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

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©2001 CRC Press LLC S i = n/V = P S /RT Invaluable information about how a substance will behave in the environment can be obtained by considering its three solubilities, namely those in air, water, and octanol. These solubilities express the substance’s relative preferences for air, water, and organic phases. Returning to the definition of Z W as (1/v Wg if R), it is apparent that Z W also can be expressed in terms of aqueous solubility, S W, and vapor pressure P S . For liquid solutes, S W is 1/g iv W. For solid solutes it is F/g iv w. The reference fugacity f R is the vapor pressure of the liquid, i.e., it is P S for a liquid and P S /F for a solid. Substituting gives Z W as S W/P S in both cases, the F cancelling for solids. The ratio P S /S is the Henry’s law constant H in units of Pa m 3 /mol, thus Z W is 1/H. Polar solutes such as ethanol do not have measurable solubilities in water, because they are miscible. This generally occurs when g is less than about 20. We can still use the concept of solubility and call it a “hypothetical or pseudo-solubility” if it is defined as 1/g iv S. For a liquid substance that behaves nearly ideally, i.e., g i is 1.0, the solubility approaches 1/v S, which is the density of the solvent in units of mol/m 3 . For water, this is about 55,500 mol/m 3 , i.e., 10 6 g/m 3 divided by 18 g/mol. For a solid solute under ideal conditions, the solubility approaches F/v S mol/m 3 . These equations are general and apply to a nonionizing chemical in solution in any liquid solvent, including water and octanol. The solution molar volumes and the activity coefficients vary from solvent to solvent. The Z value for a chemical in octanol is, by anology, 1/v Og if R, where v O is the molar volume of octanol. 5.3.3 Solutions of Ionizing Substances Certain substances, when present in solution, adopt an equilibrium distribution between two or more chemical forms. Examples are acetic acid, ammonia, and pentachlorophenol, which ionize by virtue of association with water releasing H + (strictly H 3O + ) or OH – ions. Some substances dimerize or form hydrates. For ionizing substances, the distribution is pH dependent, thus the solubility and activity are also pH dependent. This could be accommodated by defining Z as being applicable to the total concentration, but it then becomes pH dependent. A more rigorous approach is to define Z for each chemical species, noting that, for ionic species, Z in air must be zero under normal conditions, because ions as such do not evaporate. In any event, it is useful to know the relative proportions of each species, because they will partition differently. This issue is critical for metals in which only a small fraction may be in free ionic form. For acids, an acid dissociation constant Ka is defined as Ka = H + A – /HA where H + is hydrogen ion concentration, A – is the dissociated anionic form, and HA is the parent undissociated acid. The ratio of ionic to nonionic forms I is thus I = A – /HA = Ka/H + = 10 (pH – pKa)
where ©2001 CRC Press LLC pH is –log H + and pKa is –log Ka This is the Henderson-Hasselbalch relationship. For acids, when pKa exceeds pH by 2 units or more, ionization can be ignored. When considering substances which have the potential to ionize it is essential to obtain pKa and determine the relative proportions of each form. The handbook by Lyman et al. (1982) and the text by Perrin et al. (1981) can be consulted for more details of estimation methods for pKa, and for applications. Dissociation can be regarded as causing an increase in the Z value of a substance in aqueous solution. The total Z value is the sum of the nonionic and ionic contributions, which will have respective fractions 1/(I + 1) and I/(I + 1). The Z value of the nonionic form Z W can be calculated by measuring solubility, activity coefficient, or another property under conditions when I is very small, i.e., pH
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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
Page 41 and 42: of other, somewhat similar or homol
Page 43 and 44: Table 3.2 List of Chemicals Commonl
Page 45 and 46: elatively high concentrations. This
Page 47 and 48: exists between toxicologists and ch
Page 49 and 50: determine priority. This is a subje
Page 51 and 52: 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.
Page 69 and 70: are subject to two important deposi
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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
Page 83 and 84: likely using an equilibrium criteri
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: 1.0. This, then, is the fugacity or
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 and 104: Figure 5.4 Illustration of quantita
Page 105 and 106: 5.5 ENVIRONMENTAL PARTITION COEFFIC
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
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The rate constants in each case are
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©2001 CRC Press LLC 1/t O = SD Ai/
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e achieved in 10 days. Detractors o
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sulfate to sulfide or by dechlorina
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to Zepp and Cline (1977) for the or
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©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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