An investigation of fibrogenic and other toxic effects of arc-welding fume particles deposited in the rat lung.

Abstract

Lung burdens of deposited particles from fumes generated by arc-welding were established in rats by single inhalation exposures, repeated intermittent exposure or by intratracheal injection. Fumes from manual metal arc-welding using flux-coated mild-steel rods (MMA-MS) were compared with those from metal inert-gas welding with stainless steel wire (MIG-SS). After initial rapid clearance of deposited material from the lungs, persistent residual deposits remained. Such residues resulting from single inhalation were small and confined mainly to peribronchial accumulations in macrophage clusters. Deposits remaining after repeated inhalation were larger and more widespread. Intratracheal administration (50 mg) established massive residual deposits, giving nodular accumulations in peribronchial, subpleural and perivascular sites, with substantial alveolar parenchymal involvement. Deposits from both types of fumes contained predominantly iron. Particles from stainless steel also contained chromium, but concentrations of this element were low in deposits from MMA-MS fumes. MMA-MS deposits contained silica, probably amorphous. Long-term studies (up to 450 days) attempted to detect evidence of fibrosis resulting from particle burdens. Low-grade collagen fibre layers developed at margins of MMA-MS nodules. Diffuse reticulin fibre networks occurred within MIG-SS aggregates. Tissue hydroxyproline levels were increased (doubled) in lungs with intratracheal burdens of MMA-MS particles, but no significant increases resulted from MIG-SS. The major lesions were nodular aggregates of particle-laden macrophages with giant-cell formation, and alveolar epithelial thickening with atelectasis.