Evaluation on the reliability of the permeability coefficient (Kp) to assess the percutaneous penetration property of chemicals on the basis of Flynn's dataset.

PURPOSE: The permeability coefficient (Kp) is often used for prediction of the dermal penetration of chemicals. Mathematical models have mostly been derived on Kp data basis. However, confusing Kp values are reported, questioning the general reliability of this parameter. In this study, we tested the plausibility of Kp values expressing the dermal penetration velocity (cm h-1) of chemicals on a larger dataset from literature. METHODS: Kp was applied for the calculation of the time for penetration through skin membranes of defined thickness (tCrossSkin). Kp values were obtained from Flynn's dataset (1990), containing data determined mostly under similar experimental conditions using diffusion cells. Further skin penetration parameters, e.g., times at which the chemicals were firstly measured in the receptor phase, lag times, steady-state times, and exposure duration, where available, were related to Kp values. The data congruence was tested comparing Kp values from Flynn's dataset with those reported in the EDETOX database. Variables, which could bias the results, such as different experimental protocols and research groups were also considered. RESULTS: Kp data for 94 chemicals matched the inclusion criteria were evaluated. According to the Kp values, 21 (22%) compounds would require longer than 100 h, and 20 (21%) further compounds longer than 10 h of exposure to penetrate skin membranes of ~ 0.01-2.5 mm thickness. Obviously, erroneous Kp were found in studies of almost all research groups in Flynn's database, indicating that neither the observer nor the experimental conditions alone biased the values. CONCLUSIONS: Our evaluation demonstrates high implausibility of Kp values to represent the dermal penetration velocity and supports general invalidity of the parameter for implementation in studies using skin membranes. The Kp should not be used to characterize the percutaneous penetration of chemicals or in risk assessment without verification.

Dermal absorption and skin damage following hydrofluoric acid exposure in an ex vivo human skin model.

The wide industrial use of hydrofluoric acid (HF) poses a high risk for accidental dermal exposure. Despite local and systemic hazards associated with HF, information on percutaneous penetration and tissue damage is rare. In the present ex vivo study, the dermal absorption of HF (detected in terms of fluoride ions) was quantified and the skin damaging potential as a function of concentration and exposure duration was assessed. Percutaneous penetration of HF (c=5, 30, and 50%) at 3 exposure durations (3, 5, and 10 min) was investigated in a static diffusion cell model using freshly excised human skin. Alterations of skin were histologically evaluated. HF rapidly penetrated through skin under formation of a considerable intradermal reservoir (∼ 13-67% of total absorbed fluoride). Histologically, epidermal alterations were detected already after exposure to 5% HF for 3 min. The degree of skin damage increased with rising concentration and exposure duration leading to coagulation necrosis. For HF concentrations of ≥ 30%, skin damage progressed into deeper skin layers. Topically applied HF concentration was the principal parameter determining HF induced skin effects. The intradermal HF retention capacity associated with progression and prolongation of HF induced skin effects must be considered in the review of skin decontamination procedures.

Influence of artificial sebum on the dermal absorption of chemicals in excised human skin: A proof-of-concept study.

In an initial diffusion cell study, the influence of artificial sebum on dermal penetration and intradermal reservoir of ethanol and toluene was investigated in comparison with the effects of a skin cream (o/w- and w/o-emulsion) and untreated (control) skin. Human skin was exposed to neat ethanol and toluene for 4h, respectively. During the experiments, the penetration of the compounds was assessed in the receptor fluid. The amounts of the test compounds in the skin were determined at the end of exposure. In the control experiments, 42% of the total resorbed ethanol amounts were found in the intradermal reservoir after 4h, whereas 82% of the toluene amounts were found in the skin compartments. The treatment with artificial sebum showed no significant differences in dermal absorption of both test compounds compared to control skin. In contrast, the treatment with skin cream increased the percutaneous penetration (p<0.001) and the intradermal reservoir of ethanol ~2-fold but not of toluene. In all exposure scenarios, a relevant intradermal reservoir was formed. The results indicate that sebum does not influence the percutaneous penetration and the intradermal reservoir of epidermally applied chemicals, whereas the application of skin creams may increase the dermal penetration of the compounds.

Evaluation of the effect of skin cleaning procedures on the dermal absorption of chemicals.

To reduce the internal exposure, skin decontamination is the most important measure after dermal contact to chemicals. However, no harmonized skin cleaning procedure for experimental ex vivo studies is published. In our study, the impact of two skin cleaning techniques on dermal penetration kinetics and intradermal deposition of 1,4-dioxane, 5% hydrofluoric acid (HF, detected in terms of fluoride ions), and anisole was evaluated to develop a reliable ex vivo skin cleaning method using the diffusion cell technique. After exposure (duration: 3 min (HF); 1h (1,4-dioxane and anisole)) of excised human skin (n=6-8) decontamination was performed by (I) water-soaked cotton swabs or (II) direct application of water on the exposure area. The effect of skin cleaning was investigated by analysing the concentration time course of chemicals in the receptor fluid of diffusion cells and by determining the deposition in skin. Both skin cleaning procedures reduced the amount of fluoride in the skin compartments (p<0.05) and the receptor fluid (p<0.1). However, the effect of cleaning on the dermal absorption of the organic test compounds was not significant. The results demonstrate the suitability of the applied ex vivo protocol for investigating the effectiveness of skin cleaning measures following dermal exposure. In addition, data reveal that the determination of test compounds in both, skin compartments as well as receptor fluid as equivalent for the systemic uptake needs to be considered in studies assessing the effectiveness of skin decontamination procedures.

Percutaneous absorption of aromatic amines and the risk assessment resulting from the dermal pathway.

Aromatic amines (AA) are compounds of different carcinogenic potency causing occupational bladder cancer. The percutaneous absorption of AA is mostly appraised to be high. Many AA are, therefore, assigned with skin notations. However, for the assessment of the dermal exposure route only little data are available. Additionally, in many studies the skin penetration data for AA are provided as absorbed percentage of applied dose or permeability coefficients, which are less useful in risk assessment. In this overview, the toxicological relevance of percutaneous absorption of AA was evaluated and a percutaneous penetration ranking for some AA is proposed. A continuous skin exposure of hands to AA for a few minutes can exceed the inhalative exposure over 8 hours at occupational threshold limit values in the workplace air. The health risk resulting from the percutaneous absorption of AA can be considerable. Also the dermal exposure to azo dyes, which can be metabolized to AA, should be considered with caution.

Studies on percutaneous penetration of chemicals - Impact of storage conditions for excised human skin.

According to international guidelines skin penetration experiments can be carried out using freshly excised or frozen stored skin. However, this recommendation refers to data obtained in experiments with human cadaver skin. In our study, the percutaneous penetration of the occupationally relevant chemicals anisole, cyclohexanone and 1,4-dioxane was investigated for freshly excised as well as for 4 and 30 days at -20°C stored human skin using the diffusion cell technique. As indicator for the impairment of skin barrier by freezing cholesterol dissolution was determined in the solvents in exposure chambers of diffusion cells. Considering the percutaneously penetrated amounts, the following ranking was determined: 1,4-dioxane>anisole>cyclohexanone (decline to a factor of 5.9). The differences of fluxes between freshly excised and frozen stored skin (4 and 30 days) were not significant (p>0.05). Cholesterol dissolved from the skin indicates no significant differences between freshly excised and frozen stored skin. This study shows that freezing of human skin for up to 30 days does not alter the skin barrier function and the permeability of chemicals.

Potential of the octanol-water partition coefficient (logP) to predict the dermal penetration behaviour of amphiphilic compounds in aqueous solutions.

Aqueous amphiphilic compounds may exhibit enhanced skin penetration compared with neat compounds. Conventional models do not predict this percutaneous penetration behaviour. We investigated the potential of the octanol-water partition coefficient (logP) to predict dermal fluxes for eight compounds applied neat and as 50% aqueous solutions in diffusion cell experiments using human skin. Data for seven other compounds were accessed from literature. In total, seven glycol ethers, three alcohols, two glycols, and three other chemicals were considered. Of these 15 compounds, 10 penetrated faster through the skin as aqueous solutions than as neat compounds. The other five compounds exhibited larger fluxes as neat applications. For 13 of the 15 compounds, a consistent relationship was identified between the percutaneous penetration behaviour and the logP. Compared with the neat applications, positive logP were associated with larger fluxes for eight of the diluted compounds, and negative logP were associated with smaller fluxes for five of the diluted compounds. Our study demonstrates that decreases or enhancements in dermal penetration upon aqueous dilution can be predicted for many compounds from the sign of logP (i.e., positive or negative). This approach may be suitable as a first approximation in risk assessments of dermal exposure.

Comparison of experimentally determined and mathematically predicted percutaneous penetration rates of chemicals.

The aim of the study was to evaluate the predictive potential of three different mathematical models for the percutaneous penetration of industrial solvents with respect to our experimental data. Percutaneous penetration rates (fluxes) from diffusion cell experiments of 11 chemicals were compared with fluxes predicted by mathematical models. The chemicals considered were three glycol ethers (2-butoxyethanol, diethylene glycol monobutyl ether and 1-ethoxy-2-propanol), three alcohols (ethanol, isopropanol and methanol), two glycols (ethylene glycol and 1,2-propanediol), one aromatic hydrocarbon (toluene) and two aromatic amines (aniline and o-toluidine). For the mathematical prediction of fluxes, models described by Fiserova-Bergerova et al. (Am J Ind Med 17:617-635 1990), Guy and Potts (Am J Ind Med 23:711-719 1993) and Wilschut et al. (Chemosphere 30:1275-1296 1995) were used. The molecular weights, octanol-water partition coefficients (LogP) and water solubilities of the compounds were obtained from a database for modelling. The fit between the mathematically predicted and experimentally determined fluxes was poor (R(2) = 0.04-0.29; linear regression). The flux differences ranged up to a factor of 412. For 4 compounds, the Guy and Potts model showed a closer fit with the experimental flux than the other models. The Wilschut et al. model showed a lower flux difference for 4 compounds as compared to experimental data than the models of Fiserova-Bergerova et al. and Guy and Potts. The Fiserova-Bergerova et al. model showed for 3 compounds a lower flux difference to experimental data than the other models. This study demonstrates large differences between mathematically predicted and experimentally determined fluxes. The percutaneous penetration as determined in diffusion cell experiments may be considerably overestimated as well as underestimated by mathematical models. Although the number of compounds in our comparison study is small, the results point out that none of the mathematical model has significant advantages.

Enhancement of percutaneous penetration of aniline and o-toluidine in vitro using skin barrier creams.

Aniline (ANI) and the human carcinogen o-toluidine (OT) are released at the workplace during the production and processing of rubber. Recently, we showed in rubber industry workers that a frequent use of skin barrier creams (SBC) increased the internal exposure of ANI and OT. In the present study, diffusion cells were used to investigate the effects of two SBC and one skin care cream (SCC) on percutaneous penetration of neat ANI and OT as well as of OT from a mixture with a workplace specific lubricant. The experiments were carried out with untreated and with skin creams treated human skin. A considerable percutaneous penetration enhancement of test compounds was observed for treated skin compared with untreated skin; the highest enhancement (mean factors 6.2-12.3) was found for SBC (based on oil in water emulsion) treated skin. The lowest penetration enhancement showed SCC treated skin (mean factors 4.2-9.7). The in vitro data support our findings in workers that the percutaneous absorption of aromatic amines significantly increases in presence of skin creams. The efficacy of skin creams to protect the percutaneous penetration of aromatic amines is not confirmed by our own experiments.

Commentary on "Penetration of benzene, toluene and xylenes contained in gasolines through human abdominal skin in vitro".

In this commentary we refer to the new data recently published by Adami et al. [Adami, G., Larese, F., Venier, M., Barbieri, P., Lo Coco, F., Reisenhofer, E., 2006. Penetration of benzene, toluene and xylenes contained in gasolines through human abdominal skin in vitro. Toxicol. In Vitro 20, 1321-1330], which we acknowledge as a reliable basis for the retrospective assessment of percutaneous benzene absorption at the workplace. The data from Adami et al. (2006) are supported by the literature and by a German approach for calculating the contribution of the dermal uptake of benzene to the total body burden. This knowledge is important for the judgment of leukaemia suspected to be an occupational disease.

Investigations on permeation of mitomycin C through double layers of natural rubber gloves.

Treating peritoneal carcinomatosis by the aggressive cytoreductive surgery with the hyperthermic intraoperative intraperitoneal chemotherapy (HIPEC) surgeons expose their gloved hands for up to 90 min to a peritoneal dialysis solution (PDS) containing mitomycin C (MMC). We investigated the permeation of MMC through the material of three different natural rubber gloves under conditions similar to the in-use during HIPEC as well as under worst-case exposure scenario. Two different methods, a two-chamber diffusion cell and a single-chamber glass chamber method, were used to demonstrate the permeation capability. The permeation of MMC dissolved in 0.9% NaCl solution and PDS through double natural rubber glove material was tested over 2 h using four concentrations (c = 0.004, 0.008, 0.016 and 0.4 mg ml(-1)) and three receptor fluids (0.9% NaCl solution, PDS and a novel artificial sweat). In none of four glass chamber experiments and in only one of 40 diffusion cell experiments was permeation through glove material detected. The permeation occurred between 15 and 30 min under worst-case exposure scenario at a approximately 100-fold higher MMC concentration than under in-use conditions during HIPEC. The double-layer natural rubber gloves tested were effective to prevent a permeation of MMC in vitro under HIPEC-similar exposure. Our results support the glove wearing procedure in our university hospital. However, occupational exposure to antineoplastic drugs should be minimized, since there is insufficient knowledge regarding harmful effects from a long-term exposure to low doses.

Discrepancies between different rat models for the assessment of percutaneous penetration of hazardous substances.

By regulatory authorities the rat is considered to be a suitable animal model to predict the percutaneous absorption of hazardous substances in humans. In our study, the percutaneous penetration of 2-butoxyethanol (BE) and toluene was compared in different rat models. Intradermal microdialysis and static diffusion cells were used in in vivo and in vitro experiments with haired Wistar and hairless Lewis rats. Microdialysis experiments showed a steady-state penetration for BE and a penetration maximum for toluene in both rat strains at approximately 60 min after beginning of exposure. However, in diffusion cell experiments the penetration of the test compounds in both rat strains increased until the end of exposure (4 h). Additionally, in microdialysis experiments BE penetrated in hairless rats in a higher amount than in haired rats (factor: 1.4; P < 0.01), for toluene it was just the opposite (factor: 1.9; P < 0.001). In diffusion cell experiments, the penetrated amounts of both compounds were higher in hairless rats compared to haired rats. The fluxes for BE were in diffusion cell experiments at a factor of 14.5 (haired rat) and 18.1 (hairless rat) higher than in microdialysis experiments, the difference factor for toluene was 2.6 (haired rat) and 12.9 (hairless rat). The lag times indicate a significantly faster penetration in microdialysis experiments compared with diffusion cell experiments (P < 0.001). There are great differences in percutaneous penetration behaviour between the techniques and the rat strains. The diffusion cell method has difficulties to describe the percutaneous penetration kinetics, whereas microdialysis describes it more reliable. Due to these differences the reliability of a conversion factor for the transfer of percutaneous absorption data from rat to human skin, as proposed in the literature, is questionable.

Percutaneous absorption and metabolism of 2-butoxyethanol in human volunteers: a microdialysis study.

We determined percutaneous absorption kinetics of 2-butoxyethanol (BE) in volunteers using microdialysis. Four male volunteers were dermally exposed twice to 90% and 50% aqueous solutions (v/v) of BE for 4.5h. To determine percutaneous absorption kinetics the concentration of BE was measured in the dialysate samples collected at 30 min-intervals throughout exposure. The systemic absorption, which is needed to determine recovery of the BE in the dialysate, was estimated from the concentration of the main metabolite of BE, free butoxyacetic acid (BAA) in urine. A pseudo steady-state percutaneous absorption was reached approximately at 2h of exposure for both BE concentrations. The maximum dermal flux of 50% BE was higher than that of 90% BE (2.8+/-0.4, 1.9+/-0.6 mg cm(-2)h(-1), respectively). The more diluted BE solution showed shorter lag time: 25 min versus 39 min. The amount of BAA was determined in the pooled dialysate samples collected at 4 and 4.5h. The dermal metabolism seems to be low, the BAA amount ranged from 0.03% to 1.9% of the BE in the same dialysate. Our study demonstrates applicability of microdialysis technique for assessment of percutaneous absorption kinetics and dermal metabolism without interference from the systemic compartment.

Dermal absorption of aromatic amines in workers with different skin lesions: a report on 4 cases.

There are only few studies about the relationship of skin lesions and the percutaneous uptake of hazardous substances in exposed workers. Several aromatic amines are well known carcinogens for humans and/or animals. This case report emphasizes the relevance of dermal absorption of the aromatic amine ortho-toluidine considering four workers with different skin status (healthy, erythematous and burned skin as well as dishydrotic eczema) during the vulcanisation process of rubber products in a components supplier plant for automobile industry. The results of our case report show that dermal absorption of o-toluidine through damaged epidermal barrier is significantly higher than through healthy skin.

Penetration of beta-naphthylamine and o-toluidine through human skin in vitro.

Several aromatic amines (AAs) are known to be carcinogens for humans. AAs are considered to be substantially absorbed through the skin. However, the database for dermal absorption of AAs in general is limited and no specific studies on dermal absorption of beta-naphthylamine (BNA) and o-toluidine (OT) have been published. In the present study using diffusion cells, we investigated dermal penetration of BNA and OT through human skin. We have demonstrated that both AAs penetrate through human skin fast (lag time: approximately 1.2 vs. 0.8 h) and in high percentages (54 vs. 50%, respectively, of the applied dose within 24 h). A skin notation is therefore justified for these substances.

Secondary prevention of allergic symptoms in a dairy farmer by use of a milking robot.

BACKGROUND: Animal-derived allergens include lipocalins which play an increasing role in occupational respiratory sensitizations. The prevention of sensitization in stock farming is often difficult due to intense exposure, with traditional milking still requiring close animal contact. Complete avoidance of allergen exposure is only possible if stock farming is abandoned. This is, however, often not feasible in small dairy plants because of the resulting loss of income. CASE PRESENTATION: In a 37-year-old female farmer daily asthmatic complaints appeared, associated with cow dust-derived allergen exposure by milking with a conventional device. Respiratory symptoms increased during a period of 12 years. Allergic bronchial asthma was diagnosed, caused by sensitization against cow dust-derived allergens, as demonstrated by positive skin prick test and by detection of IgE antibodies. In a separate specific inhalation challenge test using a 10% extract of cow dust-derived allergens a 330% increase of airway resistance was detected. To enable further dairy farming, a milking robot was installed in 1999, i.e., an automatic milking system. The novel milking technique reduced the daily exposure from over 2 hours to approximately 10 min. The clinical course after the installation of the milking robot was favourable, with less frequent allergic and asthmatic symptoms. Furthermore, asthma medication could be reduced. Improvement was noted also in terms of lung-function and decreased total serum IgE. CONCLUSION: The case presented and the evidence from the literature indicates that the strategy of exposure minimization to allergens at workplaces can be an effective alternative to total elimination. In farmers with cow dust allergy a milking robot is an appropriate technical measure to minimize allergen-exposure.

Visible and subclinical skin changes in male and female dispatch department workers of newspaper printing plants.

UNLABELLED: BACKGROUND AND PROBLEM: Wet work and skin exposure to detergents or solvents are well-established causes of irritant hand dermatitis. In contrast, physical irritation of the skin as another potential cause of occupational hand dermatitis has been investigated less. MATERIAL AND METHODS: Our study included 71 individuals exposed to physical irritation during work in the dispatch department of two newspaper printing plants. Clinical examination and measurements of transepidermal water loss (TEWL), capacitance and skin surface pH of the skin of hands and forearms was performed. RESULTS: Erythema and/or scaliness of the hands were unexpectedly common: 26 of the 38 female inlay workers, 11 of the 13 male inlay workers and 15 of the 20 male machine operators were affected, compared to 18 of 28 printers exposed to solvents who had been investigated in a previous study. A significantly higher skin surface pH on the hands (P < 0.05) and, less pronounced, on the forearms (P > 0.05) was found in females. There was no association between domestic skin exposure, according to questionnaire data, and the bioengineering results. Skin cleansing and skin care differed between male and female workers, but were again not associated with the outcomes. CONCLUSIONS: The point prevalence of skin changes in dispatch department workers in the present study is unexpectedly high, which points to the importance of physical irritation by paper dust. Significant differences in bioengineering parameters between male and female inlay workers were found only for skin surface pH at the exposed back of hands. Future studies should (i) try to elucidate the role of skin surface pH changes and (ii) pay more attention to physical trauma to the skin.

Is the permeability coefficient Kp a reliable tool in percutaneous absorption studies?

In percutaneous absorption studies the potency of penetration of chemical substances is often described by the permeability coefficient Kp. The experimentally determined Kp is characterized according to Fick's first law of diffusion by the ratio of flux and the concentration of the test compound (Kp=Flux/C). This equation implies that in percutaneous absorption studies Kp is theoretically a more reliable parameter than flux taking the concentration into consideration, and should remain constant for each compound independent from the grade of dilution. In our study we evaluated the course of the percutaneous absorption parameters flux and Kp of neat and of 50% aqueous solution of 2-butoxyethanol (BE). An infinite dose of neat and 50% aqueous solution of non-radiolabeled BE were applied on excised human skin from two donors in static diffusion cells in parallel (for each test setting n=21). The flux of 50% aqueous BE (0.704+/-0.152 mg/cm2/h) was about 15-fold higher than that of neat BE (0.045+/-0.014 mg/cm2/h). The comparison of the Kp values of both test settings showed with a factor of about 31 (Kp=1.563 x 10(-3) cm/h) much higher values for 50% aqueous BE and Kp=0.050 x 10(-3) cm/h for neat BE. Although the flux does not consider the chemical concentration, it showed a smaller difference in both test settings as Kp; however, the flux remains a non-specific parameter for the description of percutaneous absorption. The results of our experiments showed that the permeability coefficient Kp was not able to adjust the flux of BE to the concentration. This is in agreement with the evaluation of Kp from BE data described in the literature.

Butoxyethoxyacetic acid, a biomarker of exposure to water-based cleaning agents.

The aim of the study was to investigate the suitability of butoxyethoxyacetic acid (BEAA) as a biomarker of exposure to water-based cleaning agents containing diethylene glycol mono butyl ether (DEGBE). The study was performed in two printing plants where water-based products containing 10-15% DEGBE were used for rubber and blanket washes. Thirty nine newspaper pressroom workers (exposed) and 19 employees of newspaper despatch departments (controls) were investigated. By questionnaire, the workers were asked about the use of personal protective measures. BEAA was determined in post-shift urine using GC-MS. The BEAA concentration in the urine of exposed workers ranged up to 75.1 mg/l (median 6.3 mg/l), whereas in urine samples of the controls the BEAA level was below or around the determination limit of 0.5 mg/l. A protective effect on DEGBE uptake was observed with the use of protective gloves. This observation implies that dermal penetration of DEGBE may be important in exposure monitoring.