Microbial and endotoxin contamination of water-soluble metalworking fluids.

Unlabelled: The present study is a part of a larger project on assessment of exposure to biological agents and respiratory health effects among metal workers.

Objectives: The aim of this study was to evaluate the level of microbial contamination of metalworking coolants as a potential source of harmful biological agents in three different metal industry plants in Poland.

Material And Methods: Ten samples of coolants with a different state of wear, including four fresh fluids, were analyzed. Qualitative and quantitative analysis of bacteria and mould content was performed using standard analytical methods. Bacterial endotoxin concentration was determined by the kinetic, chromogenic version of the LAL test.

Results: The analysis showed the total bacterial counts ranging from 1.0x10(1) CFU/ml to 3.2x10(7) CFU/ml, 60% to 100% of which were Gram-negative bacteria capable of producing endotoxins. Among the highly contaminated coolants, one unused concentrate was also found. The predominant species of bacteria was Shewanella putrefaciens present in 60% of the samples. As for moulds, the predominant species was Acremonium butyri. The average concentration of bacterial endotoxins was 773 EU/ml in the old coolants, and much lower in the fresh fluids 285 EU/ml. A correlation (r=0.66) was found between endotoxin concentration and the number of Gram-negative bacteria detected in the coolants.

Conclusion: Procedures should be developed for cleaning tanks during fluid replacement to minimize the risk of bacterial growth in the coolants and limit bioaerosol emission in workplace. Due to the affinity of microflora for the water phase, it is advisable to use effective biocides with appropriate partition coefficient between the water phase and oil phase.