BlOAVAllABlLlTY IN ENVIRONMENTAL RISK ASSESSMENT

Steve E. Hrudey, Weiping Chen, and Colin G. Rousseaux, Lewis Publishers/CRC Press, Inc., Boca Raton, FL, (1996), 294 Pages,[ISBN No.: 1-56670-186-41, U.S. List Price: $69.95

A major legacy of the 1990s relative to toxi- cology research and application of results to poli- cy decisions is likely to be the push toward sci- ence-based risk assessments that include all rele- vant factors. This is in contrast to the philosophy that dominated most of the 1970s through the 1980s; a philosophy that relied on studies of lab- oratory animals using pure chemicals in isolated circumstances. Major among those “relevant fac- tors’’ that now must be considered when risk assessment is performed or new regulatory poli- cies are being formulated is the concept of bioavailability. This is a concept that encompass- es the question, “Regardless of toxicity of a chem- ical compound, what environmental and other circumstances bear on the probability that living organisms will be exposed to that chemical in a way that will cause a detrimental effect?” Or, as the authors of this book more succinctly state the issue, “The term bioavailability is generally used to describe the extent and rate of absorption for a xenobiotic which enters the systemic circulation in the unaltered (parent) form from the applied (exposure) site.” The authors’ emphasis of the concept of parent form of chemicals, as contrast- ed with altered forms resulting from some envi- ronmental transformation process, is an impor- tant one; the concept illustrates the depth of thinking the authors bring to the subject. It is becoming increasingly recognized that toxicity studies employing only the parent chemical fail to present an accurate picture of overall toxicity in environmental situations, and form the basis for faulty risk assessments based on the resulting data. Xenobiotics in environmental settings are almost invariably transformed through a variety of mechanisms (biotransformation, photolysis, etc.) into other compounds. These resulting transformed compounds may be more or less toxic than the parent compound, or more or less bioavailable. There may, in fact, be synergistic effects among the range of chemicals produced through such action. This is only one of the fac- tors contributing to differential bioavailability of xenobiotics in environmental settings.

This book attempts to present an overall pic- ture of the importance of considering bioavail- ability in toxicology studies on which risk assess- ments and policy decisions will ultimately be based. It is a rather comprehensive treatise. In a

logically ordered fashion, the authors present up- to-date information about impacts of bioavail- ability on risk assessment from a number of standpoints. In seven chapters, the authors address physiological, biochemical, chemical.,environmental, and other factors that affect bioavailability in target species. Most useful is separate consideration for chemicals exhibiting characteristic behaviors in the environment. Sev- eral toxic heavy metals are covered, then dioxins, polynuclear aromatic hydrocarbons (PAHs), ben- zene, toluene, polychlorinated phenols, phenol, and aniline.

Chapter 1 (Introduction) and Chapter 2 define the basic concept of the book and of bioavailability in risk assessment, and set the stage for the more data-oriented chapters to follow. Chapter 3 provides a comprehensive overview of mechanisms of absorption of xenobiotics that contribute to bioavailability, and Chapter 4 is essentially a review of modern experimental methods for assessing bioavailability. Chapter 5 covers bioavailability issues related to the classes of chemicals listed above, and Chapter 6 is essen- tially a practicum on how studies of bioavailabili- ty can be applied in the field on actual contami- nated sites as a means of conducting meaningful toxicology studies at those sites. Chapter 7 is the real payoff of the book. Practical and philosophi- cal viewpoints are contained in this chapter con- cerning how toxicology data that were collected from experiments in which bioavailability was considered should be used in constructing health riik assessments.

I wholeheartedly recommend this book to scientists, risk assessment specialists, and policy makers for two major reasons. First, the informa- tion presented is invaluable, it is presented in a clear and comprehensive way, and the book rep- resents sound, forward thinking as regards the role of bioavailability in risk assessment. Second, the authors have thoughtfully provided compre- hensive references, a glossary, and a thorough index in the back of the book; these items make the book easy to use as well as maximally infor- mative. My view is that this book represents the mainstream, or what will be the mainstream, of thought regarding achievement of true science- based risk assessment through incorporation of bioavailability studies into modern toxicology research.

Mark Reeves, Ph.D. Director, Bioprocessing R&D Center Oak Ridge National Laboratory PO. Box 2008 Oak Ridge TN 37831-6226

BlOSOLlDS TREATMENT AND MANAGEMENT. PROCESSES FOR BENEFICIAL USE

Mark J. Girovich, Marcel Dekker, Inc., New York, hY, (1996), 453 Pages, [ISBN 0-8247- 9706-)jTl,U.s. List Price: $175.00

The regulations listed under 40 CFR Part 503, originally promulgated in 1993, have rendered a new momentum and regulatory climate for implementing beneficial use of biosolids. In response to this, Girovich and co-authors, have compiled detailed informa- tion on process equipment, the economics, and regulatory issues related to biosolids management and use.

The book is divided into several chapters written by individuals with practitioner‘s experi- ence. An introductory overview chapter is fol- lowed by a discussion of the federal regulatory requirements and their historic origin. The remaining chapters pertain to individual process- es: conditioning and dewatering, digestion, com- posting, heat drying and other thermal processes, alkaline stabilization, and land application.

The introductory chapter 1 lists physical, chemical, and biological characteristics of biosolids and the challenges (pathogen destruc- tion) and the opportunities (source of N and P) those represent. Odors are singled out as the key difficulty during biosolid generation. Of all biosolids generated, only 21.6% are land applied in agriculture, while 33.9% are still codisposed in municipal solid waste landfills.

The regulatory chapter 2 is exhaustive and informative. The 40 CFR 503 regulations are discussed that govern biosolids (deriving form domestic sewage and municipal wastewater treatment) and seepage aimed at maximizing their beneficial use by land application while minimizing potential environmental and human health risks. The history of these regula- tions as they stem from the earlier 257 rule are discussed. A detailed discussion on data gather- ing and the employed risk assessment method- ology, including the use of the HE1 concept (highly exposed individual) is presented. The rationale behind the exclusion of organic pollu- tants and retention of heavy metals in the final standards is satisfactorily explained. Finally con- cepts such as maximum cumulative loading rates and maximum annual pollutant loading rates are illustrated, while performance based standards to attain class A or class B biosolids are listed to achieve pathogen destruction requirements and vector attraction reduction.

S8 Spring 1998 Environmental Progress (Vo1.17. No. 1)