The occurrence of pneumoconiosis in a talc mining population exposed to non-asbestos elongate mineral particle

Purpose: This paper addressed the nature and level of EMP exposure found at an industrial grade talc mine (R.T. Vanderbilt Company [RTV]) in upstate NY operated from 1948 to 2008, updates the pneumoconiosis experience of these talc miners and millers and contrasts this experience to other EMP and non-EMP exposed populations. EMP was defined as any particle with a length/width ratio of 3 to 1 or greater and 5 mu m or greater length. Methods: The study population consisted of all male workers with at least one chest radiograph actively employed at the mine/mill for any period of time from 1978 to 2008 and subject to serial chest X-rays. The ILO pneumoconiosis classification system was used to classify parenchymal abnormalities by type, size, degree of profusion and progression. Pleural abnormalities were addressed as well. Studies of platy talc, amphibole asbestos workers and populations not exposed to occupational dusts were used as comparative groups. Results: The radiographic occurrence of pneumoconiosis was similar to that found among platy talc workers not exposed to EMP and the general unexposed population (below 5%) despite long exposures and elevated EMP levels for RTV talc workers. When detected, pneumoconiosis showed little progression with only one case reaching a radiographic stage > 1/1. No occurrence among a subset of formerly employed RTV talc workers after 8 years post exposure was found. The prevalence of pneumoconiosis among amphibole asbestos workers was significantly higher (30 to > 75%) with severity including category 2 or greater cases and evidence of accelerated progression at a lower cumulative EMP exposure than that found among RTV talc workers. Importantly, the total EMP airborne exposure for the talc workers exceeded the asbestos permissible fiber exposure standard by a factor of 15 to 20 and the EMP components found in NY talc that consisted of elongate amphibole cleavage fragment and fibrous/asbestiform talc each separately exceeded this standard by a factor of 7 to 10 (averaged over a span of decades). Pleural plaque in some but not all talc workers (industrial and platy) with little to no functional impairment was also noted. Discussion: The low toxicity of RTV EMPs with respect to pneumoconiosis is supported by worker mortality, animal and cell studies of this talc. Controversy involving diagnostic reliability and competing risk has occurred more recently with respect to human mesothelioma. The similar occurrence of pneumoconiosis and pleural plaques in RTV and platy talc-exposed workers with similar respirable dust exposure suggest the mineral talc is the particulate component most associated with the occurrence of pulmonary abnormalities. Conclusion: Elevated exposure in this study to a non-asbestos asbestiform EMP (talc fiber) suggests that the mineral type with its attending physiochemical/elemental properties matters - in addition to particle dimension, bio-durability and growth habit.