Water-miscible metalworking fluids (MWFs) become colonised by bacteria living in the environment if not maintained properly. The growth of bacteria is often accompanied by a decline in their nutrients and subsequent death leading to the release of toxins (e.g., endotoxin) from some types of bacteria. These toxins are potent hazards causing inflammation within the airways at concentrations as low as nanograms per cubic metre of air.
The risks to respiratory health from exposure to bacterial endotoxins are well established and have been subject to numerous reviews of the evidence. Inhalation of endotoxin has been linked with acute and chronic health effects caused by an inflammatory response within the airways. A recent report published by the Health and Safety Executive (HSE) gives an account of research undertaken to:
- review the evidence used to develop the health based recommended occupational exposure limit (HBROEL) for endotoxin of 90 endotoxin units per cubic metre (EU/m3) over an 8-hour period proposed by the Health Council for the Netherlands (DECOS); and to assess its relevance as a ‘benchmark’ to assess risks to respiratory health caused by endotoxin in metal working fluid mists;
- assess whether the published evidence on endotoxin concentration in metal working fluids provides sufficient evidence that concentrations in mist are sufficient to cause harm to human health.
The research concluded that there was a large discrepancy between concentrations of endotoxin and viable bacteria in mist compared to the concentrations in bulk fluid with airborne endotoxin levels generally falling close to or beneath the DECOS recommended level , whilst sump levels generally exceeded these by 100 to 1000 fold. Levels of viable bacteria captured in air were low compared to the levels in the sumps.
The researchers consider that further research is required to determine whether the discrepancy between bulk endotoxin and airborne levels is real or whether this is due to the impact of sampling or analytical methodology. Research Report RR1043 ‘Endotoxin in metalworking fluid (MWF) mist’ can be accessed at http://www.hse.gov.uk/research/rrhtm/rr1043.htm.
A further research report (RR1044: ‘Consultation on monitoring of water-miscible metalworking fluid (MWF) mists’), which examines metal working fluid (MWF) exposure limits and guidance set by other countries, summarises studies and investigations that examined water-miscible MWF mist as well as new techniques to monitor mist, is available at http://www.hse.gov.uk/research/rrhtm/rr1044.htm.
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