The origin of mutagenicity in S. typhimurium in response to exposure to welding fumes, a complex mixture of metallic oxides and other inorganic compounds, was studied through the quantitative use of the histidine revertant Salmonella microsome test of Ames. Dose-response experiments and factorial design studies independently showed the mutagenic activity to be due to the presence of soluble Cr(V1). A rate of 65 f 1 5 revertants per plate per pg Cr(V1) was found for all fumes produced by the metal inert gas welding of stainless steel. A significantly reduced rate was found for manual metal arc welding fumes. The presence of other metals in low oxidation states (e.g. Fe(O), Fe(II), A1(0)), results in a significant reduction of the Cr(VI), accompanied by a corresponding decrease of the absolute revertant rate per unit fume mass.
INTRODUCTIONLarge numbers of workers are exposed to the fumes from welding, a technology for the joining of metals which has been in widespread use for more than fifty years. Welding fumes consist of mono-or bidispersed aerosols containing a complex mixture of multiphase particles whose chemistry and size distribution are determined by the process technology and consumable chemistry used in each c a~e . l -~ Although there are very many types of welding, two major technologies used on two classes of material account for perhaps 70% of the worldwide welding activity.The metal inert gas (MIG) welding of mild steel (MS), using a shielding curtain of argon, produces a relatively homogeneous aerosol with mass median diameter (MMD) of approximately 0.2 p. The particulates are composed of highly crystalline iron oxide spinel, with up to several percent of other alloying elements, typically Mn and Si, with trace impurities of many elements e.g. Cu, Zn, Pb etc. In the case of MIG welding on stainless steel (SS), the additional alloying elements Cr and Ni appear in relatively high concentrations, and are characteristic for all fumes used on high alloy steels. In manual metal arc welding (MMA), the core wire is surrounded by an electrode coating whose decomposition provides protection against oxidation in the arc region, the liquefied residue covering the weld with a protective slag layer. This coating provides a second aerosol source, mostly by means of atomization of the molten slag layer by the plasma jet: the particulates formed thereby are typically composed of a metal rich (po1y)-crystalline core surrounded by a glassy matrix composed of light elements such as Ca, F, K etc., or are spongy cenospheres. These light elements are found in a separate aerosol having a MMD of 2 p . Less than 1% of the mass of fresh fumes is found in particles larger than 5 p in diameter,3t Author to whom correspondence should be addressed, although the formation of long (> 20 p) chains is characteristic for the condensation process:334 a considerable amount of ejecta (spray) can be produced under certain (usually improper) welding conditions.A number of factors affect the concentration of fumes to which a welder can be...
