The Dose Makes the Poison: A Plain-Language Guide to Toxicology, 3rd Edition

Introduction to the Third Edition xi

Preface to the Second Edition xv

1 WHAT ARE CHEMICALS? 1

Atoms and Molecules 1

Natural Chemicals 2

Synthetic Chemicals 3

Chemical Categories 6

Chemicals: “Good” and “Bad” 8

Why the “Good-Bad” Dichotomy? 10

Man-made Chemicals Are Made by Humans 11

Man-made Chemicals May Not Be Biodegradable 12

Man-made Chemicals May Be Very Complex 16

2 WHAT HARM DO CHEMICALS CAUSE? 19

Harmful Properties of Chemicals 19

Explosiveness and Reactivity 19

Flammability and Combustibility 20

Radioactivity 21

Corrosiveness 23

Irritation 23

Sensitization and Photosensitization 24

Toxicity 26

Multiple Harmful Properties 27

Definition of Poison 28

Defi nition of Hazard 28

3 WHAT IS TOXICOLOGY? 31

Empirical Toxicology 31

Paracelsus and Ramazzini 32

A Brief History of Toxicology 34

Toxicology Today 40

What Do Toxicologists Do? 44

4 WHAT FACTORS INFLUENCE THE TOXIC EFFECTS OF CHEMICALS? 47

Acute versus Chronic Toxicity 47

Significance of Divided Doses 53

Routes of Exposure 54

Dermal Exposure 54

Inhalation Exposure 55

Oral Exposure 58

Other Routes of Exposure 59

Combinations 60

Influence of Route on Toxicity 60

Metabolism 64

Routes of Elimination (Excretion) 65

Other Factors that Infl uence Toxicity 66

Species 66

Sex 70

Age 71

Nutrition 73

State of Health 73

Biochemical Individuality (Genetic Diversity) 74

Presence of Other Chemicals 75

Adaptation 77

Light 79

5 HOW IS TOXICOLOGY STUDIED? 81

Experimental Methods 82

Acute Toxicity 83

Irritant and Corrosive Effects 85

Sensitization and Photosensitization 86

Chronic Toxicity 87

Mutagenesis 90

Carcinogenesis 91

Developmental and Reproductive Toxicity 94

Units of Trace Quantities 95

Analytical Methods 96

Animal Rights 99

6 GENERAL TOXICOLOGY 103

Acute Toxicity 103

LD50 and LC50 Values 103

Signifi cance of LDs for Humans 104

Poison Prevention 109

Antidotes 112

Chronic Toxicity 114

No-Effect Levels and Thresholds 116

Margins of Safety 117

Sufficient Challenge 119

Bioaccumulation 121

7 MUTAGENESIS AND CARCINOGENESIS 129

Mutagenesis 129

Genetic Code 129

Mutations 130

Significance of Mutations 132

Mutation and Cancer 135

Carcinogenesis 138

What Is Cancer? 138

Causes of Cancer 140

Role of Mutation 141

Incidence of Cancer 142

Categories and Characteristics of Carcinogens 143

Induction Periods 146

Thresholds 147

Practical Thresholds 149

The Real World 150

Benzo[a]pyrene 150

Cancerophobia 151

8 DEVELOPMENTAL AND REPRODUCTIVE TOXICITY 153

Male and Female Reproductive Systems 154

Prepuberty Systems 154

Adult Systems 155

The Developing Individual 156

9 CASE STUDIES IN TOXICOLOGY 163

Environmental Contaminations 164

Dioxins: Seveso, Italy 164

PCBs and Dibenzofurans: Yusho Disease 169

Bophal, India 173

Minamata Disease 174

DDT 174

Consumer Products 177

Metals 177

Lead and Cadmium 178

Zinc 178

Plastics 179

Bisphenyl A 180

Indoor Air Pollution 181

Water Pollution 185

Pharmaceuticals 186

Fen-Phen 187

Vioxx 188

Thalidomide 189

10 EPIDEMIOLOGY 191

Origins of Modern Epidemiology 191

Epidemiology of Noninfectious Diseases 193

Koch’s Postulates 195

Study Design: Precepts and Pitfalls 197

Unreasonable Expectations 201

Proximate Event Approach in Assigning Cause 202

Distrust of Science and Scientists 204

11 THE STUDY OF RISK 211

Public Health Statistics 211

Inherent Risk 213

Risk Assessment 215

Perceived Risk 218

Acceptable Risk 220

Risk Benefit and Cost Benefit 222

Risk Communication 225

Risk Management 227

Bibliography 229

Abbreviations 233

Glossary 235

Appendix A 245

Index 247