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

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includes an excellent treatment of human exposure. It was originally designed to assess exposure to chemicals present in hazardous waste sites. The environmental fate equations are formulated using fugacities. Maddalena et al. (1995) compared the output of and ChemCAN and found similar results, indicating that both models were using similar predictive equations. The reader should consult the Trent website for current versions of the model software described in this text. 8.3.1 Introduction ©2001 CRC Press LLC 8.3 AN AIR-WATER EXCHANGE MODEL Air-water exchange process calculations are useful when estimating chemical loss from treatment lagoons, ponds, and lakes; for estimating deposition rates of atmospheric contaminants, and for interpreting observed air and water concentrations to establish the direction and rate of transfer. The complexity of the several processes and the widely varying physical chemical properties of chemicals of interest leads to situations in which chemical behavior is not necessarily intuitively obvious. The simple model derived here provides a rational method of estimating exchange characteristics and exploring the sensitivity of the results to assumed values of the various chemical and environmental parameters. Bidleman (1988) gives an excellent review of atmospheric processes treated by the model. An elegant application of the fugacity concept to elucidating chemical exchange in the air-water system is that of Jantunen and Bidleman (1997). Samples of air and surface water from the Bering and Chukchi Seas (between Alaska and Russia) were analysed for a-hexachlorocyclohexane (a-HCH) over a multiyear period, and the ratios of air to water fugacities were deduced using the Henry’s law constant for seawater at the appropriate temperature. Initially, in the mid 1980s, this ratio was greater than 1, indicating that a-HCH was being absorbed by the ocean. This is consistent with the source of a-HCH being evaporation of technical lindane following application in South East Asia, India, and China, with subsequent atmospheric transport. Later, in the mid 1990s, after the use of technical lindane was greatly reduced, the fugacity ratio became less than 1 (because of the drop in air fugacity), and net volatilization of a-HCH started. Essentially, the ocean acted first as a “sponge,” absorbing a-HCH, then it desorbed the a-HCH in response to changes in the concentration in air. Interpretation of data using of the fugacity ratio illustrated this clearly. It is an example to be followed in cases where there is doubt about the direction of net transport of chemicals between air and water. 8.3.2 Process Description The situation treated here, and the resulting model, are largely based on the study of air- -water exchange by Mackay et al. (1986) as is depicted in Figure 8.1. The water phase area and depth (and hence volume) are defined, it being assumed that the water is well mixed. The water contains suspended particulate matter, to
Figure 8.1 Air-water exchange processes. which the chemical can be sorbed, and which may contain mineral and organic material. The concentration (mg/L or g/m 3 ) of suspended matter is defined, as is its organic carbon (OC) content (g OC per g dry particulates). By assuming a 56% OC content of organic matter, the masses of mineral and organic matter can be deduced. Densities of 1000, 1000, and 2500 kg/m 3 are assumed for water, organic matter, and mineral matter respectively, thus enabling the volumes and volume fractions to be deduced. The air phase is treated similarly, having the same area as the water and a defined (possibly arbitrary) height and containing a specified concentration (ng/m 3 ) of aerosols or atmospheric particulates to which the chemical may sorb. By assuming an aerosol density of 1500 kg/m 3 , the volume fraction of aerosols can be deduced. No information on aerosol composition, size distribution, or area is sought or used. If the concentration of aerosols or total suspended particulates is TSP ng/m 3 , this corresponds to 10 –12 TSP kg/m 3 and to a volume fraction v Q of 10 –12 TSP/r Q, where r Q is the aerosol density (1500 kg/m 3 ). Thus, a typical TSP of 30,000 ng/m 3 or 30 mg/m 3 is equivalent to a volume fraction of 20 ¥ 10 –12 . The volumes of particles can be calculated as the product of total volume V, and respective volume fractions. Physical chemical properties of the chemical are requested. The total or bulk concentrations in the water and air phases are requested in mass/volume units. These are converted to mol/m 3 and divided by the bulk Z values to give the water and air fugacities. The quantities and concentrations in dissolved, or gaseous, and sorbed form are then calculated, i.e., the input concentrations are apportioned to sorbed and nonsorbed forms. Z and D values are calculated using the expressions in Tables 8.1 and 8.2. ©2001 CRC Press LLC
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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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metals and organic chemicals from w
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carbon figure for deeper sediments
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flows. The quality of this groundwa
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Table 4.2 Evaluative Environments A
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McKay, Donald. "Phase Equilibrium"
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Figure 5.1 Some principles and conc
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likely using an equilibrium criteri
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Another useful quantity is the rati
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experimentally, but not directly, u
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©2001 CRC Press LLC 5.3 PROPERTIES
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1.0. This, then, is the fugacity or
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where ©2001 CRC Press LLC pH is -l
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In terms of solubilities, S iA and
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The temperature coefficient is the
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(1982), Baum (1997) and Leo (2000).
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Although it may appear environmenta
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Figure 5.4 Illustration of quantita
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5.5 ENVIRONMENTAL PARTITION COEFFIC
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C S = K PC W benzene = 1.1 ¥ 0.001
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Mackay (1986), in an attempt to sim
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Compartment Definition of Fugacity
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high concentration in the fish, but
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heat capacity of 0.38 J/g°C requir
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Therefore, ©2001 CRC Press LLC f =
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©2001 CRC Press LLC Z T = S(V i/V
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©2001 CRC Press LLC air Z = P S /R
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Table 5.1 Table 5.1 Summary of Defi
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Figure 5.7 Fugacity form 1 for dedu
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Calculate the following physical-ch
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©2001 CRC Press LLC CHAPTER 6 Adve
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that all water will spend 100 days
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This enables us to conceive of, and
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©2001 CRC Press LLC f = 15/0.5 = 3
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D AS dominates. A residence time of
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and Therefore, ©2001 CRC Press LLC
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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
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
Page 173 and 174: fraction of the total volume that i
Page 175 and 176: Figure 7.6 Mass transfer at the int
Page 177 and 178: partition coefficient. The signific
Page 179 and 180: and the series retains a similar ra
Page 181 and 182: ments of resuspension rates are par
Page 183 and 184: Figure 7.8 Movement of air phase (k
Page 185 and 186: ates can thus be used to estimate m
Page 187 and 188: Figure 7.9 Combination of D values
Page 189 and 190: Figure 7.10 Four-compartment Level
Page 191 and 192: Table 7.2 Order of Magnitude Values
Page 193 and 194: Unlike the Level II calculation, it
Page 195 and 196: Figure 7.12 Sample Level III output
Page 197 and 198: McKay, Donald. "Applications of Fug
Page 199 and 200: applications. Citations are given t
Page 201 and 202: Another approach is to employ Monte
Page 203: LEVEL1B A six-compartment Level I p
Page 207 and 208: The total rates of transfer are thu
Page 209 and 210: Figure 8.2 Chemical transport and t
Page 211 and 212: mean. For chemical between depths o
Page 213 and 214: 8.5.2 Process Description The water
Page 215 and 216: learn the benefits of using fugacit
Page 217 and 218: where Figure 8.5 QWASI model: stead
Page 219 and 220: are similar to those described by M
Page 221 and 222: C F ª Z Ff W ª 1.608 mol/m 3 ª 4
Page 223 and 224: y Mackay et al. (1983), and an appl
Page 225 and 226: accordingly, but the final solution
Page 227 and 228: Figure 8.10 Fish bioaccumulation pr
Page 229 and 230: The nature of the processes control
Page 231 and 232: iomagnification is more significant
Page 233 and 234: An alternative and more elegant met
Page 235 and 236: 8.11.2 Model of a Chemical Evaporat
Page 237 and 238: Paterson et al. (1991), and Hung an
Page 239 and 240: 8.14.1 Introduction ©2001 CRC Pres
Page 241 and 242: mated again in mg/day. Food, the ot
Page 243 and 244: models. Most interest is in LRT in
Page 245 and 246: available from the University of To
Page 247 and 248: McKay, Donald. "Appendix" Multimedi
Page 249 and 250: ©2001 CRC Press LLC
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