Effect of short-term stainless steel welding fume inhalation exposure on lung inflammation, injury, and defense responses in rats

Abstract

Many welders have experienced bronchitis, metal fume fever, lung function changes, and an increase in the incidence of lung infection. Questions remain regarding the possible mechanisms associated with the potential pulmonary effects of welding fume exposure. The objective was to assess the early effects of stainless steel (SS) welding fume inhalation on lung injury, inflammation, and defense responses. Male Sprague–Dawley rats were exposed to gas metal arc-SS welding fume at a concentration of 15 or 40 mg/m³ × 3 h/day for 1, 3, or 10 days. The control group was exposed to filtered air. To assess lung defense responses, some animals were intratracheally inoculated with 5 × 10⁴ Listeria monocytogenes 1 day after the last exposure. Welding particles were collected during exposure, and elemental composition and particle size were determined. At 1, 4, 6, 11, 14, and 30 days after the final exposure, parameters of lung injury (lactate dehydrogenase and albumin) and inflammation (PMN influx) were measured in the bronchoalveolar lavage fluid. In addition, particle-induced effects on pulmonary clearance of bacteria and macrophage function were assessed. SS particles were composed of Fe, Cr, Mn, and Ni. Particle size distribution analysis indicated the mass median aerodynamic diameter of the generated fume to be 0.255 μm. Parameters of lung injury were significantly elevated at all time points post-exposure compared to controls except for 30 days. Interestingly, no significant difference in lung PMNs was observed between the SS and control groups at 1, 4, and 6 days post-exposure. After 6 days post-exposure, a dramatic increase in lung PMNs was observed in the SS group compared to air controls. Lung bacteria clearance and macrophage function were reduced and immune and inflammatory cytokines were altered in the SS group. In summary, short-term exposure of rats to SS welding fume caused significant lung damage and suppressed lung defense responses to bacterial infection, but had a delayed effect on pulmonary inflammation. Additional chronic inhalation studies are needed to further examine the lung effects associated with SS welding fume exposure.

Introduction

It has been estimated that greater than 5 million workers worldwide are exposed to welding aerosols on a daily basis. Approximately 360,000 workers are classified as full-time welders in the United States (Bureau of Labor Statistics, 2005). Welding is a common industrial process used to join metals. Complex mixtures of aerosol and gaseous by-products are formed during welding. The generated fumes are composed of an array of metals, such as iron (Fe), manganese (Mn), chromium (Cr), and nickel (Ni), volatilized from the welding electrode. Welders also are exposed to gases, such as ozone and carbon monoxide, that may affect their health.

Over the past 40 years, numerous studies have evaluated the health effects of welding (Antonini, 2003). Most studies have focused on the pulmonary effects associated with welding fume exposure. Bronchitis, metal fume fever, lung function changes, siderosis, immunosuppression, and a possible increase in the incidence of lung cancer have all been reported in welders (Antonini et al., 2003). Even less is known about the non-pulmonary effects associated with welding, specifically the potential neurological effects (Josephs et al., 2005, Racette et al., 2005).

The potential adverse health effects associated with welding fume inhalation can be challenging to study. Welders are not a homogeneous group. Their exposure can vary due to differences in industrial setting, work area ventilation, the types of welding processes and material used, and exposures to other occupational hazards, such as solvents and asbestos. Little information is available about the causes and potential mechanisms by which welding fume inhalation may adversely affect health. The use of animal models and the ability to control the welding fume exposure may be helpful in the elucidation of these mechanisms.

A NIOSH welding program has been developed in the Health Effects Laboratory Division. The goal of the program is to use animal models to assess the effects of welding fume inhalation on possible increases in lung tumorigenicity (Solano-Lopez et al., 2006), susceptibility to lung infection (Antonini et al., 2004), and the development of neurotoxicity (Antonini et al., 2006a). A welding fume generation and inhalation exposure system has been developed by NIOSH that can simulate real workplace exposures and allow for continuous welding for extended periods of time without interruption (Antonini et al., 2006b). The system is completely automated and uses a computer-controlled robotic welder, which welds and replaces materials as they are consumed during the operation. This manuscript describes a series of short-term animal inhalation studies that evaluate dose and time effects of stainless steel (SS) welding fume exposure on lung injury, inflammation, and defense response to infection. The observations and results generated from these acute studies will be the basis for designing a long-term animal inhalation study that will evaluate the potential toxic effects associated with welding fumes.