Dusts dermal absorption

Indirect evidence indicates that dermal absorption occurs in animals. Calves dusted with a 4% dust formulation of endosulfan had neurological symptoms (tremors, twitching, convulsions) and died within a day after exposure (Nicholson and Cooper 1977). Neurological effects have also been reported in preclipped rabbits and rats after repeated application of endosulfan to the skin (Dikshith et al. 1988 Gupta and Chandra 1975). Dikshith et al. (1988) reported levels of a-, [3-, and total endosulfan in liver, kidney, brain, testes, fatty tissue, and blood 30 days after dermal application of endosulfan. 

Airborne dusts settle onto food, water, clothing, and other objects, and may subsequently be transferred to the mouth. A more recent study suggests that lead, applied to the skin as lead acetate or lead nitrate, was rapidly absorbed through the skin and was detected in sweat, blood, and urine within 6 hours of application (Stauber et al. 1994). In this study, 4.4. mg of lead was applied to the skin under a covered wax/plastic patch on the forearms of human subjects of the applied dose, 1.3 mg of lead was not recovered from skin washings. The amount that actually remained in (or on) the skin and the mass balance of the fate of this lead was not determined it may have been dermally absorbed or eliminated from the skin by exfoliation of epidermal cells. Thus, while this study provides evidence for dermal absorption of lead, it did not quantify the fraction of applied dose that was absorbed. The quantitative significance of the dermal absorption pathway as a contributor to lead body burden remains uncertain. 

Despite wearing protective equipment that included disposable overalls and compressed-air-fed visors or full-facepiece masks with filters for dusts and vapors, hexachloroethane was detected in the plasma of exposed workers (Selden et al. 1993). After 5 weeks of exposure, plasma levels of hexachloroethane in 12 workers were 7.3 + 6 pg/L. Mild dermal irritation was also noted. If the skin irritation was a response to hexachloroethane rather than trauma from the protective clothing, the irritation suggests that the principal exposure route may have been dermal. Absorption of a saturated hexachloroethane solution across human skin was estimated to be 0.0230 mg/cm2/hour based on the physical properties of hexachloroethane (Fiserova-Bergerova et al. 1990). 

Human exposure to endrin may occur by ingestion, inhalation, or by dermal contact. Dermal absorption can be significant. Gastrointestinal absorption is enhanced by dietary fats. While not highly volatile, endrin-laden aerosols or dust particles can be trapped in respiratory mucus and swallowed, leading to gastrointestinal absorption. 

Workers exposed to RDX in an explosives plant complained of nausea and exhibited vomiting, epileptiform seizures, and unconsciousness, which lasted a few minutes to 24 hours with periods of stupor, nausea, vomiting, and weakness. Recovery was complete with no sequelae. In a more recent case, a worker, handling cyclonite without adequate protection, experienced malaise with dizziness, headache, and nausea that progressed to unconsciousness and generalized seizures. The role of dermal absorption was unclear because of concomitant exposure to the dust. 

Route of exposure is defined as the portal of entry to the body. Pathway is defined as the course that the contaminant takes from its source to the exposure medium, and then to the portal of entry. For a given source, exposure media and exposure routes can define the pathways. Depending upon the life stage of the child, exposure media can include amniotic fluid, breast milk, air, water, soil/dust/ sediments, food, and objects/surfaces. Exposure routes include transplacental transfer, inhalation, ingestion, dermal absorption, and indirect (non-dietary) ingestion. 

The probable route of exposure for these women was inhalation of tetryl-laden dusts. It is not clear that exposure to tetryl caused these irregularities. No other information for humans or animals was available. In order to assure that humans living near tetryl-containing hazardous waste sites are not adversely affected by this substance, oral animal reproductivity studies would need to be performed, since the most likely route of exposure for humans is through contaminated drinking water. Dermal studies may be useful if dermal absorption is found to be significant. 

Ingestion and inhalation are the primary routes of exposure. Boron can be found in dusts, water, and in fruits and vegetables. Dermal absorption will not be a factor unless the dermal barrier is compromised. 

Dermal absorption and inhalation of dusts are the common routes of exposure for tetrachlorvinphos. 

Occupational studies indicate that humans absorb elemental selenium dusts and other selenium compounds, but quantitative inhalation toxicokinetic studies in humans have not been done. Studies in dogs and rats indicate that following inhalation exposure, the rate and extent of absorption vary with the chemical form of selenium. Studies in humans and experimental animals indicate that, when ingested, several selenium compounds including selenite, selenate, and selenomethionine are readily absorbed, often to greater than 80% of the administered dose. Although a study of humans did not detect evidence of dermal absorption of selenomethionine, one study of mice indicates selenomethionine can be absorbed dermally. There is little or no information available on the absorption of selenium sulfides, but selenium disulfides are not believed to be absorbed through intact skin. 

A baseline risk assessment is conducted to assess the potential human health and environmental impacts associated with soil contamination. The primary exposure pathways evaluated for explosives contaminated surface soils are dust inhalation, soil ingestion, and dermal absorption. Reasonable Maximum Exposure (RME) concentrations are based on the 95% upper confidence interval (UCI) on the arithmetic mean of soil sampling data. The land use scenarios quantitatively evaluated may include industrial and residential use, utilizing EPA standard default exposure parameters. 

DU has the greatest potential to cause health effects when it enters the body by injection of fragments through wounds, inhalation of dust, ingestion of particles directly or in contaminated food, soil and water, wonnd contamination by DU dust and dermal absorption through external exposure to DU metal. Inhalation or ingestion of some uranium leads to internal contamination, which could result in radiation doses to the body. 

House dust contributes an average of 82 % of an adult U.S. resident s exposure to PBDEs (Lorber 2008). Although diet may also contribute to PBDE exposure (Wu et al. 2007), dust is a direct exposure pathway through incidental ingestion, inhalation of suspended particles, and dermal absorption, and it is a proxy for exposure from product use (Dodson et al. 2012 Webster et al. 2013). PBDE residues on hands were found to be strong predictors of serum levels in both children (Stapleton et al. 2012) and adults (Watkins et al. 2011), underlining the... 

Dermal Exposure Of the three major routes of exposure, the dermal (skin) route constitutes nearly 90% of chemical exposure, particularly of pesticides. Dermal exposure is common whenever chemicals are mixed or handled. Certain types of dry materials, (e.g., pesticide dusts, wet or dry powders, granules, liquid pesticides) enter the body through quick skin absorption. Many factors influence the rate of dermal exposure of a chemical these may be as follows ... 

Workers exposed to tetryl dusts, primarily by the inhalation and dermal routes, occasionally complained of systemic effects such as nausea, vomiting, and headaches, indicating possible absorption through the skin (Cripps 1917 Hardy and Maloof 1950 Hilton and Swanston 1941 Ruxton 1917 Troup 1946 Wtkowski et al. 1942). No information is available on rates or extent of exposure. No animal data are available. 

No quantitative data were located regarding absorption in humans after inhalation exposure to DNPs. A metabolite of 2,4-DNP, 2-amino-4-nitrophenol, was commonly detected by the Derrien test in the urine of workmen (women were generally not employed in dangerous processes) exposed via inhalation to vapor and airborne dust of 2,4-DNP and by direct contact of the skin with the solid chemical in the munitions industry in France (Perkins 1919). Exposure may have occurred by the dermal and possibly oral routes, as well as by inhalation. In addition, examination of the blood, unspecified organs, and urine of workmen in this industry who died from exposure to 2,4-DNP revealed the presence of 2,4-DNP and its metabolites quantitative data were not provided (Perkins 1919). Despite its limitations, the study provides some evidence of absorption from inhalation exposure. 

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