Submicron particles in smoke resulting from welding alloys and cast alloy in metalworking industry]

Background: The toxicity of welding fumes depends on both chemical composition and ability to penetrate and deposit deeply in the lungs. Their penetration and deposition in the regions of the respiratory system is mainly determined by their size. Objectives: The knowledge of the size distribution of welding fumes is a crucial information towards the estimate of the doses of toxic compounds delivered into the respiratory tract. Methods: Particle number size distribution was continuously measured during different welding operations by means of a Fast Mobility Particle Sizer, which counts and classifies particles, according to their electrical mobility, in 32 size-channels, in the range from 5.6 to 523 nm, with 1s time resolution. Results: The temporal evolution of submicrometric particles (6-523 nm), nucleation mode particles (6-16 nm) and the fraction 19-523 nm before, during and after the welding operations performed with/without local exhaust ventilation are reported and extensively discussed. Before welding, nucleation mode particles represent about 7% of submicrometric particles; after about 40 s from the welding start, the percent contribution of nucleation mode particles increases to 60%. Total and nucleation mode particle concentrations increase from 2.1x10(4) to 2.0x10(6) and from 1.6x10(3) to 1.0x10(6), respectively. Conclusions: The temporal variation of the particle number size distribution across the peaks, evidences the strong and fast-evolving contribution of nucleation mode particles: peak values are maintained for less than 10 s. The implication of such contribution on human health is linked to high deposition efficiency of the submicrometric particles in the alveolar interstitial region of the human respiratory system, where gas exchange occurs.