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SETAC Editorial
Copyright 2000 SETAC. Posted with permission of
the
Society of Environmental Toxicology and Chemistry (SETAC),
Pensacola, Florida, USA.
Celebrating QSARs
It seems only fitting
that, as we enter the next millennium, we celebrate with a symposium at
the national meeting the enduring utility of a book that was first
published in 1982 [1], was reprinted in 1990 without any revisions [2],
and continues to be a best seller to this day. This book, the Handbook
of Chemical Property Estimation Methods, presented 26 chapters that
reviewed the importance and methods of estimating physical/chemical
properties, and transport and degradation processes. The success of this
book is a tribute to the foresight of David Rosenblatt, who was with the
U.S. Army at the time, and the hard work of Warren Lyman and his
colleagues at A.D. Little. It seems also appropriate, that an update [3]
of this book is about to be released.
The SETAC Symposium
is entitled "Estimating Physical/Chemical Properties" (Chairs - Don
Mackay, Robert Boethling, and myself) and is a half-day session of
papers by authors from the new and old books, including an introduction
by Warren Lyman. For the most part, these papers will review the state
of the science in estimating these important properties for
environmental exposure.
Estimation methods
have changed considerably since the early 1980's. Back then, the user of
a recommended method often had to decide which chemical class was the
most similar to the chemical being estimated and the amount of error to
be expected for the estimate was unknown. Methods available now have
been developed on much larger data sets, and users often do not have to
select a chemical class equation and have a good indication of the error
in the prediction. Also, back in the early1980s, almost all estimations
were calculated by hand. Most estimation methods then and now involve
some complicated operations with numerous coefficients, especially for
more complex chemical structures. While it is still possible to
"hand-calculate" values for most methods, the availability of computer
software as a computational aid has became an important criterion in the
selection of an estimation method.
In general, most
physical/chemical/transport/degradation processes that are important to
the environmental fate of a chemical can be accurately predicted with a
good indication of the error involved [4]. For example, the mean error
for several octanol/water partition coefficient estimation methods is
close to the experimental error. Processes and properties that are
reasonably calculated include octanol/water partition coefficient, water
solubility, vapor pressure, Henry’s Law constant, pKa, Koc,
bioconcentration, and atmospheric oxidation. Methods that still need
improvement include biodegradation (only semi-quantitative methods are
available), photolysis (very limited methods are available), and
hydrolysis (methods for limited numbers of chemical classes, such as
esters, are available) [4].
Many believe that
the day will come when all environmentally relevant properties of all
chemicals will be calculated with acceptable accuracy from a knowledge
only of molecular structure. Indeed, this goal has been attained for
some properties and some chemicals. The Symposium in November will both
review where we are on that challenging journey and celebrate the
contributions of these pioneers.
Philip Howard
Syracuse Research
Corporation
North Syracuse, New
York, USA
References
1. Lyman WJ, Reehl WJ,
Rosenblatt DH. 1982. Handbook of Chemical Property Estimation Methods:
Environmental Behavior of Organic Compounds. McGraw-Hill, New York, NY,
USA.
2. Lyman WJ, Reehl WF,
Rosenblatt DH. 1990. Handbook of Chemical Property Estimation Methods:
Environmental Behavior of Organic Compounds. American Chemical Society,
Washington, DC, USA.
3. Boethling RS, D
Mackay, eds. 1999. Handbook of Property Estimation Methods for
Chemicals: Environmental and Health Sciences. CRC, Boca Raton, FL, USA..
4. Howard PH, Meylan
WM. 1997. Prediction of Physical Properties, Transport, and Degradation
for Environmental Fate and Exposure Assessments. In Schuurmann G, ed,
Quantitative Structure-Activity Relationships in Environmental Sciences, Vol 7. Society of Environmental Toxicology, Pensacola, FL, USA, pp
185-205
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