The key toxicokinetic processes are absorption, distribution, metabolism, and excretion. Molecular Attributes The term molecular attribute is used to describe properties related to molecular shape and size. However, lipophilicity also affects whether a chemical will be taken up by the organism i.
The focus here is on the influence of physicochemical properties on the rate of absorption of a chemical into the bloodstream, its distribution to the organs and tissues, and its rate of elimination clearance of a compound.
Colligative properties generally do not play a significant role in alternatives assessments and are not discussed further in this report.
Potential trade-offs between aquatic toxicity and degradation. It is also known that aqueous solubility, molecular size, and ionization state also influence bioavailability.
Table shows the characterization and ranges that define classification scores for logP for three frameworks. The DfE evaluates the ability of a chemical to bioaccumulate. As will be discussed in a later section, these coefficients provide insight into environmental partitioning of the molecule and the potential for bioaccumulation.
Examples of these models include: The strength of attraction between metal ions and charged sites is a function of the affinity of the metal to the charged site relative to its affinity for water molecules. Anionic metals and metalloids such as molybdenum, arsenic, mercury, and selenium also bind to iron oxides, but binding decreases with increasing pH, which is opposite to what occurs with cationic metals.
A partition-coefficient or distribution-coefficient is defined mathematically as the ratio of concentrations of a given compound across two mixed, immiscible phases at equilibrium. Colligative properties are properties of solutions that are not dependent on the chemical species but instead on the ratio of the number of solute particles to the number of solvent molecules in a solution.
Meeting two or three property limits has been shown to substantially increase the probability that a chemical will have low or no aquatic toxicity. Some transformations can increase the toxicity of the parent compound e. Current approaches for assessing physicochemical properties in several alternatives assessment frameworks are then discussed, followed by the details behind assessment of physicochemical properties and their relevance in predicting environmental fate and transport and human health hazards and ecotoxicity.
Large chemical structural databases combined with recent developments in quantitative structure property relationships have greatly expanded the potential for rapid assessment of chemicals Howard and Muir Therefore, measurement of sodium ion concentration is not always an accurate indication of alkalinity and toxic potential Cooper et al.
The algorithms based on spectroscopic data do not require knowledge of exact chemical structure Voutchkova-Kostal et al. This equation uses regression-derived correlation with logP and melting point MP for solids: The committee cautions that given the active research in the field and the potential for special case concerns to arise for a given compound e.
Finally, the committee provides additional instructions on the implementation of Step 5 in its framework.
Since there is a wide range of environmental conditions of interest especially temperature and pHthere are often no suitable literature values available. Therefore, the ability of a chemical to bioaccumulate in any organism is a function of its chemical fugacity and the fugacity capacity of that organism for that chemical.
Bioaccumulation for fish BAFF is the bioconcentration factor based on freely dissolved chemical concentration BCFD for its food items phytoplankton such as algae times the ratio of the uptake rate from the diet KD and the uptake rate from the water via respiration KR.
In addition, some models and databases have been developed to predict degradation rates Arnot et al FIGURE Relation of frontier molecular orbital energies to covalent interactions of nucleophiles and electrophiles, as illustrated with a generic nucleophilic substitution Sn2 reaction. In the context of a chemical alternatives assessment, important partition coefficients are often measured in the liquid phase.
The primary measurement of interest in chemical alternatives assessment is solubility in water. Fugacity fexpressed as Pascals Pais an inherent chemical property that governs the relative concentrations of chemicals in different environmental and biotic compartments.
As mentioned earlier, the GHS is a useful aid in evaluating and classifying physical hazards see Table for an example of its application to the DfE framework.
OECD test guidelines exist for the measurement of a variety of physicochemical properties, including Kow and determination of pH, vapor pressure, density, water solubility, and melting and boiling points, among others.
These tools provide a rapid means for obtaining physicochemical data, often at a lower cost when compared with experimental measurement.
Physical Hazards The first step in using physicochemical properties is to determine the likely physical hazards. Properties related to electron distribution are often related to chemical reactivity and biological activity Voutchkova The one detailed analysis of workers in a degreasing plant exposed to heated caustic vapor indicated that aerosols containing an average of 0.
Binding affinity also influences the toxicity of cationic metals. These properties can be readily estimated with quantum mechanic calculations when the chemical structure is known. They noted that there were clear disagreements between measured values of logP and those calculated by predictive programs.
Metals newly introduced into soils or sediments are more bioavailable than those that have aged for months to years. Page 89 Share Cite Suggested Citation:little literature available about physicochemical properties and mouth breathing.
Hence this study was undertaken to Nagi S et al.: Physicochemical properties of Saliva in Habitual Mouth Breathers and Nasal Breathers ORIGINAL RESEARCH box for immediate evaluation of bound sialic acid, unbound sialic acid and total sialic acid. The chips made with no baking soda, 10 min baking times and mm thickness were chosen as the optimal preparation for evaluation on its physicochemical properties.
Physicochemical and nutritional properties of optimized germinated soybean chips. 5 Physicochemical Properties and Environmental Fate Knowledge of the physicochemical properties of potential chemical alternatives is a requirement of the alternatives assessment process for two reasons.
properties and chemical composition of Nypa fruticans frond and petiole in order to e valuate its su itability or otherwise as the fibrous raw materials for.
Physical and Physicochemical Evaluation of Different Brands of Traditional, Low Calorie and Sugar-Free Guava Preserves Brazilian Journal of Chemical Engineering Vol.
03, pp. -July - September, A screening of 17 different commercial plant-based milk substitutes based on different cereals, nuts and legumes was performed, including the evaluation of physicochemical and glycaemic properties. Half of the analysed .Download