McKay, Donald. "Front matter" Multimedia Environmental Models ...

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We can also relate equilibrium concentrations in these phases using the three Z values and fugacity. The partition coefficients are simply the ratio of the respective Z values; e.g., K AW is Z A/Z W. The use of Z values at this stage brings little benefit, but they become very useful when we calculate partitioning to environmental media. We use Z A, Z W, and Z O to calculate Z in phases such as soils, sediments, fish, and aerosol particles, and it proves useful to have Z P as a reference point when examining the magnitude of Z values. It is enlightening to calculate all the physical chemical properties of a solid and a liquid substance as shown in the following example. Worked Example 5.3 Deduce all relevant thermodynamic air-water partitioning properties for benzene (liquid) and naphthalene (a solid of melting point 80°C) at 25°C. Benzene Vapor pressure = 12700 Pa (P S L), molar mass = 78 g/mol, solubility in water = 1780 g/m 3 . ©2001 CRC Press LLC Z A = 1/RT = 1/(8.314 ¥ 298) = 4.04 ¥ 10 –4 Solubility C S L = 1780/78 = 22.8 mol/m 3 Activity coefficient g = 1/v wC S L = 1/(18 ¥ 10 –6 ¥ 23.1) = 2440 Naphthalene H = P S L/C S L = 556, also = v WgP S L Z W = 1/H or 1/v wgP S L = 0.0018 K AW = H/RT or Z A/Z W = 0.22 Solubility = 33 g/m 3 , molar mass = 128 g/mol, vapor pressure = 10.9 Pa Z A = 4.04 ¥ 10 –4 as before F = exp(–6.79(353/298–1)) = 0.286 (mp = 353 K) P S L = P S S/F = 38.1 C S S = 33/128 = 0.26 mol/m 3 , C S L = 0.90 mol/m 3 g = 1/v wC S L = 61700 H = P S S /C S S or P S L/C S L = 42 Z W = 1/H or 0.024 = 1/v wgP S L K AW = H/RT or Z A/Z W = 0.017 Note that naphthalene has a higher activity coefficient corresponding to its lower solubility and greater hydrophobicity.
5.5 ENVIRONMENTAL PARTITION COEFFICIENTS AND Z VALUES 5.5.1 Introduction Our aim is now to use the physical chemical data to predict how a chemical will partition in the environment. Information on air-water-octanol partitioning is invaluable and can be used directly in the case of air and pure water, but the challenge remains of treating other media such as soils, sediments, vegetation, animals, and fish. The general strategy is to relate partition coefficients involving these media to partitioning involving octanol. We thus, for example, seek relationships between K OW and soil-water or fish-water partitioning. 5.5.2 Organic Carbon-Water Partition Coefficients Studies by agricultural chemists have revealed that hydrophobic organic chemicals tended to sorb primarily to the organic matter present in soils. Similar observations have been made for bottom sediments. In a definitive study, Karickhoff (1981) showed that organic carbon was almost entirely responsible for the sorbing capacity of sediments and that the partition coefficient between sediment and water expressed in terms of an organic carbon partition coefficient (K OC) was closely related to the octanol-water partition coefficient. Indeed, the simple relationship was established to be ©2001 CRC Press LLC K OC = 0.41 K OW This relationship is based on experiments in which a soil-water partition coefficient was measured for a variety of soils of varying organic carbon content (y) and chemicals of varying K OW. The soil concentration was measured in units of mg/g or mg/kg (usually of dry soil) and the water in units of mg/cm 3 or mg/L. The ratio of soil and water concentration (designated K P) thus has units of L/kg or reciprocal density. K P = C S/C W (mg/kg)/(mg/L) = L/kg If a truly dimensionless partition coefficient is desired, it is necessary to multiply K P by the soil density in kg/L (typically 2.5), or equivalently multiply C S by density to give a concentration in units of mg/L. A plot of K P versus organic carbon content, y (g/g), proves to be nearly linear and passes close to the origin, suggesting the relationship K P = y K OC where K OC is an organic carbon-water partition coefficient. In practice, there is usually a slight intercept, thus the relationship must be used with caution when y is less than 0.01, and especially when less than 0.001. Since y is dimensionless, K OC, like K P also has units of L/kg. Measurements of K OC for a
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McKay, Donald. "Front matter" Multi
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Multimedia Environmental Models The
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hensive, and reliable, and they hav
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Chapter 1 Introduction Chapter 2 So
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McKay, Donald. "Introduction" Multi
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It is now evident that our task is
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McKay, Donald. "Some Basic Concepts
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give the derived units directly wit
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Energy (joule, J) The joule, which
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particles (aerosols), or biota in w
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Worked Example 2.1 A three-phase sy
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(i) What is the concentration (C) i
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Answer ©2001 CRC Press LLC 5.1 kg,
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or or When t is zero, C is zero, th
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What is the absolute minimum piscic
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©2001 CRC Press LLC C 1 = C O/(1 +
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containing nonequilibrium quantitie
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1. Fallout of chemical from air to
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validated using real environments.
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©2001 CRC Press LLC CHAPTER 3 Envi
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of other, somewhat similar or homol
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Table 3.2 List of Chemicals Commonl
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elatively high concentrations. This
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exists between toxicologists and ch
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determine priority. This is a subje
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Another important classification of
Page 53 and 54: Figure 3.1 (continued) ©2001 CRC P
Page 55 and 56: Table 3.5 (continued) dichlorometha
Page 57 and 58: Table 3.5 (continued) total PCB 326
Page 59 and 60: Figure 3.2 Plot of log K AW vs. log
Page 61 and 62: chlorofluoro compounds are very sta
Page 63 and 64: 3.3.2.7 Arsenic Compounds Arsenic,
Page 65 and 66: McKay, Donald. "The Nature of Envir
Page 67 and 68: Figure 4.1 Evaluative environments.
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Page 73 and 74: carbon figure for deeper sediments
Page 75 and 76: flows. The quality of this groundwa
Page 77 and 78: Table 4.2 Evaluative Environments A
Page 79 and 80: McKay, Donald. "Phase Equilibrium"
Page 81 and 82: Figure 5.1 Some principles and conc
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Page 85 and 86: Another useful quantity is the rati
Page 87 and 88: experimentally, but not directly, u
Page 89 and 90: ©2001 CRC Press LLC 5.3 PROPERTIES
Page 91 and 92: 1.0. This, then, is the fugacity or
Page 93 and 94: where ©2001 CRC Press LLC pH is -l
Page 95 and 96: In terms of solubilities, S iA and
Page 97 and 98: The temperature coefficient is the
Page 99 and 100: (1982), Baum (1997) and Leo (2000).
Page 101 and 102: Although it may appear environmenta
Page 103: Figure 5.4 Illustration of quantita
Page 107 and 108: C S = K PC W benzene = 1.1 ¥ 0.001
Page 109 and 110: Mackay (1986), in an attempt to sim
Page 111 and 112: Compartment Definition of Fugacity
Page 113 and 114: high concentration in the fish, but
Page 115 and 116: heat capacity of 0.38 J/g°C requir
Page 117 and 118: Therefore, ©2001 CRC Press LLC f =
Page 119 and 120: ©2001 CRC Press LLC Z T = S(V i/V
Page 121 and 122: ©2001 CRC Press LLC air Z = P S /R
Page 123 and 124: Table 5.1 Table 5.1 Summary of Defi
Page 125 and 126: Figure 5.7 Fugacity form 1 for dedu
Page 127 and 128: Calculate the following physical-ch
Page 129 and 130: ©2001 CRC Press LLC CHAPTER 6 Adve
Page 131 and 132: that all water will spend 100 days
Page 133 and 134: This enables us to conceive of, and
Page 135 and 136: ©2001 CRC Press LLC f = 15/0.5 = 3
Page 137 and 138: D AS dominates. A residence time of
Page 139 and 140: and Therefore, ©2001 CRC Press LLC
Page 141 and 142: eaction situation in which there is
Page 143 and 144: The rate constants in each case are
Page 145 and 146: ©2001 CRC Press LLC 1/t O = SD Ai/
Page 147 and 148: e achieved in 10 days. Detractors o
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Page 151 and 152: to Zepp and Cline (1977) for the or
Page 153 and 154: ©2001 CRC Press LLC 6.7 LEVEL II C
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Figure 6.3 Fugacity Level II calcul
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McKay, Donald. "Intermedia Transpor
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Figure 7.1 Illustration of nonequil
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5. Diffusion within soils, and from
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sionally, the term flux rate is use
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©2001 CRC Press LLC N = ABDC/ Dy m
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no currents or eddies. In practice,
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diffusivity, and some unknown layer
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where ©2001 CRC Press LLC X = y/ U
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fraction of the total volume that i
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Figure 7.6 Mass transfer at the int
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partition coefficient. The signific
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and the series retains a similar ra
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ments of resuspension rates are par
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Figure 7.8 Movement of air phase (k
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ates can thus be used to estimate m
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Figure 7.9 Combination of D values
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Figure 7.10 Four-compartment Level
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Table 7.2 Order of Magnitude Values
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Unlike the Level II calculation, it
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Figure 7.12 Sample Level III output
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McKay, Donald. "Applications of Fug
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applications. Citations are given t
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Another approach is to employ Monte
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LEVEL1B A six-compartment Level I p
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Figure 8.1 Air-water exchange proce
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The total rates of transfer are thu
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Figure 8.2 Chemical transport and t
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mean. For chemical between depths o
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8.5.2 Process Description The water
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learn the benefits of using fugacit
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where Figure 8.5 QWASI model: stead
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are similar to those described by M
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C F ª Z Ff W ª 1.608 mol/m 3 ª 4
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y Mackay et al. (1983), and an appl
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accordingly, but the final solution
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Figure 8.10 Fish bioaccumulation pr
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The nature of the processes control
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iomagnification is more significant
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An alternative and more elegant met
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8.11.2 Model of a Chemical Evaporat
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Paterson et al. (1991), and Hung an
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8.14.1 Introduction ©2001 CRC Pres
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mated again in mg/day. Food, the ot
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models. Most interest is in LRT in
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available from the University of To
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McKay, Donald. "Appendix" Multimedi
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©2001 CRC Press LLC
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