposure concentration over time in all exposed groups. It appears that a steady state lung burden was achieved for the 0.1 and possibly the 1.0 mg/m³ groups, although the lung burdens at 18 months were low.
Lung burdens did not increase proportionally with exposure concentration over time. Lung burdens normalized to exposure concentration would be expected to remain constant across all exposure concentrations if the toxicinetics were linear; however, gallium and arsenic normalized lung burdens in the 1.0 mg/m³ group were considerably lower than those observed in the 0.01 or the 0.1 mg/m³ group. Although deposition rates increased proportionally to exposure concentration, the lung clearance half-lives for the 1.0 mg/m³ group were considerably less than those for the 0.1 or the 0.01 mg/m³ group.

Half-lives for gallium in the lung were 133, 96, and 37 days for the 0.01, 0.1, and 1.0 mg/m³ groups, respectively. Arsenic lung half-lives were similar.

The gallium arsenide clearance half-live for the 1.0 mg/m³ group from the 2-year study was similar to the clearance half-live for the 1.0 mg/m³ group from the 14-week study. Accordingly extended exposure for 2 years had no effect on the clearance rate and, therefore, the clearance rate was dependent on the lung burden. Increased clearance at 1.0 mg/m³ was likely due to an increase in alveolar macrophages.

The interpretation of the analytical results is difficult: in contrast to fundamental analytical experiences the standard deviations are higher with higher Gallium concentrations. This seems to be the reason why no statistically significant differences were indicated in the tables of the study report.
There seems to be an increase of the Gallium concentrations above the background level of the control animals in the 1 mg GaAs/m³ group and at the end of the study in the blood of the 0.1 mg GaAs/m³ group.
Increased mean Gallium concentrations in the serum were only found in the 1 mg GaAs/m³ group after 6 months and later.
In the testes increased mean Gallium concentrations were found after 12 months and later in the 0.1 mg GaAs/m³ group and after 2 months and later in the 1 mg GaAs/m³ group.
As expected arsenic was detected in whole blood where it is preferentially bound to erythrocytes. Mean Arsenic concentrations in whole blood were greater than those of chamber controls only in the 1.0 mg/m³ group where they were approximately 2-fold higher, but this was not a statisically significant difference. The concentration of arsenic in whole blood was small relative to the concentration of arsenic in the lung. This indicates that there was no accumulation of either gallium or arsenic in these tissues.

Metabolite characterisation studies

Metabolites identified:

no

Details on metabolites:

no data

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): no bioaccumulation potential based on study results Half-times for gallium in the lung were 133, 96, and 37 days for the 0.01, 0.1, and 1.0 mg GaAs/m³ groups, respectively. Arsenic lung half-times were similar.
The interpretation of the analytical results is difficult because of the large standard deviations. No significant statistically significant differences are indicated in the tables. Therefore differences of the means cannot be interpreted as biological effects.
The Gallium concentrations in blood, serum, and testes were small relative to the concentrations of gallium and arsenic in the lung. This indicates that there was no accumulation of either gallium or arsenic in these tissues. As expected arsenic was detected in whole blood where it is preferentially bound to erythrocytes.
Only in the 1.0 mg/m³ group arsenic concentrations in whole blood were greater than those of chamber controls. They were approximately 2-fold higher and without a statistical significance.

Executive summary:

In a 2 -year toxicity study with inhalation exposure of male rats to concentrations of 0, 0.01, 0.1, 1 mg GaAs/m³, additional animals were treated for the characterisation of the lung burden.

Lung weights increased in all male rats exposed to 0.1 or 1 mg/m³ throughout the study when compared to chamber controls and the 0.01 mg/m³ group. Lung burden for gallium and arsenic increased with increasing exposure concentration. It appears that a steady state lung burden was achieved for the 0.1 and possibly the 1.0 mg/m³ groups after 6 months, although the lung burdens at 18 months were low.

Half-lives for gallium in the lung were 133, 96, and 37 days for the 0.01, 0.1, and 1.0 mg GaAs/m³ groups, respectively. Arsenic lung half-lives were similar.

The interpretation of the analytical results is difficult because of the large differences of the standard deviations. This seems to be the reason why no statistically significant differences were indicated in the tables of the study report. Therefore differences of the means cannot be interpreted directly as biological effects.

The gallium concentrations in blood, serum, and testes were small relative to the concentrations of gallium and arsenic in the lung. This indicates that there was no accumulation of either gallium or arsenic in these tissues. As expected arsenic was detected in whole blood where it was preferentially bound to erythrocytes. Arsenic concentrations in whole blood were greater than those of chamber controls only in the 1.0 mg/m³ group where they were approximately 2-fold higher but not statistically significantly different.