Modifying welding process parameters can reduce the neurotoxic potential of manganese-containing welding fumes - PubMed (original) (raw)

Comparative Study

doi: 10.1016/j.tox.2014.12.015. Epub 2014 Dec 27.

Gary X Lin 2, Amy M Jefferson 2, Samuel Stone 2, Aliakbar Afshari 2, Michael J Keane 2, Walter McKinney 2, Mark Jackson 2, Bean T Chen 2, Diane Schwegler-Berry 2, Amy Cumpston 2, Jared L Cumpston 2, Jenny R Roberts 2, David G Frazer 2, James M Antonini 2

Affiliations

Comparative Study

Modifying welding process parameters can reduce the neurotoxic potential of manganese-containing welding fumes

Krishnan Sriram et al. Toxicology. 2015.

Abstract

Welding fumes (WF) are a complex mixture of toxic metals and gases, inhalation of which can lead to adverse health effects among welders. The presence of manganese (Mn) in welding electrodes is cause for concern about the potential development of Parkinson's disease (PD)-like neurological disorder. Consequently, from an occupational safety perspective, there is a critical need to prevent adverse exposures to WF. As the fume generation rate and physicochemical characteristics of welding aerosols are influenced by welding process parameters like voltage, current or shielding gas, we sought to determine if changing such parameters can alter the fume profile and consequently its neurotoxic potential. Specifically, we evaluated the influence of voltage on fume composition and neurotoxic outcome. Rats were exposed by whole-body inhalation (40 mg/m(3); 3h/day × 5 d/week × 2 weeks) to fumes generated by gas-metal arc welding using stainless steel electrodes (GMA-SS) at standard/regular voltage (25 V; RVSS) or high voltage (30 V; HVSS). Fumes generated under these conditions exhibited similar particulate morphology, appearing as chain-like aggregates; however, HVSS fumes comprised of a larger fraction of ultrafine particulates that are generally considered to be more toxic than their fine counterparts. Paradoxically, exposure to HVSS fumes did not elicit dopaminergic neurotoxicity, as monitored by the expression of dopaminergic and PD-related markers. We show that the lack of neurotoxicity is due to reduced solubility of Mn in HVSS fumes. Our findings show promise for process control procedures in developing prevention strategies for Mn-related neurotoxicity during welding; however, it warrants additional investigations to determine if such modifications can be suitably adapted at the workplace to avert or reduce adverse neurological risks.

Keywords: Manganese; Neurotoxicity; Parkinsonism; Parkinson’s disease; Prevention; Welding.

Published by Elsevier Ireland Ltd.

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Figures

Fig.1

Fig.1

Weld bead quality following GMA-SS welding at regular or high voltage. Gas–metal arc welding using a stainless-steel (SS) electrode was performed on A36 carbon steel base plates. Welding was performed at two different voltage settings, standard/regular voltage (25 V; RVSS) or high voltage (30 V; HVSS), keeping current and shielding gas constant. Note that both welding conditions produced very good weld bead quality, indicating their suitability for adaptation by the industry.

Fig. 2

Fig. 2

(A) Scanning electron microscopy (SEM) analysis of fume particulates generated by RVSS or HVSS welding. (a and c) Fume particles collected on filters at stage 7 (particle size cut-off = 0.56 μm) of a MOUDI particle sizer. Note the similarity in particle morphology between the two process modes. (b and d) Fume particles collected on filters at stage 10 (particle size cut-off = 0.1 μm). Note the increase in ultrafine particle fraction following HVSS welding (in d). (B and C) Particle size distribution was determined using a Micro-Orifice Uniform Deposit Impactor (MOUDI) and a Nano-MOUDI. The mass median aerodynamic diameter (MMAD) of RVSS fumes was 0.39 μm with a geometric standard deviation (GSD) of 1.65. Similarly, the MMAD of HVSS fumes was 0.36 μm with a GSD of 1.59.

Fig. 3

Fig. 3

Effect of RVSS and HVSS fume particulates on Dmt1 gene expression in dopaminergic brain areas. Rats were exposed by whole-body inhalation (40 mg/m3; 3 h/day × 5 d/week × 2 weeks; for a total of 10 days) to fume particulates generated by gas–metal arc-stainless steel (GMA-SS) welding at standard/regular voltage (25 V; RVSS) or at high voltage (30 V; HVSS). At 1 day post-exposure, the mRNA expression of Dmt1 was assayed in the striatum and midbrain by TaqMan® real-time PCR. Following normalization to the endogenous control beta actin (Actb), the values are expressed as fold change from air-exposed controls. Graphical representations are Mean ± SE (n = 6/group). * indicates significant change from corresponding air-exposed control (P < 0.05). # indicates significantly different from RVSS group.

Fig. 4

Fig. 4

Effect of RVSS and HVSS fume particulates on Ccl2 gene expression in dopaminergic brain areas. Rats were exposed by whole-body inhalation (40 mg/m3; 3 h/day × 5 d/week × 2 weeks; for a total of 10 days) to fume particulates generated by gas–metal arc-stainless steel (GMA-SS) welding at standard/regular voltage (25 V; RVSS) or at high voltage (30 V; HVSS). At 1 day post-exposure, the mRNA expression of Ccl2 was assayed in the striatum and midbrain by TaqMan® real-time PCR. Following normalization to the endogenous control beta actin (Actb), the values are expressed as fold change from air-exposed controls. Graphical representations are Mean ± SE (n = 6/group). * indicates significant change from corresponding air-exposed control (P < 0.05). # indicates significantly different from RVSS group.

Fig. 5

Fig. 5

Effect of RVSS and HVSS fume particulates on Tnfa and Nos2 gene expression in the striatum. Rats were exposed by whole-body inhalation (40 mg/m3; 3 h/day × 5 d/week × 2 weeks; for a total of 10 days) to fume particulates generated by gas–metal arc-stainless steel (GMA-SS) welding at standard/regular voltage (25 V; RVSS) or at high voltage (30 V; HVSS). At 1 day post-exposure, the mRNA expression of Tnfa and Nos2 was assayed in the striatum by TaqMan® real-time PCR. Following normalization to the endogenous control beta actin (Actb), the values are expressed as fold change from air-exposed controls. Graphical representations are Mean ± SE (n = 6/group). * indicates significant change from corresponding air-exposed control (P < 0.05). # indicates significantly different from RVSS group.

Fig. 6

Fig. 6

Effect of RVSS and HVSS fume particulates on tyrosine hydroxylase protein expression in dopaminergic brain areas. Rats were exposed by whole-body inhalation (40 mg/m3; 3 h/day × 5 d/week × 2 weeks; for a total of 10 days) to fume particulates generated by gas-metal arc-stainless steel (GMA-SS) welding at standard/regular voltage (25 V; RVSS) or at high voltage (30 V; HVSS). (A) At 1 day post-exposure, the expression of Th protein was determined by immunoblot analysis in the STR and MB. (B) Following normalization to the endogenous control alpha tubulin (Tuba), the values are expressed as percent of air-exposed controls. Graphical representations are Mean ± SE (n = 4/group). * indicates significant change from corresponding air-exposed control (P < 0.05). # indicates significantly different from RVSS group.

Fig. 7

Fig. 7

Effect of RVSS and HVSS fume particulates on the expression of PD-related markers in dopaminergic brain areas. Rats were exposed by whole-body inhalation (40 mg/m3; 3 h/day × 5 d/week × 2 weeks; for a total of 10 days) to fume particulates generated by gas–metal arc-stainless steel (GMA-SS) welding at standard/regular voltage (25 V; RVSS) or at high voltage (30 V; HVSS). (A) At 1 day post-exposure, the expression of Park5 and Park7 proteins were determined by immunoblot analysis in the STR and MB. (B) Following normalization to the endogenous control cyclophilin A (Ppia), the values are expressed as percent of air-exposed controls. Graphical representations are Mean ± SE (n = 4/group). * indicates significant change from corresponding air-exposed control (P < 0.05). # indicates significantly different from RVSS group.

Fig. 8

Fig. 8

Effect of RVSS and HVSS fume particulates on Gfap gene expression in the striatum. Rats were exposed by whole-body inhalation (40 mg/m3; 3 h/day × 5 d/week × 2 weeks; for a total of 10 days) to fume particulates generated by gas–metal arc-stainless steel (GMA-SS) welding at standard/regular voltage (25 V; RVSS) or at high voltage (30 V; HVSS). (A) At 1 day post-exposure, the expression of Gfap mRNA in the STR was assayed TaqMan® real-time PCR. Following normalization to the endogenous control beta actin (Actb), the values are expressed as fold change from air-exposed controls. Graphical representations are Mean ± SE (n = 6/group). (B) At 1 day post-exposure, the expression of Gfap protein in the STR was determined by immunoblot analysis. Following normalization to the endogenous control cyclophilin A (Ppia), the values are expressed as percent of air-exposed controls. Graphical representations are Mean ± SE (n = 4/group). * indicates significant change from corresponding air-exposed control (P < 0.05). # indicates significantly different from RVSS group.

Fig. 9

Fig. 9

Elemental composition of WF particulates generated by RVSS and HVSS welding. RVSS and HVSS fume particulates were collected on to PVC filters (n = 4 for each fume type) and subjected to elemental analysis by ICP-AES following the NIOSH method 7300, which can detect over thirty different elements. ICP-AES analysis of the samples revealed the presence Fe, Mn, Cr, Cu and Ni as the major components (>99%) of the fume particulates. The concentration of each element was calculated as μg/mg of total metal and the mean concentration was determined. The weight percent of each element that composes the total metal portion of the fume was calculated and is graphically depicted.

Fig. 10

Fig. 10

Solubility of fume particulates generated by RVSS and HVSS welding. RVSS and HVSS fume particulates were collected on to PVC filters (n = 4 for each fume type). The particulates were suspended in distilled water, sonicated and centrifuged to obtain insoluble (pellet) and soluble (supernatant) fractions. The pellet and supernatant were subject to elemental analysis by ICP-AES following the NIOSH method 7300 to determine the elemental composition of the insoluble and soluble fractions. Fe, Mn, Ni and Cu made up the major composition (>99%) of the two fractions. The concentration of each element was calculated as μg/mg total metal. Graphical representations are Mean ± SE (n = 4/group). # indicates significantly different from RVSS group.

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