Biological Effects of Mica Dust in Experimental Animals

Abstract

Earlier survey of Mica miners of Bihar province in India revealed a high incidence of silicatosis in workers handling mica. Studies dealing with the biological effects of muscovite variety of Indian mica on experimental animals were done. Pulmonary fibrotic lesions and many cholesterol cleft like structures were observed at 210 days after intratracheal injection of 5 mg of mica dust in mice. The lymph nodes showed marked density of mica in cortico-medullary zone and medullary cords where swollen macrophages were fully packed with mica. Intraperitoneal injection of 5 mg of mica dust in mice at 90 days produced thick dense reticulination together with excessive lymphoid hyperplasia in omental tissue. In lymph node slight reticulinosis was seen in the medullary region corresponding to deposition of particles. In rats, 25 mg of mica dust by intratracheal injection at 330 days, produced small compactly arranged fibrotic lesions in lung parenchyma and lymph nodes were markedly increased in size with fibrosis in the medullary region which involved reticulin and collagen fibres. In guinea pigs 75 mg of mica dust after intratracheal injection provoked fibrotic lesions with thick reticulin fibres in the lymph nodes at 365 days. The poor fibrogenic response of mica dust may not produce severe adverse effects in early stage. However, prolonged inhalation may complicate with the exposure to other environmental chemicals and/or infections. When combined with mica choline produced in rats severe fibrotic reaction, collagen formation and adenocracinoma of bronchiolar epithelium and marked lymphadenopathy with abnormal cells in the lymph nodes.