Is there an occupational exposure limit (TLV) present for cobalt? A lesson from hard metal disease in Japan

In this paper, all of the literature reporting hard-metal-related bronchopulmonary diseases in Japan have been reviewed. Since 1931, when the production of hard metal (HM) started, three population-based studies at I-IM-producing plants have been published. It is shown from these studies that bronchial asthma associated with exposure to hard metal, some of which is mediated by an immediate type allergy against cobalt, is quite prevalent among workers and that, in a few cases, there is diffuse lung disease due to PIM. Case reports of diffuse lung disease or asthma in HM workers have also accumulated through physicians' observations. Typical features of giant cell interstitial pneumonitis have been found in some cases, with the occasional presence of HM elements including cobalt in the lung tissue. Given evidence that below the cobalt concentration of 50 mu g/m(3), pulmonary function is impaired and workers are at risk for asthma, the occupational exposure limit (TLV) for cobalt recommended by the Japanese Association of Industrial Health as well as ACGIH need to be reconsidered.