Physico-chemical and toxicological characterization of welding fumes from different processes

About one million workers worldwide are engaged in welding processes, where they are exposed to a complex mixture of inhalable pollutants. Adverse effects in the respiratory system can occur due to this occupational exposure. Currently, legislative limits only exist for inhalable and alveolar particles. However, epidemiologic and toxicologic studies show that especially ultrafine particles (UFPs) are related to adverse effects on human health. Although welders can be exposed to very high concentrations of UFPs, no standards exist concerning metrology or limits. In order to enable an assessment of possible health effects and a risk management for different welding processes and their variations, a study “Nanoscaled particles at welding fume workplaces” was carried out, where different welding processes were investigated with regard to physical and chemical characterization as well as toxicologic effects of the welding fume particles, together with occupational health examinations of the exposed workers. Twelve different welding processes / process variations where chosen for the analyses, taking into account market share and toxicological relevance, among others. All welding experiments were performed at the welding training and research centre (SLV) in Duisburg, Germany. As welding produces quickly changing emissions, measurement equipment with a high time resolution is needed. Therefore, a Fast Mobility Particle Sizer (FMPS) was used to determine particle size distributions. The surface area concentration deposited in the alveolar region of the lung was measured with a Nanoparticle Surface Area Monitor (NSAM), and particle number concentrations were monitored with a water-based and a butanol-based condensation particle counter (UWCPC and UCPC). Mass concentrations were determined with a newly designed PM0.4-High Volume Sampler, together with occupational standard stationary and personal PM4samplers. Chemical analyses were conducted for Fe, Mn, Cr, Ni, Ti, Cu, Zn, Pb, Al, Sn and Mo. Morphological characterization of the particles by REM analyses was carried out on special substrates using a Nanometer Aerosol Sampler (NAS). During the study, different variations (shielding gases, materials, arc types) of gas and shielded metal arc welding were characterized. PM0.4-mass concentrations varied by a factor of ca. 7, whereas alveolar surface area and number concentrations varied by factors of about 70 and 50, respectively. During all welding, particle size distributions showed two modes, but varying in their relative importance (see figure 1). The first mode was consistently at ca. 10 nm and the second one varying from 100-150 nm. The above mentioned analysed metals accounted for 17% to 55% of the PM0.4 mass.