Bacterial contamination of preserved and non-preserved metal working fluids.

Metal working fluids (MWFs) are important facilities for certain industrial processes. Besides their advantage concerning the effective technical applicability it is disadvantageous that they are excellent culture media for bacterial and fungal growth and may therefore act as an infectious source for employees getting in contact with them. As a matter of prevention most of MWFs are nowadays treated with preservatives to eliminate the contamination of possible human pathogenic bacteria and fungi. Own investigations were concerned with the objectives of the actual and long-term study of the bacterial contamination of preserved and non-preserved MWFs from different MWF systems, the development of a standardized bacterial biotope in non-preserved MWFs and its efficacy to eliminate bacteria which caused infectious diseases in humans, the development of bacterial resistance against preservatives in preserved MWFs and the occurrence of infections and allergies in employees working with MWFs. Our results show: high numbers of different bacteria can be found in non-preserved as well as preserved MWFs; bacteria with a possible human pathogenic potential (category 2, TRBA 466) could almost exclusively be found in preserved MWFs. Those bacteria besides others were able to develop resistance against biocides and could therefore be detected in preserved MWFs for weeks and months; non-preserved MWFs develop stable bacterial biotopes which can be controlled by an artificial inoculation of bacteria. Those biotopes are able to eliminate bacteria which induce infectious diseases in humans; there are only very few data published concerning MWF caused infections or allergies. According to our results of a questionnaire 10% of employees getting in contact with MWFs, complain skin irritations/reactions. There was no difference working with preserved or non-preserved MWFs nor a clear cut correlation to the MWF contact. These data may motivate for more intensive epidemiological studies in this field. The results of our investigations point out that taking into consideration safe working conditions non-preserved MWFs even contaminated with a standardized combination of waterborne bacteria like Pseudomonas spec. up to 10(8) CFU/ml are an alternative to preserved MFWs.