Microorganisms in metalworking fluids: current issues in research and management

Microbial Community Establishment, Succession, and Temporal Dynamics in an Industrial Semi-Synthetic Metalworking Fluid Operation: A 50-Week Real-Time Tracking

Microorganisms colonizing modern water-based metalworking fluids (MWFs) have been implicated in various occupational respiratory health hazards to machinists. An understanding of the exposure risks from specific microbial groups/genera/species (pathogenic or allergenic) and their endotoxins and the need for strategies for effective, timely fluid management warrant real-time extended tracking of the establishment of microbial diversity and the prevailing fluid-related factors. In the current study, the microbial community composition, succession, and dynamics of a freshly recharged industrial semi-synthetic MWF operation was tracked in real-time over a period of 50 weeks, using a combination of microbiological and molecular approaches. Substantial initial bacterial count (both viable and non-viable) even in the freshly recharged MWF pointed to the inefficiency of the dumping, cleaning, and recharge (DCR) process. Subsequent temporal analysis using optimized targeted genus/group-specific qPCR confirmed the presence of Pseudomonads, Enterics, Legionellae, Mycobacteria (M. immunogenum), Actinomycetes, and Fungi. In contrast, selective culturing using commercial culture media yielded non-specific isolates and collectively revealed Gram-negative (13 genera representing 19 isolates) and Gram-positive (2 genera representing 6 isolates) bacteria and fungi but not mycobacteria. Citrobacter sp. and Bacillus cereus represented the most frequent Gram-negative and Gram-positive isolates, respectively, across different media and Nectria haematococca isolation as the first evidence of this fungal pathogen colonizing semi-synthetic MWF. Unbiased PCR-DGGE analysis revealed a more diverse whole community composition revealing 22 bacterial phylotypes and their succession. Surges in the endotoxin level coincided with the spikes in Gram-negative bacterial population and biocide additions. Taken together, the results showed that semi-synthetic MWF is conducive for the growth of a highly diverse microbial community including potential bacterial and fungal pathogens, the current DCR practices are inefficient in combating microbial reestablishment, and the practice of periodic biocide additions facilitates the build-up of endotoxins and non-viable bacterial population.

Sustainable utilization of the vegetable oil manufacturing waste product in the formulation of eco-friendly emulsifiable cutting fluids

The conventional Metal cutting fluids (MCFs) used are mineral-based petroleum oils that perform well but are toxic and difficult to dispose of; therefore, these are hazardous to human health as well as the environment. This issue can be solved by using natural vegetable oil-based MCF, which are readily available, environment and human-friendly, and renewable. Therefore, we synthesized various types of emulsifiers (anionic, and nonionic with different ethylene oxide units as well as mono and gemini cationic surfactants as corrosion inhibitors and biocides) based on recycled vegetable oil (RO) from spent bleaching earth (SBE), and elucidated their chemical structures by different spectroscopic techniques. The individually synthesized emulsifiers (anionic, and nonionic with different ethylene oxide units) at different ratios (8-15 by wt.%) and mixed emulsifiers (anionic/nonionic, nonionic/nonionic with different degrees of ethylene oxide) at different ratios (8-12 by wt.%) were utilized as additives in the preparation of different vegetable residual oil-based MCF formulations. The mixed emulsifiers at different ratios of nonionic/nonionic with hydrophilic-lipophilic balance (HLB) value 10 (Formulas I, II, III, and IV), and anionic/nonionic (Formula V, and VI) exhibited stable emulsions compared to individual emulsifiers. Formulas (I and VI) displayed good protection effectiveness in corrosion tests. Formula VI had better wettability (25.22 on CS, 23.68 on Al, and 22.28 on WC) and a smaller particle size (63.97 nm). Tribological properties of Formula VI were also performed. The results exhibit that Formula VI is consistent with the commercial sample. As a result, this study contributed to the resolution of one of the industry's problems.

Monitoring biofilm growth and dispersal in real-time with impedance biosensors

Microbial biofilm contamination is a widespread problem that requires precise and prompt detection techniques to effectively control its growth. Microfabricated electrochemical impedance spectroscopy (EIS) biosensors offer promise as a tool for early biofilm detection and monitoring of elimination. This study utilized a custom flow cell system with integrated sensors to make real-time impedance measurements of biofilm growth under flow conditions, which were correlated with confocal laser scanning microscopy (CLSM) imaging. Biofilm growth on EIS biosensors in basic aqueous growth media (tryptic soy broth, TSB) and an oil-water emulsion (metalworking fluid, MWF) attenuated in a sigmoidal decay pattern, which lead to an ∼22-25% decrease in impedance after 24 Hrs. Subsequent treatment of established biofilms increased the impedance by ∼14% and ∼41% in TSB and MWF, respectively. In the presence of furanone C-30, a quorum-sensing inhibitor (QSI), impedance remained unchanged from the initial time point for 18 Hrs in TSB and 72 Hrs in MWF. Biofilm changes enumerated from CLSM imaging corroborated impedance measurements, with treatment significantly reducing biofilm. Overall, these results support the application of microfabricated EIS biosensors for evaluating the growth and dispersal of biofilm in situ and demonstrate potential for use in industrial settings.

ONE-SENTENCE SUMMARY

This study demonstrates the use of microfabricated electrochemical impedance spectroscopy (EIS) biosensors for real-time monitoring and treatment evaluation of biofilm growth, offering valuable insights for biofilm control in industrial settings.

Machine operator's lung outbreak due to Eikenella corrodens

BACKGROUND

Outbreaks of hypersensitivity pneumonitis (HP) are not uncommon in workplaces where metalworking fluids (MWFs) are used. The recirculation of MWFs leads to microbiological contamination, which is responsible for outbreaks. Most outbreak reports come from USA and the UK; however, no similar reports have been published from Central Europe.

AIMS

To describe an outbreak of MWF-associated HP in workers from a compressor assembly manufacturing facility in Slovak Republic and to identify the potential antigens responsible for the outbreak.

METHODS

We investigated the history of worker's symptoms, physical examinations, lung function tests, radiographic scans and lung biopsies. The MWF samples were analysed for different strains of bacteria and fungi. Antigen extracts were produced from the microorganisms isolated from MWFs, and positive precipitin reactions were evaluated.

RESULTS

MWF-associated HP was diagnosed in 21 men and 6 women. All workers had work-related dyspnoea and cough with abnormal pulmonary diffusing capacity. Twenty-four cases had evidence of interstitial lung disease. Four cases were classified as having fibrotic HP. Nineteen microbial isolates (12 bacteria and 7 fungi) were cultured from the MWFs. Twenty-five cases had a positive response to at least one isolate. Eikenella corrodens and Bacillus subtilis were the most frequently reacting antigens (in 15 and 12 workers, respectively).

CONCLUSIONS

Despite decreasing reports of MWF-associated HP outbreaks over the past several decades, we describe one of the largest outbreaks in Europe. While the bacterium E. corrodens was found in the MWF samples, its relationship to the disease should be further investigated.

Ways to improve biocides for metalworking fluid

Metalworking fluids (MWF) are mainly emulsions of oil in water containing additives such as corrosion inhibitors, emulsifiers, defoamers, and biocides. Microbial contamination of MWF is almost systematic, and some of their constituents serve as nutrients for contaminating microorganisms. Biocides for MWF are protection products used to counter microbial contaminations and growth. Ideally, a biocide for MWF should have the following non-exhaustive criteria: have a broad-spectrum activity, be usable at low concentrations, be compatible with the formulation and the physical-chemical properties of MWF, be stable over time, retain its effectiveness in the presence of soiling, have no corrosive action on metals, present no danger to humans and the environment, be inexpensive. The future lies in the development of new molecules with biocidal activity corresponding to these ideal specifications, but in the meantime, it is possible to improve the performance of existing molecules currently on the market. Different strategies for potentiation of the activity of existing biocides are possible. The compatibility of the potentiation strategies with their use in metal working fluids is discussed.

Risk Assessment for Metalworking Fluids and Respiratory Outcomes

Background

Metalworking fluids (MWFs) are mixtures with inhalation exposures as mists, dusts, and vapors, and dermal exposure in the dispersed and bulk liquid phase. A quantitative risk assessment was performed for exposure to MWF and respiratory disease.

Methods

Risks associated with MWF were derived from published studies and NIOSH Health Hazard Evaluations, and lifetime risks were calculated. The outcomes analyzed included adult onset asthma, hypersensitivity pneumonitis, pulmonary function impairment, and reported symptoms. Incidence rates were compiled or estimated, and annual proportional loss of respiratory capacity was derived from cross-sectional assessments.

Results

A strong healthy worker survivor effect was present. New-onset asthma and hypersensitivity pneumonitis, at 0.1 mg/m³ MWF under continuous outbreak conditions, had a lifetime risk of 45%; if the associated microbiological conditions occur with only 5% prevalence, then the lifetime risk would be about 3%. At 0.1 mg/m³, the estimate of excess lifetime risk of attributable pulmonary impairment was 0.25%, which may have been underestimated by a factor of 5 or more by a strong healthy worker survivor effect. The symptom prevalence associated with respiratory impairment at 0.1 mg/m³ MWF was estimated to be 5% (published studies) and 21% (Health Hazard Evaluations).

Conclusion

Significant risks of impairment and chronic disease occurred at 0.1 mg/m³ for MWFs in use mostly before 2000. Evolving MWFs contain new ingredients with uncharacterized long-term hazards.

Quorum sensing inhibition as a promising method to control biofilm growth in metalworking fluids

Microbial contamination in metalworking systems is a critical problem. This study determined the microbial communities in metalworking fluids (MWFs) from two machining shops and investigated the effect of quorum sensing inhibition (QSI) on biofilm growth. In both operations, biofilm-associated and planktonic microbial communities were dominated by Pseudomonadales (60.2-99.7%). Rapid recolonization was observed even after dumping spent MWFs and meticulous cleaning. Using Pseudomonas aeruginosa PAO1 as a model biofilm organism, patulin (40 µM) and furanone C-30 (75 µM) were identified as effective QSI agents. Both agents had a substantially higher efficacy compared to α-amylase (extracellular polymeric substance degrading enzyme) and reduced biofilm formation by 63% and 76%, respectively, in MWF when compared to untreated controls. Reduced production of putatively identified homoserine lactones and quinoline in MWF treated with QS inhibitors support the effect of QSI on biofilm formation. The results highlight the effectiveness of QSI as a potential strategy to eradicate biofilms in MWFs.

Organometal-catalyzed synthesis of high molecular weight poly-(l-lactic acid) with a covalently attached imidazolium salt: performance-enhanced reduced graphene oxide–PLLA biomaterials

Herein, we report on the synthesis of imidazolium salt end-functionalized PLLA (PLLA-IS) and its application in the preparation of reduced graphene oxide–PLLA composites.

Optical Spectroscopy for Analysis and Monitoring of Metalworking Fluids

For various industrial manufacturing processes, water-based metalworking fluids (MWFs) are of high relevance due to their cooling and lubricating ability. They commonly form oil-in-water emulsions or solutions and hence their composition and stability is crucial for their performance in the metalworking process. To ensure a long service life of the MWF, intense monitoring is obligatory. However, examination techniques which display comprehensive and precise information about the actual state of the cooling lubricant in use are currently not available. The present study aims at testing the suitability of spectroscopic methods in terms of Fourier transform infrared, Raman, and laser-induced fluorescence spectroscopy for analyzing and monitoring MWFs. It is shown that all three techniques are capable of determining the initial composition, i.e., the ratio of water and concentrate. Fourier transform infrared provides the best performance regarding monitoring the state of the fluid over an extended period of time. The spectral signatures show distinct changes during a five-month service life in a technical environment.

Assessment of bacteria and archaea in metalworking fluids using massive parallel 16S rRNA gene tag sequencing

Determination of the bacterial diversity in industry-based liquid in-use water-miscible metalworking fluid (MWF) samples was targeted by massive parallel multiplex DNA sequencing, either directly or upon pretreatment with propidium monoazide (PMA) that allows differentiation between intact and physically damaged cells. As MWFs provide a suitable basis of life for micro-organisms, the majority is preserved by biocides. 'Bio-concept' fluids on the other hand are bactericide free, which intentionally leads to substantial bacterial populations. Samples from both fluid types were chosen: A median of 51 operational taxonomic units at genera level (OTUs) were detected per sample, but only 13 were present at or above 1·0% of the total population in any PMA-treated sample analysed. As both fluid types were mainly dominated by Pseudomonas spp., we resolved this genus on the species level and found the Pseudomonas oleovorans/pseudoalcaligenes group to predominate. We also looked for archaea and detected Methanobrevibacter spp., albeit in <3% of all samples analysed.

SIGNIFICANCE AND IMPACT OF THE STUDY

Water-miscible metalworking fluids provide a suitable base of life for micro-organisms, mainly bacteria and fungi. Earlier publications suggested that the diversity is rather low, but these studies were largely based on heterotrophic plate counts. This might have resulted in underestimation of population density and microbial diversity as some organisms might just refuse to grow. This study used high-throughput sequencing in the absence and presence of propidium monoazide to explore bacterial and archaeal presence in metalworking fluids. We established that diversity is low and bacterial populations are dominated by the genus Pseudomonas spp.

Flow Cytometry Is a Powerful Tool for Assessment of the Viability of Fungal Conidia in Metalworking Fluids

Fungal contamination of metalworking fluids (MWF) is a dual problem in automated processing plants because resulting fungal biofilms obstruct cutting, drilling, and polishing machines. Moreover, some fungal species of MWF comprise pathogens such as Fusarium solani Therefore, the development of an accurate analytical tool to evaluate conidial viability in MWF is important. We developed a flow cytometric method to measure fungal viability in MWF using F. solani as the model organism. To validate this method, viable and dead conidia were mixed in several proportions and flow was cytometrically analyzed. Subsequently, we assessed the fungicidal activity of two commercial MWF using flow cytometry (FCM) and compared it with microscopic analyses and plating experiments. We evaluated the fungal growth in both MWF after 7 days using quantitative PCR (qPCR) to assess the predictive value of FCM. Our results showed that FCM distinguishes live from dead conidia as early as 5 h after exposure to MWF, whereas the microscopic germination approach detected conidial viability much later and less accurately. At 24 h, microscopic analyses of germinating conidia and live/dead analyses by FCM correlated well, although the former consistently underestimated the proportion of viable conidia. In addition, the reproducibility and sensitivity of the flow cytometric method were high and allowed assessment of the fungicidal properties of two commercial MWF. Importantly, the obtained flow cytometric results on viability of F. solani conidia at both early time points (5 h and 24 h) correlated well with fungal biomass measurements assessed via a qPCR methodology 7 days after the start of the experiment.IMPORTANCE This result shows the predictive power of flow cytometry (FCM) in assessing the fungicidal capacity of MWF formulations. It also implies that FCM can be implemented as a rapid detection tool to estimate the viable fungal load in an industrial processing matrix (MWF).

Hypersensitivity pneumonitis: a complex lung disease

Hypersensitivity pneumonitis (HP), also called extrinsic allergic alveolitis, is a respiratory syndrome involving the lung parenchyma and specifically the alveoli, terminal bronchioli, and alveolar interstitium, due to a delayed allergic reaction. Such reaction is secondary to a repeated and prolonged inhalation of different types of organic dusts or other substances to which the patient is sensitized and hyper responsive, primarily consisting of organic dusts of animal or vegetable origin, more rarely from chemicals. The prevalence of HP is difficult to evaluate because of uncertainties in detection and misdiagnosis and lacking of widely accepted diagnostic criteria, and varies considerably depending on disease definition, diagnostic methods, exposure modalities, geographical conditions, agricultural and industrial practices, and host risk factors. HP can be caused by multiple agents that are present in work places and in the home, such as microbes, animal and plant proteins, organic and inorganic chemicals. The number of environment, settings and causative agents is increasing over time. From the clinical point of view HP can be divided in acute/subacute and chronic, depending on the intensity and frequency of exposure to causative antigens. The mainstay in managing HP is the avoidance of the causative antigen, though the complete removal is not always possible due to the difficulties to identify the agent or because its avoidance may lead to major changes in life style or occupational settings. HP is a complex syndrome that needs urgently for more stringent and selective diagnostic criteria and validation, including wider panels of IgG, and a closer collaboration with occupational physicians, as part of a multidisciplinary expertise.

Investigating a persistent odor at an aircraft seat manufacturer

An aircraft seat manufacturing company requested a NIOSH health hazard evaluation to help identify a strong odor that had persisted throughout the facility for over a year. Employees reported experiencing health effects thought to be related to the odor. We collected and analyzed area air samples for volatile organic compounds, endotoxin, bacterial and fungal metagenome, and metalworking fluid aerosol. Bulk metalworking fluid samples were analyzed for endotoxin, bacterial and fungal metagenome, and viable bacteria and fungus. We also evaluated the building ventilation systems and water diversion systems. Employees underwent confidential medical interviews about work practices, medical history, and health concerns. Based on our analyses, the odor was likely 2-methoxy-3,5-dimethylpyrazine. This pyrazine was found in air samples across the facility and originated from bacteria in the metalworking fluid. We did not identify bacteria known to produce the compound but bacteria from the same Proteobacteria order were found as well as bacteria from orders known to produce other pyrazines. Chemical and biological contaminants and odors could have contributed to health symptoms reported by employees, but it is likely that the symptoms were caused by several factors. We provided several recommendations to eliminate the odor including washing and disinfecting the metalworking machines and metalworking fluid recycling equipment, discarding all used metalworking fluid, instituting a metalworking fluid maintenance program at the site, and physically isolating the metalworking department from other departments.

Occupational hypersensitivity pneumonitis: an EAACI position paper

The aim of this document was to provide a critical review of the current knowledge on hypersensitivity pneumonitis caused by the occupational environment and to propose practical guidance for the diagnosis and management of this condition. Occupational hypersensitivity pneumonitis (OHP) is an immunologic lung disease resulting from lymphocytic and frequently granulomatous inflammation of the peripheral airways, alveoli, and surrounding interstitial tissue which develops as the result of a non-IgE-mediated allergic reaction to a variety of organic materials or low molecular weight agents that are present in the workplace. The offending agents can be classified into six broad categories that include bacteria, fungi, animal proteins, plant proteins, low molecular weight chemicals, and metals. The diagnosis of OHP requires a multidisciplinary approach and relies on a combination of diagnostic tests to ascertain the work relatedness of the disease. Both the clinical and the occupational history are keys to the diagnosis and often will lead to the initial suspicion. Diagnostic criteria adapted to OHP are proposed. The cornerstone of treatment is early removal from exposure to the eliciting antigen, although the disease may show an adverse outcome even after avoidance of exposure to the causal agent.

Occupational diseases in individuals exposed to metal working fluids

PURPOSE OF REVIEW

To examine the current occurrence of respiratory and skin disease in workers who do metal machining with metal working fluids (MWFs), a common work process in manufacturing.

RECENT FINDINGS

A summary of the 27 recognized outbreaks of respiratory disease in workers exposed to MWFs was published. New studies have identified irritative symptoms among workers with low-level exposures. There were review articles discussing the content, measurement and control of microbial agents in MWFs.

SUMMARY

The occurrence of work-related asthma and hypersensitivity pneumonitis appears to have diminished in the last 10 years. This is presumed to be secondary to lower air levels from the use of newer machining equipment, which are enclosed and have local ventilation as well as better control of microbial contaminants. However, clinicians need to be aware that at the minimum irritative symptoms of the upper respiratory tract are still being reported at these lower exposure levels and there remains the possibility of the development of asthma and hypersensitivity pneumonitis. Given the widespread use of MWFs in manufacturing facilities, clinicians need to consider the possibility that MWFs are the cause or are aggravating the respiratory and dermatologic conditions of their patients.

Skin absorption of six performance amines used in metalworking fluids

Every year, 10 million workers are exposed to metalworking fluids (MWFs) that may be toxic. There are four types of MWFs: neat oils and three water-based MWFs (soluble oil, semisynthetic and synthetic), which are diluted with water and whose composition varies according to the mineral oils ratio. MWFs also contain various additives. To determine the absorption of six amines used as corrosion inhibitors and biocides in MWFs, porcine skin flow-through diffusion cell experiments were conducted with hydrophilic ethanolamines (mono-, di- and triethanolamine, MEA, DEA and TEA respectively) and a mixture of lipophilic amines (dibutylethanolamine, dicyclohexylamine and diphenylamine). The six amines were dosed in four vehicles (water and three generic water-based MWF formulations) and analyzed using a scintillation counter or gas chromatography/mass spectrometry. These 24 h studies showed that dermal absorption significantly (P < 0.05) increased from water for the six amines (e.g. 1.15 ± 0.29% dose; DEA in water) compared to other formulations (e.g. 0.13 ± 0.01% dose; DEA in semisynthetic MWF) and absorption was greatest for dibutylethanolamine in all the formulations. The soluble oil formulation tended to increase the dermal absorption of the hydrophilic amines. The permeability coefficient was significantly higher (P < 0.05) with TEA relative to the other hydrophilic amines (e.g. 4.22 × 10(-4) ± 0.53 × 10(-4) cm h(-1) [TEA in synthetic MWF] vs. 1.23 × 10(-4) ± 0.10 × 10(-4) cm h(-1) [MEA in synthetic MWF]), except for MEA in soluble oil formulation. Future research will confirm these findings in an in vivo pig model along with dermatotoxicity studies. These results should help MWF industries choose safer additives for their formulations to protect the health of metalworkers.

Airway symptoms and biological markers in nasal lavage fluid in subjects exposed to metalworking fluids

BACKGROUNDS

Occurrence of airway irritation among industrial metal workers was investigated. The aims were to study the association between exposures from water-based metal working fluids (MWF) and the health outcome among the personnel, to assess potential effects on the proteome in nasal mucous membranes, and evaluate preventive actions.

METHODS

The prevalence of airway symptoms related to work were examined among 271 metalworkers exposed to MWF and 24 metal workers not exposed to MWF at the same factory. At the same time, air levels of potentially harmful substances (oil mist, morpholine, monoethanolamine, formaldehyde) generated from MWF was measured. Nasal lavage fluid was collected from 13 workers and 15 controls and protein profiles were determined by a proteomic approach.

RESULTS

Airway symptoms were reported in 39% of the workers exposed to MWF although the measured levels of MWF substances in the work place air were low. Highest prevalence was found among workers handling the MWF machines but also those working in the same hall were affected. Improvement of the ventilation to reduce MWF exposure lowered the prevalence of airway problems. Protein profiling showed significantly higher levels of S100-A9 and lower levels of SPLUNC1, cystatin SN, Ig J and β2-microglobulin among workers with airway symptoms.

CONCLUSIONS

This study confirms that upper airway symptoms among metal workers are a common problem and despite low levels of MWF-generated substances, effects on airway immune proteins are found. Further studies to clarify the role of specific MWF components in connection to airway inflammation and the identified biological markers are warranted.