Dermal permeation of biocides and aromatic chemicals in three generic formulations of metalworking fluids

Phosphorus Depletion as a Green Alternative to Biocides for Controlling Biodegradation of Metalworking Fluids

Metalworking fluids (MWFs) are used as lubricants and coolants in the manufacturing operations. Their biodeterioration, while in operation, is a widespread problem leading to poor performance and worker health issues. Adding biocides, though effective in reducing microbial growth, leads to the production of more recalcitrant wastewaters that are difficult to dispose or recycle on-site. Increasing environmental concerns have led to robust legislation for reducing/eliminating the use of toxic biocides in MWFs, stimulating a growing interest in the development/application of alternative biological preservation strategies. In this study, inducing nutrient imbalance was investigated for controlling microbial growth in MWFs. Phosphorus was immobilized employing insoluble La₂O₃ to form LaPO₄. Concentrations of La₂O₃ greater than 0.08%w (%w = weight percent) completely inhibited microbial growth (from 1.4 × 10⁷ to 0 CFU/mL) and hindered biodegradation. Raman spectroscopy suggested that La₂O₃ converted intracellular phosphorus into LaPO₄. The growth inhibition potentials of both 0.06%w La(NO₃)₃ and La₂O₃ were found to be superior to formaldehyde. The antimicrobial property of La₂O₃ (i.e., inhibition) was tenable by adding sufficient phosphate, acting as an on/off switch for controlling microbial growth in MWFs. This technology offers the potential to reduce/eliminate the use of biocides in MWFs, improves the feasibility of end-of-life biological treatment, and closes the water loop.

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.

Predicting skin permeability from complex chemical mixtures: incorporation of an expanded QSAR model

Quantitative structure-activity relationship (QSAR) models have been widely used to study the permeability of chemicals or solutes through skin. Among the various QSAR models, Abraham's linear free-energy relationship (LFER) model is often employed. However, when the experimental conditions are complex, it is not always appropriate to use Abraham's LFER model with a single set of regression coefficients. In this paper, we propose an expanded model in which one set of partial slopes is defined for each experimental condition, where conditions are defined according to solvent: water, synthetic oil, semi-synthetic oil, or soluble oil. This model not only accounts for experimental conditions but also improves the ability to conduct rigorous hypothesis testing. To more adequately evaluate the predictive power of the QSAR model, we modified the usual leave-one-out internal validation strategy to employ a leave-one-solute-out strategy and accordingly adjust the Q(2) LOO statistic. Skin permeability was shown to have the rank order: water > synthetic > semi-synthetic > soluble oil. In addition, fitted relationships between permeability and solute characteristics differ according to solvents. We demonstrated that the expanded model (r(2) = 0.70) improved both the model fit and the predictive power when compared with the simple model (r(2) = 0.21).

Selection of appropriate training and validation set chemicals for modelling dermal permeability by U-optimal design

Quantitative structure-activity relationship (QSAR) models are being used increasingly in skin permeation studies. The main idea of QSAR modelling is to quantify the relationship between biological activities and chemical properties, and thus to predict the activity of chemical solutes. As a key step, the selection of a representative and structurally diverse training set is critical to the prediction power of a QSAR model. Early QSAR models selected training sets in a subjective way and solutes in the training set were relatively homogenous. More recently, statistical methods such as D-optimal design or space-filling design have been applied but such methods are not always ideal. This paper describes a comprehensive procedure to select training sets from a large candidate set of 4534 solutes. A newly proposed 'Baynes' rule', which is a modification of Lipinski's 'rule of five', was used to screen out solutes that were not qualified for the study. U-optimality was used as the selection criterion. A principal component analysis showed that the selected training set was representative of the chemical space. Gas chromatograph amenability was verified. A model built using the training set was shown to have greater predictive power than a model built using a previous dataset [1].

In vitro dermal penetration of 4-chloro-3-methylphenol from commercial metal working fluid and aqueous vehicles

The biocide 4-chloro-3-methylphenol (CMP, CAS number 59-50-7) is a common additive to metal-working fluids (MWF) and building materials. National Institute for Occupational Safety and Health (NIOSH) researchers previously identified and quantified CMP in a commercial water-soluble MWF, TRIM VX, and demonstrated irritancy and sensitization potential of both TRIM VX and CMP alone after dermal exposure in a murine model. In the current study, the in vitro human epidermal permeability of CMP contained in a working dilution of TRIM VX (20% in water) was evaluated and, for comparison, permeability from an aqueous buffer was also assessed. CMP penetration was also measured from transient exposures to 20% TRIM VX. To address differences in penetration rates from 20% TRIM VX and from buffer, the role of thermodynamic activity of CMP in the 2 vehicles on dermal penetration was investigated. Static headspace gas chromatography was used to measure vapor pressures and infer fractional thermodynamic activities of CMP in the mixtures. Permeability coefficient (k(p)) of CMP from 20% TRIM VX was (4.1 +/- 0.8) x 10(-3) cm/h (mean +/- SD, n = 5), and CMP was found at a concentration of 3555 +/- 191 microg/ml in this donor. In contrast, k(p) was 0.18 +/- 0.03 cm/h (n = 5) at a similar concentration (3919 +/- 240) from buffer donor. Steady-state fluxes from 20% TRIM VX and buffer were comparable when expressed as functions of thermodynamic activity of CMP in the donor, rather than as concentrations. Transient (20 or 40 min) exposures of epidermal membranes to 20% TRIM VX (n = 4) resulted in total penetration of 4.2 +/- 1.2 and 7.3 +/- 0.8 microg/cm(2), respectively; these amounts are comparable to amounts predicted using a simple algebraic equation.