Metalworking Fluid-Related Aerosols in Machining Plants

Abstract

Respiratory problems are observed in machinists using soluble metalworking fluid (MWF). Evidences suggest that these problems could be related to the aerosolized microorganisms and their byproducts from MWF. To establish MWF aerosol exposure thresholds and to better understand their effect on human health, these aerosols must be fully characterized. This article evaluates airborne microorganisms and aerosols from soluble MWF in the working environment. Air quality parameters (endotoxin levels, culturable airborne microorganisms, fluid mist, inhalable dust and air exchange rates) were evaluated at 44 sites, in 25 shops in Quebec, Canada. Microorganism concentrations were also measured in MWF. Culturable airborne bacteria concentrations were low, ranging from 1.2 × 10¹ to 1.5 × 10³ CFU (colony forming units) m^{− 3}, even for metalworking fluid highly contaminated by bacteria (up to 2.4 × 10⁹ CFU mL^{− 1}). Inhalable dust varied between < 0.1 to 2.6 mg m^{− 3}, while air exchange rates were mostly below the standard (4 h^{− 1}) for this type of workplace, between 0.6 to 14.2 h^{− 1}. Only nine of 44 sites respected the suggested minimum value for air exchange rates. Fluid mist ranged from 0.02 to 0.89 mg m^{− 3}, which is below the threshold limit value (TLV) (ACGIH) of 5 mg m^{− 3}. Airborne endotoxin concentrations ranged from undetectable to 183 EU m^{− 3} (endotoxin units), showing no correlation with airborne microorganisms or inhalable dust. Most workstations respected the suggested minimum values for fluid mist and showed low concentrations of airborne endotoxin, culturable microorganisms and inhalable dust despite fluid contamination, even when air exchange rates were below the recommendations. Airborne Pseudomonas pseudoalcaligenes was recovered from many sites at significant concentrations. Health-associated risks following exposure to this microorganism should be further investigated.

Keywords:

• bioaerosol
• biodiversity
• endotoxin
• inhalable dust
• MWF
• oil mist

ACKNOWLEDGMENTS

Caroline Duchaine acknowledges Canadian Institutes of Health Research (CIHR)/Institut de recherche Robert-Sauvé en Santé et en sécurité du travail (IRSST) and Junior Fonds de la recherche en santé du Québec (FRSQ) scholarships. She is a member of the Health Respiratory Network of FRSQ and acknowledges a Canadian Centre for Health and Safety in Agriculture Time release support. This project was funded by IRSST. Yan Gilbert was a Quebec Respiratory Health training fellow, sponsored by the Institute of Circulatory and Respiratory Health of CIHR and the Health Respiratory Network of the FRSQ. We are grateful to Natasha Just for her review of the article.