United States
Environmental Protection
Agency
Office of Health and
Environmental Assessment
Washington DC 2046O
EPA/600/8-83/031 F
August 1985
vvEPA
Research and Development
Health Assessment Final
Document for Report
Vinylidene Chloride
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EPA/600/8-83/031 F
August 1985
Health Assessment Document for
Vinylidene Chloride
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Office of Health and Environmental Assessment
Environmental Criteria and Assessment Office
Research Triangle Park, North Carolina 27711
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I
DISCLAIMER
This document has been reviewed in accordance with the U.S. Environmental
Protection Agency's peer and administrative review policies and approved for
presentation and publication. Mention of trade names or commercial products does
not constitute endorsement or recommendation for use.
ii
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PREFACE
The Office of Health and Environmental Assessment has prepared this health
assessment to serve as a "source document" for EPA use. The health assessment
document was originally developed for use by the Office of Air Quality Planning
and Standards to support decision-making regarding possible regulation of
vinylidene chloride as a hazardous air pollutant. However, the scope of this
document has since been expanded to address multimedia aspects.
In the development of the assessment document, the scientific literature
has been inventoried, key studies have been evaluated and summary/conclusions
have been prepared so that the chemical's toxicity and related characteristics
are qualitatively identified. Observed effect levels and other measures of dose-
response relationships are discussed, where appropriate, so that the nature of
the adverse health responses are placed in perspective with observed
environmental levels. , . , ..
Any information regarding sources, emissions, ambient air concentrations,
and public exposure has been included only to give the reader a/preliminary
indication of the potential presence of this substance in the ambient air. While
the available information is presented as accurately as possible, it is
acknowledged to be limited and dependent in many instances on assumption rather
than specific data. This information is not intended, nor should it be used, to
support any conclusions regarding risks to public health.
If a review of the health information indicates that the Agency should
consider regulatory action for this substance, a considerable effort will be
undertaken to obtain appropriate information regarding sources, emissions, and
ambient air concentrations. Such data will provide additional information for
drawing regulatory conclusions regarding the extent and significance of public
exposure to this substance.
iii
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AUTHORS, CONTRIBUTORS, AND REVIEWERS
AUTHORS;
The EPA Office of Health and Environmental Assessment (OHEA) is responsible
for the preparation of this health assessment document. The OHEA Environmental
Criteria and Assessment Office (ECAO/RTP) had overall responsibility for
coordination and direction of the document and production effort (Dr. Robert M.
Bruce, Project Manager). The chapters addressing physical and chemical proper-
ties, sampling and analysis, air quality and biological effects in animals and
man were all originally written by Syracuse Research Corporation with the
exception of sections addressing mutagenicity, teratogenicity, reproductive
effects and carcinogenicity. The principal authors of these chapters are listed
below.
Dr. Dipak K. Basu
Life and Environmental Sciences Division
Syracuse Research Corporation
Syracuse, NY
Mr. John Becker
Life and Environmental Sciences Division
Syracuse Research Corporation
Syracuse, NY
Dr. Joan T. Colman
Life and Environmental Sciences Division
Syracuse Research Corporation
Syracuse, NY
Dr. Michael W. Neal
Life and Environmental Sciences Division
Syracuse Research Corporation
Syracuse, NY
Dr. Joseph Santodonato
Life and Environmental Sciences Division
Syracuse Research Corporation
Syracuse, NY
IV
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Dr. Richard Sugatt
Life and Environmental Sciences Division
Syracuse Research Corporation
Syracuse, NY
The OHEA Carcinogen Assessment Group (CAG) was responsible for preparation
of the sections on carcinogenicity. Participating members of the CAG are listed
below (principal authors of the present carcinogenicity sections are designated
by an asterisk).
Roy E. Albert, M.D. (Chairman)
Elizabeth L. Anderson, Ph.D.
Larry D. Anderson*
Steven Bayard, Ph.D.*
David L. Bayliss, M.S.*
Robert P. Bellies, Ph.D.
Chao W. Chen, Ph.D.
Margaret M.L. Chu, Ph.D.
Herman J. Gibb, M.S., M.P.H.
Bernard H. Haberman, D.V.M., M.S.
Charalingayya B. Hiremath, Ph.D.
Robert E. McGaughy, Ph.D.
Jean C. Parker, Ph.D.*
Charles H. Ris, M.S., P.E.
Dharm V. Singh, D.V.M., Ph.D.
Todd W. Thorslund, Sc.D.
The OHEA Reproductive Effects Assessment Group (REAG) was responsible for
the preparation of sections on mutagenicity, teratogenicity and reproductive
effects. Participating members of REAG are listed below (principal authors of
present sections are indicated by an asterisk). The Environmental Mutagen
Information Center (EMIC), in Oak Ridge, TN, identified literature bearing on the
mutagenicity of vinylidene chloride.
John R. Fowle, III, Ph.D.
David Jacobson-Kram, Ph.D.*
K.S. Lavappa, Ph.D.
Sheila L. Rosenthal, Ph.D.
Carol N. Sakai, Ph.D.*
Lawrence R. Valcovic, Ph.D.
Vicki-Vaughan Dellarco, Ph.D.
Peter E. Voytek, Ph.D. (Director)
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REVIEWERS;
The following individuals provided peer-review of this draft or earlier
drafts of this document:
U.S. Environmental Protection Agency
Larry Anderson, Ph.D.
Office of Health and Environmental Assessment
Carcinogen Assessment Group
H. Matthew Bills
Acting Director for Monitoring
Systems and Quality Assurance
Office of Research and Development
Robert M. Bruce, Ph.D.
Office of Health and Environmental Assessment
Environmental Criteria and Assessment Office
John B. Clements, Ph.D. ,
Environmental Monitoring and Support Laboratory, RTP
Office of Research and Development
Larry Cupitt, Ph.D.
Environmental Research Laboratory (RTP)
Office of Research and Development
Paul E. des Hosiers
Industrial and Extractive Processes Division
Office of Environmental Engineering and Technologies
Linda Erdreich, Ph.D.
Office of Health and Environmental Assessment
Environmental Criteria and Assessment Office •
James W. Falco, Ph.D.
Office of Health and Environmental Assessment
Exposure Assessment Group
Bruce Gay, Ph.D.
Environmental Sciences Research Laboratory (RTP)
Office of Research and Development
Lester D. Grant, Ph.D.
Office of Health and Environmental Assessment
Environmental Criteria and Assessment Office
Larry L. Hall, Ph.D.
Health Effects Res. Lab. (RTP)
vi
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Gary E. Hatch, Ph.D.
Health Effects Research Laboratory
Office of Research and Development
Donna Kuroda
Office of Health and Environmental Assessment
Reproductive Effects Assessment Group
James J. Lichtenberg
Environmental Monitoring and Support Lab.
Office of Research and Development
(Gin.)
Steve Lutkenhoff
Office of Health and Environmental Assessment
Environmental Criteria and Assessment Office
Robert McGaughy, Ph.D.
Office of Health and Environmental Assessment
Carcinogen Assessment Group
Raymond Merrill, Ph.D.
Industrial Environmental Res. Lab. (RTF)
Office of Research and Development
Joseph Padgett
Office of Air Quality Planning and .Standards
Strategies and Air Standards Division , . '-.
Nancy Pate, D.V.M.
Office of Air Quality Planning and Standards
Strategies and Air Standards Division
Shabeg Sandhu, Ph.D.
Health Effects Research Lab.
Office of Research and Development
Robert D. Schonbroo, Ph.D.
Environmental Monitoring Systems Laboratory
Las Vegas, Nevada
Office of Research and Development
Jerry F. Stara, D.V.M.
Office of Health and Environmental Assessment
Environmental Criteria and Assessment Office
Bruce Tichenor, Ph.D.
Industrial Environmental Research Laboratory (RTP)
Office of Research and Development
Peter Voytek, Ph.D.
Office of Health and Environmental Assessment
Reproductive Effects Assessment Group
vii
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Herbert Wiser, Ph.D.
Senior Science Advisor
Office of Research and Development
Consultants and/or Reviewers
Julian B. Andelman, Ph.D.
Professor of Chemistry
Graduate School of Public Health
University of Pittsburgh
Pittsburgh, PA
I.W'.F. Davidson, Ph.D.
Professor of Pharmacology
Bowman Gray School of Medicine
Wake Forest University
Winston-Salem, NC
Rudolph J. Jaeger, Ph.D.
Consulting Toxicologist
7 Bogert Place
Westwood, NJ
Edmond J. LaVoie, Ph.D.
Head, Metabolic Biochemistry Section
Naylor Dana Institute for Disease Prevention
American Health Foundation
Valhalla, NY
Richard R. Monson, M.D., S.C.D.
Assoc. Prof, of Epidemiology
School of Public Health
Harvard University
Boston, MA
SCIENCE ADVISORY BOARD
ENVIRONMENTAL HEALTH COMMITTEE
The content of this health assessment document on vinylidene chloride was
independently peer-reviewed in public session by the Environmental Health
Committee of the Environmental Protection Agency's Science Advisory Board.
CHAIRMAN, ENVIRONMENTAL HEALTH COMMITTEE
Dr. Herschel E. Griffen, Professor of Epidemiology, Graduate School of Public
Health, 6505 Alvarado Road, San Diego State University, San Diego,
California 92182-0405.
EXECUTIVE SECRETARY, SCIENCE ADVISORY BOARD
Dr. Daniel Byrd III, Executive Secretary, Science Advisory Board, A-101 F, U.S.
Environmental Protection Agency, Washington, D.C. 20460,
viii
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MEMBERS
Dr. Morton Corn, Professor and Director, Division of .Environmental Health
Engineering, School of Hygiene and Public Health, The Johns Hopkins
University, 615 N. Wolfe Street, Baltimore, Maryland 21205.
Dr. John Doull, Professor of Pharmacology and Toxicology, University of Kansas
Medical Center, Kansas City, Kansas 66103.
Dr. Jack D. Hackney, Chief, Environmental Health Laboratories, Professor of
Medicine, Rancho Los Amigos Hospital Campus of the University of Southern
California, 7601 Imperial Highway, Downey, California 90242.
Dr. Marvin Kuschner, Dean, School of Medicine, Health Science Center, Level 4,
State University of New York, Stony Brook, New York 11794.
Dr. D. Warner North, Principal, Decision Focus Inc., Los Altos Office Center,
Suite 200, 4984 El Camino Real, Los Altos, California 94022.
CONSULTANTS
Dr. Seymour Abrahamson, Professor of Zoology and Genetics, Department of
Zoology, University of Wisconsin, Madison, Wisconsin 53706.
Dr. Edward F. Ferrand, Assistant Commissioner for Science and Technology, New
York City Department of Environmental Protection, 51 Astor Place, New York,
New York 10003. . :
Dr. Ronald D. Hood, Professor, Developmental Biology Section, Department of
Biology, The University of Alabama, and Principal Associate, R.D. Hood and
Associates, Consulting Toxicologists, P.O. Box 1927, University, Alabama
35486.
Dr. Bernard Weiss, Professor, Division of Toxicology, P.O. Box RBB, University of
Rochester, School of Medicine, Rochester, New York 14642.
ix
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TABLE OF CONTENTS
Page
1. SUMMARY AND CONCLUSIONS ......................... ......... .. ......... 1-1
2. INTRODUCTION ........................................... .... ......... 2-1
3. PHYSICAL AND CHEMICAL PROPERTIES ......................... .. ......... 3-1
3.1 SYNONYMS AND TRADE NAMES ............................ .. ....... .. 3-1
3.2 STRUCTURAL AND MOLECULAR FORMULAE AND MOLECULAR WEIGHT ......... 3-1
3.3 PHYSICAL PROPERTIES ................................. . .......... 3-1
3.3-1 Description ............................................ 3-1
3.3.2 Boiling Point ............................... . .......... 3-1
3.3.3 Freezing Point .............................. . .......... 3-1
3.3. 4 Density ............. ..... ............................. 3-1
3.3.5 Refractive Index ............................ • ......... 3-2
3.3.6 Solubility ............................................ 3-2
3.3.7 Volatility ................................. •• ......... 3-2
3.3.8 Volatility from Water ................................. 3-2
3.3.9 Hazard Parameters .... * ...................... ........... 3-2
3.3.10 Dielectric Constant ......................... ........... 3-3
3.3.11 Thermodynamic Data .......................... ........... 3-3
3.3.12 Viscosity ................................... .......... 3-3
3.3.13 Conversion Factors at 25°C and 760 nm pressure ........ 3-3
3.4 STORAGE AND TRANSPORTATION OF THE MONOMER ..................... 3-3
3.5 CHARACTERISTICS OF THE COMMERICAL PRODUCT ....... ; ---- .......... 3-4
3.6 PURIFICATION OF THE MONOMER ................................... 3-5
3.7 CHEMICAL REACTIVITY ........ . ...................... • ........... 3-5
4. SAMPLING AND ANALYTICAL METHODS ..................................... 4-1
4.1 AIR [[[ 4-1
4.1.1 Air Sampling ........................................... 4-1
4.1.2 Storage of Samples Collected in Solid Sorbent Tubes.... 4-7
4.1.3 Analytical Methods ..................................... 4-7
4.2 WATER [[[ 4-13
4.2.1 Water Sampling ......................................... 4-13
' 4.2.2 Analytical Methods ..................................... 4-14
4.3 SOIL AND DISPOSAL SITE SAMPLES
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TABLE OF CONTENTS (cont.)
4.4 MONOMER CONTENT IN POLYMERS AND MONOMER MIGRATION INTO
FOOD-SIMULATING SOLVENTS 2j_19
4.4.1 Sample Collection 4_ig
4.4.2 Analysis — l}_ig
4.5 ANALYSIS OF FOODS AND OTHER BIOLOGICAL SAMPLES 4-21
SOURCES IN THE ENVIRONMENT 5-1
5.1 SOURCES OF AIR POLLUTION... 5-1
5.1.1 Manufacture of Vinylidene Chloride Monomer 5-2
5.1.2 Manufacture of Polymers Containing
Polyvinylidene Chloride .....,.;... 5-4
5.1.3 Processing or Fabrication of Polymers 5-9
5.1.4 Storage, Handling and Transportation
of ,the Monomer. 5-9
5.1.5 Chemical Intermediate Production 5-13
5.1.6 Incineration of Polymers Containing .;, .
Polyvinylidene Chloride 5-13
5.2 SOURCES IN WATER 5-14
5.3 SOURCES IN SOIL ...» .......... "" 5.14
5.4, SOURCES IN FOOD ....;.. .!C".... 5-15
•5.5 .SUMMARY OF ENVIRONMENTAL LOSSES. !!!'!!!.'! .* 5-15
ENVIRONMENTAL FATE, TRANSPORT, AND DISTRIBUTION ..." 6-1
6.1 ATMOSPHERIC FATE, TRANSPORT, AND DISTRIBUTION 6-1
6.1.1 Reaction with Atmospheric Radicals and Ozone.... 6-1
6.1.2 Atmospheric Photochemical Reactions. ........ 6-3
6.1.3 Atmospheric Physical Processes 6-4
6.2 AQUATIC FATE, TRANSPORT, AND BIOACCUMULATION ... 6-4
6.2.1 Fate and Transport in Water 6-5
6.2.2 Bioaccumulation of Vinylidene Chloride
in Aquatic Organisms f 6-8
6.3 FATE, PERSISTENCE, AND TRANSPORT IN SOIL... 6-8
ENVIRONMENTAL LEVELS AND EXPOSURE 7.1
7.1 AIR 7-1
7.1.1 Environmental Levels 7_1
7.1.2 Exposure.. 7-4
xi
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TABLE OF CONTENTS (cont.)
Page
7.2 WATER 7~8
7.2.1 Environmental Levels • 7-8
7.2.2 Exposure 7-13
7-3 SOIL '7-1J
7.4 FOODS '-l4
8. BIOLOGICAL EFFECTS ON PLANTS AND MICROORGANISMS 8-1
9. BIOLOGICAL EFFECTS ON AQUATIC ORGANISMS 9-1
9.1 ACUTE TOXICITY 9-1
9.1.1 Freshwater Fish 9-1
9.1.2 Freshwater Invertebrates 9-1
9.1.3 Marine Fish 9-3
9.1.4 Marine Invertebrates 9-3
9.2 SUBACUTE TOXICITY • 9-3
10. BIOLOGICAL EFFECTS IN ANIMALS AND MAN 10-1
10.1 PHARMACOKINETICS 10~1
10.1.1 Absorption and Distribution...... •• 1°~1
10.1.2 Metabolism - • ™~5
10.1.3 Excretion • ]0-2b
10.1.4 Summary of Pharmacokinetics • 10-29
10.2 ACUTE, SUBACUTE, AND CHRONIC TOXICITY 10-31
10.2.1 Acute Exposure • • 1°~h1
10.2.2 Subacute and Chronic Exposure 10-49
10.2.3 Summary of Toxicity 10-56
10.3 TERATOGENICITY AND REPRODUCTIVE TOXICITY 10-58
10.4 MUTAGENICITY • 1°-7°
10.4.1 Mutagenicity in Bacteria 10-70
10.4.2 Mutagenicity in Yeast and Plants 1°~I
10.4.3 Mutagenicity in Cultured Mammalian Cells 10-81
10.4.4 Mutagenicity in Mammalian Cells In Vivo 10-81
10.4.5 Summary 10-85
10.5 CARCINOGENICITY 1°-87
10.5.1 Animal Studies 1°~8I
10.5.2 Epidemiologic Studies 10-126
10.5.3 Risk Estimates from Animal Data. 10-131
10.5.4. Risk Estimates from Epidemiologic Data 10-149
xii
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TABLE OF CONTENTS (cont.)
11.
10.5.5 Relative Carcinogenic Potency
REFERENCES
10-1"^
xiii
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LIST OF TABLES
No. Title Page
4-1 Breakthrough Volume of Vinylidene Chloride as a
Function of Flow Rate, Concentration, and
Relative Humidity o 4-5
5-1 Monomer Production Facilities in the United States
and their Capacities » 5-3
5-2 Air Emissions of'Vinylidene Chloride During Monomer
Manufacture .. 5-3
5-3 Yearly Consumption of Vinylidene Chloride in Different
Industries .. 5-5
5-4 Polymerization Processes, Products, and Their
Applications 5-5
5-5 Polymerization Sites and Type of Polymer Produced..... 5-7
5-6 Estimated Annual Emissions of Vinylidene Chloride
from Polymer Synthesis 5-8
5-7 Major Poly Vinylidene Chloride Processors 5-10
5-8 Manufacturers of Polyvinylidene Chloride-Coated
Cellophane 5-11
5-9 Major Extruders of Polyvinylidene Chloride Film 5-11
5-10 Estimated Emissions from Polyvinylidene Chloride
Processing 5-12
5-11 Summary of Estimated Environmental Losses of
Vinylidene Chloride 5-12
7-1 Mean, Median and Range of Vinylidene Chloride
Concentrations at Different Sites in the U.S 7-5
7-2 Estimated Population Residing Near Plant Producing
or Fabricating Monomers and Polymers of Vinylidene
Chloride 7-7
xiv
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LIST OF TABLES (cont.)
No.
7-3
7-4
7-5
7-6
7-7
9-1
10-1
Title
Page
10-2
10-3
10-4
10-5
10-6
Industrial Occurrence of Vinylidene Chloride in.
Raw Wastewater ... 7-9
Industrial Occurrence of Vinylidene Chloride in .
Treated Wastewater . 7-10
Vinylidene Chloride Concentration in a Few Waters
Near Industrial Sites .* 7-12
Analysis of Food-Packaging Films for Vinylidene ;
Chloride ' ...- ........ 7-15
Migration of Vinylidene Chloride from Saran Films to'
Heptane, Corn Oil, and Water at 49°C "... 7-17
Acute Toxicity Values for Marine and Freshwater Fish
and Invertebrates Exposed to Vinylidene Chloride 9-2
i . •, . ' • . _ : . . " '• • 1 4 " :
End-Exposure Body Burdens and Disposition of -C -,
Activity in Rats 72 Hours Following Inhalation Exposure
14
to 10 or 200 ppm of C-Vinylidene Chloride '
for 6 hours 10-4
' 14
End-Exposure Body Burdens and Disposition of C
Activity in Rats and Mice 72 Hours Following '••••-'
14
Inhalation Exposure to. 10 ppm C-Vinylidene-
Chloride for .6 Hours , -... 10-13
. . . 14 - ' • ''; ' •
Covalently Bound C-Activity in Tissues 72 Hours
Following Inhalation Exposure to 10 ppm
14
C-Vinylidene Chloride for 6 Hours 10-15
14
Relative Proportions of C-Urinary Metabolites
After Intragastric Administration of 350 mg/kg
14
1- C-Vinylidene Chloride or 50 mg/kg •
Monochloroacetic Acid to Male Rats. 10-19
• 14 «
Relative Proportions of C-Excretory Products
After Intragastric Administration of 50 mg/kg of
14
1- C-Vinylidene Chloride to Male Rats or Mice 10-20
14
Metabolism of ^ C-Vinylldene Chloride and Covalent
Binding of C Activity to Rat Hepatic Tissue
14
After Intragastric Dose of C-Vinylidene
Chloride 10-22
xv
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LIST OF TABLES (cont.)
No. Title
•ill
10-7 Metabolism of ' C-Vinylidene Chloride and Covalent
Binding of C Activity to Rat Hepatic Tissue
After Inhalation Exposure to 10 or 200 ppm of
C-Vinylidene Chloride 10-23
10-8 Excretion of Radioactivity by Male Rats Given 0.5
mg/kg or 350 mg/kg C-Vinylidene Chloride
Intragastrically, Intravenously, or
Intraperitoneally 10-28
1U
10-9 Half-Lives of Excretion of C-Vinylidene Chloride,
14
C00, and Radiolabeled Urinary Metabolites of
ill d
C-Vinylidene Chloride 10-30
10-10 Influence of 24-Hour Fasting on the Effect of Oral
Administration of Vinylidene Chloride (400 mg/kg)
in Corn Oil on Plasma Urea Nitrogen Concentration
in Male Rats 10-37
10-11 Relationships of Plasma Indicators of Kidney Damage
to Dose 24 Hours After Oral Administration of
Vinylidene Chloride to Male Rats 10-38
10-12 Comparison of Prevalence of Histopathologic Effects of
Oral Administration of Vinylidene Chloride (400 mg/kg)
in Male and Female Rat Kidneys 10-39
10-13 Toxicity of 60 ppm Vinylidene Chloride in Male
Mice and Rats '... 10-48
10-14 Effect on Experimental Animals of Long Term
Inhalation of Vinylidene Chloride. 10-50
(
10-15 Pathologic Effects of Long-Term Ingestion of Vinylidene
Chloride Incorporated in the Drinking Water of
Sprague-Dawley Rats 10-57
10-16 Exposure Levels and Duration of Exposure to Vinylidene
Chloride During Gestation in Mice 10-60
10-17 Number of Animals and Exposure Levels Used to Study
the Teratogenicity of Vinylidene Chloride „. 10-62
10-18 Incidence of Fetal Alterations Among Rats Exposed to
Vinylidene Chloride By Inhalation or By Ingestion... 10-64
xvi
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LIST OF TABLES (cont.)
No. Title Page
10-19 Incidence of Fetal Malformation Among Litters of
Rabbits Exposed to Vinylidene Chloride 10-66
10-20 Summary of Mutagenicity of Vinylidene Chloride
(VDC): Bacteria 10-71
10-21 Summary of Mutagenicity of Vinylidene Chloride . .'
(VDC): Yeast and Plants 10-79
10-22 Summary of Mutagenicity of Vinylidene Chloride
(VDC): Mammalian Cells... 10-82
10-23 Results of Carcinogenicity Bioassays of Vinylidene
Chloride V * 10-88
10-24 Gas Chromatography Analysis of Vinylidene Chloride 10-90
10-25 Experiment DT401: Exposure by Inhalation to Vinylidene
Chloride in Air at 150> 100, 50, 25, and 10 ppm,
4 Hours Daily, 4-5 Days Weekly, For 52 Weeks 10-90
10-26 Exposure By Inhalation to Vinylidene Chloride in
Air at 200, 100, 50, 25, and 10 ppm, 4 Hours Daily, 4-5
Days Weekly, For 52 weeks 10-91
10-27 Experiment BT405: Exposure By Inhalation to Vinylidene
Chloride in Air at 25 ppm, 4 Hours Daily, 4-5
Days Weekly, For 52 Weeks 10-92
10-28 Experiment BT403: Exposure By Ingestion (Stomach Tube)
to Vinylidene Chloride in Olive Oil at 20, 10, and
5 mg/kg Body Weight, Once Daily, 4-5 Days Weekly,
For 52 Weeks ..... 10-93
Experiment BT404: Exposure by Ingestion (Stomach Tube)
to Vinylidene Chloride in Olive Oil at 0.5 mg/kg Body
Weight, Once Daily, 4-5 Days Weekly, for 52 Weeks ........ 10-93
10-29 Experiment BT401: Exposure By Inhalation to Vinylidene
Chloride in Air at 150, 100, 50, 25, and 10 ppm,
4 Hours Daily, 4-5 Days For 52 Weeks. Results After
137 Weeks (End of Experiment) ;.... 10-95
10-30 Experiment BT402: Exposure By Inhalation to Vinylidene
Chloride in Air at 200, 100, 50, 25, and 10 ppm,
4 Hours Daily, 4-5 Days For 52 Weeks. Results After
121 Weeks (End of Experiment) 10-97
xvii
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LIST OF TABLES (cont.)
No. Titles
10-31 Statistical Analyses of Survival, Mammary Carcinoma
Incidence and Pulmonary Adenoma Incidence For Male
And Female Swiss Mice in a Carcinogenicity Study
of Vinylidene Chloride 10-99
10-32 Tumor Incidence in Rats and Mice Exposed to Vinylidene
Chloride 10-103
1
10-33 Tumor Incidence in Rats and Mice Exposed to Vinylidene
Chloride 10-105
10-34 Vinylidene Chloride: A Chronic Inhalation Toxicity
and Oncogenicity Study in Rats. Cumulative Percent
Mortality for Male Rats 10-107
10-35 Vinylidene Chloride: A Chronic Inhalation Toxicity
and Oncogenicity Study in Rats. Cumulative Percent
Mortality for Female Rats. 10-108
10-36 Vinylidene Chloride: A Chronic Inhalation Toxicity
and Oncogenicity Study in Rats. Mean Body Weight for
Male Rats 10-110
10-37 Vinylidene Chloride: A Chronic Inhalation Toxicity
and Oncogenicity Study in Rats. Mean Body Weight for
Female Rats 10-111
10-38 Vinylidene Chloride: A Chronic Inhalation Toxicity
and Oncogenicity Study in Rats. Histopathologic
Diagnosis and Number of Tumors in Female Rats 10-112
10-39 Representative Tissue Specimens Obtained at Necropsy
From All Animals 10-115
10-40 Tumor Incidence Following Ingestion of Vinylidene
Chloride (VDC) 10-116
10-41 Tissues Examined For Histologic Changes in the NCI
Bioassay 10-117
10-42 Mean Body Weight Change (Relative to Controls) of Mice
Administered Vinylidene Chloride by Gavage 10-119
10-43 Tumors With Increased Incidence in Rats and Mice, as
Indicated by the Fisher Exact Test or the Cochran-
Armitage Test for Linear Trend 10-120
xviii
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LIST OF TABLES (cont.)
10-45
10-46
10-4?
10-48
Title
Tumor Incidence in Female BDIV Rats Treated with Vinylidene
Chloride (VDC) in Their Progeny for Life, and Controls
Estimated Cumulative Dose, Duration of Exposure, and Date
of First Exposure Among 138 Individuals Exposed
to Vinylidene Chloride
Observed and Expected Deaths Among Vinylidene Chloride
Employees by Cause
Data from Maltoni et al. Inhalation Study on Male Swiss
Mice
Relative Carcinogenic Potencies Among 54 Chemicals
Evaluated by the Carcinogen Assessment Group
as Suspect Human Carcinogens
10-123
10-127
10-129
10-132
10-157
xix
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LIST OF FIGURES
No. Title
4-1 Desorption Efficiency vs. Amount Found by GC Analysis 4-12
10-1 Metabolic Pathways for Vinylidene Chloride 10-6
10-2 Comparisons of Observed LT50 Data for Vinylidene
Chloride with Theoretical Curves Predicted for Two
Different Mechanisms of Toxicity t 10-10
r
10-3 Dose-Response Relationship for Hepatic Glutathione (GSH)
Levels, Total Metabolism of C-Vinylidene Chloride
(VDC), and Covalent Binding of Radioactivity to Hepatic
Macromolecules 10-25
10-4 Dose-Mortality Curves for Administration of Single, Oral
Doses of Vinylidene Chloride Dissolved in Corn Oil to
Fasted Male Rats of Various Sizes 10-44
10-5 Effect of Increasing Concentration of Vinylidene Chloride
on Mortality in Mature Male Rats 10-47
10-6 Mutagenic Activity of Vinylidene Chloride in the Presence
and in the Absence of Metabolic Activation 10-76
10-7 Histogram Representing the Frequency Distribution of the
Potency Indices of 54 Suspect Carcinogens Evaluated by
the Carcinogen Assessment Group 10-156
xx
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1. SUMMARY AND CONCLUSIONS
Vinylidene chloride is a highly reactive, flammable, clear, colorless
liquid that, in the presence of air, can form complex peroxides in the absence of
chemical inhibitors. The peroxides are violently explosive, and formaldehyde,
phosgene, and hydrochloric acid are produced as decomposition products.
Vinylidene chloride has a boiling point of 31.6°C at 760 mm Hg and a vapor
pressure of 600 mm Hg at 25°C. The solubility of Vinylidene chloride in water is
2250 mg/1 at 25°C, and the density of the liquid is 1.2132 g/cm3 (20°C).
Vinylidene chloride vapor is 3.31* times as dense as air. . ,
Synonyms for Vinylidene chloride are 1 , 1-dichloroethene, 1,1-DCE, and
1,1-dichloroethylene. Vinylidene chloride has a molecular weight of 96.95 and a
molecular formula of CCl The structural formula is given below.
H
\
Cl
H Cl
Vinylidene chloride monomer production capacity in the United States is
approximately 178 million pounds per year. Virtually all of the Vinylidene
chloride produced is used in the production of copolymers with vinyl chloride or
aery lonitr iie. A small percentage (456) of Vinylidene chloride is used as
chemical intermediates.
The two primary methods that have been used in recent years for the sampling
and analysis of Vinylidene chloride in ambient air are the freeze-trap method and
the sorption onto Tenax-GC method with subsequent analysis of the desorbed
Vinylidene chloride by high resolution gas chromatography with either flame
ionization, electron capture, electrical conductivity, or mass spectrometric
detectors. Both the freeze-trap and Tenax-GC methods of sample collection have
1-1
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some disadvantages. For example, the freeze-trap method using liquid oxygen is a
cumbersome method both for sample collection and transportation, and the
Tenax-GC method may suffer from serious problems of artifact formation.
The two methods commonly used for the analysis of vinylidene chloride in
grab aqueous samples are the static head-space method and the dynamic purge-trap
method. However, for aqueous samples containing very low levels of vinylidene
chloride (e.g., potable water), the dynamic purge-trap method is more suitable
than the static head-space method because of the higher sensitivity of the
former. Although gas chromatography with either flame ionization, electron
capture, electrical conductivity or mass spectrometric detectors has been used
for the final quantification of vinylidene chloride by both methods, the
electrical conductivity detector is preferable to other detectors because -of its
greater sensitivity and selectivity. The mass spectrometric method is usually
used as a confirmatory technique.
Vinylidene chloride in soil samples has been analyzed by solvent extraction
in sealed vials with subsequent quantification by gas chromatography - flame
ionization detector (GC-FID), and using mass spectrometry as the confirmatory
technique. The analysis of vinylidene chloride in food wrapping materials,
foods, and biological tissues has been performed either by the static head-space
method or by the dynamic purge-trap method in a manner similar to that employed
for aqueous samples.
Due to its high volatility, vinylidene chloride is lost to the atmosphere
during industrial manufacture of the monomer and polymer, and during storage and
handling. The total emission of vinylidene chloride to all media from these
facilities has been estimated to be 1,300,400 pounds per year. Moreover,
vinylidene chloride originally in aqueous solution is likely to contribute to air
contamination as a result of its high volatility from water.
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Under atmospheric smog conditions, the half-life of vinylidene chloride in
air has been determined to be 5 to 12 hours. In the absence of smog conditions,
vinylidene chloride may persist in the atmosphere with a half-life of
approximately 2 days. Volatilization from aquatic media is probably the most
significant fate-determining process for vinylidene chloride, although the role
of biodegradation still remains uncertain. The half-lives of volatilization of
vinylidene chloride from pond, river, and lake water have been estimated to be
6.1 days, 1.2 days, and 4.2 days, respectively. The fate of vinylidene chloride
in soils has not been evaluated with certainty. However, it has been concluded
from the limited data that both volatilization and leaching may play significant
roles in determining the fate of this chemical in soils.
The median ambient air level of vinylidene chloride in urban/suburban areas
•3
of the U.S. was estimated to be 5 ppt (20 ng/m ). However, the median
concentration value is substantially higher 2182 ppt (8.66 ng/m ) for ambient air
in the vicinity of point sources of emission. The estimated daily vinylidene
chloride intake from ambient air in urban/suburban areas through inhalation is
0.4 [ig. However, the daily inhalation exposure from ambient air may be as high
as 0.17 mg in the immediate vicinity of point sources. Vinylidene chloride has
been detected in approximately 3% of the total drinking water supplies in the
U.S. at an estimated mean concentration of 0.3 [ig/1 and a concentration range of
0.2 to 0.5 jig/1• For the majority of the U.S. population, the daily exposure to
vinylidene chloride from ingestion of drinking water has been estimated to be
less than 0.6 jig, although the maximum daily exposure in certain communities
could exceed 1 jig. Because of the paucity of data, no estimate of the dietary
intake of vinylidene chloride in the U.S. can be made at the present time.
Vinylidene chloride is acutely toxic to aquatic animals at exposure
concentrations in the milligrams per liter range. The lowest concentration
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reported to be acutely toxic to an aquatic organism is 2.4 mg/1. Reported acute
and subchronic LC^Q values ranged between 11.6 and 250 mg/1 for aquatic animals.
Vinylidene chloride was not acutely toxic to aquatic algae at concentrations of
712 to 798 mg/1. Vinylidene chloride was, however, toxic to yeast. No
information was found concerning the toxicity of vinylidene chloride to domestic
animals and non-aquatic wildlife.
Vinylidene chloride is readily absorbed by mammals following oral or
inhalation exposure. Vinylidene chloride is metabolized in the liver with a
number of possible reactive intermediates, including an epoxide, being formed.
These reactive intermediate metabolites can react with macromolecules; this is a
characteristic of many chemical carcinogens. The metabolites of vinylidene
chloride produce toxic lesions in the liver and kidneys, with inhibitors of
metabolism providing protection from vinylidene chloride toxicity. The
hepatotoxic effect can be extensive and histological effects can be noted within
2 hours after the onset of exposure. The acute hepatotoxicity of vinylidene
chloride was shown to be greater than that of any other chloroethylene. The
liver and kidneys remain the target organs for toxic effects regardless of the
route of administration (administration vehicle may influence vinylidene
chloride metabolism and therefore affect the extent of toxicity) or whether
acute, subaoute, or chronic exposure occurs.
Vinylidene chloride has been described as a possible weak teratogen in a
study using rats and mice. In this study, the experimental levels of vinylidene
chloride were toxic to the dams, confounding the interpretation of the results.
It was clear, however, that exposure of pregnant rats and mice to high levels of
vinylidene chloride could cause fetotoxicity and adversely affect the outcome of
pregnancy. Another study reported no teratogenic effect in rats or rabbits
inhaling up to 160 ppm vinylidene chloride for 7 hours per day or
1-4
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in rats given drinking water containing 200 ppm vinylidene chloride. Embryo and
maternal toxicity were observed among rats inhaling 80 or 160 ppm vinylidene
chloride and rabbits inhaling 160 ppm. At exposures causing little or no
maternal toxicity (20 ppm in rats, 80 ppm in rabbits), there was no effect on
embryo or fetal development. The effect of vinylidene chloride on reproduction
and fetal and neonatal development of rats was tested in a three generation study
with six litter groups being produced. Hepatocellular fatty changes were
observed in rats ingesting 50, 100 or 200 ppm vinylidene chloride.
A large number of studies indicate that vinylidene chloride is mutagenic to
bacteria and that this activity is largely dependent on microsomal activation,
Vinylidene chloride was reported to produce positive results for gene reversion
and conversion in yeast, which was also dependent on metabolic activation, and
was positive in Tradescantia. In mammalian systems, vinylidene chloride failed
to induce gene mutations in V79 cells at two separate loci, failed to induce
cromosomal aberrations in mouse bone marrow in vivo, and failed to induce
dominant lethals in either mice or rats. Vinylidene chloride was found to
alkylate the DNA of mice exposed through inhalation and may have caused
unscheduled DNA synthesis in the kidneys of similarly exposed mice.
Analysis of the data relating to the potential of vinylidene chloride to
behave as a human germ-cell mutagen indicates that based on the criteria
established in the Agency's Proposed Guidelines for Mutagenicity Risk
Assessment, the evidence at the present time is classified as limited. This
designation indicates that there are insufficient data on either mutagenicity or
interaction with germ cells to classify the evidence as either sufficient or
suggestive of potential germ-cell mutagenicity. However, available data also do
not permit the classification of vinylidene chloride as a non^germ-cell mutagen.
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Based on the limited evidence from animal studies, supporting evidence
from mutagenicity studies, and related biochemical and toxicity considerations,
it is recommended that vinylidene chloride be considered a "possible" carcinogen
for humans.
A total of 18 chronic studies in animals were evaluated for evidence of
carcinogenicity. The exposure regimes for these studies were as follows: 11
were inhalation, 4 were gavage, 1 was drinking water, 1 was subcutaneous
injection, and 1 was skin application. Evidence for carcinogenicity was found in
Swiss mice exposed to vinjUidene chloride by inhalation, H hours daily for 12
months. A statistically significant increase of kidney adenocarcinomas, a rare
tumor type, was observed in male mice. Statistically significant increases in
mammary carcinomas and pulmonary adenomas were observed in mice of both sexes,
although the importance of these findings is uncertain because no clear dose-
response relationship was evident. Vinylidene chloride has also been shown to be
a tumor initiator in mouse skin. The remaining 16 animal studies have negative
(assuming non-treatment related increases are also negative) findings for
carcinogenioity; however, these negative findings may be partially explained by
study characteristics such as, less than lifetime dosing, below maximum
tolerated dose levels, and single dose studies, which individually or in
combination, reduce the sensitivity of detecting a carcinogenic response. While
the number of studies are many, the inadequacy of test conditions demonstrates
the need for additional testing to elucidate the potential for human
carcinogenicity. The mutagenic activity of vinylidene chloride, its chemical
structure, its activity as a tumor initiator in mouse skin, and the ability of
metabolites to react with DNA, signal that the animal evidence should not be
lightly dismissed.
1-6
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There is only one epidemiologic study for vinylidene chloride. While the
study concluded that a carcinogenic effect could not be attributed to vinylidene
chloride, limiting characteristics made it inadequate to evaluate the
carcinogenic potential.
The carcinogenicity evidence has been evaluated using the EPA's Proposed
Guidelines for Carcinogen Risk Assessment as well as the International Agency for
Research for Cancer (IARC) criteria for assessing weight of evidence. Using the
EPA criteria, the weight of evidence is such that the animal data for
carcinogenicity is limited and the epidemiologic data is inadequate. The overall
ranking of the weight of evidence is Group C meaning that the substance is a
"possible" carcinogen for humans. Using the IARC weight-of-evidence criteria,
the animal and epidemiologic data have the same ranking as in the EPA
classification, limited and inadequate; however, the overall ranking is
considered to be Group 3. An IARC Group 3 classification means that while the
evidence may range from limited to inadequate, the overall conclusion is that the
data are "inadequate" to assess the human carcinogenic potential. The Agency
believes that its ranking criteria are more instructive for public health impact
analysis. The Group C (possible carcinogen) classification given to vinylidene
chloride is one of five that could be assigned to a substance. The five
classifications are: human carcinogen, probable human carcinogen, possible
human carcinogen, not classified (inadequate evidence for assessing
carcinogenicity), and no evidence of carcinogenicity for humans.
Although vinylidene chloride has only limited carcinogenicity evidence, an
upper-bound estimate of incremental cancer risk can be estimated from the kidney
adenocarcinoma data in male mice. The development of this risk estimate is for
the purpose of evaluating the "what-if" question: If vinylidene chloride is
carcinogenic in humans, what is the possible magnitude of the public health
1-7
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impact? Any use of the risk estimates should include a recognition of the
weight-of-evidence likelihood for the carcinogenicity of vinylidene chloride in
humans. The upper-bound incremental cancer risk is calculated to be 1.16 x 10
for 1 [ig/kg body weight/day for a continuous lifetime exposure to vinylidene
chloride under the presumption that vinylidene chloride is carcinogenic in
humans. The upper-bound nature of this estimate is such that the true risk is
not likely to exceed this value and may be lower. Expressed in terms of relative
potency, vinylidene chloride ranks in the third quartile among the 54 suspect or
known human carcinogens evaluated by EPA's Carcinogen Assessment Group.
1-8
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2. INTRODUCTION
EPA's Office of Research and Development has prepared this health assess-
ment to serve as a "source document" for Agency use. This health assessment was
originally developed for use by the Office of Air Quality Planning and Standards
to support decision-making regarding possible regulation of vinylidene chloride
under the Clean Air Act. However, the scope of this document has been expanded
to address vinylidene chloride in relation to sectors of the environment outside
of air. It is expected that this document will be able to serve the information
needs of many government agencies and private groups that may be involved in
decision-making activities related to vinylidene chloride.
The basic literature search for this document is complete up through August,
1983, with the exception of the mutagenicity section which is complete through
December, 1984. However, selected publications have been included in the
carcinogenicity section up through 1985.
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3. PHYSICAL AND CHEMICAL PROPERTIES
The data and the discussion presented below have been obtained from Hushon
and Kornreich (1978) and Wessling and Edwards (1970), except in cases where the
reference is specifically cited.
3.1 SYNONYMS AND TRADE NAMES
Chemical Abstracts Name: 1 , 1-dichloroethene
CAS No.: 75-35-4
RTECS No.: KV92750
Synonyms: VDC, 1 , 1-dichloroethene (1,1-DCE), 1 , 1-dichloroethylene,
vinylidene chloride monomer, vinylidene dichloride
3.2 STRUCTURAL AND MOLECULAR FORMULAE AND MOLECULAR WEIGHT
H
Cl
C2H2C12 Molecular Weight: 96.95
3-3 PHYSICAL PROPERTIES
3.3.1 Description
Vinylidene chloride is a clear, colorless liquid with a characteristic
"sweet" odor.
3.3.2 Boiling Point
31.56°C (at 760 mm Hg)
3.3.3 Freezing Point
-122.5°C
3.3.4 Density
Liquid density at 0°C: 1.2517 g/cm3
Liquid density at 20°C: 1.2132 g/cm3
Vapor density: 3.34 (air = 1)
Density in saturated air: 2.8 (air = 1)
Percent in saturated air: 78%
3-1
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3.3.5 Refractive Index
n2°: L 42468
3.3.6 Solubility
Solubility of vinylidene chloride in water: 2250 mg/1 (at 25°C) (Delassus
and Schmidt, 1981)
Solubility of water in vinylidene chloride: 0.35 g/1 (at 25°C)
Vinylidene chloride is soluble in acetone, ethanol, benzene, diethyl ether, and
chloroform.
3.3.7 Volatility
1 -JQIJ 29
Vapor Pressure (P) in mm Hg: log P = 6.9820 - - - 5^7 „
mm is +• £.:> i . i
(where t = temperature in °C)
Therefore, P = 600 mm Hg at 25 °C
3.3.8 Volatility from Water
Calculated Henry's law constant (unitless) at 25°C: 7.8 (Billing, 1977)
Half-life (t1/2) for evaporation from water at 25°C for a solution depth of 6.5
cm (Billing, 1977):
Calculated: 20.1 min
Experimental: 27.2 min
The theoretical equation of Billing (1977) was derived for a specific
hydrodynamic regime and may not be applicable for all waters.
3.3.9 Hazard Parameters
Flash point (tag open-cup): 3°F
Flash point (tag closed-cup): -2°F
Autoignition temperature: 1031°F
Explosive limit with air at 28 °C
lower: 7.3% by volume
upper: 16.0? by volume
3-2
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3.3-10 Dielectric Constant
4.67 (at 16°C)
3.3.11 Thermodynamic Data
Latent heat of vaporization at 25°C: 6328 cal/mol
Latent heat of vaporization at boiling point: 6257 cal/mol
Latent heat of fusion: 1557 cal/mol
Specific heat: 0.275 cal/g
Heat of combustion: 261.93 kcal/mol
Heat of polymerization: -18.0 kcal/mol
Heat of formation (liquid monomer): -6 kcal/mol
Heat of formation (gaseous monomer): 0.3 kcal/mol
Heat capacity at 25.15°C (liquid monomer): 26.745 cal/mol/degree
Heat capacity at 25.15°C (ideal gas): 16.04 cal/mol/degree
Critical parameters:
Temperature (T ): 222°C
Volume (V ): 2.19 cm3/mol
c
Pressure (PQ): 51.3 atm
3.3.12 Viscosity
0.3302 cP (centipbise) (at 20°C)
3.3.13 Conversion Factors at 25°C and 760 mm Pressure:
1 ppmS 3-97 mg/m3 (air)
3.4 STORAGE AND TRANSPORTATION OF THE MONOMER
Without added inhibitors, vinylidene chloride in the presence of air form
complex peroxide compounds at temperatures as low as -40°C. The peroxide is
violently explosive. Decomposition products of vinylidene chloride peroxide are
formaldehyde, phosgene, and hydrochloric acid. Since the peroxide is a
polymerization initiator, formation of insoluble polymer in stored vinylidene
3-3
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chloride monomer may be an indication of peroxide formation. The peroxides are
adsorbed on the precipitated polymer. Any dry composition containing more than
about 15? peroxide detonates from a slight mechanical shock or from heat;
therefore, the separation of the polymer from the monomer by filtration,
evaporation, or drying may result in explosion.
Inhibitors are used to prevent formation of peroxides in the monomer. The
most common practice to inhibit peroxide formation is the addition of 200 ppm of
the monomethyl ether of hydroquinone (MEHQ). Other inhibitors include
alkylamines, phenols, and' organic sulfur derivatives. Inhibited vinylidene
chloride is shipped under a nitrogen blanket to avoid contact with air and to
prevent the formation of peroxides. In the absence of water, light, and
excessive heat, inhibited vinylidene chloride under a blanket of nitrogen can be
stored indefinitely.
To retard polymerization, uninhibited vinylidene chloride should be kept
away from light and at a temperature below -10°C. Uninhibited vinylidene
chloride can be stored in mild steel, stainless steel, or nickel containers.
Contact with copper and" aluminum should be avoided because the acetylinic
impurities in vinylidene chloride may form copper acetylides and aluminum
acetylides, and because aluminum reacts with vinylidene chloride to form
aluminum chloroalkyls. These classes of compounds are extremely reactive and
potentially hazardous.
3.5 CHARACTERISTICS OF THE COMMERCIAL PRODUCT
A typical analysis of commercial-grade vinylidene chloride monomer
(excluding inhibitors) is as follows: vinylidene chloride 99.8$;
trans-1,2-dichloroethylene, 900 ppm; vinyl chloride, 800 ppm; 1,1,1-trichloro-
ethane, 150 ppm; cis-1,2-dichloroethylene, 10 ppm; and 1,1-dichloroethane,
ethylene chloride, and trichloroethylene—each less than 10 ppm.
3-4
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3.6 PURIFICATION OF THE MONOMER
Vinylidene chloride forms an azeotrope with 6% methanol. Distillation of
the azeotrope, followed by extraction of the methanol with water, is a method of
purification of vinylidene chloride.
3.7 CHEMICAL REACTIVITY
Vinylidene chloride, like other olefins, is expected to undergo addition
reactions. An example of this addition reaction with HC1 is as follows:
CH =CC10 + HC1 >• CH,
22 3 3
This reaction is used commercially for the production of 1,1,1-trichloroethane
(methyl chloroform).
The addition reaction of vinylidene chloride with bromine is shown below:
CH2=CC12
CH2Br-CCl2Br
The reaction product from bromination of vinylidene chloride was used as a
confirmatory method for the identification and quantification of the parent
compound (Going and Spigarelli, 1977). Other reactions of vinylidene chloride
with thiolate (McKinney et al., 1959) and cysteinate (Francis and Leitch, 1957)
are also known.
In the presence of polymerization initiators, vinylidene chloride undergoes
self-polymerization to form homopolymers, or polymerizes with other compounds—
namely, vinyl chloride, alkyl acrylates, and acrylonitrile—to yield copolymers.
Copolyraers containing various amounts of vinylidene chloride are used as
packaging films, carpet backing materials, and modacrylic fibers. When compared
with that of other monomers, the reactivity of vinylidene chloride towards
polymerization is considered to be average.
3-5
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4. SAMPLING AND ANALYTICAL METHODS
Several methods are available for the measurement of vinylidene chloride in
air, water, soil and disposal site samples, as well as in polymers, and as
migrated monomer into food-simulating solvents. The analysis of vinylidene
chloride in air is more frequently studied because atmospheric air is probably
the most prevalent medium of vinylidene chloride contamination. Because of its
high volatility, vinylidene chloride lost during its industrial production and
processing primarily enters the atmosphere. Moreover, vinylidene chloride
originally present in aqueous media is likely to contribute significantly to air
contamination as a result of its high volatility from water.
The sampling and analysis of vinylidene. chloride in different media are
discussed individually in the following sections.
4.1 AIR
4.1,1 Air Sampling
Three general methods have been used in the past for the collection of
vinylidene chloride in air samples: grab sampling, cold-trapping, and trapping
in sorbent.
Grab samples can be collected in vacuum bottles or in evacuated syringes
(Irish, 1967, cited in Hushon and Kornreich, 1978), The difficulties with this
method of collection are twofold. First, since it does not allow sample precon-
centration, the detection limit of the method is too high to permit detection of
most ambient air levels of vinylidene chloride. Second, the inherent limitation
of any grab sampling method is that samples collected by this method will not
permit the determination of time-weighted average concentrations.
The inability to collect samples representative of time-weighted average
concentrations with the grab sampling method was overcome by the use of a
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personal sampler that used the critical orifice concept (Williams et al., 1976).
The sampler consisted of an evacuated container (<1 torr) equipped with a
critical orifice (2 to 5 jim diameter). In such a sampler, the gas flow into the
container remains constant as long as a critical flow pattern exists. In order
for this to occur, the internal pressure of the container must remain less than
half the external atmospheric pressure during sampling. Thus, the length of
sampling time depends on both the size of the orifice and the volume of the
sample container. For a container of 100 ml volume equipped with a 2 |im orifice,
the critical flow will exist for 22 hours. The use of a critical orifice for time
averaged sampling has been used in source sampling for many years. The major
problem that occurs is blockage of the orifice by particulate matter.
In the cold-trap method, air containing vinylidene chloride is pumped
through a cold-trap maintained at a suitable temperature (Irish, 1967, cited in
Hushon and Kornreich, 1978). In order to avoid sample loss, the temperature of
the cold-trap must be maintained so that the trapped compound has negligible
vapor pressure under the applied pressure. The cold-trap method was used by
Singh et al. (198la,b) for the measurement of ambient air concentrations of
vinylidene chloride. In this method, sample preconcentration was conducted with
4-inch long stainless steel tubing packed with 100/120 mesh glass beads and
maintained at liquid 0? temperature.
The collection of atmospheric vinylidene chloride by sorbent-trapping has
been used by several investigators. The advantage of the sorbent-trapping method
is that it permits collection of a large volume of air and it concentrates the
compound of interest in a small volume of the sorbent. Both liquid and solid
sorbents have been used. Gronsberg (1975) bubbled air through pyridine to
collect vinylidene chloride. Guillemin et al. (1979) suggested bubbling air
through an impinger containing chilled water for the collection of halogenated
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ethylenes; however, the method was not applied for sampling air and the
efficiency of collection was not established. The disadvantage of handling the
impingers in the field and transporting them to the laboratory renders this
method unattractive.
The trapping of vinylidene chloride in a solid sorbent is a more suitable
method for its collection from air samples. Although silica gel was used in the
past (Irish, 196?, cited in Hushon and Kornreich, 1978), sorption on activated
carbon has been used extensively in recent years for the collection of vinylidene
chloride in air. Many investigators (Russell, 1975; Severs and Skory, 1975;
Foerst, 1979) used this method for the monitoring of the higher levels of vinyli-
dene chloride present in workplace atmospheres. In only one investigation (Going
and Spigarelli, 1977) was this method utilized for monitoring ambient air levels
of vinylidene chloride.
The adsorption capacity of vinylidene chloride on activated carbon depends
on the characteristics of the carbon (source, particle size, nature of pretreat-
ment) and the amount used. Generally, for short-term sampling (less than 8
hours) sample tubes containing smaller amounts of carbon are used than for long-
term sampling (about 24 hours). For example, an increase in the amount of a
specific activated charcoal (PCB 12 x 30) from 150 mg to 600 mg allowed an
increase in collection time from a minimum of 10 minutes to at least 75 minutes
at a flow rate of 1 liter/minute (Severs and Skory, 1975). The effect of
adsorption capacity on the nature of activated carbon was also demonstrated by
these investigators. Segmentation of the carbon tubes into a front and back
section is usually employed for determination of the breakthrough limit during
sample collection. If the back section retains more than a certain predetermined
percentage of vinylidene chloride, it is taken as an indication that the break-
through limit has been exceeded.
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The sampling unit usually consists of the following components assembled in
the order given: probe, charcoal tube, critical orifice, and a battery-operated
pump. The tube containing the charcoal is held vertically at a height of 4 to 6
feet from the ground and air is drawn through it at a constant flow rate for a
specified length of time. At the end of the sample collection period, the tube
is closed with caps and shipped to the laboratory for analysis.
For a known weight and nature of activated carbon, the breakthrough charac-
teristics during sample collection are dependent on several parameters:
(1) concentration of vinyli'dene chloride in air; (2) flow rate of air through the
carbon bedj (3) relative humidity of air; and (4) presence of other contaminants
in the air. The influence of the first three factors on the breakthrough volume
has been thoroughly studied by Foerst (1979). This investigator sampled
vinylidene chloride through a 100 mg front section and 50 mg back section of
MSA-8 charcoal tubes, and monitored the vinylidene chloride concentration by
GC-FID. The results of his experiments showing the dependence of breakthrough
volume on the three parameters are given in Table 4-1. It is evident from Table
4-1 that changes in flow rate and concentration of vinylidene chloride have
relatively less effect on both the breakthrough volume and loading at
breakthrough than do the changes in relative humidity.
The effect of loading on breakthrough volume of Carbosieve-B was also
studied by Russell (1975). This investigator stated that "the quantity of the
compound of interest collected affects the breakthrough volume very slightly. A
pollutant present at 20 ppm will break through at a slightly smaller volume than
when at 1 ppm." Relative humidity, however, has a more profound effect on the
breakthrough characteristics. A change in relative humidity from 17 to 95%
resulted in an almost 9055 decrease in both the breakthrough volume and loading
capacity. It should be noted that the findings of Russell (1975) regarding the
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TABLE 4-1
Breakthrough Volume of Vinylidene Chloride as a Function
of Flow Rate, Concentration, and Relative Humiditya
Concentration Flow Rate
(mg/nr5) (1/min)
Relative Humidty
(*)
Breakthrough
Volume (1)
Loading at
Breakthrough (jig)
Effect of
13.5
13.4
Effect of
114
13.5
Effect of
114
114
Flow Rate
1.00
0.20
Concentration
1.00
1.00
Humidity
0.74
1.00
87
85
95
87
17
95
8.9
6.9
6.0
8.9
56.0
6.0
121
93
684
121
6375
684
Source: Foerst, 1979
Volume at which the effluent from the charcoal tubes is equal to 555 of the
concentration being sampled.
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effect of relative humidity on breakthrough volume are consistent with those of
Foerst (1979) as shown in Table 4-1.
It is interesting to point out that the laboratory breakthrough studies done
by Going and Spigarelli (1977) employed air with a relative humidity of 39 to 42$
for sampling vinylidene chloride through a 2 g bed of Fisher activated charcoal.
They concluded that the maximum loading before breakthrough occurs at approxi-
mately 2.5? of the weight of total charcoal bed and that, for vinylidene chloride
concentrations much lower than 10 ppm (as expected in ambient air), sampling can
be performed at 1 liter/minute for 24 hours without exceeding the breakthrough
characteristics. While this may be true at 39 to 425? relative humidity, the
results of Foerst (1979) indicate that the volume and loading characteristics
will drastically change at considerably higher relative humidity. Although the
relative humidity during the collection of field samples was not recorded by
Going and Spigarelli (1977), light rain was falling during the collection of some
samples, which indicates that the relative humidity during field sampling was
much higher than 39 to 425?. The field samples collected by Going and Spigarelli
(1977) at high relative humidity at a sampling rate of 1 liter/minute for 24
hours might have exceeded the breakthrough characteristics; consequently, some
of the results reported by these investigators may be erroneous.
The possibility of using other sorbents for the preconcentration of vinyli-
dene chloride during atmospheric sample collection was studied by Pellizzari and
Bunch (1979). They used three sorbents for the evaluation: charcoal, XAD-2, and
Tenax GC for the evaluation. It was determined by these investigators that while
charcoal and XAD-2 may form traces of halogenated hydrocarbons by in situ
reactions of Cl_, olefins, and other pollutants present in the atmosphere, the
possibility of artifact formation was minimal with Tenax GC. Therefore, Tenax GC
sorbent was used by these investigators for the collection of vinylidene chloride
4-6
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and other volatile organics in the atmosphere. The performance characteristics
of Tenax GC as a sorbent for the collection of organics in ambient air were also
evaluated by Brown and Purnell (1979). It should be mentioned that although
Pellizzari and Bunch (1979) reported minimal artifact formation with Tenax GC,
Singh et al. (1979) observed "serious" artifact formation problems with this
adsorbent. In addition, Singh et al. (1979) encountered "serious difficulties"
in quantitatively adsorbing and desorbing a few specific species with this
sorbent. Walling (1984) suggested a sampling approach with Tenax GC that can be
utilized to identify the deficiencies in the monitored data due to artifact
formation in the Tenax GC bed, inadequate blank correction, and exceeding
breakthrough volume during sample collection.
4.1.2 Storage of Samples Collected in Solid Sorbent Tubes
The stability of vinylidene chloride collected in charcoal-packed tubes was
studied by a number of investigators (Severs and Skory, 1975; Going and
Spigarelli, 1977; Foerst, 1979). No loss of vinylidene chloride was detected
when the samples in charcoal-packed glass collecting tubes were stored in a
refrigerator (2 to 4°C) for 16 to 21 days (Going and Spigarelli, 1977; Foerst,
1979). Similarly, Tenax-GC cartridges stored in cooled culture tubes showed high
recoveries with halogenated aliphatic compounds (Pellizzari, 1982; Krost et al.,
1982).
4.1.3 Analytical Methods
Vinylidene chloride collected by the grab method can be analyzed by three
different methods: gas chromatography with various detectors, infrared (IR)
analysis, and Laser Stark Spectrometry. In the combined gas chromatography-mass
spectrometric (GS-MS) method applied by Grimsrud and Rasmussen (1975), 20 ml
samples were flushed onto a SCOT OV-101 chromatographic column temperature-
programmed from -60°C to 100°C. The effluents from the GC were passed to a mass
4-7
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spectrometer operated in the single-ion mode. The identity of vinylidene
chloride was established on the basis of chromatographic retention time and by
monitoring ions of masses 61 and 96 in the mass spectrum. The detection limit of
the method was 5 ppt; however, the chromatographic conditions employed could not
separate vinylidene chloride from its isomers (cis- and trans-1,2-
dichloroethylene).
A portable IR analyzer was used by Foerst (1979) for continuously monitoring
vinylidene chloride produced in a dynamic flow vapor generator. A Wilks Miran IA
;
IR analyzer was used in the absorbance mode at a wavelength of 9.1 |im, with a cell
path length of 20.25 meters, and a slit width of 2 mm. The response time for
vinylidene chloride was 4 seconds. This method, however, is unsuitable for
monitoring vinylidene chloride in atmospheric air for two reasons. First, the
concentration of vinylidene chloride in atmospheric air (on the order of ppt) is
far below the detection limit of the IR analyzer. Second, some of the other
halohydrocarbons present in atmospheric air samples will produce interference in
the vinylidene chloride determinations.
Laser Stark Spectrometry with a 9.6 \w line from a C0_ IR laser can be used
for the determination of vinylidene chloride; however, the detection limit of
this method with a 40 cm Stark cell is in the ppm range (Sweger and Travis, 1979).
A multipass Stark cell could result in a significant increase in vinylidene
chloride detection sensitivity but is not yet available. Other disadvantages of
this method include interferences from other halohydrocarbons such as Freons,
methyl chloride, methyl fluoride, and vinyl chloride (Sweger and Travis, 1979).
Both the IR and Laser Stark Spectrometry methods have the inherent
capability for continuous monitoring of vinylidene chloride levels in the work-
place where the concentration of vinylidene chloride is considerably higher than
that of atmospheric air and where few interfering substances may be present.
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A modified commercial nitrogen oxide analyzer with an ethylene supply
system substituted for the ozone source may also be used for the monitoring of
compounds containing unsaturated double bonds (Hilborn et al., 1976). This
instrument, which utilizes the principle of chemiluminescence, may be useful for
monitoring total unsaturated hydrocarbons in the atmosphere (including vinyli-
dene chloride), but is not suitable for monitoring individual unsaturated hydro-
carbons when they are present in a mixture. In addition to detecting olefinic
compounds, the instrument also responds to compounds containing sulfide and
amine groups (Hilborn et al., 1976).
In one of the more recent methods for determining vinylidene chloride in the
ambient air, Singh et al. (198la,b) collected the samples by cryogenic cooling
(see Section 4.1.1). With this method, the desorption of chemicals from the
cooling trap was accomplished by maintaining the trap at boiling water tempera-
ture and purging it with carrier gas. The desorbed vinylidene chloride was
analyzed by a long (10 meter) packed column and electron capture detector.
Gronsberg (1975) used a oalorimetric method to quantify vinylidene chloride
collected in an impinger containing pyridine. The pyridine solution containing
vinylidene chloride was heated with NaOH in a sealed container and then coupled
with barbituric acid or aniline in acetic acid to form a cyanine dye. The dye
color intensity was measured with a spectrophotometer. Neither vinyl chloride
nor acrylonitrile interfered with vinylidene chloride determination. The
detection limit of the method (10 mg/m of air), however, renders it unsuitable
for monitoring vinylidene chloride in ambient air.
Vinylidene chloride collected by bubbling air through water in an impinger
can be analyzed by injecting the aqueous solution onto a steam-modified gas-solid
chromatograph (Guillemin et al., 1979). The details of this technique are given
in Section 4.2.2. A Spherosil XOA-400 column operated at an isothermal
4-9
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temperature of 128°C with a mobile phase containing a mixture of 50 ml/minute N2
gas and 16 ml/minute steam has been successfully used for the separation and
quantification (by FID) of the haloethylenes including vinylidene chloride
(Guillemin et al., 1979). By using a 200 jil aqueous solution injection with this
method, 20 ppb vinylidene chloride in water can easily be detected.
Vinylidene chloride collected by adsorption on solid sorbents is analyzed
by a two-step method. The first step in the analysis is the desorption of
vinylidene chloride from the sorbent. The second step is the separation, identi-
fication, and quantification of the desorbed vinylidene chloride, usually by
GC-FID.
Thermal elution and solvent extraction are two commonly used methods for the
desorption of vinylidene chloride from solid sorbents. The thermal desorption
technique was used by several authors (Pellizzari and Bunch, 1979; Bozzelli et
al., 1980). In one thermal desorption method, the sampling tube was reversed
(the end where air entered during sampling was attached to the injection port) to
allow backflushing of the sorbed compounds into the injection port of a GC. With
a 2 x 0.25 inch tube packed with Carbosieve-B, Russell (1975) determined the
recovery of vinylidene chloride to be 100? (±3% standard deviation) when the tube
was heated at 270°C for 5 minutes at a nitrogen flow of 20 ml/minute. When the
dimension of the collection tube was increased to 5.5 by 0.25 inches, however,
Severs and Skory (1975) demonstrated that 10 liters of N_ gas were required to
pass through a heated (430°C) PCB 12 x 30 activated carbon collection tube to
desorb vinylidene chloride. The desorption efficiency under the above condi-
tions was determined to be 8Q%.
The sensitivity of the activated carbon adsorption and thermal desorption
technique is approximately 1 ppb for a 1-liter air sample using FID (Russell,
1975). The high temperature required for desorption, however, may cause some
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organic compounds to chemically react on the catalytic surface of the sorption
cube, thereby altering their chemical composition. For example, methyl bromide
appears to exchange a Br atom for a Cl atom (present as an impurity in the
adsorbent) during thermal desorption from Carbosieve-B. Thus, peaks from both
methyl bromide and methyl chloride appear in the chromatogram (Russell, 1975).
In some of the more recent methods that used Tenax GC as the sorbent, the
thermally desorbed vinylidene chloride was either collected in stainless steel
tubes under pressure (Bozzelli et al., 1980) or the desorbed gas purged with
helium was collected into a liquid nitrogen-cooled nickel capillary trap
(Pellizzari and Bunch, 1979). In both cases, the final separation and analysis
of vinylidene chloride was done by high resolution GC-FID.
Desorption by solvent extraction has been used by a few investigators. In
this technique, the adsorbent is added to 1 to 10 ml CS? either at room tempera-
ture in a crimp-sealed vial (Foerst, 1979), or cooled in wet ice (Severs and
Skory, 1975), or in dry ice (Going and Spigarelli, 1977). The effect of CS2 bofcn
at 30°C and at -78°C was that almost the same recovery resulted for desorption
times ranging from 15 to 90 minutes. The CS2 desorption efficiency was
determined to be 100? (Severs and Skory, 1975; Going and Spigarelli, 1977).
Foerst (1979), however, reported that the desorption efficiency was dependent on
loading level. There was a trend towards lower desorption efficiencies at lower
loadings. This dependence of desorption efficiency on loading level is shown in
Figure 4-1. The stability of dilute vinylidene chloride solutions in CS2 was
studied by Going and Spigarelli (1977). About 20% loss of vinylidene chloride
was observed whether the sample was stored at -18°C (freezer), 4°C, or 25°C for 7
days. The loss was much less (about 6%~) when the solution was stored for only 4
days at the same three temperatures. Therefore, the desorbed vinylidene chloride
in CS2 should be analyzed within 4 days, regardless of the temperature of
storage.
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The second step in the analysis of vinylidene chloride by the solvent
extraction method involves injection of the CS2 solution into a GC-FID. The
choice of FID is based upon the fact that CS has very little response with FID.
A number of columns including 1055 TCEP, OV-225, 3% Dexsil, Tenax GC, Porapak N,
and Chromosorb 102 were tested (Foerst, 1979). None of these columns were able
to separate vinylidene chloride, vinyl chloride, and CS2« The most suitable
column was found to be Durapak OPN on Porasil C (Foerst, 1979; Going and
Spigarelli, 1977). Limited success was attained with 20$ DC200 (Severs and
Skory, 1975), but the separation of vinylidene chloride from CS solvent was less
than ideal with this packing material.
The confirmation for vinylidene chloride quantified by FID was made both by
mass spectrometry and by bromination of vinylidene chloride (Going and
Spigarelli, 1977). The bromination was performed by reacting vinylidene
was
removed by 0.5 M NaOH solution. The brominated vinylidene chloride was dried
over anhydrous Na?SOj. and analyzed on a 1.55? OV-101 column equipped with an FID'.
4.2 WATER
4.2.1 Water Sampling
Grab water samples should be collected in narrow-mouth, glass, screw-cap
bottles with Teflon- faced, silicone rubber, septa cap liners (Federal Register,
1979; Going and Spigarelli, 1977; Bellar and Lichtenberg, 1 979; Bellar et al.,
1979). To avoid vinylidene chloride loss, the bottles should be filled to
overflow with water and should be sealed immediately without leaving any head-
space. If the sample contains free or combined chlorine, sodium thiosulfate (10
mg/40 ml for 5 ppm C12) should be added to the water at the time of sample
collection (Federal Register, 1979; Bellar et al. , 1979). If left unneutralized,
Cl will react with organics in water and will increase the levels of chlorinated
chloride with a 500-fold molar excess of Br? for 30 minutes. The excess
4-13
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hydrocarbons (Bellar et al., 1974, 1979). The samples collected this way should
be shipped in ice and refrigerated during storage. A sample stored at 4°C was
found to be stable for at least 9 days (Going and Spigarelli, 1977) and samples
similarly stored for up to 27 days were stable (Bellar and Lichtenberg, 1981).
It was suggested that the analysis of the stored samples be performed within 14
days (Federal Register. 1979).
4.2.2 Analytical Methods
Vinylidene chloride in water samples has been analyzed by three different
/
techniques: direct head-space analysis, direct injection on a steam-modified
gas-solid chromatograph, and by the purge-trap technique.
The direct head-space analysis studied by Piet et al. (1978) has the advan-
tage that no preconcentration and prehandling of the samples are required; there-
fore, systematic error is reduced. The additional advantages of the method are
its good GC separability due to the absence of solvents and its low detection
limit. The method can be applied for tap water, ground water, and surface
waters. In this method, 100 ml N2 is bubbled through 1 liter of water at 30°C and
the Ng containing the head-space vinylidene chloride is trapped between two
columns of water in a special apparatus (Piet et al., 1978). Up to 500 \il of the
head-space gas could be injected into a GC equipped with an electron capture
detector. The GC column used was a wide-bore glass capillary coated with OV-225
and operated isothermally at 22°C. The detection limit for a 100 |il injection
was determined to be 2 p.g/1.
Castello et al. (1982) also used the head-space technique for the determina-
tion of halocarbons in drinking water. In their technique, a 5 ml aliquot of
water was placed in a closed vial, the sample was thermostatically held at 30°C
for 1 hour in a water bath, and 200 \il of the head-space gas was injected into the
GC column attached to an electron capture detector. The authors did not provide
the detection limit for vinylidene chloride by this method.
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The steam-modified gas-solid chromatography technique, which utilizes a
composite of inert carrier gas and a controlled amount of steam as the mobile
phase, a porous packing material as the stationary phase, and a FID, appears to
be a powerful tool for the analysis of aqueous samples (Guillemin et al., 1979).
For the analysis of aqueous samples of haloethylenes including vinylidene
chloride, a Spherosil XOA-400 column operated isothermally at 128°C and a mobile
phase containing a mixture of 50 ml/minute N and 16 ml/minute steam were
sucessfully used. One advantage of this method is that it allows for direct
aqueous injections, thereby eliminating time-consuming and loss-incurring
pretreatment of samples. The other advantage of this technique over the
traditional GC technique is that large amounts of aqueous samples can be injected
onto the column without causing any fluctuation in the baseline, even at maximum
sensitivity of the detector amplifier (Guillemin et al., 1979). By using a 200
jil injection with this method, 20 ppb vinylidene chloride in aqueous samples can
easily be detected. The method may not be applicable to polluted water samples,
however, because of GC separation problems arising from co-contaminants and
rapid deterioration of the GC column due to sorption of impurities.
The purge-trap technique is the most widely applied method for the analysis
of vinylidene chloride in aqueous samples (Bellar et al., 1979; Bellar and
Lichtenberg, 1974, 1979; Going and Spigarelli, 1977; Dowty et al., 1975). This
method is applicable for vinylidene chloride analysis in a diversity of media,
including drinking water on one extreme, and raw undiluted sewage on the other
(Bellar et al., 1979). This technique has been adopted as the recommended method
for the analysis of vinylidene chloride in water samples (Federal Register,
1979). In the purge-trap technique, the water sample is purged with an inert
gas, such as N? or He, at room temperature. The purged vinylidene chloride is
adsorbed on a trapping column. The trapped vinylidene chloride is thermally
desorbed and passes through an analytical column.
4-15
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The optimum conditions for purging were determined to be either 38 ml/minute
for 10 minutes (Going and Spigarelli, 1977) or 40 ml/minute for 11 to 15 minutes
(Bellar and Lichtenberg, 1979). Increasing the purge time at the specified flow
rate of inert gas resulted in a decrease in vinylidene chloride, recovery (Going
and Spigarelli, 1977). The purged vinylidene chloride was trapped in a Tenax GC
precolumn (Going and Spigarelli, 1977; Bellar et al., 1979). The thermal desorp-
tion was performed in the backflush mode for 4 minutes at a temperature of 180°C
with an inert gas flow rate of 20-60 ml/minute (Bellar et al., 1979). The
average recovery of vinylidene chloride determined for the entire method by
multiple analyses over 21 days using repeated 5 ml aliquots of 2 jig/1 aqueous
solution was determined to be Q8% by this purge-trap thermal desorption technique
(Bellar and Lichtenberg, 1979). The sensitivity of this technique is dependent
on the method of detection and the volume of water used for purging. However,
the method is very sensitive because the entire amount of purged vinylidene
chloride is used for a single analysis. A method detection limit (MDL) of 0.003
jig/1 was reported in EPA method 502.1 (Bellar and Lichtenberg, 1981).
Analytical columns packed with four kinds of materials—0.2% Carbowax 1500
on 80/100 mesh Carbopack-C (Bellar and Lichtenberg, 1979; Going and Spigarelli,
1977), 1? SP-1000 on 60/80 mesh Carbopack-B (Federal Register, 1979), n-octane on
100/120 mesh Porasil-C (Federal Register. 1979), and 10% SF-96 and 155 Igepal CO
880 capillary column (Dowty et al., 1975)—were found to be best suited for the
separation of vinylidene chloride from co-contaminants. Proper temperature pro-
gramming was found to be necessary for successful separation.
Both flame ionization (Dowty et al., 1975; Going and Spigarelli, 1977) and
halogen specific (Bellar et al., 1979; Federal Register, 1979) detectors were
used for the quantification of vinylidene chloride. The FID is somewhat
unsuitable, however, because the calibration procedure needed with the
4-16
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purge-and-trap method requires the preparation of aqueous standards by mixing
reagent-free water with aliquots of standard solution in water-miscible
solvents, such as methanol. Consequently, the aqueous standards prepared in this
manner contain relatively large quantities of the miscible organic solvent,
relative to the compound of interest. While these organic solvents are purged
with relatively low efficiency, their relatively high concentration may lead to
significant interferences with the FID. Therefore, the halogen specific
detector is more suitable for the purge-trap technique.
The confirmation of vinylidene chloride quantified by GC-FID or GC-Hall
detector was made by the GC-MS technique (Bellar et al., 1979; Going and
Spigarelli, 1977; Dowty et al., 1975; Federal Register, 1979). Mass spectro-
metry, either in the specific ion mode (SIM) or in the mass scan mode, was used as
the confirmatory technique. The specific ion mode, however, showed better sensi-
tivity of detection (Bellar et al., 1979).
The purge-trap technique described in the preceding discussions, or
slightly modified methods, have been used by several investigators recently for
the determination of vinylidene chloride in aqueous samples (Pereira and Hughes,
1980; Otson et al., 1982a,b). The precision of the purge-trap method using GC/MS
also has been determined recently by Olynyk et al. (1981).
4.3 SOIL AND DISPOSAL SITE SAMPLES
4.3.1 Sampling
DeLeon et al. (1980) reported taking samples from 30-foot vertical borings
using the split-spoon method. The samples were placed in glass jars, sealed with
Teflon-lined screw caps, and shipped in containers maintained at temperatures
between 6°C and 10°C. Upon arrival at the laboratory, the samples were
transferred to a freezer, where they were kept at -20°C until analyzed. Speis
(1980) collected sediment with a methanol-rinsed stainless steel spatula in 40 ml
4-17
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vials sealed with teflon baked silicon septa. The vials were filled to capacity
to minimize headspace and stored up to 1 week at wet ice temperatures.
4.3-2 Analysis
DeLeon et al. (1980) solvent extracted the samples in sealed vials with
either ri-hexane (for FID quantification) or n-hexadecane (for MS confirmation)
by mixing them with a vortex for 30 seconds. Tribromomethane (bromoform) was
added as an internal standard for the samples analyzed by FID. The solvent
extracts were quanitified for vinylidene chloride by the GC-FID method and by GC
coupled with MS for confirmation. A temperature-programmed capillary column
coated with SE-52 was employed as the analytical column. This column (27 meters
long) was found to be suitable for the separation of vinylidene chloride from its
isomers cis- and trans-1,2-dichloroethylene. The recoveries of vinylidene
chloride by this method were,determined at different levels of contamination. At
vinylidene chloride levels of 10 jig/g, 100 jig/g, and 300 }ig/g, the percent
recoveries were determined to be 110.5 ± 3.5 (standard deviation), 86.9 + 8.3,
and 80.2 + 3-7, respectively. The detection limit of the method was determined
to be 10 \ig/g. '••••..
Speis (1980) transferred a weighed portion of sediment into a Hypo vial,
sealed the vial, and injected internal standards. The vials were then placed in
a sand bath at 110°C and purged with an inert gas at 40 ml/min by means of a
sharpened stainless steel tube inserted through the septum to the bottom of the
vial. The outlet was passed through a water trap to a Tenax silica gel trap.
Desorption and analysis were virtually identical to EPA Method 624. Detection
limits were reported to be 5 |ig/kg and recoveries were 67% for a 10 jig spike, 90%
for a 20 |ig spike, 81.156 for a 40 ng'spike, and 84$ for an 80 jig spike.
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4.H MONOMER CONTENT IN POLYMERS AND MONOMER MIGRATION INTO FOOD-SIMULATING
SOLVENTS
Saran film is a copolymer of vinyl chloride (15-20$) and vinylidene chloride
(80-85?). It is marketed primarily as household film (0.5 mil thickness) and as
industrial film (2.0 mil thickness). The monomers in saran films used for food
packaging applications have the potential for migration into foods. Therefore it
is important to determine the monomer content in the polymer and the extent of
the monomer's migration into food-simulating solvents.
4.4.1 Sample Collection
The saran films required for analysis of residual monomer or of its migra-
tion into food-simulating solvents can be obtained from the manufacturer or can
be purchased directly at retail stores.
4.4.2 Analysis
The analysis of saran films for the monomer concentration has been accomp-
lished by two methods. In one method (Birkel et al., 1977; Hollifield and
McNeal, 1978), the film was dissolved in tetrahydrofuran (THF) in a teflon-lined
screw cap glass bottle at 70°C. The dissolved polymer containing the monomer was
directly injected into a GC equipped with an electron capture detector for
quantification. The analytical column was packed either with Chromosorb-102
(Birkel et al., 1977) or Chromosorb-104 (Hollifield and McNeal, 1978). When THF
spiked with vinylidene chloride was used, this method yielded recoveries of
96-102? through the quantification steps (Birkel et al., 1977). When a
Chromosorb-104 column was used, the detection limit of the method was determined
to be about 1 ppm vinylidene chloride in the polymer (Hollifield and McNeal,
1978). The confirmatory technique used with gas-solid chromatography-electron
capture detectors (GSC-ECD) was GC-MS in the specific ion mode (SIM). The
disadvantage of this method is that the injections of polymer solutions leave
4-19
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polymer residue in the glass liner of the injection port. If the injection port
liner is not cleaned frequently, the polymers may enter the column and alter its
performance.
This disadvantage in the analysis of vinylidene chloride monomer by solvent
dissolution of the polymer can be overcome by analyzing the monomer content of
the polymer by the head-space technique. The additional advantage of the head-
space technique is that the method is free from solvent interference such as that
encountered with the solvent dissolution method. The head-space technique was
used by Going and Spigarel'li (1977). In this method, the polymer was crimp-
sealed in a vial (teflon-lined cap) and the vial was heated. The optimum
conditions for heating were determined to be 100°C for 90 minutes. At a higher
temperature (150°C), vinylidene chloride was found to decompose; at lower
temperatures (50°C and 75°C), vinylidene chloride was not released from the
polymer. A 100 [il head-space gas was injected into a Durapak OPN on an 80/100
mesh Porasil-C GC column and the separated vinylidene chloride was quantified by
FID. This technique, however, has its own disadvantage. The calibration of the
method requires standard' polymer samples that have known vinylidene chloride
concentration. In the absence of such a standard, it becomes impossible to
determine the recovery of vinylidene chloride from the thermal release procedure
used in the head-space technique.
In order to determine the extent of the migration of vinylidene chloride,
the analysis of food-simulating solvents in contact with polymers was performed
by Hollifield and McNeal (1978). They used three food-simulating solvents—corn
oil, heptane, and water. Strips of saran wrap were placed in 400 ml food-
simulating solvent in a sealed can and stored at 49°C; this temperature is
suggested in the Code of Federal Regulations (CFR, 1977, cited in Hollifield and
McNeal, 1978) as the most severe temperature condition to which the food
4-20
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packaging material is expected to be subjected. After the desired storage time,
20 ml of the solvent were placed in screw cap bottles sealed with teflon-lined
septa. The bottles were heated to 90°C for 30 minutes or more and 1-2 ml of the
head-space gas was withdrawn for analysis. For canned water samples, the head-
space gas at 25°C was analyzed. The quantitative analysis was done by a GC with a
Chromosorb-104 column and an BCD. A GC equipped with the same column and coupled
with a mass spectrometer operated in the selective ion mode was used as a
confirmatory analysis. The recovery of vinylidene chloride after spiking the
migration-system-solution and analyses by the head-space gas-solid chroma-
tography technique was found to be quantitative (95 to 138?). The vinylidene
chloride detection limit was determined to be 5-10 ppb in the food-simulating
solvents (Hollifield and MoNeal, 1978).
A similar head-space technique was employed by Gilbert et al. (1980) for the
determination of vinylidene chloride monomer in packaging films. In this method,
narrow strips of film were put into hypovials and sealed with rubber septa. The
hypovials were heated to 120°C by an air-circulating fan oven for 30 minutes and
1 ml of the head-space gas was removed for analysis by GC with an BCD.
4.5 ANALYSIS OF FOODS AND OTHER BIOLOGICAL SAMPLES
The analysis of vinylidene chloride in food products in contact with poly-
vinylidene chloride wrappings was performed by Gilbert et al. (1980) by a head-
space method similar to that described for wrapping materials. For cooked meat
and cheese products, the samples were ground under liquid nitrogen to a fine
powder prior to their placement into hypovials. The hypovials were heated to
60°C in a waterbath for a minimum of 90 minutes prior to analysis.
The analysis of vinylidene chloride in fish samples and in body tissues was
performed by the purge-trap method similar to that described for aqueous samples
(Lin et al., 1982; Easley et al. ,1981). Lin et al. (1982) used computerized
4-21
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GC-MS for the determination of vinylidene chloride in fish, and Easley et al.
(1981) used a GC equipped with a Hall electrolytic conductivity detector for
vinylidene chloride determination in body tissues. The approximate limit of
detection for vinylidene chloride in spiked fish samples was determined to be 10
Hg/kg by Easley et al. (1981). Lin et al. (1982) determined the absolute
detection limit of 50 [ig/kg for the analysis of vinylidene chloride in body
tissues by their method.
Hiatt (1981, 1983) analyzed fish tissue for volatile compounds including
vinylidene chloride by vacuum distillation. Whole fish, stored in dry ice, were
homogenized in a food cutter with added liquid nitrogen to prevent loss of
volatiles. A 10 g fish sample in the sample flask was then heated to 50°C at 360
torr while immersed in an ultrasonic bath. Distillation was continued for 15
min.j the volatiles were trapped at liquid nitrogen temperature. The contents of
the trap were transferred to a DBS coated fused-silica capillary column (FSCC)
(30 m x 0.32 mm, 0.1 \w film thickness) at -99°C, which was then programmed up to
180°C. Analysis was performed by mass spectrometry. Recovery was reported to be
74 + 8% as opposed to 59 + 19$ for purge and trap of a diluted sample. FSCC
ohromatography gave better resolution than packed columns for late-eluting
peaks.
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5. SOURCES IN THE ENVIRONMENT
The purpose of this document is to present available information relevant to
human health effects that could be caused by this substance.
Any information regarding sources, emissions, ambient air concentrations,
and public exposure has been included only to give the reader a preliminary
indication of the potential presence of this substance in the ambient air. While
the available information is presented as accurately as possible, it is acknow-
ledged to be limited and dependent in many instances on assumption rather than
specific data. This information is not intended, nor should it be used, to
support any conclusions regarding risks to public health.
If a review of the health information indicates that the Agency should
consider regulatory action for this substance, a considerable effort will be
undertaken to obtain appropriate information regarding sources, emissions, and
ambient air concentrations. Such data will provide additional information for
drawing regulatory conclusions regarding the extent and significance of public
exosure to this substance.
Vinylidene chloride is a man-made chemical. To date, there is no evidence
that any natural process produces this chemical. The sources of vinylidene
chloride in four different environmental media—air, water, soil, and foods are
discussed below.
5.1 SOURCES OF AIR POLLUTION
The following operations contribute to the presence of vinylidene chloride
in the air:
(1) manufacture of vinylidene chloride monomer;
(2) manufacture of polymers containing polyvinylidene chloride;
(3) processing or fabrication of polyvinylidene homopolymers and
copolymers;
5-1
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(4) storage, handling, and transportation of the monomer;
(5) chemical intermediate production; and
(6) incineration of polymers containing polyvinylidene chloride.
5.1.1 Manufacture of Vinylidene Chloride Monomer
Vinylidene chloride is manufactured industrially either as a coproduct of
ethylene dichloride, produced from the chlorination of ethane or ethylene, or by
the dehydrochlorination of 1,1,2-trichloroethane. The chemical reactions for
the processes are the following:
—> CH2=CC12 + 4HC1
2Clrt > CH^=CC1^ + 2HC1
CH -GEL •*• 3C12
CH2C1-CHC12
NaOH
NaCl
The current domestic manufacturers of Vinylidene chloride monomer and their
estimated annual capacity are given in Table 5-1•
The Lake Charles facility of PPG Industries, which used 130 million pounds
of Vinylidene chloride annually for captive consumption in the manufacture of
1,1,1-trichloroethane, now produces 1,1,1-trichloroethane by a route that does
not utilize Vinylidene chloride (PPG Industries verbal communication, 1980).
The Lake Charles facility of PPG continues to produce Vinylidene chloride,
however, for sale in the merchant market.
It is reported that the Dow facility at Freeport produces about two-thirds
of its total annual capacity (Neufeld et al., 1977). Dow captively consumes
about 85% of the total Vinylidene chloride it manufactures annually. The balance
is shipped to its other polymer-producing facilities or sold to the merchant
market.
Vinylidene chloride is emitted to the air during the manufacture of the
monomer. The air emission factors, that is, the fraction of vinylidene chloride
lost to the air during its manufacture, can be estimated from material balance.
5-2
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TABLE 5-1
Monomer Production Facilities in the United States and Their Capacities3
Manufacturer
Location
Estimated Capacity
(million Ib/yr)
PPG Industries
Dow Chemical
Lake Charles, LA
Freeport, TX and
Plaquemine, LA
78'
95-100
Source: Neufeld et al., 1977
Figure obtained from Anonymous, 1978
TABLE 5-2
Air.Emissions of Vinylidene Chloride During Monomer Manufacture3
Producer
Location
Air Emission Factor
(emission in lb/100 Annual Emission
Ib monomer produced) (thousands of Ib/yr)
PPG Industries
Dow Chemical
Lake Charles, LA 0.10
Freeport, TX and 0.48
Plaquemine, LA
62
384
Source: Neufeld et al., 1977
5-3
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These air emission factors for vinylidene chloride manufacturing processes
are given by A.D. Little, Inc. (1976, cited in Going and Spigarelli, 1977).
Based on these values and the estimated production (Q0% of capacity) of
vinylidene chloride monomer, the annual emission rates derived are shown in Table
5-2.
The total estimated emission of 450,000 pounds/year is considerably lower
than the figure given by other authors (Hushon and Kornreich, 1978). The
difference is due mainly to PPG Industries' no longer producing
1,1,1-trichloroethane from vinylidene chloride. However, PPG still produces
vinylidene chloride for sale to polymer producing facilities.
According to the unpublished data submitted by Dow Chemical (Dow, 1984), the
estimated yearly emission of vinylidene chloride from its thermal recovery units
that handle the reactor waste streams is 820 Ibs. for both plants. Dow also
estimates (Dow, 1984) 10,000 Ibs/yr for fugitive emissions from both monomer and
polymer manufacturing facilities. Based on Dow estimate, the total vinylidene
chloride emission by its monomer production facilities is 4820 Ibs/yr assuming
JJOOO Ibs/yr for fugitive emission from its monomer production facilities.
5.1.2 Manufacture of Polymers Containing Polyvinylidene Chloride
The two primary uses of vinylidene chloride are in the manufacture of
polymers and chemical intermediates. The breakdown of vinylidene chloride
consumption in different industrial uses is given in Table 5-3.
It can be seen from Table 5-3 that except for a small application as a
chemical intermediate and some export, most of the vinylidene chloride is
consumed domestically for the production of polymers. Because of its excellent
fire and barrier resistance properties, vinylidene chloride polymer has been
used in the manufacture of copolymers with other monomers. In general,
oopolymers that contain a high percentage of vinylidene chloride (70-95$) are
5-4
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TABLE 5-3
Yearly Consumption of Vinylidene Chloride in Different Industries'"
Industry
Amount consumed
(million Ib/yr)
Percent of Total
Polymers
Domestic Use
Export
108-115
20
81*
Chemical Intermediate
TOTAL
133-1^0
100?
Source: Neufeld et al., 1977
TABLE 5-4
Polymerization Processes, Products, and Their Applications'
Process
Product
Application
Emulsion polymerization
Suspension polymerization
Solution polymerization
Emulsion latex
Speciality latex
Resin
Fiber
Barrier coating
Carpet backing
Barrier coating on
multilayer laminate
Molded plastics
Extruding films and
pipes
Modacrylic fibers
Source: Neufeld et al., 1977
5-5
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used for the barrier resistance characteristic, and copolymers with a lower
percentage of vinylidene chloride (10-4056) are used for fire retardant
properties. The three different polymerization processes used industrially for
the production of polymeric materials and the uses of these polymers are shown in
Table 5-4.
Emulsion latexes used as barrier coatings usually contain 70 to 95% vinyli-
dene chloride copolymerized with a variety of other monomers such as vinyl
chloride, acrylic acid, and acrylonitrile. These copolymers have a, unique and
excellent barrier resistance to gases, water vapor, organic vapors, and odors.
The speciality latexes obtained by copolymerization of 10 to H0% vinylidene
chloride and butadiene-styrene have excellent fire retardant properties and are
used as carpet backing materials.
The solid resins obtained by converting emulsion or suspension latexes to
the powdered resin may contain different amounts of vinylidene chloride. As in
the case of latexes, the characteristics of the copolymer are strongly influenced
by the vinylidene chloride content. Solid resins are used for coating cellophane
and extrusion into film or for manufacturing multilayer laminates.
Solution polymerization of 10 to 30% vinylidene chloride with acrylonitrile
produces modacrylic fibers. The modacrylics are produced solely for the flame
retardant characteristics they impart to sleepwear fabric, drapery fabric, and
automobile upholstery.
The major plant sites for vinylidene chloride polymerization and the type of
polymer produced by these facilities are shown in Table 5-5.
The estimated annual emissions of vinylidene chloride from polymer
synthesis are given in Table 5-6.
5-6
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TABLE 5-5
Polymerization Sites and Type of Polymer Produced3
Manufacturer
Dow Chemical
W.R. Grace
Morton Chemicals
A.E. Staley
Rohm and Haas
GAP
Reichhold
Chemicals
National Starch
Eastman
Monsanto
American Cyanamid
DuPont
Location
Midland, MI
Dalton, GA
Owensburg, KY
Ringwood, IL
Lemont , IL
Knoxville, TN
Chattanooga, TN
Cheswold , DE
Meridosia, IL
Kingsport, TN
Decatur, AL
Pensacola, FL
Circleville, OH
Polymer type
•Suspension latex
Emulsion latex
Solid resin
Speciality latex
Emulsion latex
Speciality latex
Emulsion latex
Emulsion latex
Emulsion latex
Emulsion latex
Speciality latex
Emulsion latex
Speciality latex
Emulsion latex
Speciality latex
Modacrylics
Modacrylics
Modacrylics
Solid resin
Primary usage
Barrier coating
Barrier coating
Barrier coating
Carpet backing
Barrier coating
Carpet backing
Barrier coating
Barrier coating
Barrier coating
Barrier coating
Carpet backing
Barrier coating
Carpet backing
Barrier coating
Carpet backing
Fiber
Fiber
Fiber
Barrier coating
Source: Neufeld et al., 1977
5-7
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TABLE 5-6
. a
Estimated Annual Emissions of Vinylidene Chloride from Polymer Synthesis
Emission Factor
(lb/100 Ib vinylidene
Polymer chloride polymerized)
Barrier-coating latex 0.60
Latex for miscellaneous coatings 1
Synthetic fibers 1
Resin for cellophane coating 0.7
Extrusion resin (emulsion) 0.13
Extrusion resin (suspension) • 0.26
TOTAL
Annual Emissions
(thousands of Ib/yr)
120
150
160
182
27
40
679
Source: A.D. Little, Inc., 1976
5-8
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5.1.3 Processing or Fabrication of Polymers
The fabrication processes include coating of paper, glassine, paper
products, cellophane, and plastic films. Fabrication processes also include
extrusion of films and monofilament fibers and molding operations.
The major polyvinylidene chloride latex users for miscellaneous fabrication
processes are given in Tables 5-7, 5-8, and 5-9. . . .
The estimated annual emission rate of vinylidene chloride in the processing
of polyvinylidene chloride polymers is given in Table 5-10. However, according
to the unpublished data submitted by Dow Chemical (Dow, 1984), the emission of
vinylidene chloride from its polymer production facilities ranges from 172,000
to 182,000 Ibs/yr.
5.1.4 Storage, Handling, and Transportation of the Monomer
Vinylidene chloride monomer is shipped from the production sites to the user
sites in bulk railroad tank"bars or tank trucks. A small unspecified quantity is
shipped in drums (Neufeld et al., 1977). Approximately 90 million pounds of
vinylidene chloride, are transported annually in various ways. , "Vinylidene
chloride emissions can be expected to occur during storage, transfer, and filling
operations. It has been estimated that of the total vinylidene chloride loss
during its manufacture, subsequent polymerization, and processing, 25% takes
place during storage, transfer, and handling and , 75$. takes place during
processing (Neufeld et al., 1977). Since only half of the total vinylidene
chloride manufactured is transported to other locations (the other half is
captively used), this transported half is solely responsible for losses related
to storage, transportation,' and handling. The total vinylidene chloride loss
during manufacture, subsequent polymerization, and processing adds up to
1,160,000 pounds per year. Half of this figure has been used in the following
calculation to determine the losses during storage, transportation, and
handling:
5-9
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TABLE 5-7
Major Polyvinylidene Chloride Processors2
Company ,
Plant location
Barrier-coating on paper and glassine
Deerfield-Reed Corporation
American Bag and Paper
Consolidated Paper
Crown Zellerbach
Daniels
Diversa-Pax
Dixico
DuPont
Milprint
Philip Morris
Rexhara
St. Regis
Thilmany
Chase Bag Company
Print Pak
Barrier-coating on paperboard
Gordon Carton
Green Bay Packaging
Interstate Folding Box
Michigan Carton Company
Olin Kraft
Zumbril
Barrier-coating on plastic
DuPont
Cryovac
Minnesota Mining and Manufacturing
Allied Chemical Corporation
Hercules
Milprint
Cryovac
Berais
American Can Company
Standard Packaging
Sealed Air Corporation
Clifton, NJ
Philadelphia, PA
Wisconsin Falls, WI
Portland, OR
Rhinelander, WI
St. Petersburgh, FL
Dallas, TX
Circleville, OH
Milwaukee, WI
Nicholasville, KY
Memphis, TN
Rhinelander, WI
Kaukauna, WI
Hudson Falls, NY
Atlanta, GA
Baltimore, MD
Green Bay, WI
Middletown, OH
Battle Creek, MI
W. Monroe, LA
Cincinnati, OH
Circleville, OH
Simpsonville, SC
Irvington, NJ
Decatur, AL
Pittsville, PA
Covington, VA
Milwaukee, WI
Simpsonville, SC
New London, WI
Neenah, WI
Clifton, NJ
Fairlawn, NJ
Source: Neufeld et al., 1977
5-10
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TABLE 5-8
Manufacturers of Polyvinylidene Chloride-Coated Cellophane'
Manufacturer
DuPont
FMC
Olin
Share of Market
40$
35%
25%
Location
Richmond , VA
Clinton, IA
Tecumseh , KS
Freder icksburg ,
Pisgah Forrest,
Covington , VA
VA
NC
Sources: Neufeld et al., 1977; A.D. Little, Inc., 1976
TABLE 5-9
Major Extruders of Polyvinylidene Chloride Film"
Manufacturer
Plant Location
Cryovac
Oscar Mayer
Dow Chemical
American Can Company
Union Carbide Corporation
Amtech, Inc.
Simpsonville, SC
Cedar Rapids, IA
Camarillo, CA
Iowa Park, TX
Madison, WI
Chicago, IL
Davenport, IA
Philadelphia, PA
Nashville, TN
Vernon, CA
Sherman, TX
Midland, MI
Cleveland, OH
Centerville, IA
Odenton, MO
aSources: Neufeld et al., 1977; A.D. Little, Inc., 1976
This plant extrudes monofilament, which is used primarily as filter cloth
in the chemical industry.
5-11-
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TABLE 5-10
Estimated Emissions from Polyvinylidene Chloride Processing0
Process
Coating cellophane
Coating plastics, paper
and glassine
Extrusion
Miscellaneous coating
TOTAL
Emission Factor
(lb/100 Ib
Polymer Used)
0.06
0.03
0.001
0.04
Annual Vinylidene
Chloride Emissions '
(Ib/yr)
1,560
16,380
430
12,000
30,370
Source: A.D. Little, Inc., 1976
TABLE 5-11
Summary of Estimated Environmental Losses of Vinyiidene Chloride
Source
Monomer synthesis
Polymer synthesis
Polymer fabrication
Storage, handling, and
transportation
Chemical intermediate
production
Disposal of polymers
TOTAL
Vinylidene
Air
446,000
679,000
30,400
145,000
0
ob
1,300,400
Chloride Contamination
Water
0
4100
0
Oa
0
0
4100
(Ib/yr)
Soil
0
0
0
oa
0
180
180
a
'Some water and soil contamination may arise from this source.
Incineration of polymers may contaminate air with an undeterminable amount.
5-12
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1,160,000 x 0.5 x 25% = x
x = 145,000 Ib/yr
This annual loss of 145,000 pounds during storage, handling, and transpor-
tation does not include any additional losses due to accidental spillage during
transportation.
5.1.5 Chemical Intermediate Production
The primary chemical intermediate that is manufactured from vinylidene
chloride is chloroacetyl chloride. Since PPG Industries, the sole manufacturer
of 1,1,1-trichloroethane from vinylidene chloride, no longer uses this process
for 1,1,1-trichloroethane manufacture, no vinylidene chloride emissions can be
expected from this intermediate. Chloroacetyl chloride is captively used by Dow
Chemical Company and no losses of vinylidene chloride to the environment are
reported during its manufacture (Neufeld et al., 1977). The purified chloro-
acetyl chloride used as an intermediate for further chemical reaction is reported
to be free of vinylidene chloride contamination (Neufeld et al., 1977). Thus,
its usage cannot be a source of vinylidene chloride in air.
5.1.6 Incineration of Polymers Containing Polyvinylidene Chloride
Over 95? of vinylidene chloride polymers are used for packaging, in the
manufacture of textile fibers, or as a flame-retardant carpet backing (Neufeld et
al., 1977). All these consumable items are disposed of at the end of their
useful life. The ultimate disposal operation is either incineration or placement
in a solid waste landfill. If incineration is used as the disposal process, it
may contribute to small amounts of vinylidene chloride in air. The residual
monomer in the polymer may be released into the air during heating. The decom-
position of polymer to monomer is not likely to occur. The products of thermal
degradation will depend primarily on the heating temperature. Thermal degrada-
tion of polyvinylidene chloride has been studied in detail by Wess'ling and
5-13
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Edwards (1970). These investigators found that polyvinylidene chloride begins
to decompose at about 125°C. At very high temperatures, graphitization of
carbonaceous residue takes place. On pyrolysis, polyvinylidene chloride yields
70$ hydrogen chloride, 26% carbonaceous ash, and 4/6 volatile hydrocarbons
consisting of benzene, chlorobenzene, and three dichlorobenzenes (O'Mara et al.,
1973). The thermal decomposition is also catalyzed by various metal salts. The
mechanism of thermal decomposition of polyvinylidene chloride was also studied
by Ballistreri et al. (1981). Currently an estimate of the amount of vinylidene
chloride released to the air from incineration is not available. However,
incineration is not expected to be a significant source of vinylidene chloride in
air.
5.2 SOURCES IN WATER
The only industrial operation that produces liquid effluents containing
vinylidene chloride monomer is reported to be the polymerization operation
(Neufeld et al., 1977). The two main sources of vinylidene chloride loss during
polymerization operations are waste polymer sludges arising from reactor
cleaning during normal operation or from products containing bad batches, and
wastewater from condensation of gases during stripping operations. Neufeld et
al. (1977) estimate that approximately 4100 pounds per year of vinylidene
chloride loss can be attributed to this source.
A small but unknown amount of vinylidene chloride may originate in water
from the cleaning of rugs backed with speciality latexes.
5.3 SOURCES IN SOIL
The disposal of consumer products that contain processed vinylidene
chloride polymers (1 to 3 ppm residual vinylidene chloride monomer) by municipal
solid waste disposal operations may result in soil contamination. Neufeld et al.
(1977) estimate that the maximum potential quantity of vinylidene chloride
monomer in solid wastes would be 180 pounds per year.
5-14
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5.4 SOURCES IN FOODS
The three potential sources of vinylidene chloride contamination in foods
are as follows: (1) migration of monomer from the polymeric wrapping materials to
foods; (2) contaminated drinking water; and (3) edible aquatic foods that have
bioconcentrated vinylidene chloride from polluted water. All these are
secondary sources, however, whose primary sources (i.e., polymers and water)
have already been discussed.
5.5 SUMMARY OF ENVIRONMENTAL LOSSES
This section presents estimates .of the amount of vinylidene chloride
monomer lost to the atmosphere, to water streams, or to soils. The losses are
summarized in Table 5-11.
5-15
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6. ENVIRONMENTAL FATE, TRANSPORT, AND DISTRIBUTION
6.1 ATMOSPHERIC FATE, TRANSPORT, AND DISTRIBUTION
6.1.1 Reaction with Atmospheric Radicals and Ozone
Very little information is available on this subject. Upon entering the
atmosphere, vinylidene chloride, like other chloro-olefin vapors, may interact
with O-, OH» , and RO • radicals, and with ozone already present in the
atmosphere. In addition, chloro-olefins in the atmosphere will generate
chlorine atoms, which may interact with the parent molecules. The gas phase
oxidation of halo-olefins at room temperature initiated by Cl atoms, 0[ P]
radicals, and 0 has been reviewed (Sanhueza et al., 1976; Heicklen et al.,
1975). In the presence of 0_, the oxidation of vinylidene chloride by chlorine
atoms produced 98% chloroacetyl chloride, and about 2% phosgene and CO as the
reaction products. The reaction of vinylidene chloride with 0[ P] in the
presence of 0- produced CO, chloroacetyl chloride, polymer, and another
unidentified compound. The rate of 0[ P.] attack on vinylidene chloride is the
same as the rate of 0[P] attack on
(Sanhueza, 1976; Heicklen et al., 1975);
however, the relative reactivity of 0[P] with vinylidene chloride (1.0) in the
gas phase at room temperature is higher than the reactivity of Cl atoms with
vinylidene chloride (0.72) under the same conditions (Heicklen et al., ,,1975).
* o o _l —l
Based on a reaction rate constant of 7.8 x 10~ cm molecule" sec (Graedel,
1978) for 0[ P] reaction with vinylidene chloride (same as CpHj. reaction rate)
3 4
and the concentration of 0|°P] in the ambient atmosphere as 5 x 10 molecules
cm~^ (Cupitt, 1980), the half-life for this reaction can be estimated to be
approximately 206 days. . ,. .
o
In the absence of Op, 0[3p] forms the-same reaction products it produces in
the presence of 0 ; however, the quantum yield for carbon monoxide formation is
6-1
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reduced from 0.78 in the presence of 02 to 0.35 in the absence of 02 (Heicklen et
al., 1975).
The main products of 0_ interaction with vinylidene chloride in the vapor
phase at 25°C are phosgene and formaldehyde (Sanhueza et al., 1976; Heicklen et
al., 1975; Brown et al., 1975). The formation of chloroacetyl chloride, CO, CO
HC1, and possibly water has also been reported (Hull et al., 1973). The yield of
phosgene is always either comparable to or greater than the yield of formic acid
(Heicklen et al., 1975). The 0_ reaction in the presence of 02 is, however, too
slow to be important in the urban atmosphere (Sanhueza et al., 1.976; Heicklen et
al., 1975). Based on a reaction rate constant of 4 x 10~ cm molecule" sec
(Cupitt, 1980) and the concentration of ozone in the ambient atmosphere at 1 x
10 molecule cm~^ (Cupitt, 1980), the half-life for ozone reaction with
vinylidene' chloride in the atmosphere can be calculated to be approximately 201
days.
The interaction of R0_ and OH radicals with vinylidene chloride was reported
by Brown et al. (1975). The formation of phosgene and formaldehyde was reported
with both R02» and »OH radicals. The rate constant for the oxidation with OH
1 O O 1 1
radicals was reported to be 4 x 10~ cm molecule" sec" (Cupitt, 1980). If
-6
the concentration of OH radicals in the ambient atmosphere is assumed to be 10
radicals cm (Cupitt, 1980), the half -life for this reaction can be calculated
to be 2 days. The half-life for the peroxy radical's reaction with vinylidene
chloride in the atmosphere has been reported to be about 22 years by Brown et al.
(1975).
It can be concluded from the above discussion that the most significant
oxidation reaction of vinylidene chloride in the ambient atmosphere is its
reaction with hydroxyl radicals. The half-life for this reaction has been
estimated to be about 2 days .
6-2
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6.1.2 Atmospheric Photochemical Reactions
Gay et al. (1976) studied the photoreaction of vinylidene chloride in air in
the presence of nitrogen dioxide with ultraviolet radiation. At a concentration
of 4.85 ppm and in the presence of 2.26 ppra NO vinylidene chloride was found to
decompose rapidly—83% decomposition had taken place within 140 minutes. The
reaction products identified were HCOOH, HC1, CO, HCHO, 0 COClp, chloroacetyl
chloride, formyl chloride, and nitric acid.
The photolysis of vinylidene chloride under simulated atmospheric
conditions was also studied by Dilling et al. (1976). In the presence of 5 ppm NO
and at a relative humidity of 35%, 10 ppm vinylidene chloride underwent
photolysis at wavelengths greater than 290 nm, and disappeared with a half-life
of 2.1 hours. Addition of cyclohexane was found to retard the photodecomposition
rate of vinylidene chloride. Although vinylidene .chloride was not tested,
reaction of a closely related halo-olefin (trichloroethene) showed similar
reactivity with ozone and NO- as with NO.
The above experiment of Dilling et al. (1976) was conducted at an
ultraviolet radiation intensity of about 2.6 times that of natural sunlight at
noon on a summer day in Freeport, TX. Therefore, the estimated half-life of
vinylidene chloride under bright sunlight and in the presence of NO is
approximately 5 to 12 hours (Dilling et al., 1976). In the absence of NO, the
half-life for photodecomposition of vinylidene chloride under bright sunlight
may increase five-fold. This estimate is based on the experimental half-life of
a closely-related halo-olefin (trichloroethene) in the presence and absence of
NO as determined by Dilling et al. (1976). Therefore, it is estimated that
vinylidene chloride will photodecompose under bright sunlight with a half-life
of one to three days. Pearson and McConnell (1975), on the other hand, exposed
quartz flasks containing halogenated aliphatic compounds in air to incident
6-3
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radiation from the sun and estimated the tropospheric photolytic half-life to be
56 days for vinylidene chloride. Although the experiments of Pearson and
McConnell (1975) were not adequately controlled in terms of air composition,
temperature, and radiation intensity, it is difficult to explain the large
discrepancy in the photolytic half-life of vinylidene chloride between this
investigation and the work of Billing et al. (1976). That the photolysis of
vinylidene chloride in the atmosphere is a possibility has also been indicated
(but no quantitative rate data given) by Cupitt (1980). In conclusion, it can be
predicted that photolysis of vinylidene chloride in the atmosphere may be
competitive with its reaction involving hydroxyl radicals. The half-life of
vinylidene chloride in air under atmospheric smog conditions (air containing
NO , 0_, etc.) may be further reduced due to its greater photochemical reactivity
in the presence of NO and 0_.
X j
6.1.3 Atmospheric Physical Processes
Recently, the atmospheric fate of vinylidene chloride under physical and
chemical removal processes was studied by Cupitt (1980). The atmospheric half-
life of vinylidene chloride removal by rain droplets was estimated to be 110,000
years. The lifetime of vinylidene chloride removal by adsorption onto aerosol
particles was estimated to.be 5.3 x 1010 days. Therefore, the possibility of
vinylidene chloride removal by these two physical removal processes is remote.
6.2 AQUATIC FATE, TRANSPORT, AND BIOACCUMULATION
Very little experimental data pertaining to the various fate processes of
this chemical in aquatic media and its bioaccumulation potential in aquatic
organisms are available in the literature. In the following discussion the
experimental data, whenever available, have been used to predict the fate of
vinylidene chloride in aquatic media. In the absence of such data, the
prediction of the fate has been based on calculated or estimated data using
empirical or theoretical methods. Extreme caution should be exercised in
6-4
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interpreting the fate of a chemical based solely on calculated or estimated data.
This reservation concerning the estimated data is justified by the large
discrepancies observed in a few instances between the experimental and estimated
data where both types of data are available.
6.2.1 Fate and Transport in Water
The photolysis and hydrolysis of vinylidene chloride in natural aquatic
media are probably not significant processes (Mabey et al., 1981). No
experimental data on the possibility of oxidation of vinylidene chloride by
singlet oxygen ( 0^ and peroxy radicals present in aquatic media could be found.
However, based on the experimental data from closely related analogues (e.g.,
trichloroethene and tetrachloroethene), Callahan et al. (1979) concluded that
vinylidene chloride is "more amenable" to oxidation in aquatic media than both
trichloroethene and tetrachloroethene. From the calculated (based on
structure/activity relationship) rate constant values of less than 108 M~1 hr~1
and 3 M~ hr~ (Mabey et al., 1981) for singlet oxygen and peroxy radical
reactions, respectively, with vinylidene chloride in aquatic media and the
— 12 Q
estimated concentrations of 10 M and 10 M for singlet oxygen and peroxy
radicals, respectively,, in aquatic media (Mill and Mabey, 1980), the oxidation of
vinylidene chloride by either process can be calculated to be. environmentally
insignificant.
The biodegradability of vinylidene chloride was studied by Tabak et al.
(1981) by the static-culture flask-screening procedure with settled domestic
wastewater as microbial inoculum. These authors reported a significant
degradation of vinylidene chloride with the unacclimated sludge. At 5 mg/1
initial concentration of vinylidene chloride, 78% of the compound biodegraded in
7 days of incubation at 25°C. The biodegradation was only H5% when the initial
vinylidene chloride concentration was 10 mg/1 and the other conditions were the
6-5
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same. Similarly, it has been reported by Patterson and Kodukala (1981) that
activated sludge treatment of a municipal wastewater at an influent vinylidene
chloride level of 0.04 mg/1 resulted in 97% removal of the compound. It can be
concluded from these experimental results that vinylidene chloride may undergo
biodegradation in ambient aquatic media. However, until the role of
biodegradation of this compound in natural aquatic media is defined, it is not
possible to predict the significance of this process in determining its fate in
aquatic media. It should be mentioned that on the basis of limited experimental
evidence on related chloroaliphatics, Callahan et al. (1979) have concluded that
vinylidene chloride probably biodegrades in aquatic media at a slow rate.
The transport of vinylidene chloride from aquatic media ,to the atmosphere
through volatilization appears to be its primary transport process (Callahan et
al., 1979). The evaporation characteristics of vinylidene chloride in water were
studied by Billing (1977). When a 1 mg/1 aqueous solution of 6.5 cm depth was
stirred at 200 rpm in still air (<0.2 mph air current) at 25°C> the half-life for
evaporation was found to be 27.2 minutes. The measured half-life for evaporation
of vinylidene chloride from dilute aqueous solution was reasonably close to the
calculated value of 20.1 minutes (Billing, 1977) based on liquid and vapor-phase
mass transfer coefficients for exchange between the water body and the
atmosphere. However, this agreement is somewhat fortuitous since the calculated
value depends on the exchange constants, whereas the experimental values depend
on the stirring rate, air current, and other factors (Billing, 1977).
The half-life for the evaporation of vinylidene chloride from pond, river,
and lake waters can also be calculated from the reaeration rate constant of this
compound. Assuming the reaeration rate ratio (KVC/KV°) of 0.601 (calculated from
diffusion coefficient) (Mabey et al., 1981) for vinylidene chloride, and the
_1
_1
values for oxygen reaeration rate constants of 0.19 day" ,0.96 day" , and 0.24
6-6
-------
day"1 for pond, river, and lake waters, respectively (Mabey et al., 1981), the
half-lives for evaporation can be calculated to be 6.1 days, 1.2 days, and 4.2
days from pond, river, and lake waters, respectively.
No specific information pertaining to the sorption of vinylidene chloride
onto sediments could be found. However, based on the experimental data from
related analogues (e.g., trichloroethene and tetrachloroethene), Callahan et al.
(1979) concluded that the sorption of vinylidene chloride onto sediments is
probably an insignificant process. The significance of sorption of this compound
onto sediments can also be predicted from the correlation equation of
Schwarzenbach and Westall (1981). Assuming the octanol/water partition
coefficient value of 69 for vinylidene chloride (Mabey et al., 1981), the log K
oc
value (K
sorption coefficent x 100
) in sediments containing 0.5% organic
"oc " % organic carbon
carbon can be calculated to be 1.81 from the equation of Scharzenbach and Westall
(1981). This log K value is somewhat lower than the experimental log K value
of 1.92 for benzene (Schwarzenbach and Westall, 1981). Therefore, the rate of
sorption of vinylidene chloride onto sediments is expected to .be less than
benzene sorption onto sediments. In other words, the sorption of vinylidene
chloride onto sediments containing low organic carbon is not likely to be
significant but may increase as the organic carbon content in the sediment
increases.
It can be concluded from the above discussions that volatilization from
aquatic media is probably the most significant transport process for vinylidene
chloride. The role of biodegration in determining the fate of this compound in
natural aquatic media has not been definitely determined. All other aquatic
processes are probably insignificant in determining the fate of vinylidene
chloride in natural aquatic media.
6-7
-------
6.2.2 Bioaccumulation of Vinylidene Chloride in Aquatic Organisms
No experimental data are available for the bioaccumulation factor (BCF) for
Vinylidene chloride in any kind of fish or other edible aquatic organisms. A
number of theoretical correlation equations are available that relate the BCF to
either the octanol-water partition coefficient or the water solubility of the
chemical. These equations are given below:
Log BCF = 0.76 log KQW - 0.23 (Veith et al., 1979)
Log BCF = 0.542 log KQW + 0.124 (Neely et al., 1974)
Log BCF = -0.508 log S + 3-41 (Chiou et al., 1977)
where K = partition coefficient of the chemical between octanol/water,
ow '
and
S = water solubility of the chemical expressed in jj.mol/1.
The above equation of Veith et al. (1979) is applicable for the whole fish,
whereas the equations of Neely et al. (1974) and Chiou et al. (1977) are
applicable for fish muscle only. •
If the values"' of log K and S for Vinylidene chloride are assumed to be
OW
1.48 (Tute, 1971) and 2.19 x 103 junol/l (Hushon and Kornreich, 1978),
respectively, the theoretical values for BCF can be calculated to be 7.8
(equation of Veith et al., 1979) for the whole fish and 8.5 (equation of Neely et
al., 1974) or 51 (equation of Chiou et al., 1977) for fish muscle. The
relatively low value for BCF indicates that Vinylidene chloride will probably not
bioaccumulate in fish to any significant extent.
6.3 FATE, PERSISTENCE, AND TRANSPORT IN SOIL
No information pertaining specifically to the fate, persistence, and
transport of Vinylidene chloride in soils could be found. However, the fate and
transport processes of this compound can be partially predicted from the
estimated log K value of 1.81 in soils containing 0.5% organic carbon. This
oc
relatively low log K value, coupled with a solubility of 2250 mg/1 and a vapor
oc
6-8
-------
pressure of 600 mm of mercury at 25°C, would indicate that both volatilization
and leaching may play significant roles in determining the fate of this chemical
in soils. In fact, the detection of this compound in several groundwaters (see
Section 7.2) is indicative of the leaching of vinylidene chloride from soils.
Unless more experimental or calculated data are available, no prediction
regarding the microbial degradability and chemical oxidation of this chemical in
soils can be made, although Kobayashi and Rittmann (1982) have reported the
biodegradation of vinylidene chloride by soil bacteria.
6-9
-------
-------
7. ENVIRONMENTAL LEVELS AND EXPOSURE
When an environmental pollutant is suspected of being a potential health
hazard, it becomes necessary to determine the level of that pollutant in the
environment and its possible human intake from various environmental media. The
four environmental media of interest in this regard are air, water, soil, and
foods. The vinylidene chloride levels from each individual medium and the
possible human exposure therefrom are discussed in the following subsections.
The purpose of this document is to present available information relevant to
human health effects that could be caused by this substance. Any information
regarding sources, emissions, ambient air concentrations, and public exposure
has been included only to give the reader a preliminary indication of the poten-
tial presence of this substance in the ambient air. While the available informa-
tion is presented as accurately as possible, it is acknowledged to be limited and
dependent in many instances on assumption rather than specific data. This
information is not intended, nor should it be used, to support any conclusions
regarding risks to public health.
If a review of the health information indicates that the Agency should
consider regulatory action for this substance, a considerable effort will be
undertaken to obtain appropriate information regarding sources, emissions, and
ambient air concentrations. Such data will provide additional information for
drawing regulatory conclusions regarding the extent and significance of public
exposure to this substance.
7.1 AIR
7.1.1 Environmental Levels
The concentration of vinylidene chloride in air can be determined by moni-
toring its level in the atmosphere. In the absence of monitored data, the
7-i
-------
concentration can be theoretically estimated by dispersion modelling based on
the amount of vinylidene chloride losses in air from each plant. Such theore-
tical modelling, which is generally recognized to be accurate within a factor of
two in predicting the concentration of a pollutant in the vicinity of a plant,
has been used for estimating the population exposure to other atmospheric pollu-
tants, such as acrylonitrile (Suta, 1979). A vinylidene chloride model based on
analogy to 1,1,1-trichloroethane has been developed to estimate potential human
exposure (Wapora, 1982). Using dispersion modelling, Hushon and Kornreich
(1978) estimated the vinylidene chloride concentration levels at a single
distance from three vinylidene chloride monomer production sites in the United
States using atmospheric dispersion modeling. The 10-minute peak exposures of an
individual 500 m downwind from the three plants were estimated to be 0.87 ppm,
0.44 ppm, and 0.52 ppm for the Dow plant at Freeport, the Dow plant at
Plaquemine, and the PPG plant at Lake Charles, respectively. The corresponding
24-hour peak concentrations at the same three locations were estimated to be 0.52
ppm, 0.26 ppm, and 0.32 ppm. In order to estimate these values, it was assumed
that these plants have certain yearly emission rates of vinylidene chloride
(Hushon and Kornreich, 1978), the wind speed was 6 m/s, the height of the plants
was 12.3 m, and vinylidene chloride monomer would be non-reactive in the
atmosphere. The last assumption may have led to erroneous estimates of vinyli-
dene chloride concentration at longer distances. The half-life of vinylidene
chloride under simulated smog conditions was estimated to be 5 to 12 hours
(Billing et al., 1976) and approximately 2 days under atomspheric hydroxyl reac-
tions (Cupitt, 1980). This relatively rapid atmospheric oxidation may not have a
significant effect on ambient air concentration at short distances from the
source, but may have a dramatic effect at longer distances. Thus, any dispersion
modelling for estimation of vinylidene chloride concentrations at various
7-2
-------
distances from the source should include the effect of disappearance of
vinylidene chloride due to atmospheric oxidation.
One of the earlier attempts to experimentally determine atmospheric levels
of halocarbons including vinylidene chloride was made by Grimsrud and Rasmussen
(1975) in rural Pullman, WA, during the period of December 1974 to February 1975.
They used a GC-MS method for the quantification of vinylidene chloride. Because
of the limitations of the analytical methodology (inadequate GC column),
however, they could not separate vinylidene chloride from its isomers cis- and
trans-1,2-dichloroethylene, and reported the combined concentration of the three
isomers to be <5 ppt.
The monitoring of vinylidene chloride near industrial sites was conducted
by Research Triangle Institute (Research Triangle Institute, 1977a,b, cited in
Hushon and Kornreich, 1978) during the period 1976 to 1977. Vinylidene chloride
concentrations ranging from 9 ppt to 249 ppt were detected near Dow.plant sites,
one at Freeport, TX, and four at Plaquemine, LA. Seven other Dow sites at
Plaquemine, LA, showed no detectable trace of vinylidene chloride. .
The more systematic environmental monitoring for vinylidene chloride near
industrial sites was performed by Going and Spigarelli (1977) during the period
of January 1977 to April 1977. These investigators selected sampling points near
six industrial plants representing manufacturers of vinylidene chloride monomers
and polymers and fabricators of the polymers. The analyses of the samples were
performed by GC-FID and GC-MS.
The concentrations of vinylidene chloride in the ambient air throughout the
U.S. have been measured by several other investigators (Bozzelli et al., 1980;
Going and Spigarelli, 1977; Pellizzari et al., 1978a, b; Pellizzari et al., 1979;
Pellizzari and Bunch, 1979; Wallace et al., 1984,). Based on an assessment of
quality as evaluated by the reliability of sampling and analytical methodology
7-3
-------
and the quality control/quality assurance strategy employed in the measurements
(Brodzinsky and Singh, 1982), the monitoring data from these studies that are
considered acceptable are presented in Table 7-1. In the studies with the source
areas, the durations of sampling were approximately twenty-four hours.
Concentrations of vinylidene chloride in air samples collected in 1979 from Los
Angeles, CA; Phoenix, AZ; and Oakland, CA, were measured by Singh et al. (198lb).
The mean concentrations were determined to be 4.9, 29.8, and 12.6 ppt,
respectively. However, these values have not been presented in Table 7-1 because
no assessment of the quality of these data is available.
The sampling sites, sampling data, total number of sampling points
monitored at each site, the mean concentrations, the standard deviations, the
median concentrations, and the concentration ranges at each site are shown in
Table 7-1. Additionally, the corresponding values for the eight sites combined,
and the values for the sampling points categorized as urban/suburban and as
source areas are also shown in Table 7-1. It is obvious from Table 7-1 that the
median concentration of vinylidene chloride in U.S. urban/suburban ambient air
is approximately 5 ppt. However, the concentration is substantially higher (2182
ppt) for ambient air samples collected from vinylidene chloride source areas.
7.1.2 Exposure
The Office of Air Quality Planning and Standard (OAQPS), U.S. EPA, Research
Triangle Park, NC, has prepared a document estimating human exposure to vinyli-
dene chloride in the atmosphere around plants producing the monomer and the
polymer. The ranges of measured concentrations associated with the monomer and
polymer plants were 90-100 ng/m3 and 25-50 jig/m3, respectively. For a detailed
discussion, the readers are referred to the OAQPS document (Wapora, 1982).
Landau and Manos (1976) estimated the number of Americans who reside within
5 miles of 38 major plants in the United States that produce monomers and
7-4
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polymers and fabricate polymers. The estimated values are given in Table 7-2.
The values are only population estimates and are not meant to indicate the
absolute number of people exposed to vinylidene chloride. The size of the
population residing near plant sites as given in Table 7-2 may have changed
slightly due to shut down of a few plants or addition of new plants and due to
some population shifts.
The estimation of the number of people exposed to vinylidene chloride would
require knowledge of the chemical's transport characteristics. Theoretically,
dispersion modelling could provide an estimate of vinylidene chloride
concentrations at different distances from the plant sites; however, such data
are not presently available.
Experimental data could provide a solution to this problem. Going and
Spigarelli (1977) detected vinylidene chloride at a distance of 1.5 miles from a
vinylidene chloride monomer production facility. Their study was not designed to
determine vinylidene chloride levels at different distances from the source.
Therefore, the study of Going and Spigarelli (1977) cannot be used to estimate
vinylidene chloride exposure.
With the median ambient levels (averaged over 1 hour up to 1091 days) given
in Table 7-1, and assuming 20 m of air is inhaled per day by an individual, the
estimated daily vinylidene chloride intake from urban/suburban areas through
inhalation is approximately 0.4 (ig. Pellizzari et al. (1979) estimated the daily
average vinylidene chloride intake through inhalation of ambient air from the
Baton Rouge, Geismar, and Plaquemine, LA, area and the Houston, Deer Park, and
Pasadena, TX, area to be 0.7 (ig and 1.6 jig, respectively. However, the daily
inhalation exposure may be as high as 0.17 mg in the downwind direction near the
immediate vicinity of source areas if a median vinylidene chloride level of 2182
ppt (see Table 7-1) is employed to calculate the exposure value.
7-6
-------
TABLE 7-2
Estimated Population Residing Near Plant Producing or
Fabricating Monomers and Polymers of Vinylidene Chloride'
Producing or process plants
Perimeter
(miles)
0-1/2
1/2-1
1-3
3-5
TOTAL
Monomer
315
1,035
17,356
70,230
88,936
Polymer
11,114
34,091
221,966
337,547
604,718
Fabrication
37,310
100,974
1,064,994
1,676,463
2,879,741
Total
48,739
136,100
1,304,316
2,084,240
3,573,395
Source: Landau and Manos, 1976
7-7
-------
7.2 WATER
7.2.1 Environmental Levels
The presence of vinylidene chloride in water samples was reported as early
as 1975. Monitoring investigations performed prior to or during 1976 have
reported the presence of vinylidene chloride in a wide range of water samples
ranging from industrial effluents to drinking waters. Some of the earlier
attempts at analysis, however, could not separate vinylidene chloride from its
isomers due to inadequate GC column selection. The presence of unseparated
vinylidene chloride and its isomers has been reported in effluents from the
textile industry, effluents from the latex industry, effluents from sewage
treatment plants, raw-surface waters, finished drinking waters, and even in well
water (Schackelford and Keith, 1976). .
The presence of vinylidene chloride alone, separated from its isomers, has
been reported four times in industrial effluents, two times in raw surface
waters, seven times in finished drinking water, and one time in well water
(Shackelford and Keith, 1976). No quantitative values for vinylidene chloride
concentrations are available from most of these earlier reports, however,
because the vinylidene chloride concentrations were very low and mass spectro-
metry was used for its identification and not for quantification. The levels of
vinylidene chloride in industrial raw wastewaters and treated wastewaters have
been determined recently (U.S. EPA, 1981) and are shown in Table 7-3 and Table
7-4. These tables also indicate the expected vinylidene chloride loading in
surface waters due to the discharge of the wastewaters into these water bodies.
According to these tables, nonferrous metals manufacturing industries are likely
to contribute to the maximum vinylidene chloride loading into the water bodies.
In a recent publication, Keith and Telliard (1979) reported the approach
used by the U.S. EPA in establishing a priority pollutant list for toxic
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chemicals. Industrial effluents were screened by GC-MS for various pollutants,
including vinylidene chloride. Among the over 2,000 samples representing 17
different industrial categories that were analyzed up until August 1978, 7.7$
qualitatively showed the presence of vinylidene chloride.
The levels of vinylidene chloride in surface waters around a few industrial
sites were determined by Going and Spigarelli (1977). The samples were analyzed
by a combination of GC-FID and GC-MS. Table 7-5 lists the concentrations of
vinylidene chloride in these water samples.
The levels of vinylidene chloride in U.S. raw surface and ground waters used
for the abstraction of drinking waters and in potable drinking waters were
monitored as part of the National Organic Monitoring Survey (NOMS) (U.S. EPA,
1977) and National Organics Reconnaissance Survey (NORS) (Coleman et al., 1976).
The results of these two surveys were combined with four other surveys conducted
for the U.S. EPA (namely, surveys by Stanford Research Institute, Office of Toxic
Substances (OTS), Annapolis Field Study and U.S. EPA Region V Survey) by Coniglio
et al. (1980) to derive from statistics the levels of volatile organics in raw
and finished waters in the U.S. None of the surface waters from the 105 cities
monitored in this survey showed any detectable level of vinylidene chloride.
Only two finished waters abstracted from surface waters from 103 cities showed
the presence of this compound at concentrations of 0.2 ^g/1 and 0.51 fxg/1. Since
the compound was not present in the raw water, it is likely that the treatment
process is the source of vinylidene chloride in these treated waters. Going and
Spigarelli (1977) also monitored the treated surface waters from Cincinnati, OH,
Philadelphia, PA, and Lawrence, MA, for vinylidene chloride. Neither the pre-
chlorinated nor the post-chlorinated treated water from any of these cities
showed any detectable level of vinylidene chloride. Recently, Pellizzari et al.
(1979) reported the mean concentration of vinylidene chloride in the drinking
water from New Orleans and Baton Rouge, LA, areas to be 0.2 |ig/l.
7-11
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TABLE 7-5
Vinylidene Chloride Concentration in a Few Waters Near Industrial Sites'
Sample
source.
Mississippi
River
Industrial
site
Dow Chemical,
Plaquemine, LA
Industrial
process
Monomer producer
Frequency
of
Q
detection
1/2
Concentration
High Low
0.2
ND
PPG Canal
Ohio River
PPG Industries
Lake Charles,
LA
W.R. Grace,
Owensboro, KY
Monomer and 1/2
methyl chloroform
producer
Polymer producer 0/2
550
ND
ND
ND
Holston River
Tittabawasse
River
Eastman,
Kingsport, TN
Dow Chemical,
Midland, MI
Modacrylic
producer
Polymer producer
and extruder
2/4
1/3
1 ND
<1 ND
aSource: Going and Spigarelli, 1977
bThe samples were collected at different points upstream and downstream from
the discharge outfall.
°The first figure indicates the number of samples that showed presence of
compound and the second figure indicates the total number of samples analyzed.
dThis plant no longer uses vinylidene chloride to produce methyl chloroform.
ND = Not Detected.
7-12
-------
A survey of raw and treated groundwaters from 13 U.S. cities was also
conducted by Coniglio et al. (1980). Raw groundwaters from two cities both
showed detectable quantities of vinylidene chloride at a level of 0.5 p.g/1.
Vinylidene chloride was detected in treated groundwater from only one city at a
concentration of 0.2 jj.g/1. Going and Spigarelli (1977) also detected 0.059 |ig/l
and 0.045 ug/1 of vinylidene chloride in pre-chlorinated and post-chlorinated
treated groundwater, respectively, from Miami, PL. Eight state agencies (e.g.,
AL, FL, KY, ME, MA, NC, SC, and TN) also monitored the levels of dichloro-
ethylenes (three uhseparated isomers) in their well water. Of the total of 781
samples tested, 23% showed detectable levels of dichloroethylenes with a maximum
level of 860 [j.g/1 (Coniglio et al., 1980). The levels of vinylidene chloride in
378 groundwater samples from urban, suburban, rural, and dump site areas in New
Jersey were monitored by Page (1981). Approximately 44$ of the groundwaters
showed detectable levels of vinylidene chloride. Although the highest concen-
tration of vinylidene chloride detected in a groundwater, probably from a dump
site (author did not specify the site), was 17.3 rag/1, the median concentration
of vinylidene chloride in all samples was below the detection limit (10 p.g/1).
The levels of vinylidene chloride in raw and treated (both ground and
surface waters) from 30 Canadian potable water treatment facilities serving
about 5.5 million consumers across Canada were monitored by Otson et al.
(1982a,b). Vinylidene chloride was not detected in any of the raw water samples,
and only one finished water sample collected during the summer months (Aug.-
Sept.) showed a mean concentration of less than 1 }ig/l and a maximum concentra-
tion of 20 p.g/1 for vinylidene chloride.
7.2.2 Exposure
It can be concluded from the discussions in Section 7.2.1 that about 356 of
the total drinking water supplies in the U.S. contain vinylidene chloride at an
7-13
-------
estimated mean concentration of 0.3 |J.g/l. Assuming that an individual consumes 2
liters of water per day, the daily exposure to vinylidene chloride for these
consumers (3% water supplies) would be approximately 0.6 jig. For the majority of
the U.S. population, the daily exposure to vinylidene chloride from the consump-
tion of drinking water would be lower than 0.01 |ig, based on a detection limit of
0.005 jig/1 as determined by Going and Spizarelli (1977). Therefore, the daily
exposure of vinylidene chloride to the general population in the U.S. from the
consumption of drinking water would be <0.01 jig, although the maximum daily
exposure in certain communities could exceed 1 jig (see Section 7.2.1).
7.3 SOIL
DeLeon et al. (1980) analyzed over 100 soil samples within and around a few
chemical waste disposal sites for 11 chlorinated hydrocarbons including vinyli-
dene chloride. The analytical methods used were GC-ECD for quantification and
GC-MS for confirmation. One of the three samples collected from a midwestern
chemical disposal site (name not mentioned) showed 21.9 Hg/g (dry weight) of
vinylidene chloride, while none was detected in the other two samples. The
detection limit of the method was given as 10 ng/g.
7.4 FOODS
Human exposure to vinylidene chloride from foods can occur in two ways:
from consumption of food contaminated by polyvinylidene wrappings, and from
consumption of edible aquatic foods that have bioconcentrated vinylidene
chloride from water. Vinylidene chloride content has been determined both in
food-packaging materials and in the foods themselves.
The results of analysis of vinylidene chloride content in saran and meat
packaging films as determined by Going and Spigarelli (1977) are shown in Table
7-6. Hollifield and McNeal (1978) analyzed five commercial food-packaging saran
films of 0.5 mil thickness and determined that the residual monomer concentration
varied between 1.6 [ig/g and 8.1 |ig/g.
-------
TABLE 7-6
Analysis of Food-Packaging Films for Vinylidene Chloride'
Concentration
Sample
Saran Wrap
Saran Wrap
Oscar Mayer Film A
Oscar Mayer Film B
Oscar Mayer Film C
41-581
4.9
ND
ND
ND
Source: Going and Spigarelli, 1977
This saran wrap, presumably produced in 1974, contained
higher amounts of vinylidene chloride.
ND = Not Detected. The detection limit was 0.005 (ig/g.
7-15
-------
The extent of migration of residual vinylidene chloride from polyvinylidene
packaging materials into foods is customarily tested with food-simulating
solvents rather than with foods themselves (Hollifield and McNeal, 1978). The
three food-simulating solvents, which represented aqueous, oily, and fatty
foods, were water, corn oil, and heptane, respectively (Hollifield and McNeal,
1978). The extent of migration of vinylidene chloride from saran films to food-
simulating solvents at 49°C is shown in Table 7-7.
It can be concluded from Table 7-7 that the migration of the residual
monomer from the 0.5 mil film was essentially complete in corn oil and heptane in
well under 24 hours. It leveled off at about 6055 in water after 24 hours.
It is difficult to estimate the extent of human exposure to vinylidene
chloride resulting from consumption of food contaminated by polyvinylidene
packaging materials. The exposure to vinylidene chloride from consuming
contaminated edible aquatic foods is equally difficult to estimate, even when the
bioaccumulation factor is available. To calculate body burden, a knowledge of
the concentration of vinylidene chloride in the water from which the aquatic
organism originated is necessary-.
7-16
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TABLE 7-7
Migration of Vinylidene Chloride from Saran Films to Heptane,
Corn Oil, and Water at 49°Ca
Film Thickness
Heptane
0.5 mil
Corn Oil
0.5 mil
Water
0.5 mil
Residue monomer
concentration Time of contact
}ig/g (hours)
8.1 0.5
1.0
2.0
2.5
8.1 1
3
6
24
48
8.1 4
24
312
696
Concentration
found in
solvent (ppb)
34
37
41
44
18
34
40
39
41
26
27
24
24
Percent of
total
extracted
76*
88%
9456
106?
41?
76?
94?
94?
94?
59?
65?
59?
59?
Source: Hollifield and McNeal, 1978
7-17
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-------
8. BIOLOGICAL EFFECTS ON PLANTS AND MICROORGANISMS
The 96-hour EC (median effective concentration) values for the freshwater
alga Selenastrum capricornutum and the marine alga Skeletonema costatum were
found to be greater than 798 or 712 mg vinylidene chloride/1, respectively (U.S.
EPA, 1978). These were the highest concentrations tested. The reported "no
effect concentration" was <80 mg/1 for Selenastrum capricornutum and 712 mg/1 for
Skeletonema costatum. The criteria for toxic effect in these bioassays were
reduction in cell number or chlorophyll a, content in algae cultures grown for 96
hours.
No studies were found in the literature searched on the biological effects
of vinylidene chloride on microorganisms.
8-1
-------
-------
9. BIOLOGICAL EFFECTS ON AQUATIC ORGANISMS
9.1 ACUTE TOXICITY
The acute toxicity of vinylidene chloride has been determined with several
species of freshwater and marine fish and invertebrates. Acute toxicity values
are presented in Table 9-1.
9.1.1 Freshwater Fish
The .96-hour LC Q (95? confidence interval) for bluegill sunfish, Lepomis
macrochirus, tested under static exposure conditions was 73.9 (56.8-90.7) mg/1
(U.S. EPA, 1978; Buccafusco et al., 1981). This value is the same as the 24-hour
LC._n (Table 9-1), indicating that all mortalities during the test occurred Within
DU . . . '.
the first day of exposure. The "no effect" concentration was 32.0 mg/1. Dawson
et al. (1977) reported a much higher 96-hour LC for bluegill sunfish (220
mg/1). The chemical used was identified as "vinylidene chlorine1! ;and presumably
was vinylidene chloride. This test was conducted under static exposure condi-
tions. Dill et al. (n.d., cited in U.S. EPA, 1979) determined the 96-hour LC5Q
for fathead minnows, Pimephales promelas, under static and flow-through exposure
conditions. The values were 169 mg/1 and 108 mg/1, respectively. The different
results indicate that the flow-through technique gave a higher estimate of the
acute toxicity of vinylidene chloride than did the static exposure technique.
9.1.2 Freshwater Invertebrates
The water flea, Daphnia magna, is the only freshwater invertebrate for which
vinylidene chloride toxicity data are available. The 24-hour and 48-hour static
LC 0 (95% confidence interval) values were 98 (71-130) and 79 (62-110) mg/1,
respectively (LeBlanc, 1980). The "no discernible effect" concentration was
<2.4 mg/1, which was the lowest concentration tested. In another study (Dill
9-1
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9-2
-------
et al., n.d., cited in. U.S. EPA, 1979), the 48-hour static EC50 (median effective
concentration) was 11.6 mg/1, which is much lower than the previously cited LC^Q
values. The difference may be due to the different toxicity endpoints measured
(effective concentration vs. lethal concentration) or some other factor(s).
9.1.3 Marine Fish
The 96-hour LC (95% confidence interval) for sheepshead minnows,
Cyprinodon variegatus, tested under static exposure conditions, was 249
(198-338) mg/1 (U.S. EPA, 1978; Heitmuller et al., 1981). As occurred with
bluegill sunfish, the 96-hour LC^Q was the same as the 24-hour LC5Q (Table 9-1).
The "no effect" concentration was 79-8 mg/1. The only other study with marine
fish was by Dawson et al. (1977), who reported a 96-hour LC50 value of 250 mg/1
for tidewater silversides, Menidia beryllina, tested under static exposure
conditions. This value is nearly identical to the 96-hour LC5Q for sheepshead
minnows.
9.1.4 Marine Invertebrates
The mysid shrimp, Mysidopsis bahia, is the only species of marine inverte-
brate that has been tested for vinylidene chloride toxicity. The 96-hour LC5Q
value (95% confidence interval) for this species was 224 (106-434) mg/1. The
LC__ value at 24, 48, and 72 hours could not be determined precisely, but was
50
greater than 798 mg/1 for each time period. The "no effect" concentration was
14.2 mg/1. The 96-hour LC value for mysid shrimp was similar to the 96-hour
LCj-0 values for sheepshead minnows and tidewater silversides.
9.2 SUBACUTE TOXICITY
The .only information regarding the subacute effects of vinylidene chloride
on aquatic organisms concerns one species of freshwater fish.
9-3
-------
Dill et al. (n.d., cited in U.S. EPA, 1979) determined the 13-day LC for
fathead minnows under flow-through conditions. This value, 29 mg/1, was
considerable lower than the equivalent 96-hour LC value (108 mg/1).
No adverse effects were observed in a fathead minnow embryo-larval test at
2.8 mg/1, which was the highest concentration tested (U.S. EPA, 1978). In this
test, fathead minnow eggs were exposed under flow-through conditions to a series
of vinylidene chloride concentrations through the hatching and early larval life
stages.
Most of the previously cited aquatic toxicity tests were conducted under
static exposure conditions. As far as can be determined, the LC5Q values
obtained from these tests were calculated on the basis of initial nominal concen-
trations, rather than actual measured concentrations.
Due to the high volatility of vinylidene chloride (Section 3), it is
probable that test organisms in static toxicity tests would be exposed to rapidly
decreasing concentrations of vinylidene chloride. This rapid loss may account
for the observations that the static LC values for bluegill sunfish and sheeps-
head minnow (U.S. EPA, 1978) did not decrease between 24 and 96 hours of exposure
and that the static 96-hour LC5Q for fathead minnows was higher than the flow-
through 96-hour LC5Q with the same species (Dill et al., cited in U.S. EPA,
1979). Although the static tests with bluegills and sheepshead minnows produced
apparent lethal thresholds by 24 hours of exposure, Dill et al. (n.d., cited in
U.S. EPA, 1979) showed that flow-through exposure with fathead minnows resulted
in sufficient additional mortality between 4 and 13 days of exposure to lower the
LCg- from 108 to 29 mg/1. Although static tests may provide some useful informa-
tion concerning the potential ecological effects of vinylidene chloride in spill
situations, the flow-through results indicate that static tests may under esti-
mate the effects of acute and chronic exposure to constant vinylidene chloride
concentrations.
9-4
-------
In summary, the reported acute LC5Q or EC50 values for four fish species and
two invertebrate species ranged between 11.6 and 250 mg/1. The acute static "no
effect" concentrations reported in U.S. EPA (1978) decreased in this order:
sheepshead minnow (79.8 mg/1) > bluegill sunfish (32.0 mg/1) > mysid shrimp
(14.2) > Daphnia magna (<2.4 mg/1, the lowest concentration tested). However,
insufficient species have been tested to definitely establish whether or not
there may be significant differences in sensitivity to vinylidene chloride
between marine and freshwater organisms, or between fish and invertebrates. Of
the species tested, the most sensitive species appears to be Daphnia magna, which
was adversely affected at 2.4 mg/1, the lowest concentration tested with that
species in the U.S. EPA (1978) study. This concentration is lower than the
concentration (2.8 mg/1) reported in the same study to cause no adverse effects
on fathead minnows in a flow-through embryo-larval test.
Additional flow-through chronic or subchronic testing with Daphnia magna
and other freshwater and marine species would be required to estimate more
accurately the range of species sensitivity and to determine the maximum accep-
table concentrations of vinylidene chloride compatible with protection of
aquatic life.
9-5
-------
-------
10. BIOLOGICAL EFFECTS IN ANIMALS AND MAN
10.1 PHARMACOKINETICS
The available data characterize the disposition and metabolism of vinyli-
dene chloride in experimental animals when administered as a single dose or
exposure. The effects of age, sex, route, species and fasting on disposition and
metabolism are also characterized. Information on the disposition and metabo-
lism of vinylidene chloride during subchronic or chronic exposure, however, is
lacking. It should be noted that throughout Section 10.1, animals can be assumed
to be fed unless fasting is specified.
10.1.1 Absorption and Distribution
Studies with experimental animals indicate that vinylidene chloride is
readily absorbed and rapidly distributed in the body. Systemic absorption after
14
intragastric administration of C-vinylidene chloride to male or female rats
appears to be rapid and fairly complete based on the rapid appearance of labeled
vinylidene chloride in the expired air (McKenna et al., 1978b; Reichert et al.,
1979) and the extensive pulmonary and urinary excretion of radioactivity (Jones
and Hathway, 19?8a; McKenna et al., 1978b; Reichert et al., 1979). Intraperi-
tbneal administration also resulted in extensive pulmonary and urinary excretion
(Jones and Hathway, 1978a).
Anderson et al. (1979a) studied the rate of uptake of vinylidene chloride
vapor by fasted male rats. Fasting (for 18 hours) has been shown to deplete the
glutathione content of the liver, and to increase the sensitivity of rats to the
toxicity of vinylidene chloride; these observations are consistent with the role
of glutathione in the detoxification of vinylidene chloride (Section
10.1.2.2.1). Uptake was determined from disappearance of vinylidene chloride
from a closed chamber as a function of time, corrected for nonspecific loss.
10-1
-------
Uptake could be resolved into a rapid and a slow phase. The rapid phase was not
affected by pretreatment of the rats with inhibitors of microsomal metabolism and
could therefore be separated from the slow phase, in which the rate was markedly
reduced by these inhibitors (the slow phase is discussed in Section 10.1.2.1).
The rapid phase was a first-order process with a rate constant of 2.2 hr~
(half-life = 0.315 hr). The rate constant did not vary significantly with
initial concentration of vinylidene chloride. The magnitude of the rapid
component was proportional to the initial concentration of vinylidene chloride
and the weight of rats in the chamber. The concentration of vinylidene chloride
in the body as a function of concentration in the chamber at equilibrium (whole
body solubility coefficient) was 0.0163 mg/kg body weight/ppm chamber,
equivalent to a body/gas distribution coefficient of 4.04. The rapid phase was
essentially complete in 60 to 80 minutes. On the basis of these characteristics,
Andersen et al. (1979a) concluded that the rapid phase represented whole body
equilibration.
Jaeger et al. (1977a) investigated the distribution of radioactivity in
various tissues 30 minutes after cessation of a 2-hour exposure of fed and fasted
14
male rats to C-vinylidene chloride. Exposure occurred in a closed chamber; the
initial concentration of vinylidene chloride was 2000 ppm. Although there was no
significant difference between fed and fasted rats in the overall rate of uptake
of vinylidene chloride, the tissues and serum of fasted rats contained more
radioactivity than those of fed rats. The highest concentration of radioactivity
was found in kidney, and the next highest in liver. Spleen contained an inter-
mediate level of radioactivity; heart and brain contained the least. In both fed
and fasted rats, most of the radioactivity in kidney was trichloroacetic acid
(TCA)-soluble. Approximately one-third of the radioactivity in liver was
TCA-precipitable, indicating that it was covalently bound to macromolecules.
Liver contained more TCA-precipitable radioactivity than did kidney.
10-2
-------
McKenna et al. (19?8a) from the Dow Chemical Company investigated the fate
of C-vinylidene chloride in fed and fasted (deprived of food for 18 hours) male
rats 72 hours after a 6-hour inhalation exposure to 10 or 200 ppm. As presented
-ill
in Table 10-1, fasted rats had lower body burdens of C than did fed rats.
Although most of the body burdens had been excreted within 72 hours, a small but
significant amount remained in the carcasses. After the 200 ppm exposure, more
radioactivity was retained in the carcasses of fasted rats than in those of fed
rats. All of the radioactivity found in urine, feces, and tissues was nonvola-
tile and therefore was considered to represent nonvolatile metabolites of
vinylidene chloride. Seventy-two hours after exposure to either 10 or 200 ppm
vinylidene chloride, concentrations of radioactivity were highest in kidney and
liver and decreased in the following order: kidney > liver > lung > skin > plasma
> fat, muscle, and remaining carcass. At both exposure levels, concentrations of
radioactivity remaining in the tissues of fasted rats were greater than those in
the tissues of fed rats when the data were normalized to account for the lower
end-exposure body burdens of fasted rats.
In similar experiments with intragastric administration of 1 or 50 mg
1 ji
C-vinylidene chloride to fed and fasted male rats, McKenna et al. (1978b) found
at 72 hours after dosing that concentrations of radioactivity were highest in
liver and next highest in kidney. Levels of radioactivity in lung were, not as
high as noted in the inhalation experiment previously described (McKenna et al.,
1978a). Jones and Hathway (1978a) reported that whole animal autoradiography of
14
young male rats after intragastric administration of C-vinylidene chloride
14
revealed high concentrations of C in the kidneys and liver 30 minutes after
dosing, followed at 1 hour by a more general distribution of radioactivity
throughout the soft tissues. According to the authors, liver and kidney retained
radioactivity longer than did other tissues.
10-3
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10.1.2 Metabolism
The metabolism of vinylidene chloride by experimental animals has been
extensively studied. A metabolic scheme that integrates the data from several
laboratories is presented in Figure 10-1. In this scheme, vinylidene chloride is
metabolized to the following reactive intermediates: 1,1-dichloroethylene oxide,
chloroacetyl chloride, and monochloroacetic acid. These reactive intermediates
are detoxified by conjugation with glutathione (GSH), ultimately leading to the
formation of mercapturic acids (derivatives of N-acetyl cysteine) or degradation
to various thioglycolic acids. A minor pathway for detoxification of monochloro-
acetic acid involves further, oxidation to C0?. 1,1-Dichloroethylene oxide,
chloroacetyl chloride, and monochloroacetic acid can react with (i.e., alkylate)
cellular macromolecules; this type of reaction could be involved in the produc-
tion of toxic effects.
From an analysis of the literature on the metabolism of chlorinated
ethylenes, Loew et al. (1983) have concluded that the extent of metabolism of
these compounds generally decreases with increasing degree of chlorine substitu-
tion. Thus the extent of metabolism appears to be: vinyl chloride = vinylidene
chloride > trans or cis-dichloroethylene > trichloroethylene, > tetrachloro-
ethylene. These conclusions were drawn from a comparison of the results of a
number of oral and inhalation studies, taking into account species and dose
differences.
10.1.2.1 Metabolism to Reactive Intermediates
Vinylidene chloride is thought to be metabolized by the microsomal mixed-
function oxidase system to an epoxide (oxirane), 1,1-dichloroethylene oxide
(Bonse and Henschler, 1976; Liebman and Ortiz, 1977; McKenna et al., 1977).
According to Bonse and Henschler (1976), 1,1-dichloroethylene oxide is extremely
unstable and could not be isolated during attempts at chemical synthesis,.
10-5
-------
H3C-S-CH2-CO-NH-CH2-CH2-OH
Bethylth1o-acatylami noethanol
T
+Met
C1-CH2CO-NH-CH2-CH2-OH
t
Cl-CH2-CO-NH-CH2-CH20-phosphat1dy1
phosphatldyl-
ethanolamlne
react with-
H2C=CC12 -
vinyl1d1ne
chloride
BacromoleculesV -». ^
H2C CCL2
I,l-d1chloroethylene
oxide
+GSH
Gly-CO-CH-CH2-S-CH2-CO-Cl
1
lu
S-glutath1onyl acetyl chloride
" -Gly, -Glu
N-acetylat1on
R'-OC-CH-CH2-S-CH2-CO-R
CO-CH3
chloroacetyl
v Jf chloride
H2C CC12
OH OH *S +GSH
Gly-CO-CH-CH2-S-CH2-COOH
NH
Glu
S-(carboxymethy1)glutathlone
* -Gly, -Glu
HOOC-CH-CH2-S-CH2-COOH
NH2
S-(carboxymethy1)cvste1ne
N-acetyl -S-cyste1 nyl
acetyl derivative
-Gly
-Glu
HOOC-CH-CH2-S-CH2-COOH
OH i
N-acetylat1on
HOOC-CH-CH2-S-CH2-COOH
NH
CO-CH3
K-acetyl-S-(carboxvinethv1)
cystelne
HOOC-CH2-S-CH2-COOH
th1od1g1yco!1c acid
I p-th1onase
HS-CH2-COOH
rth1olygol1c add
+glyco!1c/ 4,
ado/ HOOC-CH2-S-S-CH2-COOH
d1th1oglyco11c add
C1-CH2-COOH
monochloroacetlc
acTd
HO-CH2-COOH
glycollc acid
.p
HOOC-COOH
oxalic add
I
C02
I
NH2-CO-NH2
urea
HO-CH2-CO-S-CO-COOH
thioglycolyloxallc add
Figure 10-1. Metabolic Pathways for VJnylldene Chloride. Identified metabolites are under-
lined. Identification was usually by gas chromatography-mass spectrometry.
R1 1s considered to be OH; R 1s unknown. (Adapted from Jones and Hathway,
1978a, 1978b; Relchert et al., 1979; Lelbman and Ortiz, 1977).
10-6
-------
although its expected rearrangement product, chloroacetyl chloride, was formed
after chemical oxidation of vinylidene chloride with m-chloroperbenzoic acid.
Metabolism of vinylidene chloride to this epoxide has not been directly demon-
strated, but rather is inferred by analogy with the metabolism of other chlori-
nated ethylenes (Leibman and Ortiz, 1977; Bonse and Henschler, 1976; Uehleke et
al., 1976) and from the observed metabolism of vinylidene chloride to monochloro-
acetic acid.
The metabolism of vinylidene chloride by hepatic cytochrome P-450 in micro-
somes from male Long-Evans rats was studied in vitro by Costa and Ivanetich
(1982) in an attempt to identify metabolites and detoxification pathways.
Vinylidene chloride was shown to be metabolized to dichloroacetaldehyde and to
monochloroacetic acid by hepatic microsomes, after binding to cytochrome P-450
in the presence of an NADPH-generating system. Certain forms of cytochrome P-450
•*> . * ' '."'•-'
(such as the -phenobarbital-inducible form) appear to play minor roles in the
metabolism of vinylidene chloride, while other forms may be more efficient.
Radioactively-labeled monochloroacetic acid has been identified in the
1 ij
urine of rats after intragastric administration in corn oil of C-vinylidene
14
chloride (Jones and Hathway, 1978a), in rat livers perfused with C-vinylidene
14
chloride (Reichert and Bashti, 1976), and after incubation of C-vinylidene
chloride with 9000 x g supernatants from rat liver homogenates (Leibman and
Ortiz, 1977). Monochloroacetic acid is the expected product of rearrangement of
the epoxide to chloroacetyl chloride and subsequent hydrolysis (Bonse and
Henschler, 1976; Leibman and Ortiz, 1977). Alternatively, monochloroacetic acid
could result from metabolism of the epoxide by epoxide hydrase to the diol shown
in Figure 10-1, followed by rearrangement to chloroacetyl chloride and
hydrolysis to monochloroacetic acid (Leibman and Ortiz, 1977).
10-7
-------
The relative importance -of the diol pathway is difficult to assess. Jones
and Hathway (1978b) suggested that conversion to the diol is not important
because C02, a possible degradation product, is found only in small amounts in
vivo. It is not known, however, whether the diol is metabolized to C02 to a
significant extent. Leibman and Ortiz (1977) concluded that diol formation is.
relatively unimportant in the metabolism of vinylidene chloride to monochloro-
acetic acid because 1,1,1-trichloropropene-2,3-oxide and cyclohexene oxide
(inhibitors of epoxide hydrase) stimulated, rather than inhibited, the formation
of monochloroacetic acid in incubations of vinylidene chloride with 9000 x g
supernatants from rat liver homogenates. These two inhibitors react with GSH
(Oesch and Daly, 1972). Thus the results of Leibman and Ortiz (1977) could be
explained by the depletion of GSH, thereby resulting in the accumulation of
monochloroacetic acid. Furthermore, according to Oesch (1972), there are two
types of epoxide hydrase activity—one is tightly coupled with mixed-function
oxidase activity, whereas the other is not. The coupled form is thought to be
more important in detoxifying epoxides formed by mixed function oxidases and is
relatively resistant to inhibitors (Oesch, 1972).
Andersen et al. (1979a) investigated the metabolism of vinylidene chloride
by studying the rate of uptake of vinylidene chloride vapor by fasted male rats.
Uptake was determined from the disappearance of vinylidene chloride as a function
of time (usually plotted on linear coordinates) from a closed chamber, corrected
for nonspecific loss. The uptake of vinylidene chloride by fasted male rats was
biphasic; the initial rapid phase represented tissue equilibration (Section
10.1.1) and the slow phase represented metabolism. The slow phase of uptake was
relatively independent of concentration at higher exposure levels and dependent
on concentration at lower exposures. A series of uptake experiments using
different initial concentrations of vinylidene chloride were performed. The
10-8
-------
instantaneous rates of uptake were determined from tangents to the curves at 60
to 80 minutes of exposure, so that the contribution from the rapid phase was
negligible. Instantaneous rates plotted against actual chamber concentrations
yielded a rectangular hyperbola typical of Michaelis-Menten kinetics, as would
be expected if the slow phase represented metabolism. Vfflax, the maximum velocity
at saturating exposure levels, was 132 ppm/kg/hr (equivalent to 15.8? mg of
vinylidene chloride metabolized/kg/hr). Kffi, the exposure level that produced
half the maximum velocity, was 335 ppm (equivalent to a body burden of 5.43
mg/kg).
At an initial concentration of vinylidene chloride of 300 ppm in air (below
the K ), the rate constant of the slow phase was reduced 84, 92, and 65% by
m
pretreatment with pyrazole, carbon tetrachloride, and aminotriazole, respec-
tively, but was unaffected by pretreatment with SKF 525A or 2,3-epoxy-
propan-1-ol. These compounds, with the exception of 2,3-epoxypropan-1-ol, are
inhibitors of microsomal metabolism; all have been shown to affect the acute
toxicity of vinylidene chloride (Section 10.2) (Andersen et al., 1980). At high
initial concentrations of vinylidene chloride, the Vm_v was unaffected by
IQclX
pretreatment with phenobarbital or by using fed rather than fasted rats, and was
similar for immature and mature rats (Andersen et al., 1979a).
As determined by Andersen et al. (1979b), the acute toxicity of inhaled
vinylidene chloride was relatively independent of concentration but dependent on
duration of exposure at concentrations above 200 ppm (Section 10.2). In an
attempt to correlate metabolism with toxicity, Andersen et al. (1979a) calcu-
lated the two theoretical curves shown in Figure 10-2. The solid line is based
on the assumption that the product of exposure concentration times the duration
of exposure required to produce a given effect is constant. The dashed line is
based on the assumption that the product of the rate of metabolism (at each
10-9
-------
4—
3—
1
o
5
o
1—
LT50(95%C.I.)
ppm X time = k
1000
2000
CONCENTRATION, ppm
Figure 10-2. Comparisons of observed LT50 data for vinylidene chloride
with theoretical curves predicted for two different mechanisms of toxicity.
As indicated by the symbol in upper right, data are given as LT50 and its
95% confidence interval.
Source: Andersen (1979a).
10-10
-------
exposure concentration) times the duration of exposure required to produce a
given effect is constant. The experimentally determined LT (time required to
produce 50% mortality rate) of 4.1 hours at a 200 ppm exposure concentration was
used to calculate the constant. The experimentally determined LT Q values
(Andersen et al., 1979b) fit the theoretical curve based on metabolism more
closely than they fit the theoretical curve based on exposure concentration,
suggesting that toxicity is a function of the amount of metabolite formed rather
than the concentration of vinylidene chloride (Andersen et al., 1979a).
Using an experimental protocol similar to that of Andersen et al. (1979a),
Filser and Bolt (1979) investigated the kinetics of metabolism of vinylidene
chloride in the male rat. Filser and Bolt (1979) focused on strict zero-order
and first-order kinetics, whereas Andersen et al. (1979a) focused on
Michaelis-Menten kinetics. Both groups of investigators, however, demonstrated
the saturable dose-dependent nature of vinylidene chloride metabolism. As
determined by Filser and Bolt (1979), the V (velocity for zero-order metabo-
luciX
lism) was 100 }imol/kg/hr (9-7 mg/kg/hr).
Reichert and Henschler (1978) reported that pretreatment of female rats
with an inducer of mixed-function oxidases, DDT, increased the uptake of vinyli-
dene chloride 35?, while direct addition of inhibitors (pyrazole and ethanol) of
mixed-function oxidases decreased the uptake of vinylidene chloride 35 to 40? in
isolated, perfused rat livers. Pretreatment with phenobarbital, or direct
addition of SKF 525A, 6-nitro-1,2,3-benzothiadiazole, and 5,6-dimethyl-1,2,3-
benzothiadiazole to the perfusate had little effect on uptake when low concentra-
tions of vinylidene chloride were used. The uptake of vinylidene chloride,
measured as the difference between prehepatic and posthepatic concentrations of
vinylidene chloride under steady state conditions, was taken to be equivalent to
metabolism. The authors stated that with a high concentration of vinylidene
10-11
-------
chloride in the perfusate, pretreatment with phenobarbital elevated the uptake
of vinylidene chloride by approximately 30%. The results of Reiohert and
Henschler (1978) for perfused livers of female rats are in general agreement with
the results of Andersen et al. (1979a) for intact fasted male rats except for the
stimulation of uptake (metabolism) by phenobarbital pretreatment noted by
Reichert and Henschler (1978). Pretreatment with ethanol for a 3-week period
enhanced the activity of rat liver drug-metabolizing enzymes six-fold in their
ability to convert vinylidene chloride (Sato et al.', 1980). The authors
discussed the increased rate of vinylidene chloride metabolism and noted that
this may increase the toxicity of the compound if metabolites are the actual
causative agents.
A comparison of sex, age, and species differences in metabolism and toxicity
suggests that vinylidene chloride is metabolized to a toxic intermediate by
mixed-function oxidases. In general, microsomal oxidation of compounds was
found to be greater in male rats than in female rats (Kato, 1974). Male rats were
much more susceptible to the hepatotoxic effects of vinylidene chloride than were
female rats (Andersen and Jenkins, 1977). Microsomal oxidase activity reached a
maximum in the rat at 30 to 40 days of age (Kato et al.,, 1964), an age range which
corresponded to the size (100-150 g) of rats most susceptible to the toxicity of
vinylidene chloride in the report of Andersen and Jenkins (1977). All of the
studies reviewed in Section 10.1 of this report, however,' were performed on
mature (180-350 g) rats and mature mice unless otherwise specified. ,.
A greater percentage of an orally administered dose (50 mg/kg) of 14C-
vinylidene chloride was metabolized by mice than by rats, based on quantitation
of excreted radiolabeled metabolites and unchanged vinylidene chloride (Jones
and Hathway, 1978b). Similarly, as presented in Table 10-2, mice metabolized
more vinylidene chloride per kg body weight than did rats after inhaling 10 ppm
10-12
-------
TABLE 10-2
End-Exposure Body Burdens and Disposition of C-Activity in
Rats and Mice 72 Hours Following Inhalation Exposure to
10 ppm C-Vinylidene Chloride for 6 Hours3
mg-Eq C-vinylidene ohloride/kgc
Percentage body burden
Rats'
Body burden, mg-Eq C-vinylidene
chloride/kg
Total metabolized vinylidene chloride
5.30 + 0.75
5.27 + 0.74
2.89
2.84
+ 0.24
+ 0.26
Expired vinylidene chloride
Expired 14C02
Urine
Feces
Carcass
Cage Wash
0.65 ± 0.07
4.64 ± 0.17
80.83 ± 1.68
6.58 + 0.81
5.46 + 0.41
1.83 ± 0.84
1.63 + 0.14
8.74 + 3.72
74.72 + 2.30
9.73 ± 0.10
4.75 + 0.78
0.44 ± 0.28
Source: McKenna et al., 1977
bX ± SE, n = 4.
C 1 li
Calculated from the total C-activity recovered (end-exposure body burden)
minus the C-vinylidene chloride exhaled from each rat
Mice were males of the Ha(ICR) strain.
"Rats were males of the Sprague-Dawley strain.
10-13
-------
1 C-vinylidene chloride in air for 6 hours (McKenna et al., 1977). The overall
pattern of excretion for mice and rats was similar. The concentration of
covalently-bound radioactivity in liver and kidney was much higher in mice than
in rats, as shown in Table 10-3. Binding was measured as radioactivity that was
TCA-precipitable and 80% methanol-insoluble and thus represented radioactivity
covalently bound to protein and nucleic acid. As discussed in Section 10.4.1,
the 9000 x g supernatant from mouse liver was more active than the 9000 x g
supernatant from rat liver in metabolizing vinylidene chloride to mutagenic
substances. These observations of increased metabolism and covalent binding in
mice versus rats parallel the greater sensitivity of mice to the acute lethality,
hepatotoxicity, and renal toxicity of vinylidene chloride (Short et al.,
1977a,b). A brief review of the metabolism of vinylidene chloride by rats and
mice is presented by Cooper (1980).
Hypoxia (1% oxygen), which inhibits mixed-function oxidase activity,
decreased the hepatotoxicity of inhaled vinylidene chloride to fasted male rats
(Jaeger, 1978). Disulfuram, which has been reported to inhibit hepatic mixed-
function oxidases (Zemaitis and Green, 1976), protected male mice from the acute
lethal and hepatotoxic effects of inhaled vinylidene chloride (Short et al.,
1977a,b). Measured at 4 and 24 hours after intraperitoneal (i.p.) administration
14
of C-vinylidene chloride, covalent binding of radioactivity to protein in
liver and kidney was significantly reduced in mice fed disulfuram before and
during exposure (Short et al., 1977a,b). Additional studies dealing with the
relationship between the induction and inhibition of microsomal mixed function
oxidases and the toxicity of vinylidene chloride are discussed in Section 10.2.
The identification of methylthio-acetylaminoethanol as a urinary metabolite
of vinylidene chloride suggested the alkylation of lipids by a reactive inter-
mediate (Reichert et al., 1979; Henschler and Hoos, 1981). The pathway of
10-14
-------
TABLE 10-3
Covalently Bound C-Activity in Tissues 72 Hours
Following Inhalation Exposure to 10 ppm
14 a
, C-Vinylidene Chloride for 6 Hours
C-vinylidene chloride, jig-Eq/g protein
(X + SE, n = 4)
Liver
Kidney
Mice
Rats
22.29 + 3.77
5.28 + 0.14
79.55 ± 19.11
13.14 + 1.15
Source: McKenna et al., 1977
10-15
-------
formation of methylthio-acetylaminoethanol has not yet been clarified. Reichert
et al. (1979) hypothesized that the first step could be the reaction of
chloroacetyl chloride with phosphatidyl ethanolaraine (a constituent of lipid
membranes). This postulated pathway is illustrated in Figure 10-1.
10.1.2.2 Detoxification Pathways
10.1.2.2.1 Conjugation with Glutathione
Conjugation of vinylidene chloride or its metabolites with glutathione is
indicated because administration of C-vinylidene chloride (intragastrically or
by inhalation) to rats and mice produced several S-containing radioactive meta-
bolites. The major urinary metabolites of vinylidene chloride in rats have been
identified as thiodiglycolic acid (thiodiacetic acid) (Jones and Hathway,
19?8a,b; Reichert et al., 1979; McKenna et al., 1977, 1978a,b) as well as the
following mercapturic acids: an N-acetyl-S-cysteinyl acetyl derivative shown in
Figure 10-1 (Jones and Hathway, 1978a,b), N-acetyl-S-(carboxymethyl)cysteine
(Reiohert et al., 1979), and N-acetyl-S-(2-hydroxyethyl)cysteine (McKenna et
al., 1977, 1978a,b). N-acetyl-S-(2-hydroxyethyl)cysteine is not shown as part
of the metabolic scheme in Figure 10-1 because its relationship to other
metabolites of vinylidene chloride is unclear. The major urinary metabolites of
vinylidene chloride in mice were dithioglycolic acid and an N-acetyl-S-cysteinyl
acetyl derivative shown in Figure 10-1 (Jones and Hathway, 1978b).
Vinylidene chloride itself does not appear to react with glutathione.
McKenna et al. (1977) stated that they were unable to demonstrate conjugation of
vinylidene chloride with GSH either nonenzymatically or in the presence of the
soluble fraction (which contains glutathione S-transferases) of a rat liver
homogenate. Conjugation with GSH required the presence of a microsomal enzyme
system, suggesting that vinylidene chloride was metabolized to a reactive
intermediate before conjugation with glutathione. Unfortunately, no data or
experimental details were presented.
10-16
-------
Additional evidence that the S-containing metabolites (mercapturic and
thioglycolic acids) of vinylidene chloride arise from conjugation with GSH is as
follows. The origin of the cysteine moiety in mercapturic acid derivatives of
many xenobiotics has been shown to be GSH (Chasseaud, 1973). In vivo experiments
with unlabeled vinylidene chloride, in which the cysteine-cystine pools were
14
labeled with C, resulted in the production of labeled thiodiglycolic acid
(Jones and Hathway, 1978a). Thus, at least part of the carbon skeleton of
thiodiglycolic acid must have been derived from cysteine.
Administration of vinylidene chloride to male or female rats In vivo, or
during perfusion of isolated rat livers, depleted the liver glutathione content
(Jaeger et al., 1974; Reichert et al., 1978; McKenna et al., 1977; McKenna,
1979). Depletion of GSH was maximal at about 4 hours after oral administration
of vinylidene chloride to female rats and was dependent on the dose administered
(Reichert et al., 1978). Depletion of glutathione after inhalation exposure of
male rats was similarly dose-dependent (McKenna et al., 1977; McKenna, 1979).
Reichert et al. (1978) attempted to demonstrate a correlation between the
GSH content of isolated, perfused livers from female rats and the rate of
metabolism of vinylidene chloride measured as uptake (see Section 10.1.2.1,
Reichert and Henschler, 1978). When the GSH content was decreased 80% by the
prior addition of diethyl maleate to the perfusate, an 1Q% decrease in vinylidene
chloride metabolism was measured. A less pronounced decrease in GSH content,
produced by prior fasting of the rats, was not associated with a decrease in
vinylidene chloride metabolism; a slight increase (10?) was observed, although
neither change in metabolism was statistically significant. The authors
concluded that the GSH content of liver becomes a limiting factor in the
metabolism of vinylidene chloride only when the GSH content has been severely
depleted.
10-17
-------
Evidence for the metabolic pathways shown in Figure 10-1 that involve
conjugation with GSH has been obtained from the analysis of the urinary
1li
metabolites resulting from the administration of C-labeled vinylidene
chloride, monochloroacetic acid, and other metabolic intermediates to rats and
mice. As shown in Table 10-4, the N-acetyl-S-cysteinyl acetyl derivative was
detected only when rats were given C-vinylidene chloride and not when they were
ill
given C-monochloroacetic acid. The N-acetyl-S-cysteinyl acetyl derivative
must therefore have come from conjugation of GSH with a metabolite arising prior
to the formation of monochloroacetic acid (Jones and Hathway, 1978a).
ill 14
The administration of either C-vinylidene chloride or C-raonochloroacetic
acid gave rise to C-labeled S-(carboxymethyl)cysteine, N-acetyl-S-(carboxy
methyl)cysteine, thiodiglycolic acid, thioglycolic acid, and dithioglycolic acid
(Tables 10-4 and 10-5, Hathway, 1977; Jones and Hathway, 1978a). These results
suggest that monochloroacetic acid is a key intermediate in the metabolism of
vinylidene chloride and the S-(carboxymethyl)glutathione can be metabolized to
thioglycolic acids or to a mercapturic acid.
S-(Carboxymethyl)cysteine was metabolized to thiodiglycolic acid and to C02
(Green and Hathway, 1977; Yllner, 1971; Jones and Hathway, 1978b). Because
labeled C0p was detected only when the cysteine moiety of S-(oarboxymethyl)-
cysteine was uniformly labeled with C (Jones and Hathway, 1978b) but not when
the carboxymethyl moiety was labeled (Yllner, 1971), C02 must have been produced
from the decarboxylation of cysteine. C-Thiodiglycolic acid was converted to
thioglycolic acid, dithioglycolic acid, and thioglycolyloxalic acid, indicating
that these metabolites arise from 3-thionase hydrolysis of thiodiglycolic acid
(Jones and Hathway, 1978b), shown in Figure 10-1. As can be seen from the
relative proportions of thioglycolic acids in Table 10-5, 3-thionase conversion
occurred to a greater extent in mice than in rats (Jones and Hathway, 1978b).
10-18
-------
TABLE 10-4
14
Relative Proportions of C Urinary Metabolites After Intragastric
in
Administration of 350 mg/kg 1- C-Vinylidene Chloride or 50 mg/kg
•til a
C-Monochloroacetic Acid to Male Rats
Vinylidene Chloride and
Chloroacetic Acid Metabolites
Thiodiglycolic acid
N-acetyl-S-cysteinyl-acetyl
derivative
Dithioglycolic acid
Thioglycolic acid
Chloroacetic acid
Urea
S- ( Carboxymethyl ) cysteine
N-acetyl-S- ( carboxymethyl ) cysteine
% of Urinary
Vinylidene
Chloride
37.0
48.0
5.0
3.0
3.0
0.5
0
—
Radioactivity
Chloroacetic
Acid
90.0
0
3.0
3.0
0
0.5
2.0
2.0*
Source: Hathway, 1977*5 Jones and Hathway, 1978a
10-19
-------
TABLE 10-5
Relative Proportions of C-Excretory Products After Intragastric
14
Administration of 50 mg/kg of 1- -C-Vinylidene Chloride to
Male Rats or Mice&
14
C Excretory Products
Unchanged vinylidene chloride
(pulmonary excretion)
Carbon dioxide (pulmonary
excretion)
Chloroacetic acid
Thiodiglycolic acid
Thioglycolic acid
Dithioglycolic acid
Thioglycolyloxalic acid
N-Acetyl-S-cysteinyl acetyl
(derivative)
N-Ace tyl-S- ( 2-carboxymethyl )
cysteine
Urea
14
C Expressed
Mice
6
3
0
,3
5
23
3
50
4
3
as Percent of Dose
Rats '
28
3.5
1
22
3
5
2
28
0
3.5
Source: Jones and Hathway, 19?8b
10-20
-------
Results of experiments with rats suggest that conjugation with glutathione
serves to detoxify reactive metabolites of vinylidene chloride. The hepato-
toxicity of vinylidene chloride in vivo and in the isolated perfused liver was
greater if vinylidene chloride was administered when GSH levels in the liver had
been diminished by fasting (Jaeger et al., 1974, 1975a; McKenna et al., 1978a),
diurnal variation (Jaeger et al., 1973a, 1975a), by pretreatment with diethyl
maleate (Jaeger et al., 1974, 1975a; Andersen et al., 1980), or by pretreatment
with thyroxine (Jaeger et al., 1977b). The degree to which pretreatment with
various epoxides or diethyl maleate exacerbated the acute toxicity of vinylidene
chloride was related to the degree to which these compounds depleted GSH
(Andersen et al., 1980). Increasing the levels of GSH in the liver by chemical
or surgical thyroidectomy protected against the toxicity of vinylidene chloride
(Jaeger et al., 1977b). Hypoxia, which inhibited mixed-function oxidase
activity, protected against the hepatotoxicity of vinylidene chloride and
concomitantly prevented depletion of liver GSH (Jaeger, 1978).
Additional evidence for the role of GSH in detoxification can be obtained
from studies of covalent binding. Fasting and, hence, a low level of liver GSH
14
were associated with decreased total metabolism of C-vinylidene chloride,
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centrilobular hepatic necrosis in male rats (McKenna et al., 1978a,b). Data for
intragastric and inhalation administration are shown in Tables 10-6 and 10-7,
respectively. Binding was measured 72 hours after exposure, as radioactivity
that was TCA-precipitable and 80% methanol-insoluble, and thus represents
radioactivity covalently bound to protein and nucleic acid. At the higher
exposure levels, fasted male rats had significantly greater concentrations of
bound radioactivity in their livers when the data were normalized to account for
differences in metabolism.
10-21
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-------
Jaeger et al. (1977a) studied the subcellular distribution of free and bound
1U
radioactivity in livers from fed and fasted male rats exposed to C-vinylidene
chloride. The analyses were performed 30 minutes after the cessation of a 2-hour
inhalation exposure to vinylidene chloride (initial concentration, 2000 ppm) in
a closed chamber. Significantly more radioactivity was found in all subcellular
fractions from fasted animals than was found in those from fed animals. In
livers from both fed and fasted rats, the radioactivity in the mitochondrial and
microsomal fractions was largely TCA-precipitable; radioactivity in the cyto-
plasmic fractions was largely TCA-soluble. Because substantial amounts of the
TCA-precipitable radioactivity of mitochondria and microsomes were soluble in
chloroform, the authors suggested that binding to lipid had occurred. As
discussed in Section 10.1.2.1, methylthio-acetylaminoethanol, a metabolite of
vinylidene chloride, is though to be a product of the alkylation of lipids by a
reactive intermediate of vinylidene chloride (Reichert et al., 1979; Henschler
and Hoos, 1981). The amounts (per mg protein) of radioactivity presumably
covalently bound to protein and nucleic acid (TCA-precipitable, chloroform-
insoluble material) and to lipids (TCA-precipitable, chloroform-soluble
material) were greater in mitochondrial and microsomal fractions from fasted
rats than in the corresponding fractions from fed rats. Similarly, fasted rats
had greater amounts (per mg protein) of radioactivity bound to protein and
nucleic acid of the cytoplasmic fraction than did fed rats.
The relationship among GSH depletion, total metabolism, and covalent
binding to macromolecules is not clear, as shown in Figure 10-3. Immediately
after a 6-hour inhalation exposure to C-vinylidene chloride, male rats were
sacrificed and hepatic GSH and covalent binding of radioactivity to protein and
nucleic acids were measured. Apparently, the total amount of vinylidene chloride
metabolized was measured, as indicated in the legend to Table 10-7. GSH
10-24
-------
100
<
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EXPOSURE CONCENTRATION, ppm
Figure 10-3. Dose-response relationship for hepatic glutathione (GSH)
levels, total metabolism of 14C-vinylidene chloride (VDC) (top), and
covalent binding of radioactivity to hepatic macromolecules (bottom).
Sources: Top: McKenna etal. (1977);
Bottom: McKenna etal. (1977), replotted by Dedrick (1979).
10-25
-------
depletion and metabolism of vinylidene chloride displayed a similar, non-linear,
dose dependence, whereas oovalent binding increased- linearly with increased
exposure concentrations (McKenna et al., 1977; Dedrick, 1979; McKenna, 1979).
Suggestive evidence for an enhancement of hepatic lipid peroxidation in
vitro after vinylidene chloride administration in vivo has been obtained in rats
under conditions designed to overwhelm the. GSH-conjugating capacity of the
liver: i.e., the rats were pretreated with phenobarbital to induce mixed-
function oxidases and were then treated with a very high dose of vinylidene
chloride (500 mg/kg) (Siegers et al., 1982). This dose is higher than those used
by other investigators to produce hepatic damage in noninduced rats (Section
10.2.1). In general, however, the hepatotoxic effects of vinylidene chloride are
not thought to be due to a lipoperoxidative mechanism of action (Section 10.2.1).
10.1.2.2.2 Minor Oxidative Pathway for Monochloroacetic Acid
14
Yllner (1971) demonstrated the oxidative degradation of C-monochloro-
acetic acid to glycolic acid, oxalic acid, and C02 by mice after i.p.
administration. S-(Carboxymethyl-1,2- Ocysteine was riot metabolized to
appreciable amounts of labeled C02 and hence is not an intermediate in the
metabolism of monochloroacetic acid to CC>2 (Yllner, 1971). Trace amounts of
labeled oxalic acid have been detected in experiments with C-monochloroacetic
acid in rats (Jones and Hathway, 1978a). Small amounts of labeled C02 and urea
were identified as metabolites of 1 C-vinylidene chloride, (see Table 10-5)
(Jones and Hathway, 1978b). Thus it appears that the metabolism of monochloro-
acetic acid to C02 is a minor pathway in the metabolism of vinylidene chloride.
10.1.3 Excretion
Vinylidene chloride and its metabolites are excreted fairly rapidly by
experimental animals. The influence of route of administration and size of dose
on the pattern of excretion of vinylidene chloride and its metabolites by male
10-26
-------
rats is shown in Table 10-8 (Jones and Hathway, 1978a). According to Jones and
Hathway (1978a), 60% of the 0.5 mg/kg intravenous dose of C-vinylidene chloride
was expired unchanged within 5 minutes of injection; 80% was expired unchanged
within 1 hour. These results indicated an effieient'^arterial-alveolar transfer
of vinylidene chloride. With ihtragastrie or intraperitoneal administration of
0.5 mg/kg of C-vinylidene chloride, most of the radioactivity was excreted in
the urine within the first 24 hours, whereas with 350 mg/kg, most of the radio-
activity was expired as unchanged vinylidene chloride. The percentage of radio-
activity expired as COp decreased with the higher dose of vinylidene chloride.
These changes in the pattern of excretion were attributed by Jones and Hathway
(1978a) to saturable drug metabolism and to the efficient transfer of vinylidene
chloride from systemic blood to the alveoli, leaving a relatively low concentra-
tion of vinylidene chloride available for metabolism in subsequent passes
through the liver.
Similar dose-related shifts in the relative proportion of radioactivity
excreted by various routes have been reported by Reichert et al. (1979) for
14
intragastric administration of C-vinylidene chloride (0.5, 5.0, and 50 mg/kg)
to female rats and by McKenna et al. (1978b) for intragastric administration of 1
14
and 50 mg/kg C-vinylidene chloride to fed and fasted male rats. Fed and fasted
14
male rats that inhaled 200 ppm C-vinylidene chloride exhaled a greater percen-
tage of their body burden as unchanged vinylidene chloride than did rats exposed
to 10 ppm, but this was the only significant dose-related change in excretion
(see Table 10-1) (McKenna et al., 1978a). After intragastric administration of
14
50 mg/kg C-vinylidene chloride, fasted male rats exhaled a greater percentage
of the dose as unchanged vinylidene chloride and a lesser percentage in the urine
than did fed male rats (McKenna et al., 1978b). No such difference was apparent
with a dose of 1 mg/kg. These results indicate a reduced capacity for metabolism
10-27
-------
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of vinylidene chloride in fasted animals. Fed/fasted and species differences in
excretion that have already been noted in Section 10.1.2 will not be discussed
here.
Following intragastric administration of 350 mg/kg C-vinylidene chloride,
urinary excretion of radioactivity in intact male rats was approximately equal to
the sum of the separate urinary and biliary excretions in male rats with biliary
fistulae (Jones and Hathway, 19?8a). This finding suggests that the origin of
part of the urinary radioactivity was via the enterohepatic cycle.
Reported half lives of excretion for different nutritional states (fed
versus fasted) and dose levels are compiled in Table 10-9. The only difference
between fed and fasted rats was that fed rats excreted urinary metabolites more
rapidly during the first 48 hours after administration of 200 ppm than did fasted
rats (McKenna et al., 1978b). Changes in half-lives with increasing doses are
inconsistent. It is not known whether the inconsistencies could be due to normal
experimental variation, to an effect on more than one process, or to possible
toxic effects.
10.1.4. Summary of Pharmacokinetics. Vinylidene chloride is readily absorbed
by mammals following oral or inhalation exposure. Judging from excretion in the
exhaled air and urine, most of an orally administered dose is absorbed through
the gastrointestinal tract. Data for retention (as a percent of the inhaled
concentration) during inhalation exposure were not encountered. Vinylidene
chloride is metabolized in the liver with a number of possible reactive inter-
mediates, including an epoxide, being formed. These reactive intermediates may
react with macromolecules, producing toxic effects, and are detoxified primarily
by conjugation with GSH. Excretion of metabolites and parent compound occurs
primarily via the urine and the exhaled air, with greater percentages of the dose
being exhaled as unchanged vinylidene chloride at high doses/exposures.
Vinylidene chloride does not appear to be stored or accumulated in the tissues.
10-29
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10.2 ACUTE, SUBACUTE, AND CHRONIC TOXICITY
10.2.1 Acute Exposure
As a class, the halogenated olefins and the chloroethylenes in particular
show many similarities in their biologic effects. Anesthesia, hepatotoxicity,
and nephrotoxicity are commonly measured indices of acute exposure in experi-
mental animals, although considerable differences exist in relative potency.
Factors that influence the toxicity of chloroethylenes include inherent chemical
reactivity, species, sex, diet, and exposure to exogenous chemicals that modify
drug-metabolizing enzyme activity. With the chloroethylenes (e.g., vinylidene
chloride, trichloroethylene, vinyl chloride, perchloroethylene), toxic effects
appear to be mediated by the metabolic formation of a critical intermediate,
which is probably an epoxide (Andersen and Jenkins, 1977; Andersen et al., 1979b;
Reynolds and Moslen, 1977; Jaeger, 1977).
Carpenter and coworkers (1949) published the first report on the toxicity of
vinylidene chloride. They indicated that a single 4-hour inhalation exposure to
32,000 ppm was lethal to two, three, or four rats out of a group of six (exact
number that died was not specified) over a 14-day observation period. More
subjective information on the acute inhalation toxicity of vinylidene chloride
was published by Irish (1962) at the Dow Chemical Company. He reported that
exposures to 4000 ppm could rapidly produce stupor and unconsciousness, but noted
that complete recovery from the anesthetic effect was probable if duration of
exposure was brief. No-effect levels for experimental animals were estimated at
1000 ppm for up to 1 hour and 200 ppm for up to 8 hours. These values are in
reasonable agreement with the data of Siegel et al. (1971), indicating that the
4-hour LC5Q for vinylidene chloride in rats is about 6350 ppm.
Over the past decade, several groups of investigators have explored the
biochemical mechanism of vinylidene chloride-induced hepatotoxicity in rats.
10-31
-------
These studies were prompted by early observations that the toxicity of vinylidene
chloride was similar to that of carbon tetrachloride, a well-documented hepato-
toxin (Jenkins et al., 1972). Initial studies involving the administration of
single oral doses (500 rag/kg) to rats established that vinylidene chloride
produced biochemical changes that were qualitatively similar to those produced
by carbon tetrachloride (Jenkins et al., 1972). , These included depressed liver
glucose-6-phosphatase activity and increased activities of liver alkaline phos-
phatase and tyrosine transaminase, and of plasma, alkaline phosphatase and
alanine aminotransferase. In addition, vinylidene chloride displayed greater
potency than did carbon tetrachloride in its effect on several of these bio-
chemical parameters. In contrast to carbon tetrachloride, however, the
biochemical alterations induced by vinylidene chloride were less pronounced in
female rats and were reduced by pretreatment of animals with phenobarbital, an
inducer of hepatic drug-metabolizing enzymes. On the other hand, Carlson and
Fuller (1972) demonstrated that enzyme inducers (phenobarbital and 3-methyl-
cholanthrene) as well as enzyme inhibitors (SKF 525A and Lilly 189W increased
the lethality of vinylidene chloride by inhalation in rats, whereas the opposite
effect was seen in rats receiving carbon tetrachloride. These results strongly
suggested a mechanism of toxic action for vinylidene chloride that differed from
that for carbon tetrachloride. Confirmation of this belief was provided by
Jaeger and coworkers (1973a,b), when they demonstrated that the hepatotoxic
effects of vinylidene chloride are not due to a lipoperoxidative mechanism of
action, as is the case with carbon tetrachloride.
Further studies on the hepatotoxicity of vinylidene chloride have focused
on the relationship of metabolism to acute toxicity, and the influence of nutri-
tional status, age, and sex on mortality. Jaeger and coworkers (1973a) observed
that the acute lethality of vinylidene chloride administered by inhalation in
10-32
-------
male rats was greater during the period from 6:00 p.m. to 10:00 p.m. than during
the period 6:00 a.m. to 10:00 a.m. This pattern of sensitivity to vinylidene
chloride was correlated with the diurnal variation in hepatic GSH concentration,
which is highest during the day and lowest during the night. Thus, the
hypothesis was offered that a GSH-dependent pathway mediates the detoxification
of vinylidene chloride, a mechanism which is known to be important in the
detoxification of certain carcinogenic chemical intermediates (e.g., epoxides)
(Jaeger, 1979). The importance of adequate hepatic GSH concentrations in
protecting against acute intoxication with vinylidene chloride has subsequently
been confirmed in studies using fasted animals that have reduced hepatic GSH
levels (Jaeger et al., 1974; Andersen and Jenkins, 1977). In male rats fasted
for 18 hours, the 24-hour LC5Q following a 4-hour inhalation exposure to
vinylidene chloride was 600 ppm, whereas in fed animals an estimated LCL- of
15,000 ppm was obtained (Jaeger et al., 1974). The minimum lethal concentration
of vinylidene chloride was 200 ppm in fasted animals and 10,000 ppm for fed
animals. The functional state of the thyroid gland, which apparently played a
role in the regulation of GSH levels in the liver, also influenced the
hepatotoxicity of vinylidene chloride (Jaeger et al., 1977b; Szabo et al., 1977).
Chemical or surgical thyroidectomy was associated with an increase in hepatic GSH
and a concomitant decrease in the mortality and hepatic necrosis caused by a
4-hour inhalation exposure of fasted male rats to 2000 ppm vinylidene chloride.'
The studies of Jaeger (1977) and his coworkers (Jaeger et al., 1977a,b) led
to the hypothesis that the mechanism of toxicity for vinylidene chloride involved
damage to hepatic cellular mitochondria. This postulation was supported by
evidence showing biochemical alterations following exposure of fasted male rats
to vinylidene chloride (200-500 ppm for 1-24 hours); these alterations were
indicative of an inhibition of the tricarboxylic acid cycle. Among these changes
10-33
-------
was a significant elevation of hepatic citric acid concentration in fasted (i.e.,
GSH-deficient) rats after 12 hours of exposure to 250 ppm vinylidene chloride in
air. Thus, the authors suggested that vinylidene chloride may induce
mitochondria-specific injury via the metabolic formation of monochloroacetic
acid, which may subsequently give rise to monochlorocitric acid.
Studies conducted by Reynolds et al. (1975) and Reynolds and Moslen (1977)
supported the theory that vinylidene chloride is a unique hepatotoxin in terms of
its rapid action and its effect on mitochondria. The acute hepatotoxicity of
chloroethylenes was shown to be, in decreasing order: vinylidene chloride >
trichloroethylene > vinyl chloride > perchloroethylene. Exposure of rats to
vinylidene chloride by inhalation (200 ppra, 4 hours) produced an abrupt hemorr-
hagic centrilobular necrosis. Parenchymal cell injury is characterized by
retracted cell borders with pericellular spaces forming that may contain red
blood cells and fibrin. Nuclear changes include the loss of perinucleolar
ohromatin and the aggregation of chromatin along the nuclear perimeter against
the nuclear envelope. Within 2 hours after onset of exposure, swollen and
ruptured mitochondria were observed in hepatic parenchymal cells, whereas the
rough and the smooth endoplasmic reticulum appeared normal. In contrast,
triohloroethylene, carbon tetrachloride, vinyl chloride, and perchloroethylene
all produced damage to the endoplasmic reticulum.
Reynolds et al. (1980) associated the biochemical changes in the liver, such
as sodium (Na), potassium (K), calcium (Ca), and GSH levels, with subsequent
histological changes in rats exposed to 200 ppm vinylidene chloride for T to 4
hours. By the end of the first hour of exposure, sorbital dehydrogenase (SDH)
activity was elevated and hepatic Na levels increased while GSH decreased. This
trend continued for the second hour of exposure. By the third and fourth hour
SDH, as well as serum alanine aminotransferase activity and Na and Ca levels,
10-34
-------
were greatly increased above controls. These increases remained high for 12
hours post-exposure. Histological injury included nuclear changes and
centrilobular necrosis. Ion changes were attributed to changes in the membrane
ion pumps, either directly or due to an adenosine triphosphate (ATP) deficiency.
Decreased levels of GSH were attributed to a conjugation reaction in the
metabolism of vinylidene chloride. Enzymatic activity increased during
detoxification (Reynolds et al., 1980).
Similarly, Chieco et al. (1982) combined histological and chemical analyses
to study the hepatotoxic effect of acute exposure to vinylidene chloride in rats.
Histochemical testing was conducted at 1, 2, 4, or 6 hours after oral doses of
50, 100, 150, or 200 mg vinylidene chloride. The degree of liver or hepato-
cellular damage was assessed by histology and by measurements of liver ion levels
(Na, Ca, and K) and serum transaminase activity. Injury was noted in the form of
increased transaminase activity, decreased membrane adenosine triphosphatase
activity, decreased succinate dehydrogenase activity (on the inner mitrochon-
drial membrane), and corresponding changes in the plasma and mitochondrial
membrane histology. The investigators (Chieco et al., 1982) concluded that
membranous organelles and membrane-bound enzymes were the primary sites of hepa-
tocellular damage by vinylidene chloride. These changes in turn resulted in
secondary alterations in glutathione levels, cellular ion imbalances, and
cytoplasmic changes (Chieco et al., 1982).
Recently, vinylidene chloride has been shown to inhibit the activity of rat
liver microsomal calcium pumps in the presence of a NADPH-generating system. The
calcium pumps were not inhibited when vinylidene chloride was applied in vitro in
the absence of a NADPH-generating system (Moore, 1980; Ray and Moore, 1982).
Moore (1982) also reported inhibition of the liver endoplasmic reticulum calcium
pump activity by vinylidene chloride. The concomitant rise in liver calcium
10-35
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levels occurred soon after vinylidene chloride administration and was attributed
to the inactivity of the calcium pumps. Calcium released from the endoplasmic
reticulum may serve as a trigger for the influx of extracellular calcium and,
ultimately, cytotoxicity (Moore, 1982).
Information regarding the acute toxicity of vinylidene chloride is not
restricted entirely to its effect on the liver. Jenkins and Andersen (1978)
recently reported a nephrotoxic action of vinylidene chloride following oral
administration to rats. Biochemical indices of kidney damage (plasma urea
nitrogen, plasma creatinine) were elevated in fasted male rats given a single
oral 400 mg/kg dose of vinylidene chloride (Table 10-10). Conversely, rats that
were not fasted were protected from the nephrotoxic effect. At doses below 400
mg/kg, no significant alterations were noted in plasma indicators of kidney
damage (Table 10-11). In addition, female rats were much less sensitive to the
effects of vinylidene chloride on the kidney. In both male and female rats,
however, histological evidence of renal damage was obtained at various times
following the administration of a single oral dose of 400 mg/kg vinylidene
chloride (Table 10-12). Since female rats showed the same, if not greater,
histologic damage to the kidney as did males, it was suggested that biochemical
parameters may not be sensitive indicators of kidney damage in females.
A single report has been published (Siletchnik and Carlson, 1974)
concerning the cardiac sensitizing effects of vinylidene chloride by acute
inhalation exposure in rats. Cardiac arrhythmias could not be produced by a
single 4 jig/kg injection of epinephrine to male rats; however, when rats inhaled
25,600 ppm vinylidene chloride for 80 minutes, doses of epinephrine as low as 0.5
Hg/kg could elicit serious cardiac arrhythmias, which could be further enhanced
by pretreatment of rats with phenobarbital (50 mg/kg i.p. for 4 days).
10-36
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TABLE 10-10
Influence of 24-Hour Fasting on the Effect of Oral
Administration of Vinylidene Chloride (400 rag/kg)
in Corn Oil on Plasma Urea Nitrogen Concentration
in Male Rats (341 + 7 g)a
Status
Fasted
Fasted
Fed
Fed
Hours After
Challenge Challenge
Corn Oil 24
48
72
Vinylidene 24
chloride
48
72
Corn Oil 24
48
72
Vinylidene 24
chloride
48
72
Urea Nitrogen
(mg/100 ml)
21 + 1b
20 + 1
22 + 1
51 ± 16°
82 ± 39°
50 + 3°
20 + 2
21 ± 1
22 + 1
19 ± 2
12±2d
15 ± 1°
Source: Jenkins and Andersen, 1978
All data are expressed as mean ± SE of groups of 3 to 6 rats.
°Significantly higher (p<0.05) than fasted, corn oil-challenged controls
at the same time after challenge (method of analysis not mentioned).
Significantly lower (p<0.05) than fed, corn oil-challenged controls at
the same time after challenge.
10-37
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TABLE 10-11
Relationships of Plasma Indicators of Kidney Damage to Dose 24 Hours
After Oral Administration of Vinylidene Chloride to Male Rats
(289 ± 9 g)a
Dose (mg/kg)
0
50
100
200
400
800
Urea Nitrogen
(mg/100 ml) ,
20 + 2b
23 ± 1
26 + 1
32 + 7
80 + 1°
108 + 18C
Creatinine
(mg/100 ml)
0.76 + 0
0.61 + 0
0.62 + 0
0.80 + 0
2.33 ± 0
NDd
.06
.11
.06
.06
.05°
aSource: Jenkins and Andersen, 1978
bAll data are expressed as mean + SE of groups of two to six rats.
°Significantly different from zero-dose control (p<0.05); however,
the method of analysis was not mentioned.
Not done
10-38
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Pulmonary damage has been observed in mice after either oral or i.p.
administration of vinylidene chloride (Forkert and Reynolds, 1982; Krijgsheld et
al., 1983). At 6 hours after administration, a single oral dose of 100 mg/kg
produced degeneration of the endoplasmic reticulum of the Clara cells of the
bronchiolar epithelium; a single oral dose of 200 mg/kg resulted in necrosis of
both ciliated and Clara cells, with exfoliation of the bronchiolar epithelium
(Forkert and Reynolds, 1982). Hypoxia (measured as a decrease in oxygen partial
pressure of arterial blood) was observed 24 hours after administration of the
higher dose, but the animals recovered and the bronchiolar epithelium had
regained a normal appearance by 7 days. Clinical chemistry indices of liver
damage [serum glutamic oxaloacetic transaminase (SCOT) and serum glutamic
pyruvic transaminase (SGPT) levels] were greatly elevated even at the 100 mg/kg
dose, 24 hours after administration.
Twenty-four hours after i.p. injection of mice with vinylidene chloride at a
dose of 125 mg/kg, microscopic examination of the lungs revealed necrosis and
sloughing of the Clara cells lining the bronchioles (Krigsheld et al., 1983).
Pulmonary cytochrome P-450 levels and related monoxygenase activities were
decreased; the authors suggested that these decreases may have been a reflection
of the destruction of the Clara cells, which are known to contain relatively high
levels of cytochrome P-450. The livers and kidneys of the treated mice were
relatively unaffected, as judged by microscopic appearance, cytochrome P-450
content and monoxygenase activities.
10.2.1.1 Mechanisms of Toxicity
The acute toxicity of vinylidene chloride is altered by several factors in
addition to the effects on sensitivity produced by fasting. A series of time-
course and dose-response studies that explored mechanisms of toxicity for
vinylidene chloride have recently been published.
10-41
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Chieco et al. (1981) examined the effect of the administration vehicle on
the toxicity and biological fate of vinylidene chloride in fasted and fed male
Sprague-Dawley rats. Vinylidene chloride was given at 200 mg/kg orally in corn
oil, mineral oil, or aqueous Tween-80 (0.5%', Sigma). Measurements of exhaled
vinylidene chloride (unchanged) were taken at 15-minute intervals for 5 hours and
rats were sacrificed at 6 hours for biochemical analyses as an assessment of
hepatic injury. The vehicle did not affect the overall amount of vinylidene
chloride exhaled, which ranged from 37 to 51% of the administered dose. The
nature of the administration vehicle did, however, alter the rate at which
vinylidene chloride was absorbed and exhaled. Aqueous Tween-80, which is readily
absorbed, allowed the vinylidene chloride to be readily absorbed and exhaled in a
shorter period of time. Corn oil was intermediate, while the poorly digested and
absorbed mineral oil prolonged absorption and exhalation times in fasted and fed
rats. Hepatic injury, measured as elevated SCOT and SGPT levels, was greatest in
fasted rats treated with vinylidene chloride in mineral oil or corn oil (up to
150-fold increase in SCOT and SGPT levels). Fasted rats treated with vinylidene
chloride in Tween-80 were moderately affected (15 to 18 times increase in SCOT
and SGPT levels). In fed rats treated with vinylidene chloride in corn or
mineral oil, enzymatic activity was slightly elevated (2 to 5 times) above the
enzymatic activity in fed rats, while SCOT was not different from control levels.
Chieco et al. (1981) suggested that the results of this study indicate that
decreased hepatic injury in fed animals is due to the ability of these animals to
detoxify vinylidene chloride over a longer period of time than fasted animals.
Histologically, fasted rats fed vinylidene chloride in corn or mineral oil
showed massive hepatic necrosis, which was consistent with biochemical changes.
Only scattered necrotic hepatocytes were seen in fasted animals given vinylidene
chloride in aqueous Tween-80. Fasted animals given vinylidene chloride in corn
10-42
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oil or mineral oil also had granular "heme" casts in Henle's loop of the kidney.
Concomitant high levels of free plasma hemoglobin and "pink urine" were noted in
these animals. No pathological abnormalities were observed in the heart, lungs,
spleen, adrenals, or duodenum in vinylidene chloride-treated animals (Chieco et
al., 1981).
Andersen and Jenkins (1977) observed that body size or the age of the animal
had a dramatic effect on the toxicity of vinylidene chloride when a single oral
dose was given to fasted male rats. Dose-response curves for vinylidene
chloride-induced mortality were constructed for animals of three different sizes
(Figure 10-4). Mortality among large animals (395 + 11 g) increased linearly
from 0 to 35% at doses between 50 and 100 mg/kg; however, minimum lethal doses
were found to be as low as 50 mg/kg. In medium-sized rats (224 ± 1 g), doses
between 50 and 800 mg/kg produced mortality which varied from 10 to 3358. The
most aberrant results were obtained in small rats (73 + 1 g). Mortality
increased to 10055 at a dose of 300 mg/kg, but then decreased with increases in
dose up to 800 mg/kg. The LD values calculated from the data presented in
Figure 10-4 would appear to be widely variable as shown by dependence on body
size.
In an attempt to explain the effect of body size on acute mortality,
Andersen and Jenkins (1977) examined the relationship between hepatotoxicity
(indicated by plasma enzyme levels) and body size following the administration of
a single oral 50 mg/kg dose of vinylidene chloride in corn oil. They found that
both mortality within the first 24 hours and plasma enzyme activities after 24
hours were greatest among rats weighing between 130 and 160 g. In animals of
this size, the estimated LD was less than 50 mg/kg, whereas in large rats, the
LD50 wou-'-cl be 30 times greater. The unusual dose-mortality curve for immature
rats (see Figure 10-4) was partially explained by the fact that increases in
10-43
-------
RAT WEIGHT = 73 ±1 g
200
300
400
500
600
700
800
DOSE VINYLIDENE CHLORIDE, mg/kg
O Mortality in groups of 6 rats for 30 rats weighing 395 ±11 g.
• Mortality in groups of rats for 40 weanling rats weighing 73 ±1 g.
A Mortality in groups of 10 rats for 40 rats weighing 224 ±1 g.
Figure 10-4. Dose-mortality curves for administration of single, oral doses
of vinylidene chloride dissolved in corn oil to fasted male rats of various
sizes.
Source: Andersen and Jenkins (1977a).
-------
plasma transaminase activities paralleled mortality, and the retention of orally
administered vinylidene chloride reached a maximum at a total dose of 100 mg/kg
and then leveled off.
In comparison to fasted male rats, female animals were much less susceptible
to the effects of vinylidene chloride. Plasma transaminase levels were not
altered by a 50 mg/kg dose, regardless of body size. In female rats, the
threshold dose for expression of acute toxic effects (plasma -transaminase eleva-
tion) was about 100 mg/kg. Based on their results and on analogy to other
halogenated hydrocarbons, Andersen and Jenkins (1977) postulated that vinylidene
chloride is metabolized by a saturable microsomal enzyme-mediated reaction to a
toxic intermediate that is probably an epoxide. A second enzyme-mediated
reaction that converts the toxic intermediate to a less toxic form was also
proposed. In young rats, this detoxification mechanism may be absent or present
at only low levels, thus accounting for increased susceptibility.
In subsequent studies, Andersen and coworkers (1978, 1979b) examined in
greater detail the relationship between vinylidene chloride metabolism and
expression of toxic effects. Chemical modifiers of raicrosomal enzyme activity
were administered to fasted male rats followed by a single oral dose of vinyli-
dene chloride (Andersen et al., 1978). Phenobarbital pretreatment, which causes
microsomal enzyme induction, protected rats against the lethal effects of
vinylidene chloride. This protection by phenobarbital was opposite to that
observed by Carlson and Fuller (1972) following inhalation exposure of rats.
This protective action increased with increasing body size. Conversely, the
microsomal enzyme inhibitor SKF 525A greatly enhanced the lethality of vinyli-
dene chloride in large rats (261 + 2 g) but had little influence in immature rats
(88 _+ 2 g). In addition, pretreatment of rats with the metabolic inhibitors
pyrazole, aminotriazole, and carbon tetrachloride protected animals of all sizes
10-45
-------
against the lethal action of vinylidene chloride. These results supported the
argument that two sequential enzyme-mediated reactions are involved in the
activation of vinylidene chloride. The first reaction, which is inhibited by
pyrazole, aminotriazole, and carbon tetrachloride, leads to formation of a toxic
intermediate. The second reaction, which is affected by phenobarbital and SKF
525A pretreatment, is a detoxification step that apparently exists at greater
levels in mature animals.
Subsequent studies by Andersen and coworkers (1979b) demonstrated that
mortality induced in rats by inhalation of vinylidene chloride failed to follow a
strict concentration x time relationship. Instead, mortality was more dependent
on time of exposure than on concentration once a threshold level (about 200 ppm)
had been reached (Figure 10-5). These data supported the involvement of a
saturable enzymatic reaction in the production of a metabolite that is respon-
sible for the expression of vinylidene chloride-induced toxicity. The authors
appropriately noted that, under conditions of exposure that produce enzyme
saturation, misleading estimates of the LC^Q (inhalation) or LI>5Q (oral and
parenteral) could result.
Studies by Short and coworkers (1977a,b) with rats and mice support the
conclusions reached by Andersen et al. (1978, 1979b). Non-fasted animals (groups
of 10) inhaled vinylidene chloride for 22 to 23 hours per day for up to 7 days.
Short et al. (1977a,b) found that male mice were more sensitive than were male
rats to lethal effects and hepatotoxic effects (measured by SCOT and SGPT
activities) of vinylidene chloride (Table 10-13). Histopathologic examination
revealed hepatic and renal damage among male mice exposed to 15, 30, and 60 ppm
vinylidene chloride (1-5 days); hepatic damage only was seen in male rats exposed
at 60 ppm for 3 days. When mice were given disulfuram (0.10$ in feed 23 days
before and during exposure), or thiram (0.10? in feed 3 days before and during
10-46
-------
c
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o
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90-
80—
70
60—
50—
40-
30-
20—
10—
0-
4-hour EXPOSURES
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I I
250 500
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750
1000
Figure 10-5. Effect of increasing concentration of vinylidene chloride on
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of a group of 6 animals exposed for 4 hours.)
Source: Andersen et al. (1978).
10-47 •
-------
TABLE 10-13
Toxicity of 60 ppm Vinylidene Chloride in Male Mice and Ratsc
Days
Species Exposed
Mouse 1
2
Rat 1
2
SGOT SGPT
(IU/1)D (IU/1)D
1946 + 270 3045 ± 209
751 + 150 1112 + 226
74+6 44+7
263 ± 33 198 + 29
Ratio
Dead/Exposed
2/10
8/10
0/10
0/10
a
Source: Short et al., 1977b
Mean ± SE for 2 to 5 determinations
SCOT = Serum glutamie-oxaloaoetic transaminase; SGPT = Serum glutamic-pyruvic
transaminase
10-48
-------
exposure), the acute lethality of vinylidene chloride was reduced. The authors
observed that these compounds are known to protect against drug-induced
toxicity, and may act by decreasing metabolic activation or increasing
detoxification or both.
10.2.2 Subacute and Chronic Exposure
10.2.2.1 Inhalation Studies
Several groups of investigators have characterized the toxicity of vinyli-
dene chloride by repeated administration to experimental animals. Both inges-
tion and inhalation have been employed as routes of exposure. These studies
established that, in general, the target organs affected by chronic exposures
(i.e., liver and kidneys) are the same as those affected by acute administration
of vinylidene chloride.
The first published report regarding the chronic toxicity of vinylidene
chloride was a brief summary of inhalation studies conducted by the Dow Chemical
Company (Irish, 1962). Unspecified animals exposed to 100 ppm and 50 ppm
vinylidenechloride (5 days per week, 8 hours per day for several months)
developed liver and kidney damage. Minimal lesions were also observed in the
liver and kidney of animals exposed at concentrations of 25 ppm.
Prendergast and coworkers (196?) published the first detailed account of
the chronic toxicity of vinylidene chloride. Groups of rats, rabbits, dogs, and
monkeys were exposed in one of two ways: 30 exposures, 8 hours per day, 5 days
per week to a concentration of 395 mg/rn (100 ppm) or 90 days of continuous
3 3 ^
exposure to a concentration of 189 mg/m (48 ppm), 101 mg/m (26 ppm), 61 mg/m
(16 ppm), or 20 mg/m (5 ppm). The results of these studies are summarized in
Table 10-14. The most prominent effects observed included hepatic damage in
dogs, monkeys, and rats exposed to 189 mg/m3; this damage consisted of fatty
metamorphosis, focal necrosis, hemosiderin deposition, lymphocytic infiltration,
10-49
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bile duct proliferation, fibrosis, and pseudo-lobule formation. Rats also
showed nuclear hypertrophy of the renal tubular epithelium when exposed to
vinylidene chloride at 189 mg/m .
Gage (1970) conducted limited studies in rats exposed to vinylidene
chloride by inhalation that support the previous observations of Prendergast and
coworkers (1967). Four male and four female rats received twenty 6-hour
exposures to vinylidene chloride at concentrations of 500 or 200 ppm. At the
higher concentration, retarded weight gain and nasal irritation were noted.
Liver cell degeneration was observed upon autopsy. Inhalation of 200 ppm
vinylidene chloride produced slight nasal irritation but no significant findings
at autopsy; however, the group size was very small.
Lee and coworkers (1977) exposed CD-1 mice (36 males and 36 females) to 55 ppm
of vinylidene chloride for 6 hours per day, 5 days per week, for up to 12 months.
Two male mice died on the 13th day of exposure, and revealed acute toxic hepa-
titis and tubular necrosis of the renal cortex. Hepatic hemangiosarcomas were
observed in three exposed mice, and various hepatic lesions were generally
observed that included the following: enlarged and basophilic hepatocytes,
enlarged nuclei with eosinophilic inclusions, mitotic figures, or polyploidy,
miorofoci of mononuclear cells, focal degeneration, and necrosis. Specific
incidences were not given. Hepatic hemangiosarcomas were not observed in any of
72 control mice. Bronchiole-alveolar adenomas were observed in six exposed mice
and one control mouse.
Dow Chemical Company performed an inhalation toxicity study with vinylidene
chloride and interim results, were published by Rampy and coworkers (1977). In a
90-day study, groups of HO Sprague-Dawley rats (20 male and 20 female) were
exposed for 6 hours per day, 5 days per week, to vinylidene chloride at a
concentration of 25 or 75 ppm. Eight animals of each sex were sacrificed after
10-52
-------
30 days, and the remainder killed after 90 days. Among animals exposed at both
concentrations, increased cytoplasmic vacuolation of hepatocytes was seen 30
days or longer after initial exposure. No other remarkable effects were attri-
buted to the vinylidene chloride exposure.
In another study, Rampy arid coworkers (1977) exposed Sprague-Dawley rats
for 18 months (6 hours/day, 5 days/week) to vinylidene chloride at several
concentrations in air. For the first 5 weeks, rats (104 males and 104 females)
were exposed to levels of 10 or 40 ppm, after which the concentrations were
raised to 25 and 75 ppm, respectively, for the remainder of the 18-month exposure
period. Animals were maintained for an additional 6 months after termination of
exposure. Although male rats gained weight at a slightly slower rate than
controls, no clinical evidence of overt toxicity was seen during the study. Both
male and female rats sacrificed at an interim of 1 year, however, showed hepatic
lesions consisting of increased cytoplasmic vacuolation of hepatocytes. In
addition, higher kidney weights were seen in female rats exposed at both
treatment levels of vinylidene chloride.
The final data of this 2-year inhalation study (interim results reported by
Rampy et al., 1977) were recently compiled and reported by McKenna -et al.
(1982). Data were reported on hematologic parameters, urinalysis, .clinical
chemistry, cytogenic changes in the bone marrow, body weight, major organ
weights, and histopathology following necropsy on all animals (either at interim
periods of 1, 6, 12, or 18 months or at the termination of the experiment at 734
to 736 days). Statistical evaluations of data were made using analysis of
variance and Dunnett's test (body weight, hematology, urinalysis, clinical
chemistry, and organ weight data) or by the Fischer exact test (mortality rates,
gross and microscopic pathologies, and tumor incidence). The level of signifi-
cance was chosen as P<0.05.
10-53
-------
Mortality figures for male rats exposed to vinylidene chloride at either
dose level did not reveal significant increases. Females exposed at 25 ppm
vinylidene chloride had.increased mortality rates when compared to controls from
the 15th through 22nd months. Statistically significant increased mortality
rates in females exposed at 75 ppm vinylidene chloride were noted during months
15, 17, and 21 of the study. The earlier onset of mammary tumors and higher
incidences of pneumonia in treated groups may have contributed to these higher
mortality rates.
No consistent dose-related decrease in mean body weight for male rats
exposed to 25 or 75 ppm vinylidene chloride was observed. A general trend of
decreased body weight was noted in exposed males when compared to control males
but increased mean body weights were noted in the exposed groups sporadically
throughout the study. Generally, females exposed to either 25 or 75 ppm
vinylidene chloride had higher mean body weights for the first 6 months but were
comparable to controls throughout the remainder of the study.
No significant dose-related effects in hematological, urinalysis, clinical
chemistry, or cytogenetic parameters were reported in any exposure group. The
only significant changes in organ weight were a decreased mean liver weight in
males exposed to 25 or 75 ppm vinylidene chloride at the 1-year interim sacrifice
and an increased mean kidney weight in both exposure groups of female rats at 1
year. Both organ weight changes were statistically significant when compared to
controls and considered to result from vinylidene chloride exposure (McKenna et
al., 1982).
Many gross and microscopic lesions were seen in control and vinylidene
chloride-exposed rats; most were spontaneously occurring, age-related changes
common to Sprague-Dawley rats. The incidence of lesions from chronic murine
pneumonia in exposed male and female rats was elevated, but lower levels in
10-54
-------
controls were attributed to the physical separation of exposed and control groups
which deterred the spread of pneumonia. Chronic renal disease was the predomi-
nant cause of death in male rats of the study. Females had a high incidence of
subcutaneous tumors of the mammary gland region which was frequently the cause of
death. There was a statistically significant increase in the incidence of
hepatocellular fatty change in female rats exposed to 75 ppm during the 18-month
exposure period. These changes were reversed during the 6-month post-exposure
period, however. Females treated at 25 ppm showed a similar but non-significant
trend. This reversible and non-progressive liver change was noted in males at
the 6 and 12 months interim sacrifice but not at 18 months.
The incidence of pituitary adenomas was decreased in both dose groups of
male rats and the 25 ppm vinylidene chloride dose group of females. There were
fewer pancreatic islet cell adenomas and thyroid adenocarcinomas in male rats
exposed to 75 ppm vinylidene chloride. Mammary adenocarcinomas were statis-
tically increased in female rats treated at 25 ppm vinylidene chloride.
Subcutaneous or mammary tumors were more prevalent in 75 ppm vinylidene chloride
treated females than in controls. The total number of rats with primary neo-
plasms was similar for both sexes at all dose groups-, including controls. The
total number of rats with primary neoplasms was similar (ranging from 84 to 86)
for all six dose/sex groups. Summarizing the tumor incidence data, the authors
reported that none of the statistically significant differences were considered
to be direct effects of vinylidene chloride exposure.
10.2.2.2 Ingestion Studies
A single long-term study has been conducted with vinylidene chloride
administered in the drinking water of rats. This study was conducted by the Dow
Chemical Company for the Manufacturing Chemists' Association (Humiston et al.,
1978). Groups of 96 Sprague-Dawley rats (48 males and 48 females) were exposed
10-55
-------
for 2 years to vinylidene chloride incorporated into the drinking water at
nominal concentrations of 50, 100, and 200 ppm. These dose levels corresponded
to approximate daily intakes of vinylidene chloride in the range of 5-12, 8-20,
and 16-JJO mg/kg at the 50, 100, and 200 ppm concentrations, respectively. In
comparison to control animals, vinylidene chloride-treated rats displayed no
significant or consistent differences in general appearance, body weight, food
consumption, water consumption, hematologic values, urinalysis, clinical
chemistry values, or organ weights. Gross and histopathologic examination of
tissues from treated rats, however, revealed a number of statistically signifi-
cant lesions. These are partially summarized in Table 10-15. The authors
considered the most important lesions to be the hepatocellular fatty change and
periportal hepatocellular hypertrophy which occurred in male rats at the 200 ppm
dose level and in females at all dose levels. The authors did not observe any
hepatocellular necrosis that could be considered treatment-related.
Results of this long-term, oral study with rats were subsequently published
in the open literature by Quast et al. (1983), along with results of a 97-day
oral study with dogs; the dog study was also conducted by the Dow Chemical
Company. Groups of four male and four female beagle dogs were administered
vinylidene chloride in doses of 0, 6.25, 12.5, or 25 mg/kg daily for 97 days. The
chemical and vehicle (peanut oil) or vehicle alone was administered orally in a
capsule once a day. As compared with controls, the groups of treated dogs had no
differences in general appearance or demeanor, body weight, food consumption,
hematologio and clinical chemistry values, urinalysis, organ weights and gross
and microscopic appearance of the tissues.
10.2.3 Summary of Toxicity
The biologic activity of vinylidene chloride has been thoroughly studied in
experimental mammals; no information is available concerning the effects of
vinylidene chloride on domestic animals or wildlife.
10-56
-------
TABLE 10-15
Pathologic Effects of Long-Term Ingestion of Vinylidene Chloride
Incorporated in the Drinking Water of Sprague-Dawley Ratsa
Effect
Dose Level
50 ppm 100 ppm 200 ppm
M F M F M F
Increased incidence of intra-abdominal fluid
or blood in the abdominal cavity
Increased incidence in the total number of
rats with hepatocellular fatty change or
fatty degeneration
Increased incidence of hepatocellular fatty
change with location in lobule not specified
Increased incidence in periportal
hepatocellular fatty change
Increased incidence of periportal
hepatocellular hypertrophy
Increased incidence of hepatic
centrilobular atrophy
Increased incidence of mammary gland
fibroadenomas/adenofibromas
X
Source: Humiston et al., 1978
M = male; F = female
10-57
-------
The toxioity of vinylidene chloride varies with the age, sex, and species of
the animal exposed. In the most studied animal, rat, inhalation exposure to
32,000 to 6,350 ppm has proven to be fatal. In rats fasted prior to exposure, the
LC,- value was as low as 600 ppm. For oral adminstration of vinylidene chloride,
however, the determination of an LDj-n value is difficult as a result of the
relatively flat dose/mortality curve which possesses an extended plateau region.
The target organs affected by acute exposure to vinylidene chloride are the liver
and kidneys, with evidence from studies of the liver to indicate that
mitochondrial damage occurs. Both liver and kidney damage are also observed
following subchronic and chronic exposure to vinylidene chloride by either
inhalation or ingestion. Continuous inhalation exposure of rats to 5 ppm of
vinylidene chloride has been shown to adversely affect body weight gain while
ingestion of vinylidene chloride by rats at 5 to 12 mg/kg/day produced fatty
livers. A no-observed effect level (NOEL) for inhalation exposure (<5 ppm) or
ingestion (<5 mg/kg/day) has not been demonstrated.
10.3 TERATOGENICITY AND REPRODUCTIVE TOXICITY
Short et al. (1977c) performed an extensive investigation of the toxicity
during gestation of inhaled vinylidene chloride in mice and rats (approximately
20 animals in each of the exposed groups and 60 in the control groups). This
study examined toxicity to the dams, toxicity to the fetus, and teratogenic and
behavioral effects in the pup. In the initial part of the experiment, rats (18
to 20 per group) were exposed to 15, 57, 300, and 449 ppm vinylidene chloride,
and mioe to 15, 30, 57, 144, and 300 ppm vinylidene chloride for 23 hours per day
from day 6 to 16 of gestation. In rats, appreciable deaths (over 25%} of the dams
occurred in the 300 to 449 ppm group, and maternal well-being, as measured by
food consumption and weight gain, was adversely affected in the 15 ppm and above
groups. Similar results were observed in mice, with no pregnant mice surviving
10-58
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at the 144 or 300 ppm levels, and food consumption and weight gain being reduced
in all groups except the 15 ppm animals. Early resorptions were common in
exposed animals, with 100% resorption in mice exposed to 30 and 57 ppm vinylidene
chloride (resorption in the 15 ppm groups was comparable to controls), and 49 and
64? resorption in rats exposed to 57 and 449 ppm vinylidene chloride, respec-
tively. Dams that survived the exposure at other concentration levels had
resorption rates comparable to those of controls. There were no increases in
external gross abnormalities noted in surviving pups in any of the exposed groups
of rats or mice; however, fetotoxicity was observed as soft tissue anomalies in
rats (none were observed in mice) and some skeletal ossification problems in all
groups of mice and rats. The authors concluded that these anomalies could not be
evaluated in regard to teratogenic effects, since there were overt signs of
toxicity (reduced weight gain and food consumption) due to the treatment in the
dams. Abnormalities at a similar incidence to those observed in the treated
animals were also observed in a group of animals on a food-restricted diet.
The study was continued using only mice, with groups of 10 to 24 dams
exposed to a variety of concentrations of vinylidene chloride for different
periods of time during gestation (Table 10-16), in an attempt to alleviate
maternal toxicity as usually indicated by decreased maternal weight gain. By
shortening the exposure periods, the incidence of resorption was lessened;
however, treatment-related weight loss in the dams was still evident. It was
interesting to note that exposures starting on days 10 and 12 and ending on day
15 were associated with a higher resorption rate than that observed when
exposures were started on day 8 of gestation. This may have occurred because of
some adaptation of the animals as a result of the longer exposure prior to a
critical period during the latter part of gestation. Pups from vinylidene
chloride- exposed dams again had a variety of soft tissue and skeletal anomalies,
10-59
-------
TABLE 10-16
Exposure Levels and Duration of Exposure to Vinylidene Chloride
During Gestation in Mice
Vinylidene
Chloride
ppm 678
Kh f.
7H a
(H O— —
ch Q
111 8
Cjl
81 6
CC. f.
119
R1
119
I It
119
I 1C
ft1
aSource: Short et al., 1977c
Days of Gestation
9 10 11 12 13 1
1P
Q
y
q
q
y
9— — —1?
•"•• 1 C.
9____ 19
919
__________ ___|^
1p
1 O
1 ?„„_„„
-
4 15 16
1C
1C
____1R
1C
____1C
__1C
1C
1C
1C
17
17
17
17
10-60
-------
but these occurred only when maternal welfare had been adversely affected by the
exposure to vinylidene chloride. In addition, the behavioral studies
demonstrated no major adverse effect on pups exposed in utero to vinylidene
chloride. These tests included the following: surface righting, pivoting,
auditory startle, bar-holding, righting in air, visual placing, swimming
ability, physical maturation, and activity test. The authors concluded that
vinylidene chloride was possibly a weak teratogen based on the increase in soft
tissue anomalies although these anomalies were not statistically significant.
However, a conclusion of teratogenicity is weakened by additional effects on the
pups as a result of maternal toxicity at nearly all concentrations of vinylidene
chloride used.
Murray et al. (1979) exposed rabbits to vinylidene chloride by inhalation,
and rats by inhalation and by incorporating the compound into the drinking water
(Table 10-17). Exposure occurred during days 6-15 or 6-18 of gestation for rats
and rabbits, respectively. Inhalation exposure was for 7 hours/day to vinylidene
chloride which was 99.5$ pure and contained the polymerization inhibitor mono-
methylether of hydroquinone (MEHQ) at a level of 200 to 400 ppm. An exposure
level of 200 ppm was employed in the drinking water study using redistilled
vinylidene chloride containing only 1 to 5 ppm of residual MEHQ. Upon termina-
tion of the observation period, on days 21 and 29 of gestation for rats and
rabbits, respectively, the dams were killed and examined for changes in liver
weight, and in non-pregnant animals for signs of conception. The fetuses were
measured, examined for external anomalies, and one-third of the animals were
dissected for soft-tissue alterations. All fetuses were examined for skeletal
alterations.
In the inhalation study in rats, maternal weight gain decreased in the 80
and 160 ppm groups during the exposure period and increased during the post-
10-61
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TABLE 10-17
Number of Animals and Exposure Levels Used to Study
the Teratogenicity of Vinylidene Chloride3
Route
inhalation
oral
Concentration
160
160
80
80
20
0
0
200
0
Species
rats
rabbits
rats
rabbits
rats
rats
rabbits
rats
rats
No. of Animals
30
18
30
22
44
20-47/group
16
26
24
Source: Murray et al. (1979)
10-62
-------
exposure period, while no changes (in comparison to controls) were observed in
the 20 ppm groups or the animals in the drinking water study. Food consumption
followed similar trends. Only in dams exposed to 160 ppm was there an increase
in the liver to body weight ratio, although the absolute liver weight was similar
to control animals. Exposure to vinylidene chloride did not affect the outcome
of pregnancy as indicated by number of implants, live fetuses, or resorption
rates, nor were there changes in fetal sex ratios or fetal body weights. There
was a significant increase in the crown-rump length in fetuses of rats receiving
vinylidene chloride in the drinking water. Although no increase in major
malformations (taken individually or collectively) was present, the fetuses of
animals exposed in the 80 and 160 ppm groups showed an increased incidence of
minor skeletal alterations (Table 10-18). The most common skeletal alteration
was wavy ribs, which was observed to be more severe at the higher exposure level.
Wavy ribs and delayed ossification were interpreted as fetotoxic and embryotoxic
manifestations of maternal toxicity at the higher exposure levels. The authors
noted that the consumption by rats of drinking water containing 200 ppm of
vinylidene chloride resulted in fewer adverse effects (dam and offspring) than
did exposure to either 80 or 60 ppm of the test material by inhalation. The
average daily dose of vinylidene chloride received by rats given the compound in
drinking water was calculated to be approximately 40 mg/kg/day. Estimates of the
total amount of vinylidene chloride by gavage is approximately equivalent to a
single 7-hour inhalation exposure of 120 ppm. The sensitivity of the rat to
vinylidene chloride was apparently greater when vinylidene chloride was inhaled
than when it was ingested.
The authors speculated on a possible mechanism to account for route
dependent differences in the toxicity of vinylidene chloride. Detoxification of
vinylidene chloride has been reported to occur via conjugation of its active
10-63
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metabolite with glutathione (McKenna et al., 1977). Since the levels of
glutathione have been reported to undergo diurnal variations the authors
hypothesized that the available levels of glutathione might be high enough to
prevent toxicity when vinylidene chloride was administered in drinking water but
not when the animals were exposed via inhalation. The levels of glutathione
would probably be expected to be low when the inhalation exposure was given (8:00
am - 3:30 pm) since gultathione levels are reported to peak in the evening and
early morning (Jaeger et al., 1973; Watanabe et al., 1976). Vinylidene chloride
in drinking water was made available to the rats over a 24 hour period. The
authors offered this speculation in the discussion of experimental results but
did not provide experimental data to support this hypothesis. Without actual
experimental data, it is not possible to make any conclusions on this
interpretation.
In rabbits exposed to 160 ppm of vinylidene choride, there was a decrease in
body weight gain during exposure and an increase after termination of exposure.
Only dams exposed at 80 ppm had an increase in liver to body weight ratio. There
was also an increase in the resorption rate in the 160 ppm group, with resorption
associated with animals having the greatest weight loss. Similar to the study in
rats, exposure to vinylidene chloride produced no increase in major malforma-
tions, although there was an increase in minor skeletal alterations in the 160
ppm group (Table 10-19). Again, the fetal anomalies observed in rabbits were
attributed to maternal toxicity rather than to a teratogenic .effect of vinylidene
chloride.
The effect of vinylidene chloride on reproduction and its teratogenic
potential when ingested in the drinking water was tested in a three generation
study in Sprague-Dawley rats (Nitschke et al., 1980; Nitschke et al., 1983). The
parental generation (f ), consisting of 10 male and 20 females in each of three
10-65
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TABLE 10-19
Incidence of Fetal Malformation Among Litters of Rabbits
Exposed to Vinylidene Chloride3
Vinylidene Chloride (ppm)
80
0
160
External and skeletal
examination
Soft tissue examination
External examination
No malformation
observed
116/14
No. fetuses/No, litters examined
155/18 111/13 91/12
56/18 42/13 37/12
No. fetuses (litters) affected
Soft tissue examination
Dilated cerebral
ventricles
Thinning of ventri-
cular wall of heart
Skeletal examination
Missing ribs
Extra vertebrae
Hemivertebrae and
fused ribs
Total malformed fetuses
0
0
0
0
0
0
1(1)
0
0
1(1)
1(1)
3(3)
0
0
1(1)
1(1)
0
2(2)
0
1(1)
0
0
1(1)
2(2)
Source: Murray et al., 1979
bRabbits were exposed to 80 or 160 ppm Vinylidene chloride for 7 hr/day from
days 6 to 15 of gestation. No value differed significantly from the control
value by a modified Wilcoxon test, p<0.05.
10-66
-------
treatment groups, received 50, 100, or 200 ppm vinylidene chloride. No vinyli-
dene chloride was administered to a control group of 15 males and 30 females.
Equivalent doses for males ingesting 50, 100, or 200 ppm vinylidene chloride
continuously in the drinking water were 6, 10, or 19 mg/kg/day, and 8, 13, or 26
mg/kg/day, respectively. Following 100 days of exposure to vinylidene chloride,
all groups of males and females (f ) were mated (within dose groups), resulting
in the first filial (f-..) generation. Due to the low fertility rate during this
initial breeding, the f rats were re-mated after a period of no less than 10
days after weaning of the f.., which produced the f-g offspring. The f genera-
tion rats were exposed to vinylidene chloride at the three respective doses for a
2-year toxicity study (Humiston et al., 1975). The f1A and f1B litters of all
dose groups were examined for reproductive indices (number of litters/number of
dams; survival of pups at 1, 7, 14, and 21 days). The animals to be raised as the
f.j generation adults were randomly selected from the f1B generation and continued
to-be'exposed to vinylidene chloride. All other f and f'1B fats were .sacrificed
at -21-24 days of age for internal and external examinations.- .-••-'•
At ==110 days of age, the f.. adults were mated, producing the' f« progeny.
The fp litters were examined similar to the previous litters, and randomly
selected males and females were maintained for fp adults. The remaining fg
weanlings were terminated and examined for external and internal aberrations.
Adult fp rats were mated at -110 days of age to produce the f-. gneration.
Survival of the f _. litters in all groups receiving vinylidene chloride was
decreased so the f_ adults were re-mated after the f• litters were weaned. To
determine if the decreased survival in the dose groups was due to prenatal or
postnatal exposure to vinylidene choride, one-third of the f_B litters born to
200 ppm vinylidene chloride-^treated dams were exchanged with litters of
untreated dams. No dose-related decreased survival was noted in any groups of
10-67
-------
the
™ litter. At least 10 days after the fog litters were weaned, the
parents were mated again to produce the f_,, litters to determine survival rates
30
of this group. A selected number of male and female rats from each dose group of
the f_g litters were raised for 185-213 days as f~ adults. All remaining
weanling rats of the f~», f^p, and f,P litters were sacrificed at 21-24 days of
Oil 30 JL.
age for external and internal examination (Nitschke et al., 1980).
The water containing the vinylidene chloride was available continuously
throughout this study to all treated rats. The first generation rats (f ) were
treated during their maturation, during mating periods, throughout gestation and
lactation for females, and were subsequently used in a 2-year toxicity study.
Pups were exposed prenatally and throughout their lives until their sacrifice, or
longer if they were selected as breeders of that generation (Nitschke et al.,
1980).
The results of this study indicate few, if any, dose-related effects on
reproduction or the development of progeny in rats treated with vinylidene
chloride in the drinking water at the dose levels tested (Nitschke et al., 1980).
A slight decrease in the fertility (number of litters/number of mated dams) of
the f^ rats was noted in controls and the two highest dose groups (120 and 200
ppm) when compared to historical controls of Sprague-Dawley rats. Survival of f2
progeny was decreased in all treated groups but this response was not dose-
related since animals treated at 100 ppm vinylidene chloride showed the greatest
mortality, while groups treated at 50 and 200 ppm were similar. Decreased
survival during the lactation period in the f_. generation did appear dose-
related, but survival in the f_B litters of dams given 100 and 200 ppm vinylidene
chloride was higher than controls. It was not possible to ascertain the cause,
whether it be prenatal or postnatal exposure to vinylidene chloride, of the
decreased survival in the f_fl generation mice. No decreased survival in any
10-68
-------
group of the f-,B, including those cross-fostered (control group dams rearing 200
ppm progeny and vice versa), was noted. The decreased survival of the f^
generation was negated since the similarly treated f__ generation showed no
j^
dose-related, decreased survival.
Fetal survival, litter size, and growth rates of the neonates showed no
consistent dose-related effects for any generation during this study. At
necropsy, histopathological examination revealed hepatocellular fatty change and
pronounced hepatic lobular patterns in adult f1 rats treated with 100 or 200 ppm
vinylidene chloride. Fatty changes of the hepatocytes were also noted in adult
f_ females. Liver degeneration was noted in f1 adults treated with 100 or 200
ppm vinylidene chloride and at all dose levels in f2 adults. No dose-related
malformations or changes in organ weights were revealed after necropsy of wean-
lings in any dose group or generation (Nitschke et al., 1980).
In summary, the three generation study by Nitschke et al. (1980) indicated
that vinylidene chloride in drinking water of rats at 50, 100, or 200 ppm did not
adversely affect reproduction or neonatal development. Neonatal survival was
decreased in the f_. litters, but contradictory results were shown in the f_B and
f0 litters. Histopathological examination revealed mild dose-related hepato-
3C
toxic effects in adult rats treated with vinylidene chloride, but no dose-related
changes or malformations were seen in neonates. Reproductive capacities in
adults did not appear altered by vinylidene choride exposure (Nitschke et al.,
1980).
10-69
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10.4 MUTAGENICITY
10.4.1 Mutagenicity in Bacteria
Numerous studies have shown vinylidene chloride to be a bacterial mutagen
(Table 10-20). This is largely due to the use of vinylidene chloride as a
positive control in studies analyzing the mutagenicity of chemicals that are
gases at or near room temperature. A variety of exposure conditions have been
utilized in these studies including standard plate incorporation, liquid
suspension, and host mediation. The most commonly used method, however, involves
exposure of bacteria to a defined atmosphere of vinylidene chloride in an
enclosed vessel.
Bartsch et al. (1975) tested vinylidene chloride in the Ames assay using
strains TA100 and TA1530, both of which respond to base-pair mutagens. Tester
cells were exposed to 0, 0.2%, 2%, and 20% vinylidene chloride in air (v/v) for
4 hours. The concentrations of vinylidene chloride in the incubation medium
after 2 hours of exposure to 0.2%, 2%, or 20% were 3.3 x 10~4M, 3.3 x 1CT3M,
or 3.3 x 10"%, respectively. These concentrations did not increase further
with incubations of up to 7 hours. Dose-related increases in the mutant
frequencies were seen at 0.2% and 2% vinylidene chloride and were dependent on
the presence of phenobarbital-induced mouse liver S9 in the medium. The maximum
response was seen in TA100 with an approximate 10-fold increase over baseline.
The response decreased at 20% in both bacterial strains; the authors suggested
that this may have been due to an inactivation of microsomal enzymes by vinylidene
chloride. S9 derived from mouse liver was more effective at activation
than S9 from kidney or lung. S9 derived from phenobarbital treated mice was
more active than S9 derived from untreated animals, and S9 from mice was much
more active than S9 from rats. The presence of N-acetyl-cysteine or N-acetyl-
methionine in the medium decreased the mutagenic response by 80%. These latter
10-70
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groups.
In a later publication, Bartsch et al. (1979) examined the effects of
various chemical pretreatments on the activity of rat liver derived S9 mix.
Pretreatment with phenobarbital and 3-methylcholanthrene resulted in increased
activity (200% and 150%, respectively) while pretreatment with pregnenolone-
16-alpha-carbonitrile, aminoacetonitrile, dibenamine, and dilsulfiram resulted
in decreased activity. In this same study S9 derived from four human liver
samples was also shown to be capable of activating vinylidene chloride to
mutagenic products. On the whole, human liver S9 was only one-fifth as active
as mouse S9.
In a recent study Oesch et al. (1983) compared the relative activities of
S9 derived from various species and organs at activating vinylidene chloride to
mutagenic products. The target organisms were five Ames tester strains (TA1535,
TA1537, TA98, TA100, and TA92) and E^. coli WP2 uvrA cells. Cultures were
incubated at 375, 2250, 4500, 10500, and 22500 ppm for 6 hours. Positive
results were seen at all doses with mouse liver S9 mix. The following sequence
of activating potencies were observed in TA100: mouse liver and Chinese hamster
liver > rat liver > human liver > Chinese hamster kidney > male mouse kidney >
rat kidney and female mouse kidney. The last two sources generated S9s which
were almost without 'activity. The authors demonstrated a correlation between
vinylidene chloride treatment and the activity of .the microsomal enzyme gluta-
thione transferase. They suggested that this may be a contributing factor in
species and sex differences noted for vinylidene chloride toxicity and carcino-
genicity.
Another study that examined the effects of species, organ, and induction
state on the activity of S9 mix was reported by Jones and Hathway (1978c). Ames
10-74
-------
strain TA1535 was exposed to 5% vinylidene chloride for 72 hours. S9 mixes
derived from mouse liver and kidney were more efficient at activation than
were S9 mixes derived from rat liver and kidney. In general, pretreatment of
both rats and mice with Aroclor 1254 increased the activity of S9 mixes. S9
derived from uninduced marmoset liver failed to generate mutagenic products as
did liver S9 from an uninduced human being. A second human-derived liver S9
mix from an individual after long-term phenobarbital treatment was active at
generating mutagenic metabolites.
Baden and coworkers (Baden et al., 1976, 1977, 1978) have used both liquid,
incubation and gaseous exposure of several Ames strains to analyze the mutagenic.
properties of a variety of volatile anesthetics. In all these studies
vinylidene chloride was used as a positive control. For the liquid suspension
assay the concentration typically used was 3% for 1 hour, and the target
organisms were TA100 and TA1535. For gaseous exposure TA98 and TA100 were
incubated in an atmosphere of 3% vinylidene chloride for 8 hours. Typical
responses in the presence of Aroclor—induced rat S9 mix averaged four to five
times background. These authors have also shown that pretreatment of rats
with an enzyme inducer such as Aroclor, greatly enhances the activity of
liver-derived S9 mixes, and that S9 mix derived from human liver is also active
at transforming vinylidene chloride to mutagenic products (Baden et al.,
1976, 1978).
In addition to the studies cited above, a number of additional studies
indicate that vinylidene chloride is positive in the Ames assay as well as in
other bacterial tests. Simmon et al. (1977) showed a time related increase in
the number of TA100 revertants exposed to an atmosphere of 5% vinylidene
chloride in air for 3, 6, 9, and 12 hours. Little activity was observed in the
absence of S9 mix (Figure 10-6).
10-75
-------
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300
200
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HOURS OF EXPOSURE TO 5 PERCENT VINYLIDENE CHLORIDE
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Figure 10—6. Mutagenic activity of vinylidene chloride in the presence and in
the absence of metabolic activation.
SOURCE: Simmon et al., 1977.
10-.76
-------
In a study characterizing the stability of metabolic activation systems,
Malaveille et al. (1977) showed time dependent increases in the numbers of
TA100 revertants after incubation in an atmosphere of 2% vinylidene chloride
in air for 2, 4, and 6 hours. The largest increases in the number of revertants
were up to ten times background. In agreement with other studies, S9 derived
from phenobarbital-treated mice was more active than S9 from untreated animals.
Similarly, Waskell (1978) showed a time dependent increase in the numbers
of TA100 revertants after incubation in an atmosphere of 5% vinylidene chloride
in air for 4 and 6 hours. This activity was dependent on the presence of a
rat liver S9 mix.
Greim et al. (1975), using a liquid suspension protocol, examined
vinylidene chloride-induced reverse mutation at three loci (gal, arg, nad) and
forward mutation at one locus (MTR) in E^. coli K12. Cells were incubated in
medium containing 2.5 mM vinylidene chloride for 2 hours and tested for
reversion to prototrophy (gal, arg, nad) or resistance to 5—methyl—tryptophan
(MTR). A significant increase in the mutant frequency was seen only at the
arg locus (2.3-times control) when cells were incubated in the presence of
phenobarbital—pretreated mouse S9 mix.
In a study reported in abstract form only, Cerna and Kypenova (1977)
reported that vinylidene chloride was positive in the bacterial spot test and
the Ames assay using host-mediated activation. In the spot test, 0.05 mL of
vinylidene chloride at 100%, 10%, and 1% was tested using strains TA1950, TA1951,
TA1952, TA1535, TA1538, TA100, and TA98. Positive results in strains sensitive
to both base-pair and frameshift mutagens were seen only for 100% vinylidene
chloride. In the host-mediated assay, female ICR mice were injected with
vinylidene chloride at the LD5Q and one-half of the LD5Q, and mutagenicity was
tested in strains TA1950, TA1951, and TA1952. Although positive results were
10-77
-------
noted, they were inversely related to dose.
There has been speculation as to the nature of the ultimate mutagen formed
during metabolic activation of vinylidene chloride. Bartsch et al. (1975)
have suggested that an alkylating intermediate is formed, since mutations
occur in £. typhimurium strain TA1530 which is reported by Ames et al. (1973)
to be specifically reverted by monofunctional alkylating agents. Nevertheless,
an alkylating compound was not identified in the trapping agent,
4-(4'-nitrobenzyl)-pyridine, when a gas that contained vinylidene chloride was
passed through a mouse S9 activating system, even though this system provided
activated metabolites that mutated S_. typhimurium strain TA100 (Barbin et al.,
1978). It has also been suggested that an unstable oxirane, possibly
1,1-dichloroethylene oxide, may be formed during metabolism and that this
metabolite plays a significant role in the mutagenic activity of vinylidene
chloride (Greim et al., 1975; Bonse et al., 1975; Bartsch et al., 1979).
Presently, however, there is little evidence identifying the exact metabolic
intermediates that constitute the ultimate mutagenic form(s) of vinylidene
chloride.
10.4.2 Mutagenicity in Yeast and Plants
Vinylidene chloride was tested for the induction of point mutations and
mitotic gene conversion in the diploid strain (D7) of the yeast Saccharomyces
cerevisiae (Bronzetti et al., 1981, Table 10-21). Cells were treated in a
suspension containing 10, 20, 30, 40, or 50 mM vinylidene chloride in the
presence and absence of mouse liver S10 mix. In a second procedure employing
host activation, yeast cells were injected in the retroorbital sinus of male
Swiss albino mice (CD strain) and collected after 4 hours from the liver,
lungs, and kidneys.
In the suspension assay a dose-related increase in revertants (Ilv+) and
10-78
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convertants (Trp+) was seen in the presence of S10 isolated from Aroclor 1254
treated mice. The increases in revertants (up to eight times control) and
convertants (up to five times control) were noted at vinylidene chloride
concentrations that permitted more than 50% cell survival.
In the host mediated assay, mice were given an acute oral dose of 400
mg/kg vinylidene chloride, or were chronically treated (100 mg/kg, 5 days/week
with a total of 23 administrations, plus 200 mg/kg on the day of the assay;
total dose was 2500 mg/kg). In the acute protocol there was a 10-fold increase
in the number of convertants and a 12-fold increase in the number of revertants
isolated from the liver, a 6-fold increase in convertants and a 5-fold increase
in revertants isolated from the kidney, while neither end point was increased in
cells isolated from the lung. In chronically exposed mice, convertants were in-
creased 13-fold and 6-fold in the liver and kidney, respectively, and did not
increase in the lung, while revertants increased 6-fold and 30-fold in the liver
and kidney, respectively, and again were negative in the lung. 4-methoxyphenol,
which is often added to vinylidene chloride as an antioxidant, was negative at
a concentration 10-fold higher than normally found in vinylidene chloride.
The results of testing vinylidene chloride in tradescantia were reported
in a Gene-Tox publication that evaluated the data base associated with testing
in this plant (Van't- Hof and Schairer, 1982, Table 10-21). The hybrid clone
of tradescantia used in these studies (4430) is heterozygous at a flower-color
locus. The dominant gene results in a blue flower, while inactivation of this
locus allows the expression of the recessive allele resulting in a pink flower.
Vinylidene chloride was reported to give negative results after exposure to
1288 ppm for 6 hours, while positive results (p < 0.05) were reported after
exposure to 22 ppm for 24 hours. Clearly, these results are difficult to
reconcile. Unfortunately, the original reference from which these results
10-80
-------
were derived was not cited in the Gene-Tox report.
10.4.3 Mutagenicity in Cultured Mammalian Cells
Vinylidene chloride was tested for its ability to induce gene mutations
at the hypoxanthine guanine phosphoribosyl transferase and sodium—potassium
ATPase loci in V79 cells (Drevon and Kuroki, 1979; Table 10-22). Cultured
cells were exposed to 2% and 10% vinylidene chloride in air for 5 hours. No
cytotoxicity and no increase in the mutant frequencies were noted for
vinylidene chloride-exposed cells incubated in the presence of SI5 from mouse
liver or in the absence of microsomal enzymes. Cells exposed to vinylidene
chloride in the presence of rat SI5 showed 76% and 96% cytotoxicity at
concentrations of 2% and 10%,.respectively. Again, there were no increases in
the frequencies of mutants. Both rats and mice had been pretreated with
phenobarbital, and positive results were reported when vinyl chloride was
similarly tested.
10.4.4 Mutagenicity in Mammalian Cells In Vivo
The only report on the cytogenetic effects of vinylidene chloride
was published in abstract form (Cerna and Kypenova, 1977, Table 10-22). Female
ICR mice were given vinylidene chloride in a single dose (one-half of the LD5Q)
or in repeated applications (one-sixth of the LD5Q, five intraperitoneal
doses given at one day intervals). Animals were killed 6, 24, and 48 hours
following the last injection, and the bone marrow was analyzed for aberrations.
No increase in chromosomal aberrations was found in any treatment group.
The capacity of vinylidene chloride to alkylate DNA and induce unscheduled
DNA synthesis in vivo was studied by Reitz et al. (1980, Table 10-22). These
investigators exposed CD-I mice and Sprague-Dawley rats to l^C-labeled vinylidene
chloride vapor for 6 hours at 10 and 50 ppm (mouse only). DNA was then extracted
10-81
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from the kidneys and livers and analyzed for covalently bound radiolabel. The
greatest level of binding was found in the kidneys of mice exposed to 50 ppm
(30 alkylations/10" nucleotides) followed by the kidneys of mice exposed to 10
ppm (11 alkylations/10" nucleotides). Livers of exposed mice showed lower but
still detectable levels of binding. Rats exposed to 10 ppm vinylidene chloride
showed 2.0 and 0.87 alkylations/10^ nucleotides for the kidney and liver, respec-
tively. Radioactivity was eliminated from the kidney and liver of 50 ppm mice
in a biphasic manner with a half-life of 83 and 91 hours, respectively. Rates
of elimination were dose related—the lower doses being eliminated more rapidly.
Unscheduled DNA systhesis (UDS) was measured in the kidneys and livers of
mice exposed for 6 hours to 10 and 50 ppm vinylidene chloride. Immediately
after vinylidene chloride exposure, the animals were injected with %-thymidine
alone or with ^H-thymidine plus hydroxyurea. This latter drug is given "to
block most of the replicative DNA synthesis." The authors claimed a significant
increase in UDS only in kidneys of mice exposed to 50 ppm. No effects were
claimed for liver at 50 ppm or for either organ at 10 ppm. The validity of
all these data is questionable for two reas'ons. First, the control values for
normal DNA synthesis varied from 12.9 to 80.5 cpm/mg DNA in the liver of otherwise
untreated mice and from 2.57 to 18.4 cpm/mg DNA in the livers of hydroxyurea-
treated mice. Second, the effects of hydroxyurea on normal DNA synthesis and
UDS could not be separated since this compound failed to suppress all scheduled
DNA synthesis. Thus, in the one instance where the authors claimed a significant
increase in UDS, the specific activity of DNA was lower than in the control.
The effect of vinylidene chloride on the induction of dominant lethals
has been studied in both mice (Anderson et al., 1977) and rats (Short et al.,
1977, Table 10-22). In the mouse study, 8- to 12-week-old CD males were exposed
to 10, 30, and 50 ppm in air 6 hours/day for a total of 5 days. Matings began
10-84
-------
immediately after dosing and continued (one male with two virgin females) for
a total of 8 weeks. Females were killed in midgestation after 14 to 16 days
of pregnancy. Vinylidene chloride at 50 ppm reduced fertility in treated
males up to 6 weeks following treatment. In none of the treatment groups were
there significant effects on the number of implants, the number of females
with _>. °ne early death, the mean number of early deaths per pregnancy, or the
early deaths as a percent of total implants. Vinyl chloride, which was also
tested in this study, was also reported to be negative. The positive controls,
cyclophosphamide, which was given intraperitoneally and ethylmethanesulphonate,
which was given per os, gave positive responses.
In the rat study, male CD rats were exposed to 55 ppm vinylidene chloride
in air 6 hours/day, 5 days/week, for 11 weeks (Short et al., 1977). During
week 11 of exposure, each male was housed with two unexposed virgin females
for at least seven successive evenings or until the male mated with two females.
Females were killed on day 13 of gestation, and the number of corpora lutea
and implants were determined. As in the mouse study there was a significant
decline in the number of pregnant females produced by exposed males. No effect
was observed regarding the number of corpora lutea per dam, number of implants
per dam, percent implants per corpora lutea, or percent viable embryos per
total implants.
10.4.5 Summary
A large number of studies indicate the vinylidene chloride is mutagenic
to bacteria and that this activity is largely dependent on microsomal
activation. Vinylidene chloride was reported to produce positive results for
gerie reversion and conversion in yeast, which was also dependent on metabolic
activation, and was positive in tradescantia. In mammalian systems vinylidene
chloride failed to induce gene mutations in V79 cells at two seperate loci,
10-85
-------
failed to induce chromsomal aberrations in mouse bone marrow in vivo, and
failed to induce dominant lethals in either mice or rats. Vinylidene chloride
was found to alkylate the DNA of mice exposed through inhalation and may
have caused unscheduled DNA synthesis in the kidneys of similarly exposed
mice.
Analysis of the data relating to the potential of vinylidene chloride
to behave as a human germ-cell mutagen indicates that based on the criteria
established in the Agency's Proposed Guidelines for Mutagenicity Risk Assessment,
the evidence at the present time is classified as limited. This designation
indicates that there are insufficient data on either mutagenicity or interaction
with germ cells to classify the evidence as either sufficient or suggestive
of potential germ-cell mutagenicity. However, available data also do not
permit the classification of vinylidene chloride as a non-germ cell mutagen.
10-86
-------
10.5 CARCINOGENICITY
10.5.1 Animal Studies
There have been a number of laboratory investigations of the carcinogenic
potential of vinylidene chloride. These studies have been performed using
rats, mice, and hamsters, with vinylidene chloride administered by inhalation,
gavage, incorporation into drinking water, subcutaneous injection, and topical
applications. These results are summarized in Table 10-23, and have also been
summarized by Chu and Milman (1981). Of the studies performed, only the
results reported by Maltoni et al. (1985) indicated a statistically significant
positive carcinogenic effect resulting from vinylidene chloride treatment.
Maltoni et al. (1985) exposed Sprague-Dawley rats, Swiss mice, and
Chinese hamsters to vinylidene chloride (99.95% pure, Table 10-24) in an
inhalation chamber for 4 hours daily, 4 to 5 days a week for 12 months. The
exposure concentration used depended on the species' susceptibility to vinyli-
dene chloride's toxic action; the highest tolerated dose in mice and rats was
used as the maximum concentration. The exposure level for hamsters was not
selected on the basis of achieving a maximum tolerated dose. Rats, initially
16 weeks old, were exposed to vinylidene chloride at 150, 100, 50, 25, and 10
ppm (Table 10-25), while mice, initially 16 weeks old or 9 weeks old, were
chronically exposed to vinylidene chloride at 25 and 10 ppm (Table 10-26), and
hamsters, initially 28 weeks old, were chronically exposed to a concentration
of vinylidene chloride at 25 ppm (Table 10-27). In addition, rats, initially 9
weeks old, were treated by gavage with 20, 10, 5, and 0.5 mg/kg/day of vinyli-
dene chloride dissolved in olive oil (Table 10-28). Body weights were recorded
every 2 weeks during the 12-month treatment period and monthly thereafter. The
studies were completed in 137 weeks for the inhalation study in rats, 147
weeks for the ingestion study in rats, 121 weeks for the inhalation study in
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03 I-
10-89
-------
TABLE 10-24. GAS CHROMATOGRAPHY ANALYSIS OF VINYLIDENE CHLORIDE
Compound
Amount
Vinylidene chloride (1,1-Dichloroethylene)
1,2-Dichloroethylene trans
Acetone
Methylene chloride (Dichloromethane)
Monochloroacetylene and Dichloroacetylene
Pararaethoxyphenol (as stabilizer)
999.5 g/kg
0.4 g/kg
0.1 g/kg
0.05 g/kg
0.02 g/kg
200 ppm
SOURCE: Maltoni et al., 1985.
TABLE 10-25. EXPERIMENT DT401: EXPOSURE BY INHALATION TO VINYLIDENE
CHLORIDE IN AIR AT 150, 100, 50, 25, AND 10 PPM,
4 HOURS DAILY, 4-5 DAYS WEEKLY, FOR 52 WEEKS
Group
nos.
I
II
III
IV
V
VI
Total
1
Concentration
200 - 150 ppma
100 ppm
50 ppm
25 ppm
10 ppm
No treatment
[Sprague-Dawley
Males
60
30
30
30
30
100
250
Animals
rats, 16 weeks old at start)
Females
60
30
30
30
30
100
280
Total
120
60
60
60
60
200
560
Two treatments only because of the high toxicity of this dose level.
SOURCE: Maltoni et al., 1985.
10-90
-------
TABLE 10-26. EXPOSURE BY INHALATION TO VINYLIDENE CHLORIDE IN AIR
AT 200, 100, 50, 25, AND 10 PPM, 4 HOURS DAILY,
4-5 DAYS WEEKLY, FOR 52 WEEKS
Animals
Swiss mice 16 weeks old (groups I,
II, III, IV, V, VI) and 9 weeks old
(groups IV bis and VII)
XJi WfU.p
nos.
I
II
III
IV
o
IV bis
V
VI
VII
Total
iLCdi-lUCLLL.
Concentration
200 ppm
100 ppm
50 ppm
25 ppm
25 ppm
10 ppm
No treatment
(Controls)
No treatment
(Controls)
Length
2 days ,
2 daysd
1 week
52 weeks
52 weeks
52 weeks
Males
60
30
30
30
120
30
100
90
490
Females
60
30
30
30
120
30
100
90
490
Total
120
60
60
60
240
60
200
180
980
The treatment started two weeks later than in other groups.
Controls to the groups I, II, III, IV, V.
Controls to the group IV bis.
The treatment was interrupted because of the high toxic effects and high
mortality.
SOURCE: Maltoni et al., 1985.
10-91
-------
TABLE 10-27. EXPERIMENT BT405: EXPOSURE BY INHALATION TO VINYLIDENE CHLORIDE
IN AIR AT 25 PPM, 4 HOURS DAILY, 4-5 DAYS WEEKLY, FOR
52 WEEKS
Group
nos.
I
II
Total
SOURCE:
Concentration
25 ppm
No treatment
(Controls)
Maltoni et al. , 1985.
Animals
(Chinese hamsters , 28 weeks old
Males
30
18
48
Females
30
17
47
at start)
Total
60
35
95
10-92
-------
TABLE 10-28. EXPERIMENT BT403: EXPOSURE BY INGESTION (STOMACH TUBE) TO
VINYLIDENE CHLORIDE IN OLIVE OIL AT 20, 10, AND 5 MG/KG BODY WEIGHT,
ONCE DAILY, 4-5 DAYS WEEKLY, FOR 52 WEEKS
Group
nos .
I
II
III
IV
Concentration
20 mg/kg
10 mg/kg
5 mg/kg
None (olive oil
(Controls)
(Sprague-Dawley
Males
50
50
50
alone) 100
Animals
rats , 9 weeks
Females
50
50
50
100
old at start)
Total
100
100
100
200
Total
250
250
500
EXPERIMENT BT404: EXPOSURE BY INGESTION (STOMACH TUBE) TO
VINYLIDENE CHLORIDE IN OLIVE OIL AT 0.5 MG/KG BODY WEIGHT, ONCE DAILY,
4-5 DAYS WEEKLY, FOR 52 WEEKS
Group
nos .
I
II
Concentration
0.5 mg/kg
None (olive oil
(Sprague-Dawley
Males
50
82
Animals
rats , 9 weeks
Females
50
77
old at start)
Total
100
159
Total
alone) (Controls)
132
127
259
SOURCE: Maltoni et al., 1985.
10-93
-------
mice, and 157 weeks for the inhalation study in hamsters. Animals were al-
lowed to survive until spontaneous death. Each animal was necropsied, and
normally appearing tissues and organs, as well as tumors and lesions, were
examined histopathologically.
No treatment-related effect on body weights in rats was evident. Body
weight data for mice and hamsters were not reported, but no effect attribut-
able to treatment was noted.
There were no significant (p < 0.05) differences in tumor development
between control and treated hamsters.
A number of neoplastic lesions were observed in control and treated rats,
with no treatment- or dose-related effect in evidence from either inhalation
exposure or gavage administration. The 1977 report by Maltoni et al.
presented interim (82 weeks) results showing an increased incidence of mammary
tumors in treated rats compared to controls in the inhalation study; however,
at that time, a clear dose-related effect was not evident, spontaneous mammary
tumor incidence in female controls was 32%, and histopathologic diagnosis of
the mammary tumors was ongoing. The final mammary tumor data for female rats
in this study, as described in the Maltoni et al. (1985) report and Table
10-29 herein, show statistically significant (p < 0.05) increases in the total
number of tumor-bearing animals in the 10 ppm and 100 ppm groups compared to
controls, and in the number of animals with fibromas and fibroadenomas in each
treatment group compared to controls. However, there was no clear dose-related
increase in mammary tumor incidence, latency time for mammary tumor formation
was similar among all groups, there was a high (61%) incidence of spontaneously
formed mammary tumors in controls, and mammary carcinoma incidence in treated
groups was not significantly (p < 0.05) different from and was actually con-
sistently less than that of controls. Hence, the evidence for a carcinogenic
10-94
-------
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10-95
-------
effect of inhaled vinylidene chloride in female Sprague-Dawley rats, as mam-
mary tumors, in this study would appear to be inconclusive.
In male Swiss mice, kidney adenocarcinomas were observed following inha-
lation exposure to vinylidene chloride at 25 ppm (Table 10-30). In female
Swiss mice, mammary carcinoma incidence in both the 10 ppm and combined 25 ppm
groups compared to combined controls was significantly (p < 0.01) increased,
and a small incidence of mammary carcinomas was evident in females exposed to
vinylidene chloride at 50, 100, or 200 ppm for 1 week or less (Table 10-30).
The incidence of pulmonary adenomas was significantly (p < 0.01) increased in
male and female mice exposed to vinylidene chloride at 10 and 25 ppm compared
to controls (Table 10-30); however, pulmonary carcinomas were not found in any
of the mice.
Maltoni et al. (1985) concluded that the kidney tumors in male mice
developed in response to vinylidene chloride treatment, particularly since no
corresponding spontaneous tumors were noted in the 190 control male mice.
Maltoni et al. (1985) also concluded that the toxic and carcinogenic effects
of vinylidene chloride may depend on species, strain, and sex of the tested
animals, and that the observed kidney tumors in Swiss mice may be a strain-
specific phenomenon. It has been noted that male mice of several strains are
particularly sensitive to the toxic effects of vinylidene chloride (Maltoni et
al., 1977; Maltoni, 1977; Maltoni and Patella, 1983; Maltoni et al., 1985;
Henck et al., 1979, 1980). The kidney and liver appear to be the major target
organs for vinylidene chloride toxicity. Many authors have postulated that a
reactive metabolite is responsible for both effects of vinylidene chloride.
The primary target organ for vinylidene chloride-induced toxicity in the male
mouse is the kidney (McKenna et al., 1977, 1978a, b), although the liver is
also a target organ for toxicity in mice. The kidney is also the target organ
10-96
-------
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10-97
-------
for carcinogenesis in the Maltoni et al. (1985) study. Degeneration and
necrotic changes in kidneys, especially in the tubular region, were noted by
Maltoni et al. (1985) in male Swiss mice that died from exposure to 200 ppm
vinylidene chloride, 4 hours daily, for 2 days. These investigators observed
a similar effect in the kidneys of mice that developed kidney adenocarcinomas
in the lifetime inhalation study. Therefore, they recommend that further
studies on animals of other species and strains would provide additional use-
ful information.
The significant (p < 0.01) increase in mammary carcinomas in treated
female Swiss mice would indicate evidence for the carcinogenicity of vinyli-
dene chloride in these animals. However, Maltoni et al. (1985) concluded that
for mice a direct relationship between the induction of mammary tumors, as well
as pulmonary adenomas, and vinylidene chloride exposure needs further clarifi-
cation.
Maltoni et al. (1985) also stated that survival of mice exposed to 10 and
25 ppm vinylidene chloride was higher than survival of the control groups.
Numbers of mice surviving at 27, 36, and 55 weeks are given in Table 10-30,
herein, and Maltoni et al. (1977) observed an interim survival for female mice
of: (1) 47% in the 25 ppm group (IV), 20% in the 10 ppm group (V), and 21% in
the matched control group (VI) when these groups were 98 weeks old, and (2) 40%
in the 25 ppra group (Group IV bis) and 40% in the matched control group (VII)
when these groups were 91 weeks old. Maltoni et al. (1985) presented survival
data and their statistical analyses of pulmonary adenoma and mammary carcinoma
data in mice to support their conclusions quoted above. Their analyses include
data presented in Table 10-31 which were obtained from the Maltoni et al.
(1985) report. The authors noted that "with one exception" slightly higher
mean survival times for the treatment groups were not significantly (p < 0.05)
10-98
-------
TABLE 10-31. STATISTICAL ANALYSES OF SURVIVAL, MAMMARY CARCINOMA INCIDENCE
AND PULMONARY ADENOMA INCIDENCE FOR MALE AND FEMALE SWISS MICE IK A
CARCINOGENICITY STUDY OF VINYLIDENE CHLORIDE
Mean and Standard Deviation (in weeks) of lifetime
(Test of Krauth, one-sided)
Male
Female
„ a
Group
VII
VI
V
IV bis •
IV
Animals
Lifetime
at start Mean
90
100
30
120
30
70.
75.
83.
75.
79
.7 C
.4 C
.7 x
.0
.6 *
Stand. Dev.
22.
22.
15.
15.
17
.58
.08
.77
.85
.03
Animals
at start
90
100
30
120
30
Lifetime
Mean
81.
81.
87.
84.
90.
.0
.1
.5
.3
.0
Stand
C
C
*
X
18
20
12
17
18
. Dev.
.51
.32
.97
.41
.40
Tumor incidence for MA and PA at the end of experiment; N.TU (respectively
N.MA, N.PA) is the number of animals with tumors (respectively MA, PA
(Exact Fisher Test, one-sided)
Male
Female
Group
VII
VI
V
IV bis
IV
Animals
at start
100
30
30
90
120
N.TU
7
11 X
11 X
7
43 x
N.MA°
0
0
0
0
1
N.PAd
3
11 x
7 x
3
16 x
Animals
at start
. 100
30
30
90
120
N.TU
15
15 x
17 x
12
40 x
N.MA
2
6 x
4 *
1
12 x
N.PA
4
3
7 x
2
11 *
Tumor incidence for MA and PA at the end of experiment; N.MA (respectively
N.PA) is the number of animals with MA (respectively PA) (Logrank test)
Male
Female
Group
VII
V
IV
VII
IV bis
Animals
at start
100
30
30
90
120
N.MA
0
0
0
0
1
N.PA
3
11 x
7 x
3
16 *
Animals
at start
100
30
30
90
120
N.MA
2
6 x
4
1
12 *
N.PA
4
3
7
2
11
•i-
VII - Matched control for Group IV bis, VI - Matched control for Groups V and IV,
V - 10 ppm VDC, IV bis and IV - 25 ppm VDC exposure.
N.TU — Number of animals with tumors.
N.MA — Number of animals with mammary tumors.
N.PA — Number of animals with pulmonary tumors.
C
control
*
p < 0.05
Xp < 0.01
SOURCE: Maltoni et al., 1985.
10-99
-------
different from those of their matched controls by a rank test of Krauth. The
significant (p < 0.05) differences shown in Table 10-31 for survival include
comparisons of Groups IV and V with Group VII, which was not the matched con-
trol group for these two treatment groups, and Group IV bis with Group IV,
which were the two groups exposed to 25 ppm vinylidene chloride; hence, the
authors indicated that "with one exception" significant differences in mean
survival were found only between groups which began their exposure at different
ages.
Statistically significant (p < 0.01) differences in tumor incidences
between control and treated mice shown in Table 10-30 were calculated using
the chi-square test by combining control and 25 ppm groups since, outside of
differences in age at the start of the study and the two-week difference in
the starting times of the study (Table 10-26), similar tumor incidences for
the separate control and 25 ppm groups were found with the same protocol.
Maltoni et al. (1985) found statistically significant (p < 0.05) increases in
mammary carcinoma and pulmonary adenoma incidences in treated mice compared to
matched control mice by the Fisher exact test (Table 10-31); however, their
analysis of these data by the Log Rank test, to take into account survival
patterns, indicated a lower level of statistical significance for these dif-
ferences between control and treated mice. A dose-related increase in tumor
incidence in treated mice was not clearly apparent from the data in Table 10-31.
In summary, the studies by Maltoni et al. (1985) show clearly significant
(p < 0.01) increases in the incidence of kidney adenocarcinomas in male Swiss
mice and mammary carcinomas in female Swiss mice chronically exposed to
vinylidene chloride. However, the authors concluded that the relationship
between vinylidene chloride exposure and mammary carcinoma induction in female
mice is difficult to evaluate since it is not dose-related. There was a sig-
10-100
-------
nifleant (p < 0.05) increase in the incidence of fibromas and fibroadenomas in
' each treated group of female Sprague-Dawley rats compared to controls in the
inhalation study; however, there were no significant (p < 0.05) increases in
mammary carcinoma incidence between treated and control rats, and there was no
clear dose-response for induction of mammary tumor in treated rats.
A broader evaluation of the carcinogenicity of vinylidene chloride by
Maltoni et al. (1985) might have been possible if exposure periods longer than
12 months had been used and if, at the beginning of treatment, younger animals,
such as weanlings, had been evaluated to cover the portion of their lifespans
during growth to adulthood. It is notable that of the two groups of male mice
exposed to 25 ppm vinylidene chloride, the group in which exposure was initia-
ted at 9 weeks experienced a higher incidence of kidney adenocarcinomas than
the group in which exposure initiation was delayed until 16 weeks. It does not
appear that doses as high as those maximally tolerated were used in the inhala-
tion study in hamsters and the gavage study in rats.
Viola and Caputo (1977) exposed male and female Wistar strain rats initi-
ally 2 months old in an inhalation chamber for 4 hours per day, 5 days per
week, to vinylidene chloride at 200 ppm (99.8% pure) for 5 months, followed by
an additional 7 months of reduced exposure to vinylidene chloride at 100 ppm
to avoid toxicity. All animals were observed until death (22 to 24 months).
Thirty untreated controls of each sex, 23 treated females, and 51 treated
males were examined for tumors. During the exposure period, a rapidly growing
mass appeared in the external ear duct of many of the animals, but on biopsy
examination, only signs of an inflammatory reaction were present with no indi-
cations of dermal or epidermal neoplasia. Tumors of the abdominal cavity were
present at the same incidence in both experimental (23%) and control (25%)
rats. Although histology of the tumors was described, there was no mention of
10-101
-------
which organs, if any, were routinely evaluated histologically for neoplastic
or pre-neoplastic changes. Furthermore, the 12-month exposure period was
shorter than potential lifetime exposures for laboratory rats. In a second
study using male and female Sprague-Dawley rats exposed to vinylidene chlo-
ride at 100 and 75 ppm (started in the summer of 1975) for an unspecified
duration, there was again no increased tumor incidence in the experimental
animals as compared with the controls. There were 30 rats in each control and
100 ppm group, and 21 females and 16 males in the 75 ppm group examined for
tumors. At the time of the report, only gross tumors were enumerated; results
from microscopic examination of the tissues from the Sprague-Dawley rats were
to be reported later. ,,
Lee et al. (1978), in a study primarily concerned with chronic inhalation
exposure of CD-I mice and CD rats (Charles River), initially about 2 months
old, to vinyl chloride (99.8% pure), exposed a group of rats and mice (36
males and 36 females) to a single 55 ppm concentration of vinylidene chloride.
Concurrent control groups exposed to inhalation of air alone consisted of 36
males and 36 females. The exposure was for 6 hours daily, 5 days per week for
12 months, at which time all surviving animals were terminated. Following
sacrifice, the brain, pituitary, thyroid, respiratory tract, alimentary canal,
urogenital organs, thymus, heart, liver, pancreas, spleen, mesenteric lymph
nodes, and other organs with gross pathological lesions were histologically
examined. The incidence of tumors observed in both rats and mice is given in
Table 10-32. There was no statistically significant (p < 0.05, Fisher Exact
Test) increase in tumors at any of the sites examined as compared with control
animals. However, two treated male rats developed hemangiosarcomas, one in a
mesenteric lymph node and one in the subcutaneous tissue; no such tumors
occurred in controls. Hemangiosarcomas of the liver occurred in three mice
10-102
-------
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10-103
-------
treated with vinylidene chloride; again, no such tumors occurred in controls.
The short duration (12 months) of this study may have precluded observing
tumors that have a long latency period.
In a follow-up study, Lee and coworkers (Hong et al., 1981) exposed 8 to
12 CD-I mice of each sex and 4 to 16 CD rats of each sex, initially 2 months
old, to vinylidene chloride vapors (99% pure) at a concentration of 55 ppm.
The mice were exposed 6 hours/day, 5 days/week for a period of 1, 3, or 6
months (12 mice of each sex were treated for 6 months), while the rats were
exposed on the same schedule for 1, 3, 6, or 10 months (16 rats of each sex
were treated for 10 months). Concurrent controls exposed to inhalation of air
alone consisted of 28 mice and 16 rats of each sex. All animals were observed
for an additional period of 12 months following exposure. Histologic examina-
tions were performed as described above in Lee et al. (1978). Focusing on
males and females, respectively, in the groups with the longest durations of
exposure, 18% and 21% of control mice, 50% and 42% of treated mice, 38% and
44% of control rats, and 79% and 56% of treated rats died before terminal
sacrifice. Although tumors were observed in some exposed and control animals,
the incidence of these tumors in treated animals was not significantly
(p < 0.05) increased over control levels (Table 10-33). The small number of
animals in each group weakens the ability of this study to detect a tumorigenic
response, and the exposure durations were considerably less than potential
lifetime exposures. A broader evaluation could have been made with additional
exposure levels in each study.
Two studies have been performed for the Manufacturing Chemists Associa-
tion to assess the effects of chronic inhalation and ingestion (in drinking
water) of vinylidene chloride. The studies were conducted in two phases, the
first for 90 days and the second for 2 years. Norris (1977) presented preli-
10-104
-------
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10-105
-------
minary results of these studies with a detailed final report of the drinking
water study presented by Humiston et al. (1978) and Quast et al. (1983). An
additional report of these two studies to the open literature was provided by
Rampy et al. (1977), and the final results of the inhalation study have been
presented by McKenna et al. (1982).
In the inhalation study (Rampy et al., 1977; McKenna et al., 1982),
Sprague-Dawley rats, with initial body weights of 250 to 300 g for males and
190 to 230 g for females, were exposed to vinylidene chloride (S99% pure) for
6 hours per day, 5 days per week for a period of 18 months, and animals that
survived the treatment were observed for an additional 6 months. A total of
86 males and 86 females per group were used for each exposure group plus a
concurrent untreated control group. The animals were initially exposed to
vinylidene choride at 10 or 40 ppm; however, after 5 weeks of exposure, an
interim kill revealed no effects of exposure, and the concentrations were
raised to 25 and 75 ppm, with these concentrations being used for the remain-
der of the experiment. Analytical and nominal atmospheric concentrations of
vinylidene chloride in inhalation chambers were equivalent. The overall
evaluation of toxicity included survival, body weights, organ weights, hema-
tology, urinalysis, clinical chemistry, cytogenetics, gross pathology, and
histopathology.
There were no overt signs of toxicity shown by the overall evaluation in
the treated groups, and a significant (p < 0.05) increase in mortality was
observed only in female rats exposed to 25 ppm during months 15 to 23 and 75
ppm at months 15, 17, and 21 (Tables 10-34 and 10-35). However, increases in
mortality in treated groups might have been influenced by histopathologically
diagnosed increases in chronic murine pneumonia incidence (number of rats with
pneumonia/cumulative number of animals examined) as follows: males - 0/86
10-106
-------
TABLE 10-34. VINYLIDENE CHLORIDE: A CHRONIC INHALATION TOXICITY
AND ONCQGENICITY STUDY IN RATS
CUMULATIVE PERCENT MORTALITY FOR MALE RATS
Months
on
Study
Number of rats
alive on day 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Terminal kill
30-Day Interim kill
6-Month Interim kill
12-Month Interim kill
26 Weeks cytogenetic
kill
Total rats in study
Control
number dead
(% dead)
86
1
1
1
1
1
3
. . 4
, 5
' 5
5
6
8
9
10
14
19
23
27
32
39
49
54
63
72
73
13
4
5
5
4
104
CD
(1)
(1)
(1)
CD
(4)
(5)
(6)
(6)
(6)
(7)
(9)
(11)
.(12)
(16)
(22)
(27)
(31)
(37)
(45)
(57)
(63)
(73)
(84)
(85)
Exposure
level
25 ppm
number dead
(% dead)
75 ppra
number dead
(% dead)
85
3
3
3
4
4
4
4
5
5
6
. 6
7
8
8
8
17
18
25
36
47
50
58
65
72
72
13
4
5
5
3
103C
(4)
(4)
(4)
(5)
(5)
(5)
(5)
(6)
(6)
(7)
(7)
(8)
(9)
(9)
(9)
(20
(21)
(29)
(42)
(55)
(59)
(68)
(77)
(85)
(85)
1
1
2
3
3
4
4
5
5
7
8
8
9
10
12
12
16
27
37
47
56H
66d
71
74
78
8
4
5
5
4
104
86
(1)
(1)
(2)
(4)
(4)
(5)
(5)
(6)
(6)
(8)
(9)
(9)
(ID
(12)
(14)
(14)
(19)
(31)
(43)
(55)
(65)
(77)
(83)
(86)
(91)
Excludes those rats in the interim kills and the cytogenetic kill.
Four rats per exposure level were added one month after start of study.
"Includes one rat designated for cytogenetics study but not used due to
death six weeks prior to cytogenetic kill.
Statistically different from control data when analyzed using Fisher's
Exact Probability test, p < 0.05.
SOURCE: McKenna et al., 1982.
10-107
-------
TABLE 10-35. VINYLIDENE CHLORIDE: A CHRONIC INHALATION TOXICITY
AND ONCOGENICITY STUDY IN RATS
CUMULATIVE PERCENT MORTALITY FOR FEMALE RATS
Months
on
study
Number of rats
a
alive on day 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
Terminal kill
30-Day Interim kill
6-Month Interim kill
12-Month Interim kill
26 Weeks cytogenetic
killb
Total rats in study
Control
number dead
(% dead)
84
0
0
0
1
1
1
1
1
1
1
2
2
4
4
c
8
9
16
23
30
39
46
56
64
65
19
4
5
5
4
102
(0)
(0)
(0)
(1)
CD
(1)
(1)
(1)
(1)
(1)
(2)
(2)
(5)
(5)
(6)
(10)
(11)
(19)
(27)
(36)
(46)
(55)
(67)
(76)
(77)
Exposure
level
25 ppm
number dead
(% dead)
86
0
0
0
0
0
1
1
1
3
3
6
6
9
10
18C
19C
19°
29c
37c
49c
55'
59°
65
72
75
11
4
5
5
4
104
(0)
(0)
(0)
(0)
(0)
(1)
(1)
(1)
(4)
(4)
(7)
(7)
(11)
(12)
(21)
(22)
(22)
(34)
(43)
(57)
(64)
(69)
(76)
(84)
(87)
75 ppm
number dead
(% dead)
0
0
0
0
0
1
1
1
1
1
1
5
6
1
13C
16
18C
20
29
41
51C
54
61
68
68
16
4
5
5
4
102
84
(0)
(0)
(0)
(0)
(0)
(1)
(1)
(1)
(1)
(1)
(1)
(6)
(7)
(8)
(16)
(19)
(21)
(24)
(35)
(49)
(61)
(64)
(73)
(81)
(81)
aExcludes those rats in the interim kills and the cytogenetic kill.
Four rats per exposure level were added one month after start of study.
Statistically different from control data when analyzed using Fisher's
Exact Probability test, p < 0.05.
SOURCE: McKenna et al., 1982.
10-108
-------
control, 26/85 low dose, 24/86 high dose; females - 9/84 control, 21/86 low
dose, 22/84 high dose. Although control cages were in the inhalation chamber
room during exposures, control animals were not placed in the inhalation
chambers. Decreased body weights in both treated groups of male rats compared
to controls are indicated in Table 10-36, but the relationship to a direct
effect of vinylidene chloride appears rather uncertain in that a consistent
slight but significant (p < 0.05) decrease is evident only in the low-dose
group of males, no clear dose response is evident, and information on food
consumption could have shown whether this could have affected the body weight
trends shown. Body weights between control and treated female rats were
similar (Table 10-37).
Treatment-related induction of non-neoplastic lesions was not apparent,
with the possible exception of ovarian cysts in high-dose females [6/84 in
controls; 8/86 in the low-dose group; 14/84 (p < 0.05) in the high-dose
group]. An increase in midzonal fatty changes in the livers of treated female
rats was evident [1/84 in controls; 6/86 (p > 0.05) in the low-dose group;
8/84, (p < 0.05) in the high-dose group] which may be treatment-related.
However, these changes were mainly evident in females sacrificed at the end of
exposure at 8 months, and only 1 high-dose female had this midzonal fatty
change in liver during the 6-month post-exposure period. Furthermore, the
total numbers of females with any type of fatty change in liver were as fol-
lows: 15/84 controls, 13/86 low-dose rats, and 16/84 high-dose rats.
Vinylidene chloride exposure did not result in significant (p < 0.05)
increases in tumor incidence in this study, except for the mammary tumor data
discussed below. Mammary tumor data are presented in Table 10-38 for compari-
son with mammary tumor data on female Sprague-Dawley rats exposed to vinyli-
dene chloride in the inhalation study by Maltoni et al. (1985; Table 10-26).
10-109
-------
TABLE 10-36. VINYLIDENE CHLORIDE: A CHRONIC INHALATION TOXICITY
AND ONCOGENICITY STUDY IN RATS
MEAN BODY WEIGHT FOR MALE RATS
Study
Month
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Time
Day
0
8
13
20
26
39
52
79
113
140
174
201
209
212
219
233
260
287
321
348
375
409
436
463
497
524
551
578
612
646
677
704
Controls
275.82
319.74
346.77
378.09
399.47
428.59
448 . 09
489.09
518.47
536.55
561.78
579.24
572.32
601.29
565.01
579.07
598.12
603.05
615.80
639 . 17
637.45
638.81
638.46
631.71
659.41
627.18
606.18
609.37
607.78
597.50
574.96
587.27
15 ppm
276.05
305 . 84a
340. 06a
363. 06a
385. 93a
412. 48a
431. 80a
468. 7 la
500. 00a
512.86*
528. 74a
528.15
528. 50a
563. 12a
535. 02a
550. 81a
555. lla
569. 36a
586. 04a
593. I4a
611. 82a
613.47
623.26
618.00
614. 94a
585. 60a
596.84
575.20
582.11
569.04
554.65
549.69
75 ppm
282. 56a
328. 20a
353. 56a
375.61
396.02
423.88
447.24
488.15
518.94
539.54
549.27
556. 47a
552. 79a
557. 76a
558.60
559. 3la
565. 36a
572. 19a
588. 57a
586. 36a
625.81
639.74
645.81
635.24
628. 62a
618.39
583.75
585.84
563. 10a
541.85
536.13
529.55
Significantly different from control mean, p < 0.05.
SOURCE: McKenna et al., 1982.
10-110
-------
TABLE 10-37. VINYLIDENE CHLORIDE: A CHRONIC INHALATION TOXICITY
AND ONCOGENICITY STUDY IN RATS
MEAN BODY WEIGHT FOR FEMALE RATS
Study
Month
0
I
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Time
Day
0
8
13
20
26
39
52
79
113
140
174
201
209
212
219
233
260
287
321
348
375
409
436
463
497
524
551
578
612
646
677
704
Controls
210.24
230.20
238.48
252.87
259.52
269.89
278.78
294.14
311.28
322.03
332.67
336.18
337.11
332.63
331.73
338.73
339.60
343.67
356.89
367.94
376.74
379.60
386.38
390.53
406.30
396.26
395.10
414.86
443.06
412.23
420.33
427.00
25 ppra
212.58
221. 38a
243. 40a
246. 59a
258.60
277. 79a
280.84
301. 513
317.23
329.17
342. 63a
331.11
334.58
335.27
335.80
338.93
348.01
362. 06a
370. 98a
377.14
375.25
386.23
391.36
397.31
411.39
419.26
429.48
405.68
411.72
435 . 19
460.71
462.67
75 ppm
203. 22a
241. 57a
247. 40a
255.68
264.34
280. 79a
289. 26a
308. 79a
325. 10a
335. 96a ,
342.12s
339.93
336.71
343. 73a
340.29
340 . 23
348.26
356.57
368. 90a
363.14
387.52
397. 57a
402.62
.397.10
419.64
426.13
421.21
413.13
448 . 65
457.27
469.91
438.62
aSignificantly different from control mean, p < 0.05.
SOURCE: McKenna et al.,.1982.
10-111
-------
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The incidence of adenocarcinoma without metastasis was significantly (p <
0.05) increased in low-dose females compared to controls; however, mammary ade-
nocarcinoma incidence was not significantly (p < 0.05) increased in high-dose
females, and adenocarcinoma without metastasis was found in another control
female, which causes the adenocarcinoma incidence in low-dose females to lose
significance (p > 0.05). The significant increase (p < 0.05) in total mammary
tumor incidence in high-dose females compared to control females includes
animals with both benign and malignant tumors and, according to the authors,
total mammary tumor incidence in the control group and in each treatment group
is within the historical control range for the Sprague-Dawley strain of rats
at the investigating laboratory. Thus, demonstration of an induction of
mammary tumor formation in female Sprague-Dawley rats under the conditions of
the study by McKenna et al. (1982) does not seem apparent. Overt toxicity of
vinylidene chloride in Sprague-Dawley rats does not appear evident, and an
attempt to use higher exposure levels in this study might have provided a
broader evaluation for carcinogenicity.
In the reports of Quast et al. (1983) and Humiston et al. (1978), male
and female Sprague-Dawley rats, initially 6 to 7 weeks old, were exposed to
vinylidene chloride at 50, 100, and 200 ppm (99.5% pure) in drinking water for
2 years. Because of the volatile nature of vinylidene chloride, the water was
made up at higher concentrations, and the above figures reflect the average
concentrations during 24-hour periods. The actual vinylidene chloride levels
measured in the drinking water were 68 ± 21, 99 ± 22, and 206 ± 33 ppm (mean ±
SD). When taking into account the water consumption of the rats, the time-
weighted average dose was equivalent to 7, 10, or 20, and 9, 14, or 30 mg/kg/
day in males and females, respectively. The vinylidene chloride used in this
study was distilled prior to making up the test water in order to reduce to 1
10-113
-------
to 5 ppm the concentration of the inhibitor monomethyl ether of hydroquinone
(this inhibitor would normally be at low levels in copolymers used for food
packaging applications). Each treatment group consisted of 48 rats of each
sex, and an untreated control group consisted of 80 males and 80 females.
Animals were evaluated for survival, body weight, food and water consumption,
hematology, clinical chemistry, urinalysis, gross pathology, and histopathol-
ogy. The animals were observed until morbidity, or 24 months, at which time
surviving animals were sacrificed. The specific tissues examined are presented
in Table 10-39. There was no evidence of statistically significant (p < 0.05)
treatment-related effects of vinylidene chloride on the toxicologic end points
evaluated in treated animals as compared to controls. At least 50% of each
group survived for approximately as long as 20 months.
A number of neoplastic lesions were observed in both control and experi-
mental animals. The total tumor incidence is given in Table 10-40. The tumor
frequency at specific sites, as reported by Quast et al. (1983), did not show
a treatment-related effect of vinylidene chloride. The only statistically
(p < 0.05) significant increase in a specific neoplasm was in female rats ex-
posed to vinylidene chloride at 50 ppm. These animals had an increased inci-
dence of mammary gland fibroadenomas/adenofibromas (40/48 50 ppm females vs. 53/
80 control females). This tumor was not considered by the authors to "be treat-
ment-related, since there was no dose relationship between tumor incidence,
i.e., 36/48 100 ppm females and 35/48 200 ppm females, and exposure to vinyli-
dene chloride. Also, the spontaneous incidence of mammary tumors was high
in this strain of rats, and the tumor incidence observed in the 50 ppm females
was within the limits for historical controls at the testing laboratory. Four
control, 1 low-dose, and 2 mid-dose females had mammary carcinomas. No treat-
ment-related effects of vinylidene chloride on non-neoplastic lesions were
10-114
-------
TABLE 10-39.
REPRESENTATIVE TISSUE SPECIMENS OBTAINED AT NECROPSY
FROM ALL ANIMALS
esophagus
salivary glands
stomach
large intestine
pancreas
liver
kidneys
urinary bladder
prostate
accessory sex glands
epididymides
testes
ovaries
uterus
mammary tissue (females)
brain (cerebrum, cerebellum
with brain stem)
pituitary gland
spinal cord
peripheral nerve
trachea
lungs (bronchi)
nasal turbinates
Q
sternum and sternal bone marrow
spleen ,
mediastinal lymphoid tissue
(thymus, mediastinal lymph nodes)
lymph nodes (mesenteric)
heart
aorta
skeletal muscle
adrenal glands
thyroid gland ,
parathyroid gland
adipose tissue
skin
any gross lesion or mass
eyes
Sternum and enclosed bone marrow were to be evaluated histologically
only if indicated by abnormal findings in the hematological studies.
These tissues were evaluated histologically only to the extent that
they were included in the routine sections of adjacent larger organs.
Eyes were saved in formalin if the rat died or was culled from the
study. If the rat was from the terminal kill, a portion of these
were fixed in Zenker's fixative and the remainder in formalin. Only
selected animals had their eyes microscopically examined.
SOURCE: Humiston et al., 1978.
10-115
-------
TABLE 10-40. TUMOR INCIDENCE FOLLOWING INGESTION
OF VINYLIDENE CHLORIDE (VDC)
Concentration
Total number of
neoplasms
Total number of
rats in group
Average number of
neoplasms/number
of rats
"JO. VUV-. ill
water (ppm)
0
50
100
200
Male
100
53
43
53
Female
187
132
120
124
Male
80
48
48
47
Female
80
48
48
48
Male
1.3
1.1
0.9
1.1
Female
2.3
2.8
2.5
2.6
S01JRCE: Humiston et al., 1978.
evident, except for minimal fatty change and swelling in the livers of high-
dose males and females in all treatment groups. The dose of vinylidene
chloride ingested in the drinking water appeared low enough to produce no overt
toxic effects. The use of higher exposure levels might have provided a stronger
evaluation of the carcinogenic potential of vinylidene chloride; however, the
authors indicated that 200 ppm, the maximum concentration of vinylidene chlo-
ride in water used in this study, was the highest concentration possible given
the solubility of vinylidene chloride (2.25 g/L at 25°C).
The National Cancer Institute/National Toxicology Program (NCI/NTP, 1982)
has prepared a report on a cancer bioassay of vinylidene chloride (99% pure)
performed on Fischer 344 rats and B6C3F1 mice, initially 9 weeks old. Male
and female rats (50 animals of each sex) received vinylidene chloride, dis-
solved in corn oil, by gavage at doses of 1 and 5 mg/kg, while male and female
mice (50 animals of each sex) received doses of 2 and 10 mg/kg. The animals
were treated 5 days/week for a total of 104 weeks. Animals were observed for
10-116
-------
gross signs of toxicity during the exposure period, as indicated by food con-
sumption patterns, body weight gain, and mortality. The treated and control
animals were killed after 104 weeks of exposure or when moribund, and the
tissues indicated in Table 10-41 were examined histologically for both tiimori-
genic and non-tumorigenic pathology.
TABLE 10-41. TISSUES EXAMINED3 FOR HISTOLOGIC CHANGES IN THE NCI BIOASSAY
skin
lungs and bronchi
trachea
bone and bone marrow
spleen
lymph nodes
heart
salivary gland
adrenal
thyroid
parathyroid
seminal vesicles (male)
testis (male)
thymus
esophagus
liver
pancreas
stomach
small intestine
large intestine
kidney
urinary bladder
pituitary
mammary gland
prostate
brain
uterus (female)
ovary (female)
larynx
These tissues were examined in all animals,' except where advanced autolysis
or cannibalism prevented meaningful evaluation.
SOURCE: NCI/NTP, 1982.
The survival (greater than 50% for the whole study for all groups) and
weight gain of rats were unaffected by treatment with vinylidene chloride;
however, 12 control and 10 low-dose male animals were accidentally killed as a
result of a 5-hour exposure to 37°C on week 82 of the study. Including the
male rats accidentally killed, survival of rats at terminal sacrifice was as
follows: 20/50 vehicle control males, 24/50 low-dose males, 37/50 high-dose
males, 27/50 vehicle control females, 28/50 low-dose females, and 29/50
high-dose females. In mice, only survival in the low-dose female group was
10-117
-------
adversely affected by treatment. However, at least 64% of the mice in all
groups survived the study (33/50 vehicle control males, 35/50 low-dose males,
36/50 high-dose males, 40/50 vehicle control females, 32/50 low-dose females,
and 42/50 high-dose females). Body weight gain was slightly depressed in both
dose groups of male mice and in female mice of the low-dose group as compared
to either the corresponding high-dose or control animals (Table 10-42); how-
ever, a dose-response was not evident, and body weight decreases were greater
in low-dose than in high-dose mice. Dose-related non-neoplastic lesions
consisted of liver necrosis in mice (male controls, 1/46, 2%; low-dose, 3/46,
7%; high-dose, 7/49, 14%; female controls, 0/47, 0%; low-dose, 4/49, 8%;
high-dose, 1/49, 2%) and inflammation of the kidney in rats (male controls,
26/49, 53%; low-dose, 24/48, 50%; high-dose, 43/48, 90%; female controls,
3/49, 6%; low-dose, 6/49, 12%; high-dose, 9/49, 20%). It is noted in the
NCI/NTP (1982) report that chronic nephritis is a common lesion in aging rats.
Other histopathologic changes of a non-tumorigenic type were observed randomly
in control and treated animals, and were not considered treatment-related.
In rats and mice, increased tumor incidences were observed in a number of
organs (Table 10-43). While unadjusted analyses of these data suggested that
some responses were marginally statistically significant at the p = 0.05
level, such analyses do not take into account the multiple organs compared.
As indicated by NCI/NTP (1980) and discussed in greater detail by Gart et al.
(1979), it is more accurate to account for multiplicity of comparisons by the
Bonferroni correction when using the Fisher exact test, and to account for
differing patterns of mortality among the dose groups by time-adjusted analy-
ses. Making these corrections, the only statistically significant (p < 0.05)
increased response was for lymphomas in the low-dose group female mice com-
pared to the matched controls using the Fisher exact test. Furthermore, only
10-118
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TABLE 10-42. MEAN BODY WEIGHT CHANGE (RELATIVE TO CONTROLS) OF MICE
ADMINISTERED VINYLIDENE CHLORIDE BY GAVAGE
Mean body weight
Week No .
Male
mice
Female
mice
aWeight
0
1
20
40
60
80
100
0
1
20
40
60
80
100
grams
change
Control Low dose High dose
28b
1
13
19
22
21
20
19b
2
9
12
17
19
24
change relative
Weight change
(dosed
24b
2
11
17
21
20
21
18b
2
8
12
15
18
21
to controls =
group) - Weight
25b
2
13
19
23
22
21
18b
3
9
13
18
14
24
change (control
Weight change rela-
tive to controls
(percent)
Low dose High
+100
-15
-20
-5
-5
+5
0
-11
0
-12
—5
-13
group) x 100
dose
+100
0
0
+5
+5
+5
+50
0
+8
+6
+35
0
Weight change (control group)
Initial weight
SOURCE: NCI/NTP, 1982.
10-119
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TABLE 10-43. TUMORS WITH INCREASED INCIDENCE IN RATS AND MICE, AS INDICATED
BY THE FISHER EXACT TEST OR THE COCHRAN-ARMITAGE TEST FOR
LINEAR TREND
Species
Tumor
Incidence
Control
Low Dose High Dose
rat (male)
adrenal,
pheochromo cytoma s
6/50 (12%) 5/48 (10%) 13/47 (28%)
(p=0.01)'
(p=0.045)
rat (male) pancreatic islet-cell,
f*
adenomas/carcinoma
4/49 (8%) 1/47 (2%) 8/48 (17%)
(p=0.025)a
rat (male)
testes, interstitial-cell 43/50 (86%) 39/47 (83%) 47/48 (98%)
(p=0.013)'
(p=0.034)
rat (female) pituitary, adenomas
16/48 (33%) 20/49 (41%) 24/43 (56%)
(p=0.017) (p=0.026)b
rat (male)
subcutaneous, fibromas
0/50 (0%) 1/48 (2%) 4/48 (8%)
(p=0.024)a
mice (female) lymphomas
2/48 (4%) 9/48 (18%) 6/50 (12%)
(p=0.028)b
Significant for linear trend by Cochran-Armitage test (p < 0.05).
Significant by Fisher exact test (p < 0.05).
All pancreatic tumors were carcinomas, except for adenomas in two high-dose
males. Carcinomas alone were not significant by the Cochran-Armitage test.
SOURCE: NCI/NTP, 1982.
10-120
-------
lymphomas represent a statistical increase in malignant tumors in Table 10-43.
However, a similar increase in the high-dose group was not noted, and the
Cochran-Armitage test for linear trends was not significant. Since the
matched controls had a low incidence (4%) of lymphomas when compared to the
incidence (9.8%) in historical controls, this effect was not considered to be
treatment-related. Thus, the conclusion in the NCI/NTP (1982) report is that
vinylidene chloride was not carcinogenic to F344 rats or B6C3F1 mice under the
conditions of this assay. Survival and body weight data suggest that higher
doses of vinylidene chloride could have been given to rats and mice to more
strongly challenge these animals for carcinogenicity.
Vinylidene chloride was tested for its potential as a brain carcinogen on
the basis that vinyl chloride causes neuroblastomas in animal studies and is
associated with brain neoplasms in exposed humans (Maltoni et al., 1982). No
increase in the incidence of gliomas, meningiomas, or ependymomas was reported
among Sprague-Dawley rats exposed by inhalation to vinylidene chloride at 10,
25, 50, 100, or 150 ppm for 4 or 5 days weekly for 52 weeks. Male and female
rats exposed by ingestion (gavage) to 0.5, 5, 10, or 20 mg/kg of vinylidene
chloride for 5 days weekly for 52-59 weeks did not show an increased incidence
of brain tumors when compared to controls.
Ponomarkov and Tomatis (1980) assessed the carcinogenic potential of
vinylidene chloride in BDIV rats exposed to the compound starting in utero and
continuing to 120 weeks of age. Pregnant rats (24 animals) received a single "'
150 mg/kg dose of vinylidene chloride (99% pure) by gavage in corn oil on day
17 of gestation. Following birth, the pups (89 males and 90 females) received '
vinylidene chloride by gavage at a dose of 50 mg/kg weekly for the duration of
the study. The animals were killed at the termination of the study or when
moribund, and major organs and gross lesions were examined histologically.
10-1-21
-------
There was no treatment-related effect on the reproductive success of the
dams or on the survival or weight gain of the offspring of rats treated with
vinylidene chloride. Non-tumorigenic lesions in the liver, consisting of
degeneration of the parenchymal cells, liver necrosis, and hemorrhage, were
observed in treated animals moribund after 80 weeks of treatment or killed at
termination. In cases of early death (30 weeks of treatment), lung and kidney
congestion were also observed in treated rats. The total tumor incidence in
either the dams or the offspring was not significantly increased by treatment
(Table 10-44); however, there was an increased incidence of meningiomas in
male rats, although this was also not significantly different from control
levels. Although slight differences in tumor incidence were observed follow-
ing vinylidene chloride treatment, this study did not demonstrate a statisti-
cally significant effect of vinylidene chloride treatment on the induction of
tumors in either the dams or their offspring. Although liver lesions were
seen, it appears that higher doses could possibly have been used, since no
effect was observed on survival and body weight.
Skin application has been used to assay vinylidene chloride for tumor
initiation and complete carcinogen action in lifetime studies using the two-
stage tumorigenesis model in female Ha:ICR Swiss mice (Van Duuren et al.,
1979). In two-stage tumorigenesis, an initiator agent is applied in a single
dose to the skin of a mouse. The initiator does not produce tumors at the
applied concentration, but predisposes the skin so that later repeated appli-
cations of a promotor (an agent that by itself will not produce tumors) will
cause the formation of tumors. A complete carcinogen is one which, if applied
in sufficient concentrations, can produce tumors by itself. When vinylidene
chloride was applied three times each week at a dose of 121 mg/mouse to the
shaved backs of 30 mice, no tumors were observed; however, when a single dose
10-122
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of 121 rag/mouse of vinylidene chloride was applied to the skin of 30 mice,
followed by repeated application of phorbol myristate acetate (PMA) as the
promoter, a significant increase (p < 0.005) in skin papillomas (8 mice with
papillomas/9 total papillomas) was observed as compared to controls. No skin
papillomas were observed in 30 controls treated with acetone, the dosing
vehicle, and 100 untreated controls, whereas 9 mice (10 total papillomas) of
120 mice given 0.0025 mg PMA and 6 mice (7 total papillomas) of 90 mice given
0.005 mg PMA on the same schedule as that for treated mice were found. Squa-
mous cell carcinomas on the skin in the initiation-promotion study were ob-
served on one mouse in the vinylidene chloride group, one mouse in the low-
dose PMA group, and 2 mice in the high-dose PMA group. A positive control
group of 30 mice in the initiation-promotion study given 0.02 tag/mouse of
7,12-dimethylbenz[a]anthracene as the initiating agent developed papillomas in
29 mice (317 total papillomas) and local squamous cell carcinomas in 14 mice.
In the same study, vinylidene chloride was also tested for complete carcino-
genic action in 30 female Swiss ICR/Ha mice by repeated subcutaneous injection
once a week at a dose of 2 mg/mouse. Following treatment for 548 days, no
tumors were observed at the site of injection or at sites distant from the
site of injection. Although this study indicates that vinylidene chloride is
a tumor initiator in mouse skin, it is not clear how this relates to the
processes of complete chemical carcinogenesis in other organs, or if tumor
initiation as observed here is a phenomenon solely restricted to the skin of
mice. The relevance of positive results in this tumor initiation study with
regard to the assessment of human health effects is not clear, particularly
since complete carcinogenic activity could not be demonstrated. Maximally
tolerated doses, estimated from preliminary short-term tests, were used in the
tests for carcinogenicity performed by Van Duuren et al. (1979).
10-124
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In summary, the evidence supporting the carcinogenicity of vinylidene
chloride is limited. It has been shown that vinylidene chloride is a mutagen
in bacterial and yeast assay systems, although the evidence is limited for
classifying vinylidene chloride as a human mutagen. Van Duuren et al. (1979)
have demonstrated that vinylidene chloride acts as a tumor initiator in mouse
skin; however, of the three animal species used to assess the carcinogenicity
of this compound--rats, mice, and hamsters—only one strain of mice developed
a unique tumor type (kidney carcinomas) following exposure to vinylidene
chloride. Maltoni (1977) and Norris (1982) suggested that the observed increase
in kidney tumors may be a species- and strain-specific effect. Maltoni (1977),
Maltoni et al. (1977), and Maltoni and Patella (1983) suggested a relationship
between the sensitivity to acute toxic effects of vinylidene chloride and
carcinogenic responses in the strains of rats and mice evaluated for vinylidene
chloride carcinogenicity in their studies. A statistically significant increase
in mammary carcinomas was found in female Swiss mice by Maltoni et al. (1985),
but these investigators concluded that this evidence was not conclusive and
requires further study.
There have been a number of other carcinogenicity bioassays of vinylidene
chloride in which no statistically significant increase in tumor incidence was
observed (Table 10-23). From these studies, it could be concluded that viny-
lidene chloride has not been found to be significantly carcinogenic in rats or
hamsters, nor in mice when administered by the oral route. The only published
inhalation studies in mice, except for the positive bioassay of Maltoni et al.
(1985), used either a shorter exposure period (Hong et al., 1981) or a shorter
observation period (Lee et al., 1978), although the level of exposure in both
studies was higher (55 ppm, 6 hours/day) than the high-dose group (25 ppm for
4 hours/day) used by Maltoni et al. (1985). Furthermore, higher doses possi-
10-125
-------
bly could have been tested in several of the negative studies. Nonetheless,
in view of the present evidence for vinylidene chloride carcinogenicity found
in one mouse strain in the inhalation study by Maltoni et al. (1977, 1985), the
available evidence regarding the carcinogenicity of vinylidene chloride in
animals is thus seen to be limited and not sufficient for a firm conclusion on
the potential carcinogenicity of this compound in humans.
10.5.2 Epidemiologic Studies
Adequate data regarding the carcinogenic potential of vinylidene chloride
in humans are lacking. One study, that of Ott et al. (1976) investigated 138
Dow Chemical Company workers exposed primarily to vinylidene chloride, and
gave mortality data and the results of health examinations. The Ott et al.
(1976) study is a historic prospective cohort study of 138 employees whose
first employment extends back to 1940. However, most began their employment
after 1950: 74 in the period from 1950 to 1959, and 55 from I960'to 1969. The
cut-off date for this study was January 1, 1974. The authors noted that vinyl
chloride is a common contaminant of vinylidene chloride monomer and that
liquid vinylidene chloride contained less than 0.2% by weight of vinyl chlo-
ride in recent years prior to publication of their study. In this study, time-
weighted average (TWA) exposures were estimated based on job descriptions and
industrial hygiene surveys. Based on TWA exposure estimates, each job initial-
ly fell into one of four categories: <10 ppm, 10 to 24 ppm, 25 to 49 ppm, and
50+ ppm. However, since operators in fiber production were the only workers
with exposures above 25 ppm TWA, only three concentration categories were used
to calculate cumulative dose: <10 ppm (5 ppm used for calculation); 10 to 24
ppm (17 ppm used for calculation); and S25 ppm (43 ppm used for calculation).
Cumulative career exposures were estimated by multiplying the TWA times the
duration, in months, of potential exposure (Table 10-45). As indicated in the
10-126
-------
table, the size of the population having a lengthy duration of exposure or a
long latency period since the initial time of exposure was small. Moreover,
it cannot be determined from the data presented in the study report whether
those individuals for whom the greatest time had elapsed since initial expo-
sure were also among the most heavily exposed subjects. Thus, it is possible
that for detection of long-latency diseases such as cancer, the population
examined in this study may not be adequate.
TABLE 10-45. ESTIMATED CUMULATIVE DOSE, DURATION OF EXPOSURE AND DATE OF
FIRST EXPOSURE AMONG 138 INDIVIDUALS EXPOSED TO VINYLIDENE CHLORIDE
Exposure measures
Estimated career dosage (TWA x months of exposure)
<500 ppm months
500-999 ppm months
1000-1999 ppm months
2000+ ppm months
Duration of exposure
<12 months
12-59 months
60-119 months
120+ months
Date of first exposure
1940-1949
1950-1959
1960-1969
Total population
50
28
28
32
35
43
35
25
9
74
55
Status as of January 1974.
SOURCE: Ott et al., 1976.
10-127
-------
Cohort mortality was compared with U.S. white male mortality for 1942,
1947, 1952, 1957, 1962, 1967, and 1971 by the indirect method. The most re-
cent health inventory for the cohort was compared with matched controls. For
the total cohort of 138 persons, 5 deaths were recorded versus 7.5 expected
(Table 10-46). One death of an individual with a 745 ppm cumulative dose was
attributed to malignancy (versus 1.1 expected) and this was due to respiratory
cancer; however, his smoking history was not known. The expected respiratory
cancer death rate was 0.3 for the total cohort; 0.2 for the total cohort 15+
years after first exposure to vinylidene chloride; and 0.2 for the cohort with
500+ ppm months of exposure (Table 10-46). An examination of company health
inventory records on this same cohort revealed no statistically significant
(p < 0.05) clinical difference between the vinylidene chloride-exposed group
and matched (for age and smoking) controls. Although duration of employment
appears sufficient to have provided an opportunity for exposure to vinylidene
chloride, yet, in order to observe a statistically significant elevated risk
of cancer at probability level p < 0.05 with 80% power, a minimum of 12 cancer
deaths would have had to occur (relative risk of 10.6) given that the author
expected only 1.1 in his small cohort of 138 white males without regard for
latency. If one assumes a 10-year latent period for the development of cancer,
the number of person-years of observation would be reduced by approximately 50%,
and consequently the power to detect a significant relative risk of even 10.6
would subsequently decline from 80% to 43% in that segment of the cohort where
the occurrence of cancer could most credibly be attributable to exposure to
vinylidene chloride. In order to maintain a power of 80%, the relative risk
needed to detect a significant difference at the p < 0.05 level is about 16
based upon a CAG estimate of 0.6 cancer deaths. Relative risks of such magni-
tude occur generally only with exposures to exceptionally strong carcinogens
10-128
-------
TABLE 10-46. OBSERVED AND EXPECTED DEATHS AMONG
VINYLIDENE CHLORIDE EMPLOYEES BY CAUSE
1945-1973
Total cohort
Total cohort
15+ years
after first exposure
Observed
All causes 5
Total malignancies 1
Digestive cancer
Respiratory cancer 1
All other
Cardiovascular disease 1
Pnemonia/ influenza
Pulmonary emphysema/ asthma
Cirrhosis of liver 1
External causes
All other
Expected
7.5
1.1
0.3
0.3
0.5
2.6
0.1
0.1
0.3
2.3
1.0
Observed Expected
2 2.6
1 0.5
0.1
1 0.2
0.2
0 1.2
0.0
0.0
0 0.1
0 0.5
0.3
SOURCE: Ott et al., 1976.
10-129
-------
(i.e., asbestos, cigarette smoke) or with cancers rarely occurring naturally.
Ott et al. (1976) mentioned that the cohort exposed to vinylidene chloride was
also exposed to copolymers other than vinyl chloride, and that individuals in
the matched control population might have been exposed to a number of other
chemicals. However, based on power considerations alone, the Ott et al. study
is inadequate for assessing a cancer risk, and cannot be said to support a
lesser susceptibility to potential vinylidene chloride carcinogenesis in man.
10-130
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10.5.3 Risk Estimates from Animal Data
The evidence for the carcinogenicity of vinylidene chloride reviewed in
this chapter consists primarily of kidney adenocarcinomas diagnosed in treated
male Swiss mice. Also, an increase of mammary carcinomas was observed in the
female mice and an increase in pulmonary adenomas occurred in both sexes of
these mice. An increase in mammary tumors also has been observed in female
Sprague-Dawley rats, but was not considered by the authors to be treatment-
related (see earlier discussion of animal studies, this chapter). Vinylidene
chloride has been shown to act as a tumor initiator in mouse skin, to be
mutagenic in several non-mammalian test systems, and to be metabolized to
intermediates capable of reacting with cellular macromolecules, including
DNA. The overall qualitative weight of evidence for the carcinogenicity of
vinylidene chloride in animals is only limited; however, the kidney adeno-
carcinomas in male Swiss mice (Maltoni et al., 1985) provide data which may
be used to estimate an upper limit of incremental risk under the presumption
that vinylidene chloride is a potential human carcinogen.
It is important to note that the calculations in this document for esti-
mating in quantitative terms the impact of vinylidene chloride as a carcinogen
are made independently of the overall weight of evidence for vinylidene
chloride's carcinogenic potential. This is done to answer the question of
how large the incremental cancer risk would be if vinylidene chloride were a
human carcinogen. However, there is only limited animal evidence for vinyli-
dene chloride carcinogenicity, and the calculations are made only under the
supposition that vinylidene chloride is carcinogenic in humans.
10.5.3.1 SELECTION OF ANIMAL DATA SET — For some chemicals, several
studies in different animal species, strains, and sexes, each run at several
doses and different routes of exposure, are available. A choice must be made
10-131
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as to which of these data sets to use in the mathematical extrapolation
model. A general approach is to use the most sensitive responder, i.e., the
data set that gives the highest estimate of lifetime cancer risk, on the
assumption that humans are as sensitive as the most sensitive animal species
tested. For vinylidene chloride, the Maltoni et al. (1985) inhalation study
in Swiss mice is the only animal study in which a statistically significant
treatment-related increase in tumors was observed. Swiss mice of both sexes
were exposed to 10 and 25 ppm vinylidene chloride 4 hours/day, 4 to 5 days/week
for 52 weeks of a total of 121 of weeks. The significant increase of kidney
adenocarcinomas in the male mice was the data selected for extrapolating to an
upper limit of potential human risk. These tumors were found at the 25 ppm
level (25.5% incidence) but not at the 10 ppm level (Table 10-47).
TABLE 10-47. DATA FROM THE MALTONI ET AL. INHALATION STUDY ON MALE MICE
Animal
exposure
(ppm daily
for 12
months)
0
0
10
25
25
Animal
lifetime
continuous
exposure
(ppm)
0
0
0.46
1.15
1.15
Human
lifetime
continuous
equivalent
dosec
(mg/kg/day)
0
0
0.078
0.195
0.195
Number
of ani-
mals at
start
100
90
30
30
120
Kidney adenocarcinomas/
number surviving
55 weeks from start
0/56*
0/7 Qa
0/25
3/21 (I4.3%)b
25/98(25. 5%)b
aGroups were combined since responses were not statistically different.
^These groups were combined, since responses using the same dose level were
not statistically different.
cThis dose information is derived as shown in Section 10.5.3.2.2.
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10.5.3.2 INTERSPECIES DOSE CONVERSION
10.5.3.2.1 General Considerations — A broad classification of the
main components to be considered in an extrapolation base assessment, i.e.,
the bases for extrapolation of dose-carcinogenic response relationships of
laboratory animals to man, are: 1) toxicologic data, 2) pharmacokinetics and
metabolism, and 3) covalent binding. These components have been outlined and
discussed previously by Davidson (1984) and Parker and Davidson (1984).
10.5.3.2.1.1 Toxicologic Data. The toxicity of vinylldene chloride
appears to vary with the age, sex, and species of animal exposed (see sections
on acute and chronic toxicity). A considerable difference in toxicity also
exists between continuous exposure and daily interval exposure. However,
there is evidence to suggest (with vinylidene chloride inhalation exposure) a
correlation of toxicity to metabolism, with cellular damage occurring after
formation of reactive metabolites, including the putative epoxide. This rela-
tionship is amply supported by studies demonstrating modulation of toxicity
by inhibitors or inducers of £450 metabolism.
The cellular damage and toxicity of vinylidene chloride from metabolites
formed during inhalation exposure is dependent upon two principal parameters:
1) inhalation concentration (below saturation of metabolic capacity) and 2)
duration (length) of exposure. Acute toxicity data are less relevant to the
circumstances of the carcinogenicity assays, but chronic and subchronic
studies provide directly related data for inhalation toxicity occurring at
levels well below saturation of metabolism and relevant to the exposure
concentrations used in the Maltoni et al. (1985) carcinogenesis study.
10.5.3.2.1.2 Metabolism. Vinylidene chloride is believed to be metabo-
lized by the microsomal £450 monooxygenase system, with the formation of a
reactive intermediate epoxide and possibly other reactive metabolites (see
10-133
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Section 10.1.2, Metabolism). In vivo covalent binding of vinylidene chloride
to cellular macromolecules, including DNA, has been demonstrated in the mouse
and rat, with binding twofold to threefold greater in kidney than in liver
(McKenna et al., 1977; Reitz et al., 1980). The binding is considered to be
due to reactive metabolites.
There is evidence that macromolecular covalent binding of metabolites
leading to cellular damage is related to the carcinogenic potential of
vinylidene chloride, although the primary genotoxic and epigenetic mechanisms
resulting in impairment have not yet been satisfactorily established. There
is no evidence to show that the metabolic pathways for vinylidene chloride
are significantly different, qualitatively or quantitatively, in the mouse,
rat, or man.
Experimental studies of the metabolism and pharmacokinetics of vinylidene
chloride in man have not been made, but these factors have been relatively
extensively studied in two species, the mouse and the rat (McKenna et al.,
1977; 1978a,b; Dallas et al., 1983; Putcha et al., 1984; Reitz et al., 1980;
Anderson et al., 1979a,b; Filser and Bolt, 1979). Vinylidene chloride in air
rapidly equilibrates across the lungs to provide steady-state equilibrium in
the rat within 30 to 45 minutes (Dallas et al., 1983; Putcha et al., 1984).
At equilibrium the blood concentration (and, hence, the amount of vinylidene
chloride in the body) is directly proportional to the inspired air concentra-
tion (Dallas et al., 1983). For low inhaled concentrations (0 to 150 ppm),
vinylidene chloride is metabolized at a constant rate consistent with a
constant blood concentration presented to the liver, the principal site of
metabolism, by the equilibrium maintained by pulmonary uptake (Dallas et al.,
1983; Putcha et al., 1984; Anderson et al., 1979a,b; Filser and Bolt, 1983).
Metabolic elimination of vinylidene chloride is saturable and dose-dependent,
10-134
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with saturation of metabolism in rodents occurring at inhalation concentra-
tions of about 150 to 200 ppm or about 50 mg/kg oral ingestion (Dallas et
al. , 1983; Anderson et al. , 1979a,b; Filser and Bolt, 1979). Below saturation
concentrations, metabolism is essentially first-order and virtually 100%
(Dallas et al. , 1983; Filser and Bolt, 1979). The processes of oral absorption
and metabolism of vinylidene chloride are both virtually complete at least up
to 50 mg/kg in both rats and mice (McKenna et al. , 1978b; Putcha et al. , 1984).
10.5.3.2.1.3 Covalent Binding, DNA Alkylation. Covalent binding of
vinylidene chloride closely correlates with metabolite formation. McKenna et
al. observed that covalently bound ^C activity in tissues was three times
greater in the kidney than in the liver, and was five times greater for mouse
than rat on a direct body weight (mg/kg) basis.
Reitz et al. (1980) found minimal DNA alkylation in liver and kidney of
both mouse and rat exposed to 10 and 50 ppm vinylidene chloride by inhalation
for 6 hours. The alkylation that occurs is proportional to metabolite forma-
tion. The kidney shows a twofold greater alkylation (rat) and tenfold
greater alkylation (mouse) than the liver.
10.5.3.2.2 Calculation of Human Equivalent Doses from Animal Data — The
usual approach for making interspecies comparisons has been to use standard-
ized scaling factors. The allometric equation:
Dose (for a given tumor incidence) = aWn
where W = body weight, is appropriate to use for interspecies extrapolation
of carcinogenicity bioassay data from laboratory animals to man. In extrapo-
lating dosage from mouse or rat to man, it has long been customary to use
either body weight (n = 1) or surface area (n = 0.67) as the main criterion.
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Although reliable interspecies information on the relationship of dosage to
carcinogenesis is not available, "in general other toxicologic, metabolic, and
pharmacokinetic data correlate with interspecies body weight with the power
of 0.67 to 0.75 for the majority of compounds studied. Thus, in the absence
of comparative toxicologic, metabolic, and pharmacokinetic data for a given
suspect carcinogen, the extrapolation, on the basis' of surface area (W°-67),
is considered to provide the best dose extrapolation prediction, with a
greater probability of correctness. When adequate toxicologic, metabolic,
and pharmacokinetic data are available for a suspect carcinogen in two or
more species of laboratory "animal's" "or man, the experimental data should be
used to determine and "to justify the extrapolation base. In view of the
finding that vinylidene chloride metabolism, and hence its potential for
cellular damage, in mouse and" rat" correlates1 with* body surf a'ce" area", as shown
below, using surface area for the extrapolation of a vinyli'dene chloride
human equivalent dose would seem more reasonable, especially because it
correlates better with the known" parameters "of'; metabolism 'and^physiology in
, • •-.- 'I -rV- r. .-..••:•* fas;,-- '• -' ': " '•••'',- '
general.
•••.».•, ,f - .- t ..!.-.. lfl, .ir H, ••;;.-.< .,.-,. ,,"• , ' '• ;• '-'• •
The actual experimental observations allow a calculation of assimilated
dose and metabolite formation for'the daily""vinyi"i3en"e chloride inhalation
exposure experienced by the Swiss mice of the'Malton'i et al. (1985) carcino-
genicity bioassay from the McKenna et al. (1977) balance study. McKenna et
al. exposed male mice and rat's" to ^C-vinyiidene" chloride by inhalation (10
ppm for 6 hours), and estimated the body burden from radioactivity recovered
in expired air, urine, fices,"and"carcass."'At tnis exposureT level"virtually
all of the assimilated dose was metabolized in both species; the body burdens
and amounts metabolized were as follows:
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mg/kg
mg/animal
Mouse (35 g)
Rat (250 g)
5.30
2.89
0.186
0.723
In the carcinogenicity bioassay of Maltoni et al. (1985) the mice were ex-
posed 4 hours/day at 10 to 25 ppm. At these low inhalation concentrations,
plateau or steady-state blood concentrations of vinylidene chloride are
quickly reached, and the rates of metabolism are constant with time and are
proportional to the inhalation concentration (Dallas et al., 1983). There-
fore, the body burden (and amount metabolized) can be extrapolated from
McKenna's 6-hour exposure to Maltonifs 4-hour exposures by a simple propor-
tional adjustment of 4/6. Extrapolation from 10 ppm to 25 ppm can be made
similarly, to yield the following metabolic loads for Maltoni's animals:
10 ppm
Mouse (35 g)
Rat (250 g)
Ratio (rat/mouse)
mg/kg mg/animal
3.53 0.124
1.93 0.483
0.55 3.89
25 ppm
mg/kg mg/animal
8.83 0.309
4.82 1.205
0.55 3.89
The ratio of the amount metabolized in the rat to the amount metabolized in
the mouse equals 3.89. Thus, the metabolism and pharmacokinetics for mice and
rats can be considered proportional on a W^'67 "surface area" allometric base
(as [250/35]0-67 = 3.71) but not on a W1-0 "mg/kg" base. Therefore, based on
this information, the most appropriate approach to extrapolating mouse carcino-
genicity data to man is to scale the total assimilated dosage on a W°'67 base
with a scaling factor for mouse to man of (70/0.035)0-67 = 159. The lifetime
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average daily exposure (LAE) for the Maltoni mice is given by:
LAEM = 52 weeks x 4.5 days x body burden, mg/day
121 weeks 7 days
and for humans,
LAEH = LAEM x 159
On this basis, the lifetime average human equivalent doses for the vinylidene
chloride mouse carcinogenicity bioassay, expressed in units of mg/day,
surface area/ day, and mg/kg/day, are as follows:
Inhalation
concentration
(ppm)
Equivalent lifetime average
human dosea
mg/day (mg/m2)/day (mg/kg)/day
10
25
5.44
13.60
2.94
7.35
0.078
0.195
aWhere the average weight of the male mice is assumed as 0.035 kg and
that of the standard man as 70 kg with 1.85 mr surface area (Diem
and Lentner, 1970).
10.5.3.3 CHOICE OF RISK MODEL
10.5.3.3.1 General Considerations — The data used for quantitative
estimation of unit risk for vinylidene chloride were taken from a lifetime
animal study. In animal studies it is assumed, unless evidence exists to
the contrary, that if a carcinogenic response occurs at the dose levels used
in the study, then responses will also occur at all lower doses at incidence
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determined by the extrapolation model. However, there is no solidly accepted
scientific basis for any mathematical extrapolation model that relates chem-
ical carcinogen exposure to cancer risks at the extremely low concentrations
that must be dealt with in evaluating environmental hazards. For practical
reasons, such low levels of risk cannot be measured directly either by animal
experiments or by epidemiologic studies. It is necessary, therefore, to
depend on our current knowledge of the mechanisms of carcinogenesis for
guidance as to the correct risk model to use.
At the present time, the dominant view is that most cancer-causing agents
also cause irreversible damage to DNA. This position is reflected by the fact
that a very large proportion of agents that cause cancer are also mutagenic.
There is reason to expect that the quantal type of biological response, which
is characteristic of mutagenesis, is associated with low-dose linearity and a
nonthreshold dose-response relationship. Indeed, there is substantial evi-
dence from mutagenicity studies with both ionizing radiation and a wide vari-
ety of chemicals that this type of dose-response model is the appropriate one
to use. At higher doses, there can be an upward curvature, probably reflect-
ing the effects of multistage processes on the mutagenic response. The
low-dose linearity and nonthreshold dose-response relationship is also consis-
tent with the relatively few epidemiologic studies of cancer responses to
specific agents that contain enough information to make the evaluation pos-
sible (e.g., radiation-induced leukemia, breast and thyroid cancer, skin can-
cer induced by arsenic in drinking water, liver cancer induced by aflatoxins
in the diet). There is also some evidence from animal experiments that is
consistent with the linear nonthreshold model (e.g., the initiation stage of
the two-stage carcinogenesis model in rat liver and mouse skin).
Based on the above evidence of low-dose linearity, and because very few
10-139
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compounds exhibit low-dose responses that are supralinear, the nonthreshold
model, which is linear at low doses, has been adopted as the primary basis for
risk extrapolation to low levels of the dose-response relationship. The risk
estimates made with this model should be regarded as conservative, represen-
ting the most plausible upper limit for the risk, i.e., the true risk is not
likely to be higher than the estimate, but it could be lower.
The mathematical formulation chosen to describe the dose-response rela-
tionship at low doses is the linearized multistage model. This model employs
enough arbitrary constants to be able to fit almost any monotonically increa-
sing dose-response data, and it incorporates a procedure for estimating the
largest possible linear slope (in the 95% confidence limit sense) at low
extrapolated doses that is consistent with the data at all dose levels of the
experiment.
The methods used by the GAG for quantitative assessment are consistently
conservative, i.e., tending toward high estimates of risk. The most important
part of the methodology contributing to this conservatism is the linear non-
threshold extrapolation model. There are a variety of other extrapolation
models that could be used, all of which would give lower risk estimates. These
alternative models have not been used by the GAG in the following analysis
because it feels that the limited evidence of carcinogenicity for vinylidene
chloride does not warrant that complete an analysis. Kidney adenocarcinomas in
male mice occur at only one dose level, thus allowing an estimation of only one
parameter. Furthermore, the GAG feels that with the limited data available
from the animal bioassays, very little is known about the true shape of the
dose-response curve at low environmental levels. The position is taken by the
GAG that the risk estimates obtained by use of the low-dose linear nonthreshold
model are plausible upper limits, and that the true risk could be lower.
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Extrapolations from animals to humans could also be done on the basis of
relative weights or measures other than relative surface area. The general
approach is to use the extrapolation base (mg/kg, surface area, etc.) that
can be appropriately justified by the experimental data from animals and man,
although it is usually not clear which extrapolation base is the most approp-
riate for the carcinogenic response per se. In the case where there is insuf-
ficient data or an absence of experimental data to determine an extrapolation
base either directly or indirectly, the most generally employed and conserva-
tive method is used, i.e., extrapolation from animal dose to a human equiva-
lent dose on the basis of relative surface area (W^/3). For the vinylidene
chloride inhalation studies in mice (Maltoni et al., 1985) the use of an
extrapolation based on surface area (W^/3) rather than directly on body weight
(W1'^), results in a higher unit risk estimate than direct body weight extrapo-
lation, or assuming that a certain concentration in ppm or pg/m^ in the
experimental animals is equivalent to the same concentration in humans. How-
ever, for vinylidene chloride, experimental data on metabolism and kinetics are
available and can be used in dose extrapolation from mouse to man.
10.5.3.3.2 Mathematical Description of the Low-Dose Extrapolation Model
— Let P(d) represent the lifetime risk (probability) of cancer at dose d.
The multistage model has the form
P(d)
exp [-(q0
qkdk)]
where
= °» x» 2» •••» k
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Equivalently,
Pt(d) = 1 - exp [-(q^ + q2d2 + ... + qkdk)]
where
P(d) - P(0)
1 - P(0)
is the extra risk over background rate at dose d or the effect of treatment.
The point estimate of the coefficents q^, i = 0, 1, 2, ..., k, and
consequently the extra risk function P^Cd) at any given dose d, is calculated
by maximizing the likelihood function of the data.
The point estimate and the 95% upper confidence limit of the extra risk,
^t^)» are calculated by using the computer program GLOBAL83, developed'by
Howe (1983). At low doses, upper 95% confidence limits on the extra
risk and lower 95% confidence limits on the dose producing a given risk are
"k
determined from a 95% upper confidence limit, q-p on parameter q^. Whenever
qj > 0, at low doses the extra risk Pt(d) has approximately the form P^Cd) =
qi x d. Therefore, qi x d is a 95% upper confidence limit on the extra
A
risk and R/qj^ is a 95% lower confidence limit on the dose producing an
extra risk of R. Let LQ be the maximum value of the log-likelihood function.
if A
The upper limit, qi, is calculated by increasing q^ to a value q^ such
that when the loglikelihood is remaximized subject to this fixed value, q^,
for the linear coefficient, the resulting maximum value of the log-likelihood
L^ satisfies the equation
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2 (L0 - L!> = 2.70554
where 2.70554 is the cumulative 90% point of the chi-square distribution with
one degree of freedom, which corresponds to a 95% upper-limit (one-sided).
This approach of computing the upper confidence limit for the extra risk Pt(d)
is an improvement on the Crump et al. (1977) model. The upper confidence
limit for the extra risk calculated at low doses is always linear. This is
conceptually consistent with the linear non-threshold concept discussed
£
earlier. The slope, q^, is taken as an upper-bound of the potency of the
chemical in inducing cancer at low doses. (In the section calculating the
risk estimates, Pfc(d) will be abbreviated as P.)
In fitting the dose-response model, the number of terms in the polynomial
is chosen equal to (h— 1), where h is the number of dose groups in the experi-
ment including the control group. A positive response to vinylidene chloride
exposure occurs at only one dose level in the Maltoni study. Therefore, only
one term in the polynomial, other than the constant, can be estimated.
10.5.3.4 CALCULATION OF UNIT RISK
10.5.3.4.1 Definition of Unit Risk — This section deals with the unit
risk for vinylidene chloride in air and water and the potency of vinylidene
chloride relative to other carcinogens that the GAG has evaluated. The unit
risk estimate for an air or water pollutant is defined as the increased life-
time cancer risk occurring in a hypothetical population in which all indivi-
duals are exposed continuously from birth throughout their lifetimes to a
concentration of 1 ug/m^ of the agent in the air they breathe, or to 1 pg/L
in the water they drink. This calculation is done to estimate in quantitative
terms the impact of the agent as a carcinogen. Unit risk estimates are used
for two purposes: 1) to compare the carcinogenic potency of several agents
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with each other, and 2) to give a crude indication of the population risk
which might be associated with air or water exposure to these agents, if the
actual exposures are known.
For most cases of interest to risk assessment, the 95% upper-limit risk
associated with dose units/day, as obtained by means of the GLOBAL83 compu-
ter program (Howe, 1983), can be adequately approximated by P(d) =
A
1 exp-(q^d). A "unit risk" in units X is the risk corresponding to an expo-
sure of X s 1. To estimate this value we simply find the number of dose units/
day that correspond to one unit of X, and substitute this value into the above
relationship.
10.5.3.4.2 Interpretation of Unit Risk Estimates — For several reasons,
the unit risk estimate based on animal bioassays is only an approximate indi-
cation of the absolute risk in populations exposed to known carcinogen concen-
trations. There may be important differences in target site susceptibility,
immunological responses, hormone function, dietary factors, and disease. In
addition, human populations are variable with respect to genetic constitution
and diet, living environment, activity patterns, and other cultural factors.
The unit risk estimate can give a rough indication of the relative carci-
nogenic potency of a given agent compared with other carcinogens. The compar-
ative potency of different agents is more reliable when the comparison is based
on studies in the same test species, strain, and sex, and by the same route
of exposure, although ordinarily the risk should be independent of route of
exposure except in special circumstances such as nasal or lung carcinoma with
inhalation exposure, or forestomach tumors with gavage administration.
The quantitative aspect of carcinogen risk assessment is included here
because it may be of use in the regulatory decision-making process, e.g., set-
ting regulatory priorities, evaluating the adequacy of technology-based con-
. 10-144
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trols, etc. However, it should be recognized that the estimation of cancer
risks to humans at low levels of exposure is uncertain. At best, the linear
extrapolation model used here provides a rough but plausible estimate of the
upper limit of risk, i.e., it is not likely that the true risk would be much
more than the estimated risk, but it could very well be lower. The risk esti-
mates for vinylidene chloride presented in this document should not be regar-
ded as immutable representations of the true cancer risks; they are calculated
only under the presumption that vinylidene chloride is carcinogenic. However,
the estimates presented may be factored into regulatory decisions to the
extent that the concept of upper risk limits for vinylidene chloride are
found to be useful.
This chapter gives the estimates of q^, 95% upper-limit slope from the
linearized multistage model.
10.5.3.4.3 Estimation of Unit Risk Using the Maltoni et al. (1985)
Inhalation Study —
10.5.3.4.3.1 Unit Risk for Air. The only animal study showing a signi-
ficant increase in tumors is the inhalation study of Maltoni et al. (1985),
in which male Swiss mice developed kidney adenocarcinomas. The pertinent
long-term (52 weeks) exposure-response data from this study are presented in
Table 10—47. The two control groups were combined, as well as the two groups
treated at 25 ppm, since the responses within treatment groups were not statis-
tically different. Lacking information on early mortality and scheduled sacri-
fice, the number surviving to the time of the first kidney adenocarcinoma is
used as the denominator.
The calculation of the cancer risk estimates by the multistage model,
allowing for a two-stage process, yields a maximum likelihood estimate (MLE)
for the linear term of q-^ = 0, and a quadratic term of ^2 ~ 6.79 (mg/kg/day) .
10-145
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The 95% upper limit on the linear term is
q± = 1.16 (mg/kg/day)"1
&
The unit risk, q^, can also be expressed in terms of excess cancer risk
per ppm of continuous lifetime exposure to vinylidene chloride. To express
the unit risk in terms of ppm, the animal data are used to calculate a human
equivalency (see Section 10.5.3.2.2) in mg/day or mg/kg/day. A continuous
lifetime exposure to vinylidene chloride in ppm calculated from the experimen-
tal exposure is:
10 ppm x 4/24 x 4.5/7 x 52/121 = 0.46 ppm
Thus, if a 0.46 ppm continuous lifetime exposure results in a daily human
dose of 0.078 mg/kg/day, then 1 ppm continuous lifetime exposure results in a
daily human dose of 0.17 mg/kg. The conversion follows simply as:
q* = 1.16 (mg/kg/day) l x 0.17 mg/kg/day = 2.0 x 10 1 (ppm) 1
ppm
or
q* = 2.0 x 10~4 (ppb)"1
The same value of q^ in units of (ppm) or (ppb) could have been derived
directly by extrapolating on a direct ppm animal-to-human equivalence. This is
because of the proportionality assumptions necessary to determine equivalent
10-146
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doses in Table 10-47. To express the unit risk in terras of yg/m3, the
following conversion is used:
1 yg/m3 = 1 (yg/m3) x 1CT3 (m3/L)/1.2 (g/L) x MW (VDC)/MW (air) =
10~3/(1.2 x 97/28.8) yg/g = 2.5 x 10~* ppm
For a lifetime continuous exposure to 1 yg/m3 of vinylidene chloride,
the corresponding estimate is
q* = 2.0 x 10"1 (ppm)'1 x 2.5 x 10"4 = 5.0 x 10~5 (yg/m3)"1
10.5.3.4.3.2 Unit Risk for Drinking Water. The unit risk for water in-
gestion can be derived using two basic approaches: a) converting the doses in
the Maltoni et al. (1985) inhalation study to an equivalent oral dose and using
the kidney tumor incidence data, and b) estimating an upper-limit value from the
negative data of the Quast et al. (1983) drinking water study in Sprague-Dawley
rats or from the negative NCI/NTP (1982) gavage study in Fischer 344 rats and
B6C3F1 mice.
Both approaches have limitations. Although the first approach is based on
positive tumor response data, the uncertainty of determining the effective up-
take via inhalation is a limitation. The data of McKenna et al. (1977) help
to clarify the situation in rats, but the lack of human uptake data via the
inhalation route is still a limitation. The second approach assumes that a
response occurs via ingestion, although there is no direct evidence that this
is the case.
For the first approach, extrapolation from the Maltoni et al. inhalation
study above yields a 95% upper limit on the linear term of q, = 1.16 (mg/kg/
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day)" • The upper-limit incremental unit risk for drinking water, assuming
2 L/day of intake and 100% absorption, can be estimated by first noting that
the intake from a concentration of 1 pg/L is
1 ug/L x 2 L/day x 10~3 rag/pg x 1/70 kg = 2.86 x 10~5 mg/kg/day
The risk from this intake is
R = 1.16 x 2.86 x 10~5
= 3.3 x 10~5
which is the unit risk for 1 ug/L in drinking water derived from the Maltoni
et al. inhalation data.
In the second approach, the data on total tumors in the Quast et al.
(1983) study (Table 10-40) in male rats is used. After converting the average
number of tumors per animal to expected incidence of animals with tumors, the
doses were converted to their human equivalents using the surface area factor,
and the linearized multistage model was used to find the upper 95% confidence
A ^fc — 1
limit of the slope, q1. The result is q± = 0.159 (mg/kg/day)
The same method was used for the data of the NCI/NTP study in rats and
mice (Table 10-43). In this calculation, data on the male rat adrenal pheo-
chromocytomas, the male rat subcutaneous fibromas, and the female mouse lympho-
mas were used. The upper-bound slope estimates were as follows:
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Data set
Male rat adrenal
Male rat fibromas
Female mouse lymphomas
Upper—bound
slope estimate
(mg/kg/day)"1
0.577
0.284
0.364
The range of these upper-bound estimates from the negative studies is from
0.16 to 0.58 (mg/kg/day)"1. The interpretation of this range is that if a
response does occur via ingestion of vinylidene chloride, the slope is not
higher than 0.58 (mg/kg/day)"1. Assuming 2 L/day of drinking water intake,
the unit risk from a water concentration of 1 yg/L can be calculated as
follows: the dose from a concentraton of 1 yg/L as shown above is 2.86 x 10~->
mg/kg/day. The upper-bound incremental risk resulting from the dose is
R = 0.58 (mg/kg/day)"1 x 2.86 x 10~5 mg/kg/day
= 1.66 x 10~5
This,is the upper-bound unit risk estimate for 1 pg/L of vinylidene chloride
in drinking water. This value is approximately one-half of the estimate ob-
tained directly from the positive Maltoni et al. inhalation data. The
estimate based on oral studies is chosen over the one derived from the Maltoni
at al. inhalation study because the oral route of administration is more appro-
priate.
10.5.4 Risk Estimates from Epidemiologic Data
10.5,4.1 SELECTION OF EPIDEMIOLOGIC DATA SETS — Whenever possible,
human data are used in preference to animal bioassay data. If epidemiologic
studies and sufficiently valid exposure information are available for a com-
pound, they may be used in several ways. If these data show a carcinogenic
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effect, they are analyzed to give an estimate of the linear dependence of
cancer rates on lifetime average dose, which is equivalent to the factor B^
(see Section 10.5.4.2 for definition). If no carcinogenic effects are seen
in the epidemiologic studies when positive animal evidence is available, the
assumption is that a risk does exist, but that it is too small to be obser-
vable in the epidemiologic data. An upper limit to the cancer incidence is
then calculated, assuming hypothetically that the true incidence is below the
level of detection in a human cohort of the size studied.
Very little information exists that can be used for extrapolating from
high-exposure occupational studies to low environmental -levels. However, if
a number of simplifying assumptions are made, it is possible to construct a
crude dose-response model whose parameters can be estimated using vital
statistics, epidemiologic studies, and estimates of worker exposures. Thus,
the Ott et al. (1976) study provides data which may be used to calculate 95%.
upper-limit estimates on relative risk, although this study does not provide
evidence for the carcinogenicity of vinylidene chloride.
10.5.4.2 DESCRIPTION OF RISK MODEL — In human studies, the response is
measured in terms of the relative risk of the exposed cohort of individuals as
compared to the control group. The mathematical model employed assumes that
for low exposures the lifetime probability of death from a specific cancer,
PO, may be represented by the linear equation
P0 = A + BHX
where A is the lifetime probability in the absence of the agent, and X is the
average lifetime exposure to environmental levels in units such as ppm. The
factor BJJ is the increased probability of cancer associated with each unit in-
10-150
-------
crease of the agent in air.
If we make the assumption that R, the relative risk of lung cancer for
exposed workers in comparison to the general population, is independent of the
length or age of exposure but depends only upon the average lifetime exposure,
it follows that
R
R
X2)
or
RP0 = A + BH
+ X2)
where X^ = lifetime average daily exposure to the agent for the general pop-
ulation, X2 = lifetime average daily exposure to the agent in the occupational
setting, and PQ = lifetime probability of dying of cancer with no or neglig-
ible epichlorohydrin exposure.
Substituting PQ = A + BH X} and rearranging gives
BH = P0 (R - 1)/X2
To use this model, estimates of R and X2 must be obtained from the epidemio-
logic studies. The value PQ is derived by means of life table methodology
from the age-cause-specific combined death rates for males found in the
U.S. Vital Statistics tables. For total cancer, the estimate of PQ is 0.23.
This model is used in section 10.5.3.10, which deals with unit risk estimates
based on human studies.
10-151
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10.5.4.3 CALCULATION OF UPPER LIMITS OF RISK — Although the epidemio-
logic studies on vinylidene chloride provide no evidence for its carcinogeni-
city, they can still be used to provide information on an upper limit of risk
to be expected. The GAG adopts this procedure of using negative epidemiologic
studies for providing upper limits when animal studies are positive. Such
use of negative human studies can modify estimates of potency.from the posi-
tive animal studies.
10.5.4.4 COMPARING ANIMAL AND HUMAN INHALATION STUDIES — This section
investigates whether or not the estimates of cancer risk extrapolated from
kidney adenocarcinoma response in the Maltoni et al. (1985) inhalation study
on Swiss male mice reasonably reflect the observed response of the Ott et al.
(1976) study of vinylidene chloride-exposed humans. Both animals and humans
were exposed to comparable levels but for different portions of their life-
times—10 ppm and 25 ppm for 4 hours/day, 4-5 days/week for 52 weeks for the
animals, and < 5 ppm to about 70 ppm for an 8-hour time-weighted average
(TWA), 5 days/week for an average exposure of about 5.7 years for humans.
Average follow-up for the animals was 121 weeks; for the 138 vinylidene
chloride workers average follow-up was about 15.7 years. Based on the figures
in Table 10-45, we estimate the average 8-hour TWA exposure to have been 16.5
ppm over the exposure period.
The observed effects in the workers were 5 deaths overall (7.5 expected)
and one cancer death (1.1 expected). As discussed in the epidemiology sec-
tion, disregarding latent period, at least 12 cancer deaths (relative risk of
10.6) would have had to occur to be able to detect a significantly elevated
risk at the p < 0.05 level with 80% power. In order to determine the proba-
bility of human response predicted by animal extrapolation, we must make some
assumptions of proportionality which might not hold for vinylidene chloride
10-152
-------
dose-response. Specifically, we must assume proportional responses from 5.7
years average exposure and 15.7 years average observation (out of 50 years
possible remaining for workers). For extrapolation from animal data we use
the MLE estimates, which are nonlinear (quadratic) in the experimental
range. The MLE extrapolations to humans converted to ppm are qg ='0 and qo '.=
0.195 (ppm)~2. Based on the above assumptions of proportionality, we,can .
estimate individual cancer risk to the average worker as the lifetime predic-
ted cancers .(based on animal risk extrapolation to the human exposure condi-
tions) as follows:
P = 1 - exp [- 0.195 (ppm)~2 (16.5 ppm x _8_ x 240 x 5.7)2]
24 365 50
=0.033
with an upper 95% confidence limit of
1 -
exp (- 0.20 x 16.5 x 8/24 x 240/365 x 5.7/50) - 0.79
For 138 employees at risk for an average of 15.7 years, we would expect to see
138 x 0.033 x 15.7 = 1.44 cancers.
50
This figure is not significantly (p > 0.25) larger than that observed, based
on the Poisson probability test (the probability of observing as few as 1
cancer death if 2.5 [1.44 + 1.1] are expected). The risk based on animal
extrapolation appears consistent with the -human data.
Even if we consider a 15-year latent period for expression of the cancer
effect, the results do not change appreciably. Although the effects for this
10-153
-------
subcohort cannot be directly predicted, we note that 83 of the 138 had a
potential follow-up of at least 15 years and that 103 of the 138 were still
working as of the observation cutoff date. Thus, it seems reasonable to
assume that at least half of the -original cohort would have had sufficient
exposure and latent period to have developed an effect. However, the sample
size is still very small.
However, the weaknesses of the Ott et al. study become still more apparent
when we try to use its dose-response information directly. In order to make an
estimate from this negative study, our procedure is to base the estimate on a
95% upper limit. The model, presented in section 10.5.3.6, requires an
estimate of the 95% upper limit of the observed SMR of 91 (95% upper confi-
dence limit = 505) and an estimate of continuous lifetime equivalent exposure.
As presented above for the cohort of 138, this is
16.5 ppm x _8^ x 240 x 5.7 = 0.41 ppm
24 365 50
Thus, based on the relative risk model for human data, the 95% upper-limit
unit risk, B*, for a continuous lifetime exposure to 1 ppm vinylidene chloride
in air is
B* =
x
0.23 (4.05) = 2.27 (ppm)"1
0.41
where PQ • 0.23 is the approximate lifetime probability of death from cancer
based on 1976 U.S. Vital Statistics death rates. This is greater than the 95%
upper-limit estimate q^ = 0.20 (ppm) from the animal study. The basic
problem arises from the weakness of the Ott study due to the small sample size
10-154
-------
and short follow-up. Thus, based on the above analyses, we conclude that the
extrapolations from the animal data are consistent with the human response.
In addition, because of the uncertainty due to the small size and limited
observation in the epidemiology study, the extrapolation from the animal
study cannot be dismissed as too high. The 95% upper-limit incremental unit
^ — 1
risk from the animal study, q^ = 0.20 (ppm) is chosen as the 95% upper-
limit incremental unit risk estimate, because it is lower than the 95% upper-
& —l
limit estimate, qi = 2.27 (ppm) based on the negative human study.
10.5.5 Relative Carcinogenic Potency
10.5.5.1 DERIVATION — One of the uses of the concept of unit risk is to
compare the relative potency of carcinogens. To estimate the relative potency
on a per mole basis, the unit risk slope factor is multiplied by the molecular
weight, and the resulting number is expressed in terms of (mmol/kg/day)"•*•.
This is called the relative potency index.
Figure 10-7 is a histogram representing the frequency distribution of
potency indices of 54 chemicals evaluated by the GAG as suspect carcinogens.
The actual data summarized by the histogram are presented in Table 10-48.
Where human data were available for a compound, they were used to calculate
the index. Where no human data were available, animal oral studies and animal
inhalation studies were used, in that order. Animal oral studies were selec-
ted over animal inhalation studies because most of the chemicals have been
tested with animal oral studies, thus better allowing potency comparisons by
route.
10.5.5,2 POTENCY INDEX — The potency index for vinylidene chloride based
on kidney adenocarcinomas in the Maltoni et al. (1985) inhalation bioassy is
1.1 x 10+2 (mmol/kg/day)~l. This is derived as follows: the 95% upper-limit
slope estimate from the Maltoni study is 1.16 (mg/kg/day)"^-. Multiplying by
10-155
-------
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10-156
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10-160
-------
the molecular weight of 97 gives a potency index of 1.1 x 10+2. Rounding off
to the nearest order of magnitude gives a value of 10"^, which is the scale
presented on the horizontal axis of Figure 10-7. The index of 1.1 x lO"1"^
lies in the third quartile of the 54 suspect carcinogens.
Ranking of the relative potency indices is subject to the uncertainty
involved in comparing potency estimates for a number of chemicals based on
different routes of exposure in different species using studies whose quality
varies widely. Furthermore, all the indices are based on estimates of low-
dose risk using linear extrapolation from the observational range. Thus,
these indices are not valid for the comparison of potencies in the experimen-
tal or observational range if linearity does not exist there. Furthermore,
for vinylidene chloride this quantitative estimate is subject to the further
uncertainties of the limited evidence of carcinogenicity and the response in
mice only at the higher dose.
10.5.6 Summary
10.5.6.1 QUALITATIVE — Eighteen animal studies have been identified
which provide information about the carcinogenic potential of VDC. Eleven of
the studies involve inhalation exposure, five are oral (four gavage, one drinking
water), and one each by skin application and subcutaneous injection. Some of
the studies were designed and conducted as cancer bioassays while others were
conducted to detect toxicity. None of the 11 inhalation studies had a full
lifetime exposure, the exposures being for 12 months or less, while 3 of the 5
gavage studies were lifetime exposure.
The carcinogenicity of vinylidene chloride was evaluated by inhalation
exposure of both sexes of Swiss mice and Sprague-Dawley rats to vinylidene
chloride concentrations as high as those maximally tolerated (25 ppm for mice
and 150 ppm for rats) for 12 months followed by lifetime observation. In
10-161
-------
addition, Chinese hamsters were exposed to 25 ppm vinylidene chloride (less
than a maximally tolerated dose) for 12 months followed by lifetime observation
(Maltoni et al., 1985). A statistically significant increase in kidney adeno-
carcinomas was found in male Swiss mice, and, although a statistically signif-
icant increase in mammary carcinomas in treated female Swiss mice was evident,
the investigators concluded that a direct relationship between this response
in female mice and vinylidene chloride treatment remains open, largely due to
stated results of their statistical analysis, indicating a weaker response
when the data are adjusted for survival and lack of a dose-related response
over the course of the study. A carcinogenic effect of vinylidene chloride
in Sprague-Dawley rats and Chinese hamsters was not apparent. The 12-month
exposure period used in this study was below lifetime exposures.
Additional inhalation exposure studies of vinylidene chloride in animals
have been done (Table 10-23). Exposure of male and female Sprague-Dawley
rats to 25 ppm and 75 ppm vinylidene chloride for 18 months followed by 6
months of observation did not show a carcinogenic effect (McKenna et al.,
1982); however, the exposure levels used did not appear to be overtly toxic,
and use of additional higher exposure levels might have provided a broader
evaluation for carcinogenicity.
No statistically significant increase in tumor formation in treated ani-
mals was shown in any of the following separate studies of exposure to
vinylidene chloride:
(1) Male and female Wistar rats exposed to 200 ppm for 5 months and 100
ppm for 7 months followed by observation for an additional 12 months (Viola
and Caputo, 1977);
(2) Male and female Sprague-Dawley rats exposed to 75 ppm and 100 ppm
for an unspecified duration (Viola and Caputo, 1977);
10-162
-------
(3) CD-I mice and CD rats exposed to 55 ppm and observed for a period
of 12 months (Lee et al., 1978);
(4) CD-I mice exposed to 55 ppm for as long as 6 months and observed
for 12 additional months (Hong et al., 1981); and
(5) CD rats exposed to 55 ppm for as long as 10 months and observed for
an additional 12 months (Hong et al. , 1981).
The known exposure periods of 12 months or less used in these studies
were shorter than potential lifetime exposure periods, and use of more than
one exposure level in the studies with CD-I mice and CD rats could have
provided a stronger evaluation of dose-response.
Several carcinogenicity studies in which vinylidene chloride was adminis-
tered orally to experimental animals have been reported as negative. These
studies include:
(1) Gavage administration of vinylidene chloride in olive oil at doses
as high as 20 mg/kg to male and female Sprague-Dawley rats for 12 months,
followed by lifetime observation (Maltoni et al., 1985);
(2) Administration of vinylidene chloride in drinking water at levels
of maximum water solubility (200 ppm) to male and female Sprague-Dawley rats
for 2 years (Quast et al., 1983; Humiston, et al., 1978);
(3) Gavage administration of vinylidene chloride in corn oil to male
and female Fischer 344 rats at 1 and 5 mg/kg and male and female B6C3F1 mice
at 2 and 10 mg/kg for 2 years (NCI/NTP, 1982);
(4) Gavage administration of 150 mg/kg of vinylidene chloride in corn
oil to pregnant BDIV rats on day 17 of gestation, followed by weekly gavage
doses of 50 mg/kg of vinylidene chloride to the pups for their lifetimes
following birth (Ponomarkov and Tamatis, 1980).
The 12-month exposure in Sprague-Dawley rats given vinylidene chloride
10-163
-------
by gavage was below the potential lifetime exposure, and a maximally tolerated
dose does not appear to have been selected. The lack of a clear effect on
survival and body weight in Fischer 344 and B6C3F1 mice given vinylidene
chloride in corn oil suggests that higher doses could have'been tested to
challenge the animals more strongly for carcinogenicity. A broader evaluation
of vinylidene chloride carcinogenicity in BDIV rats might have been possible
with the addition of more than the one dose level used in the study, and with
more than one treatment each week.
Vinylidene chloride was not carcinogenic in female ICR/Ha mice when
applied to the skin at 121 mg/mouse three times per week, or when injected
subcutaneously at 2 mg/mouse once weekly at maximum tolerated doses in
lifetime studies (Van Duuren et al., 1980). When a single application of 121
mg/mouse of vinylidene chloride was followed by repeated application of the
tumor-promoting agent phorbol myristate acetate, skin papillomas resulted in
ICR/Ha mice.
One epidemiologic study on a population on 138 workers (Ott et al.,
1976) showed no carcinogenic effects attributable to vinylidene chloride.
At the time the study was published in 1976, the dates of first exposures for
55 workers were between 1960 and 1969, thus indicating that nearly 40% of the
workers had no more than 16 years latency since first exposure and that
continued follow-up could strengthen the evaluation for carcinogenicity.
10.5.6.2 QUANTITATIVE — Only the Swiss mice inhalation study of Maltoni
et al. (1985) provides sufficient data for a quantitative cancer risk estimate
for vinylidene chloride. This estimate is made under the presumption that
vinylidene chloride is a human carcinogen. Based on kidney adenocarcinomas
in male mice, the upper-bound incremental unit risk estimate for cancer from
a lifetime of continous exposure to 1 ppb (vinylidene chloride) (air) is 2.0
10-164
-------
x 10 [5.0 x lO^Cpg/m3)"! ]. An estimate of the upper-bound incremental unit
risk for 1 yg/L of vinylidene chloride in drinking water is .1.7 x 10"^,
based on the highest slope estimate from negative gavage and drinking water
studies in rats and mice. The route of administration for these studies is
more appropriate for extrapolating to drinking water exposures. The relative
potency of vinylidene chloride, expressed in molar units, is 1.1 x 10+2
(mmol/kg/day)~l. Among 54 chemicals that the CAG has evaluated as suspect
carcinogens, vinylidene chloride ranks in the third quartile.
10.5.7 Conclusions
Evidence of the carcinogenicity of vinylidene chloride was found in Swiss
mice in an inhalation study (Maltoni et al., 1985). Although the exposure
period was only 12 months, in which the mice were exposed for only 4 hours
daily, kidney adenocarcinomas, a rare tumor type, were diagnosed in treated
male Swiss mice. A statistically significant increase of mammary carcinomas
was evident in female mice, and a statistically significant increase in pul-
monary adenomas occurred in mice of both sexes at both dose levels. However,
because no clear dose-response relationship exists, a direct correlation
between induction of mammary carcinomas or pulmonary adenomas and vinylidene
chloride exposure is uncertain, and therefore, the response is only weakly sup-
portive in a weight-of-evidence context. Statistically significant increases
in mammary tumors were observed in two studies in female Sprague-Dawley rats
exposed to vinylidene chloride by inhalation and in drinking water, but these
increases are not considered to be treatment-related since this strain of rats
has a high background incidence of mammary tumors and there was no dose-
reponse relationship between tumor incidence and exposure to vinylidene
chloride. Van Duuren et al. (1979) demonstrated that vinylidene chloride
10-165
-------
acts as a tumor initiator in mouse skin.
Although no other inhalation studies on the carcinogenic!ty of vinylidene
chloride demonstrated any statistically significant increase of tumors, all
of these studies had one or more deficiencies: shortened exposure or obser-
vation periods, did not reach a maximum tolerable dose, and/or used only a
single dose level. None of the five oral studies show a statistically
significant response, yet only two of the five were lifetime, multiple dose
studies and the dosing appears to be less than the MTD.
There is no adequate epidemiologic data to assess the carcinogenicity of
vinylidene chloride in humans.
Vinylidene chloride has been shown to be mutagenic in several strains of
bacteria, in yeast, and in the plant Tradescantia; it has even been used as a
positive control in a bacterial study assessing the mutagenic potential of
volatile compounds. Vinylidene chloride does require metabolic activation in
order to produce a mutagenic response in bacteria and yeast; livers from a
variety of species, including man, have been used to metabolically activate
vinylidene chloride in in vitro assays.
Vinylidene chloride can be metabolized to intermediates capable of
reacting with macromolecules. At doses similar to those used in the positive
mouse bioassay, covalent binding of active metabolites to macromolecules is
greater in the kidney (the target organ in the bioassay) than in the liver;
DNA alkylation does occur at low levels and is also greater in the kidney
than in the liver, particularly in the mouse.
Applying the International Agency for Research on Cancer (IARC) approach
for classifying carcinogenic agents, the level of evidence for vinylidene
chloride carcinogenicity in animals is considered to be limited. Applying
the IARC approach for evaluating epidemiologic data, the currently available
10-166
-------
data is considered inadequate for making a judgment on the carcinogenicity of
vinylidene chloride. Based on the overall evidence, vinylidene chloride
would be a Group 3 chemical according to the IARC approach, and by definition,
a Group 3 chemical cannot be classified as to its carcinogenic potential for
humans. However, the mutagenic activity of vinylidene chloride, its chemical
structure, its activity as a tumor initiator in mouse skin, and the ability
of metabolites to react with DNA, raise a concern that the total body of
evidence should not be lightly dismissed. The negative results from many
studies do not contradict this position since unfortunately all of the studies
are flawed in their sensitivity to detect a carcinogenic response.
Based on EPA's Proposed Guidelines for Carcinogen Risk Assessment (U.S.
EPA, 1984), the animal evidence for vinylidene chloride would result in an
overall classification of Group C, meaning that the chemical is a "possible"
human carcinogen.
Although vinylidene chloride has only limited animal evidence for carcin-
ogenicity (Group 3 chemical according to the IARC classification system and
Group C according to the EPA classification system), the kidney adenocarcinomas
in male Swiss mice provide data that have been used for estimating an upper
bound of the incremental unit risk, under the presumption that vinylidene
chloride is a potential human carcinogen. The upper-limit incremental cancer
risk is 5.0 x 10"^ for a lifetime continuous exposure to 1 pg (vinylidene
chloride)/m^ in air and 1.7 x 10~5 for exposure to 1 pg/L in drinking water.
Expressed in terms of 1 pg/kg bw/day continuous lifetime exposure to vinyli-
dene chloride, the upper-limit incremental cancer risk is 1.16 x 10~3.
Expressed in terms of relative potency, vinylidene chloride would rank in the
third quartile among the 54 chemicals that the GAG has evaluated as suspect
or known human carcinogens.
10-167
-------
-------
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