The toxicology of gallium oxide in comparison with gallium arsenide and indium oxide.

Gallium arsenide (GaAs) and indium oxide (InO) are used in electronic industries at high and increasing tonnages since decades. Gallium oxide (GaO) is an emerging wide-bandgap transparent conductive oxide with as yet little industrial use. Since GaAs has received critical attention due to the arsenic ion, it seemed reasonable to compare its toxicology with the respective endpoints of GaO and InO toxicology in order to find out if and to what extent arsenic contributes. In addition, the toxicology of GaO has not yet been adequately reviewed, Therefore, this review provides the first evaluation of all available toxicity data on GaO. The acute toxicity of all three compounds is rather low. Subchronic inhalation studies in rats and mice revealed persistent pulmonary alveolar proteinosis (PAP) and/or alveolar histiocytic infiltrates down to the lowest tested concentration in rats and mice, i.e. 0.16 mg GaO/m. These are also the predominant effects after GaAs and InO exposure at similarly low levels, i.e. 0.1 mg/m each. Subchronic GaO exposure caused a minimal microcytic anemia with erythrocytosis in rats (at 6.4 mg/m and greater) and mice (at 32 and 64 mg/m), a decrease in epididymal sperm motility and concentration as well as testicular degeneration at 64 mg/m. At comparable concentrations the hematological effects and male fertility of GaAs were much stronger. The stronger effects of GaAs are due to its better solubility and presumed higher bioavailability. The database for InO is too small and subchronic testing was at very low levels to allow conclusive judgements if blood/blood forming or degrading and male fertility organs/tissues would also be targets.