تولید ازن O3 و گونه های اکسیژن فعال (ROS) بعد از جوشکاری

ABSTRACT Production of Ozone and Reactive Oxygen Species After Welding

The relation between welding and many occupational health effects, including respiratory illness (Antonini et al. 1998), neurotoxicity (Antonini et al. 2006; Bowler et al. 2003), and genotoxicity (Yu et al. 2004), is well known. A study also has indicated that breathing frequency increases and tidal volume decreases within several minutes when the rat exposed to welding fumes (Saito et al. 2000). However, the phenomenon disappears after repeated exposures. Welding joins pieces of metal or sheet metals by producing very high heat. A filler metal from a consumable electrode wire is continuously fed into the weld. Many toxic substances including heavy metals, toxic gases (ozone, carbon monoxide, carbon dioxide, and nitrogen oxides) are generated during welding (Antonini 2003). Ozone (O3) is produced in a photochemical reaction induced by ultraviolet light with atmospheric oxygen gas during the welding process.

Findings have shown that O3 alters pulmonary morphology, physiology, and biochemistry, and it also is a proven cause of asthma in school children (Cheng et al. 2003; Fauroux et al. 2000; Grievink et al. 1998). Furthermore, O3 is a strong oxidant that generates reactive oxygen species (ROS) in tissue, and even causes DNA damage (Cheng et al. 2003). Oxidative stress may be involved in the genetic changes associated with the initiation, promotion, and progress of carcinogenesis (Dreher and Junod 1996), and it has been implicated in the pathogenesis of certain diseases, including lung, skin, and breast cancers (Matsui et al. 1999; Rosenkranz 1993; Sozzi et al. 1991; Yeh et al. 2005). The rate of O3 production depends on the wavelengths and the intensity of ultraviolet light generated during welding, which in turn is affected by the material being welded and the type of electrode used (Pattee et al. 1973). Ozone has been evaluated during the welding process (Dennis et al. 1997), but there is no published comprehensive analysis of O3 production after welding has been completed.

In addition to O3, welding has other hazardous byproducts, for example, the fumes of metals including cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), lead (Pb), manganese (Mn), and others. Findings have shown that exposure to some heavy metals, including Cd, Mn, Cr, and Fe, is related to the generation of ROS (Pourahmad et al. 2003; Ranieri et al. 2005; Wang et al. 2004). Antonini et al. (1998) reported that freshly generated stainless steel welding fumes induced greater lung inflammation than ‘‘aged’’ fumes. They interpreted this as indicating a higher concentration of ROS on fresh fume surfaces. A later study by Churg (2003) also suggested that the combination of particles and O3, cigarette smoke, or reagent hydrogen peroxide augments the inflammatory response to particles, increases cell proliferation, and liberates higher levels of chemo-attractant mediators. Therefore, complex mixtures of pollutants produced as welding by-products are important in terms of industrial hygiene. The current study aimed to assess the ambient exposure of the welding operator to ROS and O3, and to assess the distribution of ROS and O3 before the start of welding, during welding, and after welding in an effort to determine what protective equipment should be used during welding. Many types of welding including manual shielded metal arc welding (also known as ‘‘stick welding’’), gas metal arc welding, flux-cored arc welding, gas tungsten arc welding, and others provide a powerful manufacturing tool for the high-quality joining of metal components. Shielded metal arc welding uses an electric arc between a flu covered metal electrode (the ‘‘stick’’) and the metal objects to be joined (the base metal and the weld metal). Heat from the arc melts the flux, forming gas and slag that shield the arc and the molten weld pool. In this study, the ambient sampling was taken during shielded metal arc welding.