The morbidity and mortality of vermiculite miners and millers exposed to tremolite‐actinolite: Part III. Radiographic findings

Abstract

A study was conducted to estimate the exposure-response relationship for tremolite-actinolite fiber exposure and radiographic findings among 184 men employed at a Montana vermiculite mine and mill. Workers were included if they had been employed during 1975-1982 and had achieved at least 5 years tenure at the Montana site. Past fiber exposure was associated with an increased prevalence of parenchymal and pleural radiographic abnormalities. Smoking was not significantly related to the prevalence of small opacities. However, the number of workers who had never smoked was small, and this prevented measurement of the smoking effect. Under control for smoking and age, the prevalence of small opacities was significantly greater for vermiculite workers with greater than 100 fiber/cc-years exposure than for comparison groups (cement workers, blue collar workers, and coal miners) who had no known occupational fiber exposure. A logistic model predicted an increase of 1.3% in the odds ratio for small opacities at an additional exposure of 5 fiber-years.

Localized pleural thickening: Smoking and exposure to Libby vermiculite

“…It is possible that the age or time from first exposure could act as a proxy for smoking and vice versa, as among smokers, older/longer employed individuals would generally have a longer smoking history. Age is known to be significantly associated with risk of pleural changes even after controlling for LAA exposure 10 ; however, neither age nor time from first exposure were significant here, nor did they improve the model fit as measured by the AIC. This is likely because of the decision to include only those workers hired in 1972 or later, which made workers in the sub-cohort more similar to each other in age and time from first exposure.…”

“…In the Libby workers cohort, McDonald et al 11 assessed pleural thickening of the chest wall and found smoking status (current, former, or never smoker) was of borderline statistical significance (P ¼ 0.10) in a regression model, controlling for LAA exposure and age. Amandus et al 10 also evaluated radiographic abnormalities, constructing separate models for the full cohort, and restricting to current and former smokers. The parameter estimates for LAA exposure were not significant for the two models when controlling for age.…”

“…7,8 Libby amphibole asbestos (LAA) is a mixture of amphibole fibers identified in the Rainy Creek complex and present in ore from the vermiculite mine near Libby, MT, USA. 9 Epidemiological studies of worker cohorts in Libby, MT, USA, 10,11 and Marysville, OH, USA, 12,13 exposed to LAA fibers indicate increased risk of radiographic abnormalities, and that the latency period for development of radiographic abnormalities may be relatively short (median latency of 8.6 years for pleural plaques in retrospective investigation of serial radiographs). 14 Each of these cohort studies considered smoking in their analytic approach.…”

A risk assessment for exposure to grunerite asbestos (amosite) in an iron ore mine

“…‡ For amosite (grunerite asbestos) the Fe 2ϩ is present in at least 5 of the 7 available x structural sites. The health effects among the miners and millers in Libby, Montana exposed to vermiculite containing tremolite asbestos have been studied by two groups of investigators (13)(14)(15)(16)(17). Each investigation was designed as a mortality study and a crosssectional chest radiographic survey.…”

“…Each investigation was designed as a mortality study and a crosssectional chest radiographic survey. Slightly different criteria were used to define each cohort: the McDonald study (13,14) contained 406 men with 165 deaths, and the Amandus study (15)(16)(17) contained 575 men with 161 deaths. Both research groups used historical air samples to estimate exposure indices for the cohort members.…”