The fibrogenicity and carcinogenicity of three mineral slags used as substitutes for silica sand in abrasive blasting operations were investigated in male Fischer-344-rats. Slag samples were reduced by milling, suspended in deionized water and intratracheally instilled in a single 20 milligram dose. Positive controls were two samples of quartz (14808607), Min-U-Sil and novaculite; vehicle only controls were also used. Interim sacrifices were performed at 6, 12, and 18 months post exposure with the terminal sacrifice at 22 months. Animals were necropsied for gross and histopathological examination. No rats injected with slags showed any granulomas, nor were there areas of dense collagen. Only a slight increase in the size and number of alveolar wall cells and very minimal interstitial fibrosis could be seen at the sites of particle deposition of the slags. Tumor incidence in these animals was similar to that of vehicle controls, one to two tumors per test group. In contrast, the first lung tumor, an adenocarcinoma, was seen in a rat injected with Min-U- Sil at 12 months. By final sacrifice, the incidence of lung tumors in the Min-U-Sil group was 45 percent, all adenocarcinomas. Four tumors arose in dense scars, scars constituting most of the tumor mass. The other adenocarcinomas consisted of cuboidal or columnar cells, with some tumors containing squamous or large undifferentiated cells. In the novaculite group, lung tumor incidence was 29 percent. One cancer was an epidermoid carcinoma, the rest were adenocarcinomas. Seven arose in dense scars. The histology of the adenocarcinomas was the same as that observed in the Min-U-Sil induced tumors. In both groups, tumor incidence was greater in the left than the right lung. The authors conclude that quartz induces lung tumors in rats. The slag samples are apparently not carcinogenic.
Division of Biomedical and Behavioral Science, NIOSH, U.S. Department of Health and Human Services, Cincinnati, Ohio, 28 pages, 8 references