A Framework to Guide Selection of Chemical Alternatives (2014) / Chapter Skim
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5 Physicochemical Properties and Environmental Fate
5 Physicochemical Properties and Environmental Fate
Pages 47-68
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From page 47... ...
to chemical alternatives assessment can be used to First, the inherent hazard of a chemical, such as its identify physical hazards and to understand or capacity to interfere with normal biological predict a chemical's environmental fate, human processes, and its physical hazards and toxicity, or ecotoxicity (see Figure 5-2)
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48 A Framework to Guide Selection of Chemical Alternatives FIGURE 5-1 The committee's framework, with Step 5 highlighted.
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From page 49... ...
across a range of solvents and phases, the phase partition coefficient most often encountered when assessing physicochemical properties is Solvation Properties from a system where one solvent is water or an aqueous phase and the second is organic and Solvation properties14 describe a chemical's hydrophobic, such as 1-octanol (i.e., 14 The terms solvation properties and solution properties are often used interchangeably. Solvation is the term used in this report.
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From page 50... ...
and determination of pH, vapor pressure, density, water solubility, and melting and boiling points, among others. A number of comprehensive review Molecular Attributes texts have been authored on the measurement and The term molecular attribute is used to describe estimation of physicochemical properties (Boethling properties related to molecular shape and size.
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LogD for acids/bases can be readily calculated from logP when pKa values are known. Thus, only Other factors that influence water solubility methods for determining logP will be discussed here.
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Some of these relate to section of this chapter entitled "Use of molecular size, shape, and volume, others relate to Physicochemical Properties to Predict Aquatic the distribution of electrons in the molecule, and yet Bioavailability and Toxicity," there is an example of another set is based on frontier orbital energies. the applicability of HOMO-LUMO gap for identifying Properties that describe molecular size and chemicals most likely to exhibit high acute aquatic shape include solvent accessible surface area, toxicity.
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The reactivity of nucleophiles with HOMO energies close to the LUMO energies of the electrophiles will be higher than ones with larger differences, assuming steric effects are held constant. PHYSICOCHEMICAL PROPERTIES IN provides a chart with some guidance on OTHER FRAMEWORKS categorization of different physical hazards based on common labeling standards.
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confinement, not explosive) Substances that on GHS Category 1 GHS Category 2 GHS Category 3 GHS not contact with water (In contact with (In contact with (In contact with classified emit flammable water releases water releases water releases gases flammable gases flammable gases flammable gases)
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SOURCE: EPA 2012; IC2 2011; TURI 2010 Solvation Properties and Molecular one of the alternatives assessment hazard Attributes classification schemes include a metric for bioaccumulation (see Appendix B for more Several reviewed frameworks provide an information)
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As tool provides a suite of physical/chemical property and mentioned earlier, the GHS is a useful aid in environmental fate estimation programs. evaluating and classifying physical hazards (see Table 19 SPARC (SPARC Performs Automated Reasoning in 5-1 for an example of its application to the DfE Chemistry)
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well as human/mammalian alveolar absorption Frontier orbital energies Reflects chemical reactivity with nucleophiles and (HOMO, LUMO) electrophiles, which translates to reactivity with parameters Electronic biomolecules in vivo Molecular electronic Important in determining the energy, geometry, and dipole moments, μ, and intermolecular forces of molecules, and are often related dipole polarizabilities, α to biological activity Biodegradation Indicator of persistence, and persistence is tied to Inherent measures of environmental fate ecotoxicity Bioconcentration factor Bioconcentration enhances the hazard potential of (BCF)
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For some classes of materials, it is structural framework for determining potential possible to obtain useful, predictive information chemical distribution based on intrinsic properties of about potential persistence from physicochemical fugacity (f) , which is an inherent chemical property data, such as structural markers on the molecule and that governs the relative concentrations of chemicals partition coefficients.
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. 24 In the design of chemicals and components for Potential trade-offs between aquatic toxicity and formulating products, there is a tension between stability degradation.
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This order differs slightly for environmental hazard based solely on standard electrostatic binding to clays and other negatively aquatic toxicity tests using dissolvable salts is not charged particles, with nickel having the highest adequate. Therefore, the field of ecotoxicology is binding affinity and lead the lowest.
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. In light of this these data should be given preference over BCF complexity, no one physicochemical property or set values for estimating bioaccumulation potential in of properties is currently adequate to define all hazard classification and ranking.
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The physicochemical property limits making it questionable to directly extrapolate fish listed in Table 5-4 are known to favor reduced acute BAF values to birds and mammals. The relative and/or chronic aquatic toxicity.
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In addition to the use of physicochemical data to predict aquatic toxicity, these properties can also be used to estimate the toxicity of a given chemical in Physicochemical Properties That Influence humans and other animals as they influence Bioavailability in Humans toxicokinetic and toxicodynamic parameters.27 While the toxicodynamic interactions of chemicals are very Chemicals that are highly bioavailable to mammals challenging to relate to specific physicochemical through particular exposure routes have also been properties, the influence of such properties on defined by a set of property limits. These property toxicokinetic behavior of chemicals can be more limits were originally defined to assess the readily defined and used to prioritize the human probability of drug candidates entering the human health assessment of chemical alternatives.
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From page 64... ...
The are provided in Table 5-5 and are further discussed importance of molecular size reflects the paracellular in Chapter 8. The inverse of these property limits is pore sizes in the corneal and conjunctival likely to increase the probability of minimal human epitheliums, and lipophilicity appears to affect the bioavailability, but concrete studies to support this route of entry into the body, whether through the assertion are still lacking.
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physicochemical space for optimum human oral bioavailability. They showed that molecular weight, In addition to size, other physical and chemical ionization state, lipophilicity, polar descriptors, and properties can also influence transpulmonary free rotatable bonds (RB)
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between the can be used to help screen chemicals for their physicochemical property of a chemical potential to induce human toxicity. For example, the alternative and the chemical of interest.
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of mammalian exposure physical hazards may be particularly critical if the and bioavailability, as well the likelihood for high consumer will be directly exposed to the aquatic toxicity. Information gleaned for chemical in question (as opposed to an physicochemical properties should be made intermediate in a production/synthesis process, available to members of the assessment team which is only handled under controlled performing Step 6 (comparative exposure conditions)
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