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

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 partitioning
tendencies between air, water, soils, sediments, and biota. Such calculations
are useful when assessing or implementing remedial measures to treat alreadycontaminated
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 environment.
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 chemicals
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 describing
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 transform
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 thermodynamics,
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