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

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Figure 8.12 Transport and transformation in a multicompartment pharmacokinetic model as applied to humans. of chemical contamination in vulnerable tissues with levels that are believed to cause adverse effects. There is clearly a need to link environmental and pharmacokinetic modeling efforts to build up a comprehensive capability of assessing the journey of the chemical from source to environment to organism and ultimately to the target site. ©2001 CRC Press LLC
8.14.1 Introduction ©2001 CRC Press LLC 8.14 HUMAN EXPOSURE TO CHEMICALS The multimedia environmental models described in this chapter lead to estimates of fugacities and concentrations in air, water, soil, and sediments. These abiotic fugacities can be used to deduce fugacities and concentrations in fish, and possibly in other animals and plants. The primary weakness is probably that they do not yet adequately quantify partitioning into the variety of vegetable matter that is consumed by animals and humans. For some compounds, such as the dioxins, the air-grasscow-milk-dairy product-human route of transfer is critical. In this chapter, we discuss briefly the principles by which these concentration data can be used to assess the impact of chemicals on humans and other organisms. The reader is directed to reviews such as that by Paustenbach (2000) for a detailed treatment of exposure and risk assessment. The first obvious use of these abiotic and biotic concentrations is to compare them with concentration levels that are believed to cause adverse effects. These levels are usually developed by regulatory agencies and published as guidelines, objectives, or effect-concentrations of various types. Target or objective concentrations can be defined for most media. For example, from considerations of toxicity or aesthetics, it may be possible to suggest that water concentrations should be maintained below 1 mg/m 3 , air below 1 mg/m 3 , and fish below 1 mg/kg. These concentrations can be compared as a ratio or quotient to the estimated environmental concentrations. A hypothetical example is given in Table 8.4, illustrating the quotient method. In this example, the primary concern is with air inhalation and fish ingestion. The proximities of the estimated prevailing concentrations to the targets are expressed as quotients, which can be regarded as safety factors. A large quotient implies a large safety factor and low risk. The high-risk situations correspond to low quotients. This quotient is also called a toxicity/exposure ratio or TER. The concentration level in fish may not be directly toxic to fish but may pose a threat to humans if the fish is consumed on a regular basis. The reciprocal ratio is also used in the form of a PEC/PNEC ratio, i.e., predicted environmental concentration/predicted no effect concentration. In this case, a high value implies high risk. Table 8.4 Comparison of Predicted or Measured <strong>Environmental</strong> Concentrations with Concentrations Producing a Specified Effect, or No Effect Concentrations Medium Predicted Level Effect Level Quotient Air (m/m3 ) 3 60 20 Water (mg/L) 10 3000 300 Fish (mg/g) 2 10 5 Soil (mg/g) 1 100 100 Difficulties are encountered when suggesting target concentrations in soil and sediment, because these media are not normally consumed directly by organisms.
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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
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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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Page 189 and 190: Figure 7.10 Four-compartment Level
Page 191 and 192: Table 7.2 Order of Magnitude Values
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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 and 204: LEVEL1B A six-compartment Level I p
Page 205 and 206: Figure 8.1 Air-water exchange proce
Page 207 and 208: The total rates of transfer are thu
Page 209 and 210: Figure 8.2 Chemical transport and t
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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
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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: Paterson et al. (1991), and Hung an
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
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Page 249 and 250: ©2001 CRC Press LLC
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