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There are 20 studies dealing with the metabolism and kinetics of GaAs. Unfortunately 18 of them are of very doubtful quality so that their results are not reliable.

The remaining 2 studies were performed together with other NTP studies, well documented, and performed under a quality assurance system: a 90-day (14 -week) rat (F344N) study and a 2-year rat (F344N) study, both with inhalative exposure:

These and the other NTP studies (NTP, 2000) with rats and mice revealed that after repeated inhalative exposure to a fine dust of GaAs a local reaction in the lung is triggered. This reaction can be described as pulmonary alveolar proteinosis leading to chronic active inflammation.

The toxicokinetic investigations revealed:

- Lung burden analyses for male rats in the 14-week and 2-year studies indicates that the percentages of Gallium and Arsenic in the lung relative to the total lung burden were similar at all exposure concentrations throughout the study.

- Lung burden for gallium and arsenic increased proportionally throughout the 14-week or 2-year studies.

- However lung clearance half-lives decreased with increasing exposure concentrations. The clearance half-live of 37 days for Gallium in the 1.0 mg GaAs/m³ group was considerably less than the 133 or 96 days for the 0.01 or 0.1 mg GaAs/m³ groups in the 2-year study, respectively, Arsenic half-lives were similar.

- In the 2-year toxicity study with inhalative exposure of male rats to concentrations of 0, 0.01, 0.1, 1 mg GaAs/m³ 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.

- 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. The means of the 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 difference was not statistically significant.

- The blood levels of Gallium and Arsenic of the rats in the 0.01 or 0.1 mg GaAs/m³ groups were similar to those of the control animals.

(In the NTP-report a half-life of 1 to 2 hours is given for plasma gallium levels as a citation from studies of Dudley et al., 1949.

Unfortunately the original publication does not contain such a statement. All 5 cited publications of Dudley et al. give only very poor and insufficient data on the performed investigations. Therefore this literature is classed with the reliability 4 (not assignable) according to Klimisch et al., 1997, and is not used for the evaluation.)

The good consistency of the data between all the NTP studies supports the reliability of the results of the 2 toxicokinetic studies.