Assessment of the Dermal Bioavailability of Soil-Aged Benzo(a)pyrene

Exposure to polycyclic aromatic hydrocarbons (PAHs) in soil is a major health concern because of their mutagenic and carcinogenic properties. The aim of this research was to determine the dermal bioavailability of benzo(a)pyrene (BaP) aged in either a sandy or a clay soil in order to assess the health risks and remediation goals for the chemical. In vitro flow-through diffusion cell studies were conducted utilizing dermatomed male pig skin. The amount of radioactive chemical was measured that penetrated skin into receptor fluid and which was bound to skin following soap and water decontamination. BaP bioavailability was decreased by 95 to 98% after 3 months of aging in soil relative to the pure compound. Less than 0.3% of the dose was detected in receptor fluid for all treatments. While most of the dose was bound to skin after administering the pure compound, the majority of the radioactivity was found in the soil and decontaminate after aging. The results indicate that the health risk from exposure to BaP is significantly reduced as the compound ages in soil and that less soil cleanup would be needed at sites contaminated with aged BaP.     

Impact of Aging Time on the Dermal Penetration of Phenol in Soil

Phenol is released to soil through accidental spills, manufacturing processes, and waste disposal. With time, chemicals can become more sequestered in soil (aging). Since skin is the body's primary route of entry for phenol, the impact of aging time on the dermal penetration of phenol was assessed in Atsion and Keyport soils. In vitro studies were conducted on dermatomed male pig skin using a flow-through diffusion cell methodology and radiolabeled phenol. After 3 and 6 months of aging in the Atsion soil, dermal penetration decreased from 84% of the initial dose for pure phenol (without soil) to 15% and 8%, respectively, while the dermal penetration of phenol aged in the Keyport soil was reduced to 22% and 17%, respectively. Atsion soil has a higher organic matter content (4.4%) than Keyport soil (1.6%) suggesting that the lower bioavailability of phenol aged in the Atsion soil may be due to the amount of organic matter in that soil. Although the data indicate that the potential health risk from dermal exposure to phenol would be lower after aging in soil than to pure chemical, further experiments are warranted at lower soil loads and with additional concentrations of phenol to quantify the risk.     

In Vitro Penetration of Pig Skin by Heavy Metals in Soil

The potential health risk from exposure to heavy metal contaminated soil is often based on the quantity of metal that can be removed from soil by vigorous extraction procedures. This approach can overestimate risk since it ignores complex interactions between metals and soil that can result in a reduction in the amount of metal that desorbs from soil and is subsequently absorbed by the body. The aim of this research was to determine the relative contribution of the soil matrix and heavy metal sequestration in soil with time (“aging”) on the dermal penetration of arsenic, mercury, and nickel, respectively, as arsenic acid, mercuric chloride, and nickel chloride. In vitro flow-through diffusion cell studies were performed utilizing dermatomed male pig skin and radioactive compounds to measure total penetration (the sum of each metal in receptor fluid and skin). For arsenic and nickel, the soil matrix produced a 78–87% reduction in dermal penetration compared to 12–19% after aging. A greater effect was observed with aged mercury (52–56% decrease in dermal penetration) than in freshly spiked soil (40–43%). The results indicate that the potential health risk from dermal exposure to the metals can be significantly reduced by soil and aging.     

Development of a Biokinetic Model to Evaluate Dermal Absorption of Polycyclic Aromatic Hydrocarbons from Soil

The high carcinogenic potency of polycyclic aromatic compounds often results in the dermal pathway indicating significant risk to human health at sites with contaminated soils, resulting in the establishment of conservative, risk-based remediation goals. The sorptive properties of soil sequester chemical contaminants, making them less available for uptake by receptors. Recent studies of desorption from soil indicate that PAHs follow a nonlinear desorption pattern that can be estimated by two phases: a rapid, followed by a slow, desorbing fraction. In this work, we adapt a fugacity-based model to evaluate the availability of polycyclic aromatic hydrocarbons (PAHs) from soil to human skin. Incorporating two-site desorption kinetics into the fugacity model renders a less available fraction of chemical in soil for absorption, decreasing predicted dermal uptake. We explore the impacts to dermal bioavailability of removing the “fast-desorbing” fraction of chemical from the soil. The model predicts uptake within a factor of two when compared with experimental data on dermal uptake. Soil moisture and soil loading rates emerge as potential limiting variables; however, the model is most sensitive to the size of the fast desorbing fraction of chemical in soil     

Age-related disruption of autophagy in dermal fibroblasts modulates extracellular matrix components

Autophagy is an intracellular degradative system that is believed to be involved in the aging process. The contribution of autophagy to age-related changes in the human skin is unclear. In this study, we examined the relationship between autophagy and skin aging. Transmission electron microscopy and immunofluorescence microscopy analyses of skin tissue and cultured dermal fibroblasts derived from women of different ages revealed an increase in the number of nascent double-membrane autophagosomes with age. Western blot analysis showed that the amount of LC3-II, a form associated with autophagic vacuolar membranes, was significantly increased in aged dermal fibroblasts compared with that in young dermal fibroblasts. Aged dermal fibroblasts were minimally affected by inhibition of autophagic activity. Although lipofuscin autofluorescence was elevated in aged dermal fibroblasts, the expression of Beclin-1 and Atg5—genes essential for autophagosome formation—was similar between young and aged dermal fibroblasts, suggesting that the increase of autophagosomes in aged dermal fibroblasts was due to impaired autophagic flux rather than an increase in autophagosome formation. Treatment of young dermal fibroblasts with lysosomal protease inhibitors, which mimic the condition of aged dermal fibroblasts with reduced autophagic activity, altered the fibroblast content of type I procollagen, hyaluronan and elastin, and caused a breakdown of collagen fibrils. Collectively, these findings suggest that the autophagy pathway is impaired in aged dermal fibroblasts, which leads to deterioration of dermal integrity and skin fragility.     

Bioavailability of Soil-Borne Chemicals: Abiotic Assessment Tools

The abiotic tools that are available, or under development, for evaluating the oral and dermal bioavailability of contaminants from soils are described in this article. These tools generally rely on one of two approaches: (1) characterizing the form of the contaminant and the chemical binding of the contaminant to the soil matrix, and (2) chemical extractions intended to evaluate the fraction of the chemical that would be liberated in biological fluids (gastrointestinal fluid or sweat). For the purpose of human health risk assessment, abiotic methods to estimate the bioavailability of inorganic contaminants in soil are considered generally to be “screening” level tools at this time. Development work for physiologically based extraction tests (PBETs) is ongoing for many inorganic contaminants, and these methods hold great promise for eventual use in making quantitative bioavailability adjustments in risk assessment. The availability of abiotic tools to evaluate the bioavailability of organic contaminants from soils lags behind that for metals, due to the difficulty in conducting in vivo bioavailability studies with organic compounds and their complex interactions with soil. However, considerable research is being conducted in this field, and new assessment tools are being validated for use in human health risk assessment.     

A Tiered Approach for Assessing Dermal Exposure to Constituents in Latex Paint

Latex paint is commonly used by professional and consumer painters. Potential inhalation exposure to chemical vapors from paint has been studied extensively. Potential dermal exposure is not as well studied and existing exposure evaluation methods assume the paint remains wet for the duration of skin contact. However, latex paint may dry quickly and this limits the bioavailability of paint constituents due to the decreased diffusion through a dry film. This study presents a tiered in silico (i.e., computer modeling) approach to evaluate potential dermal exposure to nonvolatile substances using a technique that begins with exposure to a wet paint film and transitions to a dry film. Experiments were performed to help quantify a key parameter, latex paint drying time, and the experimental results were used in a case study to demonstrate the tiered approach. The predicted dermal penetration ranged from 100% of the applied substance for a simple conservative approach to 5% of the applied substance for the refined wet/dry film approach. Assuming the paint film was partially wiped further reduced the predicted penetration to 2%. This study addresses only latex paint but the tiered approach could be modified to evaluate other products.     

In vitro 3-D model based on extending time of culture for studying chronological epidermis aging

Skin aging is a complex phenomenon in which several mechanisms operate simultaneously. Among them, intrinsic aging is a time-dependent process, which leads to gradual skin changes affecting its structure and function such as thinning down of both epidermal and dermal compartments and a flattening and fragility of the dermo-epidermal junction. Today, several approaches have been proposed for the generation of aged skin in vitro, including skin explants from aged donors and three-dimensional skin equivalent treated by aging-inducing chemical compounds or engineered with human cells isolated from aged donors.The aim of this study was to develop and validate a new in vitro model of aging based on skin equivalent demonstrating the same phenotypic changes that were observed in chronological aging.By using prolonged culture as a proxy for cellular aging, we extended to 120 days the culture time of a skin equivalent model based on collagen–glycosaminoglycan–chitosan porous polymer and engineered with human skin cells from photo-protected sites of young donors. Morphological, immunohistological and ultrastructural analysis at different time points of the culture allowed characterizing the phenotypic changes observed in our model in comparison to samples of non photo-exposed normal human skin from different ages.We firstly confirmed that long-term cultured skin equivalents are still morphologically consistent and functionally active even after 120 days of culture. However, similar to in vivo chronological skin aging a significant decrease of the epidermis thickness as well as the number of keratinocyte expressing proliferation marker Ki67 are observed in extended culture time skin equivalent. Epidermal differentiation markers loricrin, filaggrin, involucrin and transglutaminase, also strongly decreased. Ultrastructural analysis of basement membrane showed typical features of aged skin such as duplication of lamina densa and alterations of hemidesmosomes. Moreover, the expression of hyaluronan and its surface receptor CD44 drastically decreased as observed during chronological skin aging. Finally, we found that the level of p16INK4A expression significantly increased supporting cellular senescence process associated to our model.To conclude, the major morphological and ultrastructural epidermal modifications observed in both our extended culture skin equivalent model and skin biopsies from old donors validate the relevance of our model for studying chronological aging, understanding and elucidating age-related modifications of basic skin biological processes. In addition, our model provides a unique tool for identifying new targeted molecules intended at improving the appearance of aging skin.     

A review of the bioavailability of petroleum constituents

Exposure to petroleum constituents at contaminated sites may occur through a variety of pathways, including inhalation of vapors and particulates, ingestion of water and soils, and dermal contact with water and soils. Accurately assessing the human health risks from such exposures requires information on the medium‐ and route‐specific bioavailability of petroleum constituents (e.g., how well these chemicals enter the body via the gastrointestinal tract and skin). For example, when the medium or exposure route in an animal toxicity assay (e.g., ingestion of water) differs from the actual route of human exposure at the petroleum contaminated site (e.g., dermal contact with soil), adjustments should be made that reflect the relative bioavailability of the chemical in the different media. The focus of this article is on (1) the availability of oral and dermal absorption data for one PAH (benzo[a]pyrene, (B[a]P) and three VOCs in soil (benzene, toluene, and xylene); (2) factors affecting the uptake of these PAHs and VOCs from soil; and (3) ways to incorporate bioavailability data into human health risk assessments. Based on our review, we recommend the following default values for the oral and dermal absorption of B[a]P, benzene, toluene, and xylene from soil:

A review of the bioavailability of petroleum constituents

All authors

Jennifer Bramard & Barbara D. Beck

https://doi.org/10.1080/15320389209383417

Published online:

02 December 2008

Display Table

Site‐specific information such as chemical concentrations in soil, soil characteristics, soil loadings on the skin, contact site, and contact time could result in modifications of these numbers. As shown, our default absorption values are generally less than those recommended by the U.S. EPA (1991a,b,c). The implications of these estimates of bioavailability for risk assessment and for the selection of soil cleanup levels at petroleum‐contaminated sites are discussed.     

Epidermal stem cells are retained in vivo throughout skin aging

In healthy individuals, skin integrity is maintained by epidermal stem cells which self-renew and generate daughter cells that undergo terminal differentiation. It is currently unknown whether epidermal stem cells influence or are affected by skin aging. We therefore compared young and aged skin stem cell abundance, organization, and proliferation. We discovered that despite age-associated differences in epidermal proliferation, dermal thickness, follicle patterning, and immune cell abundance, epidermal stem cells were maintained at normal levels throughout life. These findings, coupled with observed dermal gene expression changes, suggest that epidermal stem cells themselves are intrinsically aging resistant and that local environmental or systemic factors modulate skin aging.     

Mass transfer and hydrocarbon biodegradation of aged soil in slurry phase

Addition of toluene into slurry phase laboratory microcosm is proposed in order to increase desorption rate of hydrocarbons and as an alternative to improve bioavailability of hydrocarbon in aged soils. Our studies showed that toluene has a positive effect on desorption of total petroleum hydrocarbons (TPH). Addition of 14,000 mg toluene/kg of soil, in highly polluted soil, increased the consumption rate of hydrocarbons three times in comparison to control without solvent. In 30 days the initial TPH concentration in soil, 292,000 mg/kg, diminished 45%. Although toluene was able to dissolve complex organic compounds such as asphaltene fraction, it probably yielded a highly toxic toluene-hydrocarbons phase. The inhibitory effect of toluene-TPH was also studied. A substrate inhibition model was used: the k(m) and k(i) constants were 57 and 490 mg TPH/L liquid phase, respectively. Experimental data were well described when the proposed model included sequential desorption and biodegradation phenomena. Damk?hler number evaluation showed that rate of mass transfer was the limiting step in overall biodegradation in nonsolvent control. When high concentration of toluene was added, then bioreaction was the limiting step, but inhibitory effect should be considered. However, toluene addition at low concentrations facilitates the biodegradation of aromatic compounds.     

Age-associated reduction of cell spreading induces mitochondrial DNA common deletion by oxidative stress in human skin dermal fibroblasts: implication for human skin connective tissue aging

Background

Reduced cell spreading is a prominent feature of aged dermal fibroblasts in human skin in vivo. Mitochondrial DNA (mtDNA) common deletion has been reported to play a role in the human aging process, however the relationship between age-related reduced cell spreading and mtDNA common deletion has not yet been reported.

Results

To examine mtDNA common deletion in the dermis of aged human skin, the epidermis was removed from full-thickness human skin samples using cryostat. mtDNA common deletion was significantly elevated in the dermis of both naturally aged and photoaged human skin in vivo. To examine the relationship between age-related reduced cell spreading and mtDNA common deletion, we modulated the shape of dermal fibroblasts by disrupting the actin cytoskeleton. Reduced cell spreading was associated with a higher level of mtDNA common deletion and was also accompanied by elevated levels of endogenous reactive oxygen species (ROS). Boosting cellular antioxidant capacity by using antioxidants was found to be protective against mtDNA common deletion associated with reduced cell spreading.

Conclusion

mtDNA common deletion is highly prevalent in the dermis of both naturally aged and photoaged human skin in vivo. mtDNA common deletion in response to reduced cell spreading is mediated, at least in part, by elevated oxidative stress in human dermal fibroblasts. These data extend current understanding of the mitochondrial theory of aging by identifying the connection between mtDNA common deletion and age-related reduction of cell spreading.     

Extracellular matrix regulation of fibroblast function: redefining our perspective on skin aging

The dermal extracellular matrix (ECM) comprises the bulk of skin and confers strength and resiliency. In young skin, fibroblasts produce and adhere to the dermal ECM, which is composed primarily of type I collagen fibrils. Adherence allows fibroblasts to spread and exert mechanical force on the surrounding ECM. In this state, fibroblasts display a “youthful” phenotype characterized by maintenance of the composition and structural organization of the dermal ECM. During aging, fibroblast-ECM interactions become disrupted due to fragmentation of collagen fibrils. This disruption causes loss of fibroblast spreading and mechanical force, which inextricably lead to an “aged” phenotype; fibroblasts synthesize less ECM proteins and more matrix-degrading metalloproteinases. This imbalance of ECM homeostasis further drives collagen fibril fragmentation in a self-perpetuating cycle. This article summarizes age-related changes in the dermal ECM and the mechanisms by which these changes alter the interplay between fibroblasts and their extracellular matrix microenvironment that drive the aging process in human skin.     

辽西水土保持林土壤改良效应的研究

通过分析比较油松纯林和油松-固N树种混交杯土壤的理化性质和油松生长量,结果表明,油松-固N树种混交杯土壤有机质含量、全N、全P、速效P和水解N含量都比油松纯林显著提高,土壤容重减小,硬度降低,初渗速度增大．油松胸径和树高生长量也有较明显提高,对土壤的改良作用比油松纯林效果更加显著．通过土壤酶活性和固N树种固N活性的测定,对不同水土保持林的土壤肥力状况作出了综合评价。     

Bioavailability of 2, 4, 6-Trinitrotoluene (TNT) to Earthworms in Three Different Types of Soils in China

To study the effects of aging time (the length of time when contaminants are sequestered in soil) and soil properties on TNT bioavailability in soil, earthworms (Eisenia fetida) were exposed to three types of soils (fluvo-aquic soil, loessal soil, and black soil) contaminated by TNT for 7, 14, 21, 28, 35, and 42 days. The Earthworm-Soil Accumulation Factor (ESAF) of TNT and soil properties were analyzed. The ESAFs in black soil were significantly lower than those in fluvo-aquic soil and loessal soil (P < 0.05). In loessal soils, the ESAF increased with aging time, while that in black soils decreased. The ESAF of TNT had a significantly negative correlation with soil organic matter content, clay contents, and cation exchange capacity, which were the main factors affecting the TNT bioavailability in soils (P < 0.01). There was more quartz and feldspar in black soil, as well as more particles and micropores on the surface, which resulted in the easy adsorption and lower bioavailability of TNT. In conclusion, TNT bioavailability in soils is affected by aging time, soil physical and chemical properties, and mineral and surface properties, which must be considered when biotreatment for TNT in soils is applied.     

Assessment of Potential Human Health Risks from Arsenic in CCA-Treated Wood

Chromated copper arsenate (CCA) is a chemical preservative used to treat wood for a variety of outdoor uses, including decks, fencing, and play structures. This article describes a methodology to quantify exposures to arsenic from CCA-treated wood. Exposure was evaluated for ingestion and dermal contact with arsenic-containing residue on treated wood surfaces (dislodgeable arsenic), and ingestion, dermal contact, and inhalation of soil containing arsenic originating from treated wood structures. Standard approaches were used to quantify exposures to arsenic in soil. In the absence of standard approaches for exposures to dislodgeable residue, an empirical approach was developed, extrapolating from studies of soil loadings on hands and soil ingestion rates to estimate the amount of dislodgeable residue on hands that is subsequently ingested. Results from animal studies were used to develop relative bioavailability estimates for dislodgeable and soil arsenic. A focused sensitivity analysis demonstrated that the assumptions used regarding hand loading and subsequent incidental ingestion of dislodgeable arsenic had the most significant impact on the results. This assessment indicates low uptake of arsenic into the body, resulting in incremental lifetime cancer risks within USEPA's target risk levels. We compare this approach to other methodologies used to assess exposures to treated wood.     

Estimation of bioavailability and potential risks of naphthalene in soils with solid phase microextraction

A series of batch experiments were conducted to observe the variations of bioavailability of naphthalene in different types of soil with indigenous microorganisms. Solid phase microextraction (SPME) was employed to estimate the bioavailability of naphthalene in the soils. Various soil properties were attained by artificially modifying soil organic matter (SOM) with the addition of bagasse compost and textures with the addition of original silt and clay to determine the correlation between the amount of biodegraded naphthalene after 300 h and the amount of extractable naphthalene by SPME. Experimental results indicated that the biodegradation rate increased from 0.30 (sandy loam) to 0.48 (silty loam) μg g⁻¹ h⁻¹ when soils had more silt/clay. In contrast, the biodegradation rate slightly decreased from 0.30 (1.3% SOM) to 0.20 (5.2% SOM) μg g⁻¹ h⁻¹ when the SOM was high. Distributions of naphthalene in soils after biodegradation were affected by the addition of bagasse compost. It showed that the bioavailability of naphthalene in soils decreased with an increase in SOM. Sequestration as measured by ultrasonic extractability evidently occurred within 4 months in aged soil samples. However, the amounts extracted by sonication after 4 and 16 months of aging did not statistically differ from each other. The SPME measurements correlated well with the amount of biodegraded naphthalene by indigenous microorganisms. Results of this study demonstrate that SPME is a promising method to estimate the bioremediation efficacy of naphthalene-contaminated soils with various properties.     

土壤中有机污染物的老化概念探讨

有机污染物进入土壤后,随着其与土壤颗粒接触时间的延长,生物可利用性明显下降,发生老化现象,存在锁定行为.国内外已经广泛开展了与土壤中有机污染物老化相关的研究,但对老化的概念和内涵却没有明确界定,造成了理解上的偏差.基于目前国内外学者对老化的理解和认识,在明确生物可利用性的基础上,阐述了老化的概念及内涵,并对其进行了清晰的界定,同时对国内外现存的相关概念进行了区分.这些探讨将为相关研究的深入开展奠定基础,为土壤中有机污染物的环境化学行为与生物修复研究提供理论支持.