Impact of Clay Minerals and DOM on the Competitive Sorption/Desorption of PAHs

Two model compounds were used to investigate sorptive phenomena of a silty-sand soil under single and binary solute systems at different concentrations. In the sorption isotherms, the presence of phenan-threne (PHE) exhibited a statistically significant (P<0.05) sorption competition over pyrene (PYR), regardless of the concentration. PYR influenced the PHE isotherms only when it was present at 15?mg/L. The concentration dependence in sorption competition was only evident for the more hy-drophobic PYR. In the presence of PHE, the fraction of desorbed PYR was significantly increased with an increase in PYR concentration. PHE desorption enhancement was the most observable with the higher initial concentration (15?mg/L). However, the presence of PYR did not affect PHE desorption. This study found that, based on equivalent solid mass, soils containing only clay minerals sorbed 12.2% more PHE than soils with only soil organic matter (SOM) for 3?mg/L PHE. Clay minerals also impacted desorption as evidenced by a 65% decrease in desorbed PYR fraction compared with when the soil only contained SOM. The dissolved organic matter (DOM) amendment did not increase desorption. Instead, PHE desorption was significantly inhibited by the added DOM. For this study, co-sorption was found to be the mechanism for the inhibited desorption.     

Effect of dioxane on the structure and hydration-dehydration of alpha-chymotrypsin as measured by FTIR spectroscopy

A new experimental approach based on FTIR spectroscopic measurements was proposed to study simultaneously the adsorption/desorption of water and organic solvent on solid enzyme and corresponding changes in the enzyme secondary structure in the water activity range from 0 to 1.0 at 25 degrees C. The effect of dioxane on the hydration/dehydration and structure of bovine pancreatic alpha-chymotrypsin (CT) was characterized by means of this approach. Dioxane sorption exhibits pronounced hysteresis. No sorbed dioxane was observed at low water activities (a(w)<0.5) during hydration. At a(w) about 0.5, a sharp increase in the amount of sorbed dioxane was observed. Dioxane sorption isotherm obtained during dehydration resembles a smooth curve. In this case, CT binds about 150 mol dioxane/mol enzyme at the lowest water activities. Three different effects of dioxane on the water binding by the initially dried CT were observed. At a(w)<0.5, water adsorption is similar in the presence and absence of dioxane. It was concluded that the presence of dioxane has little effect on the interaction between enzyme and tightly bound water at low a(w). At a(w)>0.5, dioxane increases the amount of water bound by CT during hydration. This behavior was interpreted as a dioxane-assisted effect on water binding. Upon dehydration at low water activities, dioxane decreases the water content at a given a(w). This behavior suggests that the suppression in the uptake of water during dehydration may be due to a competition for water-binding sites on chymotrypsin by dioxane. Changes in the secondary structure of CT were determined from infrared spectra by analyzing the structure of amide I band. Dioxane induced a strong band at 1628 cm(-1) that was assigned to the intermolecular beta-sheet aggregation. Changes in the intensity of the 1628 cm(-1) band agree well with changes in the dioxane sorption by CT. An explanation of the dioxane effect on the CT hydration and structure was provided on the basis of hypothesis on water-assisted disruption of polar contacts in the solid enzyme. The reported results demonstrate that the hydration and structure of alpha-chymotrypsin depend markedly on how enzyme has been hydrated - whether in the presence or in the absence of organic solvent. A qualitative model was proposed to classify the effect of hydration history on the enzyme activity-a(w) profiles.     

Thermodynamic functions of biopolymer hydration. I. Their determination by vapor pressure studies,discussed in an analysis of the primary hydration process

The primary hydration process of native biopolymers is analyzed in a brief review of the literature, pertaining to various aspects of biopolymer–water systems. Based on this analysis, a hydration model is proposed that implies that the solution conformation of native biopolymers is stable at and above a critical degree of hydration (h_p′ = 0.06–0.1 g H₂O/g polymer). This water content corresponds to the fraction of strongly bound water, and amounts to ～20% of the primary hydration sphere. In order to test this model, detailed sorption–desorption scanning experiments were performed on a globular protein (α-chymotrypsin). The results obtained are consistent with the proposed hydration model. They show that under certain experimental conditions, sorption isotherms can be obtained that do not exhibit hysteresis. These data represent equilibrium conditions and are thus accessible to thermodynamic treatment. Valid thermodynamic functions, pertinent to the interaction of water with biopolymers in their solution state, can be obtained from these sorption experiments.     

The mechanical properties of stratum corneum: I. The effect of water and ambient temperature on the tensile properties of newborn rat stratum corneum

The tensile properties of the outermost layer of skin of neonatal rats, the stratum corneum, were investigated at a constant strain rate as a function of moisture content and ambient test temperature. The results show that the mechanical behavior of this membrane, whose primary constituent is the fibrous protein keratin, can be significantly altered by variations in both the sorbed water content and ambient temperature. In particular, a brittle to ductile transition was observed at 25°C once the hydration level exceeded 70% relative humidity. Similarly, an identical phenomenon moisture concentrations were maintained at 10 g H₂O/100 g dry protein. Differential scanning calorimetry measurements showed the presence of a molecular relaxation process which migrated from 42°C at 40% relative humidity to −18°C at 95% relative humidity. It is postulated that this relaxation process, possibly corresponding to the glass transition of the fibrous protein component of stratum corneum, is primarily respnsible for the observed behavior.     

Modification of the interaction betweenEscherichia coli and bacteriophage in saline sediment

The effects of sorption phenomena on the interaction between a parasite and its host bacterium have been investigated using anEscherichia coli-bacteriophage-saline sediment system. The sediment contained organic matter and a high proportion of clay, predominantly montmorillonoid. BothE. coli and phage remained firmly sorbed to saline sediments or montmorillonite, but were rapidly desorbed following dilution of the electrolyte below a critical concentration. This desorption coincided with the dispersal of sediment colloids.Escherichia coli was protected from phage attack by the presence of sediment, montmorillonite, or organic matter at salinty levels both above and below this critical point for dispersal and desorption. Evidence is presented indicating thatE. coli is protected from phage attack at low electrolyte concentrations by an envelope of sorbed colloidal materials around the cell, whereas at high electrolyte concentrations protection results both from the colloid envelope around the cells as well as from the sorption of cells and phages to solid particles. The protection ofE. coli and possibly other fecal bacteria may result in their accumulation in saline sediments, producing a possible health hazard in estuaries and lagoons if the bacteria are desorbed following dilution as a result of heavy rainfall.     

Factors affecting aluminium sorption by calcium pectate

Extracellular processes, particularly the adsorption of aluminium (Al) by pectate in the cell wall, have been proposed as important in the expression of Al toxicity to plant roots. In vitro studies were conducted on the effects of Al concentration (generally ≤ 32 μM), calcium (Ca) concentration (0.05 to 10 mM) and pH (3.2 to 5.4) on Al sorption by Ca pectate. There was a rapid reaction between Al and Ca pectate, there being no difference in Al remaining in solution after reaction times of 1 to 16 min, and only a slight decrease after 24 h. Increased Al concentration in solution increased linearly the sorption of Al by Ca pectate, with 70 to 84% of the Al originally in solution sorbed with ≤32 μM Al. In contrast, Al sorption decreased with increased Ca concentration in solution, and as pH decreased from 5.4 to 3.2. Only ≤30% of the sorbed Al was desorbed after 1 h by 1 mM CaCl₂, 10 mM CaCl₂ or 1 mM HCl. The amount of Al desorbed increased with a desorption period of 5 h, particularly with 1 mM HCl. These studies suggest that Al sorbed by Ca pectate in root cell walls is in equilibrium with Al in solution, and that Al toxicity is associated with the strong binding between Al and Ca pectate external to the cytoplasm.     

Modeling of composite sorption isotherm for stratum corneum

Equilibrium water sorption in stratum corneum (SC) is considered by treating it as a biocomposite with two main phases, namely, corneocytes and lipids. To validate the rule of mixtures for the individual phase sorption isotherms, a new flexible fitting model is introduced by accounting for characteristic features observed in the variations of the thermodynamic correction factors corresponding to the individual sorption isotherms. The comparison of the model fitting performance with that of the five-parameter Park's model shows a remarkably good ability to fit experimental data for different types of sorption isotherms. The effect of the lipids content on the variance of the composite sorption isotherm of stratum corneum is highlighted. The sensitivity analysis reveals that for the typical water content 20–30 wt%, which corresponds to the SC in a stable condition, the sensitivity of the composite sorption isotherm to the variation of the lipids content on dry basis is predominantly positive and sufficiently small. The good agreement observed between the experimental sorption isotherm for SC and the composite isotherm, which is based on the rule of mixtures for the individual phase sorption isotherms, yields a plausible conclusion (hypothesis) that the corneocytes–lipids mechanical interaction during unconstrained swelling of the SC membrane in the in vitro laboratory experiment is negligible.     

Nuclear magnetic resonance relaxation time and self-diffusion coefficient measurements of water in frog ovarian eggs (Rana pipiens)

Self-diffusion coefficient measurements of water in untreated ovarian eggs of Rana pipiens using nuclear magnetic resonance indicate that cytoplasmic water has reduced translational mobility compared with pure water. Using a simple two-state model, we find that ～67% is “relatively immobile.” Consideration of the nuclear magnetic resonance spin-lattice and spin-spin relaxation times indicates that the decreased mobility can largely be ascribed to hydration. Our value for the self-diffusion coefficient (6.8 × 10^?6 cm²/sec) is lower than those reported by other investigators using isotopic water exchange techniques on frog eggs chemically treated to remove the membrane. However, the results reported here are in agreement with unpublished data on untreated frog eggs implying that chemical treatment has modified the cytoplasm in some manner.     

Effect of Soil Chemical and Physical Properties on Sorption and Desorption Behavior of Lead in Different Soils of India

Lead (Pb) is a non-biodegradable contaminant, present in the environment, especially near lead-based industrial sites, agricultural lands, and roadside soils. Bioavailability of Pb in the soil is controlled by the sorption and desorption behavior of Pb, which are further controlled by the soil chemical and physical properties. In this study, sorption and desorption amounts of Pb in soil were compared with soil physical (sand, silt, clay content) and chemical (pH; electrical conductivity, EC; percent organic carbon, (%OC); cation exchange capacity, CEC) properties. Twenty-six surface soils (0–5cm), expected to vary in physical and chemical properties, were collected from different parts of India and were treated with known concentration of Pb solution (40 μg/L). The amount of Pb sorbed and desorbed were measured and correlated with soil properties using simple linear regressions. Sorption was significantly (p ≤ 0.05) and positively correlated with pH, and %OC; desorption was significantly (p ≤ 0.05) negatively correlated with the same two factors. Stepwise multiple regressions were performed for better correlations. Predicted sorption and desorption amounts, based on multiple regression equations, showed reasonably good fit (R² = 0.79 and 0.83, respectively) with observed values. This regression model can be used for estimation of sorption and desorption amounts at contaminated sites.     

Comparative evaluation for the sorption capacity of four carbonaceous sorbents to phenol

Sorption kinetics and isotherms of phenol by four carbonaceous sorbents (activated carbon (AC), mesoporous carbon (MPC), bamboo biochar (BBC) and oak wood biochar (OBC)) were compared in this study. MPC has the fastest sorption rate and initial sorption potential, which were indicated by sorption rate constants and initial sorption rate “h” in a pseudo-second-order kinetic model. The ordered and straight pore structure of MPC facilitated the accessibility of phenol. The AC showed the greatest sorption capacity towards phenol with maximum sorption of 123 mg/g as calculated by the Langmuir model. High surface area, complexity of pore structure, and the strong binding force of the π–π electron-donor-acceptor interaction between phenol molecules and AC were the main mechanisms. The BBC and OBC had much slower sorption and lower sorption capacity (33.04 and 29.86 mg/g, respectively), compared to MPC (73.00 mg/g) and AC, indicating an ineffective potential for phenol removal from water.     

Coffee polyphenols extracted from green coffee beans improve skin properties and microcirculatory function

Coffee polyphenols (CPPs), including chlorogenic acid, exert various physiological activities. The purpose of this study was to investigate the effects of CPPs on skin properties and microcirculatory function in humans. In this double-blind, placebo-controlled study, 49 female subjects with mildly xerotic skin received either a test beverage containing CPPs (270 mg/100 mL/day) or a placebo beverage for 8 weeks. The ingestion of CPPs significantly lowered the clinical scores for skin dryness, decreased transepidermal water loss, skin surface pH, and increased stratum corneum hydration and the responsiveness of skin blood flow during local warming. Moreover, the amounts of free fatty acids and lactic acid in the stratum corneum significantly increased after the ingestion of CPPs. These results suggest that an 8-week intake of CPPs improve skin permeability barrier function and hydration, with a concomitant improvement in microcirculatory function, leading to efficacy in the alleviation of mildly xerotic skin.     

Effect of dioxane on the structure and hydration–dehydration of α-chymotrypsin as measured by FTIR spectroscopy

A new experimental approach based on FTIR spectroscopic measurements was proposed to study simultaneously the adsorption/desorption of water and organic solvent on solid enzyme and corresponding changes in the enzyme secondary structure in the water activity range from 0 to 1.0 at 25 °C. The effect of dioxane on the hydration/dehydration and structure of bovine pancreatic α-chymotrypsin (CT) was characterized by means of this approach. Dioxane sorption exhibits pronounced hysteresis. No sorbed dioxane was observed at low water activities (a_w < 0.5) during hydration. At a_w about 0.5, a sharp increase in the amount of sorbed dioxane was observed. Dioxane sorption isotherm obtained during dehydration resembles a smooth curve. In this case, CT binds about 150 mol dioxane/mol enzyme at the lowest water activities. Three different effects of dioxane on the water binding by the initially dried CT were observed. At a_w < 0.5, water adsorption is similar in the presence and absence of dioxane. It was concluded that the presence of dioxane has little effect on the interaction between enzyme and tightly bound water at low a_w. At a_w > 0.5, dioxane increases the amount of water bound by CT during hydration. This behavior was interpreted as a dioxane-assisted effect on water binding. Upon dehydration at low water activities, dioxane decreases the water content at a given a_w. This behavior suggests that the suppression in the uptake of water during dehydration may be due to a competition for water-binding sites on chymotrypsin by dioxane. Changes in the secondary structure of CT were determined from infrared spectra by analyzing the structure of amide I band. Dioxane induced a strong band at 1628 cm^?1 that was assigned to the intermolecular β-sheet aggregation. Changes in the intensity of the 1628 cm^?1 band agree well with changes in the dioxane sorption by CT. An explanation of the dioxane effect on the CT hydration and structure was provided on the basis of hypothesis on water-assisted disruption of polar contacts in the solid enzyme. The reported results demonstrate that the hydration and structure of α-chymotrypsin depend markedly on how enzyme has been hydrated — whether in the presence or in the absence of organic solvent. A qualitative model was proposed to classify the effect of hydration history on the enzyme activity-a_w profiles.     

Effects of water gradients and use of urea on skin ultrastructure evaluated by confocal Raman microspectroscopy

The rather thin outermost layer of the mammalian skin, stratum corneum (SC), is a complex biomembrane which separates the water rich inside of the body from the dry outside. The skin surface can be exposed to rather extreme variations in ambient conditions (e.g. water activity, temperature and pH), with potential effects on the barrier function. Increased understanding of how the barrier is affected by such changes is highly relevant for regulation of transdermal uptake of exogenous chemicals. In the present study we investigate the effect of hydration and the use of a well-known humectant, urea, on skin barrier ultrastructure by means of confocal Raman microspectroscopy. We also perform dynamic vapor sorption (DVS) microbalance measurements to examine the water uptake capacity of SC pretreated with urea. Based on novel Raman images, constructed from 2D spectral maps, we can distinguish large water inclusions within the skin membrane exceeding the size of fully hydrated corneocytes. We show that these inclusions contain water with spectral properties similar to that of bulk water. The results furthermore show that the ambient water activity has an important impact on the formation of these water inclusions as well as on the hydration profile across the membrane. Urea significantly increases the water uptake when present in skin, as compared to skin without urea, and it promotes formation of larger water inclusions in the tissue. The results confirm that urea can be used as a humectant to increase skin hydration.     

Biosorption of Cr, Cu and Al bySargassum biomass

The biosorption and desorption of Cr, Cu and Al were carried out using brown marine algaeSargassum fluitans biomass, known as the good biosorbent of heavy metals. The content of alginate bound to light metals could be changed by physical and chemical pretreatment. The maximum uptake of Cr, Cu and Al was independent of the alginate content. The maximum uptake of Al was two times(mole basis) than those of Cu and Cr. The aluminum-alginate complex was found in the sorption solution of raw and protonated biomass. Most of Cu, Al and light metals sorbed in the biomass were eluted at pH 1.1. However, only 5 to 10% of Cr sorbed was eluted at pH 1.1. The stoichometric ion exchange between Cu and Ca ion was observed on Cu biosorption with Ca-loaded biomass. A part of Cr ion was bound to biomass as Cr(OH)₂ ⁺ or Cr(OH)²⁺. Al was also bound to biomass as multi-valence ion and interfered with the desorbed Ca ion. The behavior of rawS. fluitans in ten consecutive sorption-desorption cycles has been investigated in a packed bed flow-through-column during a continuous removal of copper from a 35 mg/L aqueous solution at pH 5. The eluant used was a 1%(w/v) CaCl/HCl solution at pH3.     

Assessment of Bioavailability of Soil-Sorbed Atrazine

Bioavailability of pesticides sorbed to soils is an important determinant of their environmental fate and impact. Mineralization of sorbed atrazine was studied in soil and clay slurries, and a desorption-biodegradation-mineralization (DBM) model was developed to quantitatively evaluate the bioavailability of sorbed atrazine. Three atrazine-degrading bacteria that utilized atrazine as a sole N source (Pseudomonas sp. strain ADP, Agrobacterium radiobacter strain J14a, and Ralstonia sp. strain M91-3) were used in the bioavailability assays. Assays involved establishing sorption equilibrium in sterile soil slurries, inoculating the system with organisms, and measuring the CO₂ production over time. Sorption and desorption isotherm analyses were performed to evaluate distribution coefficients and desorption parameters, which consisted of three desorption site fractions and desorption rate coefficients. Atrazine sorption isotherms were linear for mineral and organic soils but displayed some nonlinearity for K-saturated montmorillonite. The desorption profiles were well described by the three-site desorption model. In many instances, the mineralization of atrazine was accurately predicted by the DBM model, which accounts for the extents and rates of sorption/desorption processes and assumes biodegradation of liquid-phase, but not sorbed, atrazine. However, for the Houghton muck soil, which manifested the highest sorbed atrazine concentrations, enhanced mineralization rates, i.e., greater than those expected on the basis of aqueous-phase atrazine concentration, were observed. Even the assumption of instantaneous desorption could not account for the elevated rates. A plausible explanation for enhanced bioavailability is that bacteria access the localized regions where atrazine is sorbed and that the concentrations found support higher mineralization rates than predicted on the basis of aqueous-phase concentrations. Characteristics of high sorbed-phase concentration, chemotaxis, and attachment of cells to soil particles seem to contribute to the bioavailability of soil-sorbed atrazine.     

New insights into the structure and hydration of a stratum corneum lipid model membrane by neutron diffraction

The structure and hydration of a stratum corneum (SC) lipid model membrane composed of N-(-hydroxyoctadecanoyl)-phytosphingosine (CER6)/cholesterol (Ch)/palmitic acid (PA)/cholesterol sulfate (ChS) were characterized by neutron diffraction. The neutron scattering length density across the SC lipid model membrane was calculated from measured diffraction peak intensities. The internal membrane structure and water distribution function across the bilayer were determined. The low hydration of the intermembrane space is a major feature of the SC lipid model membrane. The thickness of the water layer in the SC lipid model membrane is about 1 Å at full hydration. For the composition 55% CER6/25% Ch/15% PA/5% ChS, in a partly dehydrated state (60% humidity) and at 32°C, the lamellar repeat distance and the membrane thickness have the same value of 45.6 Å . The hydrophobic region of the membrane has a thickness of 31.2 Å . A decrease of the Ch content increases the membrane thickness. The water diffusion through the SC lipid model multilamellar membrane is a considerably slow process relative to that through phospholipid membranes. In excess water, the membrane hydration follows an exponential law with two characteristic times of 93 and 44 min. At 81°C and 97% humidity, the membrane separates into two phases with repeat distances of 45.8 and 40.5 Å . Possible conformations of CER6 molecules in the dry and hydrated multilayers are discussed.     

Assessment of bioavailability of soil-sorbed atrazine

Bioavailability of pesticides sorbed to soils is an important determinant of their environmental fate and impact. Mineralization of sorbed atrazine was studied in soil and clay slurries, and a desorption-biodegradation-mineralization (DBM) model was developed to quantitatively evaluate the bioavailability of sorbed atrazine. Three atrazine-degrading bacteria that utilized atrazine as a sole N source (Pseudomonas sp. strain ADP, Agrobacterium radiobacter strain J14a, and Ralstonia sp. strain M91-3) were used in the bioavailability assays. Assays involved establishing sorption equilibrium in sterile soil slurries, inoculating the system with organisms, and measuring the CO(2) production over time. Sorption and desorption isotherm analyses were performed to evaluate distribution coefficients and desorption parameters, which consisted of three desorption site fractions and desorption rate coefficients. Atrazine sorption isotherms were linear for mineral and organic soils but displayed some nonlinearity for K-saturated montmorillonite. The desorption profiles were well described by the three-site desorption model. In many instances, the mineralization of atrazine was accurately predicted by the DBM model, which accounts for the extents and rates of sorption/desorption processes and assumes biodegradation of liquid-phase, but not sorbed, atrazine. However, for the Houghton muck soil, which manifested the highest sorbed atrazine concentrations, enhanced mineralization rates, i.e., greater than those expected on the basis of aqueous-phase atrazine concentration, were observed. Even the assumption of instantaneous desorption could not account for the elevated rates. A plausible explanation for enhanced bioavailability is that bacteria access the localized regions where atrazine is sorbed and that the concentrations found support higher mineralization rates than predicted on the basis of aqueous-phase concentrations. Characteristics of high sorbed-phase concentration, chemotaxis, and attachment of cells to soil particles seem to contribute to the bioavailability of soil-sorbed atrazine.     

An Easy Synthesis of (E)-9-Oxo-2-decenoic Acid,the Queen Substance of the Honey Bee,and (Z)-6-Heneicosen-ll-one,the Sex Pheromone of the Douglas Fir Tussock Moth†

We investigated the effect of dietary phospholipid (PL) concentrate from bovine milk on the epidermis. Thirteen-week-old hairless male and female mice (Hos:HR-1) were separated into two experimental groups, each fed two experimental diets: the control group and the PL group. The mice were given the experimental diets for 6 weeks. Stratum corneum hydration and transepidermal water loss (TEWL) were measured using Corneometer CM825 and Tewameter TM300 (Courage and Khazaka Electronics, Cologne, Germany) at 3 weeks and 6 weeks. After the feeding period, ceramides in stratum corneum were analyzed. We found that stratum corneum hydration and ceramides in the PL group were significantly higher than those in the control group and that TEWL in the PL group tended to decrease.

These results indicate that dietary PL concentrate improves epidermal function by increasing the amount of ceramides, resulting in higher hydration.     

Uptake and recovery of gold ions from electroplating wastes using eggshell membrane.

The animal byproduct, hen eggshell membrane (ESM), was evaluated for its ability to sorb gold ions (dicyanoaurate(I) and tetrachloroaurate(III)) from solutions and electroplating wastewater. The gold uptake was dependent on pH, temperature and co-ions present in the solutions, with pH 3.0 being the optimum value. The equilibrium data followed the Langmuir isotherm model with maximum capacities of 147 mg Au(I)/g dry weight and 618 mg Au(III)/g, respectively. Desorption of sorbed gold(I) with 0.1 mol/l NaOH resulted in no changes of the biosorbent gold uptake capacity through five consecutive sorption/desorption cycles. In column experiments, selective recovery of gold from electroplating wastewater containing various metal ions was noted. The affinity of metal sorption was in the order Au > Ag > Co > Cu > Pb > Ni > Zn.     

Dietary phospholipid concentrate from bovine milk improves epidermal function in hairless mice

We investigated the effect of dietary phospholipid (PL) concentrate from bovine milk on the epidermis. Thirteen-week-old hairless male and female mice (Hos:HR-1) were separated into two experimental groups, each fed two experimental diets: the control group and the PL group. The mice were given the experimental diets for 6 weeks. Stratum corneum hydration and transepidermal water loss (TEWL) were measured using Corneometer CM825 and Tewameter TM300 (Courage and Khazaka Electronics, Cologne, Germany) at 3 weeks and 6 weeks. After the feeding period, ceramides in stratum corneum were analyzed. We found that stratum corneum hydration and ceramides in the PL group were significantly higher than those in the control group and that TEWL in the PL group tended to decrease. These results indicate that dietary PL concentrate improves epidermal function by increasing the amount of ceramides, resulting in higher hydration.