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in the Food Supply Strategies to Decrease Exposure SO Committee on the Implications of Dioxin in the Food Supply Food and Nutrition Board INSTITUTE OF MEDICINE OF THE NATIONAL ACADEMIES THE NATIONAL ACADEMIES PRESS Washington, D.C. www.nap.edu
THE NATIONAL ACADEMIES PRESS 500 Fifth Street, N.W. Washington, DC 20001 NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Insti- tute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. Support for this project was provided by the U.S. Food and Drug Administration of the U.S. Department of Health and Human Services and the U.S. Department of Agriculture under contract number 223-99-2321. The views presented in this report are those of the Institute of Medicine Committee on the Implications of Dioxin in the Food Supply and are not necessarily those of the funding agencies. Library of Congress Cataloging-in-Publication Data Dioxins and dioxin-like compounds in the food supply: strategies to decrease exposure / Committee on the Implications of Dioxin in the Food Supply, Food and Nutrition Board. p. ; cm. Includes bibliographical references. ISBN 0-309-08961-1 (pbk.); 0-309-52548-9 (PDF) 1. Dioxins Toxicology. 2. Food contamination. [DNLM: 1. Dioxins adverse effects. 2. Food Contamination prevention & control. 3. Environmental Monitoring methods. 4. Food Supply standards. 5. RiskManage- ment. WA 701 D595 2003] I. National Academy of Sciences (U.S.). Committee on the Implications of Dioxin in the Food Supply. RA1242.DSSD573 2003 615.9'512 dc22 2003016085 Additional copies of this report are available from the National Academies Press, 500 Fifth Street, N.W., Lockbox 285, Washington, DC 20055; (800) 624-6242 or (202) 334- 3313 (in the Washington metropolitan area); Internet, http://www.nap.edu. For more information about the Institute of Medicine, visit the IOM home page at: www.iom.edu. Copyright 2003 by the National Academy of Sciences. All rights reserved. Printed in the United States of America. The serpent has been a symbol of long life, healing, and knowledge among almost all cultures and religions since the beginning of recorded history. The serpent adopted as a logotype by the Institute of Medicine is a relief carving from ancient Greece, now held by the Staatliche Museen in Berlin.
"I(nowing is not enough; we invest apply. Willing is not enough; we must do." Goethe ........... .... ................................ .......... ...... ........ . ......... .. .: ::::: INSTITUTE OF MEDICINE OF THE NATIONAL ACADEMIES Shaping the Future for Health
THE NATIONAL ACADEMIES Advisers to the Nation on Science, Engineering, and Medirine The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Wm. A. Wulf is president of the National Academy of . ~ . . . ~ nglneerlng. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the respon- sibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Acad- emies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. Wm. A. Wulf are chair and vice chair, respectively, of the National Research Council. www. nationa l-academies.org
COMMITTEE ON THE IMPLICATIONS OF DIOXIN IN THE FOOD SUPPLY ROBERT S. LAWRENCE (chair), Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland DENNIS M. BIER, Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas ROBERT E. BROYLES, Chesterfield, Missouri DOROTHY R. CALDWELL, North Carolina Initiative for Healthy Weight in Children and Youth, Division of Public Health, Raleigh, North Carolina DAVID O. CARPENTER, Environmental Health and Toxicology, School of Public Health, University at Albany, Rensselaer, New York JULIE A. CASWELL, Department of Resource Economics, University of Massachusetts, Amherst KEITH R. COOPER, Department of Biochemistry and Microbiology, Rutgers University, Cook College, New Brunswick, New Jersey ,IAMES K. HAMMITT, Department of Health Policy and Management, Harvard School of Public Health, Boston, Massachusetts GAIL G. HARRISON, Department of Community Health Sciences, UCLA School of Public Health, Los Angeles, California ,IAMES T. HEIMBACH, JHeimbach LLC, Washington, DC BARBARA A. KNUTH, Department of Natural Resources, Cornell University, Ithaca, New York ,IAMES D. MCKEAN, Department of Veterinary Diagnostic and Production Animal, Iowa State University, Ames PIETER ,1.,1. SAWER, Department of Pediatrics, University of Groningen, University Hospital, Groningen, Netherlands ROBERT E. SMITH, R.E. Smith Consulting, Inc., Newport, Vermont MICHAEL R. TAYLOR, Resources for the Future, Washington, DC KATHERINE L. TUCKER, Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts Consultant A. JOHN BAILER, Department of Mathematics and Statistics, Miami University, Oxford, Ohio v
Food and Nutrition Board Staff ANN YAKTINE, Study Director TAZIMA A. DAVIS, Research Assistant SANAIT TESFAGIORGIS, Senior Project Assistant (through September 2002) SYBIL BOGGIS, Senior Project Assistant (from September 2002) Contributing Stafifrom the National Academies TINA ROUSE, Program Officer, Board on Agriculture and Natural Resources ABIGAIL MITCHELL, Program Officer, Board on Environmental Studies and Toxicology vim
FOOD AND NUTRITION BOARD CATHERINE E. WOTEKI (chair), College of Agriculture, Iowa State University, Ames ROBERT M. RUSSELL (vice chair), U.S. Department of Agriculture Jean Mayer Human Nutrition Research Center on Aging, Tufts University, Boston, Massachusetts LARRY R. BEUCHAT, Center for Food Safety, University of Georgia, Griffin BENJAMIN CABALLERO, Center for Human Nutrition, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland SUSAN FERENC, SAF Risk, LC, Madison, Wisconsin NANCY F. KREBS, Department of Pediatrics, University of Colorado Health Sciences Center, Denver SHIRIKI KUMANYIKA, Center for Clinical Epidemiology and Biostatistics, University of Pennsylvania School of Medicine, Philadelphia LYNN PARKER, Child Nutrition Programs and Nutrition Policy, Food Research and Action Center, Washington, DC PER PINSTRUP-ANDERSEN, Division of Nutritional Sciences, Cornell University, Ithaca, New York A. CATHERINE ROSS, Nutrition Department, The Pennsylvania State University, University Park BARBARA O. SCHNEEMAN, Department of Nutrition, University of California at Davis NICHOLAS I. SCHORK, Polymorphism Research Laboratory, University of California, San Diego JOHN W. SUTTIE, Department of Biochemistry, University of Wisconsin, Madison STEVE L. TAYLOR, Department of Food Science and Technology and Food Processing Center, University of Nebraska, Lincoln BARRY L. ZOUMAS, Department of Agricultural Economics and Rural Sociology, The Pennsylvania State University, University Park Staff ALLISON A. YATES, Director LINDA MEYERS, Deputy Director GAIL SPEARS, Staff Editor GERALDINE KENNEDO, Administrative Assistant GARY WALKER, Financial Associate . . via
Reviewers This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures ap- proved by the NRC's Report Review Committee. The purpose of this indepen- dent review is to provide candid and critical comments that will assist the institu- tion in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confiden- tial to protect the integrity of the deliberative process. We wish to thank the following individuals for their review of this report: Ransom L. Baldwin, University of California, Davis Alfred O. Berg, University of Washington School of Medicine Tim Byers, University of Colorado Health Sciences Center Edward M. Cooney, Congressional Hunger Center Joanna T. Dwyer, Tufts New England Medical Center George Fries, Silver Spring, Maryland Helen H. Jensen, Iowa State University J. Michael McGinnis, Robert Wood Johnson Foundation Lars Noah, University of Florida College of Law Timothy D. Phillips, Texas A&M University Frank E. Speizer, Wolfson Institute of Preventive Medicine Virginia A. Stallings, Children's Hospital of Philadelphia Lynn B. Willett, The Ohio State University Six
REVIEWERS X Although the reviewers listed above have provided many constructive com- ments and suggestions, they were not asked to endorse the conclusions or recom- mendations nor did they see the final draft of the report before its release. The review of this report was overseen by Patricia A. Buffler, University of Califor- nia, Berkeley, and John C. Bailar, III, University of Chicago. Appointed by the NRC and IOM, they were responsible for making certain that an independent examination of this report was carried out in accordance with institutional proce- dures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.
Preface Dioxin and dioxin-like compounds, or DLCs, are found throughout the envi- ronment: in soil, water sediments, and air. Exposure to these unintentional con- taminants occurs largely through the food supply, although at low levels. Even though DLC levels in the environment and in foods have been declining over the past several decades, public concern persists because DLCs are widespread, and there remains a great deal of uncertainty about their potential adverse health effects. There is additional concern regarding the potential impact of exposure on the population groups that are particularly sensitive to exposure to toxic com- pounds (e.g., developing infants) and those that are more highly exposed than the general population (e.g., breastfeeding infants and groups for whom fish and wild game are important subsistence or cultural food sources). Against the background of increasing knowledge about potential public health effects of dioxins in the food supply, the National Science and Technology Council's Interagency Working Group (IWO) on Dioxin recognized the need for an independent group to examine the scientific evidence of the impact of the presence of dioxins and related compounds in the food supply on food safety and to assess options to reduce exposure to dioxins through foods that would maintain optimal health and nutritional status for the population. IWG, with support from the U.S. Department of Agriculture, the U.S. Department of Health and Human Services, and other agencies and sponsors, asked the National Academies to explore these issues. Thus, the Institute of Medicine, in consultation with the National Research Council, convened a committee with a diverse background and a broad scope of expertise to address the task put to them by the sponsors. x~
xt! PREFACE The committee was charged to review the scientific evidence to identify potential ways to reduce the level of DLCs in foods. Importantly, the committee was instructed to consider the need to protect the public and to assess the poten- tial impact of its recommendations to food and nutrition policies, particularly public education and food assistance programs. The study sponsors recognized that data limitations would allow only quali- tative estimates of net risk, descriptions of exposure reduction, and identification of data needs. In response, the committee offered the sponsoring agencies an array of options to reduce DLC exposure through foods while gathering the data needed to determine future action. These options should also be of use to stake- holders in the agricultural and food-processing industries and to public health professionals. The final recommendations are selected from the array of options and reflect the committee's conclusion that, because uncertainties exist, the level of risk must be determined with greater certainty before regulatory action can be taken, and that it is in the public' s best interest for the government to develop a strategic action plan that includes interim steps to reduce exposure as long as the steps do not lead to undesirable consequences to human health and do not impinge unduly upon the cultural norms of the population. ACKNOWLEDGMENTS The Committee on the Implications of Dioxin in the Food Supply was aided in its challenging tasks by the invaluable contributions of a number of individu- als. First and foremost, many thanks are due to the committee members who volunteered countless hours to the research, deliberations, and preparation of the report. Their dedication to this project and to a stringent timeline was commend- able and was the basis of our success. Many individuals volunteered significant time and effort to address and educate our committee members during the workshops, and the committee thanks them. The committee wishes to acknowledge the invaluable contributions of the FNB study staff, Ann Yaktine, study director; Tazima Davis, research assistant; and Sanait Tesfagiorgis and Sybil Boggis, senior project assistants. The commit- tee is grateful for the contributions of Tina Rouse and Abigail Mitchell, program officers. Special thanks also to Roberta Wedge, senior program officer, and Jamie Jonker, program officer, for their helpful review and suggestions. The committee also thanks Geraldine Kennedo for logistical arrangements, Marcia Lewis for drawing the chemical structures, and Gail Spears for technical editing. This project benefited from the general guidance of Allison Yates, director, and Linda Meyers, deputy director, of the Food and Nutrition Board. ROBERT S. LAWRENCE, Chair Committee on the Implications of Dioxin in the Food Supply
Contents ACRONYMS AND GLOSSARY EXECUTIVE SUMMARY 1 INTRODUCTION Background, 13 The Committee and Its Charge, 14 Organization of the Report, 15 References, 16 2 A SUMMARY OF DIOXIN REPORTS, ASSESSMENTS, AND REGULATORY ACTIVITY Evaluations by Governmental Bodies, 17 Dioxin Regulations and Guidelines, 36 References, 50 3 SOURCES OF DIOXINS AND DIOXIN-LIKE COMPOUNDS IN THE ENVIRONMENT Major Sources of DLCs in the Environment, 54 General Information About the Quantitative Inventory of Releases of DLCs, 58 Environmental Fate and Transport of DLCs, 60 Entry of DLCs into the Food Chain, 63 References, 65 . . . x~ xv . . 13 17 53
xlv 4 ANIMAL PRODUCTION SYSTEMS Direct and Indirect DLC Pathways into Food Products, 71 Livestock Production Systems, 74 Animal Husbandry Practices, 79 Fish and Seafood, 88 Wild Animals, 90 Animal Feeds, 91 Food Processing and Packaging, 99 Imported Foods, 104 Summary, 106 References, 107 HUMAN FOODS AND FOOD-CONSUMPTION PATTERNS Dietary-Intake Patterns, 111 Current Dietary Patterns, 127 Dietary Guidance, 140 Summary, 143 References, 144 6 FRAMEWORK FOR THE DEVELOPMENT OF POLICY OPTIONS TO REDUCE EXPOSURE TO DIOXINS AND DIOXIN-LIKE COMPOUNDS Categorizing Possible Risk-Management Options, 152 The Range of Possible Risk-Management Options, 154 Legal Framework for the Implementation of Interventions, 156 Analytical Tools for Health Risk Decision-Making, 161 Risk-Relationship Analysis, 162 Overview of the Proposed Framework, 165 Research Needs, 171 Conclusion, 171 References, 172 POLICY OPTIONS TO REDUCE EXPOSURE TO DIOXINS AND DIOXIN-LIKE COMPOUNDS Introduction and Background, 174 Environmental Considerations, 178 Pathway I: Animal Production Systems, 178 Pathway II: Human Foods, 188 Pathway III: Food-Consumption Patterns, 194 CONTENTS 71 110 150 174
CONTENTS 8 RISK-MANAGEMENT RECOMMENDATIONS AND RESEARCH PRIORITIES General Strategic Recommendations, 203 High-Priority Risk-Management Interventions, 206 Other Risk-Management Interventions That Deserve Consideration, 210 Research and Technology Development to Support Risk Management, 213 Conclusion, 216 APPENDIXES A Data Tables B Total Diet Study Report: Dioxin Concentrations in Foods C Open Session and Workshop Agendas D Committee Member Biographical Sketches xv 202 217 281 309 313
Congener - One of two or more compounds of the same kind, as of animal or plant with respect to classification. Correlation coefficient - measures the degree of dependence of two variables; the more depenclent they are, the closer the absolute value of the coefficient is to I. De novo - Anew; often applied to particular biochemical pathways in which metabolites are newly biosynthesized (e.g., de novo purine biosynthesis). Dose - A quantity to be administered at one time, such as a specifier! amount of medication. Epidemiology - The study of the distribution and determinants of health-related states and events in populations and the control of health problems, the study of epidemic disease. Exposure - The condition of being subjected to the effects of a substance, such as infectious agents, extremes of weather or radiation, which may have a harmful effect. Genotoxin - A toxin (poisonous substance) which harms the body by damaging DNA molecules, causing mutations that may lead to tumors, or neoplasms. Halogenated - refers to a chemical compound or mixture that contains halogen atoms. Halogen refers to those elements in the seventeenth column of the periodic table: fluorine (F), chlorine (CI), bromine (Br), iodine Ail, and astatine (At). Hepatotoxin - A toxin that is destructive to parenchymal cells of the liver. Heterogeneous - Not of uniform composition, quality or structure. Hydrolysis - The splitting of a compound into fragments by the addition of water, the hyclroxy! group being incorporated in one fragment and the hydrogen atom in the other. Immunologic - Pertaining to immunology, (a subfield of biology that deals with the study of antigens and the immune process and how humans and higher animals fight off disease). isotope dilution -A technique that can be used to determine the amount of a single substance in a mixture, using radioactive tracers. Lactation - The period of the secretion of milk. Lipophlic - An element which has an affinity for fat. Muktuk - The skin ant! underlying fat (blubber) layer of whale. Narwhal Mattak - The mukLuk (skin and underlying fat (blubber) layer) of the whale, Monodon monoceros. "Mattak" is commonly used as the dialect representation of "muktuk" in Baffin Inuktitut language. Neurobehavioral - Relating to neurological status as assessed by observation of behavior. Neurodevelopment - Development of the central and peripheral nervous system starting at conception and going through the life span of an organism. Odds ratio - The odds of the outcome of interest occurring in the group with exposure compared to the ocicis in the group without the exposure; or, conversely, the odds of having the exposure of interest in the group with the outcome of interest compared to the odds in the group without the outcome of interest. Persistent organic pollutant - Chemical substances that persist in the environment, bioaccumulate through the food web, and pose a risk of causing adverse effects to human health and the environment. Photolysis - I,ight induced cleavage of a chemical bond, as in the process of photosynthesis. Regression coefficient - Amount by which the outcome of interest chances ner unit change in an independent variable, such as an exposure measure. ~ ~ lo, Relative risk - Rate of the outcome of interest in the population of interest compared to the rate in the reference population. Temporal - Pertaining to time; limited as to time. XVI F
Acronyms and Glossary ORGANIZATIONS, PROGRAMS, STUDIES AAP American Academy of Pediatrics AHA American Heart Association ATSDR Agency for Toxic Substances and Disease Registry CDC Centers for Disease Control and Prevention CERCLA Comprehensive Environmental Response, Compensation, and Liability Act CFIA Canadian Food Inspection Agency CSFII Continuing Survey of Food Intakes by Individuals EC European Commission EPA U.S. Environmental Protection Agency EU European Union FAO Food and Agriculture Organization of the United Nations FDA U.S. Food and Drug Administration FDCA Food, Drug and Cosmetics Act FSIS Food Safety and Inspection Service JECFA Joint FAD/WHO Expert Committee on Food Additives HACCP Hazard Analysis and Critical Control Point HHS U.S. Department of Health and Human Services IARC International Agency for Research on Cancer NHANES National Health and Nutrition Examination Survey TDS Total Diet Study UK United Kingdom xv
. . . xvit! USDA WHO WIC CDD CDF DLC dscf dscm EDo1 GAP GMP HCDD HMIWI HxCDF I-TEF I-TEQ LED MRL N-TEQ OCDD OCDF PCB PCDD PCDF PCP PeCDD PeCDF POPs SMR TCDD TCDF TDI TEF TEQ TWI ACRONYMS AND GLOSSARY U.S. Department of Agriculture World Health Organization Special Supplement Nutrition Program for Women, Infants and Children TERMS chlorinated dibenzo-p-dioxin chlorodibenzofuran dioxin-like compound; in this report, DLCs are the dioxins, furans, and polychlorinated biphenyls that possess dioxin-like activity dry standard cubic feet dry standard cubic meter 1 percent effective dose Good Agricultural Practice Good Manufacturing Practice hexachlorodibenzo-p-dioxin hospital/medical/infectious waste incinerator hexachlorodibenzo -p -furan international toxicity equivalency factor system international toxicity equivalents lower 95 percent confidence interval on the 1 percent effective dose minimum risk level Nordic toxicity equivalents octachlorodibenzo-p-dioxin octachlorodibenzofuran polychlorinated biphenyl polychlorinated dibenzo-p-dioxin polychlorinated dibenzofuran pentachlorophenol pentachlorodibenzo-p-dioxin pentachlorodibenzofuran persistent organic pollutants standardized mortality rate 2,3 ,7,8-tetrachlorodibenzo-p-dioxin 2,3 ,7,8-tetrachlorodibenzofuran tolerable daily intake toxicity equivalency factor toxicity equivalents tolerable weekly intake
ACRONYMS AND GLOSSARY XlX GLOSSARY Aerobic Growing, living, or occurring in the presence of molecular oxygen; for example, bacteria that require oxygen to survive. Anaerobic Growing, living, or occurring in the absence of molecular oxygen. Beluga whale fat Fat of the white whale, Delphinapterus leucas; the fat is commonly called blubber. Body burden The total amount of a chemical, metal, or radioactive substance present at any time after absorption in the body of a human or animal. Brominated Combined or saturated with bromine or any of its compounds. Carcinogen An agent capable of initiating development of malignant tumors; may be a chemical, a form of electromagnetic radiation, or an inert solid body. Chlorinated Any organic chemical that includes chlorine atoms; chlorinated organic compounds, along with other halogenated organics, have been implicated in health risks such as cancer, endocrine system disruption, birth defects, compromised immune systems, and reduced fertility. Congener One of two or more compounds of the same kind with respect to classification. De nova Anew; often applied to particular biochemical pathways in which metabolites are newly biosynthesized (e.g., de nova purine biosynthesis). Dose A quantity to be administered at one time, such as a specified amount of medication. Epidemiology The study of the distribution and determinants of health-related states and events in populations and the control of health problems; the study of epidemic disease. Exposure The condition of being subjected to the effects of a substance, such as infectious agents, that may have a harmful effect. Genotoxin A toxin (poisonous substance) that harms the body by damaging DNA molecules, causing mutations that may lead to tumors or neoplasms. Halogenated refers to a chemical compound or mixture that contains halogen atoms; halogen refers to those elements in the seventeenth column of the periodic table: fluorine, chlorine, bromine, iodine, and astatine. Heterogeneous Not of uniform composition, quality, or structure. Hydrolysis The splitting of a compound into fragments by the addition of water, the hydroxyl group being incorporated in one fragment and the hydrogen atom in the other. Immunologic Pertaining to immunology, a subfield of biology that deals with the study of antigens and the immune process and how humans and higher animals fight off disease. Isotope dilution A technique using radioactive tracers that can be used to determine the amount of a single substance in a mixture. Lactation The period of the secretion of milk.
xx ACRONYMS AND GLOSSARY Lipophilic An element that has an affinity for lipid. Muktuk The skin and underlying fat (blubber) layer of a whale. Narwhal mattak The skin and underlying fat (blubber) layer of the whale Monodon monoceros. Mattak is commonly used as the dialect representation of muktuk in Baffin Inuktitut language. Neurobehavior Neurological status as assessed by observation of behavior. Neurodevelopment Development of the central and peripheral nervous systems starting at conception and going through the life span of an organism. Persistent organic pollutant Chemical substance that persists in the environment, bioaccumulates through the food web, and poses a risk of causing adverse effects to human health and to the environment. Photolysis Light induced cleavage of a chemical bond, as in the process of photosynthesis. Relative risk Rate of the outcome of interest in a population compared with the rate in the reference population. Temporal Pertaining to time; limited as to time. Toxicity The quality of being poisonous, especially the degree of virulence of a toxic microbe or of a poison. Toxicokinetic modeling The time course of disposition (absorption, distribution, biotransformation, and excretion) of xenobiotics (foreign chemicals to which organisms are exposed) in the whole organism. Tropospheric Pertaining to the lower layer of the earth's atmosphere in which the change of temperature with height is relatively large; it is the region where clouds form, convection is active, and mixing is continuous and more or less complete. Vapor phase Phase when substances transition from a liquid state to gaseous state through the breaking of molecular bonds. Volatile Readily vaporizable at a low temperature.
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