Occupational Exposure to Formaldehyde from Metalworking Fluids Containing the Antimicrobial Agent Methylenebismorpholine

The objective of this study was to measure formaldehyde present in the atmosphere of a machine shop using a water-based emulsion metalworking fluid containing the formaldehyde-generating antimicrobial agent methylenebismorpholine. Measured formaldehyde values were compared to estimated atmospheric values calculated from vapor-liquid equilibrium (evaporative) and aerosol (mist) generation. Good correlation was observed between calculated and measured values of atmospheric formaldehyde exposure for metalworking operations using methylenebismorpholine. Further, atmospheric formaldehyde levels were several orders of magnitude below current occupational exposure limits (OEL). Introduction Formaldehyde condensates have been used as antimicrobials (commonly referred to as bactericides or biocides) in water-based metalworking fluids for many decades due to their effective control of microbial growth and reasonable cost. Over this time, there has been debate regarding exposure to formaldehyde liberated during use of this class of antimicrobials. In 2004, the International Agency for Research on Cancer (IARC) working group categorized formaldehyde as a Group I human carcinogen (IARC, 2006), a decision based largely on a recent epidemiology study (Hauptmann et al., 2004) (1) . It should be noted that incidences of nasopharyngeal cancer reported in the Hauptmann study were not associated with the metal machining industry. Re-analysis of this data by Marsh and Youk (2005) (2) showed that the Hauptman conclusions were confounded by anomalous findings for one of ten study sites, and an alternative causation was proposed (Marsh et al., 2007) (3) . In light of the uncertainty related to the carcinogenicity of occupational formaldehyde, it is prudent to understand the exposure profile of formaldehyde in metalworking shops using formaldehyde condensate antimicrobial agents. Data related to exposure to atmospheric formaldehyde in the metalworking industry is available in the literature. Cohen (1995) (4) reported formaldehyde exposure levels resulting from the use of hexahydrotriazine in metalworking fluids typically did not exceed 0.1ppm (550 air samples). Reliable occupational formaldehyde exposure studies are difficult to conduct and continual monitoring of a machining facility can be quite expensive. Therefore, the development of a theoretical model to predict atmospheric formaldehyde in metalworking operations has significant value. The proposed model takes into consideration formaldehyde exposure from three possible sources: 1) background exposure from sources extraneous to the antimicrobial agent in the metalworking fluid (e.g., formaldehyde in outdoor air, released from other materials in a production facility such as plywood and insulation materials, as well as facility operations such as welding processes or fork lifts) (Ross et al., 2004) (5) , 2) volatilization of unbound formaldehyde from the metalworking fluid sumps or machining streams, and 3) formaldehyde liberated from methylenebismorpholine in the aerosols generated during the machining process. Each of these sources has been examined. Materials, Methods and Conditions All field data were collected at one site, located in Europe. Atmospheric sampling of formaldehyde was conducted over a three-day period during the day shift. This study was observational in nature. Worksite air samples were taken in the proximity (within 2 meters) of three metalworking machines, two of which utilized methylenebismorpholine as the machining fluid antimicrobial agent in semi-synthetic (waterbased) type coolants. The third machine used cutting oil (neat) that contained no antimicrobial agent of any type, and the formaldehyde data collected in the proximity of this machine was considered operation control. Two other background samples were collected approximately 25 meters from the nearest machining activity and several meters from a cordoned vending area. Table I summarizes the fluids used and their properties. Table I Fluids Used and their Properties Parameter Machine# 1 Machine# 2 Fluid type Low oil semi-synthetic Low oil semi-synthetic Sump size 3000 liters 1000 liters Fluid concentration 4.7-5.5% 5.5-7.6 pH 9.1-9.2 9.1-9.3