Modeling Exposure
Samuel C. Morris in Cancer Risk Assessment, 2020
Groundwater modeling is at a reasonably high level of sophistication, but the more advanced models are seldom suitable for exposure assessment as a part of risk assessment. On the other hand, the simple, worst case analysis sometimes used for regulatory screening is to assume no attenuation or delay in the groundwater system; the entire mass of contaminant in a leachate release is diluted only by the amount of drinking water drawn from the aquifer. This is unsatisfactory for even the most rudimentary exposure analysis. The simplest realistic exposure analysis is to assume the release is diluted by the uncontaminated ground water. Unlike a river, however, the amount of groundwater available for dilution is not immediately available or easily obtainable information. Some level of modeling of the flow field in the ground-water system is necessary. Key mechanisms of pollutant mobility typically included in models are advection, hydrodynamic dispersion, adsorption and desorption, and degradation or decay. While the simplest models assume contaminants do not sorb or otherwise interact with the soil media and, thus, travel at the same rate as the groundwater, even the more sophisticated screening-level models include sorption. Groundwater is obviously in much more intimate contact with soil than surface water with the result being much greater importance of sorption. The contaminant sorption process is usually described by a constant, Kd, representing the ratio between the contaminant adsorbed to the soil matrix and the contaminant dissolved in solution.
Solid State Testing of Inhaled Formulations
Anthony J. Hickey, Sandro R.P. da Rocha in Pharmaceutical Inhalation Aerosol Technology, 2019
Dynamic vapor sorption can be performed to examine solid-water interactions by monitoring the mass change of the sample as a function of RH. The RH is programmed to step up and down sequentially at a constant temperature to obtain sorption-desorption isotherms (Ward and Schultz 1995, Buckton and Darcy 1995). The sample mass increases and decreases during the sorption and desorption phases, respectively. Water absorbed into amorphous regions may act as a plasticizer and lowers the glass transition temperature. This may trigger the recrystallization of these regions and results in a sudden mass loss due to the partial desorption of water upon the formation of crystalline regions, which have lower water affinity than their amorphous counterparts. The recrystallization event can be verified by running the sample through two sorption-desorption cycles. If the recrystallization of amorphous regions was completed in the first cycle, then the corresponding mass loss should not recur in the second cycle. The sample should also be less hygroscopic in the second cycle because it is crystalline (Ward and Schultz 1995).
Evaluating Effects of Conditioning Formulations on Hair
Randy Schueller, Perry Romanowski in Conditioning Agents for Hair and Skin, 2020
Finally, proteins constitute an important class of conditioner raw materials. They are claimed to impart softness to the hair, increase tensile strength, add body and gloss, enhance springiness, and improve the overall look and feel of hair. While there is little peer-review literature to support the effect of proteins on the physicochemical properties of hair, the substantivity of polypeptides to hair keratin is well established. Quantitative sorption work has been reported by Karjalla et al. (19), Turowski et al. (20), Mintz et al. (21), and other authors.
Solid amorphous formulations for enhancing solubility and inhibiting Erlotinib crystallization during gastric-to-intestinal transfer
Published in Pharmaceutical Development and Technology, 2023
L. Mugnier, F. Espitalier, J. Menegotto, S. Bell, M. I. Ré
Considering ERL-HPMCAS L HME a choice formulation as it demonstrated the best results in solubility and dissolutions studies, supplementary analyses were performed on this formulation aiming to have some information concerning its physical stability. On one side, a water sorption isotherm at 25 °C was used to obtain information about the affinity between the chosen formulation and water, upon exposure to stressed humidity. Figure 9 displays the DVS isotherm plots for the studied sample, showing the change in mass percentage as a function of changing relative humidity (RH) in the range 0 to 95% RH. The measured sorption over the RH 0-95% is a contribution of both adsorption (surface phenomenon) and absorption (volume phenomenon). Water vapor is absorbed into structure of amorphous solids and not simply adsorbed on the surface.
4-Formylphenyl boronic acid grafted amino MCM-41 for efficient adsorption of Cu(II) ions in aqueous medium: isotherm, kinetic and optimization studies
Published in Toxin Reviews, 2022
Inderpreet Kaur, Navjot Kaur, Bhupinder Pal Singh, Rajeev Kumar, Jyoti Chawla
The Langmuir isotherm describes homogeneous sorption with monolayer formation, where the sorption of each sorbate ion (or molecule) onto the surface has equal sorption activation energy. The Langmuir sorption isotherm is often used to describe sorption of a solute from a liquid solution and expressed as: Ce (mg/L) = Concentration of Cu(II) in the aqueous solution at equilibriumqe (mg/g) = Amount of Cu(II) adsorbed per unit mass of b-MCM at equilibriumqmax (mg/g) = Maximum adsorption capacity of b-MCMb (L/mg) = Langmuir constant related to the adsorption rate
Addition of Trichocladium canadense to an anaerobic membrane bioreactor: evaluation of the microbial composition and reactor performance
Published in Biofouling, 2021
Hadi Fakhri, Duygu Nur Arabacı, İlayda Dilara Ünlü, Cigdem Yangin-Gomec, Suleyman Ovez, Sevcan Aydin
It has been previously reported that trace organic contaminants with high hydrophobicity (i.e. log Kow>4.0) demonstrated higher sorption, whereas compounds of a hydrophilic nature (i.e. log Kow<2.5) demonstrated lower sorption (Koeck et al. 2015). ERY, TET and SMX all have hydrophilic tendencies, as suggested by their log Kow values of 3.06, −1.37 and 0.89, respectively (Hansch et al. 1995). Among these antibiotics, SMX was observed to have the highest sorption, even though ERY was expected to have the highest sorption according to their respective hydrophobicity. Furthermore, ERY sorption to the biofilm was considerably less in the control reactor compared with the TC reactor, while SMX and TET showed significant increases. One possible explanation could be the decreased mass transfer into the biofilm EPS structure due to a significant difference in the molecular mass of ERY (733.93g mol−1), which was almost three times that of SMX (253.279g mol−1) and twice that of TET (444.435g mol−1). This aspect could be further investigated in future studies for removal of toxic compounds from aquatic environments through sorption. The combination of antibiotics could also be one of the impacting factors in the removal and accumulation of antibiotics. Hence, for full-scale industrial application, the combination of antibiotics at the highest concentrations in the wastewater should be taken into consideration while choosing the appropriate treatment method.
Related Knowledge Centers
- Absorption
- Adsorption
- Catalysis
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- Ion Exchange
- Molecule
- Ion
- Electrolyte
- Solution
- Coordination Complex