The Science of Toxicology

Chemicals are double-edged swords, providing benefits to society while also posing risks. For the chemicals that society seeks to harness for its purposes, the benefits are generally easy to see and agree on. Their downsides are often less well understood. 

The universe of chemicals exhibits a variety of harmful properties. Chemicals may be explosive, flammable, radioactive, corrosive, irritating, sensitizing, and/or toxic. This book addresses one harmful property, toxicity. While other harmful effects occur at the point where a chemical contacts the body, toxicity is unique in that it is almost always manifested in tissues and organs that are distant from the point of contact. Toxicology is sometimes called the science of poisons. With few exceptions, a toxic chemical travels through the bloodstream to reach the cells it harms. 

Toxicological science is concerned with what might be referred to broadly as living systems. Examples of living systems include individual organisms such as a human being or a sea urchin populations of organisms such as the people who live in a town located downwind from a power plant or coho salmon that spawn in a particular tributary of the Snake River, where water quality is threatened and ecosystems 

Classification based on chemical classes, e.g., polycyclic aromatic hydrocarbons, organic solvents, chlorinated hydrocarbons, and heavy metals 

Classification based on exposure pathways, e.g., air pollutants, water pollutants, toxic chemicals in the workplace, and toxic chemicals in the home 

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The science of toxicology, which we define as the study of the adverse effects of chemicals on health and of the conditions under which those effects occur, has begun to take on a well-defined shape only in the past four to five decades. The science is still struggling for a clear identity, but it has begun to find one. One of the reasons for... 

Silent Spring was immensely popular and influential. Carson s work almost single-handedly created modern society s fears about synthetic chemicals in the environment and, among other things, fostered renewed interest in the science of toxicology. It also helped pave the way for the introduction of several major federal environmental laws in the late 1960s and early 1970s, and for the creation of the EPA in 1970. 

The two ultimate sources of chemicals - nature and industrial and laboratory synthesis - are then briefly described. This review sets the stage for a discussion of how human beings become exposed to chemicals. The conditions of human exposure are a critical determinant of whether and how a chemical will produce injury or disease, so the discussion of chemical sources and exposures naturally leads to the major subject of the book - the science of toxicology. 

Although strychnine and nux vomica has been used for several hundred years medicinally, it is best known as a powerful poison. The use of poison for murder has been used for thousands of years, but several events in the 19 th century contributed to strychnines notoriety as a poison. These included the development of the science of toxicology and practical pathological methods to identify the use of specific poisons, sensationalizing high-profile murder cases that used strychnine, and the use of strychnine as an exotic poison in fictional accounts. 

The science of toxicology requires an appreciation of the fact that not all effects observed are toxicologically relevant. Toxicity is a damaging effect on whole or part of a living system. 

As the science of toxicology developed, the requirements for establishing safety became more demanding. At one time the LD50 was sufficient to establish safety. The effect of dose level is very important in toxicology. The effects, which vary from no effect dose (NED) levels to fatal effect, have been summarized in Figure 12-2 (Concon 1988). Two types of substances exist type I shows no beneficial effects and type II shows nutritional and/or therapeutic beneficial effects. 

This encyclopedic, three-volume set provides an excellent in-depth review of the science of toxicology, its specializations, and practice. This latest edition has been extensively revised and contains 35 new chapters. 

There are a number of subdivisions to the science of toxicology, and these vary according to the particular interests of the toxicologist concerned. No single classification system of categorization is entirely satisfactory. About 35 years ago, however, T.A. Loomis divided the science of toxicology into three... 

Other ABT objectives are to encourage the study of the science of toxicology and to stimulate its advancement by promulgation of standards for professional practice. It is ABT policy that Diplomats demonstrate a continual commitment to excellence in the science of toxicology. Successful achievement of these goals as outlined by the Board will result in an individual maintaining recognition as a Diplomat by the ABT. 

In order that the Encyclopedia of Toxicology may be useful to as wide a readership as possible, a Glossary of key terms has been provided by the publisher. For the purpose of the article text itself, it is important to use the established technical vocabulary of the science of toxicology, in the interest of accuracy, brevity, and consistency. 

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