PURPOSE: Despite relatively high historical silica exposure levels, there has been a puzzling lack of silicosis in the brick industry. It has been hypothesized that aluminum and other metal ions in the quartz particles are effective in reducing the toxicity of inhaled quartz. We conducted a radiographic study of a representative group of brickworkers to determine the prevalence of radiographic signs of silicosis among workers making structural clay bricks in the United States.
METHODS: Thirteen brickworks were randomly selected from 94 facilities operated by member companies of the Brick Industry Association. Of the 974 eligible workers, 702 chest x-rays were obtained. All roentgenograms were classified according to the 200 ILO Classification System by two NIOSH-certified B-readers. When the two primary readers disagreed on the presence or extent of parenchymal or pleural findings, the chest x-ray was classified by a third B-reader, unless the disagreement was for profusion within category 0. For chest x-rays interpreted by all three readers, the median classification was accepted as consensus.
RESULTS: No chest x-rays were classified as being consistent with silicosis. Three had consensus readings > 1/0 but none had small rounded opacities characteristic of silicosis (i.e., all had irregular opacities), and one was thought to be the result of processes unrelated to dust exposure. Pleural plaques were found in 12 chest x-rays, but these were unlikely to be related to silica exposure in the brick industry.
CONCLUSION: The prevalences of parenchymal and pleural abnormalities were below those found among individuals not occupationally exposed to dusts. These results are consistent with previous studies. The presence of aluminum and possibly other ions may reduce the toxicity of silica in the brick industry.
CLINICAL IMPLICATIONS: Silicosis does not appear to be a hazard in the clay brick industry in the United States. Aluminum and/or other ions found in the brick-making process may affect the toxicity of silica in this industry. For a given level of silica dust exposure, silicosis risk may vary among industrial settings.
DISCLOSURE: Robert Glenn, No Product/Research Disclosure Information; Consultant fee, speaker bureau, advisory committee, etc. This work was supported by the Brick Industry Association. Mr. Glenn and Dr. Hessel serve as science consultants to the association.