Year

1985

Degree Name

Doctor of Philosophy

Department

Department of Chemistry

Abstract

This thesis describes physical, chemical and biological studies of fumes from six types of flux-coated welding rods, and a companion study the bacterial mutagenicity of 24 metal salts. The choice of the welding rods was based on market availability and use, and chemical considerations. Fume was generated using an automatic arc welder (MMAW process). The mutagenicity study focussed on nickel (II) and chromium (VI), putative carcinogens present in certain welding fumes. Summaries of individual fume and mutagenicity studies are given below: (1) The generation rate and chemical composition of fume from AC welding of E316L-16 stainless steel electrodes were studied under a wide range of current (80- 120A) and voltage (20-40V) conditions. The marked variations observed in the fume generation rates and fume composition are discussed In terms of arc temperature, gas shielding effects and the volatility and thermodynamic stability of fume components. (2) Fume from E316L-16 stainless steel electrodes was examined by x-ray photoelectron spectroscopy. Fourteen elements were determined. Necessary chemical information on the fume was obtained using various analytical techniques. It is demonstrated that NaF and KF are preferentially enriched on the particle surfaces and that Na, K, F and CrtVI) are appreciably leachable by water. The toxicological significance of the results is discussed. (3) Fume generation rates (FGRs) and electrode melting rates (EMRs) of three types of hardfacing and two types of HSLA steel electrodes were determined at optimum values of current. Significant variations were observed in the FGRs and EMRs when arc voltage (and hence arc current and power) was varied at a fixed current setting on the power supply. The processes responsible for the observed variations are discussed. Both AC and DC processes are examined. (4) Fume from AC welding of a high-manganese hardfacing electrode showed no significant variation in chemical composition with particle-size range In the size fractions i 1.1, 1.1 -2.0,2.0-3.3, 3.3-7.0 and >7.0 urn equivalent aerodynamic diameter. The physical properties of the fumes from the hardfacing and HSLA steel electrodes lie in the range: density = 3.0-4.4 g cm"^; mass mean aerodynamic diameter - 0.5-0.9 urn (92-96% of fume < 7 urn); and BET surface area - 13-28 m2 g"1. (5) Elemental composition of the flux, fume and water-soluble fume fractions from the hardfacing and HSLA steel electrodes were determined using a wide range of analytical techniques. The results obtained (including chromium speciation data) are discussed alongside existing toxicological information. (6) Chromium(VI) and seleniiMVI) were found to be mutagenic in standard Ames plate-incorporation assays. Cadmium (II), beryllium (II), chromic (VI) and r^vanadiu* (V) were detected in standard fluctuation assays. It was not possible to detect nickel (and cadmium (II) in modified Ames and fluctuation assays (trimetaphosphate in the nutrient media in place of orthopnosphate prevent precipitation of these metals as orthophosphates). Metavanadate (V) was however detected in the modified Ames assays. The results indicate that metal mutagens such as nickel (II) and chromium (VI) act by different mechanisms. (7) After treatment with potassium chromate at concentrations causing ultramicroscopic cellular lesions (3.7 x 10-5M), only 25% of revertant colonies of Salmonella TAIOO replicate on fresh minimal plates containing biotln. Detailed investigations show that temporary growth inhibition may be responsible for most of the non-replicating colonies detected in Ames plate-incorporation assays of chromium (VI). (8) Mitotic inhibitory activity and sister chromatid exchange (SCE) Induction in cultured Chinese hamster lung (Don) cells correlate with the chromium (VI) contents of the water-soluble extracts of welding fumes. The growth inhibitory and genotoxic action of insoluble fume particles is more complex and cannot be explained on the basis of chromium (VI) alone. (9) Published values of equilibrium constants were used to calculate the percentage of CrO^", Cr207 2", HCr04" and H2Cr04 present in aqueous solution at total chromium (VI) concentrations of I0"2 - 10"6M, In the pH range 1-8. This Is the first compilation of such data.

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