The Poisoned Weed: Plants Toxic to Skin
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The Poisoned Weed: Plants Toxic to Skin DONALD G. CROSBY OXFORD UNIVERSITY PRESS THE POISONED WEED DONALD G. CROSBY The poisoned weed PLANTS TOXIC TO SKIN 1 2004 1 Oxford New York Auckland Bangkok Buenos Aires Cape Town Chennai Dar es Salaam Delhi Hong Kong Istanbul Karachi Kolkata Kuala Lumpur Madrid Melbourne Mexico City Mumbai Nairobi Sa˜o Paulo Shanghai Taipei Tokyo Toronto Copyright # 2004 by Oxford University Press Published by Oxford University Press, Inc., 198 Madison Avenue, New York, New York 10016 www.oup.com Oxford is a registered trademark of Oxford University Press All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of Oxford University Press. Library of Congress Cataloging-in-Publication Data Crosby, Donald G. The Poisoned Weed: Plants toxic to skin / Donald G. Crosby. p. cm. Includes bibliographical references and index. ISBN 0-19-515548-3 1. Dermatotoxicology. 2. Poisonous plants. 3. Plant toxins. I. Title. RL803.C76 2003 616.5007—dc21 2003046272 987654321 Printed in the United States of America on acid-free paper To Nancy, whose struggles with T. diversilobum, T. radicans, M. indica, S. terebinthefolius, E. maculata, U. dioica, and sundry other plants inspired this book. This page intentionally left blank PREFACE Human dermatitis from plants is almost universal. In the United States alone, more than two-thirds of the population reacts to poison oak, poison ivy, and their relatives—more than 160 million people, including me. Many familiar plants in our homes, fields, and gardens produce substances toxic to skin, and allergenic and irritant species are found on every continent except Antarctica. Considering the misery they cause, I was surprised at how few guides to them were available. The idea for this project developed over a period of years as I watched my wife, Nancy, react to a series of toxic plants until, at age 60, I too became sensitized to poison oak. Then, in preparing a classroom lecture in the late 1980s, I discovered that the only existing book on poison oak and poison ivy (by James B. McNair) had been published in 1923—before the toxic con- stituents were identified, before a mechanism was proposed for their toxic action, and before the name Toxicodendron was established for their genus—even before I was born. An update seemed long overdue, but as reference material accumulated, so many other species with similar aller- gens and effects emerged that the scope had to expand. As plans proceeded, I became aware of several recent books on poison oak and poison ivy for the lay reader, in particular those by Edward Frankel (1991) and Susan Hauser (1996). However, none was sufficiently technical for my purposes, and the classic Botanical Dermatology by John Mitchell and Arthur Rook (1979) and Dermatologic Botany edited by Javier Avalos and Howard Maibach (2000) were too detailed. Unfortunately, I did not discover the especially helpful 1986 Clinics in Dermatology volume on plant dermatitis, edited by Jere Guin and John Beaman, until my manu- script was almost complete. My sincere appreciation for the efforts of all these writers. Other key references are listed in appendix G. The present book reviews the history, occurrence, classification, toxic constituents, and health aspects of allergenic and irritant plants that people contact in everyday life. Because the reaction of human skin to the poison ivy (cashew) family is especially severe and widespread, those species re- ceive the most attention, but other familiar weeds, crop plants, ornamentals, and wild species are discussed also. Coverage is not intended to be en- cyclopedic, and references are provided for further exploration. Because chemistry defines a plant’s dermatotoxic activity, species whose active constituents are still unidentified generally have been excluded. The writing is intended to inform a broad cross section of chemical, medical, and biological scientists and students about common plant species and products that are toxic to human skin. However, parts of this book also may interest people involved with forestry, firefighting, utilities, parks, gardening, agriculture, outdoor recreation, and anyone else who has fre- quent contact with plants. The reaction of an individual’s skin to any par- ticular plant is unpredictable and recognizes no geographical boundary, so the coverage is international. Almost all previous books on the subject have been written or edited by dermatologists, so one of my aims is to provide the viewpoint of a chemist and toxicologist. Consequently, the contents are heavily slanted toward the toxic species, their constituents, and people’s exposure to them, and many biological and medical aspects are left to others more knowledgable. Because the information cuts across so many fields of activity, a glossary has been provided. The choice of illustrations was difficult. Given the limited number agreed upon with the publisher, I chose those I thought would be especially in- teresting and representative of my own experience. Also, I wanted plants that were widely accessible, so most of the photos were taken near my home in Davis, California. Except where noted, the photographs and line drawings are my own, but I acknowledge, with thanks, permission to publish others, as indicated in their captions. I am indebted to many friends and colleagues for their help. John Hylin, Howard Maibach, Bob McCandliss, Bob Rice, Warren Roberts, and Ellen Zagory provided helpful reviews of the various sections; Rick Crosby, Jere Guin, and Sandy Ogletree assisted with some of the photos, and I appreciate the help and advice of Senior Editor Kirk Jensen and Production Editor Lisa Stallings; any errors are mine, not theirs. I am especially grateful to my wife, Nancy, for her continued input, encouragement, and knowledge of plants. viii PREFACE CONTENTS ONE THE SETTING 3 1.1 History 3 1.2 The Plants 6 1.3 The Poisons 9 1.4 Skin 12 1.5 Exposure 15 1.6 Adverse Effects 16 1.7 Prevention and Treatment 19 1.8 Conclusions 20 TWO POISON OAKS, POISON IVIES, AND RELATIVES 22 2.1 Family Ties: The Anacardiaceae 22 2.2 Toxicodendrons 22 2.3 What to Look For 32 2.4 Habitats and Geographical Distribution 33 2.5 Propagation 36 2.6 Conclusions 37 THREE OTHER ALLERGENIC PLANTS 39 3.1 Dermatotoxic Plants 39 3.2 More Anacardiaceae 39 3.3 Quinone-Containing Plants 47 3.4 Asteraceae (Compositae) 51 3.5 Other Flowering Plants 58 3.6 Lower Plants 63 3.7 Photoallergenic Plants 64 3.8 Conclusions 65 FOUR PHOTOTOXIC AND IRRITANT PLANTS 66 4.1 Phototoxic Plants 66 4.2 Irritant Plants 73 4.3 Conclusions 86 FIVE ALLERGENS RELATED TO URUSHIOL 87 5.1 Urushioid Allergens 87 5.2 Urushiols and Laccols 87 5.3 Isolation, Identification, and Analysis 92 5.4 Physical and Environmental Properties 97 5.5 Reactions with Proteins 101 5.6 Synthetic Urushioids 102 5.7 Natural Urushioids 103 5.8 Conclusions 106 SIX OTHER PLANT ALLERGENS 108 6.1 Other Kinds of Allergens 108 6.2 Quinones and Hydroquinones 108 6.3 Lactones 113 6.4 Acetylenic Alcohols 119 6.5 Essential Oils 120 6.6 Lichen Substances 124 6.7 Rubber Latex 126 6.8 Conclusions 126 Seven PHOTOTOXIC AND IRRITANT CONSTITUENTS 128 7.1 More Dermatotoxicity 128 7.2 Photodynamic Agents 128 7.3 Irritant Esters 135 7.4 Organosulfur Compounds 140 7.5 Irritant Amines and Amides 147 7.6 Calcium Oxalate 149 7.7 Conclusions 149 EIGHT EXPOSURE 151 8.1 Forms of Exposure 151 8.2 Direct (Primary) Exposure 152 8.3 Casual (Nonoccupational) Exposure 157 8.4 Indirect (Secondary) Exposure 163 8.5 Individual Characteristics 165 8.6 Cross–reactions 165 8.7 Economic Significance 167 8.8 Limiting Exposure 168 8.9 Conclusions 171 NINE ADVERSE EFFECTS 172 9.1 Intoxication 172 9.2 Penetration 172 9.3 ‘‘Toxicity’’ 175 x CONTENTS 9.4 Symptoms of Contact Dermatitis 176 9.5 Mechanisms 181 9.6 Tumorigenesis 186 9.7 Sensitivity Differences 187 9.8 Relation of Structure to Activity 188 9.9 Conclusions 191 TEN PREVENTION AND TREATMENT 193 10.1 Prevention and Treatment 193 10.2 Patch Tests 193 10.3 Prevention 195 10.4 Treatment: What Works, What Doesn’t 199 10.5 ‘‘Rational’’ Treatment 201 10.6 Future Possibilities 203 10.7 Conclusions 205 Appendices 207 References 215 Glossary 247 Index of Plant Names 251 Index of Chemical Common Names 259 General Index 263 CONTENTS xi This page intentionally left blank THE POISONED WEED This page intentionally left blank ONE THE SETTING ‘‘The poysoned weede is much in shape like our English Ivie, but being but touched, causeth rednesse, itchinge, and lastly blysters, the which howsoever after a while they passe away of themselves without further harme...’’ —Captain John Smith, 1609 Captain Smith’s ‘‘Ivie’’ was well known to his Powhatan Indian neighbors. For centuries, they and other Native Americans had used it for medicine. Navajos made arrow poison from this native plant, and California’s Miwoks made the Western version, it-tum in their language, into black dye for baskets (Balls, 1962). They were very aware of its harmful character—in Mexico, it was called mala mujer, the wicked woman—but to unwary European settlers, the attractive weeds became familiar as ‘‘poison ivy’’ and ‘‘poison oak.’’ With the latter blanketing the Pacific Coast and the former growing rampant over much of the rest of the continent, the two species were to become our nation’s best-known toxic plants. Contrary to popular belief, Native Americans were just as susceptible to the poisons, and as fearful of them, as those whose skins were white or brown.