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

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concentrations are likely to be large and thus easier to determine accurately. When monitoring for PCBs in lakes, it is thus common to sample sediment or fish rather than water, since the expected concentrations in water are very low. Likewise, those concerned with PCB behavior in the atmosphere may measure the PCBs on aerosols or in rainfall containing aerosols, since concentrations are higher than in the air. In general, when assessing the likely environmental behavior of a new chemical, it is useful to calculate the various Z values and from them identify the larger ones, since it is likely that the high Z compartments are the most important. It is no coincidence that solutes such as halogenated hydrocarbons, about which there is great public concern, have high Z values in humans! It should be borne in mind that, when calculating the environmental behavior of a solute, Z values are needed only for the phases of concern. For example, if no atmospheric partitioning is considered, it is not necessary to know the air-water partition coefficient or H. An arbitrary value of H can be used to define Z for water and other phases, because H cancels. Intuitively, it is obvious that H, or vapor pressure, play no role in influencing water-fish-sediment equilibria. In summary, in this chapter we have introduced the concept of equilibrium existing between phases and have shown that this concept is essentially dictated by the laws of thermodynamics. Fortunately, we do not need to use or even understand the thermodynamic equations on which equilibrium relationships are based. However, it is useful to use these relationships for purposes such as correlation of partition coefficients. It transpires that there are two approaches that can be used to conduct equilibrium calculations. First is to develop and use empirical correlations for partition coefficients. Using these coefficients, it is possible to calculate the partitioning of the chemical in a multimedia environment. The second approach, which we prefer, is to use an equilibrium criterion such as fugacity or, in the case of involatile chemicals, an aquivalent concentration. The criterion can be related to concentration for each chemical and for each medium using a proportionality constant or Z value. The Z value can be calculated from fundamental equations or from partition coefficients. We have established recipes for the various Z values in these media using information on the nature of the media and the physical chemical properties of the substance of interest. This enables us to undertake simple multimedia partitioning calculations. ©2001 CRC Press LLC 5.7 LEVEL I CALCULATIONS Calculation of the equilibrium Level I distribution of a chemical is simple, but it can be tedious. It is ideal for implementation on a computer. The obvious steps are 1. Definition of the environment, i.e., volumes and compositions 2. Input of relevant physical chemical properties 3. Calculation of Z values for each medium (see Table 5.1) 4. Input of chemical amount 5. Calculation of fugacity, and hence concentrations, amounts, and percent distribution
Table 5.1 Table 5.1 Summary of Definitions of Z Values and Equations Used in Level I Calculations Definitions of Z values Z A = 1/RT Z W = 1/H = C S /P S = Z A/K AW Z O = Z W K OW (octanol) Z P = 1/v PP S (pure phase) Z S = y OCK OCZ W (r S/1000) (soils, sediments) ©2001 CRC Press LLC K OC = 0.41 K OW Z Q = Z AK QA (aerosols) K QA = 6 ¥ 10 6/P S L or y OMK OA (r Q/1000) Z B = LZ O (fish, biota) where R is the gas constant (8.314 Pa m 3 /mol K) T is absolute temperature (K) H is Henry’s law constant (Pa m 3 /mol) C S is solubility in water (mol/m 3 ) P S is vapor pressure (Pa) K AW is air–water partition coefficient K OW is octanol–water partition coefficient K OC is organic carbon–water partition coefficient v P is molar volume of pure chemical (m 3 /mol) y OC is mass fraction organic carbon y OM is mass fraction organic matter r S is density of soil, etc., (kg/m 3 ) r Q is density of aerosols (kg/m 3 ) K QA is aerosol–air partition coefficient P S L is vapor pressure of liquid or subcooled liquid L is lipid content (volume fraction) Note that the Z value of a bulk phase consisting of continuous and dispersed material, e.g., water plus suspended solids, is given by the volume fraction weighted Z values. Z T = S v iZ i where v i is the volume fraction of phase i. Fugacity equation f = M/SV iZ i where f is fugacity (Pa) M is total amount of chemical (mol) V is volume (m 3 ) C i = Z if m i = C iV i = V iZ if m i is amount in phase i (mol)
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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
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Figure 3.1 (continued) ©2001 CRC P
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Table 3.5 (continued) dichlorometha
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Table 3.5 (continued) total PCB 326
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Figure 3.2 Plot of log K AW vs. log
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chlorofluoro compounds are very sta
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3.3.2.7 Arsenic Compounds Arsenic,
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McKay, Donald. "The Nature of Envir
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Figure 4.1 Evaluative environments.
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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 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 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: ©2001 CRC Press LLC air Z = P S /R
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
Page 149 and 150: sulfate to sulfide or by dechlorina
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
Page 155 and 156: Figure 6.3 Fugacity Level II calcul
Page 157 and 158: McKay, Donald. "Intermedia Transpor
Page 159 and 160: Figure 7.1 Illustration of nonequil
Page 161 and 162: 5. Diffusion within soils, and from
Page 163 and 164: sionally, the term flux rate is use
Page 165 and 166: ©2001 CRC Press LLC N = ABDC/ Dy m
Page 167 and 168: no currents or eddies. In practice,
Page 169 and 170: diffusivity, and some unknown layer
Page 171 and 172: 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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