Metal oxides containing either Ni alone (NiO's) or both Ni and Cu (Ni‐CuO's) are encountered during Ni refining. Six NiO compounds calcined at temperatures ranging from 650 to 1045° and four Ni‐CuO's containing from 6.9 to 28% Cu and 44 to 69% Ni were screened for their in vitro cytotoxicity to alveolar macrophages (AM). NiO's were less toxic to rat AM than were the Ni‐CuO compounds. The toxicity of the Ni‐CuO compounds increased with increasing Cu content and decreasing Ni content of the molecules, indicating that the toxicity was due to the Cu content of the molecules. AM obtained from beagle dogs, F344/N rats, and B6C3F1mice displayed the following species sensitivities: dog rat ∼ mouse, with dog AM being most sensitive. The observed differences in species sensitivities correlated with differences in the phagocytic abilities of dog, rat, and mouse AM, with the ranking of phagocytic abilities of the AM in decreasing order of ability being dog rat mouse.
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