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

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There is therefore a compelling incentive to identify those chemicals that can undertake long-range transport and implement international agreements to control them. A start on this process has been made recently by the United Nations Environment Program (UNEP), which has identified 12 substances or groups for international regulations or bans. These substances, listed in Table 3.3, are also identified as persistent, bioaccumulative, and toxic. Others are scheduled for restriction or reduction. They may represent merely the first group of chemicals that will be subject to international controls. Most contentious of the 12 is DDT, which is still widely and beneficially used for malaria control. Table 3.3 Substances Scheduled for Elimination, Restriction, or Reduction by UNEP Scheduled for Elimination Scheduled for Restriction 3.2.6 Other Effects Finally, there is a variety of other adverse effects that are of concern, including • the ability to influence atmospheric chemistry (e.g., freons) • alteration in pH (e.g., oxides of sulfur and nitrogen causing acid rain) • unusual chemical properties such as chelating capacity, which alters the availability of other chemicals in the environment • interference with visibility • odor (e.g., from organo-sulfur compounds) • color (e.g., from dyes) • the ability to cause foaming in rivers (e.g., detergents or surfactants) • formation of toxic metabolites or degradation products 3.2.7 Selection Procedures A common selection procedure involves scoring these factors on some numeric hazard scale. The factors then may be combined to give an overall factor and ©2001 CRC Press LLC Scheduled for Reduction Aldrin DDT PAHs Chlordane Hexachlorocyclohexanes Dioxins/furans DDT Dieldrin Endrin Heptachlor Hexabromobiphenyl Hexachlorobenzene Mirex Polychlorinated biphenyls Toxaphene Polychlorinated biphenyls Hexachlorobenzene
determine priority. This is a subjective process, and it becomes difficult for two major reasons. First, chemicals that are subject to quite different patterns of use are difficult to compare. For example, chemical X may be produced in very large quantities, emitted into the environment, and found in substantial concentrations in the environment, but it may not be believed to be particularly toxic. Examples are solvents such as trichloroethylene or plasticizers such as the phthalate esters. On the other hand, chemical Y may be produced in minuscule amounts but be very toxic, an example being the “dioxins.” Which deserves the higher priority? Second, it appears that the adverse effects suffered by aquatic organisms and other animals, including humans, are the result of exposure to a large number of chemicals, not just to one or two chemicals. Thus, assessing chemicals on a caseby-case basis may obscure the cumulative effect of a large number of chemicals. For example, if an organism is exposed to 150 chemicals, each at a concentration that is only 1% of the level that will cause death, then death will very likely occur, but it cannot be attributed to any one of these chemicals. It is the cumulative effect that causes death. The obvious prudent approach is to reduce exposure to all chemicals to the maximum extent possible. The issue is further complicated by the possibility that some chemicals will act synergistically, i.e., they produce an effect that is greater than additive; or they may act antagonistically, i.e., the combined effect is less than additive. As a result, there will be cases in which we are unable to prove that a specific chemical causes a toxic effect but, in reality, it does contribute to an overall toxic effect. Indeed, some believe that this situation will be the rule rather than the exception. A compelling case can be made that the prudent course of action is for society to cast a fairly wide net of suspicion (i.e., assemble a fairly large list of chemicals) then work to elucidate sources, fate, and effects with the aim of reducing overall exposure of humans, and our companion organisms, to a level at which there is assurance that no significant toxic effects can exist from these chemicals. The risk from these chemicals then becomes small as compared to other risks such as accidents, disease, and exposure to natural toxic substances. This approach has been extended and articulated as the “Precautionary Principle,” the “Substitution Principle,” and the “Principle of Prudent Avoidance.” One preferred approach is to undertake a risk assessment for each chemical. Formal procedures for conducting such assessments have been published, notably by the U.S. <strong>Environmental</strong> Protection Agency (EPA). The process involves identifying the chemical, its sources, the environment in which it is present, and the organisms that may be affected. The toxicity of the substance is evaluated and routes of exposure quantified. Ultimately, the prevailing concentrations or doses are measured or estimated and compared with levels that are known to cause effects, and conclusions are drawn regarding the proximity to levels at which there is a risk of effect. This necessarily involves consideration of the chemical’s behavior in an actual environment. Risk is thus assessed only for that environment. Risk or toxic effects are thus not inherent properties of a chemical; they depend on the extent to which the chemical reaches the organism. ©2001 CRC Press LLC
Page 1 and 2: McKay, Donald. "Front matter" Multi
Page 3 and 4: Multimedia Environmental Models The
Page 5 and 6: hensive, and reliable, and they hav
Page 7 and 8: Chapter 1 Introduction Chapter 2 So
Page 9 and 10: McKay, Donald. "Introduction" Multi
Page 11 and 12: It is now evident that our task is
Page 13 and 14: McKay, Donald. "Some Basic Concepts
Page 15 and 16: give the derived units directly wit
Page 17 and 18: Energy (joule, J) The joule, which
Page 19 and 20: particles (aerosols), or biota in w
Page 21 and 22: Worked Example 2.1 A three-phase sy
Page 23 and 24: (i) What is the concentration (C) i
Page 25 and 26: Answer ©2001 CRC Press LLC 5.1 kg,
Page 27 and 28: or or When t is zero, C is zero, th
Page 29 and 30: What is the absolute minimum piscic
Page 31 and 32: ©2001 CRC Press LLC C 1 = C O/(1 +
Page 33 and 34: containing nonequilibrium quantitie
Page 35 and 36: 1. Fallout of chemical from air to
Page 37 and 38: validated using real environments.
Page 39 and 40: ©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: exists between toxicologists and ch
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
Page 71 and 72: metals and organic chemicals from w
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
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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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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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