Predicted chemical warfare agent VX toxicity to uniformed soldier using parathion in vitro human skin exposure and absorption

Dimethoate absorption: A complementary in vitro and in vivo assessment

This work attempts to evaluate dermal exposure (DE) of farm workers to dimethoate after 4 h of routine application to a lemon plantation. Dimethoate was measured on the workers' clothes as well as in stratum corneum (SC) and in saliva. In vitro permeation tests (IVPT) were performed through rat, pig and human skin and pig buccal, esophageal and sublingual mucosas. The mean of dimethoate DE was 342.19 ± 487.14 mg/d, the percentage of toxic dose per hour was higher than the other pesticides, and the SC penetration factors ranged between 0.5 and 14.81 and 0.05-53.96 % for back of neck and arms respectively. In the supporting IVPT study, dimethoate absorption through human skin was 14.75 % and the default value in the absence of experimental data for this product is 70%. These results show that in family farming the deficiency of correct clothing during the application of pesticides leaves workers more vulnerable.

Analysis of the absorption kinetics following dermal exposure to large doses of volatile organic compounds

A mathematical method was developed to study the skin penetration of volatile organic compounds (VOCs) after exposure to a high dose of the substance. While closed-form solutions exist to describe the diffusion and evaporation from small amounts, numerical approaches are often implemented to predict dermal transport involving large doses. This work offers a Laplace transform-based method to estimate the time constant and dynamic and steady-state behaviors. First, the process was divided into two stages, separated by the time it took for excess chemicals to be depleted from the skin surface. Series solutions were written for the percutaneous VOC concentration, absorption and evaporation in the first stage. Application of Laplace transform methods yielded transient profiles after the compound dissipated from the surface of the stratum corneum. In addition, the procedure facilitated the calculation of the time constant and steady-state values. The method was validated using benchtop and fume hood experiments conducted with N,N-diethyl-3-methylbenzamide (DEET) and air velocities of 0.165 m/s and 0.72 m/s, respectively. The increase in the flow rate decreased the total amount of VOC absorbed and reduced the period required for the surface fluid to disappear.

Regional variation in percutaneous absorption in in vitro human models: a systematic review

Percutaneous absorption is of importance given its role in topical medicaments, transdermal drug systems, and dermatotoxicology. Many factors influence percutaneous penetration, including anatomical region, although little is currently known regarding this parameter. Hence, the aim of this study was to summarize existing data on regional variation in percutaneous penetration in in vitro human models. PubMed, Embase, Web of Science, and US patent literature were explored, and relevant data collected. Eight eligible articles were identified, which together, explored 15 anatomical locations. Four investigations compared percutaneous penetration between scalp and abdominal skin, and all concluded that the former was more permeable. Within those four studies, 10 penetrants of varying physical/chemical properties were tested indicating that in those particular study conditions, anatomical location exerted a greater effect on percutaneous absorption than the physicochemical properties of the penetrants. In addition, torso area was less absorptive than scrotum in both studies in which these sites were compared. In conclusion, the scrotum and scalp appear to be highly susceptible to percutaneous absorption compared to other locations such as the abdomen. This is postulated to be largely due to the high density of hair follicles in these areas, enabling greater penetration via the appendageal pathway. However, there is a paucity of conclusive data regarding the penetrability of other anatomical locations. Investigations testing and ranking the susceptibility of different anatomical regions is of vital importance given the importance of (1) transdermal drug delivery and decontamination protocols and (2) understanding the underlying mechanisms and degree of these variances might aid our pharmacologic/toxicologic judgments.

Percutaneous absorption of chemicals from fabric (textile)

Percutaneous penetration of chemicals from clothing can result in both acute and chronic toxicities. Although personal protective equipment composed of nonwoven material can provide thorough protection, it is often uncomfortable under normal occupational conditions. Certain everyday textiles are often utilized as protective clothing due to their cost, comfort, and convenience. Although common textiles may cover most skin, certain regions remain exposed by such outfits. The body areas covered by the fabric are at risk for fabric permeation and percutaneous penetration of chemical, either immediately or over time, dependent on the fabric composition and the characteristics of the chemical used. in vitro and in vivo publications studied percutaneous penetration of chemicals from contaminated fabric and show that everyday textiles are superior to bare skin. The increased protection offered can be attributed to properties of the fabric such as weave, thickness, fabric finish, absorbency, and the overall barrier provided. Although common textiles do offer some protection, they remain inferior to nonwoven personal protective equipment. Much remains unknown regarding percutaneous penetration and protection offered by everyday textiles.

Developing Health-Based Pre-Planning Clearance Goals for Airport Remediation Following a Chemical Terrorist Attack: Decision Criteria for Multipathway Exposure Routes

In the event of a chemical terrorist attack on a transportation hub, post-event remediation and restoration activities necessary to attain unrestricted facility re-use and re-entry could require hours to multiple days. While timeframes are dependent on numerous variables, a primary controlling factor is the level of pre-planning and decision-making completed prior to chemical release. What follows is the second of a two-part analysis identifying key considerations, critical information and decision criteria to facilitate post-attack and post-decontamination consequence management activities. Decision criteria analysis presented here provides first-time, open-literature documentation of multi-pathway, health-based remediation exposure guidelines for selected toxic industrial compounds, chemical warfare agents, and agent degradation products for pre-planning application in anticipation of a chemical terrorist attack. Guideline values are provided for inhalation and direct ocular vapor exposure routes as well as percutaneous vapor, surface contact, and ingestion. Target populations include various employees as well as transit passengers. This work has been performed as a national case study conducted in partnership with the Los Angeles International Airport and The Bradley International Terminal. All recommended guidelines have been selected for consistency with airport scenario release parameters of a one-time, short-duration, finite airborne release from a single source followed by compound-specific decontamination.

Toward a better understanding of pesticide dermal absorption: diffusion model analysis of parathion absorption in vitro and in vivo

Human skin absorption of radiolabeled parathion was studied in vitro at specific doses (mass loadings) of 0.4, 4.0, 41, or 117 microg/cm(2), with and without occlusion. The compound was applied in small volumes of acetone solution to split-thickness skin. Permeation of radiolabel into the receptor solutions was monitored for 76 h, after which the tissue was dissected and analyzed for residual radioactivity. For the 3 lower doses, cumulative permeation after 76 h was approximately dose-proportional, ranging from 28.5-30.5% of applied dose (unoccluded) to 45.5-55.7% (occluded). Total absorption, calculated as receptor fluid plus dermis content, followed a similar pattern. Both permeation rate and total absorption continued to increase up to the highest dose tested, consistent with results from other laboratories. These results are compared with predictions from a previously developed skin diffusion model (Kasting et al., 2008a). The model predicted total absorption to within a factor of 1.4 at 0.4 microg/cm(2) and 1.6 at 4 microg/cm(2), but substantially underpredicted absorption at the 2 higher doses. The analysis showed that parathion partitioned more favorably into the stratum corneum than the diffusion model prediction. Nevertheless, comparison of the model predictions to a previously reported human study showed that the skin absorption model, when corrected for surface losses occurring in vivo, satisfactorily described in vivo dermal absorption of parathion applied at 4 microg/cm(2) to various body sites.

Percutaneous penetration and distribution of VX using in vitro pig or human excised skin validation of demeton-S-methyl as adequate simulant for VX skin permeation investigations

The organophosphorus (OP) chemical warfare V agent O-ethyl-S-[2(di-isopropylamino)ethyl] methyl phosphonothioate (VX), is a highly toxic compound which mainly penetrates the body via percutaneous pathways. Hence, the following prerequisite: to ascertain compound absorption and percutaneous profile distribution with a view to further assessing the efficacy of topical skin protectants. We first selected the most appropriate receptor fluid to carry out in vitro VX absorption experiments, namely: Hanks's Balanced Salt Solution (HBSS). After a 24-h topical exposure time lapse, we measured altogether the percentage of applied dose unabsorbed and absorbed, penetration rate, lag time, permeability coefficient (K(p)), and dose of VXeq present in skin. To such an end, we used full-thickness and split-thickness pig-ear or human abdominal skin membranes. Further, we scrutinised the potential use of two specific molecules as suitable surrogates for VX percutaneous penetration analyses: thus, we compared the present VX toxicokinetic parameters to earlier findings from our research unit, with respect to OP insecticides demethon-S-methyl (DSM) and paraoxon (POX). Within the framework of our study, we wish to highlight the following evidence: (a) pig-ear skin proves a relevant model to predict in vitro human abdominal skin, taking into account a 2-fold higher skin permeability to VXeq; (b) both full or split-thickness skin membranes may be used indiscriminately to gauge penetration rate and absorbed dose; (c) DSM applied on full-thickness pig-ear skin is the most relevant model to mimic the in vitro VX absorption through full-thickness skin model.

In vitro percutaneous penetration of organophosphorus compounds using full-thickness and split-thickness pig and human skin

Organophosphorus compounds (OPs), such as pesticides and chemical warfare agents like sarin (GB), soman (GD) and VX, are highly toxic compounds. The OP vapours and their liquid forms are readily absorbed through the skin, therefore, protecting the skin of people who are potentially exposed to these agents is crucial. The development of effective countermeasures relies on a better knowledge of the percutaneous penetration of such molecules. The purpose of this present study is to determine the in vitro percutaneous penetration parameters of two pesticides DSM and DFP, as potential simulants of V and G agents, respectively, using four in vitro systems: full-thickness and split-thickness human abdominal and pig-ear skin membranes mounted on static diffusion cells. Based on the toxicokinetic parameters of the percutaneous penetration of DSM and DFP, we demonstrated that (a) pig-ear skin is a relevant model to predict the in vitro human skin permeability taking into account a 2-fold difference between these two species (b) both full and split-thickness skin membranes could be used indiscriminately, (c) DSM and DFP would be appropriate surrogates for V and G agents to perform skin permeation studies.

In vitro dermal absorption of methyl salicylate, ethyl parathion, and malathion: first responder safety

In vitro tests with fresh dermatomed (0.3 to 0.4 mm thick) female breast skin and one leg skin specimen were conducted in Bronaugh flow-through Teflon diffusion cells with three chemicals used to simulate chemical warfare agents: 14C-radiolabeled methyl salicylate (MES), ethyl parathion (PT), and malathion (MT), at three dose levels (2, 20, and 200 mM). Tests were conducted at a skin temperature of 29 degrees C using a brief 30-min exposure to the chemical and a 6.5-h receivor collection period. Rapid absorption of all three chemicals was observed, with MES absorbed about 10-fold faster than PT and MT. For MES, PT, and MT, respectively, there was 32%, 7%, and 12% absorption into the receivor solution (Hank's HEPES buffered saline with 4% bovine serum albumin [BSA], pH 7.4) at the low dose (2 mM), 17%, 2%, and 3% at the medium dose (20 mM), and 11%, 1%, and 1% at the high dose (200 mM) levels. Including the skin depot for MES, PT, and MT, respectively, there was 40%, 41%, and 21% (low dose), 26%, 16%, and 8% (medium dose), and 13%, 19%, and 10% (high does) absorption. Efficacy of skin soap washing conducted at the 30 min exposure time ranged from 31% to 86%, varying by chemical and dose level. Skin depot levels were highest for the relatively lipophilic PT. "Pseudo" skin permeability coefficient (K(p)) data declined with dose level, suggesting skin saturation had occurred. An in-depth comparison with literature data was conducted and risk assessment of first responder exposure was briefly considered.

Acute lung injury following inhalation exposure to nerve agent VX in guinea pigs

A microinstillation technique of inhalation exposure was utilized to assess lung injury following chemical warfare nerve agent VX [methylphosphonothioic acid S-(2-[bis(1-methylethyl)amino]ethyl) O-ethyl ester] exposure in guinea pigs. Animals were anesthetized using Telazol-meditomidine, gently intubated, and VX was aerosolized using a microcatheter placed 2 cm above the bifurcation of the trachea. Different doses (50.4 microg/m3, 70.4 micro g/m(m3), 90.4 microg/m(m3)) of VX were administered at 40 pulses/min for 5 min. Dosing of VX was calculated by the volume of aerosol produced per 200 pulses and diluting the agent accordingly. Although the survival rate of animals exposed to different doses of VX was similar to the controls, nearly a 20% weight reduction was observed in exposed animals. After 24 h of recovery, the animals were euthanized and bronchoalveolar lavage (BAL) was performed with oxygen free saline. BAL was centrifuged and separated into BAL fluid (BALF) and BAL cells (BALC) and analyzed for indication of lung injury. The edema by dry/wet weight ratio of the accessory lobe increased 11% in VX-treated animals. BAL cell number was increased in VX-treated animals compared to controls, independent of dosage. Trypan blue viability assay indicated an increase in BAL cell death in 70.4 microg/m(m3) and 90.4 microg/m(m3) VX-exposed animals. Differential cell counting of BALC indicated a decrease in macrophage/monocytes in VX-exposed animals. The total amount of BAL protein increased gradually with the exposed dose of VX and was highest in animals exposed to 90.4 microg/m(m3), indicating that this dose of VX caused lung injury that persisted at 24 h. In addition, histopathology results also suggest that inhalation exposure to VX induces acute lung injury.

Molecular size as the main determinant of solute maximum flux across the skin

One of the most important determinants of dermatological and systemic penetration after topical application is the delivery or flux of solutes into or through the skin. The maximum dose of solute able to be delivered over a given period of time and area of application is defined by its maximum flux (J(max), mol per cm(2) per h) from a given vehicle. In this work, J(max) values from aqueous solution across human skin were acquired or estimated from experimental data and correlated with solute physicochemical properties. Whereas epidermal permeability coefficients (k(p)) are optimally correlated to solute octanol-water partition coefficient (K(ow)) and molecular weight (MW) was found to be the dominant determinant of J(max) for this literature data set: log J(max)=-3.90-0.0190MW (n=87, r(2)=0.847, p<0.001). Estimated solubility in octanol (S(oc)) was also a determinant, but improvement in the regression by the addition of log S(oc) was small (r(2) increased to 0.856). Addition of other physicochemical parameters to MW by forward stepwise regression only marginally improved the regression with a melting point (Mpt) term (r(2)=0.879) and then hydrogen bonding acceptor capability (H(a)) (r(2)=0.917) is significant. Validation of the equation above was carried with a number of other data sets: an aqueous vehicle with full- and split-thickness skin (r(2)=0.784, n=56), some pure solutes (r(2)=0.537, n=34), an aqueous vehicle with ionizable solutes (r(2)=0.282, n=54) and solutes from a propylene glycol vehicle (r(2)=0.484, n=36). An analysis of the entire database gave the equation log J(max)=-4.52-0.0141MW (n=278, r(2)=0.688, p<0.001), with inclusion of Mpt and H(a) increasing r(2) to 0.760 (n=269). Separate analysis of full- and split-thickness skin data confirmed that the dermal resistance term had only a marginal effect on overall J(max). Application of the latter model to an in vivo situation where the dermal capillary bed is slightly below the epidermal-dermal junction revealed that the dermal resistance term was unnecessary for in vivo predictions for most solutes.