Multimedia Environmental Models - Chapter 1 ppsx

McKay, Donald. "Front matter"
Multimedia Environmental Models
Edited by Donald McKay
Boca Raton: CRC Press LLC,2001
Multimedia
Environmental
Models
The Fugacity Approach
Second Edition
Donald Mackay
LEWIS PUBLISHERS
Boca Raton London New York Washington, D.C.
Multimedia
Environmental
Models
The Fugacity Approach
Second Edition

©2001 CRC Press LLC

Preface

This book is about the behavior of organic chemicals in our multimedia envi-
ronment or biosphere of air, water, soil, and sediments, and the diversity of biota
that reside in these media. It is a response to the concern that we have unwisely
contaminated our environment with a large number of chemicals in the mistaken
belief that the environment’s enormous capacity to dilute and degrade will reduce
concentrations to negligible levels. We now know that the environment has only a
finite capacity to dilute and degrade. Certain chemicals have persisted and accumu-
lated to levels that have caused adverse effects on wildlife and even humans. Some
chemicals have the potential to migrate from medium to medium, reaching unex-

pected destinations in unexpectedly high concentrations. We need to understand
these processes, not only qualitatively in the form of assertions that DDT evaporates
and bioaccumulates, but quantitatively as statements that DDT in a particular region
evaporates at a rate of 100 kg per year and bioaccumulates from water at a concen-
tration of 1 ng/L to fish at levels of 1

m

g/g.

We have learned that chemical behavior in the complex assembly of environ-
mental media is not a random process like leaves blowing in the wind. The chemicals
behave in accordance with the laws of nature, which dictate chemical partitioning
and rates of transport and transformation. Most fundamentally, the chemicals are
subject to the law of conservation of mass, i.e., a mass balance exists for the chemical
that is a powerful constraint on quantities, concentrations, and fluxes. By coupling
the mass balance principle with expressions based on our understanding of the laws
of nature, we can formulate a quantitative accounting of chemical inputs and outputs.
This book is concerned with developing and applying these expressions in the form
of mathematical statements or “models” of chemical fate. These accounts or models
are invaluable summaries of chemical behavior. They can form the basis of remedial
and proactive strategies.
Such models can confirm (or deny) that we really understand chemical fate in
the environment. Since many environmental calculations are complex and repetitive,
they are particularly suitable for implementation on computers. Accordingly, for
many of the calculations described in this book, computer programs are described
and made available on the Internet with which a variety of chemicals can be readily
assessed in a multitude of environmental situations.
The models are formulated using the concept of fugacity, which was introduced
by G.N. Lewis in 1901 as a criterion of equilibrium and has proved to be a very

convenient and elegant method of calculating multimedia equilibrium partitioning.
It has been widely and successfully used in chemical processing calculations. In this
book, we exploit it as a convenient and elegant method of explaining and deducing
the environmental fate of chemicals. Since publication of the first edition of this
book ten years ago, there has been increased acceptance of the benefits of using
fugacity to formulate models and interpret environmental fate. Multimedia fugacity
models are now routinely used for evaluating chemicals before and after production.
Much of the experience gained in these ten years is incorporated in this second
edition. Mathematical simulations of chemical fate are now more accurate, compre-

©2001 CRC Press LLC

hensive, and reliable, and they have gained greater credibility as decision-support
tools. No doubt this trend will continue, especially as young environmental scientists
and engineers take over the reins of environmental science and continue to develop
new fugacity models.
This book has been written as a result of the author teaching graduate-level
courses at the University of Toronto and Trent University. It is hoped that it will be
suitable for other graduate courses and for practitioners of the environmental science
of chemical fate in government, industry, and the private consulting sector. The
simpler concepts are entirely appropriate for undergraduate courses, especially as a
means of promoting sensitivity to the concept that chemicals, which provide modern
society with so many benefits, must also be more carefully managed from their
cradle, in the chemical synthesis plant, to their grave of ultimate destruction.
At the end of most chapters is a “Concluding Example” in which a student may
be asked to apply the principles discussed in that chapter to one or more chemicals
of their choice. Necessary data are given in Table 3.5 in Chapter 3. I have found
this useful as a method of assigning different problems to a large number of students,
while allowing them to explore the properties and fate of substances of particular
interest to them.

We no longer regard the environment as a convenient, low-cost dumping ground
for unwanted chemicals. When we discharge chemicals into the environment, it must
be with a full appreciation of their ultimate fate and possible effects. We must ensure
that mistakes of the past with PCBs, mercury, and DDT are not repeated. This is
best guaranteed by building up a quantitative understanding of chemical fate in our
total multimedia environment, how chemicals will be transported and transformed,
and where, and to what extent they may accumulate. It is hoped that this book is
one step toward this goal and will be of interest and use to all those who value the
environment and seek its more enlightened stewardship.

Donald Mackay

©2001 CRC Press LLC

Acknowledgments

It is a pleasure to acknowledge the contribution of many colleagues. Much of
the credit for the approaches devised in this book is due to the pioneering work by
George Baughman, who saw most clearly the evolution of multimedia environmental
modeling as a coherent and structured branch of environmental science amid the
often frightening complexity of the environment and the formidable number of
chemicals with which it is contaminated. Brock Neely, Russ Christman, and Don
Crosby were instrumental in encouraging me to apply the fugacity concept to
environmental calculations.
I am indebted to my former colleagues at the University of Toronto, especially
Wan Ying Shiu and Sally Paterson, whose collaboration has been crucial in devel-
oping the fugacity approach. I am grateful to my more recent colleagues at Trent
University, and our industrial and government partners who have made the Canadian
Environmental Modelling Centre a successful focus for the development, validation,
and dissemination of mass balance models.

This second edition was written in part when on research leave at the Department
of Environmental Toxicology at U.C. Davis, where Marion Miller, Don Crosby, and
their colleagues were characteristically generous and supportive. At Trent, I was
greatly assisted by David Woodfine, Rajesh Seth, Merike Perem, Lynne Milford,
Angela McLeod, Adrienne Holstead, Todd Gouin, Alison Fraser, Ian Cousins, Tom
Cahill, Jenn Brimecombe, and Andreas Beyer. I am particularly grateful to Steve
Sharpe for the figures, to Matt MacLeod and Christopher Warren for their critical
review and comments, and to Eva Webster for her outstanding scientific and editorial
contributions.
Without the support and diligent typing of my wife, Ness, this book would not
have been possible. Thank you.
I dedicate this book to Ness, Neil, Ian, Julia, and Gwen, and especially to Beth,
who was born as this edition neared completion. I hope it will help to ensure that
her life is spent in a cleaner, more healthful environment.

©2001 CRC Press LLC

Contents

Chapter 1

Introduction

Chapter 2

Some Basic Concepts
2.1 Introduction
2.2 Units
2.3 The Environment as Compartments
2.4 Mass Balances

2.5 Eulerian and Lagrangian Coordinate Systems
2.6 Steady State and Equilibrium
2.7 Diffusive and Nondiffusive Environmental Transport Processes
2.8 Residence Times and Persistence
2.9 Real and Evaluative Environments
2.10 Summary

Chapter 3

Environmental Chemicals and Their Properties
3.1 Introduction and Data Sources
3.2 Identifying Priority Chemicals
3.3 Key Chemical Properties and Classes
3.4 Concluding Example

Chapter 4

The Nature of Environmental Media
4.1 Introduction
4.2 The Atmosphere
4.3 The Hydrosphere or Water
4.4 Bottom Sediments
4.5 Soils
4.6 Summary
4.7 Concluding Example

Chapter 5

Phase Equilibrium
5.1 Introduction

5.2 Properties of Pure Substances
5.3 Properties of Solutes in Solution
5.4 Partition Coefficients
5.5 Environmental Partition Coefficients and Z Values
5.6 Multimedia Partitioning Calculations
5.7 Level I Calculations
5.8 Concluding Examples

Chapter 6

Advection and Reactions
6.1 Introduction

©2001 CRC Press LLC

6.2 Advection
6.3 Degrading Reactions
6.4 Combined Advection and Reaction
6.5 Unsteady-State Calculations
6.6 The Nature of Environmental Reactions
6.7 Level II Computer Calculations
6.8 Summary
6.9 Concluding Example

Chapter 7

Intermedia Transport
7.1 Introduction
7.2 Diffusive and Nondiffusive Processes
7.3 Molecular Diffusion within a Phase

7.4 Turbulent or Eddy Diffusion within a Phase
7.5 Unsteady-State Diffusion
7.6 Diffusion in Porous Media
7.7 Diffusion between Phases: The Two-Resistance Concept
7.8 Measuring Transport D Values
7.9 Combining Series and Parallel D Values
7.10 Level III Calculations
7.11 Level IV Calculations
7.12 Concluding Examples

Chapter 8

Applications of Fugacity Models
8.1 Introduction, Scope, and Strategies
8.2 Level I, II, and III Models
8.3 An Air-Water Exchange Model
8.4 A Surface Soil Model
8.5 A Sediment-Water Exchange Model
8.6 QWASI Model of Chemical Fate in a Lake
8.7 QWASI Model of Chemical Fate in Rivers
8.8 QWASI Multi-segment Models
8.9 A Fish Bioaccumulation Model
8.10 Sewage Treatment Plants
8.11 Indoor Air Models
8.12 Uptake by Plants
8.13 Pharmacokinetic Models
8.14 Human Exposure to Chemicals
8.15 The PBT–LRT Attributes
8.16 Global Models
8.17 Closure

Appendix

Fugacity Forms
References and Bibliography
McKay, Donald. "Introduction"
Multimedia Environmental Models
Edited by Donald McKay
Boca Raton: CRC Press LLC,2001

©2001 CRC Press LLC

C

HAPTER

1
Introduction

Since the Second World War, and especially since the publication of Rachel Carson’s

Silent Spring

in 1962, there has been growing concern about contamination of the
environment by “man-made” chemicals. These chemicals may be present in indus-
trial and municipal effluents, in consumer or commercial products, in mine tailings,
in petroleum products, and in gaseous emissions. Some chemicals such as pesticides
may be specifically designed to kill biota present in natural or agricultural ecosys-
tems. They may be organic, inorganic, metallic, or radioactive in nature. Many are
present naturally, but usually at much lower concentrations than have been estab-

lished by human activity. Most of these chemicals cause toxic effects in organisms,
including humans, if applied in sufficiently large doses or exposures. They may
therefore be designated as “toxic substances.”
There is a common public perception and concern that when these substances
are present in air, water, or food, there is a risk of adverse effects to human health.
Assessment of this risk is difficult (a) because the exposure is usually (fortunately)
well below levels at which lethal toxic effects and even sub-lethal effects can be
measured with statistical significance against the “noise” of natural population
variation, and (b) because of the simultaneous multiple toxic influences of other
substances, some taken voluntarily and others involuntarily. There is a growing
belief that it is prudent to ensure that the functioning of natural ecosystems is
unimpaired by these chemicals, not only because ecosystems have inherent value,
but because they can act as sensing sites or early indicators of possible impact on
human well-being.
Accordingly, there has developed a branch of environmental science concerned
with describing, first qualitatively and then quantitatively, the behavior of chemicals
in the environment. This science is founded on earlier scientific studies of the
condition of the natural environment—meteorology, oceanography, limnology,
hydrology, and geomorphology and their physical, energetic, biological, and chem-
ical sub-sciences. This newer branch of environmental science has been variously
termed

environmental chemistry, environmental toxicology,

or

chemodynamics

.

©2001 CRC Press LLC

It is now evident that our task is to design a society in which the benefits of
chemicals are enjoyed while the risk of adverse effects from them is virtually
eliminated. To do this, we must exert effective and cost-effective controls over the
use of such chemicals, and we must have available methods of calculating their
environmental behavior in terms of concentration, persistence, reactivity, and parti-
tioning tendencies between air, water, soils, sediments, and biota. Such calculations
are useful when assessing or implementing remedial measures to treat already-
contaminated environments. They become essential as the only available method for
predicting the likely behavior of chemicals that (a) may be newly introduced into
commerce or that (b) may be subject to production increases or introduction into
new environments.
In response to this societal need, this book develops, describes, and illustrates a
framework and procedures for calculating the behavior of chemicals in the environ-
ment. It employs both conventional procedures that are based on manipulations of
concentrations and procedures that use the concepts of activity and fugacity to
characterize the equilibrium that exists between environmental phases such as air,
water, and soil. Most of the emphasis is placed on organic chemicals, which are
fortunately more susceptible to generalization than metals and other inorganic chem-
icals when assessing environmental behavior.
The concept of fugacity, which was introduced by G.N. Lewis in 1901 as a more
convenient thermodynamic equilibrium criterion than chemical potential, has been
widely used in chemical process calculations. Its convenience in environmental
chemical equilibrium or partitioning calculations has become apparent only in the
last two decades. It transpires that fugacity is also a convenient quantity for describ-
ing mathematically the rates at which chemicals diffuse, or are transported, between
phases; for example, volatilization of pesticides from soil to air. The transfer rate
can be expressed as being driven by, or proportional to, the fugacity difference that
exists between the source and destination phases. It is also relatively easy to trans-

form chemical reaction, advective flow, and nondiffusive transport rate equations
into fugacity expressions and build up sets of fugacity equations describing the quite
complex behavior of chemicals in multiphase, nonequilibrium environments. These
equations adopt a relatively simple form, which facilitates their formulation, solution,
and interpretation to determine the dominant environmental phenomena.
We develop these mathematical procedures from a foundation of thermodynam-
ics, transport phenomena, and reaction kinetics. Examples are presented of chemical
fate assessments in both real and evaluative multimedia environments at various
levels of complexity and in more localized situations such as at the surface of a lake.
These calculations of environmental fate can be tedious and repetitive, thus there
is an incentive to use the computer as a calculating aid. Accordingly, computer
programs are made available for many of the calculations described later in the text.
It is important that the computer be viewed and used as merely a rather fast and
smart adding machine and not as a substitute for understanding. The reader is
encouraged to write his or her own programs and modify those provided.
The author was “brought up” to write computer programs in languages such as
FORTRAN, BASIC, and C. The first edition of this book was regarded as very
advanced by including a diskette of programs in BASIC. Such programs have the

©2001 CRC Press LLC

immense benefit that the sequence and details of calculations are totally transparent.
Executable versions can be run on any computer. Unfortunately, it is not always
easy to change input parameters or equations, and the output is usually printed tables.
The modern trend is to use spreadsheets, such as Microsoft EXCEL

®

, which have
improved input and output features, including the ability to draw graphs and charts.

Spreadsheets have the disadvantages that calculations are less transparent, there may
be problems when changing versions of the spreadsheet program, and not everyone
has the same spreadsheet.
Sufficient information is given on each mass balance model that readers can
write their own programs using the system of their choice. Microsoft Windows

®

software for performing model calculations is available from the Internet site
www.trentu.ca/envmodel. Older DOS-based models are also available. They are
updated regularly and are subject to revision. In all cases, the equations correspond
closely to those in this book (unless otherwise stated), and they are totally transpar-
ent. Some are used in a regulatory context, thus the user is prevented from changing
the coding, although all code can be viewed.
Preparing a second edition of this book has enabled me to update, expand, and
reorganize much of the material presented in the first (1991) edition. I have benefited
greatly from the efforts of those who have sought to understand environmental
phenomena and who have applied the fugacity approach when deducing the fate of
chemicals in the environment. There is no doubt that, as we enter the new millen-
nium, environmental science is becoming more quantitative. It is my hope that this
book will contribute to that trend.