The first international conference on the environmental health and safety of jet fuel

In Vitro Rat Hepatic Metabolism of n-Alkanes: Nonane, Decane, and Tetradecane

Jet propellant 8 (JP-8) jet fuel is a complex mixture of aromatic and aliphatic hydrocarbons. The aim of this study was to determine in vitro metabolic rate constants for semivolatile n-alkanes, nonane (C9), decane (C10), and tetradecane (C14), by rat liver microsomal oxidation. The metabolism was assessed by measuring the disappearance of parent compound by gas chromatography. Various concentrations of n-alkanes were incubated with liver microsomes from adult male F-344 rats. Nonlinear kinetic constants for nonane and decane were Vmax(nmol/mg protein/min) = 7.26 ± 0.20 and 2.80 ± 0.35, respectively, and KM( μM) = 294.83 ± 68.67 and 398.70 ± 42.70, respectively. Metabolic capacity as assessed by intrinsic clearance ( Vmax/ KM) was ~four-fold higher for nonane (0.03 ± 0.005) than for decane (0.007 ± 0.001). There was no appreciable metabolism of tetradecane even with higher microsomal protein concentration and longer incubation time. These results show a negative correlation between metabolic clearance and chain length of n-alkanes. These metabolic rate constants will be used to update existing physiologically based pharmacokinetic (PBPK) models for nonane and decane as part of developing a PBPK model for JP-8.

Membrane transport of naphthalene and dodecane in jet fuel mixtures

Jet fuels are formulated with numerous aliphatic and aromatic components that are thought to cause dermal irritation in air force personnel. However, diffusion of these components in such a complex mixture is not well understood. The purpose of this study is to evaluate the physicochemical properties of these mixtures in the context of how they influence partitioning, diffusion, and absorption of aromatic (14C-naphthalene) and aliphatic (14C-dodecane) markers in porcine skin and silastic membranes in vitro. In these 5-h flowthrough diffusion studies, Jet-A, JP-8, and JP-8(100) fuels, and weathered JP-8 (JP-8 (Puddle)) were tested. In both membrane systems and across all jet fuels tested, naphthalene absorption (1.29-1.84% dose) was significantly greater than dodecane absorption (0.14-0.28% dose). However, significantly more dodecane than naphthalene was observed in the stratum corneum (SC; 4.23-7.23% dose vs. 1.88-4.08% dose) and silastic membranes (59.2-81.7% dose vs. 30.5-36.7% dose). Naphthalene was least likely to be retained on the skin surface compared to dodecane, while this trend was reversed in silastic membranes. In porcine skin. weathered JP-8 significantly increased dodecane absorption, permeability (0.19×10−4 cm/h), and diffusivity, and also naphthalene deposition in the SC compared to other jet fuels. In contrast, weathered JP-8 appears to decrease naphthalene flux (1.56 μg/cm2/h) and permeability (1.14×10−4 cm/h) in skin. There were no differences among the three jet fuels in terms of their ability to influence naphthalene or dodecane disposition in skin and, generally, no significant differences among the four jet fuel mixtures were observed in silastic membranes. In conclusion, these transport studies suggest that absorption and deposition of naphthalene and dodecane are different when dosed in various jet fuel mixtures, and disposition in weathered jet fuel is significantly different from that in commercial and military fuels. These interactions may not only be related to the unique chemistry of these components, but also specific membrane interactions in the SC and viable epidermis.

Commentary on the contributions and future role of occupational exposure science in a vision and strategy for the discipline of exposure science

Exposure science is a holistic concept without prejudice to exposure source. Traditionally, measurements aimed at mitigating environmental exposures have not included exposures in the workplace, instead considering such exposures to be an internal affair between workers and their employers. Similarly, occupational (or industrial) hygiene has not typically accounted for environmental contributions to poor health at work. Many persons spend a significant amount of their lifetime in the workplace, where they maybe exposed to more numerous chemicals at higher levels than elsewhere in their environment. In addition, workplace chemical exposures and other exogenous stressors may increase epigenetic and germline modifications that are passed on to future generations. We provide a brief history of the development of exposure science from its roots in the assessment of workplace exposures, including an appendix where we detail current resources for education and training in exposure science offered through occupational hygiene organizations. We describe existing successful collaborations between occupational and environmental practitioners in the field of exposure science, which may serve as a model for future interactions. Finally, we provide an integrated vision for the field of exposure science, emphasizing interagency collaboration, the need for complete exposure information in epidemiological studies, and the importance of integrating occupational, environmental, and residential assessments. Our goal is to encourage communication and spur additional collaboration between the fields of occupational and environmental exposure assessment. Providing a more comprehensive approach to exposure science is critical to the study of the "exposome", which conceptualizes the totality of exposures throughout a person's life, not only chemical, but also from diet, stress, drugs, infection, and so on, and the individual response.

Characterization of inhalation exposure to jet fuel among U.S. Air Force personnel

BACKGROUND

Jet propulsion fuel-8 (JP-8) is the primary jet fuel used by the US military, collectively consuming ~2.5 billion gallons annually. Previous reports suggest that JP-8 is potentially toxic to the immune, respiratory, and nervous systems. The objectives of this study were to evaluate inhalation exposure to JP-8 constituents among active duty United States Air Force (USAF) personnel while performing job-related tasks, identify significant predictors of inhalation exposure to JP-8, and evaluate the extent to which surrogate exposure classifications were predictive of measured JP-8 exposures.

METHODS

Seventy-three full-time USAF personnel from three different air force bases were monitored during four consecutive workdays where personal air samples were collected and analyzed for benzene, ethylbenzene, toluene, xylenes, total hydrocarbons (THC), and naphthalene. The participants were categorized a priori into high- and low-exposure groups, based on their exposure to JP-8 during their typical workday. Additional JP-8 exposure categories included job title groups and self-reported exposure to JP-8. Linear mixed-effects models were used to evaluate predictors of personal air concentrations.

RESULTS

The concentrations of THC in air were significantly different between a priori exposure groups (2.6 mg m(-3) in high group versus 0.5 mg m(-3) in low, P < 0.0001), with similar differences observed for other analytes in air. Naphthalene was strongly correlated with THC (r = 0.82, P < 0.0001) and both were positively correlated with the relative humidity of the work environment. Exposures to THC and naphthalene varied significantly by job categories based on USAF specialty codes and were highest among personnel working in fuel distribution/maintenance, though self-reported exposure to JP-8 was an even stronger predictor of measured exposure in models that explained 72% (THC) and 67% (naphthalene) of between-worker variability. In fact, both self-report JP-8 exposure and a priori exposure groups explained more between-worker variability than job categories.

CONCLUSIONS

Personal exposure to JP-8 varied by job and was positively associated with the relative humidity. However, self-reported exposure to JP-8 was an even stronger predictor of measured exposure than job title categories, suggesting that self-reported JP-8 exposure is a valid surrogate metric of exposure when personal air measurements are not available.

The utility of naphthyl-keratin adducts as biomarkers for jet-fuel exposure

We investigated the association between biomarkers of dermal exposure, naphthyl-keratin adducts (NKA), and urine naphthalene biomarker levels in 105 workers routinely exposed to jet-fuel. A moderate correlation was observed between NKA and urine naphthalene levels (p = 0.061). The NKA, post-exposure breath naphthalene, and male gender were associated with an increase, while CYP2E1*6 DD and GSTT1-plus (++/+-) genotypes were associated with a decrease in urine naphthalene level (p < 0.0001). The NKA show great promise as biomarkers for dermal exposure to naphthalene. Further studies are warranted to characterize the relationship between NKA, other exposure biomarkers, and/or biomarkers of biological effects due to naphthalene and/or PAH exposure.

The Occupational JP8 Exposure Neuroepidemiology Study (OJENES): repeated workday exposure and central nervous system functioning among US Air Force personnel

One of the most prevalent workplace chemical exposures historically and currently confronting the global military and civilian workforce is jet propellant (JP) fuel (e.g., JP4, JP5, JP8, jet A1), a complex mixture of numerous hydrocarbon compounds and additives. To date, numerous protective and preventive strategies (e.g., federal exposure limits, workplace procedure protocols, protective gear such as goggles, respirator use, gloves, and coveralls) have been put in place to minimize acutely toxic exposure levels. However, questions remain regarding the effect of repeated exposures at lower (than regulated) levels of JP fuel. The Occupational JP8 Exposure Neuroepidemiology Study (OJENES) was designed to examine the relationships between occupational JP8 exposure over multiple, repeated workdays and specific aspects of central nervous system (CNS) functioning among Air Force (AF) personnel. In this report, we present the OJENES methodology, descriptive findings related to participant characteristics, JP8 exposure levels observed over a work week among higher and lower exposure groups, and neuropsychological task performances at the first study assessment. Results indicated minimal differences between participants in the high and lower exposure groups in terms of descriptive characteristics, other than daily JP8 exposure levels (p<0.001). In addition, neuropsychological task performances for most task measures were not found to be significantly different from reported reference ranges. These findings demonstrated that confounding and misclassification of exposure and outcome status are not major concerns for the study. Therefore, future OJENES analyses targeting the more focused research questions regarding associations between JP8 exposure and CNS functioning are likely to provide valid conclusions, as they will be less influenced by these research biases.

Observing the human exposome as reflected in breath biomarkers: heat map data interpretation for environmental and intelligence research

Over the past decade, the research of human system biology and the interactions with the external environment has permeated all phases of environmental, medical and public health research. Similar to the fields of genomics and proteomics research, the advent of new instrumentation for measuring breath biomarkers and their associated meta-data also provide very useful, albeit complex, data structures. The biomarker research community is beginning to invoke tools from system biology to assess the impact of environmental exposures, as well as from internal health states, on the expression of suites of chemicals in exhaled breath. This new approach introduces the concept of the exposome as a complement to the genome in exploring the environment-gene interaction. In addition to answering questions regarding health status for the medical community, breath biomarker patterns are useful for assessing public health risks from environmental exposures. Furthermore, breath biomarker patterns can inform security risks from suspects via covert interrogation of blood borne chemical levels that reflect previous activities. This paper discusses how different classes of exhaled breath biomarker measurements can be used to rapidly assess patterns in complex data. We present exhaled breath data sets to demonstrate the value of the graphical 'heat map' approach for hypothesis development and subsequent guidance for stochastic and mixed effect data interpretation. We also show how to graphically interpret exhaled breath measurements of exogenous jet fuel components, as well as exhaled breath condensate measurements of endogenous chemicals.

Jet fuel toxicity: skin damage measured by 900-MHz MRI skin microscopy and visualization by 3D MR image processing

The toxicity of jet fuels was measured using noninvasive magnetic resonance microimaging (MRM) at 900-MHz magnetic field. The hypothesis was that MRM can visualize and measure the epidermis exfoliation and hair follicle size of rat skin tissue due to toxic skin irritation after skin exposure to jet fuels. High-resolution 900-MHz MRM was used to measure the change in size of hair follicle, epidermis thickening and dermis in the skin after jet fuel exposure. A number of imaging techniques utilized included magnetization transfer contrast (MTC), spin-lattice relaxation constant (T1-weighting), combination of T2-weighting with magnetic field inhomogeneity (T2*-weighting), magnetization transfer weighting, diffusion tensor weighting and chemical shift weighting. These techniques were used to obtain 2D slices and 3D multislice-multiecho images with high-contrast resolution and high magnetic resonance signal with better skin details. The segmented color-coded feature spaces after image processing of the epidermis and hair follicle structures were used to compare the toxic exposure to tetradecane, dodecane, hexadecane and JP-8 jet fuels. Jet fuel exposure caused skin damage (erythema) at high temperature in addition to chemical intoxication. Erythema scores of the skin were distinct for jet fuels. The multicontrast enhancement at optimized TE and TR parameters generated high MRM signal of different skin structures. The multiple contrast approach made visible details of skin structures by combining specific information achieved from each of the microimaging techniques. At short echo time, MRM images and digitized histological sections confirmed exfoliated epidermis, dermis thickening and hair follicle atrophy after exposure to jet fuels. MRM data showed correlation with the histopathology data for epidermis thickness (R(2)=0.9052, P<.0002) and hair root area (R(2)=0.88, P<.0002). The toxicity of jet fuels on skin structures was in the order of tetradecane>hexadecane>dodecane. The method showed a sensitivity of 87.5% and a specificity of 75%. By MR image processing, different color-coded skin structures were extracted and 3D shapes of the epidermis and hair follicle size were compared. In conclusion, high-resolution MRM measured the change in skin epidermis and hair follicle size due to toxicity of jet fuels. MRM offers a three-dimensional spatial visualization of the change in skin structures as a method of toxicity evaluation and for comparison of jet fuels.

Inhalation exposure to jet fuel (JP8) among U.S. Air Force personnel

As jet fuel is a common occupational exposure among military and civilian populations, this study was conducted to characterize jet fuel (JP8) exposure among active duty U.S. Air Force personnel. Personnel (n = 24) were divided a priori into high, moderate, and low exposure groups. Questionnaires and personal air samples (breathing zone) were collected from each worker over 3 consecutive days (72 worker-days) and analyzed for total hydrocarbons (THC), benzene, toluene, ethylbenzene, xylenes, and naphthalene. Air samples were collected from inside the fuel tank and analyzed for the same analytes. Linear mixed-effects models were used to evaluate the exposure data. Our results show that the correlation of THC (a measure of overall JP8 inhalation exposure) with all other analytes was moderate to strong in the a priori high and moderate exposure groups combined. Inhalation exposure to all analytes varied significantly by self-reported JP8 exposure (THC levels higher among workers reporting JP8 exposure), a priori exposure group (THC levels in high group > moderate group > low group), and more specific job task groupings (THC levels among workers in fuel systems hangar group > refueling maintenance group > fuel systems office group > fuel handling group > clinic group), with task groupings explaining the most between-worker variability. Among highly exposed workers, statistically significant job task-related predictors of inhalation exposure to THC indicated that increased time in the hangar, working close to the fuel tank (inside > less than 25 ft > greater than 25 ft), primary job (entrant > attendant/runner/fireguard > outside hangar), and performing various tasks near the fuel tank, such as searching for a leak, resulted in higher JP8 exposure. This study shows that while a priori exposure groups were useful in distinguishing JP8 exposure levels, job task-based categories should be considered in epidemiologic study designs to improve exposure classification. Finally, the strong correlation of THC with naphthalene suggests that naphthalene may be an appropriate surrogate of JP8 exposure. [Supplementary materials are available for this article. Go to the publisher's online edition of the Journal of Occupational and Environmental Hygiene for the following free supplemental resource: a pdf file containing a table detailing concentrations of JP8 components.].

Detection, expression and quantitation of the biodegradative genes in Antarctic microorganisms using PCR

In this study, 28 hydrocarbon-degrading bacterial isolates from oil-contaminated Antarctic soils were screened for the presence of biodegradative genes such as alkane hydroxylase (alks), the ISPalpha subunit of naphthalene dioxygenase (ndoB), catechol 2,3-dioxygenase (C23DO) and toluene/biphenyl dioxygenase (todC1/bphA1) by using polymerase chain reaction (PCR) methods. All naphthalene degrading bacterial isolates exhibited the presence of a 648 bp amplicon that shared 97% identity to a known ndoB sequence from Pseudomonas putida. Twenty-two out of the twenty-eight isolates screened were positive for one, two or all three different regions of the C23DO gene. For alkane hydroxylase, all 6 Rhodococcus isolates were PCR-positive for a 194 bp and a 552 bp segment of the alkB gene, but exhibited variable results with primers located at different segments of this gene. Three Pseudomonas spp. 4/101, 19/1, 30/3 amplified 552 bp segment of alkB. Only two Pseudomonas sp. 7/156 and 4/101 amplified a segment of alkB exhibiting 89-94% nucleotide sequence identity with the existing sequence of alkB in the GenBank sequence database. Transcripts of three genes, alkB2, C23DO and ndoB, that were amplified by DNA-PCR in three different bacterial isolates also exhibited positive amplification by reverse transcriptase PCR (RT-PCR) method confirming that these genes are functional. A competitive PCR (cPCR) method was developed for a quantitative estimation of ndoB from pure cultures of the naphthalene-degrading Pseudomonas sp. 30/2. A minimum of 1 x 10(7) copies of the ndoB gene was detected based on the comparison of the intensities of the competitor and target DNA bands. It is expected that the identification and characterization of the biodegradative genes will provide a better understanding of the catabolic pathways in Antarctic psychrotolerant bacteria, and thereby help support bioremediation strategies for oil-contaminated Antarctic soils.

Development of a Physiologically Based Pharmacokinetic Model for Decane, a Constituent of Jet Propellent-8

Decane, a 10-carbon n-alkane and one of the highest vapor phase constituents of jet propellent-8 (JP-8), was selected to represent the semivolatile fraction for the initial development of a physiologically based pharmacokinetic (PBPK) model for JP-8. Rats were exposed to decane vapors at time-weighted average concentrations of 1200, 781, or 273 ppm in a 32-L Leach chamber for 4 h. Time-course samples for 1200 ppm and end-of-exposure samples for 781 and 273 ppm decane exposures were collected from blood, brain, liver, fat, bone marrow, lung, skin, and spleen. The pharmacokinetics of decane could not be described by flow-limited assumptions and measured in vitro tissue/air partition coefficients. A refined PBPK model for decane was then developed using flow-limited (liver and lung) and diffusion-limited (brain, bone marrow, fat, skin, and spleen) equations to describe the uptake and clearance of decane in the blood and tissues. Partition coefficient values for blood/air and tissue/blood were estimated by fitting end-of-exposure pharmacokinetic data and assumed to reflect the available decane for rapid exchange with blood. A portion of decane is speculated to be sequestered in "deep" pools in the body, unavailable for rapid exchange with blood. PBPK model predictions were adequate in describing the tissues and blood kinetics. For model validation, the refined PBPK model for decane had mixed successes at predicting tissue and blood concentrations for lower concentrations of decane vapor, suggesting that further improvements in the model may be necessary to extrapolate to lower concentrations.

Human Metabolism and Metabolic Interactions of Deployment-Related Chemicals

It has been suggested that chemicals and, more specifically, chemical interactions, are involved as causative agents in deployment-related illnesses. Unfortunately, this hypothesis has proven difficult to test, because toxicological investigations of deployment-related chemicals are usually carried out on surrogate animals and are difficult to extrapolate to humans. Other parts of the problem, such as the definition of variation within human populations and the development of methods for designating groups or individuals at significantly greater risk, cannot be carried out on surrogate animals, and the data must be derived from humans. The relatively recent availability of human cell.fractions, such as microsomes, cytosol, etc., human cells such as primary hepatocytes, recombinant human enzymes, and their isoforms and polymorphic variants has enabled a significant start to be made in developing the human data needed. These initial studies have examined the human metabolism by cytochrome P450, other phase I enzymes, and their isoforms and, in some cases, their polymorphic variants of compounds such as chlorpyrifos, carbaryl, DEET, permethrin, and pyridostigmine bromide, and, to a lesser extent, other chemicals from the same chemical and use classes, including solvents, jet fuel components, and sulfur mustard metabolites. A number of interactions at the metabolic level have been described both with respect to other xenobiotics and to endogenous metabolites. Probably the most dramatic have been seen in the ability of chlorpyrifos to inhibit not only the metabolism of other xenobiotics such as carbaryl and DEET but also to inhibit the metabolism of steroid hormones.

Inhibition of jet fuel aliphatic hydrocarbon induced toxicity in human epidermal keratinocytes

Jet propellant (JP)-8, the primary jet fuel used by the U.S. military, consists of hydrocarbon-rich kerosene base commercial jet fuel (Jet-A) plus additives DC1-4A, Stadis 450 and diethylene glycol monomethyl ether. Human epidermal keratinocytes (HEK) were exposed to JP-8, aliphatic hydrocarbon (HC) fuel S-8 and aliphatic HC pentadecane (penta), tetradecane (tetra), tridecane (tri) and undecane (un) for 5 min. Additional studies were conducted with signal transduction pathway blockers parthenolide (P; 3.0 microm), isohelenin (I; 3.0 microm), SB 203580 (SB; 13.3 microm), substance P (SP; 3.0 microm) and recombinant human IL-10 (rHIL-10; 10 ng ml(-1)). In the absence of inhibitors, JP-8 and to a lesser extent un and S-8, had the greatest toxic effect on cell viability and inflammation suggesting, as least in vitro, that synthetic S-8 fuel is less irritating than the currently used JP-8. Each inhibitor significantly (P < 0.05) decreased HEK viability. DMSO, the vehicle for P, I and SB, had a minimal effect on viability. Overall, IL-8 production was suppressed at least 30% after treatment with each inhibitor. Normalizing data relative to control indicate which inhibitors suppress HC-mediated IL-8 to control levels. P was the most effective inhibitor of IL-8 release; IL-8 was significantly decreased after exposure to un, tri, tetra and penta but significantly increased after JP-8 exposure compared with controls. Inhibitors were not effective in suppressing IL-8 release in JP-8 exposures to control levels. This study shows that inhibiting NF-kappa B, which appears to play a role in cytokine production in HC-exposed HEK in vitro, may reduce the inflammatory effect of HC in vivo.

Effects of brief cutaneous JP-8 jet fuel exposures on time course of gene expression in the epidermis

The jet fuel jet propulsion fuel 8 (JP-8) has been shown to cause an inflammatory response in the skin, which is characterized histologically by erythema, edema, and hyperplasia. Studies in laboratory animal skin and cultured keratinocytes have identified a variety of changes in protein levels related to inflammation, oxidative damage, apoptosis, and cellular growth. Most of these studies have focused on prolonged exposures and subsequent effects. In an attempt to understand the earliest responses of the skin to JP-8, we have investigated changes in gene expression in the epidermis for up to 8 h after a 1-h cutaneous exposure in rats. After exposure, we separated the epidermis from the rest of the skin with a cryotome and isolated total mRNA. Gene expression was studied with microarray techniques, and changes from sham treatments were analyzed and characterized. We found consistent twofold increases in gene expression of 27 transcripts at 1, 4, and 8 h after the beginning of the 1-h exposure that were related primarily to structural proteins, cell signaling, inflammatory mediators, growth factors, and enzymes. Analysis of pathways changed showed that several signaling pathways were increased at 1 h and that the most significant changes at 8 h were in metabolic pathways, many of which were downregulated. These results confirm and expand many of the previous molecular studies with JP-8. Based on the 1-h changes in gene expression, we hypothesize that the trigger of the JP-8-induced, epidermal stress response is a physical disruption of osmotic, oxidative, and membrane stability which activates gene expression in the signaling pathways and results in the inflammatory, apoptotic, and growth responses that have been previously identified.

Dermal absorption and penetration of jet fuel components in humans

Jet propulsion fuel 8 (JP-8) is the largest source of chemical exposures on military bases. Dermal exposure to JP-8 has been investigated in vitro using rat or pig skin, but not in vivo in humans. The purpose of this study was to investigate the absorption and penetration of aromatic and aliphatic components of JP-8 in humans. A surface area of 20 cm2 was delineated on the forearms of human volunteers and 1 ml of JP-8 was applied to the skin. Tape-strip samples were collected 30 min after application. Blood samples were taken before exposure (t=0 h), after exposure (t=0.5 h), and every 0.5 h for up to 4 h past exposure. The tape-strip samples showed evidence of uptake into the skin for all JP-8 components. The blood data was used to estimate an apparent permeability coefficient (Kp). The rank order of the apparent Kp was naphthalene>1-methyl naphthalene=2-methyl naphthalene>decane>dodecane>undecane. This rank order is similar to results from rat and pig-skin studies. However, this study demonstrates that rat and pig models of the skin over predict the internal dose of JP-8 components in humans.

Comparative in vivo toxicity of topical JP-8 jet fuel and its individual hydrocarbon components: identification of tridecane and tetradecane as key constituents responsible for dermal irritation

Despite widespread exposure to military jet fuels, there remains a knowledge gap concerning the actual toxic entities responsible for irritation observed after topical fuel exposure. The present studies with individual hydrocarbon (HC) constituents of JP-8 jet fuel shed light on this issue. To mimic occupational scenarios, JP-8, 8 aliphatic HC (nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane) and 6 aromatic HC (ethyl benzene, o-xylene, trimethyl benzene, cyclohexyl benzene, naphthalene, dimethyl naphthalene) soaked cotton fabrics were topically exposed to pigs for 1 day and with repeated daily exposures for 4 days. Erythema, epidermal thickness, and epidermal cell layers were quantitated. No erythema was noted in 1-day in vivo HC exposures but significant erythema was observed in 4-day tridecane, tetradecane, pentadecane, and JP-8 exposed sites. The aromatic HCs did not produce any macroscopic lesions in 1 or 4 days of in vivo exposures. Morphological observations revealed slight intercellular and intracellular epidermal edema in 4-day exposures with the aliphatic HCs. Epidermal thickness and number of cell layers significantly increased (p < 0.05) in tridecane, tetradecane, pentadecane, and JP-8-treated sites. No significant differences were observed in the aromatic HC-exposed sites. Subcorneal microabscesses containing inflammatory cells were observed with most of the long-chain aliphatic HCs and JP-8 in 4-day exposures. Ultrastructural studies depicted that jet fuel HC-induced cleft formation within intercellular lipid lamellar bilayers of the stratum corneum. The degree of damage to the skin was proportional to the length of in vivo HC exposures. These data coupled with absorption and toxicity studies of jet fuel HC revealed that specific HCs (tridecane and tetradecane) might be the key constituents responsible for jet fuel-induced skin irritation.

Effect of in vivo jet fuel exposure on subsequent in vitro dermal absorption of individual aromatic and aliphatic hydrocarbon fuel constituents

The percutaneous absorption of topically applied jet fuel hydrocarbons (HC) through skin previously exposed to jet fuel has not been investigated, although this exposure scenario is the occupational norm. Pigs were exposed to JP-8 jet fuel-soaked cotton fabrics for 1 and 4 d with repeated daily exposures. Preexposed and unexposed skin was then dermatomed and placed in flow-through in vitro diffusion cells. Five cells with exposed skin and four cells with unexposed skin were dosed with a mixture of 14 different HC consisting of nonane, decane, undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, ethyl benzene, o-xylene, trimethyl benzene (TMB), cyclohexyl benzene (CHB), naphthalene, and dimethyl naphthalene (DMN) in water + ethanol (50:50) as diluent. Another five cells containing only JP-8-exposed skin were dosed solely with diluent in order to determine the skin retention of jet fuel HC. The absorption parameters of flux, diffusivity, and permeability were calculated for the studied HC. The data indicated that there was a two-fold and four-fold increase in absorption of specific aromatic HC like ethyl benzene, o-xylene, and TMB through 1- and 4-dJP-8 preexposed skin, respectively. Similarly, dodecane and tridecane were absorbed more in 4-d than 1-dJP-8 preexposed skin experiments. The absorption of naphthalene and DMN was 1.5 times greater than the controls in both 1- and 4-d preexposures. CHB, naphthalene, and DMN had significant persistent skin retention in 4-d preexposures as compared to 1-d exposures that might leave skin capable of further absorption several days postexposure. The possible mechanism of an increase in HC absorption in fuel preexposed skin may be via lipid extraction from the stratum corneum as indicated by Fourier transform infrared (FTIR) spectroscopy. This study suggests that the preexposure of skin to jet fuel enhances the subsequent in vitro percutaneous absorption of HC, so single-dose absorption data for jet fuel HC from naive skin may not be optimal to predict the toxic potential for repeated exposures. For certain compounds, persistent absorption may occur days after the initial exposure.

Comparative mixture effects of JP-8(100) additives on the dermal absorption and disposition of jet fuel hydrocarbons in different membrane model systems

Jet fuel are complex mixtures of hydrocarbon fuel components and performance additives. Three different membrane systems, silastic, porcine skin and the isolated perfused porcine skin flap (IPPSF) were used to gain insight into the possible mechanism for additive interactions on hydrocarbon component absorption. Influence of JP-8(100) additives on the dermal kinetics of 14C-naphthalene and 14C/3H-dodecane as markers of hydrocarbon absorption, were evaluated using analysis of means (ANOM) and analysis of variance (ANOVA). This study indicated that the naphthalene absorption through silastic membrane was significantly different with JP-8 plus individual additives as compared to controls, i.e. JP-8 and JP-8(100). The porcine skin data indicated that neither individual nor combinations of additives affected naphthalene absorption. The third membrane system (IPPSF) showed that only MDA and BHT were important additives altering naphthalene absorption. MDA was a significant suppressor while BHT was a significant enhancer of naphthalene absorption. MDA significantly decreased dodecane absorption in skin flaps. All individual and combinations of two additives with JP-8 affected naphthalene and dodecane surface retention in silastic membrane. The IPPSF indicated that only 8Q405 is a significant modulator of surface retention for both marker hydrocarbons. The 8Q405 significantly reduced naphthalene contents in dosed silastic and skin indicating a direct interaction between additive and marker hydrocarbons. The MDA and BHT, which significantly retained naphthalene in the stratum corneum of porcine skin individually, led to a statistical decrease in its retention in the stratum corneum when in combination (MDA + BHT) suggesting a potential biological interaction. These observations demonstrate that the single membrane system may not be suitable for the final prediction of complex additive interactions in jet fuels. Rather a combination of different membrane systems may provide the insight to elucidate the possible mechanism for additive interactions. Finally, it is important to assess all components of a chemical mixture since the effects of single components administered alone or as pairs may be confounded when all are present in the complete mixture.

Priorities for mixtures health effects research

In order to better inform scientific decision making in the occupational environment, we need a better understanding of the toxicology of mixed exposures. In particular, we need an understanding of the dose-response relationship from the level of individual or population exposure down to the molecular level (and then back up again from the molecular level to the specific health-related response of the organism as a whole). Mixtures toxicology is proving to be different from single-chemical toxicology in several fundamental but barely recognized ways: Knowledge gained in mixtures research should be able to improve current risk assessment and mitigation or intervention methods. In NIOSH's National Occupational Research Agenda (NORA) three priority areas have been identified:

Evaluation of gene expression profile of keratinocytes in response to JP-8 jet fuel

The skin is the principal barrier against any environmental insult. Therefore, there is a high risk for a large number of military and civilian personnel exposed to jet fuel JP-8 to suffer percutaneous absorption of this fuel. This paper reports the use of cDNA microarray to identify the gene expression profile in normal human epidermal keratinocytes exposed to JP-8 for 24-h and 7-day periods. The effects of JP-8 exposure on keratinocytes at these two different periods induced a set of genes with altered expression in response to this type of insult. Microarray data were visualized using a novel algorithm based on simple statistical analyses to reduce data dimensionality and identify subsets of discriminant genes. Predictive neural networks were built using a multiplayer perceptron to carry out a proper classification task in microarray data in the untreated versus JP-8-treated samples. The pattern of expressions in response to JP-8 provides evidences that detoxificant-related and cell growth regulator genes with the most variability in the level of expression may be useful genetic markers in adverse health effects of personnel exposed to JP-8. The approaches in our analysis provide a simple, safe, novel, and effective method that is reliable in identifying and analyzing gene expression in samples treated with JP-8 or over potential toxic agents. Gene expression data from these studies can be used to build accurate predictive models that separate different molecular profiles. The data establish the use and effectiveness of these approaches for future prospective studies.

Dose-dependent production of urinary naphthols among workers exposed to jet fuel (JP-8)

BACKGROUND

Jet propulsion fuel-8 (JP-8) is one of the largest sources of chemical exposures among Air Force personnel. Urinary naphthols have been suggested as useful biomarkers of exposure to JP-8.

METHODS

Multivariate linear regression models were applied to evaluate the effects of environmental and work-related factors upon production of urinary naphthols among 323 Air Force personnel.

RESULTS

Naphthalene exposure, smoking status, and their interaction, plus self-reported skin irritation explained about two-thirds of the variation in naphthol levels. The exposure-smoking interaction was consistent with induction by smoking of one or more steps in the metabolism of naphthalene and naphthalene-1,2-oxide (NapO). A supralinear dose-response relationship was observed between urinary naphthols and naphthalene exposure.

CONCLUSIONS

Urinary naphthols were associated with specific sources of exposure to JP-8, arising from both inhalation and dermal contact. Smokers and nonsmokers metabolized naphthalene at different rates, consistent with induction of at least two metabolic pathways by smoking.

The levels of kerosene components in biological samples after repeated dermal exposure to kerosene in rats

The current study was experimentally investigated using rats whether or not kerosene components are accumulated from daily repeated dermal exposure. Rats received daily 1h-exposure to kerosene for 5 days (5K), daily 1h-exposure for 4 days and left for 1 day (4KL), a single 1h-exposure (1K), a single 1h-exposure and left for 1 day (1KL), or a single 1h-exposure, sacrificed and left dead for 1 day (1KLD). Kerosene components, trimethylbenzenes (TMBs) and aliphatic hydrocarbons (AHCs) in blood and tissues were determined by GC-MS. In blood, almost the same concentrations of TMBs were detected in the rats sacrificed immediately after exposure (5K, 1K and 1KLD), and only trace levels were detected in the rats sacrificed 1 day after exposure (4 and 1KL). Almost the same levels of AHCs in blood were detected among groups except for the rats sacrificed 1 day after a single exposure (1KL), in which AHCs were slightly lower. These results suggest that (1) AHCs tend to be accumulated from daily exposure, while TMBs do not, (2) the proportions of detected kerosene components in blood can be an indicator of whether the last exposure occurred just before death or not, (3) the kerosene levels last at least 1 day without blood circulation.

Skin toxicity of jet fuels: ultrastructural studies and the effects of substance P

Topical exposure to jet fuel is a significant occupational hazard. Recent studies have focused on dermal absorption of fuel and its components, or alternatively, on the biochemical or immunotoxicological sequelae to exposure. Surprisingly, morphological and ultrastructural analyses have not been systematically conducted. Similarly, few studies have compared responses in skin to that of the primary target organ, the lung. The focus of the present investigation was 2-fold: first, to characterize the ultrastructural changes seen after topical exposure to moderate doses (335 or 67 microl/cm2) of jet fuels [Jet A, Jet Propellant (JP)-8, JP-8+100] for up to 4 days in pigs, and secondly, to determine if co-administration of substance P (SP) with JP-8 jet fuel in human epidermal keratinocyte cell cultures modulates toxicity as it does to pulmonary toxicity in laboratory animal studies. The primary change seen after exposure to all fuels was low-level inflammation accompanied by formation of lipid droplets in various skin layers, mitochondrial and nucleolar changes, cleft formation in the intercellular lipid lamellar bilayers, as well as disorganization in the stratum granulosum-stratum corneum interface. An increased number of Langerhans cells were also noted in jet fuel-treated skin. These changes suggest that the primary effect of jet fuel exposure is damage to the stratum corneum barrier. SP administration decreased the release of interleukin (IL)-8 normally seen in keratinocytes after JP-8 exposure, a response similar to that reported for SP's effect on JP-8 pulmonary toxicity. These studies provide a base upon which biochemical and immunological data collected in other model systems can be compared.

Urinary biomarkers of exposure to jet fuel (JP-8)

Benzene, naphthalene, and 1- and 2-naphthol were measured in urine samples obtained from 322 U.S. Air Force personnel categorized a priori as likely to have low, moderate, or high exposure to jet fuel [jet propulsion fuel-8 (JP-8)]. In postexposure samples, levels of these analytes in the high-exposure group were 3- to 29-fold greater than in the low-exposure group and 2- to 12-fold greater than in the moderate-exposure group. Heavy exposure to JP-8 contributed roughly the same amount of benzene and more than three times the amount of naphthalene compared with cigarette smoking. Strong correlations were observed among postexposure levels of naphthalene-based biomarkers in urine and naphthalene in air and breath. We conclude that urinary naphthalene and the naphthols can serve as biomarkers of exposure to jet fuel. Of these, the naphthols are probably more useful because of their greater abundance and slower elimination kinetics.

Macroarray analysis of the effects of JP-8 jet fuel on gene expression in Jurkat cells

The jet fuel JP-8 is widely used and a large number of military and civilian personnel is, therefore, exposed to it. Treatment of several cell lines, including human Jurkat cells, with JP-8 induces cell death that exhibits various biochemical and morphological characteristics of apoptosis. The molecular mechanism of JP-8 cytotoxicity, however, has remained unclear. The effects of exposure of Jurkat cells to JP-8 (1/10,000 dilution) for 4 h on gene expression have now been examined by cDNA macroarray analysis. We had previously shown in these cells that under the above conditions, JP-8 causes significant apoptosis, based upon the observation that caspase-3 activation occurs at approximately 4 h and consequently most of the other classical apoptotic biochemical and morphological alterations progress until apoptotic cell death at 24 h. Of the 439 apoptosis- or stress response-related genes examined, the expression of 16 genes was up-regulated and that of ten genes was down-regulated by a factor of > or =2. The changes in the expression of 11 of these 26 genes were confirmed by reverse transcription and polymerase chain reaction analysis. These results provide insight into the mechanism of JP-8 toxicity and the associated induction of apoptosis.

Mixture effects of JP-8 additives on the dermal disposition of jet fuel components

Aliphatic and aromatic components in formulated jet fuels can cause occupational dermatitis. However, the influence of JP-8 performance additives (DIEGME, 8Q21, and Stadis450) on the dermal disposition of fuel components is not well understood. These additives are formulated with commercial Jet-A to form military JP-8 fuel. The purpose of this study is to assess the influence of these additives on the dermal disposition of marker aromatic and aliphatic components, naphthalene and dodecane, respectively. Porcine skin sections in an in vitro system were used to characterize chemical-biological interactions that modulate diffusion of jet fuel components and isolated perfused porcine skin flaps (IPPSFs) were used to evaluate diffusion in a viable skin model with an intact microvasculature. In these 5-h studies, Jet-A, Jet-A + DIEGME, Jet-A + 8Q21, and Jet-A + Stadis450, Jet-A + DIEGME + 8Q21, Jet-A + DIEGME + Stadis450, Jet-A + 8Q21 + Stadis450, and JP-8 mixtures were tested. In general, naphthalene absorption (0.76-2.39% dose) was greater than dodecane absorption (0.10-0.84% dose), while the IPPSFs alone demonstrated that dodecane absorption was significantly greater in JP-8 than in Jet-A. Synergistic interactions with 8Q21 + Stadis450 appear to enhance systemic absorption of either naphthalene or dodecane, while DIEGME + Stadis450 increased naphthalene (1.88% dose) and dodecane (2.02% dose) penetration into the skin and fat tissues of IPPSFs. These findings were supported by the fact that 8Q21 + Stadis450 significantly increased dodecane flux and permeability in porcine skin sections, but 8Q21 alone reduced marker diffusion in both membrane systems. Furthermore, dodecane is more likely than naphthalene to remain in the stratum corneum and skin surface at 5 h, and DIEGME mixtures played a significant role in skin and surface retention of both markers. In summary, the data suggest that various combinations of these three performance additives in JP-8 can potentially alter the dermal disposition of aromatic and aliphatic fuel components in skin. More importantly, products of two-factor interactions were not predictable from single-factor exposures and, by extension, cannot be extrapolated to three-factor interactions.

Evaluation of immunotoxicity induced by single or concurrent exposure to N,N-diethyl-m-toluamide (DEET), pyridostigmine bromide (PYR), and JP-8 jet fuel

Approximately 5,000 to 80,000 of the US service personnel involved in the Persian Gulf War have complained of a variety of nonspecific symptoms since their return in 1991. These symptoms have been collectively labeled Gulf War Illness and include muscle fatigue, general malaise, myalgia, impaired cognition, ataxia, headaches, fever, joint pain, skin rash, gastrointestinal disturbances, sleep disturbances, and respiratory difficulties. Exposures of military and service personnel were diverse and included the prescribed anti-nerve gas agent pyridostigmine bromide (PYR), N.N-diethyl-m-toluamide (DEET) insect repellent, and environmental exposures to jet fuel. Thus, studies in our laboratory were undertaken to determine if concurrent exposure to these agents, singly or in combination, would contribute to significant alterations in immunological function and disease susceptibility. To assess immune status, eight-week old B6C3F1 female mice were exposed for 14 days to single compounds or tertiary mixtures of 15.5 mg/kg DEET, 2 mg/kg PYR, and 500 mg/kg JP-8 (termed low dose), or 31 mg/kg DEET, 5 mg/kg PYR, and 1,000 mg/kg JP-8 (termed high dose). Immunosuppression was assessed 24 h after the last exposure. No remarkable alterations were evident in hematological parameters, spleen and thymus organ weight and total cellularity, natural killer (NK) cell activity, cytotoxic T-cell activity, or mitogen-induced lymphocyte proliferation after exposure to either single or tertiary mixtures at low or high doses. A few changes in CD4/CD8 flow cytometric lymphocyte subpopulations were detected after exposure to the tertiary mixture at the high dose. Delayed type hypersensitivity (DTH) was decreased by 88% after exposure to the high-dose mixture, and suppression of antibody-specific IgM immune responses (plaque-forming cell, PFC) occurred after exposure to all single and tertiary mixtures at both dose levels. In the PFC response, antagonism was apparent in the mixture, while coexposure to these agents resulted in a synergistic effect in the DTH response. Susceptibility to B16F10 tumor or Listeria monocytogenes challenge was not affected after single or tertiary exposures. These data suggest that combined exposure to DEET, PYR, and JP-8 does not profoundly alter many immunological endpoints, but does selectively target functional endpoints such as the PFC and DTH response. This should be considered when assessing human health risks in the military environment.

Proteomic analysis of the renal effects of simulated occupational jet fuel exposure

We analyzed protein expression in the cytosolic fraction prepared from whole kidneys in male Swiss-Webster mice exposed 1 h/day for five days to aerosolized JP-8 jet fuel at a concentration of 1000 mg/m3, simulating military occupational exposure. Kidney cytosol samples were solubilized and separated via large-scale, high-resolution two-dimensional electrophoresis (2-DE) and gel patterns scanned, digitized and processed for statistical analysis. Significant changes in soluble kidney proteins resulted from jet fuel exposure. Several of the altered proteins were identified by peptide mass finger-printing and related to ultrastructural abnormalities, altered protein processing, metabolic effects, and paradoxical stress protein/detoxification system responses. These results demonstrate a significant but comparatively moderate JP-8 effect on protein expression in the kidney and provide novel molecular evidence of JP-8 nephrotoxicity. Human risk is suggested by these data but conclusive assessment awaits a noninvasive search for biomarkers in JP-8 exposed humans.

Proteomic analysis of simulated occupational jet fuel exposure in the lung

We analyzed protein expression in the cytosolic fraction prepared from whole lung tissue in male Swiss-Webster mice exposed 1 h/day for seven days to aerosolized JP-8 jet fuel at concentrations of 1000 and 2500 mg/m3, simulating military occupational exposure. Lung cytosol samples were solubilized and separated via large scale, high resolution two-dimensional electrophoresis (2-DE) and gel patterns scanned, digitized and processed for statistical analysis. Significant quantitative and qualitative changes in tissue cytosol proteins resulted from jet fuel exposure. Several of the altered proteins were identified by peptide mass fingerprinting, confirmed by sequence tag analysis, and related to impaired protein synthetic machinery, toxic/metabolic stress and detoxification systems, ultrastructural damage, and functional responses to CO2 handling, acid-base homeostasis and fluid secretion. These results demonstrate a significant but comparatively moderate JP-8 effect on protein expression and corroborate previous morphological and biochemical evidence. Further molecular marker development and mechanistic inferences from these observations await proteomic analysis of whole tissue homogenates and other cell compartment, i.e., mitochondria, microsomes, and nuclei of lung and other targets.