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OAR Box 1131 

Prepped by Ollie Stewart 

Document Number: 

116)11-1-121 

Docket Number: 

A-83-22 

Printed 4/21/2008 2:34:11 PM Sheet 116 of 162 
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EPA 600/8 77 017 

December 1977 

Special Series 

Air Quality Criteria for 

WDEJI 

Office of Research and Development " 

U.S. Environmental Protection Agency

 ; -egg? 

Washington, D.C. 20460 'T^ T 
P.3 

RESEARCH REPORTING SERIES 

Research reports of the Office of Research and Development, U.S. Environmental Protection 

Agency have been grouped into series. These broad categories were established to facilitate further 

development and application of environmental technology. Elimination of traditional grouping 

was consciously planned to foster technology transfer and a maximum interface in related fields. 

These series are: 

1. Environmental Health Effects Research 

2. Environmental Protection Technology 

3. Ecological Research 

4. Environmental Monitoring 

5. Socioeconomic Environmental Studies 

6. Scientific and Technical Assessment Reports (STAR) 

7. Interagency Energy-Environmental Research and Development 

8. "Special" Reports 

9. Miscellaneous Reports 

This report has been assigned to the SPECIAL series. Air quality criteria documents are issued, as 

mandated by the Clean Air Act, to provide the basis for decisions by the Administrator, EPA, 

regarding the need for national ambient air quality standards. 

EPA REVIEW NOTICE 

This report has been reviewed by the Office of Research and Development, EPA, and approved for 

publication. Mention of trade names or commercial products does not constitute endorsement or 

recommendation for use. 

AVAILABILITY NOTICE 

This document is available through the Library Services Office, MD-35, Research Triangle Park, 

N.C. 27711. The printed version will also be available from the Superintendent of Documents, U.S. 

Government Printing Office, Washington, D.C. 20402. 

Publication No. EPA-600/8-77-017 
P.4 

EPA-600/8-77-017 

December 1977 

AIR QUALITY CRITERIA 

FOR 

LEAD 

U.S. ENVIRONMENTAL PROTECTION AGENCY 

OFFICE OF RESEARCH AND DEVELOPMENT 

WASHINGTON, D.C. 20460 

For sal e by the Superintendent of Documents', U.S. Government 

Printing Office, Washington, D.C. 20402 
P.5 

PREFACE 

This document has been prepared pursuant to Section 108(a)(2) of the Clean Air 

Act, as amended, and the Administrator's action on March 31,1976, of listing lead 

as a criteria pollutant. Under the Act, the issuance of air quality criteria is a vital 

step in a program of responsible technological, social, and political action to protect the public from the adverse effects of air pollution. 

These health and welfare criteria fulfill the regulatory purpose of serving as the 

basis upon which the Administrator must promulgate national primary and secondary ambient air quality standards for lead under Section 109 of the Clean Air Act. 

The proposed standards are being published concurrently with the publication of 

this criteria document. 

Although the preparation of a criteria document requires a comprehensive 

review and evaluation of the current scientific knowledge regarding the air pollutant in question, the document does not constitute a complete, in-depth scientific 

review. The references cited do not constitute a complete bibliography. The objective is to evaluate the scientific data base and to formulate criteria which may serve 

as the basis for decisions regarding the promulgation of a national ambient air 

quality standard for lead. 

In the case of lead, as well as other air pollutants, adverse health effects are a 

consequence of the total body burden resulting from exposure via all routes of intake. It is necessary, therefore, to evaluate the relative contribution made by inhalation and ingestion of atmospheric lead to the total body burden. 

The Agency is pleased to acknowledge the efforts and contributions of all persons' and groups who have participated as authors or reviewers to this document. In 

the iast analysis, however, the Environmental Protection Agency is responsible for 

its content. 

DOUGLAS M. COSTLE 

Administrator 

U.S. Environmental Protection Agency 

in 
P.6 

ABSTRACT 

This document summarizes current knowledge about the relationships of airborne lead to man and his environment. The effects that have been observed to occur when airborne lead has reached or exceeded specific levels for specific time 

periods constitute the central criteria on which EPA will base a national ambient 

air quality standard for lead. 

Although this document deals mainly with airborne lead, it also outlines other 

environmental routes of exposure. Primary exposure to airborne lead occurs 

directly via inhalation, and its sources are relatively easy to identify. Secondary exposure may occur through ingestion of foods from crops contaminated by airborne 

lead or, especially in children, through mouthing of nonfood items and materials so 

contaminated. Exposures to nonairborne lead may also be direct and indirect, and 

routes include ingestion of foods containing lead attributable to natural uptake and 

to processing. 

In man, lead primarily affects red blood cells, the central and peripheral nervous 

systems, soft tissues such as liver and kidney, and bone; the latter ultimately sequesters 95 percent of the body's lead burden. Significant biological indices of exposure to lead include microgram quantities of lead and of erythrocyte protoporphyrin (EP) per deciliter of blood (/xg/dl). Adverse effects range from elevated EP and mild anemia at 20 to 40 fig Pb/dl—through gastrointestinal, renal, 

and hepatic pathologies—to severe neurobehavioral impairment at >80 to 120 fig 

Pb/dl, sometimes culminating at those levels in convulsions and abrupt death. 

Preschool children and developing fetuses are the populations at greatest risk. 

IV 
SCIENCE ADVISORY BOARD 

SUBCOMMITTEE ON SCIENTIFIC 

CRITERIA FOR ENVIRONMENTAL LEAD 

P.7 

1 

The substance of this document was review by a Subcommittee on Scientific Criteria for Environmental Lead, Science Advisory Board, in public session. 

CHAIRMAN: 

Dr. Roger O. McClellan, Director of Inhalation Toxicology Research Institute, 

Lovelace Foundation, P.O. Box 5890, Albuquerque, New Mexico 87115 

CONSULTANTS: 

Dr. J. Julian Chisolm, Jr., Senior Staff Pediatrician, Baltimore City Hospital, 

4940 Eastern Avenue, Baltimore, Maryland 21224; and Associate Professor 

of Pediatrics, Johns Hopkins University School of Medicine 

Dr. Paul B. Hammond, Professor of Environmental Health, Department of Environmental Health, University of Cincinnati Medical Center, 3223 Eden 

Avenue, Cincinnati, Ohio 45267 

Dr. James G. Horsfall, Director Emeritus, Department of Plant Pathology and 

Botany, Connecticut Agriculture Experiment Station, New Haven, Connecticut 06504 

MEMBERS: 

Dr. Samuel S. Epstein, Professor of Occupational and Environmental Medicine, 

School of Public Health, University of Illinois, P.O. Box 6998, Chicago, Illinois 60680 

Dr. Edward F. Ferrand, Assistant Commissioner for Sciences and Technology, 

New York City Dept. for Air Resources, 51 Astor Place, New York, New 

York 10003 

Dr. Sheldon K. Friedlander, Professor of Chemical Engineering and Environmental Health Engineering, W. M. Keck Laboratory, California Institute of 

Technology, Pasadena, California 91109 

Dr. Jennifer L. Kelsey, Associate Professor of Epidemiology, Yale University 

School of Medicine, Department of Epidemiology and Public Health, 60 College Street, New Haven, Connecticut 06504 

Dr. Ruth Levine, Chairman, Graduate Division of Medicine and Dentistry, 

Boston University College of Medicine, Boston, Massachusetts 02118 

Mailing address: 212 Crafts Road, Chestnut Hill, Brookline, Massachusetts 

02167 

Dr. Bailus Walker, Jr., Director, Environmental Health Administration, Department of Environmental Services, Government of the District of Columbia, 

801 North Capitol, NE, Washington, D.C. 20002 

STAFF OFFICER: 

Mr. Ernst Linde, Scientist Administrator, Science Advisory Board, U.S. Environmental Protection Agency, Crystal Mall Building 2, 1921 Jefferson Davis 

Highway, Arlington, Virginia 20460 
P.8 

CONTRIBUTORS AND REVIEWERS 

Mr. Gerald G. Akland, Environmental Monitoring and Support Laboratory, Environmental Research Center, U.S. Environmental Protection Agency, 

Research Triangle Park, North Carolina 27711 

Dr. C. Alex Alexander, Adjunct Professor of Medicine and Chief of Hospital 

Medical Staff, School of Medicine, Wright State University, Dayton, Ohio 

45431 

Dr. A. P. Altshuller, Director, Environmental Sciences Research Laboratory, 

Environmental Research Center, U.S. Environmental Protection Agency, 

Research Triangle Park, North Carolina 27711 

Dr. Anna Baetjer, Professor Emeritus of Environmental Medicine, Department 

of Environmental Medicine, School of Hygiene and Public Health, The Johns 

Hopkins University, 615 North Wolfe Street, Baltimore, Maryland 21205 

Dr. Donald Barltrop, Pediatrics Unit, St. Mary's Hospital Medical School, London W2 1PG, England 

Ms. Gayla Benignus, Technical Consultant, Research Triangle Park, North 

Carolina 27709 

Dr. Irwin H. Billick, Program Manager, Lead-Based Paint Poisoning Prevention 

Research, Division of Housing Research, Office of the Assistant Secretary for 

Policy Development and Research, Department of Housing and Urban 

Development, Washington, D.C. 20410 

Dr. Robert P. Botts, Environmental Research Laboratory, Environmental 

Research Center, U.S. Environmental Protection Agency, 200 SW 35th 

Street, Corvallis, Oregon 97330 

Dr. Robert Bornschein, Department of Environmental Health, College of 

Medicine, University of Cincinnati, Cincinnati, Ohio 45267 

Dr. Ronald L. Bradow, Environmental Sciences Research Laboratory, Environmental Research Center, U.S. Environmental Protection Agency, Research 

Triangle Park, North Carolina 27711 

Dr. Kenneth Bridbord, Director, Office of Extramural Coordination and Special 

Projects, National Institute for Occupational Safety and Health, 5600 Fishers 

Lane, Rockville, Maryland 20852 

Dr. Marijon Bufalini, Environmental Sciences Research Laboratory, Environmental Research Center, U.S. Environmental Protection Agency, Research 

Triangle Park, North Carolina 27711 

Dr. Robert Burger, Senior Scientist, Research Triangle Institute, P.O. Box 

12194, Research Triangle Park, North Carolina 27709 

Dr. John B. Clements, Environmental Monitoring and Support Laboratory, Environmental Research Center, U.S. Environmental Protection Agency, 

Research Triangle Park, North Carolina 27711 

Mr. Stanton Coerr, Strategies and Air Standards Division, Office of Air Quality 

Planning and Standards, U.S. Environmental Protection Agency, Research 

Triangle Park, North Carolina 27711 
Ms. Josephine S. Cooper, Strategies and Air Standards Division, Office of Air 

Quality Planning and Standards, U.S. Environmental Protection Agency, 

Research Triangle Park, North Carolina 27711 

Mr. Gunther F. Craun, Health Effects Research Laboratory, U.S. Environmental 

Protection Agency, Cincinnati, Ohio 45268 

Dr. Annemarie Crocetti, Professor of Epidemiology, New York Medical College, 

New York, New York 10029 

Dr. Terri Damstra, Office of Health Hazard Assessment, National Institute of 

Environmental Health Services, Research Triangle Park, North Carolina 

27709 

Dr. Cliff Davidson, Graduate Research Assistant, California Institute of Technology, Mail Stop 138-78, Pasadena, California 91109 

Dr. Ivan Diamond, Department of Neurology, School of Medicine, University of 

California, San Francisco, California 94143 

Dr. Michael Dowe, Jaycor, Incorporated, Research Triangle Park, North 

Carolina 27709 

Dr. Ben B. Ewing, Professor and Director, Institute for Environmental Studies, 

University of Illinois, 408 S. Goodwin Avenue, Urbana, Illinois 61801 

Dr. Harold Furst, Professor of Epidemiology, New York Medical College and 

New York City Health Department, New York, New York 10029 

Mr. Warren Galke, Health Effects Research Laboratory, Environmental 

Research Center, U.S. Environmental Protection Agency, Research Triangle 

Park, North Carolina 27711 

Dr. J.H.B. Garner, Health Effects Research Laboratory, Environmental 

Research Center, U.S. Environmental Protection Agency, Research Triangle 

Park, North Carolina 27711 

Dr. John T. Gatzy, Associate Professor of Pharmacology, School of Medicine, 

University of North Carolina, Chapel Hill, North Carolina 27514 

Dr. Robert Goyer, Department of Pathology, University of Western Ontario, 

London 72, Ontario, Canada 

Dr. Lester D. Grant, Associate Professor of Psychiatry, School of Medicine, 

University of North Carolina, Chapel Hill, North Carolina 27514 

Mr. Daniel Greathouse, Health Effects Research Laboratory, U.S. Environmental Protection Agency, Cincinnati, Ohio 45268 

Dr. Vic Hasselblad, Health Effects Research Laboratory, Environmental 

Research Center, U.S. Environmental Protection Agency, Research Triangle 

Park, North Carolina 27711 

Dr. Derek Hodgson, Professor, Department of Chemistry, C448 Kenan, University of North Carolina, Chapel Hill, North Carolina 27514 

Dr. John Horn, Environmental Consultant, 758 Oxford Street, West, London, 

Ontario, Canada N6M1V2 

Dr. Robert J. M. Horton, Senior Research Advisor, Health Effects Research 

Laboratory, Environmental Research Center, U.S. Environmental Protection 

Agency, Research Triangle Park, North Carolina 27711 

Mr. Allen G. Hoyt, Health Effects Research Laboratory, Environmental 

Research Center, U.S. Environmental Protection Agency, Research Triangle 

Park, North Carolina 27711 

Dr. F. Gordon Hueter, Associate Director, Health Effects Research Laboratory, 

Environmental Research Center, U.S. Environmental Protection Agency, 

Research Triangle Park, North Carolina 27711 

Dr. Emmett S. Jacobs, Division Head, Additives and Environmental Studies, E. 

I. du Pont de Nemours and Company, Inc., Petroleum Laboratory, 

Wilmington, Delaware 19898 

vn 
^ p in 

Mr. Gary L. Johnson, Industrial Environmental Research Laboratory, Environmental Research Center, U.S. Environmental Protection Agency, Research 

Triangle Park, North Carolina 27711 

Mr. Robert Kellam, Strategies and Air Standards Division, Office of Air Quality 

Planning and Standards, U.S. Environmental Protection Agency, Research 

Triangle Park, North Carolina 27711 

Dr. Carole A. Kimmel, National Center for Toxicological Research, Jefferson. 

Arkansas 72079 

Dr. Robert R. Kinnison, Environmental Monitoring and Support Laboratory, 

U.S. Environmental Protection Agency, P.O. Box 15027, Las Vegas, Nevada 

89114 

Dr. John H. Knelson, Director, Health Effects Research Laboratory, Environmental Research Center, U.S. Environmental Protection Agency, Research 

Triangle Park, North Carolina 27711 

Dr. Martin R. Krigman, Professor of Pathology, School of Medicine, University 

of North Carolina. Chapel Hill, North Carolina 27514 

Dr. Robert E. Lee, Deputy Director, Health Effects Research Laboratory, Environmental Research Center, U.S. Environmental Protection Agency, 

Research Triangle Park, North Carolina 27711 

Dr. G. J. Love, Epidemiology Consultant, Research Triangle Park, North 

Carolina 27709 

Dr. James MacNeill, Pediatrician, Hillside Medical Center, El Paso, Texas 

79903 

Dr. Kathryn R. Mahaffey. Division of Nutrition. Food and Drug Administration, 

Department of Health, Educat ion. and Welfare, 1090 Tusculum Avenue, 

Cincinnati. Ohio 45226 

Dr. Alec E. Martin, Visiting Scientist, Office of Health Hazard Assessment, National Institute of Environmental Health Sciences, P.O. Box 12233, Research 

Triangle Park, North Carolina 27709 

Dr. Edward B. McCabe. 3225 Knollwood Way. Madison, Wisconsin 53713 

Mr. Gary D. McCutchen, Emission Standards and Engineering Division, Office 

of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711 

Mr. Thomas B. McMullen, Health Effects Research Laboratory, Environmental 

Research Center, U.S. Environmental Protection Agency, Research Triangle 

Park, North Carolina 27711 

Mr. Joseph Merenda. Office of Mobile Source Air Pollution Control, Office of 

Air and Waste Management, U.S. Environmental Protection Agency, Washington, D.C. 20460 

Ms. Margarita M. Morrison, Technical Information Specialist, Program Operations Office, Health Effects Research Laboratory, Environmental Research 

Center, U.S. Environmental Protection Agency, Research Triangle Park, 

North Carolina 27711 

Dr. Paul Mushak, Associate Professor of Pathology, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27514 

Dr. D. F. Nataush, Professor of Chemistry, Colorado State University, Fort Collins, Colorado 80523 

Dr. John C. Nduaguba, Assistant Professor of Medicine, School of Medicine, 

Wright State University, Dayton, Ohio 45431 

Dr. Herbert L. Needleman, The Children's Hospital Medical Center, 300 Longwood Avenue, Boston, Massachusetts 02115 

Dr. Stata Norton, Department of Pharmacology, University of Kansas Medical 

Center, Kansas City, Kansas 66110 

viii 
P.11 

Mr. John O'Connor, Strategies and Air Standards Division, Office of Air Quality 

Planning and Standards, U.S. Environmental Protection Agency, Research 

Triangle Park, North Carolina 27711 

Dr. Sergio Piomelli, Professor of Pediatrics and Director of Pediatric 

Hematology, School of Medicine, New York University Medical Center, 550 

First Avenue, New York, New York 10016 

Dr. Herbert Posner, Office of Health Hazard Assessment, National Institute of 

Environmental Health Sciences, Research Triangle Park, North Carolina 

27709 

Dr. Jerry Ptasnik, Director of Special Education, El Paso City Schools, El Paso, 

Texas 79903 

Dr. Michael J. Quigley, Health Effects Consultant, Research Triangle Park, 

North Carolina 27709 

Dr. Keturah Reinbold, Associate Research Biologist, Institute for Environmental 

Studies, University of Illinois, 405 S. Goodwin Avenue, Urbana, Illinois 

61801 

Dr. Lawrence Reiter, Health Effects Research Laboratory, Environmental 

Research Center, U.S. Environmental Protection Agency, Research Triangle 

Park, North Carolina 27711 

Dr. John F. Rogers, Assistant Professor of Medicine, School of Medicine, 

University of North Carolina, Chapel Hill, North Carolina 27514 

Dr. Gary L. Rolfe, Associate Professor of Forestry, Institute for Environmental 

Studies, University of Illinois, 408 S. Goodwin Avenue, Urbana, Illinois 

61801 

Dr. Donald Routh, Professor of Clinical Psychology, School of Medicine, 

University of North Carolina, Chapel Hill, North Carolina 27514 

Mr. Robert C. Ryans, Writer-Editor, Environmental Research Laboratory, U.S. 

Environmental Protection Agency, College Station Road, Athens, Georgia 

30605 

Mr. Edward A. Schuck, Environmental Monitoring and Support Laboratory, 

U.S. Environmental Protection Agency, P.O. Box 15027, Las Vegas, Nevada 

89114 

Dr. R. K. Skogerboe, Professor of Chemistry, Colorado State University, Fort 

Collins, Colorado 80523 

Dr. Cecil Slome, Professor of Epidemiology, School of Public Health, University 

of North Carolina, Chapel Hill, North Carolina 27514 

Mr. James R. Smith, Health Effects Research Laboratory, Environmental 

Research Center, U.S. Environmental Protection Agency, Research Triangle 

Park, North Carolina 27711 

Dr. R. D. Snee, Biostatistician, E. I. du Pont de Nemours and Company, Inc., 

Petroleum Laboratory, Wilmington, Delaware 19898 

Mr. Andrew G. Stead, Statistician, Health Effects Research Laboratory, Environmental Research Center, U.S. Environmental Protection Agency, Research 

Triangle Park, North Carolina 27711 

Mr. Orin W. Stopinski, Health Effects Research Laboratory, Environmental 

Research Center, U.S. Environmental Protection Agency, Research Triangle 

Park, North Carolina 27711 

Dr. Richard J. Thompson, Environmental Monitoring and Support Laboratory, 

Environmental Research Center, U.S. Environmental Protection Agency, 

Research Triangle Park, North Carolina 27711 

Ms. Beverly E. Tilton, Health Effects Research Laboratory, Environmental 

Research Center, U.S. Environmental Protection Agency, Research Triangle 

Park, North Carolina 27711 

IX 
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********

Mr. Ian von Lindern, Environmental Engineer, Department of Health and 

Welfare, Division of the Environment, State of Idaho, 324 2nd Street, East, 

Twin Falls, Idaho 83301 

Ms. P. A. Warrick, Technical Consultant, School of Public Health, University of 

North Carolina, Chapel Hill, North Carolina 27541 

Mr. Tony Yankel, Division of the Environment, Department of Health and 

Welfare, Statehouse, Boise, Idaho 83720 

Dr. R. L. Zielhuis, Universiteit von Amsterdam, Coronel Laboratorium, Eerste 

Constantijn Huygersstcaat 20, Amsterdam, Netherlands 

Dr. R. L. Zimdahl, Professor of Botany and Plant Pathology, Colorado State 

University, Fort Collins, Colorado 80523 
CONTENTS 

Paiie 

PREFACE iii 

ABSTRACT iv 

SCIENTIFIC ADVISORY BOARD 

SUBCOMMITTEE ON SCIENTIFIC CRITERIA 

FOR ENVIRONMENTAL LEAD v 

CONTRIBUTORS AND REVIEWERS vi 

FIGURES xvi 

TABLES xix 

ABBREVIATIONS AND SYMBOLS xxiii 

1. SUMMARY AND CONCLUSIONS 1-1 

1.1 Introduction 1-1 

1.1.1 Potential Exposure to Environmental Lead 1-1 

1.1.2 Sources of Environmental Lead 1-2 

1.1.3 Monitoring of Environmental Lead 1-3 

1.2 Effects of Lead on Man and His Environment 1-4 

1.2.1 Effect of Lead on Man 1-4 

1.2.2 Effects of Lead on the Ecosystem 1-9 

1.3 Effects of Lead on Populations 1-10 

1.4 Assessment of Risk from Human Exposure to Lead 1-11 

1.4.1 Use of Blood-Lead Levels in Risk Assessment 1-11 

1.4.2 Use of Biological and Adverse Health Effects of Lead in 

Risk Assessment 1-12 

1.4.3 Populations at Risk 1-14 

2. INTRODUCTION 2-1 

3. CHEMICAL AND PHYSICAL PROPERTIES 3-1 

3.1 Elemental Lead 3-1 

3.2 General Chemistry of Lead 3-1 

3.3 Organometallic Chemistry of Lead 3-2 

3.4 Complex Formation and Chelation 3-2 

3.5 References for Chapter 3 3-4 

4. SAMPLING AND ANALYTICAL METHODS FOR LEAD 4-1 

4.1 Introduction 4-1 

4.2 Sampling 4-2 

4.2.1 Sampler Site Selection 4-2 

4.2.2 Sampling Errors 4-2 

4.2.3 Sampling for Airborne Particulate Lead 4-3 

4.2.4 Sampling for Vapor-Phase Organic Lead Compounds. . 4-4 

4.2.5 Sampling for Lead in Other Media 4-4 

4.2.6 Source Sampling 4-6 

4.2.7 Filter Selection and Sample Preparation 4-7 

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4.3 Analysis 4-8 

4.3.1 Colorimetric Analysis 4-8 

4.3.2 Atomic Absorption Analysis 4-8 

4.3.3 Anodic Stripping Voltammetry 4-9 

4.3.4 Emission Spectroscopy 4-9 

4.3.5 Electron Microprobe 4-10 

4.3.6 X-Ray Fluorescence 4-10 

4.3.7 Methods f©r Compound Analysis 4-11 

4.4 Conclusions 4-11 

4.5 References for Chapter 4 4-11 

5. SOURCES AND EMISSIONS 5-1 

5.1 Natural Sources 5-1 

5.2 Man-Made Sources 5-1 

5.2.1 Production 5-1 

5.2.2 Utilization 5-1 

5.2.3 Emissions 5-2 

5.3 References for Chapter 5 5-5 

6. TRANSFORMATION AND TRANSPORT 6-1 

6.1 Introduction 6-1 

6.2 Physical and Chefiical Transformations in the Atmosphere .. . 6-1 

6.2.1 Physical Transformations 6-1 

6.2.2 Chemical Transformations 6-4 

6.3 Transport in Air 6-8 

6.3.1 Distribution Mechanisms 6-8 

6.3.2 Removal Mechanisms 6-12 

6.3.3 Models 6-19 

6.4 Transformation and Transport in Other Environmental Media 6-20 

6.4.1 Soils 6-20 

6.4.2 Water 6-21 

6.4.3 Plants 6-23 

6.5 References for Chapter 6 6-25 

7. ENVIRONMENTAL CONCENTRATIONS AND POTENTIAL 

EXPOSURES 7-1 

7.1 Ambient Air Exposures 7-1 

7.1.1 National Air Surveillance Network (NASN) Data 7-1 

7.1.2 Airborne Particle Size Distribution 7-4 

7.1.3 Vertical Gradients of Lead in the Atmosphere 7-4 

7.2 Mobile Source Exposures 7-6 

7.3 Point Source Exposures 7-7 

7.4 Dietary Exposures 7-9 

7.4.1 Food 7-9 

7.4.2 Water 7-11 

7.5 Occupational Exposures 7-12 

7.5.1 Exposures in Lead Mining, Smelting, and Refining ... . 7-12 

7.5.2 Exposures in Welding and Shipbreaking 7-13 

7.5.3 Exposures in the Electric Storage Battery Industry ... . 7-13 

7.5.4 Exposures in the Printing Industry 7-13 

7.5.5 Exposures in Alkyl Lead Manufacture 7-13 

7.5.6 Exposures in Other Occupations 7-13 

7.5.7 Exposures Resulting from Manmade Materials 7-14 

7.5.8 Historical Changes 7-14 

7.6 References for Chapter 7 7-14 

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8. EFFECTS OF LEAD ON ECOSYSTEMS 8-1 

8.1 Effects on Domestic Animals, Wildlife, and Aquatic Organisms 8-1 

8.1.1 Domestic Animals 8-1 

8.1.2 Wildlife 8-3 

8.1.3 Aquatic Organisms 8-5 

8.2 Effects on Plants 8-8 

8.2.1 Routes of Plant Exposure 8-8 

8.2.2 Effects on Vascular Plants 8-10 

8.2.3 Effects on Nonvascular Plants 8-11 

8.3 Effects on Relationships Between Arthropods and Litter Decomposition 8-13 

8.4 References for Chapter 8 8-13 

9. QUANTITATIVE EVALUATION OF LEAD AND BIOCHEMICAL INDICES OF LEAD EXPOSURE IN PHYSIOLOGICAL 

MEDIA 9-1 

9.1 General Sampling Procedures for Lead in Biological Media. .. 9-1 

9.2 Blood Lead 9-2 

9.3 Urine Lead 9-3 

9.4 Soft-Tissue Lead 9-3 

9.5 Hair Lead 9-3 

9.6 Lead in Teeth and Bone 9-3 

9.7 Comparative Studies of Methods for Measurement of Lead in 

Biological Media 9-4 

9.8 Measurements of Urinary 8-Aminolevulinic Acid (ALA-U) .. . 9-4 

9.9 Measurements of 8-Aminolevulinic Acid Dehydratase (ALAD) 9-5 

9.10 Measurements of Free Erythrocyte Protoporphyrin (FEP)... . 9.6 

9.11 References for Chapter 9 • 9-6 

10. METABOLISM OF LEAD 10-1 

10.1 Introduction 10-1 

10.2 Absorption 10-1 

10.2.1 Respiratory Absorption 10-1 

10.2.2 Gastrointestinal Absorption 10-2 

10.2.3 Cutaneous Absorption 10-5 

10.3 Distribution 10-5 

10.3.1 Human Studies 10-5 

10.3.2 Animal Studies 10-6 

10.4 Elimination 10-7 

10.4.1 Human Studies 10-7 

10.4.2 Animal Studies 10-7 

10.5 Alkyl Lead Metabolism 10-8 

10.6 Metabolic Considerations in the Identification of Susceptible 

Subgroups in the Population 10-8 

10.7 References for Chapter 10 10-9 

11. BIOLOGICAL EFFECTS OF LEAD EXPOSURE 11-1 

11.1 Introduction 11-1 

11.2 Cellular and Subcellular Effects of Lead 11-1 

11.2.1 Effects on Enzymes , 11-1 

11.2.2 Organellar and Cellular Effects 11-1 

11.2.3 Effects of Lead on Chromosomes 11-4 

11.2.4 Carcinogenesis 11-5 

11.3 Clinical Lead Poisoning 11-6 

11.4 Hematological Effects of Lead 11-7 

xiii 
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Page 

11.4.1 Anemia 11-7 

11.4.2 Effects of Lead on Erythrocyte Morphology and Survival 

11-7 

11.4.3 Effects of Lead on Heme Synthesis 11-8 

11.4.4 Other Hematological Effects 11-13 

11.4.5 Summary of Effects of Lead on the Hematopoietic 

System 11-13 

11.5 Effects of Lead on Neurophysiology and Behavior 11-14 

11.5.1 Human Studies 11-15 

11.5.2 Animal Studies 11 -26 

11.6 Effects of Lead on the Renal System 11 -44 

11.6.1 Acute Effects 11 -44 

11.6.2 Chronic Effects 11 -44 

11.7 Reproduction and Development 11 -45 

11.7.1 Human Studies 11 ^46 

11.7.2 Animal Studies 11 -48 

11.8 The Endocrine System 11-51 

11.9 The Hepatic System 11-52 

11.1 OThe Cardiovascular System 11-52 

11.11 The Immunologic System 11-53 

11.12 The Gastrointestinal System 11 -54 

11.13 References for Chapter 11 11-54 

12. ASSESSMENT OF LEAD EXPOSURES AND ABSORPTION IN 

HUMAN POPULATIONS 12-1 

12.1 Introduction 12-1 

12.2 Lead in Human Populations 12-1 

12.2.1 Statistical Descriptions and Implications 12-1 

12.2.2 Geographic Variability in Human Blood Lead Levels . 12-4 

12.2.3 Demographic Variables and Human Blood Lead Levels 12-6 

12.3 Relationships Between External Exposures and Blood Lead 

Levels 12-10 

12.3.1 Air Exposures 12-10 

12.3.2 Soil and Dast Exposures 12-29 

12.3.3 Food and Water Exposures 12-32 

12.3.4 Effects of Lead in the Housing Environment: Lead in 

Paint 12-33 

12.3.5 Secondary Exposure of Children From Parents' Occupational Exposure 12-36 

12.3.6 Miscellaneous Sources of Lead 12-38 

12.4 Summary 12-38 

12.5 References for Chapter 12 12-39 

13. EVALUATION OF HUMAN HEALTH RISKS FROM EXPOSURE 

TO LEAD AND ITS COMPOUNDS 13-1 

13.1 Introduction 13-1 

13.2 Sources, Routes, arid Mechanisms of Entry 13-1 

13.2.1 Sources 13-1 

13.2.2 Routes and Mechanisms of Entry 13-2 

13.3 Evidence of Increased Blood Lead Levels in Humans Exposed to 

Environmental Lead 13-2 

13.3.1 Relationships Between Blood Lead Levels and SingleSource Exposures 13-2 

13.3.2 Multiple-S®urce Exposures 13-3 

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Page 

13.3.3 Effect of Host Factors on Blood Lead Levels 13-3 

13.3.4 Summary of the Quantitative Relationship 13-3 

13.4 Averaging-Time Considerations 13-4 

13.5 Biological and Adverse Health Effects of Lead in Man 13-4 

13.5.1 Assessment of Hematological Effects of Lead 13-4 

13.5.2 Assessment of Neurobehavioral Effects of Lead 13-6 

13.5.3 Effects of Lead on Reproduction and Development.... 13-7 

13.5.4 Other Health Effects 13-8 

13.5.5 Dose Effect/Response Relationships 13-8 

13.6 Populations at Risk 13-11 

13.6.1 Children as a Population at Risk 13-11 

13.6.2 Pregnant Women and the Conceptus as a Population at 

Risk , 13-12 

13.7 Description of United States Population in Relation to Probable 

Lead Exposures 13-13 

13.8 References for Chapter 13 13-14 

APPENDICES 

A. GLOSSARY A-l 

B. PHYSICAL/CHEMICAL DATA FOR LEAD COMPOUNDS B-l 

C. ADDITIONAL STUDIES OF ENVIRONMENTAL CONCENTRATIONS OF LEAD C-l 

D. UNITS AND METRIC CONVERSION FACTORS D-l 

E. A REVIEW OF THREE STUDIES ON THE EFFECTS OF LEAD 

SMELTER EMISSIONS IN EL PASO, TEXAS E-l 

xv 
T"*-

FIGURES 

Page 

4-1 Sequence of operations involved in monitoring for lead in the environment 4-2 

5-1 Approximate flow of lead through U.S. industry in 1975 5-1 

5-2 Location of major lead operations in the United States, 1976 5-3 

6-1 Simplified ecologic flow chart for lead showing principal cycling 

pathways and compartments 6-1 

6-2 Effect of various driving conditions on the amount of lead exhausted 6-2 

6-3 Effect of speed on size distribution of exhaust particles at different 

road load cruise conditions and using Indolene HO O fuel 6-2 

6-4 Cumulative mass distributions for lead aerosol in auto exhaust and at 

Pasadena, a receptor sampling site 6-3 

6-5 Differential mass distributions for lead 1 m from a freeway and at 

Pasadena sampling sites 6-3 

6-6 Cumulative mass distribution of lead particles by size 6-4 

6-7 Air-lead values as a function of traffic volume and distance from the 

highway 6-9 

6-8 Relationship of the diameter of the particles (mass) to distance from 

the highway 6-9 

6-9 Lead concentration profiles in the oceans 6-9 

6-10 Midpoint collection location for atmospheric samples collected from 

R. V. Trident north of 30°N, 1970 through 1972 6-10 

6-11 The EFcrus t values for atmospheric trace metals collected in the 

North Atlantic westerlies and at the South Pole 6-10 

6-12 Lead concentration profile in snow strata of northern Greenland .. 6-11 

6-13 World lead smelter and alkyl lead production since 1750 A.D. .. . 6-11 

6-14

 210Pb in Storbreen glacier ice, 1954-1966 6-11 

6-15 Predicted deposition velocity at indicated height for fi » = 20 cm/sec 

and z 0 = 3.0 cm 6-14 

6-16 Predicted deposition velocities at 1-m height for z 0 = 3.0 cm ... . 6-14 

6-17 Predicted deposition velocities at 1 m for /x « = 200 cm/sec 6-14 

6-18 Regression of percentage lead particulates removed by dry deposition with distance from roadway 6-15 

6-19 Comparison of size distribution of lead particulates collected at 20 

and 640 ft from an expressway north of Cincinnati, Ohio 6-15 

6-20 Atmospheric concentrations of lead and carbon monoxide as a function of log of distance from edge of highway 6-15 

6-21 Atmospheric lead concentration at freeway site in Palo Alto, California, on August 15, 1966 6-16 

6-22 Average lead in dry fallout as a function of distance from the freeway 

6-16 

6-23 Fate of lead contributed from automotive traffic in Los Angeles 

Basin 6-17 

xvi 
P.19 

Number Page 

6-24 Contamination of dust by lead emissions from two secondary 

smelters 6-17 

6-25 Total deposition of lead on Teflon plates at various heights above the 

roof of Keck Laboratories, California Institute of Technology, 

Pasadena 6-19 

6-26 Lead distribution between filtrate and suspended solids in stream 

water from urban and rural compartments 6-22 

7-1 Seasonal patterns and trends in quarterly average urban lead concentrations 7-3 

7-2 Nationwide trends in regular, premium, and unleaded gasoline sales, 

1960-1976 7-4 

7-3 Nationwide trends in lead content of regular and premium gasoline, 

1960-1976 7-4 

7-4 Annual ambient air lead concentration near a smelter, by area, 

before the August 1974 and August 1975 surveys 7-8 

8-1 Simplified ecologic flow chart for lead showing principal cycling 

pathways and compartments 8-1 

8-2 Concentration of lead in three species of small mammals trapped 

beside major and minor roads and at arable and woodland sites 8-5 

8-3 Mean lead content in grouped insect samples taken from low and 

high lead emission areas for sucking, chewing, and predatory feeding types 8-7 

8-4 Mean lead levels in representative organisms and sediments of the 

compartments of the drainage basin of the Saline Branch of the 

Vermilion River, Illinois 8-7 

8-5 Tree ring analysis of lead concentrations in urban and rural trees . 8-9 

11-1 Lead effects on heme biosynthesis 11-8 

11-2 McCarthy general cognitive index scores as a function of degree of 

lead exposure 11-21 

11-3 Scores on McCarthy subscales as a function of degree of lead exposure 11-21 

11-4 Peroneal nerve conduction velocity versus blood lead level, Idaho, 

1974 11-25 

12-1 Estimated cumulative distribution of blood lead levels for populations in which the geometric mean level is 15, 25, or 40 /xg/dl.. 12-2 

12-2 Estimated cumulative distribution of blood lead levels for populations having a geometric mean blood lead level of 25 /xg/dl, but 

geometric standard deviations of 1.2, 1.3, or 1.5 12-2 

12-3 Geometric means for blood lead values by race and age, New York 

City, 1971 12-9 

12-4 Arithmetic mean of air lead levels by traffic count, Dallas, 1976.. 12-12 

12-5 Blood lead.concentration and traffic density by sex and age, Dallas, 

1976 12-12 

12-6 Monthly ambient air lead concentrations in Kellog, Idaho, 1971 

through 1975 12-16 

12-7 Annual ambient air lead concentration, by area, before the August 

1974 and August 1975 surveys 12-16 

12-8 Blood lead versus air lead for urban male workers 12-25 

12-9 Cumulative distribution of lead levels in dwelling units 12-34 

12-10 Cumulative distribution of lead levels by location in dwelling, all 

ages 12-35 

12-11 Cumulative distribution of lead levels in dwelling units with unsound 

paint conditions 12-35 

xvii 
P.20 

12-12 Cumulative frequency distribution of blood lead levels found in 

Pittsburgh housing survey 12-36 

12-13 Correlation of children's blood lead levels with fractions of surfaces 

within a dwelling having lead concentrations > 2 mg Pb/cm2 12-36 

13-1 Dose-response curve for percent ALAD inhibition for adults and 

children as a function of blood lead level 13-9 

13-2 Dose-response curve for ALA in urine (ALA-U) as a function of 

blood lead level 13-9 

13-3 Dose-response curve for FEP as a function of blood lead level.... 13-9 

13-4 Dose-response curve for FEP as a function of blood lead level.... 13-9 

13-5 Dose-response curve for FEP as a function of blood lead level.... 13-10 

13-6 EPA calculated dose-response curve for ALA-U (from Azar et al.) 13-10 

C-l Locations of fixed sampling stations in Kanawha River Valley.... C-3 

C-2 Air sampling sites for Southern Solano, California, study C-3 

C-3 Omaha, Nebraska, study: mean monthly composite atmospheric lead 

at industrial, commercial, mixed, and two residential sites C-4 

C-4 Settleable particulate lead radial distribution from Helena Valley 

environmental pollution study C-5 

C-5 Annual average of settleable particulate lead at sites near Missouri 

lead mine and smelter C-6 

C-6 Schematic plan of lead mine and smelter from Meza Valley, 

Yugoslavia, study C-7 

C-7 Soil transects by two streets: Curve A = low traffic volume (400 

veh/day); Curve B = high traffic volume (14,000 veh/day) C-8 

C-8 Surface soil levels of lead in El Paso, Texas, and Dona Ana County, 

New Mexico, 1972 C-8 

xvin 
P.21 

TABLES 

Page 

1-1 Blood lead levels versus lowest-observed-effects levels 1-13 

1-2 Estimated percentage of subjects with ALA-U exceeding 5 mg/1 for 

various blood lead levels 1-14 

1-3 Estimated percentage of children with EP exceeding specified cutoff 

points for various blood lead levels 1-14 

3-1 Properties of elemental lead 3-1 

3-2 Isotopes of lead 3-1 

3-3 Properties of major organolead compounds 3-2 

4-1 Daily food intake 4-6 

5-1 U.S. consumption of lead by product category 5-2 

5-2 Estimated atmospheric lead emissions for the United States, 1975 . 5-3 

6-1 Comparison of size distributions of lead-containing particles in major sampling area 6-4 

6-2 Results of atmospheric sampling for organic and particulate lead. . 6-5 

6-3 Percentage of particulate versus vapor-phase lead in urban air samples 6-5 

6-4 Analyses of five replicate samples taken in an underground parking 

garage 6-5 

6-5 Average composition of particulate lead compounds emitted in auto 

exhaust 7 6-6 

6-6 Effects of aging on lead compounds in samples of auto exhaust as 

determined by electron microprobe 6-6 

6-7 Concentration range and mean EFcrust values for atmospheric trace 

metals collected over the Atlantic north of 30° N 6-10 

6-8 Lead aerosol production in the northern hemisphere compared with 

lead concentrations in Camp Century, Greenland, snow at 

different times 6-11 

6-9 Terminal velocities of spherical particles of unit density at ground 

level 6-12 

6-10 Summary of field data from Palo Alto, California 6-17 

6-11 Deposition of lead at the Walker Branch Watershed, 1974 ...... . 6-17 

6-12 Lead compounds identified in roadside soils by X-ray powder 

diffraction techniques 6-21 

7-1 Number of NASN urban stations whose data fall within selected annual average lead concentration intervals, 1966-1974 7-2 

7-2 Number of NASN nonurban stations whose data fall within selected 

annual average lead concentration intervals, 1966-1974 7-2 

7-3 Cumulative frequency distributions of quarterly lead measurements 

at urban stations by year, 1970 through 1974 7-2 

7-4 Cumulative frequency distributions of quarterly lead measurements 

at nonurban stations by year, 1970 through 1974 7-2 

7-5 NASN stations with annual average lead concentrations > 3.0 /xg/m3 

7-3 

xix 
P.22 

Number Page 

7-6 Quarterly and annual size distributions of lead-bearing particles for 

six cities, 1970 7-5 

7-7 Lead in air on Main Street, Brattleboro, Vermont, September 12 and 

13, 1972 7-5 

7-8 Airborne lead concentrations at 5- and 20-ft elevations above street 

level 7-6 

7-9 Monthly average lead concentrations for 1975 Los Angeles catalyst 

study 7-6 

7-10 Lead dust on and near heavily traveled roadways 7-7 

7-11 Lead content in or on roadside soil and grass as a function of distance 

from traffic and grass depth in profile 7-7 

7-12 Lead dust in residential areas 7-8 

8-1 Accumulation of certain heavy metals from seawater by fish (Ammodytes and Clupea) and a puffin 8-3 

8-2 Summary of lead concentrations in bird organs and tissues from areas 

of high-lead and low-lead environments 8-4 

8-3 Mean lead concentrations in organs and tissues of small mammals 

from indicated areas of environmental lead exposures 8-6 

8-4 Lead concentrations of insects at two distances from a high-trafficvolume road (interstate highway) 8-6 

8-5 Lead concentrations of predominant organisms from the rural, urban, and combined compartments of the drainage basin of the 

Saline Branch of the Vermilion River, 111 8-8 

8-6 Summary of goldfish toxicity data 8-8 

8-7 Concentrations of selected heavy metals in fresh water and in freshwater algal blooms 8-12 

10-1 Lead content of fresh, processed, and canned foodstuffs 10-3 

10-2 Effect of different diets on lead absorption expressed as the ratio of 

mean retention for experimental and control subjects 10-4 

10-3 Percent absorption of different lead compounds relative to lead acetate 10-4 

11-1 Enzymes affected by lead in animal studies 11-2 

11 -2 Enzymes affected by lead in human studies 11-2 

11 -3 Comparison of test results in lead and control groups 11 -22 

11-4 Summary of results of human studies on neurobehavioral effects at 

"moderate" blood lead levels 11 -27 

11 -5 Effects of lead exposure on locomotor activity in laboratory animals 11 -30 

11-6 Lead exposure and resulting blood lead levels in experiments 

measuring locomotor activity in rats 11 -32 

11 -7 Protocols used for the study of animal learning 11 -35 

11 -8 Stage of learning 1.1-37 

11-9 In vivo effects of lead exposure on neurochemistry 11 -39 

11-10 Statistics on the effect of lead on pregnancy 11-46 

11-11 Reproductive performance of F, lead-toxic rats 11 -49 

12-1 Analysis of variance for the logarithms of blood lead values for 

selected studies 12-3 

12-2 Blood lead levels of remote populations 12-4 

12-3 Age and smoking-adjusted geometric mean blood leads in urban versus suburban areas of three cities : 12-5 

12-4 Blood lead concentrations in six urban and one rural population.. 12-5 

12-5 Mean blood lead values for children in 14 intermediate-sized cities 

in Illinois, 1971 12-6 

xx 
Number ft*' 

12-6 Blood lead levels (whole blood) in children in U.S. smelter and comparison towns, 1975 12-7 

12-7 Geometric mean and geometric standard deviations (in parentheses) 

of blood lead levels by age and study sector 12-7 

12-8 Proportion of children with blood lead values between 50 and 99 

Mg/dl, by age, Chicago, 1971-1975 12-7 

12-9 Mean blood lead by age, sex, and G6PD status in 1559 urban black 

children 12-8 

12-10 Geometric mean blood-lead levels in New York City lead screening 

program 12-8 

12-11 Number of children's initial screens in New York City programs by 

race/ethnicity and year, 1970-1977 12-9 

12-12 Blood lead levels in military recruits, by race and place 12-9 

12-13 Geometric mean blood lead levels in New York lead screening program, 1970-1976, for children up to 72 months of age, by race and 

year 12-10 

12-14 Mean blood lead levels for study and control groups, Houston.... 12-11 

12-15 Arithmetic and geometric mean blood lead levels for Los Angeles 

and Lancaster, California, by sex and age 12-11 

12-16 Mean air lead levels indoors and outdoors at two traffic densities, 

Dallas, Texas, 1976 12-12 

12-17 Soil lead levels by traffic density 12-12 

12-18 Blood lead concentrations in relation to soil lead concentrations and 

traffic density 12-13 

12-19 Blood lead levels in children aged 1 to 5 in Newark, New Jersey, in 

relation to distance of residence from a major roadway, 1971 . . 12-13 

12-20 Geometric mean blood lead levels by area compared with estimated 

air lead levels for 1- to 9-year-old children living near Idaho 

smelter 12-15 

12-21 Mean blood lead levels in children living in vicinity of a primary 

lead smelter, 1974 and 1975 12-17 

12-22 Mean blood lead levels in selected Yugoslavian populations, by estimated weekly, time-weighted, air lead exposure 12-18 

12-23 Lead concentrations in air, dustfall, and blood, Omaha, Nebraska, 

study, 1970-1977 12-19 

12-24 Geometric mean air and blood lead levels for five city-occupation 

groups 12-21 

12-25 Geometric mean air and blood lead values for 11 study populations 12-22 

12-26 Mean air and blood lead values for five zones in Tokyo study ... . 12-22 

12-27 Length of time needed for mean blood lead values to reach specified 

levels at two exposure levels 12-23 

12-28 Estimated blood lead to air lead ratios for four air lead concentrations 12-25 

12-29 Yearly mean air and blood lead levels of black females in relation to 

distance of residence from a busy highway :.. . . 12-26 

12-30 Blood and air lead levels by sex in Finnish population study 12-27 

12-31 Blood and air lead data from clinical study 12-28 

12-32 Estimated percentage of population exceeding a specific blood lead 

level in relation to ambient air lead exposure 12-28 

12-33 Comparison of blood lead levels in children with air lead levels for 

1974 and 1975 12-29 

12-34 Mean blood and soil lead concentrations in English study 12-30 

12-35 Summary of soil lead/blood lead relationships 12-32 

xxi 
P.24 

Number Page 

12-36 Blood lead levels of 771 persons in relation to lead content of drinking water, Boston, Massachusetts 12-33 

12-37 Results of screening and housing inspection in childhood lead 

poisoning control project by fiscal year 12-36 

12-38 Geometric mean blood lead levels of children by parental employment 12-37 

12-39 Geometric mean blood lead levels for children based on reported occupation of father, history of pica, and distance of residence from 

smelter 12-37 

13-1 Sources of lead for human exposures 13-2 

13-2 Summary of lowest observed effect levels 13-8 

13-3 Percentage of subjects with ALA-U exceeding 5 mg/1 for various 

blood lead levels 13-10 

13-4 Estimated percentages of children with EP exceeding cut-off points 

for various blood lead levels 13-11 

13-5 Population and percent distribution, urban and rural, by race, 1970 

census 13-13 

13-6 Number of births by race and size of population 13-14 

B-l Physical properties of inorganic lead compounds B-l 

B-2 Temperature variation of the vapor pressures of common lead compounds B-2 

C-1 Summary of monthly average lead concentrations found in seven-city 

study C-2 

C-2 Seasonal lead concentrations in Birmingham, Alabama, area, 

1964-1965 C-2 

C-3 Lead data from Kanawha Valley Study C-3 

C-4 Data on lead deposition in 77 midwestern cities C-3 

C-5 Lead concentrations in air determined by analysis of suspended particulate, Southern Solano County, California, March-May 1970. C-4 

C-6 Total lead and lead fallout determined by analysis of dustfall samples, Southern Solano County, California, June-September 1970 C-4 

C-7 Lead concentrations in suspended particulate air samples from El 

Paso, Texas, 1971 C-5 

C-8 Particulate data summary from Helena Valley, Montana, environmental pollution study C-5 

C-9 Peak deposition rates of lead measured in Southeast Missouri C-6 

C-10 Atmospheric lead concentrations (24-hr) in the Meza Valley, 

Yugoslavia, November 1971 to August 1972 C-7 

C-11 Comparison of lead levels in the surroundings of two lead industry 

facilities and an urban control area C-7 

C-12 Lead content of soil near 3-year-old Russian smelter, E. Kazakhstan C-8 

C-13 Lead content of soil in vicinity of Russian lead plant in Kazakhstan C-9 

xxn 
ABBREVIATIONS AND SYMBOLS 

A 

AAS 

ALA 

ALAD 

ALAS 

ALA-U 

8-ALA 

APHA 

ASTM 

ASV 

b.p. 

B.W. 

°C 

Ca 

Cd 

CDC 

(Ch3)4Pb 

(CH3)6Pb2 

(C2H5)4Pb 

(C6H5)4Pb 

(C2H5)6Pb2 

cm 

CNS 

co3= 

CP 

CPG 

CP-U 

Cu 

DA 

dl 

DNA 

EDTA 

EP 

EPA 

°F 

Angstrom (101 0 meter) 

Atomic absorption spectroscopy 

Delta-aminolevulinic acid 

Delta-aminolevulinic acid 

dehydratase 

Delta-aminolevulinic acid 

synthetase 

Delta-aminolevulinic acid in urine 

Delta-aminolevulinic acid 

American Public Health 

Association 

American Society for Testing and 

Materials 

Anodic stripping voltammetry 

Boiling point 

Body weight 

Degrees Celsius (centigrade) 

Calcium 

Cadmium 

Center for Disease Control 

(Atlanta, Ga.) 

Tetramethyl lead (also TML or 

Me4Pb) 

Hexamethyl lead 

Tetraethyl lead (also TEL or 

Et4Pb) 

Tetraphenyl lead 

Hexaethyl lead 

Centimeter 

Central nervous system 

Carbonate ion 

Coproporphyrin 

Coproporphyrinogen 

Coproporphyrin in urine 

Copper 

Dopamine 

Deciliter 

Deoxyribonucleic acid 

Ethylenediaminetetraacetate 

Erythrocyte protoporphyrin; also 

erythrocyte porphyrin 

U.S. Environmental Protection 

Agency 

Degrees Fahrenheit 

FDA 

59Fe 

Fe 2 03 

FEP 

ft 

g 

GSH 

G-6-PDH 

ha 

5-HIAA 

hr 

IARC 

ICRP 

in 

i.p. 

K 

kcal 

RCR 

kg 

km 

1 

LC, 

LC50 

m 

M 

max 

Me3PbAc 

(Me3Pb)2S 

MeV 

MEPPs 

mg 

Mg 

min 

MMED 

ml 

mo 

m.p. 

Food and Drug Administration 

Radioisotope of iron 

Ferric oxide 

Free erthythrocyte protoporphyrin; 

also free erythrocyte porphyrin 

Foot 

Gram 

Glutathione (reduced) 

Glucose-6-phosphate 

dehydrogenase 

Hectare 

5-Hydroxyindole acetic acid 

Hour 

International Agency for Research 

on Cancer 

International Radiological 

Protection Commission 

Inch 

Intraperitoneal 

Potassium 

Kilocalorie 

Respiratory control rate 

Kilogram 

Kilometer 

Liter 

Concentration lethal to 1 percent of 

recipients 

Concentration lethal to 50 percent 

of recipients 

Meter 

Molar 

Maximum 

Trimethyl lead acetate 

Trimethyl lead sulfide 

Mega electronvolts (106 

electronvolts) 

Miniature end-plate potentials 

Milligram 

Magnesium 

Minute 

Mass median equivalent diameter 

Milliliter 

Month 

Melting point 

XXlll 
P.26 

MT 

Na 

NADH 

NAS 

NASN 

NE 

ng 

Ni 

nm 

NO"3 

NSF 

NVS 

P 

Pb 

204pb 

Pb + + 

Pb-A 

Pb-B 

PbBr2 

PbBrCl 

Metric ton 

Sodium 

Reduced(hydrogenated) 

nicotinamide adenine dinucleotide 

National Academy of Sciences 

National Air Surveillance 

Networks 

Norepinephrine 

Nanogram 

Nickel 

Nanometer 

Nitrate ion 

National Science Foundation 

Nonvolatile solids 

Phosphorus 

Lead 

Isotope of Lead (2l0Pb, etc.) 

Diavalent lead ion 

Concentration of lead in air 

Concentration of lead in blood 

Lead bromide 

Lead (II) bromochloride 

PbBrCl-NH4CI Lead bromochloride-ammonium 

[Pb(C2H302)2-

2Pb(OH)2] 

PbCl2 

PbC03 

PbCr64 

PbF2 

Pb(N03)2 

PbO 

PbOx 

(PbO)2 

Pb3 04 

Pb(OCOCH3)2 

Pb(OH)2 

Pb(OH)Br 

Pb(OH)Cl 

Pb(OH)2C03 

PbO.PbS04 

Pb4 0(P04 ) 2 

chloride 

Basic lead (II) acetate 

Lead chloride 

Lead carbonate 

Lead chromate 

Lead fluoride 

Lead nitrate 

Lead oxide 

Lead oxides 

Lead oxide dimer 

Lead (IV) oxide 

Lead (II) acetate 

Lead hydroxide 

Lead (II) hydroxybromide 

Lead hydroxychloride 

Basic lead carbonate 

Basic lead sulfate 

Lead oxyphosphate 

Pb(P03)2 

Pb3(P04)2 

Pbs(P04)3OH 

PbS 

PbS04 

PBG 

pCi 

PIXE 

PH 

PO? 

PP 

ppb 

ppm 

PVC 

RBC 

RNA 

s.c. 

scm 

sec 

SGOT 

SGPT 

SH 

S02 

SO? 

85Sr 

STEL 

TEL 

TML 

TVL 

USPHS 

Zn 

ZnS 

ZPP 

Mg 

fi\ 

jum 

> 

< 

xxiv 

Lead metaphosphate 

Lead orthophosphate 

Lead hydroxqpmxqpqwzn 

Lead sulfide 

Lead sulfate 

Porphobilinogen 

Picocurie (IO"12curie) 

Proton-induced X-ray emissions 

Log of the reciprocal of the 

hydrogen ion concentration 

Phosphate ion 

Protoporphyrin 

Part per billion 

Part per million 

Polyvinyl chloride 

Red blood cell; erythrocyte 

Ribonucleic acid 

Subcutaneous 

Standard cubic meter 

Second 

Serum glutamic oxaloacetic 

transaminase 

Serum glutamic pyruvic 

transaminase 

Sulfhydryl 

Sulfur dioxide 

Sulfate ion 

Radioisotope of strontium 

Short-term exposure limit 

Tetraethyl lead 

Tetramethyl lead 

Threshold value limit 

U.S. Public Health Service 

Zinc 

Zinc sulfide 

Erythrocyte zinc protoporphyrin 

Microgram 

Microliter 

Micrometer 

Greater than 

Less than 

Approximately 
1. SUMMARY AND CONCLUSIONS 

1.1 INTRODUCTION 

The first portion of this document is devoted to 

lead in the environment: its physical and chemical 

properties; its monitoring and measurement in 

various environmental media; its environmental 

sources, emissions, and concentrations; and its transport and transformation within the environment 

(Chapters 3 through 7). 

Chapters 8 through 13 are concerned with the 

effects of lead on ecosystems and, most important, 

on human health. Among the questions that have 

been specifically addressed in this document are: 

1. What are the sources of lead in the environment? 

2. What are the routes and mechanisms by 

which lead from these sources enters the 

body? 

3. Once lead enters the body, where is it 

deposited? 

4. Once lead is in the body, what are its health 

effects? 

5. Are there groups within the population that 

are particularly vulnerable to lead? 

6. What is the magnitude of the risk in terms of 

the number of persons exposed in various 

subgroups of the population? 

This document has been prepared to reflect the 

current state of knowledge about lead — 

specifically, those issues that are most relevant to 

establishing the objective scientific data base that 

will be used to recommend an air quality standard 

for lead that will adequately safeguard the public 

health. 

1.1.1 Potential Exposure to Environmental Lead 

Lead is unique among the toxic heavy metals in 

that it is relatively abundant in the earth's crust. 

Because of its easy isolation and low melting point, 

lead was among the first metals to be used by man 

thousands of years ago. The environmental significance of lead is a result both of its utility and of its 

abundance. World production exceeds 3.5 million 

tons/year, a far larger quantity than the production 

of any other toxic heavy metal. 

Lead is present in food, water, air, soil, dustfall, 

paint, and other materials with which the general 

population comes in contact. Each of these represents a potential pathway for human lead exposure 

via inhalation or ingestion. The actual lead content 

in each source may vary by several orders of magnitude. Potential exposure patterns are further confounded by human activity patterns and by 

differences between indoor and outdoor environments. The number and extent of variables involved 

make it very difficult to determine the actual lead 

intake of individuals in their normal environment. 

As a result of centuries of the mining, smelting, 

and use of lead in human activities, natural background concentrations are difficult to determine. 

Geochemical data indicate that the concentrations 

of lead in most surface materials in the United States 

range from 10 to 30 ppm (figlg). Trace amounts of 

lead occur naturally in air and water as a result of 

wind and rain erosion, and in air as a result of 

volcanic dusts, forest fires, sea salt, and the decay of 

radon. Natural background concentrations of airborne lead have been estimated to approximate 

0.0006 fig Pb/m3 of air (or 5 x 107 /xg Pb/g air). 

Natural concentrations in fresh water have been estimated to be about 0.5 /xg/liter of water (about 5 x 

IO4 fig Pb/g water) and in ocean water about 0.05 

fig Pb/liter of water (about 4.9 x 10"5 fig Pb/g 

water). As a consequence of the extensive and 

diverse uses of lead, present concentrations of lead 

in air, soil, and water are substantially higher than 

these estimated background levels. Nonurban lead 

concentrations average 0.1 fig Pb/m3 of air (about 8 

x 105 fig Pb/g air). Concentrations of airborne lead 

in U.S. cities, at sites not conspicuously influenced 

by major sources, average 1 fig Pb/m3 of air (8 x IO4 

fig Pb/g air). Expressed on a weight basis with 

respect to the total suspended particulate (TSP) in 

the air, this amount is approximately equivalent to 

10" fig Pb/g TSP. 

The shape of buildings in urban areas may cause 

large horizontal and vertical variations in lead con1-1 
P.28 

centrations. In the absence of such structures, the 

vertical gradient would usually be relatively small. 

During periods of maximum traffic density on freeways, airborne concentrations of lead immediately 

adjacent to the freeways may reach 20 /xg/m3 for a 

few hours. In the immediate vicinity of large stationary sources having no air pollution controls, concentrations of airborne lead may reach 300 /xg/m3 

under unfavorable meteorological conditions. 

Consequently, exposure via inhalation of airborne 

inorganic lead particulates may vary by a factor of at 

least 100, depending on location and activity patterns. The small number of indoor air lead studies 

conducted have shown indoor concentrations to be 

one-third or less the level measured outdoors. Indoor levels vary widely depending on type of structure, air conditioning, wind, etc. 

Dust is a generic term and consequently imprecise 

when used to describe potential human exposure. 

Dust in the popular sense usually refers to solid particles that have settled on a surface and that can be 

readily redispersed in the atmosphere. In an aerometric sense, dust is solid particles suspended in the 

atmosphere; consequently, it is an integral part of 

total suspended particulates. In an occupational 

sense, dust may encompass even larger particles discharged into the work environment by mechanical 

means. Dustfall is a measure of the settled particulate, or that deposited in or on the collection 

devices; thus dustfall is more closely related to the 

popular definition of dust. In this document, dustfall 

is treated as a separate pathway for potential exposure to lead via ingestion of these settled particles, 

but only in a qualitative manner. 

Lead concentrations in dustfall vary widely with 

the type and distribution of sources. The highest 

values occur in the immediate vicinity of sources and 

diminish rapidly with distance. Potential exposure 

to lead in dustfall depends on the total accumulation 

of dust in accessible areas. The accumulation depends on the deposition rate and the frequency and 

efficiency with which accessible surfaces are 

cleaned. Lead accumulation resulting from deposition from the air may be augmented in the homes of 

lead workers by transportation of lead-containing 

dusts from the workplace. The level of accumulated 

lead potentially available both indoors and outdoors clearly may vary by one to two orders of magnitude. 

Concentrations of lead in solution in most urban 

water supplies are below 10 /xg Pb/liter of water 

(0.01 fig Pb/g water), but some values >50 /xg/liter 

(the U.S. Public Health Service standard for lead in 

drinking water) have been reported. Suspended 

solids contain the major fraction of lead in river 

waters. Concentrations of lead in tap water may be 

considerably higher than those in municipal supplies. Lead values as high as about 2000 /xg/liter 

have been reported for homes with lead pipes and 

lead-lined storage tanks. 

Sea spray, rainwater leaching, and flaking paint 

from older buildings can contribute significantly to 

lead levels in adjacent soil. Direct ingestion of the 

soil or of re-entrained dust, as well as ingestion of 

the paint chips themselves, constitute an important 

source of lead in areas where these conditions exist. 

The contribution of food to human exposure to 

lead is highly variable and not well quantified. Estimates of daily intake vary from about 100 to 350 fig 

Pb/day. Recent studies in the Unitd States estimate 

the adults ingest about 200 fig Pb/day in food. 

Beverages and foods that are stored in lead-soldered 

cans or stored or served in lead-glazed pottery have 

been identified as having high lead content. Processed milk has been reported to contain more lead 

than fresh cow's milk — about 20 to 40 /xg/liter 

compared to about 5 to 10 /xg/liter, respectively. If 

these values are correct, processed milk could be a 

significant source of lead exposure for infants. 

For adults, illicitly distilled whiskey and old automobile batteries used as home heating fuel represent 

two nonindustrial sources of overt lead poisoning. 

Of much greater significance as a health problem, 

however, are various sources of occupational exposure. 

Workers involved in uncontrolled (without pollution controls) mining, smelting, and manufacturing 

processes where lead is used, have the highest level 

of potential exposure. Although occupational conditions have generally been substantially improved, in 

some cases lead concentrations in the air in work 

places have been measured at 1000 /xg/m3 or 

greater. The major occupational exposure problems 

occur where adequate hygiene programs have not 

been implemented or where individuals fail to take 

the recommended precautions. The major route of 

occupational exposure is the inhalation of dust and 

fumes; in addition, dust transported on clothing 

from the work place to the home or automobile may 

be a significant pathway of exposure for workers and 

their families. 

1.1.2 Sources of Environmental Lead 

The mining, smelting, and use of lead in human 

activities has significantly altered the natural distribution of lead in the environment. Contamination 

1-2 
has occurred primarily in the vicinity of sources and 

in densely populated areas. 

The lead used in gasoline antiknock additives 

represents a major fraction of the total U.S. lead 

consumption, and motor vehicle emissions constitute the major source of lead emissions to the atmosphere. In 1975, some 189,000 MT of lead (16 

percent of total production) used in antiknock compounds were converted to 142,000 MT of atmospheric emissions (88 percent of total lead emissions). As a result of legislation setting a maximum 

limit on the lead content of gasoline, the production 

and use of alkyl lead additives has decreased in recent years and will probably continue to do so. 

Based on 1975 estimates, combustion of waste oil 

and incineration of solid waste are the major contributors of lead emissions from stationary sources 

(12,060 MT/year). This figure represents only that 

portion of waste oil that is reprocessed and burned 

in oil-fired or coal-fired boilers and municipal incinerators. Other stationary sources of lead emissions include iron and steel production in plants 

with poor pollution controls, primary and secondary 

smelting, battery manufacturing, and lead alkyl 

manufacturing. Lead that may be emitted to the 

environment from these operations includes that in 

stack emissions and fugitive dusts. Contamination 

from the major stationary emitters may determine 

environmental concentrations for a radius of several 

kilometers around the sources. Fugitive dusts may 

result in a high level of contamination in the immediate vicinity of small, uncontrolled battery recycling operations. 

In terms of mass balance, lead from mobile and 

industrial sources is transported and distributed 

mainly via the atmosphere. Certain waste disposal 

operations that discharge large amounts of lead into 

soil and water result only in highly localized contamination. Lead is emitted to the atmosphere primarily in the form of inorganic particulates; 

however, small amounts of organic vapors have been 

reported in the vicinity of gasoline service stations, 

garages, and heavy traffic areas. These organic 

vapors undergo photochemical decomposition in the 

atmosphere, but they may also be adsorbed on dust 

particle surfaces. 

Based on the limited data available, it is estimated 

that 75 percent of the particulate lead emitted from 

automobiles is removed from the atmosphere in the 

immediate vicinity of traffic sources. 

Particles smaller than those from mobile sources, 

and emissions from tall stacks will remain airborne 

longer and be transported over greater distances. 

Submicron particles may reside in the atmosphere a 

week or more before they are removed by dry 

deposition (diffusion and inertial mechanisms) and 

by precipitation. The tendency toward uniform vertical and horizontal distribution (mixing with concomitant distribution) increases with an increase in 

residence time. 

The chemistry of lead aerosols discharged into the 

environment has not been studied as extensively as 

the chemistry of some of the other major air pollutants. Much of the work on lead particulate chemistry before 1973 was limited to elemental analyses 

and did not include analyses of associated ions. Information from elemental analyses is not sufficient 

to permit a thorough examination and understanding of (1) transformation and transport processes that occur among the environmental media, 

(2) mobility of lead in soils, (3) uptake and distribution of lead in plants, and (4) the overall impact 

of lead pollution on human health and ecosystems. 

Information is needed on the chemical forms and 

interactions of lead and its tendency to form compounds of low solubility with the major anions. Only 

a few studies have been conducted on the chemical 

forms of lead in soil and plants. They show that the 

principal lead form found in soils is sulfate, and the 

principal form found in plants is phosphate. 

Lead dissolved from primary lead sulfide ore 

tends to combine with carbonate or sulfate ions to 

form relatively insoluble lead carbonate or lead sulfate, or to be absorbed by ferric hydroxide. The 

amount of lead that can remain in solution in water 

is a function of the concentration of other ions, 

especially hydrogen ions. 

1.1.3 Monitoring of Environmental Lead 

Lead has been monitored in air, water, soil, food, 

and biological samples such as blood and urine for 

many years, but the accuracy of the early sampling 

and analytical techniques was quite low. Consequently, these earlier data can be used only in a 

qualitative or semiquantitative manner. External 

contamination has been the major problem in all 

sampling procedures, particularly in sampling for 

blood lead analyses. Sampling and analytical techniques for environmental lead have enjoyed considerable improvement and refinement in the past 

few years. Some of the best methods, however, are 

tedious and expensive and are available only in 

relatively specialized laboratories. Those analytical 

techniques that are less sophisticated produce results 

of limited value. The capability now exists for 

achieving high precision in lead monitoring; but in 

1-3 
P.30 

general practice, precise and accurate results are 

difficult to obtain, particularly for biological samples. Atomic absorption spectroscopy is the most 

successful analytical method used in recent years. 

The primary problem faced in environmental 

monitoring — that is, sampling and analysis — is to 

determine the type of monitoring procedures to be 

used to accomplish specific objectives, and to establish and maintain adequate quality control. 

Ambient air monitoring procedures designed 

specifically for assessing population exposure patterns present particularly difficult problems. Total 

mass concentration, particle size distribution, and 

chemical composition of lead aerosols all vary considerably with space and time. In using atmospheric 

measurements to determine population exposures, 

human activity patterns are a further complication. 

Thus the relationship between measurements of atmospheric concentration of lead, duration of exposure, and incremental changes in blood lead levels 

is not constant. Although measurements of atmospheric lead levels are an essential ingredient in 

population exposure assessment, other indices of exposure such as blood lead and free erythrocyte 

porphyrin (FEP) levels are also essential for the 

characterization of human population exoosures. 

Blood lead may be measured by several general 

techniques that presently appear to be satisfactory in 

the hands of qualified analysts who have a sophisticated technical appreciation of the many problems 

associated with measuring an element that is both 

present at trace levels and ubiquitously distributed 

as a contaminant. Extensive interlaboratory comparisons have demonstrated the need for standardizing methodology, using reference standards, and obtaining blood lead determinations from those 

laboratories having highly skilled personnel accustomed to handling a large number of samples. 

The present existence of a number of regional and 

national analytical proficiency testing programs will 

help improve the quality of analysis and the 

reliability of consequent clinical and epidemiological data. Measurements ofbiological indicators such 

as erythrocyte porphyrin, 8-ALA, and 8-ALAD are 

also a problem. A standardized method exists for 

urinary ALA, and a program is underway in the 

United States to evaluate standardizations of 

methodology for determining erythrocyt e 

porphyrin. 

1.2 EFFECTS OF LEAD ON MAN AND HIS 

ENVIRONMENT 

In the summary material presented in the preceding section, attention was directed to all the exposure aspects of lead. The biological aspects of the 

lead pollution problem are discussed in this section. 

These aspects include not only the effects of lead on 

man, but also its effects on a myriad of ecosystems 

that support man and contribute to his general 

welfare. 

1.2.1 Effects of Lead on Man 

The effects of lead on man are summarized in sequential statements of present knowledge concerning: 

1. Man's metabolism of lead. 

2. Biological and adverse health effects in man. 

3. Effects of lead on populations. 

4. Risks man incurs from exposure to lead. 

1.2.1.1 METABOLISM 

Metabolism, as discussed here, encompasses the 

physiological processes in man that relate to absorption, distribution, excretion, and net retention. It 

can be discussed in terms of routes of lead exposure 

and the physiological distinctions existing within 

certain segments of the population that modify these 

processes. Special attention is focused on the factors 

that may place the developing fetus and the child in 

a category of higher risk than the adult. 

Nearly all lead exposures result from inhalation 

and ingestion. The quantities of lead absorbed via 

these routes are determined by many factors such as 

the physical and chemical form of the lead, and the 

nutritional status, metabolic activity, and previous 

exposure history of those exposed. 

Clinical studies on the desposition of airborne 

lead particulate matter in the human respiratory 

tract suggest that 30 ± 10 percent of the ambient air 

lead particulates inhaled will be deposited. Of the 

lead thus deposited in the respiratory tract, it has 

been estimated that as much as 50 percent or more is 

absorbed and enters the blood stream. This deposition may vary considerably, depending on particle 

size and pattern of respiration. Part of the fraction 

deposited in the respiratory tract, that portion 

removed via the mucociliary escalator, is swallowed 

and enters the gastrointestinal tract. Animal studies 

suggest that the relative efficiency of lung clearance 

mechanisms may be impaired at high levels of airborne lead. 

In children, approximately 40 percent of the lead 

taken into the gastrointestinal tract is absorbed, 

whereas the corresponding value for adults is about 

10 percent. In one study assessing net gastrointestinal absorption, an inverse relationship be1-4 
P.31 

tween calcium intake and lead absorption was 

shown. This relationship has also been demonstrated 

in experimental animals. 

In discussing the routes by which man may be exposed to environmental lead, it is important to distinguish between primary and secondary exposure to 

atmospheric lead. Primary exposure is direct, and 

secondary is indirect. Primary exposure to airborne 

lead consists of its direct inhalation, whereas secondary exposure to airborne lead consists of ingestion of lead that is of atmospheric origin (that is, 

lead that is transported by the airborne route to the 

ingested material). 

Lead may contaminate foodstuffs by atmospheric 

fallout, with subsequent adsorption onto plant surfaces or absorption into plants. This contamination 

may involve primary food (plants consumed by 

man) or animal food crops. Soil lead taken into 

plants may come from atmospheric fallout or from 

leaching from natural as well as industrial sources. 

The absorption of soil lead by plants, however, is 

thought to be relatively poor, although data on lead 

accumulation in tree rings suggest that absorptidn 

from soil may occur in at least some plants. In any 

case, the contribution of air lead to food lead levels 

is probably small on the basis of a nationwide food 

distribution system; but adequate quantification 

does not yet exist to allow precise statements on this 

point to be made. It is clear, however, that commercial processing raises the lead content of food significantly. 

Another important depot of lead in the environment is soil or dust. The ultimate source of this lead 

varies from place to place; it can be dustfall from the 

atmosphere (coming from either stationary or 

mobile sources), or it can be soil or dust into which 

leaded paint has eroded. This exposure route is 

thought to be more important for children than for 

adults. Studies have consistently shown associations 

between soil or dust lead levels and blood lead 

levels in children when such exposures exceed 1000 

ppm. It is thought that lead reaches the children 

through their normal mouthing behavior. Lead is 

picked up on children's hands through their play and 

is then transferred to their mouths by their customary habit of putting their hands, objects, and 

materials in their mouths. There is evidence demonstrating a relationship between dust lead and lead on 

fingers, but as yet there is no direct evidence linking 

lead on fingers with lead in the blood. In children 

with pica, however, the importance of this source 

could be greatly magnified. 

It has been shown repeatedly that levels of lead in 

blood increase when oral intake increases, but 

studies do not show a precise, quantitative expression of this relationship. Rather, a number of studies 

show that, with sustained daily ingestion of 100 /xg 

of lead, the maximum increase in steady-state levels 

of blood lead ranges from 6 to 18 /xg/dl. These 

variations probably relate to nutritional factors, 

biological variability, unreported sources of exposure, differences in analytical techniques, or previous exposure history —or to a combination of 

these factors. Since children, particularly infants, 

absorb a larger percentage of lead than adults do, 

the relative contribution of oral intake is undoubtedly greater for them. Because of higher metabolic 

activity, children also inhale relatively more airborne lead than do adults. Therefore, the contribution of airborne lead to total lead intake may be 

greater in children than in adults, but one must keep 

in mind that children also eat correspondingly more 

on a body weight basis. 

A number of experimental animal studies have 

assessed the effects of nutrition and other factors on 

gastrointestinal absorption as reflected by blood 

lead levels. It is clear from these studies that the 

status of essential nutrients such as calcium, iron, 

phosphorus, fat, and protein is very important. 

The absorption, distribution, and accumulation of 

lead in man is conveniently described by a threecompartment model. The first compartment, circulating red blood cells, distributes lead to the other 

two, soft tissues (primarily liver and kidney) and 

bone, where it accumulates. This accumulation 

begins in fetal life as a result of transplacental transfer. In nonoccupational^ exposed adults, such 

storage approaches 95 percent of the total body 

burden. The skeleton is a repository of lead that reflects the long-term cumulative exposure of the individual ; body fluids and soft tissues reflect more recent exposure. 

Since the nonaccumulating body burden in soft 

tissues has a greater toxicological significance than 

that fraction sequestered in bone, the mobilizable 

lead burden is a more important concept than total 

body burden. In this connection, chelatable urinary 

lead has been shown to provide an index of the 

mobile portion of the total body burden, as has the 

lead level in blood, which is the more generally used 

indicator of internal dose. 

There is a time frame in which changes in exposure register as a perturbation in the blood lead 

level. Clinical studies show that (1) a controlled 

daily intake results in a constant concentration of 

blood lead after 110 days, depending on the ex1-5 
P.32 

posure setting, and (2) a single, acute, controlled exposure yielded a blood lead half-life of about 2 days 

compared to approximately 17 days in the case of 

repeated exposures. Following cessation of exposure 

after long exposure periods (e.g., years), however, 

the half-life of blood lead can be expected to be substantially longer than 17 days. 

Fecal excretion represents the major route by 

which ingested lead is eliminated from the body. 

Though excretion by this route is usually much 

greater than by urinary elimination, the total fecal 

lead content includes unabsorbed lead as its major 

component. 

1.2.1.2 BIOLOGICA L AND ADVERS E 

HEALTH EFFECTS OF LEAD IN MAN 

There are various physiological levels and exposure ranges at which the effects of lead in man occur. Furthermore, lead affects man at the subcellular, cellular, and organ system levels. 

Among subcellular components, both nuclei and 

mitrochondria generally show the most pronounced 

responses to cellular invasion by lead. The 

mitochondria, however, are most vulnerable and 

sustain the greatest functional impairment. 

Mitochondrial injury, both in terms of cellular 

energetics and morphological aberration, has been 

shown in a number of experimental animals. In man, 

the evidence for mitochondrial impairment has been 

morphological rather than functional. Those subcellular changes observed are primarily the development of nuclear inclusion bodies in kidney cells as 

well as mitochondrial changes in renal tubular cells 

in persons exposed occupationally. 

Any discussion of the subcellular effects of lead 

must consider the question of chromosomal aberrations and carcinogenesis. At the present time, no 

conclusive statements can be made about the induction of chromosomal damage by lead. The literature 

on this issue either yields conflicting information or 

describes studies that are difficult to compare with 

each other. Some experimental animal studies relate 

the development of cancer to relatively high doses of 

lead, but as is true in the case of other suspected carcinogens, there are no data corroborating these findings in man. 

Among the systemic and organic effects of lead, 

important areas are its hematologic, neurobehavioral, and renal effects. Attention must also be 

given, however, to the effects of lead on reproduction and development as well as its hepatic, endocrine, cardiovascular, immunologic, and gastrointestinal effects. 

A number of significant effects of lead on the 

hematopoietic system in humans have been observed 

in lead poisoning. These effects are prominent in 

clinical lead poisoning but are still present to a 

lesser degree in persons with a lower level of lead 

exposure. 

Anemia is a clinical feature of lead intoxication, 

resulting from both increased erythrocyte destruction and decreased hemoglobin synthesis. In 

children, a threshold blood lead level for production of these symptoms of anemia is approximately 

40 fig Pb/dl, and the corresponding value for adults 

appears to be 50 /xg Pb/dl. 

Hemoglobin synthesis is impaired by lead via inhibition of synthesis of the globin moiety and inhibition at several steps in the synthesis of heme. The 

step most sensitive to lead in the heme synthetic 

pathway is that mediated by the enzyme 

8-aminolevulinic acid dehydratase (8-ALAD), 

which connects two units of 8-aminolevulinic acid 

(8-ALA) to form porphobilinogen. The result is an 

increase in plasma level and enhanced urinary excretion of 8-ALA. Also inhibited by lead is the incorporation of iron into protoporphyrin to form 

heme, the prosthetic group of hemoglobin. This 

results in the accumulation of coproporphyrin, 

which is excreted in the urine, and of protoporphyrin, which is retained in the erythrocytes. The 

overall effect of lead is a net decrease in heme synthesis. (This also derepresses 8-ALA synthetase, the 

enzyme involved in the first step of heme synthesis.) 

Inhibition of 8-ALAD occurs at extremely low 

blood lead levels and has been shown to start at a 

blood lead level as low as 10 /xg/dl. Though the 

health-effect significance of inhibition at a blood 

level of 10 /xg/dl is open to debate, the increased 

urinary 8-ALA excretion that occurs with increasing 

inhibition at 40 /xg/dl is accepted as a measure of 

probable physiological impairment in vivo. This 

threshold level for urinary 8-ALA excretion (40 

/xg/dl) appears to be true for both adults and 

children. 

An increase in free erythrocyte protoporphyrin 

(FEP) occurs at blood lead levels of 16 /xg/dl in 

children. In adult females, this threshold is probably 

similar. In adult males, the value is 20 to 25 /xg/dl. 

The precise threshold for coproporphyrin, while not 

well established, is probably similar to that for 

8-ALA. Elevation ot free erythrocyte protoporphyrin has the same implications of physiological 

impairment in vivo as urinary 8-ALA. To the extent 

that the protoprophyrin elevation is a likely indicator of the impairment of mitochondrial function in 

1-6 
erythroid tissue, it may be even more important. For 

these reasons, physicians who participated in the 

development of the 1975 statement by the Center for 

Disease Control and the American Academy of 

Pediatrics reached a consensus that elevated FEP 

should be used as an indicator of increased exposure 

to lead. 

The effects of lead on the nervous system range 

from acute intoxication and fatal encephalopathy to 

subtle behavioral and electrophysiologic changes associated with lower level exposures. Changes 

throughout the range of effects are related to blood 

lead levels. 

It would appear that surprisingly low levels of 

blood lead may sometimes be associated with the 

most extreme effects of lead poisoning — servere, irreversible brain damage as indexed by the occurrence of acute or chronic encephalopathy symptoms 

and/or death. Though for most adults such damage 

does not occur until blood lead levels substantially 

exceed 120 /xg/dl, some evidence suggests that acute 

encephalopathy and death may occur in some adults 

at blood lead levels slightly below 100 /xg/dl. For 

children, the effective blood levels for producing encephalopathy or death are lower than for adults, 

with such effects being seen somewhat more often, 

starting at approximately 100 /xg/dl. Again, 

however, evidence exists for the occurrence of 

encephalopathy in a very few cases at lower levels, 

down to about 80 /xg/dl. 

It should be noted that once encephalopathy occurs, death can be a frequent outcome, regardless of 

the level of medical intervention at the time of the 

acute crisis. It is also crucial to cite the rapidity with 

which acute encephalopathy or death can develop in 

apparently asymptomatic individuals or in those apparently only mildly affected by elevated body burdens of lead. It is not unusual for rapid deterioration 

to occur, with convulsions or coma suddenly appearing and progressing to death within 48 hr. 

This suggests that at high blood lead levels, even 

when individuals are asymptomatic, rather severe 

neural damage can exist without overt manifestations. Studies show that apparently asymptomatic 

children with high blood lead levels of over 80 to 

100 /Ag/dl are permanently impaired cognitively, as 

are individuals who survive acute episodes of lead 

encephalopathy. These studies tend to support the 

hypothesis that significant if albeit subtle changes in 

neural function occur at what were once considered 

tolerable blood lead levels. 

Other evidence tends to confirm rather well that 

some type of neural damage does exist in asymptomatic children, and not necessarily only at very high 

levels of blood lead. The body of studies on low- or 

moderate-level lead effects on neurobehavioral 

functions present overall an impressive array of data 

pointing to that conclusion. Several well-controlled 

studies find effects that are clearly statistically significant, and many others report nonsignificant but 

borderline effects. Since some of the effects at low 

levels of lead exposure discussed in this document 

are of a subtle nature, the findings are not always 

striking in individual cases. Nevertheless, when the 

results of all of the studies on neurologic and behavioral effects at subclinical exposures are considered in an overall perspective, a rather consistent 

pattern of impaired neural and cognitive functions 

appears to be associated with blood lead levels 

below those producing the overt symptomatology of 

lead encephalopathy. The blood lead levels at which 

neurobehavioral deficits occur in otherwise 

asymptomatic children appear to start at a range of 

50 to 60 /xg/dl, although some evidence tentatively 

suggests that such effects may occur at slightly lower 

levels for some children. 

Data obtained for the effects of lead on the nervous system in laboratory animals are also quite extensive. Encephalopathy is produced by high-level 

perinatal exposure to lead; in different species, this 

occurs to varying degrees as characterized by the 

relative extent of neuronal degeneration and 

vasculopathy. It seems clear that the animal data 

support the contention that the developing organism 

represents the population at greatest risk for central 

nervous system toxicity. 

There is also good evidence that perinatal exposure of laboratory animals to lead at moderate 

levels will produce delays in both neurological and 

sexual development. Since these effects have been 

demonstrated to occur in the absence of either 

undernutrition or growth retardation, it has been 

suggested that they may represent more or less direct 

effects of lead in the respective systems. 

In animal studies, locomotor activity has been the 

most commonly used behavioral index of lead toxicity. Data indicate that increased locomotor activity in young animals occurs only at moderately 

high exposure levels. It may be, in view of the levels, 

that the changes in activity currently reported in 

laboratory animals are more diagnostic of a postencephalopathic hyperactivity than of subclinical 

effects. Interestingly, the reactivity changes seen in 

older animals are associated with much lower blood 

lead levels. 

Finally, reports on the effects of lead exposures on 

1-7 
P.34 

the acquisition and/or performance of operant 

responses indicate that perinatal exposure to moderate or low levels of lead may disrupt this type of 

behavior. Thus at blood lead levels ranging from 30 

to 80 /xg/dl, cognitive function appears to be disrupted in animals. 

Excessive lead exposure can result in acute as well 

as chronic renal injury in man. The acute renal 

effects of lead are seen in persons dying of acute lead 

poisoning where lead-induced anemia and/or 

encephalopathy may also be seen. These effects are 

manifested by nonspecific degenerative changes in 

renal tubular lining cells, cloudy swelling, and some 

degree of cellular necrosis. In addition, nuclear inclusion bodies form in tubule cells, and there are 

functional and ultrastructural changes in tubular 

mitochondria. Aminoaciduria, glycosuria, and 

hyperphosphaturia are noted, with aminoaciduria 

being a rather consistent feature of tubular damage 

in children. These effects are usually reversible. It is 

not possible at the present time to state what level of 

lead in blood is associated with aminoaciduria or 

any of the other specific indices of acute renal injury. 

Prolonged lead exposure in humans can result in 

chronic lead nephropathy. The pathology of these 

chronic changes is different from that seen in acute 

renal injury. It is characterized by the gradual onset 

of pronounced arteriosclerotic changes, fibrosis, 

glomerular atrophy, hyaline degeneration, and 

reduction in kidney size. This can be a progressive, 

irreversible condition resulting in death from renal 

failure. A threshold of lead exposure for these 

chronic changes cannot yet be stated, however, as a 

result of the typical inaccessibility of data needed for 

the accurate assessment of the preceding long-term 

exposure history. 

Considerable evidence for the adverse effects of 

lead on reproduction and development in man has 

been accumulating for many years. Many of the 

early data on the induction of abortions, stillbirths, 

and neonatal deaths were for occupationally exposed pregnant women, where such effects were 

demonstrated at high blood lead levels. Of more 

pressing present interest are certain recent studies in 

this area focusing on two aspects of the effects of low 

to moderate lead exposure on reproduction: gametotoxicity and post-conception events. 

In regard to potential lead effects on human 

ovarian function, one study has shown that shortterm exposure at ambient air levels of less than 7 

/ig/m3 may cause an increase in the anovular cycle 

and disturbances in the lutein phase. This study, 

however, requires confirmation before conclusive 

statements can be made. Another recent report involving occupational exposure similarly suggests 

that moderately increased lead absorption (blood 

lead mean = 52.8 /ig/dl) may result in direct 

testicular impairment; however, the design of this 

study is such that this observation also requires 

verification. 

Thus, it is clear that gametotoxic, embryotoxic, 

and teratogenic effects at a gross level can be induced in laboratory animals with lead, but it should 

be emphasized that the production of such effects 

probably requires acute, high exposures. Unfortunately, a paucity of information exists on the 

teratogenicity and developmental toxicity of chronic 

low or moderate lead exposures. Available data on 

the subject do suggest, however, that chronic lowlevel lead exposure may induce postnatal developmental delays in rats. 

Our present knowledge about the effects of lead in 

man on the hepatic, cardiovascular, immunologic, 

and endocrine systems is fragmentary, rendering it 

difficult to make any conclusive statements about 

quantitative relationships. For example, effects of 

lead on the endocrine system are not well defined at 

present. Thyroid function in man, however, has been 

shown to be decreased in occupational plumbism. 

Also, effects of lead on pituitary and adrenal function in man have been observed, with decreased 

secretion of pituitary gonadotrophic hormones being 

noted but adrenal function effects being a less consistent finding. 

The response of the hepatic system to lead has not 

been well characterized in man; instead, much of the 

literature deals with hepatic effects in experimental 

animals. Lead-poisoned animals show significantly 

impaired drug-metabolizing activities, thus suggesting an effect on the hepatic mixed-function oxidase 

system. Since detoxification in animals depends on 

the microsomal heme protein, cytochrome P450, 

and since heme biosynthesis is impaired in lead exposure, such an effect is a logical consequence of 

lead poisoning. 

Of more direct interest in terms of reproductive 

efficiency are the effects of lead exposure on pregnant women — not only on fetal health and development, but also on maternal complications. Placental 

transfer of lead has been demonstrated both by fetal 

tissue analysis and comparison of newborn umbilical 

cord blood lead with maternal blood lead. One must 

not only consider the resulting absorption of lead by 

the fetus, but also the specific points in embryonic 

development at which exposure occurs. Fetal tissue 

uptake of lead occurs by the end of the first tri1-
mester, which may be a sensitive period in 

embryonic development of the nervous system. 

Studies comparing umbilical cord blood lead 

levels in newborns with simultaneously sampled 

maternal blood show that the newborn and maternal 

levels are closely correlated. The studies have also 

shown that the newborns of mothers in an urban setting are born with generally higher blood levels than 

those of corresponding newborns from rural areas. 

That the prenatal exposure of the fetus to lead, 

even in the absence of teratogenic effects, is of consequence for adverse health effects is shown by studies 

relating fetal levels to changes in fetal heme synthesis and to the incidence of premature births. Some 

suggestions in the literature that heme biosynthesis 

in a newborn may be affected require confirmation. 

In evaluating maternal complications related to 

lead exposure, one must consider that pregnancy is a 

physiological stress that may place the pregnant 

woman at higher risk to lead exposure effects. Both 

iron and calcium deficiency increase the susceptibility of an individual to lead toxicity. Women 

have an increased risk of both deficiencies during 

pregnancy and postpartum. 

Some available but unconfirmed information indicates that the risk of premature rupture of the amniotic membrane may be higher in cases of elevated 

exposure than in age-matched controls without such 

exposure. 

The literature leaves little doubt about the 

deleterious health effects of lead on reproduction, 

but most reports do not provide specific descriptions 

of exposure levels at which specific reproductive 

effects are noted. Maternal blood lead levels of 

approximately 30 /xg/dl may be associated with a 

higher incidence of premature delivery and premature membrane rupture, but these observations 

require confirmation. In adult males, levels of 50 to 

80 /xg/dl may be sufficient to induce significant 

spermatotoxic effects, but this effect has not been 

conclusively demonstrated. 

Lead has not been shown to be teratogenic in man, 

but animal experiments have demonstrated that high 

levels of lead that are still compatible with life in 

sexually mature animals interfere with normal 

reproduction; these studies include assessment of 

lead effects in both parents. Reduction in offspring 

number, weight, and survival and an increase in fetal 

resorption is a consistent finding in rats, mice, and 

other species over a range of high-level lead exposures. Effects on offspring have been shown to involve the gametotoxic effect of lead on males as well 

as females in a number of animal species. 

At lead levels presently encountered in occupational exposure, no significant cardiovascular effects 

are discernible. Clinical data for children suffering 

from chronic lead poisoning resulting in death indicate that extensive myocardial damage occurs. It is 

not clear that the associated morphological changes 

are a specific response to lead intoxication. However, in many instances where encephalopathy is 

present, the electrocardiographic abnormalities disappear with chelation therapy. 

There are insufficient data pertaining to the effects 

of elevated blood lead levels and the incidence of infectious diseases in man to allow the derivation of a 

dose-response relationship. Neither can a doseresponse relationship be defined for the effects of 

elevated blood lead levels on the gastrointestinal 

tract, even though colic is usally a consistent early 

symptom of lead poisoning in adults exposed 

occupationally and in infants and young children. 

1.2.2 Effects of Lead on the Ecosystem 

As a natural constituent, lead does not usually 

pose a threat to ecosystems. The redistribution of 

naturally occurring lead in the environment, however, has now caused some concern that lead may 

represent a potential threat to the ecosystem. For example, studies have shown a fivefold increase in lead 

in tree rings during the last 50 years; this accumulation may serve as a useful index of patterns of environmental lead accumulation. 

There are also documented effects of lead on 

domestic animals, wildlife, and aquatic life. Lead 

poisoning in domestic animals produces varying 

degrees of derangement of the central nervous 

system, gastrointestinal tract, muscular system, and 

hematopoietic system. As is true in man, younger 

animals appear to be more sensitive than older ones. 

Wildlife are exposed to a wide range of lead 

levels. Toxic effects from ingestion of lead shot have 

long been recognized as a major health problem in 

waterfowl. Several species of small mammals trapped along roadways were tested for lead concentrations. All but one of the species living in habitats adjacent to high-volume traffic showed high concentrations of lead. This was especially true in urban 

areas. 

Lead toxicity in aquatic organisms has been observed and studied experimentally. Symptoms of 

chronic lead poisoning in fish include anemia, possible damage to the respiratory system, growth inhibition, and retardation of sexual maturity. 

There is evidence that lead has both harmful and 

beneficial effects on plants. Plants are exposed to 

lead through the leaves, stems, bark, or roots, and 

1-9 
P.36 

the extent of the effects depends on the form, 

amount, and availability of that lead. The 

morphology of the plant surface plays the major role 

in determining the type and quantity of material retained by plants. Meteorological factors are also important in determining the fate of lead that comes 

into contact with plants. Large deposits of inert insoluble metal compounds on the leaves are probably 

of little consequence to plants, as the most important 

factor is the solubility of the metal. Thus, because inorganic lead compounds are generally of low 

solubility, there is little incorporation and accumulation within the leaves of plants. 

The majority of studies reporting lead toxicity in 

plants have been conducted with plants grown in 

artificial nutrient culture. These studies have promoted the concept that the effects of lead are dependent on a variety of environmental factors, including 

anions and cations within the plant and in the growth 

media, and the physical and chemical characteristics 

of the soil itself. As lead interacts with many 

environmental factors, specific correlations between 

lead effects and lead concentrations are extemely 

difficult to predict. 

1.3 EFFECTS OF LEAD ON POPULATIONS 

The frequency distribution of blood lead levels in 

homogeneous human populations has almost invariably been found to be lognormal. Most data sets of 

homogeneous populations display a geometric standard deviation (GSD) of 1.3 to 1.5. This would 

roughly correspond, for example, to an arithmetic 

standard deviation of 5.3 to 8.5 /xg/dl at a mean 

blood lead of 20 /xg/dl. 

From the lognormal distribution, given a mean 

blood lead level and estimated GSD, it is possible to 

predict the percentage of a population whose blood 

lead levels exceed or fall below a specified value. It 

is also possible to estimate the probable increase in 

mean blood lead levels for a population exposed to a 

specific increases in environmental lead. These two 

procedures, used together, provide a method by 

which air quality standards may be chosen to protect 

the health of the population. 

Blood lead levels vary with geographic location. 

They are lowest in some remote populations, higher 

in most rural settings, higher still in suburban areas, 

and highest in inner-city areas. This gradient follows 

the presumed lead exposure gradient. Blood lead 

values also vary by age, sex, and race, although in a 

somewhat more complex fashion. Generally, young 

children have the highest levels, with little 

difference noted between sexes at this age. In older 

segments of the population, after elimination of occupational exposure in lead workers, males still 

have a higher blood lead than females. Only limited 

published data are available comparing the blood 

levels of the various racial and ethnic groups of the 

population. These data suggest that urban blacks 

have higher lead levels than whites, with levels in 

Puerto Ricans frequently being intermediate. 

Results of the numerous studies of environmental 

lead exposures of man have indicated strongly that 

man does indeed have cumulative uptake from each 

source to which he is exposed. Equally important, 

these studies have shown that the blood lead level 

represents a summation of the absorption from each 

of these sources. 

Data for the two most widespread environmental 

sources of lead other than food permit summary 

statements concerning their quantitative relationship with blood lead levels: air and soil/dust. Blood 

lead levels were found to increase with rising air 

lead concentrations. The relationships were found to 

be either log-linear or log-log. Evaluation of the 

equations at various commonly observed air lead 

levels revealed that the ratio between changes in 

blood and changes in air lead varied generally between 1 and 2 and that it was not constant over the 

range of air exposures. This implies that an increase 

of 1 /xg/m3 of air lead results in an average increase 

of 1 to 2 /xg/dl in blood lead levels. Suggestive evidence indicates that children may have higher ratios 

than adults and that males may have higher ratios 

than females. 

One of the most extensive data sets on blood lead 

in children comes from a study by the U.S. Department of Housing and Urban Development on the 

blood lead values of approximately 180,000 

children in New York City. These data covered the 

period March 1970 through December 1976. A preliminary analysis of these important research findings was presented to the Subcommittee on Lead of 

EPA's Science Advisory Board in October 1977. 

The following patterns appear to be indicated by 

these data: 

1. There is a definite difference in blood lead 

values for racial and ethnic groups, blacks 

having higher mean lead levels, and Hispanics and whites having lower levels. 

2. Analysis shows that the mean blood lead 

level is related to race and ethnicity, age, 

and year of sampling. This age dependence is 

similar for all years: The 1 - to 12-month-old 

group has the lowest levels, and generally 

the maximum is found in 2- to 4-year-olds. 

1-10 
3. There was a consistent decrease of mean 

blood lead levels over the course of the 

study. This decrease was coincident with a 

reduction in lead levels in gasoline in the 

New York City area. 

4. There appears to be a likely corresponding 

decrease in the air lead. However, it should 

be pointed out that air lead data for New 

York City are sparse and that it would be unwise to assume that the air lead level as 

measured at a single location would be the 

same for all locations. Because of the height 

of the sampler, it is also questionable 

whether the air lead level would represent 

the level to which the population is exposed. 

Consistent relationships between blood lead levels 

and exposure to lead-containing soil have been 

shown. Also, children exposed to higher concentrations of soil and house dust lead have been 

shown to have elevated concentrations of lead on 

their hands. The intermediate link, from elevated 

hand levels of lead to elevated blood levels, has not 

yet been established. Quantitatively, blood lead 

levels have been shown to increase 3 to 6 percent 

given a doubling of the soil or dust lead content. 

Significant water lead exposures in this country 

have only occurred in places having a soft water supply and using leaded pipes. Such exposures have 

been shown to be associated with significant elevations of blood lead. They have also been linked to 

cases of mental retardation. 

Exposure to leaded paint still constitutes a very 

serious problem for American children in urban settings. Although new regulations of the lead content 

of paint should alleviate the problem in new housing, the poorly enforced regulation and lack of 

regulation of the past have left a heavy burden of 

lead exposures. Most of the studies on lead poisoning in children have assumed an association with 

leaded paint. It is very difficult in these studies to 

measure the actual amount of exposure. There is 

nevertheless incontrovertible evidence that the contribution from this source is very significant for certain segments of the population. 

Food lead exposures are thought to be a source of 

a significant portion of blood lead. Precise quantitative estimates of the relationship between food and 

blood lead are not available, however. Similarly, 

precise quantitative estimates are not available for 

the relative contributions of different sources to the 

total amount of lead in the diet. It is clear, however, 

that probably the largest proportion of dietary lead 

is derived from food processing (e.g., from solder in 

the seams of cans), and some is also derived from 

lead in the air and the soil. 

1.4 ASSESSMENT OF RISK FROM HUMAN 

EXPOSURE TO LEAD 

Of the estimated 160,000 metric tons of lead emitted into the atmosphere in 1975, the combustion of 

gasoline additives and waste oil accounted for 95 

percent of the total. Once lead is introduced into the 

air, it is subject to a variety of processes, including 

dry deposition, precipitation, and resuspension. 

Other uses of lead result in other avenues of exposure: (1) Lead in paint makes lead available by ingestion; (2) lead in plumbing for potable water 

where the water is soft (low pH) permits leaching 

and makes lead available by ingestion; (3) lead in 

the diet, introduced by processing, packaging, and 

raw food stock, also makes lead available by ingestion. It is therefore important to realize that 

human exposure to lead is the summation of all these 

complex and individual sources. 

The factors that govern the quantitative aspects of 

inhalation and ingestion of lead have been pointed 

out, and attention has been given to the fact that ingestion includes both food and nonfood materials. 

In the case of children, the nonfood material has 

especially important implications. Thus the total internal dose is a function of all external sources with 

which the body comes into contact. The relative significance of any given exposure source depends on 

the specific exposure circumstances and certain attributes of the population at risk. 

1.4.1 Use of Blood Lead Levels in Risk Assessment 

The evidence for increased blood lead levels, the 

usual accepted indicator of lead exposure, has 

evolved from studies of both single-source and 

multiple-source exposures. Studies of single sources 

of air lead have included both epidemiological and 

clinical investigations. Clinical data uniformly 

demonstrate and quantify the actual transfer of lead 

in air to blood. The epidemiological data are not as 

definitive, but they are more relevant to the real 

world and clearly support such a relationship. 

Studies concerned with dust and soil lead exposures may be considered jointly, since most 

studies have not attempted to isolate their relative 

contributions. Strong evidence exists to show that 

these sources can be significant determinants of 

blood lead levels. Furthermore, investigations involving children exposed to lead-contaminated dust 

have demonstrated lead on the children's hands. 

1-11 
P.38 

providing strong inferential evidence for an oral 

route of entry. 

Lead-based paint is associated with overt clinical 

intoxication and widespread excess absorption in 

children. Screening programs in all major urban 

areas have sought to abate this severe public health 

problem, but only with limited success. These 

children represent a particularly high risk group 

with respect to the incremental lead exposure attributable to direct inhalation of atmospheric lead as 

well as with respect to the ingestion of dust contaminated by lead from the atmosphere. 

Studies centered around primary lead smelters 

and secondary industrial sources in urban settings 

have consistently and independently demonstrated a 

relationship between blood lead levels and these 

mixed sources. Most characteristics that mediate the 

relationship between blood lead level and lead exposure have been examined in several studies. Age is 

certainly a significant factor in determining blood 

lead levels, particularly in children under 6 years of 

age. With regard to sex differences, there appear to 

be none among children, whereas in adults, males 

generally exhibit higher levels than females. Though 

one study has reported that black children have 

higher lead levels than white children, the overall 

data are too sparse to establish a conclusive relationship. Socioeconomic variables such as income and 

education, as well as general health status, have not 

been examined in these studies. 

A number of summary statements may be made 

about the quantitative relationships pertaining to 

blood lead. The weight of evidence indicates that 

blood lead levels follow a log-normal distribution 

with a geometric standard deviation of about 1.3 to 

1.5. The log-normal distribution possesses properties that make it of value in arriving at acceptable 

maximal exposures, since it makes it possible to estimate a proportion of a population whose blood lead 

levels exceed any specified level. 

The increase in blood lead level resulting from an 

increase in air lead concentration is not constant in 

magnitude over the range of air lead levels commonly found in the environment. The relationship is 

dependent on many factors, including rate of current 

exposure and the history of past exposure. The observed ratios vary from air lead level to air lead 

level; they are generally between 1 and 2. Evidence 

suggests that the ratios for children may be higher 

than those of adults; also it suggests that ratios for 

males may be higher than those for females. 

There is general agreement that blood lead levels 

begin to increase when soil levels are 500 to 1000 

ppm. Mean percent increases in blood lead levels, 

given a twofold increase in soil lead levels, ranged 

from 3 to 6; this is remarkably consistent given the 

divergence of the populations studied. 

One of the most important aspects of risk assessment is the evaluation of effects of long-term, lowlevel, or intermittent exposures. In such circumstances, blood lead levels do not always correlate 

well with the exposure history. In one clinical study 

of lead exposure by inhalation, an average air level 

of 3.2 /xg/m3 over a period of about 7 weeks was related to a significant rise in blood lead after about 7 

weeks. When exposed to clean air, the blood lead 

levels of these same subjects returned to pre-exposure levels. 

1.4.2 Use of Biological and Adverse Health 

Effects of Lead in Risk Assessment 

Lead is not conclusively known to have any 

biological effect on man that can be considered 

beneficial. Therefore, any of the biological and adverse health effects on man at this time must be considered from a medical point of view that 

acknowledge s the absence of any health 

benefit/health cost ratio. 

Earlier discussion considered the biological and 

adverse health effects of lead across the entire range 

of lead exposures. In risk assessment, the primary 

focus is on those biological and adverse physiological effects that relate to the general population. 

Though the literature dealing with the health 

effects of lead embraces virtually all of the major 

organ systems in man, hematological and neurological effects are of prime concern. These effects are 

summarized in Table 1-1. It should be pointed out 

that Table 1-1 is a lowest-observed-effects level 

tabulation; i.e., it lists the lowest blood lead levels at 

which particular effects have been credibly reported 

for given subpopulations. Four hematological effects 

are considered: anemia, inhibition of the enzyme 

8-ALAD, urinary 8-ALA excretion, and elevation 

of free erythrocyte porphyrin (FEP). 

Anemia is found in children with and without concomitant iron deficiency. Increased lead intake 

prompts a more severe anemia. This is of special importance in children 1 to 6 years old of lower socioeconomic status, since this group also has a high incidence of iron deficiency. 

The literature relating blood lead levels to a 

statistically significant reduction in hemoglobin 

points to a threshold level of 40 /xg/dl for children 

and a corresponding value of 50 /Ag/dl for adults. 

The question of a low-threshold or no-threshold 

1-12 
TABLE 1-1. BLOOD LEAD LEVELS VERSUS LOWESTOBSERVED-EFFECTS LEVELS 

Lowest level 

lor observed 

effects, tig Pb/dl 

whole blood 

10 

15 to 20 

20 to 25 

40 

40 

40 

50 

50 to 60 

50 to 60 

80 to 100 

100 to 120 

Observed effect 

ALAD inhibition 

Free erythrocyte 

porphyrin elevation 

Free erythrocyte 

porphyrin elevation 

Increased urinary 

ALA excretion 

Anemia 

Coproporphyrin 

elevation 

Anemia 

Cognitive (CNS) 

deficits 

Peripheral 

neuropathies 

Encephalopathy 

symptoms 

Encephalopathy 

symptoms 

Population group 

Children and adults 

Adult females 

and children 

Adult males 

Children and adults 

Children 

Adults and children 

Adults 

Children 

Adults and children 

Children 

Adults 

level for the inhibitory effect of lead on the enzyme 

8-ALAD is overshadowed by the larger issue of the 

health significance of this observation. In any event, 

a value of 10 /xg/dl blood lead appears to represent a 

threshold level. Elevation of urinary 8-ALA levels, 

however, appears to be considered an index of 

physiological impairment, and the threshold level of 

this effect is approximately that for anemia in 

children (i.e., 40 /xg/dl). This value seems to apply 

for both children and adults. 

Elevation of erythrocyte porphyrin is better accepted as.an indicator of physiological impairment. 

On the basis of a number of studies, threshold values 

of blood lead at which erythrocyte protoporphyrin is 

elevated appear to be 15 to 20 /xg/dl for children 

and adult females and 20 to 25 /xg/dl for adult 

males. 

The hematological effects described above are the 

earliest physiological impairments encountered as a 

function of increasing lead exposures as indexed by 

blood lead elevations; as such, those effects may be 

considered to represent critical effects of lead exposure. Although it may be argued that certain of the 

initial hematological effects (such as ALAD inhibition) constitute relatively mild, nondebilitating 

symptoms at low blood lead levels, they nevertheless 

signal the onset of steadily intensifying adverse 

effects as blood lead elevations increase. Eventually, 

the hematological effects reach such magnitude that 

they are of clear-cut medical significance as indicators of undue lead exposure. 

Of even greater concern than early symptoms of 

lead exposures (i.e., hematological impairments) are 

the neurologic effects of lead that begin to be encountered as the hematological deficits reach clinical magnitudes. Children are most clearly the 

population at risk for neurologic effects. The 

neurologic effects, including both peripheral neuropathies and signs of CNS damage, are first encountered for some children as blood lead levels reach 50 

to 60 /xg/dl; and they very rapidly intensify in 

severity as a function of increasing blood lead elevations. Of great medical concern is the very steep upward rise in the risk for permanent, severe 

neurological damage or death as blood lead elevations approach and exceed 80 to 100 /xg/dl in 

children. Inner city children are of particular concern with respect to the manifestation of lead-induced neurologic deficits, as documented by the evidence discussed in Section 11.5. 

Some evidence has recently been advanced that 

suggests that long-term neurobehavioral deficits 

may also be induced by in utero exposures of human 

fetuses to lead, as indicated by the apparent higher 

incidence of postnatal mental retardation among 

children born of mothers experiencing elevated lead 

exposure before or during pregnancy. Thus women 

of childbearing age may be another group at special 

risk by virtue of the potential in utero exposures of 

fetuses. However, the paucity of information on exact exposures experienced by these mothers and the 

lack of other confirmatory studies do not allow firm 

statements to be made about probable threshold 

lead exposure levels for pregnant women that may 

induce later neurobehavioral deficits in their 

children. 

It is even more difficult to speak of risk-to-health 

assessment in terms of threshold levels for effects of 

lead on reproduction, since the relevant data are 

sparse. However, in no other aspect of health effects 

is the potential for deleterious health effects of lead 

as inherently great as in the area of reproduction and 

development. In particular, lead crosses the placental barrier, placing the human fetus at direct risk. 

And such exposure begins at a stage of gestation 

when neural embryonic development is beginning. 

Placental transfer, coupled with the fact that an 

effective blood-brain barrier is not present in human 

fetus, means that there is effectively a direct path 

from maternal lead exposure to the fetal nervous 

system. 

Available information suggests that there are 

several possible consequences to the newborn arising 

from lead exposure. Premature birth is suggested as 

1-13 
P.40 

being associated with elevated blood lead levels in 

women, and some impairment in the heme biosynthetic pathway may exist in the newborn children of 

mothers having elevated blood lead levels. 

Much of the discussion above has dealt with 

relationships between blood lead levels and various 

biological effects of lead. This discussion was primarily concerned with threshold levels at which 

health effects of lead are first observed in different 

population groups. Of additional interest is the proportion of a population exhibiting a health effect at a 

given blood lead level (i.e., the dose-response 

curve). Three different assessments of dose-response 

relationships for hematological effects have been 

carried out and published. These effects are the inhibition of ALAD, elevation of ALA-U, and elevation of EP levels in the blood. As noted elsewhere in 

this summary, some question exists concerning the 

relevance of ALAD inhibition to human health. The 

other two hematological effects are relevant. Table 

1-2 shows ALA-U data from two studies, one published and one done by EPA (see Chapter 13). 

TABLE 1-2. ESTIMATED PERCENTAGE OF SUBJECTS WITH 

ALA-U EXCEEDING 5 mg/lrt«r FOR VARIOUS BLOOD LEAD 

LEVELS 

Blood lead 

level, pg/dl 

10 

20 

30 

40 

50 

60 

70 

Zielhuis 

estimate. % 

0 

0 

6 

24 

48 

76 

96 

Azar et al. 

estimate. % 

2 

6 

16 

31 

50 

69 

84 

Published studies (see Chapter 13) of dose-response 

relationships also exist for erythrocyte protoporphyrin and are presented in Table 1-3. 

TABLE 1-3. ESTIMATED PERCENTAGE OF CHILDREN WITH 

EP EXCEEDING SPECIFIED CUTOFF POINTS FOR VARIOUS 

BLOOD LEAD LEVELS 

Blood lead 

level. /ig/dl 

10 

20 

30 

40 

50 

60 

70 

80 

Zielhuis 

estimate.8 % 

0 

6 

22 

37 

49 

~ 

-

-

Roels et al. 

estimate,15 % 

3 

27 

73 

100 

-

— 

-

-

Piomelli 

estimate,0 % 

9 

11 

48 

80 

-

-

-

-

EP >EP of children with blood lead levels <20 pg/dl. 

bEP >82(ifl/<ll cells. 

C

EP >33MS/<1I1.4.3 Populations at Risk 

The concept of "special risk" is defined as a 

population segment exhibiting characteristics associated significantly higher probability of developing 

a condition, illness, or other abnormal status as a 

result of exposure to a given toxic agent. With 

respect to lead, two such segments of human populations are currently definable: preschool children and 

unborn fetuses, with pregnant women as the recipient population of concern. 

1.4.3.1 PRESCHOOL CHILDREN 

There is an impressive body of data that indicates 

that children are inherently more susceptible to lead 

by virtue of physiology and that they have a different 

relationship to exposure sources. These physiological factors include: (1) greater lead intake on a perunit-body-weight basis; (2) greater net respiratory 

intake as well as greater net absorption and retention 

of lead entering the gastrointestinal tract; (3) rapid 

growth, which reduces the margin of safety against a 

variety of stresses, including nutritional deficiency; 

(4) certain incompletely developed defense mechanisms in very young children, such as the blood-brain 

barrier in newborns; and (5) different partitioning of 

lead in the bones of children compared to that of 

adults, with only 60 to 65 percent of the lead body 

burden occurring in bone, and that fraction probably being more labile than in adults. 

An important aspect of the dietary habits of very 

young children in connection with lead exposure is 

their normal mouthing activity, such as thumb-sucking or tasting of nonfood objects. Such behavior 

poses a risk of increased contact with dust and soil 

contaminated with lead. Clinical evidence also exists to indicate children are at special risk for lead 

effects. Thresholds for anemia and erythrocyte 

protoporphyrin elevation are lower for children, 

and a number of neurological effects appear at lower 

levels of lead in children than in adults. 

1.4.3.2 PREGNANT WOMEN 

Considerable evidence indicates that pregnant 

women are a population segment at risk with respect 

to lead mainly because of increased risk to the fetus 

and maternal complications. Lead crosses the placental barrier and does so at an early stage in 

embryonic development. Although quantitative expressions of this risk cannot be stated, certainly the 

potential for damage exists. 

Pregnancy places a physiological stress on a 

woman in terms of nutritional states that lead to iron 

and calcium deficiency, in consequence of which 

1-14 
P.41 

bone lead may be mobilized and the hematopoietic 

system may be placed at higher risk to lead exposure. In addition, data suggest that elevated blood 

lead levels in pregnant women may result in increased incidence of premature membrane rupture, 

placing the mother as well as her newborn in a 

special risk category. 

1.4.3.3 UNITED STATES POPULATION IN 

RELATION TO PROBABLE LEAD EXPOSURES 

With the exception of those living in areas with 

primary lead smelters, most populations exposed to 

lead live in urban areas. Residents of the central city 

are at the highest risk in these urban areas. Therefore, for other than point stationary sources of lead, 

it is the urban population that is at risk, and in particular, central city residents. Blacks and Hispanics 

are probably subject to greater exposure to airborne 

lead because higher proportions of these segments of 

the population live in urban areas. In the United 

States in 1970, 149 million persons were reported to 

live in urban areas, and 64 million in the central 

cities. These figures include about 12 million 

children under 5 years of age, with approximately 5 

million of these children living in central-city areas. 

There are an estimated 600,000 children in the 

United States with blood lead values greater than 40 

/xg/dl. These values do not result from exposure to 

airborne lead alone; they also include exposure to 

leaded paint and lead in food. In view of the narrow 

margin of safety from currently observed urban 

blood lead levels, children exposed to an additional 

increment of lead from the air would be at great risk 

for adverse health effects. 

Of the roughly 3 million U.S. pregnancies per 

year, inner-city women are estimated to account for 

500,000. In view of available data, these women and 

their unborn children are also at high risk. 

1-15 
2. INTRODUCTION 

According to Section 108 of the Clean Air Act of 

1970, as amended in June 1974, a criteria document 

for a specific pollutant or class of pollutants shall 

. . . accurately reflect the latest scientific 

knowledge useful in indicating the kind 

and extent of all identifiable effects on 

public health or welfare which may be expected from the presence of such pollutant in the ambient air, in varying quantities. 

Air quality criteria are of necessity based on presently available scientific data, which in turn reflect 

the sophistication of the technology used in obtaining those data as well as the magnitude of the experimental efforts expended. Thus air quality criteria for 

atmospheric pollutants are a scientific expression of 

current knowledge and uncertainties. Specifically, 

air quality criteria are expressions of the scientific 

knowledge of the relationships between various concentrations— averaged over a suitable time 

period — of pollutants in the same atmosphere and 

their adverse effects upon public health and the environment. Criteria are issued to help make decisions about the need for control of a pollutant and 

about the development of air quality standards 

governing the pollutant. Air quality criteria are 

descriptive; that is, they describe the effects that have 

been observed to occur as a result of external exposure at specific levels of a pollutant. In contrast, 

air quality standards are prescriptive; that is, they 

prescribe what a political jurisdiction has determined to be the maximum permissible exposure for a 

given time in a specified geographic area. 

In the case of criteria for pollutants that appear in 

the atmosphere only in the gas phase (and thus remain airborne), the sources, levels, and effects of exposure must be considered only as they affect the 

human population through inhalation of or external 

contact with that pollutant. 

Lead, however, is found in the atmosphere primarily as inorganic particulate, with only a small 

fraction normally occurring as vapor-phase organic 

lead. Consequently, inhalation and contact are but 

two of the routes by which human populations may 

be exposed to lead. Some particulate lead may remain suspended in the air and enter the human body 

only by inhalation, but other lead-containing particles will be deposited on vegetation, surface waters, 

dust, soil, pavements, interior and exterior surfaces 

of housing — in fact, on any surface in contact with 

the air. Thus criteria for lead must be developed that 

will take into account all principal routes of exposure of the human population. 

This criteria document sets forth what is known 

about the effects of lead contamination in the environment on human health and welfare. This requires that the relationship between levels of exposure to lead, via all routes and averaged over a 

suitable time period, and the biological responses to 

those levels be carefully assessed. Assessment of exposure must take into consideration the temporal 

and spatial distribution of lead and its various forms 

in the environment. 

This document focuses primarily on lead as found 

in its various forms in the ambient atmosphere; in 

order to assess its effects on human health, however, 

the distribution and biological availability of lead in 

other environmental media have been considered. 

The rationale for structuring the document was 

based primarily on the two major questions of exposure and response. The first portion of the document is devoted to lead in the environment — physical and chemical properties; the monitoring of lead 

in various media; sources, emissions, and concentrations of lead; and the transport and transformation 

of lead within environmental media. The latter section is devoted to biological responses and effects on 

human health and ecosystems. An effort has been 

made to limit the document to a highly objective 

analysis of the scientific data base. The scientific 

literature has been reviewed through March 1977. 

The references cited do not constitute a complete 

bibliography but they are hoped to be sufficient to 

reflect the current state of knowledge on those issues 

most relevant to the establishment of an air quality 

standard for lead. 

The status of control technology for lead has not 

been treated. For information on the subject, the 

reader is referred to appropriate control technology 

documentation published by the Office of Air 

Quality Planning and Standards (OAQPS), EPA. 

The subject of adequate margin of safety stipulated 

in Section 108 of the Clean Air Act also is not 

treated here; this topic will be considered in depth 

by EPA's Office of Air Quality Planning and Standards in documentation prepared as a part of the 

process of establishing an air quality standard. 

2-1 
3. CHEMICAL AND PHYSICAL PROPERTIES 

3 1 ELEMENTAL LEAD 

Lead is a gray-white metal of bright luster that, 

because of its easy isolation and low melting point 

(327.4°C), was among the first of the metals to be 

placed in the service of man. Lead was used as early 

as 2000 B.C. by the Phoenicians, who traveled as far 

as Spain and England to mine it. Its most abundant 

ore is galena, in which lead is present as the sulfide 

(PbS), and from which metallic lead is readily obtained by roasting. The metal is soft, malleable, and 

ductile; it is a poor electrical conductor, and it is 

highly impervious to corrosion. This unique combination of physical properties has led to its use in 

piping and roofing, and in containers for corrosive 

liquids. By the time of the Roman Empire, it was already in wide use in aqueducts and public water 

systems, as well as in cooking and storage utensils. 

Lead is unique among the toxic heavy metals in 

that it is relatively abundant in the earth's crust; its 

abundance is estimated1 to be more than 100 times 

that of cadmium and mercury, two other systemic 

metallic poisons. The great environmental significance of lead is the result both of its utility and of its 

abundance; lead is produced in far larger quantities 

than any other toxic heavy metal, with world production exceeding 3.5 million tons per year.2

 The 

properties of elemental lead (Pb) are summarized in 

Table 3-1. 

TABLE 3-1. PROPERTIES OF ELEMENTAL LEAD 

Property Description 

Atomic weight 

Atomic number 

Oxidation states 

Density 

Melting point 

Boiling point 

Covalent radius (tetrahedral) 

Ionic radii 

Resistivity 

207.19 

82 

+2, +4 

11.35g/cm3at20°C 

327.4°C 

1744°oC 

1.44 A 

1.21 A (+2), 0.78 A (+4) 

21.9 xlO"6 ohm/cm 

There are eight isotopes of lead: Four are stable 

and four are radioactive. The average abundances of 

the stable isotopes and the decay characteristics of 

the radioactive isotopes are listed in Table 3-2. The 

stable isotopic compositions of naturally occurring 

lead ores are not identical, but rather show variations reflecting geological evolution.3

 There is no 

radioactive progenitor for

 2<)4Pb. However, 206Pb, 

207Pb, and 2tmPb are produced by the radioactive 

decay of

 238U, 23SU, and 232Th, respectively. Thus 

the observed isotopic ratios depend on the U/Pb and 

Th/Pb ratios of the source from which the ore is 

derived and the age of the ore deposit. The 

2(|oPb/204Pb isotopic ratio, for example, varies from 

approximately 16.5 to 21, depending on the source.4 

TABLE 3-2. ISOTOPES OF LEAD 

Isotope 

204Rb 

206pb 

207Rb 

208pb 

210pb 

210pb 

211 p b 

211pb 

212pb 

212pb 

214pb 

214Rb 

Average 

abundance. % 

1.4 

26.3 

20.8 

51.5 

— 

— 

— 

— 

— 

— 

— 

— 

Decay mode 

Stable 

Stable 

Stable 

Stable 

Ii 

a 

Ii 

a 

Ii 

a 

ii 

a 

Energy. MeV 

— 

— 

— 

0.017 

0.047 

1.4 

0.82 

0.36 

0.24 

0.72 

0.35 

Half-life 

Stable 

Stable 

Stable 

Stable 

22 yr 

22 yr 

36.1 min 

36.1 min 

10.6 hr 

10.6 hr . 

26.8 min 

26.8 min 

3.2 GENERAL CHEMISTRY OF LEAD 

Lead is the heaviest element in Group IVB of the 

periodic table; this is the group that also contains 

carbon, silicon, germanium, and tin. Unlike the 

chemistry of carbon, however, the inorganic chemistry of lead is dominated by the divalent ( + 2) oxidation state rather than the tetravalent ( +4) oxidation 

state. This important chemical feature is a direct 

result of the fact that the strengths of single bonds 

between the Group IV atoms and other atoms 

generally decrease as the atomic number of the 

Group IV atom increases.5 Thus, the average energy 

of a C-H bond is 100 kcal/mole, and it is this factor 

that stabilizes CH4 relative toCH r For lead, the PbH energy is only approximately 65 kcal/mole, and 

this is too small to compensate for the Pb(II) —* 

Pb(IV) promotional energy. It is this same feature, 

of course, that explains the marked difference in the 
P.44 

tendencies to catenation shown by these elements. 

Though C-C bonds are present in literally millions 

of compounds, lead is not known to form any catenated inorganic compounds. 

A listing of the solubilities and physical properties 

of the more common compounds of lead is given in 

Appendix B. As can be discerned from those data, 

most inorganic lead salts are sparingly soluble (e.g., 

PbF2, PbCl 2 ) or virtually insoluble (PbS04 , 

PbCr04) in water; the notable exceptions are lead 

nitrate, Pb(N03)2, and lead acetate, Pb(OCOCH3)2. 

Inorganic lead (II) salts are generally relatively 

high-melting-point solids with correspondingly low 

vapor pressures at room temperatures. The vapor 

pressures of the most commonly encountered lead 

salts are also tabulated in Appendix B. The decay of 

lead salts in the atmosphere is discussed in Section 

6.2.2. 

3.3 ORGANOMETALLIC CHEMISTRY OF 

LEAD 

The properties of organolead compounds (i.e., 

compounds containing bonds between lead and carbon) are entirely different from those of the inorganic compounds of lead. The Pb-C bond energy 

is approximately 130 kcal/mole,6 or twice the Pb-H 

value cited above. Consequently, the organic 

chemistry of lead is dominated by the tetravalent 

( + 4) oxidation state. An important property of most 

organolead compounds is that they undergo photolysis when exposed to light. The physical properties 

of some of the more important organolead compounds are summarized in Table 3-3. 

TABLE 3-3. PROPERTIES OF MAJOR ORGANOLEAD COMPOUNDS 

Compound 

Tetramethyl lead 

Tetraethyl lead 

Tetraphenyl lead 

Hexamethyl lead 

Hexaethyl lead 

Formula 

(CH3)4Pb 

(C2H5)4Pb 

(C6H5)4Pb 

(CH3)6Pb2 

(C2H5)6Pb2 

Appearance 

Colorless liquid 

Colorless liquid 

White solid 

Pale oil 

Yellow oil 

m.p.. C 

-27.5 

-130 

223 

38 

36 

b.p.. C 

110 

82a 

Decomposes 

Decomposes 

100b 

At 13 mm pressure. 

At 2 mm pressure. 

Because of their use as antiknock agents in 

gasoline and other fuels, the most important 

organolead compounds are the tetraalkyl compounds tetraethyl lead (TEL) and tetramethyl lead 

(TML). As would be expected for such nonpolar 

compounds, TEL and TML are insoluble in water 

but soluble in hydrocarbon solvents (e.g., gasoline). 

These two compounds are manufactured in extremely large quantities (Chapter 5) by the reaction 

of the alkyl chloride with lead-sodium alloy:7 

4NaPb + 4C2H,C1 — (C2H5)4Pb + 3Pb + 4NaCI 

The methyl compound, TML, is also manufactured 

by a Grignard process involving the electrolysis of 

lead pellets in methylmagnesium chloride:7 

2CHJvlgCI + 2CH3C1 + Pb (CH3)4Pb + 

2MgCl 2 

These lead compounds are removed from auto or 

other internal combustion engines by a process 

called lead scavenging, in which they react in the 

combustion chamber with halogenated hydrocarbon 

additives (notably ethylene dibromide and ethylene 

dichloride) to form lead halides, usually bromochlorolead. Such inorganic compounds apparently originate as vapors in the combustion 

chamber of an automobile engine. During their 

passage through the exhaust system, however, they 

condense to form small spherical particles with 

diameters on the order of a few tenths of a 

micrometer; they also condense or absorb onto the 

surfaces of co-entrained particles derived from the 

intake air or from corrosion of the exhaust system. 

Consequently, lead halides emitted from automobile 

exhaust are present as vapors, as pure solid particles, 

and as a coating on the surface of particulate substrates. Mobile source emissions are discussed in 

detail in Chapter 6 (Section 6.2.2.1). 

Several hundred other organolead compounds 

have been synthesized, and the properties of many of 

them are reported by Shapiro and Frey.7 Some of 

these are used in the commercial preparation of 

organomercury compounds used as fungicides, and 

their use as catalysts and stabilizers in industrial 

processes has been investigated extensively. 

3 4 COMPLEX FORMATION AND CHELATION 

The bonding in organometallic derivatives of lead 

is principally covalent rather than ionic because of 

the small difference in the electronegativities of lead 

(1.8) and carbon (2.6). As is the case in virtually all 

metal complexes, however, the bonding is of the 

donor-acceptor type, in which both electrons in the 

bonding orbital originate from the carbon atom. 

The donor atoms in a metal complex could, of 

3-2 
course, be almost any basic atom or molecule; the 

only requirement is that a donor, usually called a 

ligand, must have a pair of electrons available for 

bond formation. In general, the metal atom occupies 

a central position in the complex, as exemplified by 

the lead atom in tetramethyl lead (a), which is 

H3C# CH, 

H,C CH, 

(a) 

tetrahedrally surrounded by four methyl groups. In 

these simple organolead compounds, the lead is 

usually present as Pb(IV), and the complexes are 

relatively inert. These simple ligands, which bind to 

metal at only a single site, are called monodentate 

ligands. Some ligands, however, can bind to the 

metal atom by more than one donor atom, so as to 

form a heterocyclic ring structure. Rings of this 

general type are called chelate rings, and the donor 

molecules which form them are called polydentate 

(as opposed to monodendate) ligands or chelating 

agents. In the chemistry of lead, chelation normally 

involves Pb(ll), leading to kinetically quite labile 

(although highly stable) complexes that are usually 

six-coordinate. A Wide variety of biologically significant chelates with ligands, such as amino acids, 

peptides, nucleotides, and similar macromolecules, 

are known. The simplest structure of this type is with 

the amino acid, glycine, as represented in (b) for a 

1:2 (metal: ligand) complex. 

H2 0 

O 

O. 

CH. / 

Pb 

NH„ 

.NH. 

\ 

\ CH, 

I 

•C 

O 

H2 0 

The importance of chelating agents in the present 

context is their widespread use in the treatment of 

lead and other metal poisoning. 

Since Pb(II) is a relatively soft (or class b) metal 

ion,8 it forms strong bonds to soft donor atoms like 

the sulfur atoms in the cysteine residues of proteins 

and enzymes; it also coordinates strongly with the 

imidazole groups of histidine residues and with the 

carboxyl groups of glutamic and aspartic acid 

residues. In living systems, therefore, lead atoms 

bind to these peptide residues in proteins, thereby 

preventing the proteins from carrying out their functions by changing the tertiary structure of the protein 

or by blocking the approach by a substrate to the active site of the protein. The role of the chelating 

agents is to compete with the peptides for the metal 

by forming stable chelate complexes that can then be 

transported from the protein and eventually excreted by the body. For simple thermodynamic 

reasons (see Appendix B), chelate complexes are 

much more stable than monodentate metal complexes, and it is this enhanced stability that is the basis 

for their ability to compete favorably with proteins 

and other ligands for the metal ions. The chelating 

agents most commonly used for the treatment of 


 

O 

I 

O-C-CH. 

O 

I <x> 

CH2 -CO 

N-CH2-CH2-N 

/ 

/ 

J 

\ 

O-C-CH. 

O 

CH2 -CO . 

O 

EDTA 

(c) 

CH. 

HS — C CH c ; 

CH3 NH2 

PENICILLAMINE 

O 

OH 

(b) (d) 

3-3 
P.46 

lead poisoning are ethylenediaminetetraacetate ions 

(EDTA) (c), D-penicillamine (d), and their derivatives. EDTA is known to act as a hexadentate ligand 

toward metals.9 Recent X-ray diffraction studies 

have demonstrated that D-penicillamine is a tridentate ligand (binding through S, N, and O) toward 

cobalt,10 chromium," and lead,12 but monodentate 

toward mercury.1315 

It should be noted that both the stoichiometry and 

structures of metal chelate depend on pH, and that 

different structures may occur in crystals from those 

manifest in solution. It will suffice to state, however, 

that several ligands can be found that are capable of 

sufficiently strong chelation with lead present in the 

body under physiological conditions to enable their 

use in the effective treatment of lead poisoning. 

3.5 REFERENCES FOR CHAPTER 3 

1. Moeller, T. Inorganic Chemistry. John Wiley and Sons, 

Inc., New York. 1953. 966 p. 

2. Dyrssen, D. The changing chemistry of the oceans. Ambio. 

/(l):21-25, 1972. 

3. Russell, R. and R. Farquhar. Lead Isotopes in Geology, 

lnterscience. New York. I960. 

4. Doe, B. Lead Isotopes. Springer-Verlag, New York. 1970. 

p. 3-80. 

5. Cotton, F. A. and G. Wilkinson. Advanced Inorganic 

Chemistry. John Wiley and Sons, Inc., New York. 1972. 

6. Shaw, C. F.. Ill, and A. L. Allred. Nonbonded interactions 

in organometallic compounds of Group IV B. 

Organometallic Chem. Rev. A 30:95, 1970. 

7. Shapiro, H. and F. W. Frey. The Organic Compounds of 

Lead, lnterscience Publishers, John Wiley and Sons, Inc., 

New York, 1968,486 p. 

8. Basolo, F. and R. G. Pearson. Mechanisms of Inorganic 

Reactions. J. Wiley and Sons, Inc., New York. 1967. p. 

23-25, 113-119. 

9. Richards, S., B. Pedersen, J. Silverton, and J. L. Hoard. 

Stereochemistry of ethylenediaminetetraacetate complexes. Inorg. Chem. 5:27-33, Jan. 1964. 

10. de Meester. P. and D. J. Hodgson. Model for the binding 

of D-penicillamine to metal ions in living systems: Synthesis and structur e of L-histidinyl-D-penicillaminatocobalt (III) monohydrate. [CO(L-his) (Dpen)]H2 0. J. Am. Chem. Soc. 99(1 ):10l-104. 1977. 

11. de Meester, P. and D. J. Hodgson. Synthesis and X-ray 

structure of L-histidinyl-D-penicillaminatocobalt (III) 

and L-histidinyl-D-penicillaminatochromium (111). J. 

Chem. Soc. Chem. Commun. 280, 1976. 

12. Freeman, H. C , G. N. Stevens, and 1. F. Taylor, Jr. Metal 

binding in chelation therapy: The crystal structure of Dpenicillaminatolead (II). J. Chem. Soc. Chem. Commun. 

/ 0:366-367, 1974. 

I 3. Wong. Y. S.. P. C. Chieh, and A. J. Carty. The interaction 

of organomercury pollutants with biologically important 

sites. Can. J. Chem. 5/:2597, 1973. 

14. Wong, Y. S., P. C. Chieh, and A. J. Carty. Binding of 

methylmercury by amino-acids: X-ray structure of D, Lpenicillaminatomethylmercury (II). J. Chem. Soc. Chem. 

Commun. 741, 1973. 

15. Carty, A. J. and N.J. Taylor. Binding of inorganic mercury 

at biological sites. J. Chem. Soc. Chem. Commun. 214. 

1976. 

3-4 
4. SAMPLING AND ANALYTICAL METHODS FOR LEAD 

4 1 INTRODUCTION 

Monitoring for lead in the environment, which includes sampling and measurement, is a demanding 

task that requires careful attention. Lead is receiving 

careful scrutiny as a pollutant, and the accurate 

assessment of its impact on the environment is contingent on the acquisition of valid monitoring data. 

Furthermore, the movement and accumulation of 

lead in ecosystems occur via complex pathways and 

compartments. In addition, many difficulties are inherent in the identification and tracing of lead in its 

various forms in the environment. Airborne lead 

originates from manmade sources, primarily the 

automobile, and is extracted from the atmosphere by 

animals, vegetation, soil, and water. Knowledge of 

the concentrations of lead in these various media 

and the movement of lead between and among them 

is critical for controlling lead pollution and for 

mitigating the adverse effects of lead in the environment on people. 

Sampling and analytical methods for monitoring 

lead have been devised for almost every purpose. 

Some methods are too tedious or expensive for 

general use; others are relatively easily applied but 

produce results of limited utility or questionable 

validity; and others are appropriate for use in 

monitoring lead in certain systems but not in others. 

The monitoring of environmental lead can be carried out with almost any precision deemed necessary, but actually obtaining precise and accurate 

results is not a trivial task in many instances. (See 

Chapter 9 for a discussion of the difficulties in 

reproducing blood lead analyses.) The primary 

problem is that of determining what types of 

monitoring procedures are necessary to realize 

societal objectives for protecting human health on a 

practical basis. The objective of this chapter is to 

review the status of the monitoring procedures available. Another serious problem is the present lack of 

instrumentation for the continuous analysis of aerosol. 

Monitoring for lead involves an operational sequence, based on the scientific method, as shown 

schematically in Figure 4-1. The type of data to be 

collected must be defined clearly on the basis of the 

question(s) to be answered. The required accuracy of 

the data must be determined and assured by means 

of a quality assurance strategy for all aspects of the 

monitoring operation. Similarly, the sampling 

strategy must be based on the type of data needed 

and yet take into account requirements imposed by 

the analytical methods to be used. The selection and 

application of the analytical methods are in turn influenced by the kind of data needed, the types of 

samples collected, the analytical capabilities available, and other factors. Ultimately, analysis of the 

data obtained determines whether the sequence has 

reached a satisfactory conclusion or if modifications 

of any particular segments of the sequence are required. Although there are numerous technical 

sources of information concerning sampling 

strategy, sampling methods, sample preparation, 

and analyses, only a few of the most noteworthy are 

cited here. These include the National Academy of 

Sciences report on lead,1 Stern's three-volume compendium on air pollution,2

 the Geological Survey 

review of lead in the environment,3 and the National 

Science Foundation publication, "Monitoring for 

Lead in the Environment."4 

In succeeding sections, the specific operations involved in monitoring are discussed. Site selection is 

treated succinctly because of the dearth of criteria in 

the literature and the necessity for establishing 

specific site criteria for each sampling requirement. 

Much remains to be done toward establishing criteria for location of samplers. The various samplers 

used to collect lead data are described. Methods for 

collecting dustfall, water, soil, and vegetation samples are reviewed along with current sampling 

methods specific for mobile and stationary sources. 

The processing of samples for analysis is critical and 

influences the selection of filter materials and 

characteristics. This is an area of monitoring that is 

receiving much attention because of the interferences that have been encountered. 

The analytical section is lengthy because of the 

4-1 
P.48 

FORMULATE HYPOTHESIS OR 

DELINEATE QUESTIONS TO BE ANSWERED 

DEFINE TYPE OF DATA NEEDED 

AND QUALITY ASSURANCE REQUIRED 

PLAN SAMPLING STRATEGY 

SELECT 

SITE 

CHOOSE 

COLLECTION 

METHODS 

DETERMINE 

SAMPLE 

STORAGE AND 

TRANSPORT 

REQUIREMENTS 

OBTAIN SAMPLES 

ANALYZE SAMPLES 

PREPARE 

SAMPLE !

« » MEASURE I 

LEAD j 

MAKE 

QUALITY 

ASSURANCE 

CHECKS 

ANALYZE/INTERPRET DATA 

HYPOTHESIS CONFIRMED? 

QUESTIONS ANSWERED? 

NO 

YES (END) 

Figure 4-1. Sequence of operations involved in monitoring for 

lead in the environment. 

large variety of methods applied to lead analysis. 

Analysis is the most advanced area of monitoring 

operations, and if used properly, analytical methods 

are already available that are capable of providing 

all the required data. 

4.2 SAMPLING 

The purpose of sampling is to obtain lead-containing particles, adsorbed gases, liquids, and solid samples that will provide a measure of the nature and 

concentration of lead at various points in the 

environment. Sampling encompasses not only the 

method of sample collection, but also the selection 

of sampling sites and procedures applicable to the 

processing of samples. 

4.2.1 Sampler Site Selection 

The location of sample collection devices has important and pervasive effects on the data obtained. 

In monitoring ambient air for lead, the proximity to 

the sampler of mobile and stationary sources is of 

prime importance. Also of importance are the height 

of the sampler intake above the ground and the local 

topography, climate, and lead level in the soil. Ott5 

has enumerated the problems and difficulties encountered in comparing data obtained from air 

monitoring stations in different cities. 

General guidelines for locating ambient air 

samplers include the following: 

1. Samplers should be a uniform height above 

the ground, although to assess the risk to 

children, some samplers should also be located at a child's height (2 to 3 ft). 

2. Sampler inlets should be at least 3 m from 

any obstruction. 

3. Samplers should be located in areas free of 

local source influence and convection or 

eddy currents. 

Most existing sampler sites do not meet these criteria, and information on sampler location is not 

usually provided with data. 5 The number of 

monitoring sites in an air monitoring network should 

be related to geography, population, and sources.6 

Since there is no suitable, continuous method for 

measuring lead in air, the sampling period and frequency are also important in the overall sampling 

strategy. It should be noted, however, that it is not 

possible to discuss sampling plans outside the context of a particular objective (e.g., characterization 

of rural or urban background levels, assessment of 

health hazards to people, determination of source 

effects, or delineation of transport mechanisms).4 

The treatment of sampling in detail is outside the 

scope of this discussion, but reference should be 

made to the available sources.6'

7 

4.2.2 Sampling Errors 

The fidelity with which a sample reflects the quantity and nature of lead in any medium being sampled 

is basic to the obtaining of valid data and therefore 

to an understanding of the phenomena being investigated. In Section 4.2.1, the importance of site 

selection for collecting samples of airborne lead was 

noted. In Section 4.2.6.2, the problems of dilution of 

samples from mobile sources are noted. A general 

sampling error associated with sampling of airborne 

particulates is discussed here. 

Most ambient sample collections are obtained 

nonisokinetically; that is, as the air is drawn into the 

sampler inlet, the speed and direction of the air are 

changed. The inertial characteristic of suspended 

particulates bring about losses of larger particles 

both by drift from the sampled air stream and by impaction on the surface of the sampler inlet. It has 

been shown that appreciable errors may result from 

nonisokinetic sampling, primarily because of the loss 

of large particles (those with diameters exceeding 10 

4-2 
fim).8

 Generally, it is not possible to estimate the error under any specified conditions. But such errors 

may be minimized by avoiding eddy formation, turbulence, divergence or convergence, and changes in 

direction of the sampled air stream. 

4.2.3 Sampling for Airborne Particulate Lead 

Airborne lead is primarily carried by particulates 

or aerosols, but in smaller concentrations, it may occur in the form of organic gases. Samplers range 

from the widely used high-volume filter sampler to a 

variety of other collectors that employ filters, impactors, and impingers. 

4.2.3.1 HIGH-VOLUME SAMPLER 

The most widely used method for sampling airborne particulates in the 0.1- to ]0-fim range is the 

high-volume air sampler,910 which is routinely used 

in the National Air Surveillance Networks. The 

method requires a vacuum cleaner type of air blower 

that draws air through a filter at rates as high as 2 

m

3

/min. Since the normal sampling period is 24 hr, 

particulates from a sample volume of about 2000 m3 

are collected. Because the air flow varies with filter 

type and the degree of filter loading, it is necessary 

at least to measure initial and final air flows. Gross 

particulate loading is determined by carefully 

weighing the filter before and after sample collection. The lead content is then determined by one of 

the analytical methods described in the following. 

Commercial high-volume samplers in which the 

filter is held in a horizontal plane and protected 

from dustfall by a housing are available.9 An 8- by 

10-in. glass fiber filter is usually recommended. 

Problems with filter selection are discussed in a subsequent section. 

High-volume samplers are inexpensive, easy to 

operate, and in widespread use. A measure of their 

precision and ease of operation can be deduced from 

the observation that an interlaboratory relative standard deviation for total particulate collection has 

been reported of 3.7 percent over the range 80 to 

125 /ug/m-\ The disadvantages of the high-volume 

sampler include the lack of separation of particulates by size, the interferences by impurities in the 

filters with some analytical procedures, and the particle fracturing that occurs on impact, which 

precludes subsequent determination of size distribution.9

 In addition, high-volume samplers are 

usually operated nonisokinetically; this results in an 

underestimation of the airborne concentration of 

large particles. "I f there is appreciable mass in particles with aerodynamic diameters greater than 

about 10 fim, this effect may be important. 

Isokinetic impactor measurements run in Los 

Angeles have indicated that the mass median 

equivalent diameters are apparently larger than 

those measured under nonisokinetic conditions.12 

This topic is also discussed in Section 6.3.2.1. 

An interlaboratory comparison program being 

conducted in Europe has compared total particulate 

results from high- and low-volume samplers.13 

Based on the low-volume sampler data, the precision of total particulate collection of the highvolume sampler is estimated at ± 0.5 /ug/m3

. Of 

course, such comparisons apply only to the particular conditions and methodology of sampling and 

analysis used in that study. 

4.2.3.2 DICHOTOMOUS SAMPLER 

The size distribution of airborne particulates can 

be determined by using multistage impactors and 

impingers or by analyzing unfractionated samples. 

Such information is desirable for monitoring sources 

of a pollutant as well as for assessing potential 

effects of the pollutant on human health. The above 

techniques are expensive to use on a large scale and 

generally require extended sampling periods. 

Measurements'4 have indicated that airborne particulates usually have a bimodal size distribution and 

also that there is a distinct difference in the effects of 

small and large particles on humans.15 

A dichotomous sampler for particulates has been 

designed to collect and fractionate samples into two 

size ranges.16 The dichotomous sampler uses virtual 

impaction to avoid the particle bounce errors frequently encountered with cascade impactors.17

 Virtual impaction involves the separation of particles 

into separate air streams by inertial means.16 In the 

apparatus, the largest portion of the air stream is 

pulled through an annular path so that it changes 

direction, while a small air flow is maintained in a 

straight path. The inertia of the larger particulates 

tends to keep them in the straight path while the 

smaller particles are diverted with the main stream. 

Two stages of virtual impaction have been used to 

obtain better fractionation. Membrane filters in the 

two air paths collect the respective samples. The 

particle diameter demarcation of the two fractions is 

normally between 2.0 and 3.5 fim in various 

designs. Commercial dichotomous samplers are 

available, but they are considerably more expensive 

than high-volume samplers. 

Tests of a prototype dichotomous sampler in St. 

Louis indicated16 that 80 percent of the particulate 

lead was contained in particles less than 2 fim in 

4-3 
P.50 

diameter, whereas only 20 percent was found to be 

in larger particles. Other tests to evaluate the performance of dichotomous samplers are under way.18 

4.2.3.3 TAPE SAMPLER 

Though dustfall and high-volume collectors 

usually require 24 hr sampling periods to obtain a 

sufficient analytical sample, there may be a need in 

source and transport studies to monitor airborne 

particulates for shorter time intervals. The tape 

sampler draws air through a spot on a filter tape that 

advances automatically at preset intervals (e.g., every 2 hr).9

 At a sampling rate of about 0.56 m3/hr 

(20 ft3/hr) for a 2-hr interval and with a 2.54-cm 

(1 -in.) spot diameter, it is possible to analyze the 

collected sample for lead using anodic stripping 

voltammetr y analysis. 1 9 Atmospheri c concentrations of lead ranging from 0.1 to 2.0 /xg/m3 

were measured at monitoring stations in Chicago 

and Washington using tape samplers.19 Diurnal cycles in airborne lead concentrations were obtained 

that correlate with manmade sources of lead. 

4.2.3.4 IMPACTORS AND IMPINGERS 

Impactors are multistage particulate collection 

devices designed to provide a number of size fractions. The modified Andersen cascade impactor 

used in the National Air Surveillance Networks 

(NASN) is described here.20 Others are described in 

standard texts.2-

21 

The cascade impactor fractionates particles in a 

series of five or six collection stages.20 Particles pass 

through a series of jets, 400 per stage, that are 

progressively smaller. Under each series of jets is a 

collection plate. The size fraction of particles collected at each stage depends on the air velocity, 

geometry, and previous stages. The last stage consists of a filter. Air is pumped through the impactor 

at 0.14 to 0.17 m3/min by means of an air pump on 

the downstream side. Aluminum foil is used as the 

collector, and the size fraction is determined by 

weighing before and after a 24-hr sample is collected. Five fractions are usually obtained: < 1.1, 

1.1 to 2.0, 2.0 to 3.3, 3.3 to 7, and > 7 ^m. 

Results obtained by the NASN22 indicate that lead 

particulates typically have mass median diameters in 

the range of 0.25 to 1.43 fim. Analysis by optical 

emission spectrography indicated that for particles 

less than 0.5 fim in diameter, the lead content was 2 

to 4 percent. A cascade impactor has also been applied to multielement size characterization of urban 

aerosols.23 

A size-selective particle sampler using cyclones 

has also been described,24 and a ten-fraction-size 

sample can be obtained with the Lundgren impactor.25 

Impingers collect atmospheric aerosols by impingement onto a surface submerged in a liquid.29 

Impactors are sometimes called dry impingers. As in 

impactors, impingement relies on the inertia! 

characteristics of the particle for collection on a surface. High collection efficiencies for particles as 

small as 0.1 fim may be obtained in wet impingers.2 

4.2.4 Sampling for Vapor-Phase Organic Lead 

Compounds 

In determining the total quantity of lead in the atmosphere, air is drawn through a membrane or glass 

filter for collecting particulate lead and then 

through a suitable reagent or absorber for collection 

of gaseous compounds that pass through the filter.26 

Since the normal filter used has a nominal 0.45-/um 

pore size, analysis by this method will include any 

material that passes through these pores, although it 

is considered to be primarily organic lead. Organic 

lead may be collected on iodine crystals, adsorbed 

on activated charcoal, or absorbed in an iodine 

monochloride solution.4 Reviews of the procedures 

are available.2728 

The procedures using iodine monochloride have 

been described and are claimed to be effective.26 In 

one experiment, two bubblers containing the solution were placed in series in the sampling train. 

Head levels corresponding to about 2.0 /xg/m3 of 

organic lead were obtained in the first bubbler, 

whereas the second gave a blank response, indicating 

that the collection efficiency of the first bubbler was 

essentially 100 percent and that the method is quantitative. Analyses were accomplished with atomic 

absorption spectrometry after chelation of the lead 

and extraction into an organic solvent. It should be 

noted, however, that the detection sensitivity was 

low and that the use of bubblers limits the sample 

volume. 

4.2.5 Sampling for Lead in Other Media 

In some respects, sampling for lead in water, soil, 

dustfall, or vegetation can be easier than sampling 

for airborne lead. However, the sampling conditions 

may be equally as complex and have a first-order 

impact on the measurements. 

4.2.5.1 WATER 

Heavy metals may be distributed in water as ions, 

as chemical complexes, or as species adsorbed on 

suspended matter.4 Methods for sampling and 

4-4 
P.51 

analysis of lead in water have been extensively described.2930

 Sample containers may be either glass 

or plastic. Thedynamicsof the water body should be 

considered, and defined procedures and precautions 

should be followed.4 A variety of procedures, each 

associated with particular objectives, exists (e.g., 

separation of dissolved and suspended lead and 

preservation of water samples to retain their original 

state). 

Analysis of lead in water is typically accomplished 

with atomic absorption and emission spectroscopy, 

although analytical methods for other media are 

also applicable. The natural lead content of lakes 

and rivers lies in the range of 1 to 10 /ttg/liter, with 

an average value of 6.6 /ug/liter for North American 

rivers.1 Thus, it is commonly found necessary to 

concentrate the sample by chelating and extracting 

the lead or by evaporating the water.3 Techniques 

for water analysis have been reviewed recently by 

Fisherman and Erdman.31 

4.2.5.2 SOIL 

Lead in soil samples collected from nearly 1000 

locations around the United States ranges from less 

than 10 to about 700 ppm, with a mean concentration of 16 ppm.3

 Deposition of lead on soil from the 

atmosphere results in extreme vertical concentration 

gradients, since lead is relatively immobile in soil.4 

It has been estimated that an average of 1 /xg 

Pb/cm2' year from rainout or washout or both, and 

0.2 fig Pb/cm2' year from dust accumulates at or 

near the soil surface.32 Horizontal gradients of lead 

concentrations in soil occur as the result of natural 

and manmade sources. The lead content of soil 

decreases rapidly with distance from emission 

sources; for example, reductions of 75 percent are 

observed in moving from 8 to 32 m from a highway.33

 This point is discussed in detail in Chapter 6. 

Soil sampling is not complex.4 Vegetation and 

large objects should be avoided, and a representative site should be selected. The vertical integrity of the sample should be preserved and noted. 

The sample should be air-dried and stored in sealed 

containers. The sampling should be planned to obtain results representative of the conditions being investigated. Most of the analytical procedures used 

for airborne particulates are applicable to soils, but 

the results may not be comparable. Many techniques, including optical emission spectrography, Xray spectrography, atomic absorption, and the 

electron microprobe have been used for soil lead 

analysis.3 X-ray diffraction has been used to analyze 

soil samples for lead emitted by automobiles.34 

4.2.5.3 DUSTFALL 

All particles suspended in air are affected by gravitational settling. The settling velocities of larger 

particles (^ 5 to 10 fim) are such that they will be 

transported shorter distances than the smaller particles ( < 1 fim), which have nearly negligible settling 

velocities. Thus dustfall collections can be used to 

monitor the dispersion of particulate lead from a 

specific source. The collections are made by placing 

open containers at appropriate sites free of overhead 

obstructions.910 Using buckets to measure dustfall 

can lead to inaccurate data; wind eddies created by 

the walls of the bucket may greatly affect deposition. 

The dustfall surface should be smooth and flat, presenting as little disturbance to the wind as possible. 

These points are discussed by Patterson.35 

Dustfall is generally reported in units of grams per 

square meter per month (g/m2-mo) and may be 

analyzed by the methods described for particulates 

collected on filters.9 The "ASTM Standard Method 

for Collection and Analysis of Dustfall" provides 

detailed procedures.36 One comparison of lead 

quantities collected by dustfall and by filtration indicated consistently that the lead content of particulates collected by filtration in the high-volume 

sampler was higher than in dustfall.37 This is a result 

primarily of the low settling velocities of the smaller 

particles, which make up a significant fraction of the 

total particulate. 

4.2.5.4 VEGETATION 

Lead analysis of plant tissues has been less extensive than studies in other media. Lead deposited on 

leaf surfaces by fallout can be removed and 

analyzed.38 Lead in plants is usually observed to be 

less than 1 figlg dry weight, although levels as high 

as 31 figlg have been cited.1 Plants can absorb soluble lead from soils, but most soil lead is in forms not 

available to plants.1 Leafy portions of plants often 

exhibit higher concentrations of lead, but in general, 

at least 50 percent of this lead can be removed by 

washing.' Since the presence of lead inside the plants 

may manifest different effects than that on the plant 

surface, attempts should be made to differentiate between these two conditions. 

Little mention appears in the literature of 

methods for the field sampling of plant life for 

environmental studies. The standard methods and 

procedures usually are focused on statistical sampling for determination of nutrient elements in food 

crops. 

Plant tissue collection and treatment have been 

reviewed by Skogerboe et al.4 Sampling of plant 

4-5 
P.52 

materials is generally carried out by random selection of the indigenous species representative of a 

given area of interest. Where the entire plant is not 

collected, emphasis is usually placed on the portion 

of the plant consumed by herbivores or harvested for 

market. In developing sampling plans, there should 

be close coordination between plant and animal 

sampling groups, especially where foodchains are involved. 

Before analysis, a decision must be made as to 

whether or not the plant material should be washed 

to remove surface contamination from fallout and 

soil particles. If the plants are sampled in a study of 

total lead contamination, or if they serve as animal 

food sources, washing should be avoided. If the 

effect of lead on plant processes is being studied, or 

if the plant is a source of human food, the plant samples should be washed. In either case, the decision 

must be made at the time of sampling, as washing 

cannot be effectively used after the plant materials 

have dried. Neither can fresh plant samples be 

stored for any length of time in a tightly closed container before washing, because molds and enzymatic 

action may affect the distribution of lead on and in 

the plant tissues. Freshly picked leaves stored in 

sealed polyethylene bags at room temperature 

generally mold in a few days. Storage time may be 

increased to approximately 2 weeks by refrigeration. 

Methods reported in the literature for removing 

surface contamination vary considerably, ranging 

from mechanical wiping with a camel-hair brush to 

leaching in mineral acids or EDTA. Removal of surface contamination with minimum leaching of constituents from leaf tissue can generally be accomplished by using dilute solutions of selected synthetic detergents followed by rinsing in deionized 

water. 

After collection, plant samples should be dried as 

rapidly as possible to minimize chemical and 

biological changes. Samples that are to be stored for 

extended periods of time or to be ground should be 

oven-dried for at least 4 hr at 70°C to arrest 

enzymatic reactions and render the plant tissue 

amenable to the grinding process. Storage in sealed 

containers is always advisable. 

4.2.5.5 FOODSTUFFS 

In 1972, lead was included in the Food and Drug 

Administration Market Basket Survey, which involves nationwide sampling of foods representing 

the average diet of an 18-year-old male (i.e., the individual who on a statistical basis eats the greatest 

quantity of food).39 Various food items from the 

different food classes are purchased in local markets 

and made up into meals in the proportion that each 

food item is ingested; they are then cooked or otherwise prepared as they would be consumed. Foods are 

grouped into 12 food classes, then composited and 

analyzed chemically. The quantities represented in 

the Total Diet Survey and the percentages of these 

foods grouped in the diet are presented in Table 4-1. 

TABLE 4-1. DAILY FOOD INTAKE39 

I 

II 

III 

IV 

V 

VI 

VII 

VIII 

IX 

X 

XI 

XII 

Food group 

Dairy products 

Meat, fish, and 

poultry 

Grain and cereal 

products 

Potatoes 

Leafy vegetables 

Legume vegetables 

Root vegetables 

Garden fruits 

Fruits 

Oils, fats, and 

shortening 

Sugar and adjuncts 

Beverages 

(including water) 

Total 

Food consumption 

Avg. 

g/day 

consumed 

756 

290 

369 

204 

59 

74 

34 

88 

217 

52 

82 

697 

2922 

% ol 

total 

diet 

26.1 

9.9 

12.6 

7.0 

2.0 

2.5 

1.2 

3.0 

7.4 

1.8 

2.8 

24.9 

4.2.6 Source Sampling 

Sources of lead have been well identified and include automobiles, smelters (lead and other nonferrous metals), coal-burning facilities, battery 

manufacturing plants, chemical processing plants, 

and facilities for scrap processing and welding and 

soldering operations. An important secondary 

source is fugitive dust from mining operations and 

from soils contaminated with automotive emissions.34

 A complete discussion of sources of lead 

emissions is given in Chapter 5. The following sections discuss the sampling of stationary and mobile 

sources, which require different sampling methods. 

4.2.6.1 STATIONARY SOURCES 

Sampling of stationary sources for lead requires 

the use of a sampling train at the source to sample 

the effluent stream. Both particulates and vapors 

must be collected by the sampling train, and often a 

probe is inserted directly into the stack or exhaust 

stream. In the tentative ASTM method for sampling 

for atmospheric lead, air is pulled through a 

0.45-/xm membrane filter and an activated carbon 

adsorption tube.40 In a study of manual methods for 

4-6 
measuring emission concentrations of lead and other 

toxic materials,41 use of a filter, a system of impingers, a metering system, and a pump was recommended. The recommended solution in the impingers was nitric acid. More recently, impinger 

solutions containing iodine monochloride have been 

shown to be effective.26 

Since lead in stack emissions may be present in a 

variety of physical and chemical forms, source sampling trains must be designed to trap and retain both 

gaseous and particulate lead. 

4.2.6.2 MOBILE SOURCES 

A variety of procedures has been used to obtain 

samples of auto exhaust aerosols for subsequent 

analysis for lead compounds. 

In one such procedure, a large horizontal air dilution tube was designed to segregate fine combustionderived aerosols from larger lead particles ablated 

from combustion chamber and exhaust deposit.42 In 

this procedure, hot exhaust was ducted into a 56-cmdiameter, 12-m-long, air dilution tunnel and mixed 

with filtered ambient air in a 20-m-diameter mixing 

baffle in a concurrent flow arrangement. Total exhaust and dilution air flow rate was 28 to 36 m3

/min, 

which produced a residence time of about 5 sec in 

the tunnel. At the downstream end of the tunnel, 

samples of the aerosol were obtained by means of 

isokinetic probes facing upstream, using filters or 

cascade impactors. Properly designed air dilution 

tubes of this type have very few aerosol losses for 

particles smaller than about 2 fim, the size that can 

be respired into human lungs.43 

Air-diluted aerosols from cyclic auto emissions 

tests have been accumulated in a large plastic bag. 

Filtration or impaction of aerosols from the bag 

samples produces samples suitable for lead 

analysis.44 Because of the rather lengthy residence 

time, the bag technique may result in the measurement of anomalously large aerosol sizes because of 

condensation of low-vapor-pressure organic substances onto the lead particles. This effect may be 

offset, however, by fallout processes that apply primarily to larger particles (see above). 

A low-residence-time sampling system has been 

used that is based on proportional sampling of raw 

exhaust, followed by air dilution and filtration or 

impaction.45^

46

 A relatively large sample of aerosol 

constituents can be obtained because of the high 

sampling rates of the raw exhaust. Since a constant 

proportion of the sample flow to the total exhaust 

flow must be maintained, this technique may be 

limited by the response time of the equipment to 

operating cycle phases that cause relatively small 

transients in the exhaust flow rate. 

Most research on aerosol emissions in recent years 

has used various configurations of the horizontal air 

dilution tunnel.42 Several polyvinyl chloride dilution tunnels have been used with good success.434748 

These 46-cm-diameter tunnels of varying lengths 

have been limited by exhaust temperatures to total 

flows above approximately 11 m3/min. Buildup of 

electrostatic charge on the walls of these plastic 

systems can cause abnormally high wall losses, but 

these can be avoided by wrapping the tunnel with a 

grounded conductive cable at about 30-cm intervals.47

 Similar tunnels have been used in which a 

centrifugal fan located upstream is used rather than 

a positiv e displacemen t pum p locate d 

downstream.43 This geometry produces a slight positive pressure in the tunnel and expedites transfer of 

the aerosol to holding chambers for studies of aerosol growth. Since the total exhaust plus dilution air 

flow is not held constant in this system, there may be 

slight sample disproportionation. However, these 

errors can be minimized by maintaining a very high 

dilution air/exhaust flow ratio.43 

There have also been a number of studies performed using total filtration of the exhaust stream to 

arrive at material balances for lead using rather low 

back-pressure metal filters.4549-

51

 The cylindrical 

filtration unit used in these studies is better than 99 

percent effective in retaining lead particles.51 Supporting data for lead balances generally confirm this 

conclusion.52 

Thus a wide variety of sampling and total exhaust 

filtration procedures have been used to measure the 

mass emissions of lead compounds from automobiles. Each has its appropriate area of application, depending on the objectives of the various 

research program carried out. The air dilution tunnel technique is most convenient, is compatible with 

the usual gas emission measurements, and has 

therefore been most commonly used. 

4.2.7 Filter Selection and Sample Preparation 

In sampling for lead particulates, air is drawn 

through filter materials such as fiber glass, asbestos, 

cellulosic paper, or porous plastics. 2 4 These 

materials include trace elements that can interfere in 

the subsequent analysis.5355 If the sample is large, 

then the effects of these trace elements are negligible, but this is not always the case.56

 When samples 

are prepared for analysis, reduction of the mass of 

filter material is often accomplished by ashing, 

either chemically or in an oven.4 The nature of the 

4-7 
P.54 

filter determines the ashing technique. In other 

methods of analysis — X-ray fluorescence, for example — analysis can be performed directly on the 

filter if the filter material is suitable.16 Because the 

nature and performance of filter materials are still 

under investigation, general criteria for their selection cannot be given.4

 A general review of filter 

materials is available.57 

The main advantages of glass-fiber filters are their 

low pressure drop and high particle collection efficiency at high flow rates. The main disadvantage is 

the variable lead content. In one investigation of 

Nuclepore filters, examples were given in which the 

analysis of samples and blanks showed results that 

did not differ sufficiently to allow use of the data.4 

Others have shown that the variability of residual 

impurities in some glass filters makes their use inadvisable in most cases,5455

 and they place a high 

priority on the standardization of a suitable filter for 

high-volume samples.56 Other investigations have 

indicated, however, that glass-fiber filters are available now that do not present a lead interference 

problem.58 The collection efficiencies of filters, and 

also of impactors, have been shown to be dominant 

factors in the quality of the derived data.59 The relative effectiveness of dry ashing (either at low temperatures in an oxygen plasma or at high temperatures) and of wet ashing by acid dissolution is a 

subject of current concern. Either technique will 

give good results if employed properly.455 

4.3 ANALYSIS 

A variety of useful analytical procedures is available for determination of lead in the environmental 

samples. The choice of the best method in a given 

situation depends on the nature of the data required, 

the type of sample being analyzed, the skill of the 

analysts, and the equipment available. For general 

determination of elemental lead, atomic absorption 

spectroscopy is coming into wider use. However, if 

multielement analysis is required, and if the equipment is available, X-ray fluorescence has been 

shown to be capable of rapid, inexpensive 

analyses.16 Other analytical methods have specific 

advantages that call for their continued use in 

special studies. Only those analytical techniques 

receiving current use in lead analysis are described 

in the following. More complete reviews are available in the literature.3429 

4.3.1 Colorimetric Analysis 

Colorimetric or spectrophotometric analysis for 

lead using dithizone (diphenylthiocarbazone) as the 

reagent has been used for many years.60"

62

 This 

method is the primary one recommended in a National Academy of Sciences report on lead,1

 and it is 

the basis of the tentative method of testing for lead in 

the atmosphere by the American Society for Testing 

and Materials.40 Because of its history, it has served 

as a reference by which other methods have been 

tested. 

Dithizone is an organic compound that reacts with 

lead salts to form an intensely colored chelated complex. This complex has an absorption maximum, 

with a known extinction coefficient, at a wavelength 

of 510 nm, which is the basis of the measurement. 

Standards can be prepared for calibration purposes 

by adding known quantities of lead to reagents. 

The procedures for the colorimetric dithizone 

analysis require a skilled analyst if reliable results 

are to be obtained. The method has been analyzed,4 

and the procedures are given in the literature.440 

The American Society for Testing and Materials 

conducted a collaborative test of the dithizone 

method63 and concluded that the ASTM dithizone 

procedure gave satisfactory precision in the determination of particulate lead in the atmosphere. 

The colorimetric dithizone method has the advantage of acceptability by professional organizations. 

In addition, the required apparatus is simple and 

relatively inexpensive, the absorption is linearly related to the lead concentration, the method requires 

only a few micrograms of lead in the sample, large 

samples can be used, and interferences can be 

removed.4 Realization of these advantages depends 

on meticulous attention to the procedures and 

reagents. This requires a relatively lengthy procedure and thus a high cost per sample. 

4.3.2 Atomic Absorption Analysis 

Atomic absorption (AA) spectroscopy is the more 

generally accepted method for the measurement of 

lead in environmental sampling.4 A variety of lead 

studies using AA analysis have been reported.26

.

55

.

58

.

64

-

65 

In AA, the lead determination is made by measuring the resonance absorption of lead atoms. The attenuation of the light beam passing through the sample is logarithmically related to the concentration of 

the atoms being measured. The lead atoms in the 

sample must be vaporized either in a precisely controlled flame or in a nonflame medium. The sample 

solution enters the flame through a nebulizer. The 

lead absorption wavelengths are precisely at 217.0 

nm and 283.3 nm. These wavelengths are produced 

in a hollow cathode lamp containing lead. The light 

4-8 
beam, after passing through the flame, is separated 

in a monochromator and detected with a photomultiplier. AA requires frequent use of calibration 

standards to obtain precision and accuracy. Typical 

precision is 1 to 5 percent. Several hundred samples 

can be analyzed in an 8-hr day if sample preparation 

procedures are simple. 

In an analysis using AA and high-volume 

samplers, atmospheric concentrations of lead were 

found to be 0.63 ± 0.30 ng/scm at the South Pole.64 

Lead analyses of 995 particulate samples from the 

NASN were accomplished by AA to an indicated 

precision of 11 percent, with a 0.15 /ug/m3 detection 

limit.58 

Atomic absorption requires as much care as other 

techniques to obtain highly precise data. Background absorption, chemical interferences, background light losses, and other factors can cause errors. A major problem with AA is that it has become 

so popular that untrained operators are using it in 

many laboratories. But for general purposes, AA is 

the most readily applicable of any of the analytical 

methods. 

Techniques for AA are still evolving, and improved performance involving nonflame atomization systems, electrode-less discharge lamps, and 

other equipment refinements and technique 

developments are to be expected.4 

4.3.3 Anodic Stripping Voltammetry 

Electroanalytical methods of microanalysis based 

on electrochemical phenomena are found in a 

variety of forms.6667 They are characterized by a 

high degree of sensitivity, selectivity, and accuracy 

derived from the relationships between current, 

charge, potential, and time for electrodes in solutions. The electrochemistry of lead is based primarily on the plumbous ion, which behaves reversibly in ionic solutions and has a reduction potential 

near -0.4 volt versus a standard calomel electrode.4 

Voltammetry, the electrometric method with 

greatest sensitivity for lead, is discussed here. Other 

methods are described in the references cited above. 

Anodic stripping voltammetry (ASV) describes 

the process by which the component of interest, lead, 

is selectively deposited on an electrode by reduction 

in order to concentrate the component.66 The working electrode may be a mercury film on a waximpregnated graphite electrode. After all of the lead 

in solution is reduced onto the electrode, the 

analysis involves a stripping process. In this, the lead 

is oxidized by means of a linearly variable voltage 

that is applied to the electrode. The voltammogram, 

a plot of current versus voltage, shows a peak corresponding to the oxidation of the lead. The area of the 

peak corresponds to the quantity of lead ions available at the stripping voltage. 

ASV was applied to the analysis of lead in 2-hr 

samples obtained with a spot tape sampler.19 Between 80 ng and 2.4 /xg of lead was present in the 

samples. The average standard deviation obtained in 

the lead measurements was 5.9 percent. A detailed 

procedure for sample preparation and analysis has 

been published.19 

Voltammetry was also used in analysis of particulate lead collected by an impactor from the ambient 

atmosphere.68 Lead concentrations found were in 

the 600- to 3000-ng/m3 range. 

Current practice with commercially available 

ASV equipment allows lead determination at the 1 

ppb level with routine 5- to 10-percent relative precision.4

 Extension to 0.1-ppb levels is attainable 

with modified techniques. 

Differential ASV69 and differential-pulsed ASV70 

are reported to give improved sensitivity and to 

facilitate more rapid analysis, thus lowering the cost. 

4.3.4 Emission Spectroscopy 

Optical emission spectroscopy has been used to 

determine the lead content of soils, rocks, and 

minerals at the 5- to 10-ppm level with a relative 

standard deviation of 5 to 10 percent;62 this method 

has also been applied to the analysis of a large number of air samples.58

-

71

 The primary advantage of 

this method is that it allows simultaneous analysis 

for a large number of elements in a small sample of 

the material. 

Emission spectroscopy essentially consists of observing the optical emission spectra of material excited in a spark, arc, or flame. The wavelength and 

intensity of the characteristic emission wavelengths 

of the elements provide both qualitative and quantitative data on composition. Before 1960, the emission spectrometer was the most common instrument 

in trace-detection laboratories.72 

When used for a single element such as lead, emission spectroscopy is at a disadvantage because of the 

expense of the equipment, the required special 

operator training, and the use of photographic film 

in the detection process.4 In a study of environmental contamination by automotive lead, sampling 

times were much reduced by using a sampling technique in which lead-free porous graphite was used 

both as the filter medium and the electrode in the 

spectrometer.7073 Lead concentrations of 1 to 10 

4-9 
P.56 

/xg/m3 could be detected after a half hour flow at 

800 to 1200 ml/min through the filter. 

Scott et al. analyzed composited particulate samples obtained with high-volume samplers for about 

24 elements, including lead, using a direct-reading 

emission spectrometer.74 Over 1000 samples collected by the NASN in 1970 were analyzed. Careful 

consideration of accuracy and precision led to the 

conclusion that optical emission spectrometry is a 

rapid and practical technique for analysis of particulates. 

4.3.5 Electron Microprobe 

When an intense electron beam is incident on a 

material, it produces, among other forms of radiation, X rays whose wavelengths depend on the elements present in the material and whose intensity depends on the relative quantities of these elements. 

This X-radiation is the basis of the electron microprobe method of analysis. An electron beam that 

gives a spot size as small as 0.2 fim is possible. The 

microprobe is often incorporated in a scanning 

electron microscope that allows precise location of 

the beam. Under ideal conditions, the analysis is 

quantitative, with an accuracy of 1 to 3 percent. The 

mass of the analyzed element may be in the IO14 to 

IO"16 grange.75 

Ter Haar and Bayard76 applied the electron 

microprobe method to the analysis of the composition of airborne lead-containing particles. Particles 

collected on membrane filters were mounted on 

special substrates and analyzed for lead compounds.76

 The analysis was based on the ratios of 

elemental X-ray intensities. From an environmental 

monitoring viewpoint, the ability to determine the 

composition of complex lead particulates with high 

precision was demonstrated. The percentage composition of lead compounds in the sample ranged 

from a low of 0.1 percent to a high of over 37 percent. 

Electron microprobe analysis is not a widely applicable monitoring method. It requires expensive 

equipment, complex sample preparation, and a highly trained operator. The method is unique, however, 

in providing composition information on individual 

lead particles, thus permitting the study of dynamic 

chemical changes and perhaps allowing improved 

source identification. 

4.3.6 X-Ray Fluorescence 

X-ray fluorescent emissions that characterize the 

elemental content of a sample occur when atoms are 

irradiated at sufficient energy to remove an innershell electron. 4

 This fluorescenc e allows 

simultaneous identification of a range of elements, 

including lead. For example, 22 elements were identified and quantitatively analyzed in particulate 

samples from dichotomous samplers without intermediate sample preparation.16

 This analytical 

method is identical to that described for the electron 

microprobe in the preceding section but utilizes 

different excitation sources. 

X-ray fluorescence requires a high-energy irradiation source. X-ray tubes,16'

23

 electron beams,75 and 

radioactive isotope sources77 have been used extensively.78'

79

 To reduce background, secondary 

fluorescers have been employed.16 The fluorescent 

X-ray emission from the sample may be analyzed 

with a crystal monochromator and detected with 

scintillation, with proportional counters,4 or with 

low-temperature semiconductor detectors that 

discriminate the energy of the fluorescence. The latter technique requires a very low level of excitation.16 

X-ray emission induced by charged-particle excitation (proton-induced X-ray emission, or PIXE) 

offers an attractive alternative to the more common 

techniques.80"

82

 Recognition of the potential of 

heavy-particle bombardment for excitation occurred in 1970, and an interference-free sensitivity 

down to the picogram range was demonstrated.80 

The excellent capability of accelerator beams for Xray emission analysis is partially due to the 

relatively low background radiation associated with 

the excitation. The main contributio n is 

Bremsstrahlung from secondary electron emission. 

The high particle fluxes obtainable from accelerators also contribute to the sensitivity of the PIXE 

method. Literature reviews83"

86

 on approaches to Xray elemental analysis agree that protons of a few 

MeV energy provide a preferred combination for 

high sensitivity analyses under conditions less subject to matrix interference effects. As a result of this 

premise, a system designed for routine analysis has 

been described,81 and papers involving the use of 

PIXE for aerosol analysis have recently appeared.81'

82 

Advantages of X-ray fluorescence methods include the ability to detect a variety of elements, the 

ability to analyze with little or no sample preparation, and the availability of automated analytical 

equipment. Disadvantages include the need for low 

blank filters, expensive equipment, liquid nitrogen 

(e.g., for energy-dispersive models, and highly 

trained analysts. The detectability level for lead is 

about 20 ng/cm2 of filter area, which is well below 

4-10 
the quantity obtained in normal sampling periods 

with the dichotomous sampler.16 

4.3.7 Methods for Compound Analysis 

Colorimetry, atomic absorption, and anodic stripping voltammetry are restricted to measurement of 

total lead and thus cannot identify the various compounds of lead. The electron microprobe and other 

X-ray fluorescence methods provide approximate 

data on compounds on the basis of the ratios of elements present.76

 Gas chromatography using the 

electron capture detector has been demonstrated to 

be useful for organic lead compounds.28 Powder Xray diffraction techniques have been applied to the 

identification of lead compounds in soil.34 

4.4 CONCLUSIONS 

To monitor lead aerosol in air, sampling with the 

high-volume sampler and analysis by atomic absorption spectrometry have emerged as the most widely 

used method. Sampling in this way does not provide 

for fractionation of the particles according to size, 

nor does it allow determination of the gaseous 

(organic) concentrations; these capabilities may 

prove important for special studies. The size distribution of lead aerosol is important in considering 

questions regarding exposure by inhalation; sampling with cascade impactors or dichotomous 

samplers is necessary to such evaluations. To determine gaseous lead, it is necessary to back the filter 

with chemical scrubbers or a crystalline iodine trap. 

X-ray fluorescence and optical emission 

spectroscopy are applicable to multielement analysis 

and are convenient to apply to the measurement of 

lead in such studies. Because of the many environmental variables implicit in site monitoring, the 

development of useful biological monitoring techniques may be of more direct utility. 

4.5 REFERENCES FOR CHAPTER 4 

1. Lead: Airborne Lead in Perspective. National Academy of 

Sciences, Washington, D. C. 1972. 330 p. 

2. Stern, A. C. (ed.). Air Pollution. 2nd ed. Academic Press, 

New York, 1968. 

3. Lovering, T. G. (ed.). Lead in the Environment. Geological Survey Professional Paper 957. U.S. Government 

Printing Office, Washington, D.C. 1976. 90 p. 

4. Skogerboe, R. K., A. M. Hartley, R. S. Vogel, and S. R. 

Koirtyohann. Monitoring for lead in the environment. In: 

Lead in the Environment. (W. R. Boggs, ed.). Report to 

NSF® RANN. U.S. Government Printing Office, Washington, D.C. 1977. (In press.) 

5. Ott, W. R. Development of criteria for siting air monitoring stations. In: Proc. 68th Annual Meeting, Air Pollution 

Control Association, Boston, Vol. 2, Paper No. 75-14.2. 

June 1975. 17 p. 

6. Guidelines: Air Quality Surveillance Networks. U.S. Environmental Protection Agency, Office of Air Programs, 

Research Triangle Park, N.C. Publication No. AP-98. May 

1971. 16 p. 

7. Sampling Location Guidelines. U.S. Environmental Protection Agency, Division of Atmospheric Surveillance. 

November 1972. 

8. Watson, H. H. Errors due to anisokinetic sampling of 

aerosols. Am. Ind. Hyg. Assoc. Q. /5(l):21-25. 1954. 

9. Warner, P. O. Analysis of Air Pollutants. John Wiley & 

Sons, New York. 1976. 329 p. 

10. Air Quality Criteria for Particulate Matter. U.S. Dept. of 

Health, Education, and Welfare, National Air Pollution 

Control Administration, Washington, D.C. Publication 

No. AP-49. 1969. 

11. Wedding, J. B., A. R. McFarland, and J. E. Cermak. Large 

particle collection characteristics of ambient aerosol 

samplers. Envir. Sci. Tech. //:387, 1977. 

12. Davidson, C. I. Ph.D. Dissertation. Calif. Inst. Technology, Pasadena, Calif. 1977. 

1 3. Berlin, A., P. Del Castilho, and J. Smeets. European intercomparison programs. In: Environmental Health Aspects 

of Lead. Commission of the European Communities. Luxembourg. 1973. p. 1033-1049. 

14. Whitby, K. T„ R. B. Husar, and B. Y. H. Liu. The aerosol 

size distribution of Los Angeles smog. J. Colloid Interface 

Sci. J9(l): 177-204, 1972. 

15. Lippmann, M. and W. B. Harris. Size-selective samples for 

estimating "respirable" dust concentrations. Health 

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4-11 
P.58 

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42. Habibi, K. Characterization of particulate lead in vehicle 

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53. Gandrud, B. W. and A. L. Lazrus. Design of system for 

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4-13 
5. SOURCES AND EMISSIONS 

5.1 NATURAL SOURCES 

Lead enters the biosphere from lead-bearing 

minerals in the lithosphere through both natural and 

human-mediated processes. Measurements of surface materials taken at 8-in. depths in the continental United States1

 show a median lead concentration 

of 15 ppm. Ninety-five percent of these measurements show 30 ppm of lead or less, with a maximum 

sample concentration of 700 ppm. In natural processes, lead is first incorporated in soil in the active 

soil zone, from which it may be absorbed by plants, 

leached into surface waters, or eroded into 

windborne dusts.25 In addition, minute amounts of 

radioactive

 210Pb reach the atmosphere through the 

decay of radon gas released from the earth.6 

Because lead has been used for centuries, it is 

difficult to determine the range of natural background levels. Calculations of natural contributions 

using geochemical information, however, indicate 

that natural sources contribute a relatively small 

amount of lead to the environment. For example, if 

the typical 25 to 40 ju-g/m3 or rural airborne particulate matter were derived from surface materials containing 15, and rarely more than 30, ppm lead as 

cited above, then the natural contribution to airborne lead would range from 0.0004 to 0.0012 

Mg/m3. In fact, levels as low as 0.0012 to 0.029 

/ug/m3 have been measured at a site in California's 

White Mountains.7 In contrast, however, annual 

average lead concentrations in urban suspended particulate matter8

 range as high as 6 /Lig/m3. Clearly, 

therefore, most of this urban particulate lead stems 

from man-made sources. 

5.2 MAN-MADE SOURCES 

5.2.1 Production 

Lead occupies an important position in the U.S. 

economy, ranking fourth among the nonferrous 

metals in tonnage used. The patterns of its flow 

through industry are identified in Figure 5-1.9 Approximately 85 percent of the primary lead produced in this country is from native mines,10

 where it 

is often associated with minor amounts of zinc, cadmium, copper, bismuth, gold, silver, and other 

minerals.10 Missouri ore deposits account for about 

80 percent of the domestic production. 

EXTERNAL EMISSIONS 

SCRAP 

598 

DOMESTIC 

ORES 

483 

FOREIGN 

ORES 

96 

METAL 

IMPORTS 

90 

SECONDARY 

PLANTS 

512 

PRIMARY 

PLANTS 

582 

TOTAL 

SUPPLY 

1363 

METAL 

PRODUCTS 

245 

CERAMICS 

AND PIGMENTS 

72 

ALKYLS 

190 

BATTERIES 

634 

OTHER 

36 

EXPORT 

19 

UNREPORTED 

USES AND 

STOCK CHANGES 

187 

Figure 5-1. Approximate flow of lead through U.S. industry in 

1975, metric tons.9 

5.2.2 Utilization 

The reported uses of lead, listed by major product 

categories in Table 5-1, " stood at nearly 1.2 million 

MT in 1975, with an estimated consumption for 

1976 of 1.35 million MT.12 

Certain products, especially batteries, cables, 

plumbing, weights, and ballast, contain lead that is 

economically recoverable as secondary lead. This 

reserve of lead in use is estimated at 3.8 million MT, 

of which about 0.6 million MT is recovered annually. Lead in pigments, gasoline additives, ammunition, foil, solder, and steel products is widely 

dispersed and therefore is largely unrecoverable. 

5-1 
P.61 

TABLE 5-1. U.S. CONSUMPTION OF LEAD BY PRODUCT CATEGORY11 

(MT/yr) 

Product category 

Storage batteries 

Gasoline antiknock 

additives 

Pigments and ceramics 

Ammunition 

Solder 

Cable coverings 

Caulking lead 

Pipe and sheet lead 

Type metal 

Brass and bronze 

Bearing metals 

Weight ballast 

Other 

Total 

1971 

616,581 

(679,803)a 

239,666 

(264,240) 

73,701 

(81,567) 

79,423 

(87,567) 

63,502 

(70,013) 

47,998 

(52,920) 

27,204 

(29,993) 

41,523 

(45,781) 

18,876 

(20,812) 

18,180 

(20,044) 

14,771 

(16,285) 

15,830 

(17,453) 

41,128 

(45,345) 

1,298,383 

(1,431,514) 

1972 

661,740 

(729,592) 

252,454 

(278,340) 

80,917 

(89,214) 

76,822 

(84,699) 

64,659 

(71,289) 

41,659 

(45,930) 

20,392 

(22,483) 

37,592 

(41,447) 

18,089 

(19,944) 

17,963 

(19,805) 

14,435 

(15,915) 

19,321 

(21,302) 

43,803 

(48,294) 

1,349,846 

(1,488,254) 

1973 

697,888 

(769,447) 

248,890 

(274,410) 

98,651 

(108,766) 

73,091 

(81,479) 

65,095 

(71,770) 

39,006 

(43,005) 

18,192 

(20,057) 

40,529 

(44,685) 

19,883 

(21,922) 

20,621 

(22,735) 

14,201 

(15,657) 

18,909 

(20,848) 

42,110 

(46,428) 

1,397,876 

(1,541,209) 

1974 

772,656 

(851,881) 

227,847 

(251,210) 

105,405 

(116,213) 

78,991 

(87,090) 

60,116 

(66,280) 

39,387 

(43,426) 

17,903 

(19,739) 

34,238 

(37,749) 

18,608 

(20,516) 

20,172 

(22,240) 

13,250 

(14,609) 

19,426 

(21,418) 

42,680 

(47,056) 

1,450,679 

(1,599,427) 

1975 

634,368 

(699,414) 

189,369 

(208,786) 

71,718 

(79,072) 

68,098 

(75,081) 

52,011 

(57,344) 

20,044 

(22,099) 

12,966 

(14,296) 

35,456 

(39,092) 

14,703 

(16,211) 

12,157 

(13,404) 

11,051 

(12,184) 

18,156 

(20,018) 

36.368 

(40,097) 

1,176,465 

(1,297,098) 

a

 Short lons/yr given in parentheses. 

5.2.3 Emissions 

Lead or its compounds may enter the environment 

at any step during its mining, smelting, processing, 

use, or disposal. Recent estimates of the dispersal of 

lead emissions into the environment by principal 

sources indicate that the atmosphere is the major initial recipient. Estimated lead emissions to the atmosphere in 1975 are shown in Table 5-2. 

Mobile and stationary sources of lead emissions, 

although found throughout the nation, tend to be 

concentrated in areas of high population density, 

with the exception of smelters. Figure 5-2 shows the 

approximate locations of major lead mines, primary 

smelters, alkyl lead plants, and manufacturers of 

lead storage batteries.13 

5.2.3.1 MOBILE SOURCES 

The largest source, by far, of lead emissions to the 

atmosphere is the exhaust of motor vehicles powered 

by gasoline that contains lead additives.14 These 

mobile-source emissions collectively constitute an 

estimated 88 percent of total lead emissions (Table 

5-2).9 Other mobile sources, including aviation 

usage of leaded gasoline and diesel and jet fuel combustion, contribute insignificant lead emissions to 

the atmosphere. 

Lead particulates emitted in automotive exhaust 

may be divided into two size classes. Particles initially formed by condensation of lead compounds in 

the combustion gases are quite small in size (well 

under 0.1 fim in diameter). Particles in this size 

category that become airborne can remain suspended in the atmosphere for long periods and thus 

can travel substantial distances from the original 

sources. Larger particles are also formed as a result 

of agglomeration of smaller condensation particles. 

5-2 
TABLE 5-2. ESTIMATED ATMOSPHERIC LEAD EMISSIONS FOR THE UNITED STATES, 1975»•» 

Source category 

Annual emissions, 

MT/yr 

Emissions as percentage of 

Subtotal 

Mobile subtotal 142,000 100 

Gasoline combustion 

Stationary subtotal 

Waste oil combustion 

Solid waste incineration 

Coal combustion 

Oil combustion 

Gray iron production 

Iron and steel production 

Secondary lead smelting 

Primary copper smelting 

Ore crushing and grinding 

Primary lead smelting 

Other metallurgical 

Lead alkyl manufacture 

Type metal 

Portland cement production 

Pigments 

Miscellaneous 

Total 

142,000 

19,225 

100 

100 

10,430 

1,630 

400 

100 

1,079 

844 

755 

619 

493 

•400 

272 

1,014 

436 

313 

112 

54.3 

8.5 

2.1' 

0.5 

5.6 

4.4 

3.9 

3.2 

2.5 

2.1 

1.4 

5.3 

2.3 

1.6 

0.6 

328 

161,225 

1.7 

88.1 

6.5 

1.0 

0.2 

0.1 

0.7 

0.5 

0.4 

0.4 

0.3 

0.2 

0.2 

0.6 

0.3 

0.2 

0.1 

0.2 

100 

a

 Inventory does not include emissions from exhausting workroom air. burning of lead-painted surfaces, welding of lead-painted steel structures, or weathering of painted 

surfaces. 

O LEAD SMELTING AND REFINING PLANTS (7); • TETRAMETHYL AND TETRAETHYL LEAD PLANTS (5) 

PRIMARY PRODUCTION FOR 1976 = 652, 877 MT 

A STORAGE BATTERY MANUFACTURERS (> 188) 

Figure 5-2. Location of major lead operations in the United States, 1976.1' 

• LEAD MINES (25 LARGEST); 

PRODUCTION = > 95% OF DOMESTIC OUTPUT 

5-3 
P.63 

These larger particles, which may be tens of 

micrometers or larger in diameter, behave in the atmosphere like the larger lead particulates emitted 

from most stationary sources and fall to the ground 

in the vicinity of the traffic producing them. The distribution of lead exhaust particles between the 

smaller and larger size ranges appears to depend on 

a number of factors, including the particular driving 

pattern in which the vehicle is used and its past driving history (Chapter 6). But as an overall average, it 

has been estimated15 that during the lifetime of the 

vehicle, approximately 35 percent of the lead contained in the gasoline burned by the vehicle will be 

emitted as fine particulate, and approximately 40 

percent will be emitted as coarse particulate. The remainder of the lead consumed in gasoline combustion is deposited in the engine and exhaust system. 

Engine deposits are, in part, gradually transferred to 

the lubricating oil and removed from the vehicle 

when the oil is changed. Moreover, some oils and 

lubricants contain lead naphthenate as a detergent. 

The fate of spent oil and its lead content is of considerable importance. A measure of its significance 

is reflected in the waste oil combustion values in Table 5-2. In addition, some of the lead deposited in 

the exhaust system gradually flakes off, is emitted in 

the exhaust as extremely large particles, and rapidly 

falls into the streets and roads where it is incorporated into the dust and washed into sewers or onto adjacent soil. 

The use of lead additives in gasoline, which was 

increasing in total volume for many years, is now 

decreasing as cars designed to use lead-free gasoline 

constitute a growing portion of the total automotive 

population (see Section 7.1.1). Regulations promulgated by EPA16

 that limit the average concentration 

of lead additives in gasoline will contribute to a 

further reduction in future automotive lead emissions. 

5.2.3.2 STATIONARY SOURCES 

As shown in Table 5-2 (based on 1975 emission 

estimates9), solid waste incineration and combustion 

of waste oil are the principal contributors of lead 

emissions from stationary sources, accounting for 

two-thirds of stationary source emissions. The 

manufacture of consumer products such as lead 

glass, storage batteries, and lead additives for 

gasoline also contributes significantly to stationary 

source lead emissions. Since 1970, the quantity of 

lead emitted from the metallurgical industry has 

decreased somewhat because of the application of 

control equipment and the closing of several plants, 

particularly in the zinc and pyrometallurgical industries. 

A new locus for lead emissions emerged in the 

mid-sixties, however, with the opening of the 

"Viburnum Trend" or "New Lead Belt" in southeastern Missouri. The presence of seven mines and 

two accompanying lead smelters in this area makes it 

the largest lead-producing district in the world and 

has moved the United States into first place among 

the world's |ead-producing nations. An extensive 

study to assess the impact of the expanding lead industry in Missouri and to stimulate new emission 

control technology has been initiated.17 

Although some contamination of soil and water 

occurs as a result of such mechanisms as leaching 

from mine and smelter wastes, quantitative estimates 

of the extent of this contamination are not available. 

Spillage of ore concentrates from open trucks and 

railroad cars, however, is known to contribute significantly to contamination along transportation 

routes. For example, along two routes used by ore 

trucks in southeastern Missouri, lead levels in leaf 

litter ranged from 2000 to 5000 figlg at the roadway, declining to a fairly constant 100 to 200 figlg 

beyond about 400 ft from the roadway.17 

Another possible source of land or water contamination is the disposal of particulate lead collected by air pollution control systems. The potential for impact on soil and water systems of the disposal of dusts collected by these control systems has 

not been quantified. 

The lead-containing particles emitted from stationary sources occur in various sizes. Those emitted 

from uncontrolled stationary sources generally include particles larger than 1- to 2-fim mass mean 

diameter, and therefore tend to settle out near the 

source. These large-particle emissions add considerable lead to the dust, soil, water, and vegetation 

in the neighborhood of the source (see Section 7.2). 

Uncontrolled sources also contribute substantial 

quantities of smaller-diameter particles to the atmosphere, where iong-range transport may occur. 

When controls are applied to stationary sources, the 

total mass of the emissions is reduced significantly. 

But the number of particles being emitted may not 

be affected greatly if most of the particles emitted 

are small, because current particulate control 

methods are usually more effective in removing the 

larger-diameter particles. The smaller-diameter 

particles (below 2 fim) may be far greater in number 

than the larger, more massive particles; and with 

diminishing size, an increasing proportion is likely 

to escape collection. Generally, control methods are 

5-4 
applied to emissions from stacks, vents, and other 

process outlets. But lead-containing particles may 

also be emitted as fugitive dusts in the larger size 

range (>2-fim diameter) from less controllable 

sources such as windows and doors, conveyors, and 

waste piles. Available emission inventories do not 

include emissions from the exhaust of workroom air, 

burning of lead-painted surfaces, weathering of 

lead-painted surfaces, etc. The magnitude of emissions from these sources is unknown. 

5.3 REFERENCES FOR CHAPTER 5 

1. Shacklette, H. T., J. C. Hamilton, J. G. Boerngen, and J. 

M. Bowles. Elemental Composition of Surficial Materials 

in the Conterminous United States. U.S. Geological 

Survey. Washington, D.C. Professional Paper 574-D. 

1971. 74 p. 

2. Chamberlain, A. C. Interception and retention of radioactive aerosols by vegetation. Atmos. Environ. 4:57-77, 

1970. 

3. Chow, T. J. and C. C. Patterson. The occurrence and significance of lead isotopes in pelagic sediments. Geochim. 

Cosmochim. Acta. (London). 26:263-308, 1962. 

4. Lead: Airborne Lead in Perspective. National Academy of 

Sciences. Washington, D. C. 1972. 330 p. 

5. Patterson, C. C. Contaminated and natural lead environments of man. Arch. Environ. Health. 77:334-360, 1965. 

6. Burton, W. M. and N. G. Stewart. Use of long-lived 

natural radio-activity as an atmospheric tracer. Nature. 

756:584-589, 1960. 

7. Chow, T. J., J. L. Earl, and C. B. Snyder. Lead aerosol 

baseline: Concentration at White Mountain and Laguna 

Mountain, California. Science. 7 78(4059):401-402, 1972. 

8. Akland, G. G. Air Quality Data for Metals, 1970 through 

1974, from the National Air Surveillance Network. U.S. 

10 

II 

Environmental Protection Agency, Research Triangle 

Park, N.C., Pub. No. EPA 600/4-76-401. 1976. 

Control Techniques for Lead Air Emissions. (Draft final 

report.) Office of Air Quality Planning and Standards, U.S. 

Environmental Protection Agency, Research Triangle 

Park, N.C. EPA Contract No. 68-02-1375. 1976. 424 p. 

Mineral Facts and Problems. U.S. Bureau of Mines 

Bulletin 667, U.S. Department of Interior, Washington, 

D.C. 1975. p. 1243. 

Lead Industry in May 1976. Mineral Industry Surveys. 

U.S. Department of Interior, Bureau of Mines, Washington, D.C. August 1976. Cited in: Control Techniques for 

Lead Air Emissions. (Draft final report.) Office of Air 

Quality Planning and Standards, U. S. Environmental Protection Agency, Research Triangle Park, N. C. EPA Contract No. 68-02-1375. 1976. 424 p. 

Commodity Data Summaries, 1977. U.S. Department of 

The Interior, Bureau of Mines, Washington, D. C. January 

1977. 

Commodity Files, 1976. U.S. Dept. of Interior, Bureau of 

Mines, Washington, D.C. 1976. 

14. EPA's Position on the Health Implications of Airborne 

Lead. U.S. Environmental Protection Agency, Washington, D.C. 1973. 116 p. 

Ter Haar, G. L., D. L. Lenane, J. N. Hu, and M. Brandt. 

Composition, size, and control of automotive exhaust particulates. J. Air Poll. Control Assoc. 22(l):39-46, 1972. 

Federal Register. Regulation of fuels and fuel additives. 

5S(234):33. 734-33. 741, Dec. 6. 1973. 

Wixson, B. G. and J. C. Jennett (eds.). An Interdisciplinary Investigation of Environmental Pollution by Lead and 

Other Heavy Metals from Industrial Development in the 

New Lead Belt of Southeastern Missouri. (Interim report.) 

National Science Foundation, Research Applied to National Needs (RANN), Rolla and Columbia, Missouri, The 

University of Missouri. 1974. 480 p. 

12 

13 

15 

16 

17 

5-5 
6. TRANSFORMATION AND TRANSPORT 

6 1 INTRODUCTION 

The circulation of lead in the environment (shown 

conceptually in Figure 6-1) illustrates that lead 

released into the atmosphere ca.n be delivered to 

man (animals) via several routes. At present, it is 

possible to obtain only qualitative or semiquantitative estimates of the movement of lead within and 

among the various environmental media. This is 

largely because the physical and chemical transformations occurring within the lead cycle are not well 

understood. The purpose of this chapter is to summarize the available data that reflect what is known 

about the transformation and transport mechanisms 

controlling the distribution and.fate of lead in the 

environment in its various chemical forms. Primary 

emphasis is placed on the atmosphere, since.it serves 

as the principal medium for transport of lead from 

manmade sources. 

FOOD 

PROCESSING 

.; WATER : 

:

: SUPPLIES :: 

> PLANTS •:•>: 

:•:•:•:•:•:•:•:•:•:•:•: 

• EARTH : 

:

 ISOILI : 

MINING 

OPERATIONS 

JO'lN'D'OStRV > 

u. r , , 

. » / ^.AUTOMOBILES j—•- ;, 

L ± I 

; ATMOSPHERE ;. 

I (LEAD AEROSOL \-

: AN D ;'• 

; ORGANIC LEAD) ;'• 

:£:£;£: "Ir^x^'oust':::::::!"^' Si::::::::::*:::*:::*:::*:*: 

OTHER LEAD 

CONTAINING 

PRODUCTS 

AND WASTES 

" ' FALLOUT" " ly.'.; 

:-:::

:

 AN D RAINOU T '•:•:'•: 

T ~~ 

:':'.yy.'': OCEANS #$ + - * ^ESTUARIES-:;! 

LAKES AND RIVERS 

'•>:•:•: SEDIMENT S •: 

Figure 6-1. Simplified ecologic flow chart for lead showing 

principal cycling pathways and compartments. 

6.2 PHYSICAL AND CHEMICAL TRANSFORMATIONS IN THE ATMOSPHERE 

Although lead is introduced into the atmosphere 

primarily in the particulate form, relatively small 

amounts are also emitted in the vapor phase. Once 

lead is introduced into the atmosphere, important 

physical and chemical changes occur before its 

transfer to other environmental media. The discussion of these changes will be divided into mobile and 

stationary source categories. This division is somewhat arbitrary in that the pollutants from both 

source categories are well mixed in the atmosphere. 

In those cases in which one type of source predominates (e.g., freeways or smehers), the approach 

should be reasonably realistic. 

6.2.1 Physical Transformations 

6.2.l.l SIZE DISTRIBUTION OF PARTICLES 

FROM MOBILE SOURCES 

Automotive exhaust is the primary source of particulate lead introduced ubiquitously into the atmosphere in urban areas. The size of the particles 

emitted may range from a few hundredths of a 

micrometer in diameter to several millimeters, depending on the operating mode, age of exhaust 

system, fuel lead content, speed and load, acceleration, deceleration, engine condition, and other factors. 

Numerous environmental processes, including 

transformation, transport, deposition, and mechanisms of impact, are prominently influenced by the 

particle sizes. It is significant, for example, that the 

sizes of the particles directly affect the probability of 

lead's being transported via the respiratory system. 

Because of the importance of lead particle sizes in 

relation to numerous environmental questions, the 

size distributions of those particles emitted from 

automobiles have been studied by many investigators.1

"

10

. 

Figure 6-2 shows the results of a series of variable 

speed tests made by Hirschler and Gilbert4 on an 

auto after about 25,000 miles of deposit accumula6-1 
I i u p i Ii •»•'»'" 'I 

P.66 

tion in the exhaust system. The data demonstrate 

that smaller lead particles make up the largest fraction of those exhausted, and that there is significant 

exhaust system accumulation of lead particles in 

both size categories under city-driving conditions. 

During acceleration, release of these accumulations 

is quite rapidly induced, but the increased emission 

drops off during the period of constant highway 

speed. The effect of speed on the particle size distribution shown in Figure 6-3, as found by Ganley and 

Springer,3 also demonstrates that the mean particle 

sizes emitted decrease with increasing speed. The 

results of these two studies imply that although 

larger lead particles are most likely to be deposited 

in the exhaust system, the deposits are released by 

ablative processes that cause decreases in particle 

size. Figure 6-4 compares size distributions at receptor sites in California with those typical of undiluted 

auto exhaust. The smaller sizes at the receptor sites 

reflect the decrease in the mean size caused by gravitational settling and other scavenging processes 

that occur during atmospheric transport. Figure 6-5 

compares differential mass distributi@ns at the 

California receptor sites with those at a freeway site. 

These distributions are generally bimodal, indicating that particulate lead in the atmosphere may consist of lead emitted by autos and lead that has been 

deposited on surfaces (soil) and re-entrained via atmospheric turbulence (fugitive dust); or fihe bimodal 

distribution may reflect emission patterns. The 

results of these studies generally indicaue that more 

than half of the lead particles are typically less than 

1 fim in diameter, but these estimates may be biased 

by the failure to use isokinetic sampling techniques 

(see Section 4.2.3.1). 

Lee et al.9 measured the concentrations and size 

distributions of particulate emissions from automobile exhaust and found that 95 percent of the 

total particulate lead was in particles with mass median equivalent diameters (MMED) less than 0.5 

fim. All samples were taken at steady-cruise conditions and thus do not represent the typical discharge 

of particles under wide-open-throttle accelerations, 

decelerations, and short-term cruise and idle conditions typical of urban traffic. The varying modes 

result in the discharge of much larger particles. 

Robinson and Ludwig" reported MMIED of 0.25 

fim for urban and rural areas; 25 percent of the particles were smaller than 0.16 fim, and 25 percent 

were larger than 0.43 fim (Table 6-1). Cholak et 

al.,12 Lee et al.,13 and Flesch14 observed similar 

distributions; however, their data also indicate that 

these distributions change very little over distances. 

< 50 — 

1000 

500 

100 

50 

10 

5 

r 

-

-

— 

_ 

~ 

i 

1 

i 

1 

I / 1 / 

\i 

i 

i\ 

V 

1 

1 

l 1 

T ^ 

h 

(I 

ii 

/?! •v. \. 

ONSTO60MPH ELERAT 

k CITY-TYPE DRIVING -*| o 

l l I 

1 1 I I 

TOTAL LEAD EXHAUSTED 

FINE PARTICLES. 0-5 um _ 

AND UNCLASSIFIED LEAD: 

I COARSE PARTICLES, > 5 HIT 

A l 

1 i -

\ 1 }'-

V

 \ \ '- \ \\ 1 -

iV h 

60 MPH | 

ROAD ] CITY-TYPE 1 

LOAD [• DRIVING J -

1 1 1 1 

636 640 650 

RUN NO. 

Figure 6-2. Effect of various driving conditions on the amount 

of lead exhausted.4 

30 40 50 60 70 80 90 

PARTICLES WITH DIAMETER <D,wl % 

Figure 6-3. Effect of speed on size distribution of exhaust particles at different road load cruise conditions and using Indolene HO 0 fuel.3 

Gillette and Winchester15 examined the effect of age 

on the size distribution of lead aerosols. They found 

that lead aerosol size distributions do not vary 

greatly from one source area (essentially an area of 

heavy automobile traffic) to another, and that the 

6-2 
crometen 

UJ a 

UJ OIAM 

UJ PARTIC NAMIC 

O 

UJ 

10.0 

8.0 

6.0 

4.0 

2.0 

1.0 

0.8 

0.6 

0.4 

I 

— 

-

/ l 

I I I I I I I k 

M — AUTO EXHAUST / 

/

 Pb

 / / 

J 1 PASADENA Pb 

A-^ ^ A" 111/72) 

/ ^^ T (2/74) 

I 

/ — 

-

— 

_ 

— 

— 

— 

_ 

— 

I.. 

40 60 80 90 95 

MASS IN PARTICLES < D , percent 

Figure 6-4. Cumulative mass distributions for lead aerosol in 

auto exhaust and at Pasadena, a receptor sampling site. The 

abscissa is a log-normal scale, and D_ is the aerodynamic, 

unit density particle diameter.''' 

0.2 

a. 

a 

ro 

< «- — 0.6 

hE 

E 

< 0.4 

FREEWAY Pb ' 

*•* 

• 

* 

PASADENA Pb 

~ ,*--^ -

- /* # 

, ' / 

'"' 

1 

(5/7:0 rj 

A. / \ 

£*W a 

^ ^ -

(11/721 

1 

1 

r \ / ^ 

\f \ 

o \ -

V (2/74) — 

.Nft ^ 

O 0.2 — 

0.1 1.0 10 

MEAN DIAMETER ID I, micrometers 

Figure 6-5. Differential mass distributions for lead 1 m from a 

freeway, May 1973, and at Pasadena sampling sites, November 1972 and February 1974. (The abscissa is the mean 

diameter, and the dashed lines assume that the smallest particle size is 0.01 /um and the largest 50 /im. Alog Dp = interval of log of aerodynamic particle diameter; mT = total mass 

loading of lead in airborne particulates; Am = mass of lead 

occurring in a fraction, defined in terms of size, of the total 

particulates; im/m T = fraction of mass occurring in a given 

particle size range.)1" 

lead aerosol size distributions do not respond 

noticeably to changes in weather within a source 

area during 24-hr sampling periods. The results of 

their study suggest little modification of the characteristics of the lead aerosol size distribution as a 

result of nonprecipitative atmospheric mechanisms 

for equivalent particle radii larger than 0.2 fim. 

Electron microscope studies have shown that 

many of the fine particles in exhaust emissions are 

nearly spherical in shape and are electron-dense. 

The coarser particles are much more irregular, and 

some are filamentous in outline. Particles collected 

at a constant cruise speed of 30 mph were found to 

be composed of a carbon core or matrix, on or in 

which were distributed spherical or crystalline 

electron-dense lead particles <0. l fim in 

diameter.316 Electron micrographs of the exhaust 

particles have shown that although the particle aggregates of about 0.5 fim were stable, samples of the 

gas that had been inhaled showed mor e 

homogeneous aggregates I to 2 micrometers in 

diameter than larger aggregates in the exhaled gas. 

A similar effect was obtained by drawing the gas 

through a humidifier.'7 

6.2.1.2 SIZE DISTRIBUTION OF PARTICLES 

FROM STATIONARY SOURCES 

High-temperature combustion and smelting processes generate submicrometer-sized lead particulate, whereas lead emissions from material handling 

and mechanical attrition operations associated with 

smelters consist of larger ( > 1 fim) dust particles. 

Actual data on the size distribution of lead particles 

emitted from stationary sources are limited. Fugas et 

al.,18 using a five-stage impactor, obtained samples 

in the Meza Valley (influenced by a lead smelter) 

and in the urban area of Zagreb. The results are 

shown in Figure 6-6. A considerable difference was 

found in the size distribution of lead particles in the 

industrial (Meza Valley) versus the urban (Zagreb) 

area. In the industrial area, only 10 percent of the 

lead particles had diameters smaller and 1 fim, 

whereas in the urban area, 75 percent were smaller 

than 1 fim. This implies that the fugitive dust from 

the mechanical rather than the direct-smelting 

operation is the primary emission. 

Lead emissions from stationary sources are probably affected by topographic influences in a manner 

similar to other pollutants. Because of the mountainous location of half of the six primary lead 

smelters in the United States, however, and because 

these three smelters are probably the largest singlepoint emitters of lead, the topographic influence on 

transport and dispersion is important. 

6-3 
P.68 

TABLE 6-1. COMPARISON OF SIZE DISTRIBUTIONS OF LEAD-CONTAINING PARTICLES IN MAJOR SAMPLING AREAS11 

Sample area 

Chicago 

Cincinnati 

Philadelphia 

Los Angeles 

(DTN) 

Pasadena 

Vernon (rural) 

San Francisco 

Cherokee (rural) 

Mojave (rural) 

No. Ol 

samples 

12 

7 

7 

8 

7 

5 

3 

1 

1 

25% 

Avg. 

0.19(7)b 

0.15(3) 

0.14(3) 

0.16(7) 

0.18 

0.17(4) 

0.11 

0.25 

— 

Range 

0.10-0.29 

0.09-0.24 

0.09-0.25 

0.10-0.22 

0.05-0.25 

0.12-0.22 

0.06-0.13 

— 

— 

Distributio 

Avg. 

0.30 

0.23 

0.24 

0.26 

0.24 

0.24 

0.25 

0.31 

0.27 

i by particle size. u,m 

MMEDa 

Range 

0.16-.64 

0.16-0.28 

0.19-0.31 

0.19-0.29 

0.08-0.32 

0.18-0.32 

0.15-0.31 

— 

— 

75% 

Avg. 

0.40(10) 

0.44 

0.41 

0.49(7) 

0.48(6) 

0.40 

0.45(2) 

0.71 

0.34 

Range 

0.28-0.63 

0.30-0.68 

0.28-0.56 

0.39-0.60 

0.13-0.67 

0.28-0.47 

0.44-0.46 

— 

— 

MMED = mass median equivalent diameter. 

Numbers in parentheses indicate number ol samples available for a specific value when different from total number of samples. 

I I T 

MEZA VALLEY 

ZAGREB 

SEP-OCT 1971 

JAINJ-FEB 1972 _ 

MAY-JUL 1972 " 

AUG-SEP 1972 

JAN-FEB 1973 

1 5 10 30 SO 70 90 95 99 

MASS < DIAMETER, percent 

Figure 6-6. Cumulative mass distribution of lead particles by 

size.18 

At least four general conclusions about lead from 

mobile and stationary sources can be based on the 

results of the above studies: 

1. Lead is emitted into the atmosphere principally in the particulate form. 

2. The mass median equivalent diameters of the 

lead-bearing particles are typically less than 

l fim, and the size distributions are fairly 

uniform from area to area. 

3. The particle sizes in urban and rural areas 

are such that the lead can be transported 

over relatively large distances via typical atmospheric convection and turbulence processes. 

4. The size distributions are such that significant fractions of the total atmospheric lead 

concentrations are within the respirable size 

range. 

6.2.2 Chemical Transformations 

6.2.2.1 MOBILE SOURCE EMISSIONS 

Tetraethyl lead (TEL) and tetramethyl lead 

(TML), as well as the mixed-lead alkyls, are used 

widely as additives in gasoline. Although these 

organic compounds are less volatile than gasoline, 

small amounts may escape to the atmosphere by 

evaporation from fuel systems or storage facilities. 

TEL and TML are light-sensitive and undergo 

photochemical decomposition when they reach the 

atmosphere.1019 The lifetime of TML appears to be 

longer than that of TEL. Exposure of dust to TEL, 

both in the presence and absence of water vapor, 

results in sorption of organic lead on dust particle 

surfaces.20 Laveskog21 found that transient peak 

lead alkyl concentrations up to 5000 fig lead/m3 in 

exhaust gas may be reached in a cold-started, fully 

choked, and poorly tuned vehicle. If a vehicle with 

such emissions were to pass a sampling station on a 

street where the lead alkyl level might typically be 

0.02 to 0.04 /ng/m3of air, a peak of about 0.5 /ug/m3 

could be measured as the car passed by. The data reported by Laveskog were obtained with a procedure 

that collected very small (100 ml), short-time (10 

min) air samples. The sensitivity reported was much 

better than that reported by other investigators, who 

have not been able to duplicate his results.22 Harrison et al.22

 found levels as high as 0.59 /xg/m3 (9.7 

percent of total lead) at a busy gasoline service station. 

Purdue et al.23 measured particulate and organic 

lead in atmospheric samples. Some results are shown 

in Tables 6-2 through 6-4. These data demonstrate 

that in all of the cities studied, particulate lead levels 

are much higher (an average of approximately 20 

6-4 
P.69 

times higher) than organic lead levels. The results 

are entirely consistent with the studies of Huntzicker 

et al.,10 who report an organic component of 6 percent of the total airborne lead in Pasadena for a 3-

day period in June 1974, and of Skogerboe,24 who 

measured fractions in the range of 4 to 12 percent at 

a site in Fort Collins, Colorado. It is noteworthy, 

however, that in the underground garage (Table 

TABLE 6-2. RESULTS OF ATMOSPHERIC SAMPLING 

6-4), total lead concentrations are approximately 

five times those in the urban areas, and the percentage of organic lead increases to approximately 

17 percent. Consequently, the concentration of 

organic lead in an underground garage site is ten 

times that in the open urban environment (see Tables 6-2 and 6-4), and the potential exposure level is 

similarly magnified. 

FOR ORGANIC AND PARTICULATE LEAD23(Mg/m3) 

Sample 

no.a 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

Avg. 

Cincinnati 

Organic Particulate0 

0.2 

0.0 

0.0 

0.2 

0.4 

0.2 

0.2 

0.4 

0.2 

0.2 

0.2 

1.5 

0.9 

0.9 

1.9 

3.7 

1.6 

1.8 

1.3 

1.5 

2.4 

1.7 

Den 

Organic 

0.2 

0.5d 

1.4d 

0.3 

0.2 

0.1 

0.0 

0.2 

0.2 

0.5d 

0.2 

ver 

Particulate 

2.3 

1.8 

1.6 

1.7 

1.0 

1.8 

2.2 

1.8 

2.0 

— 

1.8 

Washington, D.C. 

Organic Particulate 

0.0 

0.2 

0.1 

0.3 

0.1 

0.1 

0.1 

0.2 

0.4 

0.2 

0.2 

1.4 

1.4 

1.5 

1.0 

1.1 

0.8 

1.7 

1.2 

0.8 

1.6 

1.2 

St. 

Organic 

0.5 

0.2 

0.4 

0.2 

0.3 

0.2 

0.3 

0.4 

0.4 

1.3d 

0.3 

Louis 

Particulate 

2.0 

2.0 

1.8 

2.5 

1.9 

1.8 

2.2 

2.2 

2.0 

1.2 

2.0 

Philadelphia 

Organic Particulate 

0.5 

1.1d 

0.2 

0.4 

0.8 

0.4 

0.0 

0.3 

0.1 

0.1 

0.3 

1.3 

1.7 

2.9 

2.4 

1.1 

1.1 

1.7 

2.1 

1.8 

2.3 

1.8 

Chi 

Organic 

0.2 

0.4 

0.2 

1.6d 

0.2 

0.2 

0.3 

0.1 

0.2 

0.2 

0.2 

:ago 

Particulate 

5.9 

5.6 

5.3 

3.5 

4.6 

5.5 

5.8 

4.8 

5.0 

5.1 

5.1 

Sample no. represents order in which samples were taken. Cities were not sampled concurrently. 

All values are average ot two determinations, 

determined by NASN method (6). 

Organic lead averages do not include these values because the replicate values tor these samples were more than twice the standard deviation from the average. 

TABLE 6-3. PERCENTAGE OF PARTICULATE VERSUS 

VAPOR-PHASE LEAD IN URBAN AIR SAMPLES23 

City 

Cincinnati 

Denver 

Washington, D.C. 

St. Louis 

Philadelphia 

Chicago 

aAII values are averages 

Total lead3 

Organic. 

ug/m 

0.2 

0.2 

0.2 

0.3 

0.3 

0.2 

of ten determinations 

particulate Pb x 

Particulate, 

jig/m3 

1.7 

1.8 

1.2 

2.0 

1.8 

5.1 

too 

Particulate. 

% of total 

89 

90 

86 

87 

86 

96 

TABLE 6-4. ANALYSES OF FIVE REPLICATE SAMPLES 

TAKEN IN AN UNDERGROUND PARKING GARAGE23 

Organic 

lead, 

Sample no. /J.g/m 

1 1.9 

2 1.9 

3 1.9 

4 1.8 

5 2.2 

Average (X) 1.9 

Relative standard 

deviation (Srel)a 7.9% 

a0 . Standard deviation ,„ „ Srel = x 100 

Organic 

lead. 

% 

15.7 

17.1 

17.6 

14.9 

18.0 

16.7 

7.9% 

Particulate 

lead, 

/ig/m3 

10.3 

9.2 

8.9 

10.3 

10.0 

9.7 

6.7% 

Total 

lead. 

Mg/m3 

12.2 

11.1 

10.8 

12.1 

12.2 

11.6 

5.2% 

Average 

As the lead alkyl compounds of gasoline are subjected to the elevated temperatures and pressure of 

combustion, they are converted to lead oxides, 

which function to inhibit engine knock. The lead oxides react with other additives in the fuel and leave 

the combustion chambers in a variety of complex 

compounds. The results of composition studies by 

Hirschler and Gilbert,4 Ter Haar et al.,2 and Ter 

Haar and Bayard25 are shown in Tables 6-5 and 6-6, 

respectively. 

Habibi et al.5 determined the composition of particulate matter emitted from a test car operating on a 

typical driving cycle. The main conclusions drawn 

from the study were: 

1. Composition of emitted exhaust particles is 

related to particle size. 

2. Very large particles greater than 200 fim 

have a composition similar to lead-containing material deposited in the exhaust system, 

confirming that they have been re-entrained 

or have flaked off from the exhaust system. 

These particles contain approximately 60 to 

65 percent lead salts, 30 to 35 percent ferric 

oxide (Fe203), and 2 to 3 percent soot and 

carbonaceous material. The major lead salt 

is lead bromochloride (PbBrCl), with large 

amounts (15 to 17 percent) of lead oxide 

6-5 
P.70 

TABLE 6-5. AVERAGE COMPOSITION OF PARTICULATE LEAD COMPOUNDS EMITTED IN AUTO EXHAUST8'

2

'

4 

Compound, wt. % 

aNH„CI- /3NH4CI- 2NH4CI- 3Pb3 (P04 lj" 

Exhaust source PbCIBr 2PbCIBr 2PbCiBr PbCIBr "bCIBr 

CarB: 

City type cycle, fuel plus TEL motor mix only 68 24 6 2 — 

City type cycle, added sulturc 70 30 — — — 

City type cycle, added phosphorusd 35 18 17 10 20 

Constant speed, 60 mph, road load 60 20 20 — — 

Full-throttle accelerations 85 10 5 —- — 

CarM: 

City type cycle, fuel plus TEL motor mix only 33 40 5 22 — 

Constant speed, 60 mph, road load 30 30 35 5 — 

Full-throttle accelerations 90 10 — — — 

aX-ray diffraction analyses made in situ on material deposited on glass slides mounted within the precipitator of the sampler. 

In addition to the tabulated compounds. PbSO. and PbO-PbCI-Br-hLO occurred ocasionally in concentrations of 5 percent or less. 

cSulfur content increased from 0.025 to 0.105 weight percent by addition of disulfide oil. 

0.4 theory phosphorus added. 

TABLE 6-6. EFFECTS OF AGING ON LEAD COMPOUNDS IN SAMPLES OF AUTO EXHAUST AS DETERMINED BY ELECTRON 

MICROPROBE25 

Percentage of total particles sampled 

Black bag3 Eight-Mile Roadb 

Lead compound Zero time 18 hour Near road 400 yd Rural site0 

PbCi^ 104 83 iT2 105 5~4 

PbBr2 5.5 0.5 4.0 0.7 0.1 

PbBrCI 32.0 12.0 4.4 0.6 1.6 

Pb(OH)CI 7.7 7.2 4.6 8.8 4.0 

Pb(OH)Br 2.2 0.1 2.0 1.1 — 

(PbO)2PbCI2 5.2 5.6 2.8 5.6 1.5 

(PbO)2-PbBr2 1.1 0.1 0.7 0.3 — 

(PbO)2PbBrCI 31.4 1.6 2.0 0.6 1.0 

PbC03 1.2 13.8 15.6 14.6 30.2 

Pb3(P04)2 — — 0.2 0.3 — 

PbOx 2.2 21.2 12.0 25.0 20.5 

(PbO)2PbC03 1.0 29.6 37.9 21.3 27.5 

PbOPbS04 — 0.1 1.0 4.6 5.0 

PbS04 0.1 — 2.2 6.0 3.2 

Sample collected directly from tailpipe in black bag to prevent irradiation of exhaust. Analyzed immediately and again 18 hr later to determine effect of aging. 

State highway in Detroit carrying about 100,000 cars a day. 

°Samples were taken 400 yd from a lightly traveled roadway. 

(PbO) occurring as the 2 PbC^PbBrCl dou- by X-ray diffraction. This is particularly 

ble salt. Lead sulfate and lead phosphate ac- true for particles in the 2- to 0.5-micrometer 

count for 5 to 6 percent of these deposits. size range. 

(These compositions resulted from the com- 6. There is considerably more soot and carbustion of low-sulfur and low-phosphorus bonaceous material associated with small 

fuel.) particles than with coarse particles re3. PbBrCI is the major lead salt in particles of 2 entrained after having been deposited after 

to 10 micrometers equivalent diameter, with emission from the exhaust system. This car2 PbBrCI -NH4C1 present as a minor constit- bonaceous material accounts for 15 to 20 

uent. percent of the finer particles. 

4. Submicrometer-sized lead salts are pri- 7. Particulate matter emitted under typical 

marily 2PbBrCl-NH4Cl. driving conditions is rich in carbonaceous5. Lead-halogen molar ratios in particles of type material. There is substantially less such 

less than 10 microns MMED indicate that material emitted under continuous hot 

much more halogen is associated with these operation. 

solids than the amount expected from the 8. Only small quantities of 2PbBrCl«NH4CI 

presence of 2PbBrCl»NH4Cl, as identified were found in samples collected at the tail6-6 
P.71 

pipe from the hot exhaust gas. Its formation 

therefore takes place primarily during cooling and mixing of exhaust with ambient air. 

Hirschler and Gilbert4 found similar results and 

speculated that higher gas temperature during fullthrottle operations reduced the tendency for the ammonium-lead halide complexes to be present since 

they are unstable at high temperatures. 

Based on the above studies, it seems quite clear 

that the size.distribution of lead particles emitted 

from automobiles and the relative concentrations of 

the complex compounds in those particles vary significantly with driving conditions, engine condition, 

type of fuel, and age of exhaust system. Particles > 2 

fim in the exhausted particulate are primarily lead 

bromochloride. The very large particles, a consequence of deposits in the exhaust system, are also 

primarily lead bromochloride. 

The fates of these lead compounds, once they are 

introduced into the atmosphere from automobiles, 

are not completely understood. There is disagreement in the early literature concerning the loss of 

halogens by these lead compounds. Pierrard26 suggested that PbBrCI undergoes photochemical 

decomposition with the formation of a lead oxide 

and the release of free bromine and chlorine, but 

later suggested a hydrolytic conversion mechanism. 

Ter Haar and Bayard25 and Robbins and Snitz27 

confirm the loss of halogen from freshly emitted Pb 

salts, but they do not support the photochemical 

mechanism. Ter Haar and Bayard25 suggest that 

lead halides are eventually converted to lead carbonates and lead oxides. Pierrard26obtained data on 

aged lead aerosol that indicated that the lead particle surfaces had already been converted to a 

relatively insoluble form such as oxide, carbonate, 

or basic halide; this would be consistent with a conversion mechanism expected to release the less reactive hydrogen halide rather than the more reactive 

molecular halogen. Dzubay and Stevens28 observed 

a diurnal variaton in the bromine-to-lead concentration ratio in atmospheric particulate indicative of the loss of halogens during atmospheric 

transport. Ter Haar and Bayard25 studied the effects 

of aging on automobile exhaust collected in a black 

bag, using an electron probe. The results, shown in 

Table 6-6, indicate that 75 percent of the bromine 

and 30 to 40 percent of the chlorine associated with 

the compounds contained in the particulates were 

lost in 18 hr; data presented suggest that the proportions of lead carbonates ana lead oxides increased. Since these chemical reactions occurred in a 

black bag, photolytic processes would not likely be 

responsible for the decrease in halides. At the very 

least, therefore, this experiment demonstrates the 

existence of nonphotolytic decomposition pathways 

for lead halides in the atmosphere. Consequently, 

the chemical composition of lead in the atmosphere 

from automobile emissions almost certainly depends 

to some extent on the age of the particles as well as 

the presence of other pollutants with which the lead 

compounds can react. 

The results of Lee et al.9 show that the percentage 

of water-soluble particulate lead increased when 

diluted exhaust was irradiated by light in the wavelength region of 3000 to 6000 A. This region is in the 

near-ultraviolet and visible regions of the spectrum 

and is available from direct sunlight. The percentage 

of water-soluble lead in the diluted exhaust also was 

increased by irradiation in the presence of 0.5 ppm 

S02 . Irradiation significantly increased the sulfate 

concentration of the particulates and was accompanied by a shift to smaller particle sizes. A shift of 

nitrate-bearing particles to smaller sizes, with and 

without addition of S02 , was also observed with irradiation. The amount of nitrate present was 

decreased in the presence of S02 . The lead nitrate, 

which is much more soluble in water than the other 

lead salts present, cannot be totally responsible for 

the increased water solubility observed if the N0 3 

concentrations decrease. 

The information available regarding the chemical 

composition of lead particles emitted from automobiles may be summarized as follows: 

1. Lead halogen compounds are the principal 

forms emitted; lead chlorobromide is the 

most prominent of these. 

2. The particulates undergo compositional 

changes during transport away from the 

source. These changes appear to consistently 

involve: 

a. Losses of halogens, the rate of which might 

be photochemically enhanced, but which 

also occur in the absence of light. 

b. General increases in the water solubilities 

of the particles with concomitant shifts 

toward smaller mean particle sizes. These 

latter changes are enhanced by the presence of SOz, in which case the amounts of 

nitrate present decrease. 

3. Although several reports have suggested that 

the lead halogen compounds are converted 

to oxides and/or carbonates, the only specific 

examination of the composition after aging 

was that of Ter Haar and Bayard.25 Unfortunately, their experimental approach did 

6-7 
P.72 

not rely on a particularly definitive method 

of identification. Indeed, the electron microprobe approach used can only be regarded as 

a crude qualitative tool for the identification 

of compounds; the simultaneous occurrences 

of other elements in lead-bearing particles 

and the general morphological characteristics of the particles can provide only circumstantial indications of the compounds 

that are present. This is particularly true for 

lead-bearing particles because compounds of 

several other elements are also typically present. Habibi et al.,5

 for example, have shown 

that the particles often include iron as well as 

lead compounds. The percentage composition data given in Table 6-6 should also be 

evaluated, taking into account that they are 

number rather than mass percentages. Thus, 

although lead carbonate, for example, may 

comprise a relatively high number percentage of the total, its mass percentage may be 

quite different, depending on the size distributions involved and whether the particle 

compositions are size dependent. 

These general conclusions and qualifications are 

consistent with and supportive of the results of the 

study reported by Olson and Skogerboe.29 They 

determined that the principal form of lead found in 

lead-contaminated soils from highway medians as 

well as in street dusts was lead sulfate. Although this 

study included evaluation of 18 soil and/or dust 

samples collected from different U.S. locations, significant amounts of the lead halogen compounds 

were found in any case. The conversion of lead 

halides to other compounds appears to have been 

quite complete for these aged lead aerosol deposits. 

6.2.2.2 STATIONARY SOURCE EMISSIONS 

Measurements are not available to confirm the 

chemical form of lead emissions from stationary 

sources. Barltrop and Meek30 indicate the presence, 

without reference to specific measurements, of lead 

sulfide or lead chloride in the mining industry, lead 

oxide in smelters, and lead carbonate and lead chromate in pigments used in older paints. Lead oxide is 

the principal form of the metal used in battery 

manufacturing. 

The association of lead sulfide with mining is 

clearly rational, since this is the primary mineral 

form (galena). While lead oxide may certainly be 

derived from the smelting process, the amounts produced may be relatively small in comparison to the 

amounts of lead sulfide released as fugitive dust to 

the atmosphere around a smelter. Moreover, the 

release of S0 2 usually associated with lead smelting 

operations, coupled with the possible interactions 

between lead particles and SOz, imply that the compounds released may well undergo conversion to 

other forms. Thus, although the compounds 

generally associated with stationary sources are not 

particularly soluble, the possibility of conversion to 

more soluble compounds or accumulation of the 

particles in the lungs of exposed populations should 

not be ignored. 

6.3 TRANSPORT IN AIR 

The mechanisms of atmospheric transport, 

removal, and resuspension of lead particulates interact in a complex manner. The transport mechanisms are functions of the particle size distribution, 

particle morphology, meteorology, and local 

topography. 

6.3.1 Distribution Mechanisms 

The transport and diffusion of gaseous and particulate materials in the atmosphere are consequences 

of molecular diffusion and the three-dimensional 

motion field, the latter being the dominant factor. A 

detailed treatment of these phenomena will be found 

in many standard textbooks on meteorology. The 

three-dimensional motion field can be assumed to be 

composed of a mean wind (transport) vector and a 

turbulent component. The turbulent component is 

analogous to molecular diffusion, but the coefficient 

of turbulent eddy diffusion is usually of much 

greater magnitude. The turbulent component tends 

to spread the material vertically and laterally about 

the mean horizontal transport vector. Therefore, 

assuming a pollution plume from a local line or 

point source, the atmospheric motion serves to 

dilute and transport the pollutants. 

Since lead emitted to the atmosphere is primarily 

in the inorganic particulate form, its transport and 

dispersion will depend primarily on particle size as 

well as chemical stability, the height of injection, 

and the intensity and stability of the atmospheric 

motion field. Large particles injected at low elevations will settle to the surface in the immediate 

vicinity of the source, whereas the smaller particles 

will be transported over greater distances. 

A study by Daines et al.31 related atmospheric 

lead to traffic volume and distance from a highway. 

They found the effect of traffic on lead content of the 

air to be striking, but limited to a rather narrow zone 

bordering primarily the lee side of the highway, as 

shown in Figure 6-7. About 65 percent of the lead in 

6-8 
the air between 30 and 1750 ft from the highway 

consisted of particles under 2 fim, and 85 percent 

were under 4 fim in diameter. Figure 6-8 shows a 

typical relationship of particle size to distance from 

the highway. Cholak etal. 1 2 and Schuck and Locke32 

did similar studies with similar results. As shown in 

Figures 6-4 and 6-5, Huntzicker et al.10 demonstrated that the large particle mode (Dp >7 fim) in 

the freeway distribution is severly attenuated at the 

Pasadena site. 

0 I 1 1 I 

-

-

-

TRAFFIC VOLUME, 

vehicles/day 

1 0 - 58,000 

\ 6 - 47.000 

ft • - 44,000 

\ O - 19,800 

"^-o^ZjZlI^ 

1 1 1 1 

1 

• -

-

-

—o1 

200 300 400 

DISTANCE FROM HIGHWAY, feet 

Figure 6-7. Air-lead values as a function of traffic volume and 

distance from the highway.31 

% HAVING MEAN MASS DIAMETER LESS THAN 

Figure 6-8. Relationship of the diameter of the particles 

(mass) to distance from the highway.31 

Knowledge of lead concentrations in the oceans 

and glaciers provides some insight into the degrees 

of atmospheric mixing and long-range transport. 

Tatsumato, Patterson, and Chow3335 measured dissolved lead concentrations in sea water off the coast 

of California, in the Central North Atlantic (near 

Bermuda), and in the Mediterranean. The profiles 

obtained are shown in Figure 6-9. Surface concentrations in the Pacific were found to be higher 

than those of the Mediterranean or the Atlantic, and 

decreased abruptly to relatively constant levels with 

depth. The vertical gradient was found to be much 

less in the Atlantic. Based on the Pacific data, 

Tatsumato and Patterson33 estimated an average 

surface lead concentration of 0.2 /ig/kg in the northern hemispheric oceans. Chow and Patterson35 

revised this estimate downward to 0.07 figlkg. There 

appears to be no difference between lead concentrations in deep water in the Atlantic and Pacific. These 

investigators calculated that industrial lead is currently being added to the oceans at about 10 times 

the rate of introduction by natural weathering, with 

significant amounts being removed from the atmosphere by precipitation and deposited directly 

into the ocean. Their data suggest considerable contamination of surface waters near shore, diminishing 

toward the open ocean.35 These investigators conclude that lead emissions from automobiles are the 

primary source of pollution of ocean surface water. 

0 

1000 

20OO 

3000 

4000 -1 

—<r 

i f 

fi It 

6 

i 

o— 1 

1 

^ ^ ** <*? 

1 

1 f 

O - ATLANTIC 

(BERMUDA) 

O - MEDITERRANEAN 

40°39'N, 05°48'E 

d- PACIFIC 

29°13'N, 117°37'W 

I 

-

— 

LEAD IN SEA WATER, vg/kg 

Figure 6-9. Lead concentration profiles in the oceans. " ^ 

Duce, Taylor, Zoller, and their co-workers36'

38 

have investigated trace-metal concentrations (including lead) in the atmosphere in remote northern 

and southern hemispheric sites. The natural sources 

for such atmospheric trace metals include the oceans 

and the weathering of the earth's crust, whereas the 

manmade source is particulate pollution. Enrichment factors for concentrations relative to standard 

values for the oceans and the crust were calculated 

(Table 6-7); the mean crustal enrichment factors for 

the North Atlantic and the South Pole are shown in 

Figures 6-10 and 6-11. The significance of the com6-9 
P.74 

parison in Figure 6-11 is that 90 percent of the particulate pollutants in the global troposphere are injected in the northern hemisphere.39

 Since the residence times for particles in the troposphere40

 are 

much less than the interhemispheric mixing time, it 

is unlikely that significant amounts of particulate 

pollutants can migrate from the North Atlantic to 

Antarctica via the troposphere; however this does 

not rule out stratospheric transfer. In the case of 

lead (and all other metals studied except vanadium), 

the enrichment factors were very similar at the two 

locations. This suggests (but does not prove) that the 

atmospheric concentrations of these metals may 

originate primarily from natural (rather than manmade) sources. 

TABLE 6-7. CONCENTRATION RANGE AND MEAN EFcru8 t 

VALUES FOR ATMOSPHERIC TRACE METALS COLLECTED 

OVER THE ATLANTIC NORTH OF 30° N 36 

Concentralion 

range, 

ng'scm 

t rcrust. 

qeom. mean3 

Al 

Se 

Fe 

Co 

Mn 

Cr 

V 

Zn 

Cu 

Cd 

Pb 

Sb 

Se 

8-370 

0.0008-0.011 

3.4-220 

0.006-0.09 

0.05-5.4 

0.07-1.1 

0.06-14 

0.3-27 

0.12-10 

0.003-0.62 

0.10-64 

0.05-0.64 

0.09-0.40 

1.0 

0.8 

1.4 

2.4 

2.6 

11 

17 

110 

120 

730 

2,200 

2,300 

10,000 

Calculated on the basis of the mean crustal abundances of Taylor." 

Figure 6-10. Midpoint collection location for atmospheric 

samples collected from R. V. Trfdenf north of 30°N, 1970 

through 1972.36'

38 

Murozumi et al.41 have presented supportive evidence. Their data show that long-range transport of 

lead aerosols emitted from automobiles has significantly polluted the polar glaciers. They collected 

• NORTH ATLANTIC WESTERLIES 

D SOUTH POLE 

CogivTB" 

M 

s«n 

|Pb«- U -

rffB" 

J * JBL 

Figure 6-11. The EFcrug t values for atmospheric trace metals 

collected in the North Atlantic westerlies and at the South 

Pole. The horizontal bars represent the geometric mean 

enrichment factors, and the vertical bars represent the 

geometric standard deviation of the mean enrichment factors. The EFcrus t for lead at the South Pole is based on the 

lowest lead concentration (0.2 mg/scm).36'

38 

samples of snow and ice from Greenland and the 

Antarctic. As shown in Figure 6-12, they found that 

the concentration of lead varied inversely with the 

geological age of the sample. The authors attribute 

the gradient increase after 1750 to the Industrial 

Revolution and the enhanced increase after 1940 

to the increased use of lead alkyls in gasoline. The 

most recent levels fround in the antarctic snows 

were, however, less than those found in Greenland 

by a factor of 10 or more. Before 1940, the concentrations in the Antarctic were below the detectable level ( < 0.001 /xg/kg) and have risen to 0.2 

Mg/kg in recent snow. A graph of the world lead 

smelter and lead alkyl production presented by 

Murozumi et al.41 is shown in Figure 6-13; supporting data are shown in Table 6-8. 

The results and conclusions of Murozumi et al. 

were criticized by Mills,42 who suggested the increase in the snow lead after 1940 could be due to 

aircraft operating from Thule Air Force Base. 

Bryce-Smith43 countered Mills' argument by stating 

that the greatest amount of lead found to be 

deposited in the snow was during winter months 

when air traffic was lightest; there was no horizontal 

gradient between the air base and the collecting site; 

the collecting site was predominantly upwind from 

the air base; and, finally, the major increase in lead 

levels began about 20 years before the nearest 

operating base was established. 

Jaworowski44 found that lead concentrations in 

two glaciers have increased by a factor of 10 during 

the last century. The concentrations in the most re6-10 
0.20 

0.18 

0.16 

0.14 

0.12 

0.10 

0.08 

O.OE 

0.04 

0.02 

n 

' I T-TV" 1 1 1 1 

J.iy , T l 1 1 

1 , 1 1 1 1 | 

o 

. 1,,, , 1 

1 1 1 

0 

J. 1 1 

1 1 ' 

o 

1 1 . 

-rr 

o 

-LXJ 

1 ' ' 

J -

1 -

0 / — 

joX -

j -

l°-

-

-

— 

1 1 1 

I 1 1 r 

- O - LEAD SMELTED IN NORTHERN HEMISPHERE 

D - LEAD SMELTED IN SOUTHERN HEMISPHERE 

& - LEAD BURNED AS ALKYLS IN NORTHERN HEMISPHERE 

800 

h«-B,C, »| « 

1800 1850 

A. D. 

AGE OF SAMPLES 

Figure 6-12. Lead concentration profile in snow strata of 

Northern Greenland.41 

Figure 6-13. World lead smelter and alkyl lead production 

since 1750 A.D.41 

TABLE 6-8. LEAD AEROSOL PRODUCTION IN THE NORTHERN HEMISPHERE COMPARED WITH LEAD CONCENTRATIONS IN 

CAMP CENTURY, GREENLAND, SNOW AT DIFFERENT TIMES41 

Date 

1753 

1815 

1933 

1966 

Lead 

smelted. 

103 tons/yr 

1 

2 

16 

31 

Fraction 

converted 

to 

aerosols. 

% 

2 

2 

16 

0.06 

Lead 

aerosols 

produced 

from smelteries.. 

103 tons'yr 

2 

4 

8 

2 

Lead burned 

as alkyls. 

103 lons/yr 

— 

— 

0-1 

3 

Fraction 

converted 

to 

aerosols. 

% 

— 

— 

40 

40 

Lead 

aerosols 

produced 

from alkyls. 

103 tons/yr 

• — 

— 

4 

100 

Total lead 

aerosols 

produced. 

103 tons/yr 

2 

4 

12a 

102a 

Lead 

concentration 

at Camp Century. 

/ig/kg snow 

0.01 

0.03 

0.07 

0.2 

aValues corrected. 

cent ice layers were extremely high (148 fig/kg). 

Jaworowski et al.45 also studied stable and radioactive pollutants from ice samples from Storbreen 

glaciers in Norway. The mean stable lead concentration in Storbreen glacier ice in the 12th century was 

2.13 figlkg. The mean for more recent samples was 

9.88 /u.g/kg. Around 1870, the average lead concentration in Norwegian glacier ice was 5.86 figlkg, 

whereas that for glaciers in Poland was 5.0 figlkg. A 

century later, the mean concentration in the Norwegian glacier was 9.88 Mg/kg, whereas the mean 

concentration in the Polish glacier reached 148 

Mg/kg. Jaworowski et al.45 attributed the large increase of lead concentrations in the Polish glacier to 

local sources. 

Jaworowski et al.45 also measured

 2,0Pb in the 

glacier ice. The values found in the Storbreen glacier 

ice are shown graphically in Figure 6-14. The highest value was found in 1961. A similar value was 

found in Polish glaciers and in the Alps the same 

year.44 The values and irregularities observed in 

^

10Pb concentrations in the investigations suggest 

that part of the atmospheric

 2l0Pb may have originated from artificial sources — nuclear explosions 

in the Arctic, or energy production in fossil-fuel 

power stations. Based on their findings, Jaworowski 

et al.45 concluded that long-range transport of lead 

YEAR. AS DETERMINED BY DEPTH 

1966 65 64 63 62 61 60 59 58 57 56 5S 54 

4 0.5 

z 

2 0.4 H < -210 CONCENT 

o o 

Q 

m 0.1 

-i 

l l I l I l I 1 I I I l I 

r -IT 

— 

-

__ 

. 

-

-

I 1IIII I I I I I 

1 2 3 4 ,5 6 7 8 9 10 11 

DEPTH, meters 

Figure 6-14.

 210Pb In Storbreen, Norway, glacier Ice, 

1954-1966, 

45 

6-11 
"*r*~ 

P.76 

pollutants in the atmosphere is a reality, but the 

authors suggest that the rate of contamination of 

glacier ice correlates better with the total annual input of coal burning to the energy system of the world 

than with lead emissions from automobiles. 

6.3.2 Removal Mechanisms 

The principal mechanisms for removal of inorganic lead particulate from the atmosphere are 

dry deposition and precipitation. Detailed discussions of these processes will be found in standard 

textbooks by Sutton,46 Pasquill,47 Fletcher,48 

Junge,49 Green and Lane,50 and Slade.51 The 

removal efficiency of these processes varies significantly, depending on physical characteristics of the 

suspended material, atmospheric conditions, and the 

nature of the receiving surface. 

6.3.2.1 DRY DEPOSITION 

Dry deposition removal processes include sedimentation, diffusion, and inertial mechanisms such 

as impaction. Sedimentation, or settling of particles, 

occurs when the mass of the particle is large enough 

to overcome the buoyancy force and the lifting 

forces of convective currents. Freely falling particles 

of the size range found in suspended aerosols rapidly 

attain their terminal, or constant, velocity when the 

aerodynamic drag on the particle is equal to the 

weight of the particle. The terminal velocity depends 

on the particle size, its density, and gravitational acceleration. When a particle is of a size comparable to 

the mean free path of the gas molecules, bombardment by the molecules results in a random or 

Brownian motion that is superimposed on its downward motion. If a particle is very small and its motion is observed for only a short period of time, its 

fall may be completely masked by the Brownian motion. Residence times or, conversely, the rate of 

fallout of aerosols or dust particles containing lead 

in the atmosphere are then primarily a function of 

particle size. The shape of the suspended particles 

also has a significant effect on the settling velocity. 

Usually the settling velocity of particles of various 

geometrical forms is calculated in terms of the settling velocity of spherical particles of the same 

volume. The aerodynamic particle size, conventionally used when discussing airborne particulate, 

is defined as the size of a sphere of unit density that 

has identical aerodynamic behavior to the particle in 

question. Particles having the same aerodynamic 

size may have differing shapes and dimensions. 

Airborne particles are generally divided into 

three size ranges: Aitken nuclei (particle radius 

< 0.1 fim), large nuclei (particle radius 0.1 to 1 

fim), and giant nuclei (particle radius > 1 fim). Extremely small particles (radius < 0.001 fim) tend to 

coagulate rapidly to form larger ( ~ 0.05 to 0.5 

fim), less mobile particles.50 Fletcher48 derived an 

approximate equation to predict the rate at which 

the concentration number, n, of particles of radius, 

r, will decrease in a relatively uniform aerosol. For r 

= 0.005 /Am and n = 105/cm3 (typical in urban air), 

the time required for particle concentration to 

decrease by one-half was calculated to be 30 min. 

For r = 0.\fimandn= 103/cm3, 50 percent reduction was calculated to require 500 hr. The size distributions of large and giant nuclei are not significantly affected by coagulation. 

Settling or terminal velocities of spherical, particles, as reported by Green and Lane50

 and Israel and 

Israel ,

52

 are shown in Table 6-9. 

TABLE 6-9. TERMINAL VELOCITIES OF SPHERICAL 

PARTICLES OF UNIT DENSITY AT GROUND LEVEL 

Particle radius. 

/un 

0.01 

0.05 

0.1 

0.2 

0.5 

1.0 

2.0 

5.0 

10.0 

20.0 

50.0 

Terminal velocity 

Israel and Israel 

1.43 x10"5 

— 

2.32 X10-4 

— 

— 

1.32 x10"2 

— 

— 

1.23x10° 

— 

— 

cm/sec 

Green ond Lane 

8.71 x 10"5 

2.27 X10-4 

6.85 x 10"4 

3.49 x10"3 

1.29 x10"2 

5.00 x10'2 

3.03 x10"1 

1.20x10° 

4.71 

24.7 

Airborne particles are also removed from the atmosphere by inertial mechanisms. In turbulent inertial deposition, turbulent wind fluctuations perpendicular to a horizontal surface impart sufficient 

inertia to propel the particles through the boundary 

layer and onto the surface. This mechanism is important for both smooth and rough surfaces. When 

the roughness elements on a surface protrude sufficiently far into the windstream, inertial impaction 

may become important. The mean horizontal flow of 

the wind, rather than turbulent fluctuations, controls impaction. This mechanism occurs when particles cannot follow the air streamlines as they pass 

around a roughness element. In this case, the mean 

windflow supplies the inertia that drives the particles onto the surface. 

Inertial mechanisms are dependent on atmospheric conditions and the characteristics of the 

surface. The small-scale surface structure may be 

especially significant. For example, small particles 

6-12 
are preferentially retained on leaf surfaces, where 

they may be tightly retained by small hairs on the 

leaf, by surface pores, and by tacky substances excreted by the leaves. Impaction of submicrometersized particles on leaf surfaces is possible at normal 

wind speeds.53 Pine needles and similarly shaped 

surfaces appear to be aerodynamically attractive for 

impaction of particulate matter. Therefore, pine 

trees near a surface source of lead particulate pollution may increase the rate at which lead aerosols are 

removed from the atmosphere. Heichel and 

Hankin54 reported soil lead concentrations in front 

of and within a roadside windbreak of pine trees as 

being 50 percent and 100 percent higher, respectively, than soil lead concentrations at corresponding distances in a nearby open field that bordered 

the same side of the road. 

Particle removal rates from the atmosphere are 

usually described in terms of deposition velocity. 

Historically, deposition velocities have been defined 

as the ratio of deposition flux to the airborne concentration with units of length/time usually reported 

as cm/sec.49 Sehmel and Hodgson55 have published a 

model for the prediction of dry deposition velocities 

based on this concept. 

K|_ c 

(6-1) 

where K is the deposition velocity, N is the deposition flux, and C is the airborne concentration for 

monodispersed particles measured 1 cm above the 

deposition surface. The deposition velocity, K, 

assumes that particle deposition is described by a 

one-dimensional, steady-state continuity equation. 

The basic assumptions in the model are that the flux 

is constant with height, that a relationship for particle eddy diffusivity can be determined, that the 

effect of gravity can be described by the terminal settling velocity, that agglomeration does not occur, 

and that particles are completely retained on the 

surface. The model was designed to predict deposition velocities for simple surfaces. Actual removal 

rates are non-steady-state processes dependent on 

the delivery capability of the upper atmosphere and 

the surface resistance. Based on the above assumptions, Sehmel and Hodgson55

 write the equation for 

deposition flux as: 

N = -(e + D) — -v.C (6-2) 

dz 

where vt is the absolute value of the terminal settling 

velocity, € is the particle eddy diffusivity, D is the 

Brownian diffusivity, C is the airborne concentration, and z is the reference height. For small particles, the sedimentation term (-v,C) is negligible so 

that deposition velocity is a function of the Brownian and eddy diffusivity term only. For large particles, the diffusivity term is negligible, and the 

deposition velocity is equal to the terminal velocity. 

Incorporating the concepts of friction velocity: 

u.= -^—L — (6-3) 

K lm(z/z 0 ) 

where k is von Karman's constant, u is the 

windspeed, z is height, and zo is the roughness 

height. Roughness height is defined as a measure of 

the roughness of a surface over which fluid is flowing: 

z

o=H/3 0 (6 . 4 ) 

where H is the average height of surface irregularities. Sehmel and Hodgson55 developed prediction deposition velocity curves for a range of 

roughness heights and friction velocities. Representative curves are shown in Figures 6-15 through 

6-17. Deposition velocities are shown to be a function of particle diameter and have their smallest 

values in the 0.1 to 1 fim particle diameter range. 

The mean diameter of lead-containing particles in 

the atmosphere, remote from major sources, falls approximately in this range. In the case of larger particles, both increased effective eddy diffusion in surface boundary layer (as a result of greater particle 

inertia) and increased gravitational settling rates 

tend to increase the predicted deposition velocities 

above the minimum. The lower limit of the predicted deposition velocities is the sedimentation 

velocity. For smaller particles, deposition velocities 

increase with decreasing particle diameters because 

of increased mass transfer by Brownian motion. 

Deposition velocities for 0.01-Mm particles are 

relatively insensitive to changes in particle diameter 

at elevated heights above 10 cm. Deposition 

velocities at 1 cm above the ground are extremely 

large; consequently, in the 0.01-Mm particlediameter range, the deposition velocities are controlled by atmospheric diffusion in the layers immediately above the canopy. As indicated by Sehmel 

and Hodgson,55 the model should predict reasonably well the deposition velocities for simple surfaces, 

assuming the wind direction is persistent over sufficient distance. It should not, however, be expected 

to predict deposition velocities for a city because of 

the complexity in the geometry of the surface and 

because of local wind conditions. 

Values of lead deposition velocities found in the 

literature generally range from about 0.1 to 0.5 

cm/sec.56 These values are based on total lead flux 

and total airborne concentrations, without regard to 

6-13 
P.78 

particle size. Since large particles may control lead 

deposition in certain cases, it is necessary to examine 

the entire size distribution of particles in order to 

calculate deposition rates. Further, accurate 

isokinetic measurements of large airborne particles 

are required to relate airborne concentrations to 

deposition. Davidson56 found a deposition velocity 

of 0.29 cm/sec in Pasadena, based on total flux and 

total airborne concentrations. Based on the fraction 

of lead particles greater than 10 microns, however, 

the deposition velocity was 1.3 cm/sec. Huntzicker 

et al.10found a deposition velocity of 1.80 cm/sec on 

a Teflon plate placed on the shoulder of a Los 

Angeles freeway. 

£ 10 

E 

* 

> ELOC OSITION V 

EL 

o 

• •i yi T 

1 cm\ 

- 1 0 cm 

~"^, v 

IIMI | rii i IIIT | T—r t»1111f i v 

TYPICAL: / 

UPPER BOUND; UNSTABLE, L - 10 meters/ 

. /LOWER BOUND;STABLE, L »10meters/ A YJ 7 J 

•--'••:-iL 'k\ / S .'S"7l 

l 10 meters 

i l i 

*"'*- —-"* /*~u„- 0 

1 mi l »l l 1 l/lUl L 1 L 

_ i 

Jz 

' z 

-

' 

1 1 1 Illll 

10'' 1 10 

PARTICLE DIAMETER, micrometers 

Figure 6-15. Predicted deposition velocity of particles at indicated height for u. = 20 cm/sec and ZQ = 3.0 cm.55 

—I 1 I I Mill I—I I I I IM | I I I I 11II | I—Illl l 

.UNSTABLE, L =-10 meters 

..f STABLE. L - 10 meters 

-"••'*-„ 

S • -^^ **-. u. . cm/sec - S \ I /:: 

— ^ >. > • . ' 

V - * 

"•^ 10 , ' 

I I I I 11 u l J iL 

10 1 10 

PARTICLE DIAMETER, micrometers 

Figure 6-16. Predicted deposition velocities of particles at 1-m 

height for z 0 = 3.0 cm, 55 

Johnson57 sampled particles with an instrumented 

aircraft flying at 300 m altitude in the vicinty of St. 

Louis, Missouri. Particles were collected by exposing a small (1.0- by 7.5-cm) glass slide covered with 

a thin layer of high-viscosity silicone oil to the free 

air stream outside the skin of the aircraft. Particles 

were counted and sized manually from photographs. 

Samples were obtained upwind and downwind of St. 

I I I I Illll 1—I I I I lll| 

^UNSTABLE, L » -10 meters 

„STABLE,L" 

I I I Illll 

10 1 10 

PARTICLE DIAMETER, micrometers 

10 

Figure 6-17. Predicted deposition velocities of particles at 1 m 

for u. = 200 cm/sec.55 

Louis on each of 11 days during the period July l 

through July 18, 1975. The results indicated typical 

number concentrations of airborne particles larger 

than 10 fim in diameter of 7,500 particles/m3 upwind and 11,000 particles/m3

 downwind. Particles 

larger than 30 fim in diameter were found in concentrations of 200 particles/m3

 upwind and 425 particles/m3

 downwind of the city. For the downwind 

particle number densities of > 10 Mm and >30 Mm 

particles, and with the assumed density of 2 g/m3, the 

mass concentrations would be about 0.01 ng/m3 and 

0.012 ng/m3, respectively. The results reported indicate that particles >30 fim can be transported to 

altitudes of 300 m by convective currents; therefore, 

all large particles are not removed by sedimentation 

in the immediate vicinity of sources. Assuming a 

sedimentation velocity of 0.3 cm/sec for a 10 fimdiameter particle and an initial height of 300 m, the 

particle could remain airborne for approximately 27 

hr and be transported about 200 km with a uniform 

wind of 2 m/sec. This type of long distance transport 

has been observed by Gillette and Winchester15 over 

Lake Michigan. The actual concentrations observed 

are very small, however, and would contribute little 

to ambient air loading or dustfall accumulation in 

regions remote from the source. 

Lynam58 studied the atmospheric diffusion of carbon monoxide and lead from an expressway (1-75, 

north of Cincinnati, Ohio). The significant results 

are shown in Figures 6-18 through 6-20. Approximately 50 percent of the lead emitted from the automobile traffic was removed from the atmosphere by 

6-14 
dry deposition within 640 ft of the edge of the roadway (Figure 6-18). The size distribution of the lead 

particles was not significantly altered between 20 

and 640 ft (~ 6 and —195 meters). Wind speeds 

ranged from approximately 0.5 to 3.8 m/sec. Assuming a mean wind speed of 2 m/sec, the 50-percent 

reduction within 640 ft would correspond to about 

1.5 min of travel time. The concentration of lead 

decreased from about 7 Mg/m3 at 20 ft to about 1.5 

Mg/m3 at 640 ft, a decrease by a factor of about 5. 

The data were not sufficient to determine the relative efficiency of sedimentation versus impaction in 

the total removal process; however, Figures 6-19 

and 6-20 indicate that the removal mechanism was 

not strictly limited to sedimentation. Daines et al.,31 

in their study of the relationship of atmospheric lead 

to traffic volume and distance from a highway, 

found a 50-percent reduction in lead between 10 and 

150 ft of the edge of the roadway. 

1—I Illl l 

% LEAD REMOVED = 

_ R = 0.68 

i—r i i 11 

i IIII I 

40 60 80 100 150 200 400 600 

TRAVEL DISTANCE, feet 

Figure 6-18. Regression of percentage lead particulates 

removed by dry deposition with distance from roadway.68 

(Legend:—= regression line;—= 95% confidence limits for 

regression line; = 95% confidence limits for single 

value; R = correlation coefficient.) 

Smith59 investigated lead contamination of white 

pine growing along an east-west section of Interstate 

95 in Connecticut. He found that lead contamination decreased regularly with increasing distance 

from the road and was greatest on the sides of the 

trees nearest the highway. Based on the much higher 

concentration of lead deposited on the needles 

nearest the roadway, Smith concluded that pine trees 

may serve as rather efficient air filters. 

6.3.2.2 PRECIPITATION 

Precipitation, or wet deposition, removal processes include rainout and washout. Rainout occurs 

8 

b 

4 

2 

1.0 

0.8 

0.6 

0.4 

0.2 

-

-

-

. 

-

1 1 

—0— 

--•--

1 1 

1 Illl l 

SAMPLING STATION 

20 ft FROM EDGE 

OF EXPRESSWAY 

SAMPLING STATION 

640 ft FROM EDGE 

OF EXPRESSWAY 

1 Illl l 

l 1 /A 

1 

1 

ifa 

1 

a 

aJ 

1 

1 1 

DO | | 

1 

. 

-

-

-

-

-

.. 

-

— 

-

-

-

1 

10 20 50 70 90 95 98 99 

Pb PARTICULATES <STATE D SIZE, percent 

Figure 6-19. Comparison of size distribution of lead particulates collected at 20 and 640 ft from an expressway north of 

Cincinnati. Ohio. Determined by seven-stage Andersen 

sampler.58 

- | 1—|—i i i i | | 1—i—|— r 

Pb CONC. = 12.1147667 - 3.8993135 X LOG DISTANCE 

R " -0.7 8 

CO CONC. - 6.51989 - 1.7138467 X LOG DISTANCE 

R = -0.6 0 

_ i _ _ i _ _L _i_ JL50 100 200 

DISTANCE FROM EDGE OF HIGHWAY, feet 

Figure 6-20. Atmospheric concentration of lead and carbon 

monoxide as a function of log of distance from edge of highway (R = correlation coefficient).58 

when particulate matter is present in the supersaturated environment of a growing' cloud. The 

small particles (0.1 to 0.2 fim) act as nuclei for the 

formation of small droplets, which grow into 

raindrops.49 Droplets also collect particles under 

0.1 Mm by Brownian motion and by the water-vapor 

gradient. The nucleation process may also occur on 

particulate matter present below cloud level, producing droplets large enough to be affected by sedimentation. These processes are referred to as 

rainout. A second process (washout) occurs when 

falling raindrops collect particles by diffusion and 

impaction on the way to the ground. Rainout and 

6-15 
•Ill PI I ••••• • 

P.80 

washout together are known as wet deposition. 

Although data on the lead content of precipitation 

are rather limited, those that do exist indicate a high 

variability. Lazrus et al.60 sampled precipitation at 

32 U.S. stations and found a correlation between 

gasoline use and lead concentration in* rainfall in 

each area. Similarly, there is probably a correlation 

between lead concentration in rainfall ajid distance 

from large stationary point sources of lead emissions 

in the vicinity of such sources. The authors pointed 

out that at least twice as much lead is found in precipitation as in water supplies, inferring the existence of a process by which lead is depleted after 

precipitation reaches the ground. Russian studies61 

point to the insolubility of lead compounds in surface waters and acknowledge this removal by 

natural sedimentation and filtration. 

The intensity of rainfall appears to be negatively 

correlated with the amount of lead washed out of the 

atmosphere. Ter Haar et al.62 found tfoat showers 

had lower concentrations than slow, even rainfall. 

Data presented by Jaworowski44 show tbat in recent 

years, the lead content in rainwater ranged from 0 to 

1858 Mg/l'ter. 

A laboratory study in which simulated rainfall 

was used to determine the efficiency with which 

automotive lead particulates could be washed out 

indicated that the efficiency was less than 1 percent.63 

Concentrations of

 210Pb in rainwater have also 

been reported by Jaworowski44 as highly variable (as 

much as two orders of magnitude im the same 

locality) and not related to season or amiount of precipitation. Values ranged from 0.2 to 300 

pCi/liter.44 High concentrations were found in samples collected from northern continental localities, 

and low concentrations were found in samples from 

oceanic and Antarctic locations. Jaworowski suggests that the differences might be attributed in part 

to artificial contamination by nuclear esxplosions. 

6.3.2.3 FIELD STUDIES 

Atkins and Kruger64 conducted a field sampling 

program in Palo Alto, California, to determine the 

effectiveness of sedimentation, impaction, rainout, 

and washout in removing lead contaminants from 

the atmosphere. Rainfall in the area averages 

approximately 33 cm (13 in)/year and occurs primarily during the late fall and winter months. Airborne concentrations at a freeway site varied from 

0.3 Mg/m3to a maximum of 19 Mg/m3 iffl t*he fall and 

winter seasons, and were a maximum of'9.3 Mg/m3 in 

the spring. During periods of light rawfall in the 

spring, the maximum concentration observed was 

7.4 Mg/m3- A typical daily concentration profile observed is shown in Figure 6-21. More than 90 percent of the lead pollutants reaching the surface during the 1-year sampling period were collected in dry 

fallout. Dry deposition as a function of distance 

from the freeway is shown in Figure 6-22.* Approximately 1 percent of the total dry fallout collected 

near the expressway was lead. Wet deposition (approximately 33 cm or 13 in of rain per year) accounted for 5 to 10 percent of the lead removal at 

the sampling sites. A summary of the field data is 

shown in Table 6-10. 

E 

•5 15 

MID- 2 

NIGHT 

4 6 8 10 NOON 2 

TIME OF DAY 

4 6 8 10 MIDNIGHT 

Figure 6-21. Atmospheric lead concentration at freeway site 

in Palo Alto, California, on August 15,1966.63 

? 1.0 

N 

en 

E 

1 v ] I I I II I I I 

— ^ V l=STD . DEV. 

1 N . X.9.0x10VB06L 

N . (SEE FOOTNOTE IN TEXTI 

-

-

-

-

1 • 1 1 1 I t I I 

1 

-

-

-

-

-

'x -

IN 

100 200 500 1000 2000 500010,000 50.000 100,000 

DISTANCE FROM FREEWAY {X), foot 

Figure 6-22. Average lead in dry fallout as a function of distance from the freeway.63 

'Figure 6-22 is a semi-log plot of the three average lead values as a function nf distance from the freeway. The data appear to fall along a straight line, suggesting that 

the relationship hetween lead in fall out. I., and distance from the freeway. X. can 

he described by X = aeh l- where a and b are constants. From the semi-plot, the appropriate values for a and b are a = 9.0 x I0 4

; b o -8.06. if L is expressed in 

mgm2-wtc and X is expressed in feet. Therefore X = 9.0 x IO4 e**- 0ft k The area 

under this curve, from X , = 50 ft to X3 = 26,900 ft, should represent the total 

amount of lead deposited in the Palo Alto area for each l-fi section of freeway. This 

value is 7.85 g/ft. The area under the curve from L = 0.95 mg/ft^-wk to L • 0 

should represent the total amount of lead that was removed hy sedimentation, 

assuming that the data can be extrapolated past 26,900 ft. This value is I I.I g/ft. 

This indicated that an average of 70 percent o f the lead that was removed hy sedimentation was removed within 5 miles of the source. 

6-16 
P.81 

TABLE 6-10. SUMMARY OF FIELD DATA FROM PALO ALTO, 

CALIFORNIA' 64 

Freeway3 

{Bayshore) 

Residential Foothills 

Lead in dry fallout: 

Average, mg/fr-wk 

Amount removed, mg/ft -yr 

Lead in rainfall: 

Average, mg/liter 

Amount removed, mg/ft -yr 

Average air concentration, 

Mg/m3 

Pb/total solids in air 

Pb/nonvolatile solids 

in dry fallout 

0.92 

49.4 

0.181 

3.25 

7.30 

0.042 

0.24 

11.7 

0.149 

3.66 

2.28 

0.018 

0.153 

8.3 

0.035 

0.92 

1.90 

0.016 

0.0112 0.0102 0.0049 

Andren et al.65 evaluated the contribution of wet 

and dry deposition of lead in a study of the Walker 

Branch Watershed, Oak Ridge, Tennessee, during 

the period June 1973 to July 1974. The mean precipitation in the area is approximately 130 cm/year 

(51 in/year). The major atmospheric emissions in 

the vicinity of Oak Ridge are derived primarily from 

three coal-fired steam plants. A foundry and ferroalloy plant approximately 64.5 km (40 miles) to 

the west were assumed to have a minor impact 

because of orographic barriers. Results reported for 

the period January through June of 1974 are presented in Table 6-11. Rainfall, or wet deposition, 

contributed approximately 67 percent of the total 

deposition for the period. 

TABLE 6-11. DEPOSITION OF LEAD AT THE WALKER 

BRANCH WATERSHED, 197465 

Lead deposition (g/ha) 

Dry 

January 

February 

March 

April 

May 

June 

Total 

Average 

34.1 

6.7 

21.6 

15.4 

26.5 

11.1 

115.4 

19.2 

< 16.7 

3.3 

10.6 

7.5 

13.0 

5.4 

56.5 

9.4 

a

Total deposition — 172 g/ha. Wet deposition — 67 percent ol total. 

yuntzicker et al.10 estimated the flow of automobile-emitted lead in the Los Angeles Basin based on 

measurements of particle size, atmospheric concentrations, and surface deposition of lead at various 

sites around the Basin. A flow diagram based on the 

study and modified by Schuck and Morgan66 is 

shown in Figure 6-23. Of the lead emitted from automobile exhaust in the Basin (estimated to be about 

18 tons per day), the investigators calculated that 

about 56 percent was deposited near the source (near 

deposition), 12 percent was deposited in the Basin 

but in areas removed from the source (far deposition), and about 32 percent was transported out of 

the Basin by the wind. The values presented for 

deposition and wind removal were for dry weather 

only (i.e., dry deposition only). 

INPUT 

23.7 metric tons Pb/day 

25% 

t 

REMOVED 

BY STREET 

CLEANING 6% 

SEWAGE 

40% J 

NEAR DEPOSITION 

STREET 

8% 

LAND 

32% 

RUNOFF 2% V 

0.64 metric 

tons Pb/day 

I 10% 

FAR 

DEPOSITION 

LAND 

T ^ 

COASTAL WATERS 

Figure 6-23. Fate of lead contributed from automotive traffic 

in Los Angeles Basin.03 

Roberts et al.67 found an exponential decrease in 

dustfall with distance around two secondary 

smelters (Figure 6-24). The authors concluded that 

the high rate of fallout around the smelters originated from episodal large-particulate emissions 

from low-level fugitive sources rather than from the 

stack. This being the case, sedimentation would be 

the principal removal process. The lead in dustfall 

values decreased well over 90 percent within a distance of 300m. 

1000 

500 

I I 1 

SMELTER A: 

\ SMELTER B: 

1 1 1 

Y = 6,100 -2.560 log X 

R = -0.8 1 

p < 0.001 

96 SAMPLES AT 16 SITES 

— 

Y = 896 - 340 log X 

R - -0.63 

p <0.001 

34 SAMPLES AT 6 SITES 

-

U 

200 300 400 500 

DISTANCE FROM STACK, meters 

Rgure 6-24. Contamination of dust by lead emissions from 

two secondary smelters. Solid and dashed lines are fitted 

curves corresponding to the regression equations; dotted 

lines are an extrapolated fit; U indicates corresponding 

values found In urban control areas.66 

6-17 
P.82 

Studies such as those described above clearly indicate that lead is effectively removed from the atmosphere by dry and wet deposition processes, and 

that atmospheric concentrations are significantly influenced by these removal mechanisms even in the 

immediate vicinity of the source. The rate of 

removal is highly dependent, however, on the size 

distribution of the particles, the nature and characteristics of the deposition surfaces, airborne concentrations, and atmospheric conditions including 

stability, winds, and precipitation. In dry weather, 

the lead will be deposited on surfaces in the form of 

dustfall by sedimentation, diffusion, or inertial 

mechanism, depending primarily on the size of the 

particles. Mass deposition near the sources will be 

controlled primarily by sedimentation of large particles, whereas the smaller particles will remain airborne longer, be transported further by the wind, 

and be removed primarily by diffusion and inertial 

mechanisms. 

The characteristics of the surfaces on which the 

lead is deposited will significantly influence the 

deposition and retention. Deposition will be greater 

in a wooded area than on paved surfaces or short 

grass. Buildings also will influence the dry deposition, although there are few data available to quantify the effect. In areas with higher annual rainfall, 

removal by precipitation (wet deposition) becomes 

more important and may be the dominant process. 

All of these factors substantially influence potential human lead-exposure patterns — both inhalation of airborne lead and possible ingestion of dust 

containing lead. The dry deposition removal 

mechanisms deplete the airborne concentrations but 

deposit the material in the form of dust. The factors 

controlling dry deposition then become extremely 

important from the standpoint of potential exposure 

patterns for dust, since they may strongly influence 

temporal and spatial variations. Because of sedimentation of large particles, dustfall rates (mass) 

will be highest immediately adjacent to roadways 

with dense automobile traffic and near stationary 

sources of all types where lead may be emitted. 

These rates will diminish to a rather low value in 

areas remote from sources and where the small particles are removed primarily by diffusion and inertial mechanisms. 

The accumulation on the deposition surfaces will 

depend on the rate of deposition and the rate at 

which the material is cleaned from the surfaces by 

precipitation or by mechanical means such as street 

sweeping or vacuuming. Dust entering buildings or 

homes by air transport will usually be deposited on 

flat surfaces such as floors or furniture. The same 

physical processes will control the rate of deposition. The potential exposure level, particularly for 

young children, will depend on the accumulation, 

which again will be influenced by the deposition rate 

and the frequency and methods of cleaning. In occupational environments where fugitive dust emissions are high, accumulation will be rapid if surfaces 

are not frequently cleaned. Significant amounts of 

this dust may be carried on clothing into the homes 

of workers and contribute further to the total leaddust loading in the home environment. 

Emission rates from automobile traffic and from 

stationary sources are highly variable in time, even 

on an hourly basis. Since the residence time of large 

particles in the atmosphere is on the same order or 

less, the dustfall rates in the immediate vicinity of 

sources should also be highly variable. This is 

reflected in airborne concentrations measured very 

near the source. 

As a consequence of the number of variables involved and of the temporal and spatial variations 

occurring, it is not possible to quantify human exposure in uncontrolled cases without the use of personal monitors. Estimates of such exposure may vary 

by an order of magnitude or greater. For a given 

emission pattern, one can generally conclude that 

potential exposure from lead in dust should be 

greatest (1) in dry seasons, (2) in areas with sparse 

vegetation, (3) within a few hundred meters of the 

sources, (4) under conditions of stable atmospheres, 

(5) during the morning and afternoon traffic rush 

hours in the vicinity of freeways, and (6) during peak 

production periods of stationary sources (usually 

during the day). 

6.3.2.4 RESUSPENSION 

The threshold stress, which must be exceeded 

before a particle is resuspended from a surface, is a 

function of the particle properties, particle size, and 

the surface properties. A particle of a given size and 

density will resuspend more easily from a smooth 

surface than from an irregular surface such as an 

asphalt road. Particles on a dirt road or other soil 

surfaces may become attached to soil particles and 

behave quite differently from an inert free particle. 

This process of weathering tends to reduce resuspension. Moisture, influenced by atmospheric variables 

such as wind, precipitation, humidity, and solar 

radiation, may inhibit resuspension. 

Data in the literature on resuspension show that 

this process is not well understood, and hence resuspension rates cannot yet be predicted to any degree 

6-18 
of accuracy. For example, Mishima68

 indicates that 

reported resuspension factors* vary over 10 orders 

of magnitude from 10"2 to 10"". (The resuspension 

factor, in m1, equals the airborne concentration, in 

ng/m3, divided by the ground source concentration, 

in ng/m2.) It is useful, however, to examine data 

from more controlled resuspension experiments in 

order to obtain a qualitative idea of expected lead 

resuspension rates. 

Sehmel69 has examined the resuspension of ZnS 

particles smaller than 25 microns from an asphalt 

road surface. He found that when a car was driven 

across the recently applied tracer, 0.001 percent to 

1.0 percent of the material was resuspended. 

However, the fraction resuspended decreased by 2 to 

3 orders of magnitude when a 30-day period elapsed 

between application of the tracer and the car 

passage. 

The fraction resuspended per vehicle passage increased as a function of vehicle speed and was independent of wind velocities for the test conditions. 

The fraction resuspended per vehicle passage was 

greater for a drive through the tracer test lane than 

on the adjacent lane and greater for a 3/4-ton truck 

than for a car. These results suggest that resuspension of lead from roadways may play a significant role in the overall transport of lead away from 

automotive sources. This may be important considering the conclusions of Huntzicker et al.10

 that a 

considerable fraction of the emitted lead deposits 

directly on the roadways. 

In another experiment, Sehmel and Lloyd70 examined the resuspension of \0-fim monodisperse 

uranine particles from a smooth surface in the 

laboratory. They found that the fraction of material 

resuspended per second varied from IO"6 to 10"3 for 

wind speeds of 16.5 to 18.3 m/sec. They also 

measured the resuspension of CaMo4 over sandy 

soil.70 The fraction of material resuspended per second ranged from 2 x 10 l 0 t o 2.2 x 108

for winds of 

1.3 to 20 m/sec. 

A limited amount of data on lead resuspension is 

also available. Figure 6-25 shows the deposition of 

lead found as a function of height above a roof surface.72

 The lead was deposited on flat Teflon plates 

mounted at various heights. The greater depositions 

close to the roof are believed by the investigators to 

be due to resuspended roof dust. 

The environmental consequence of salt particle 

resuspension from roads has been reported by 

Smith.73 Needles from white pine planted adjacent 

to an interstate highway in Connecticut showed excessive sodium and calcium content resulting from 

airborne salt resuspension from the highway. The 

deposition of airborne salt appears to be similar to 

that of lead from automobile exhaust.69 

350 

300 

250 

200 

150 

100 

50 

1 1 

-

-

-

-

1 1 

! 

/ 

_ 

-

> 

\ 

1 °^U 

20 

Pb DEPOSITION, ng/cm'-day 

Figure 6-25. Total deposition of lead on Teflon plates at 

various heights above the roof of Keck Laboratories, California Institute of Technology, Pasadena.71 

Baum et al.74 sampled airborne particulate for a 

period of about 2 years at several locations in Portland, Oregon, using paraffin-coated Mylar films 

with four- and five-stage Lundgren impactors. Soil 

and dust samples, both surface and subsurface, were 

also taken at the air-sampling sites. Samples were 

analyzed for lead and other elements. Chemical elemental balance methods were used to calculate soil 

and dust burdens in the air. The authors report that 

greater than 90 percent of the submicrometer-sized 

airborne particles were associated with automotive 

emissions. The larger particles were reported to be 

contributed about equally by resuspended street 

dust and direct emissions from automobiles. 

These data suggest that lead resuspension may 

play an important role in the transport of lead. At 

present, however, it is not possible to reach quantitative conclusions about this mechanism. Size distribution measurements of ambient lead presented here 

and elsewhere in the literature represent airborne 

data that have been influenced by the combined factors of atmospheric transport, deposition, and 

resuspension. 

6.3.3 Models 

There is an extensive body of literature on at6-19 
P.84 

mospheric transport and diffusion models.75'

79

 A 

detailed discussion is beyond the scope of this document. The mathematical models are usually based 

on the basic Gaussian plume model emanating from 

the early work of Sutton46 and Pasquill47 and well 

described by Gifford.76 Stern77 provided an excellent review of air quality modeling techniques for 

both rural and urban modeling situations. Experimental data describing the pollutant concentrations 

from point sources show that, in spite of wide variations, these plumes exhibit a strong tendency toward 

a Gaussian or normal distribution as a statistical 

average. In simple terms, parameters reflecting the 

turbulent component define the horizontal and vertical dimensions of a pollutant cloud in a vertical 

plane perpendicular to the mean wind velocity. 

Cermack et al.80 have used the wind tunnel to 

model physically the atmospheric boundary layer 

over urban areas to determine the pollutant 

transport characteristics. 

6.4 TRANSFORMATION AND TRANSPORT 

IN OTHER ENVIRONMENTAL MEDIA 

6.4.1 Soils 

Numerous studies have shown significant contamination of soils by the emission of lead from 

mobile and stationary sources and through the disposal of waste products. Excellent reviews of the 

early literature, as well as reports on more recent 

research, have been published by members of a joint 

research staff from Colorado State University and 

the Universities of Missouri and Illinois.2029 Many 

of the studies of lead before 1973 were limited to 

analysis for elemental lead and did not include 

analysis for associated ions. Such information is not 

sufficient to permit a thorough examination and 

understanding of (1) transformation and transport 

processes that occur among the environmental 

media, (2) mobility of lead in soils, (3) uptake and 

distribution of lead in plants, and (4) the overall impact of lead on human health and ecosystems. Information on the chemical forms of lead is needed. 

Soil is a complex matrix composed of several 

hundred different compounds, only a small fraction 

of which are lead. Most analytical techniques are not 

capable of providing positive identification of 

specific compounds unless separation methods are 

used that do not alter the lead compounds. Recently, 

nondestructive separation/preconcentration techniques have been developed and used by the Colorado State University research group to determine 

lead compounds in soil and plants.10 

Lead contaminants are deposited on soil by dry 

and wet deposition processes. Present understanding 

of the chemical reactions involving these particles 

once they are deposited into or on the soil is incomplete.81

 Early work indicates that lead probably 

reacts with soil anions, e.g., S0 4

=

, P0 4

=

, or C0 3

=

, 

or with some organic or clay complex.82 These reactions would tend to make the Pb insoluble, thus inhibiting rapid mobility in the soil or plant as well as 

microbial uptake. Direct evidence supporting these 

reactions is limited. In a study by Lagerwerff and 

Brower,83 lead was precipitated in Na

 +-treated, 

alkalized soils. The solubility of the precipitate increased with decreasing pH and concentration of 

NaCl. Furthermore, absorption of soil lead by hydrous oxides of iron and manganese, and its consequent immobilization, has been reported by Gadde 

and Laitinen.84 

Studies have identified cation exchange capacity, 

organic matter content, pH, soil type, and soil drainage as the important factors influencing the mobility 

of lead in soils.85 Santillan-Medrano and Jurinak86 

conducted batch equilibrium studies to obtain 

solubility data for lead and cadmium in soil. Lead 

solubility decreased in the soils as pH increased. The 

lowest values were obtained in calcareous soil. In 

noncalcareous soil, the solubility of lead appears to 

be regulated by Pb(OH)2, Pb3(P0)4)2, Pb4 0(P04 ) 2 , 

Pb5 (P04 ) 3 0H, and even PbC03 , depending on the 

pH. 

The creation of organic chelating agents by 

biologic activity serves as one of the most effective 

processes of metal mobilization or immobilization in 

the soil. These agents are either plant products, 

microbial metabolities, or humic compounds (humic 

acids). The latter are capable of precipitating lead. 

The amounts and types of organic matter present appear to provide an important control 

mechanism for the movement of heavy-metal ions in 

soil systems. The association of lead and organic 

matter, however, is not always empirically consistent.87 

Olson and Skogerboe29 preconcentrated lead 

compounds in roadside soil samples and used X-ray 

powder diffraction techniques for compound identification. The lead compounds in each soil fraction 

examined are shown in Table 6-12. The most abundant lead salt found was the relatively insoluble 

PbSo4. The authors note that generally 70 percent or 

more of the total lead in the soils examined was contained in the dense fractions and that the majority 

(>5 0 percent) of this lead was present as sulfate. 

The results indicate that oxides present in the soil 

6-20 
were minor constituents compared to the sulfate 

concentrations. Since lead bromochloride compounds are the principal constituents of fresh automobile exhaust emissions, conversion to lead sulfate 

must have occurred either in the atmosphere or in 

the soil. The authors suggest that sulfuric acid 

formed from S02 in the atmosphere or at the soil 

interface may react with the lead particulate to form 

lead sulfate. Reaction with the sulfate ion also may 

occur in the soil in contact with groundwater.24 The 

results of Lee et al.9 (Section 6.2.2.1) support these 

general contentions. 

Data are limited regarding the chemical composition of lead in soil contaminated by emissions from 

stationary sources. Lead sulfide and lead chloride 

are thought to be the major constituents in soils in 

the vicinity of mining industries, and lead oxide is 

the chief one in the vicinity of smelters. The presence 

of lead sulfide as the primary compound in soils 

along a mine-access road in Missouri has been reported, (Table 6-12). Analytical data confirming the 

other compounds mentioned above are not available. 

6.4.2 Water 

6.4.2.1 INORGANIC 

The chemistry of lead in an aqueous solution is 

highly complex because the element can be found in 

a multiplicity of forms. Hem and Durum have 

reivewed the chemistry of lead in water in detail,88 

and the aspects of aqueous lead chemistry that are 

germane to this document are discussed in Chapter 

3. 

Natural concentrations of lead in lead-ore 

deposits do not normally move appreciably in 

ground or surface water. Any lead dissolved from 

primary lead sulfide ore tends to combine with carbonate or sulfate ions to (1) form insoluble lead carbonate or lead sulfate, or (2) be absorbed by ferric 

hydroxide.87 An outstanding characteristic of lead is 

its tendency to form compounds of low solubility 

with the major anions of natural water. The hydroxide, carbonate, sulfide, and more rarely the sulfate 

may act as solubility controls. The amount of lead 

that can remain in solution in water is a function of 

the pH of the water and the dissolved salt content. 

Equilibrium calculations show that the total 

solubility of lead in hard water (pH >5.4) is about 

30 fig/\iter and about 500 ^tg/liter in soft water (pH 

<5.4). 8 9 Lead sulfate (PbS04) is present in soft 

water and limits the lead concentration in solution. 

Above pH 5.4, PbC03 and Pb2 (OH) 2C03 limit the 

TABLE 6-12. LEAD COMPOUNDS IDENTIFIED IN ROADSIDE 

SOILS BY X-RAY POWDER DIFFRACTION TECHNIQUES29 

Location and 

soil fraction 

Fort Collins: 

Magnetic 

Nonmagnetic 

Denver: 

Magnetic 

Nonmagnetic 

Chicago: 

Magnetic 

Nonmagnetic 

Chicago: 

Magnetic 

Nonmagnetic 

Missouri: 

Magnetic 

Nonmagnetic 

Compounds 

found 

PbS04 

PbS04 

PbOPbS04 

Pb02 

PbO° 

PbS04 

PbS04 

PbS04 

PbO 

PbS04 

PbS04 

PbS04 

Nonec 

PbS 

PbS04 

Estimated 

concentrations8 

Major 

Major 

Minor 

Trace 

Trace 

Major 

Major 

Major 

Major 

Minor 

Major 

Major 

Major 

Minor 

aMajor indicates the principal portion of lead present in the soil fraction indicated 

and. therefore, the principal portion of the soil sample. Minor refers lo approximately 1 to 10 percent ol the lead in the respective fractions. Trace quantities are 

less than approximately 1 percent of the total in each fraction. 

DAssignment is based on the presence of only the most intense d-spacing and is 

therefore questionable. 

cComplex d-spacing pattern obtained with all intensities low; positive assignment of any one compound or group of compounds is questionable. 

concentration. The carbonate concentration is in 

turn dependent on the partial pressure of C0 2 as 

well as the pH. Calculations by Hem and Durum88 

show that many river waters in the United States 

have lead concentrations near the solubility limits 

imposed by their pH levels and contents of dissolved 

C 0 2 species. Because the influence of changing temperature and pH may be substantial, observed lead 

concentrations may vary significantly from 

theoretically calculated ones. 

Lazrus et al.60 calculated that as much as 138 

g/ha-mo of lead may be deposited by rainfall in «ome 

parts of the northeastern United States. Assuming an 

average annual rainfall runoff of 50 cm (—20 in), 

the average concentration of lead in the runoff 

would have to be about 330 /ug/liter to remove the 

lead at the rate of 138 g/ha-mo. Concentrations as 

high as 330 /txg/liter could be stable in water with pH 

near 6.5 and an alkalinity of about 25 ng bicarbonate ion/liter of water. Water having these properties is common in runoff areas of New York State 

and New England; hence, the potential for high lead 

concentrations exists there. In other areas, the 

average pH and alkalinity are so high that less than 1 

/ug/liter of lead could be retained in solutions at 

equilibrium.87 

6-21 
P.86 

A significant fraction of the lead carried by river 

water may be in an undissolved state. This nonsolute 

lead can consist of colloidal particles in suspension 

or larger undissolved particles of lead carbonate, 

oxide, hydroxide, or other lead compounds incorporated in other components of particulate lead 

from runoff, either as sorbed ions or surface coatings 

on sediment mineral particles or carried as a part of 

suspended living or nonliving organic matter.87 A 

laboratory study by Hem90 of sorption of lead by cation exchange indicated that a major part of the lead 

in stream water may be adsorbed on suspended sediment. Figure 6-26 illustrates the distribution of lead 

outputs between filtrate and solids in stream water 

from both urban and rural compartments, as reported by Rolfe and Jennett.91

 The majority of lead 

output is associated with suspended solids in both 

urban and rural compartments with very little dissolved in the filtrate. The ratio of lead in suspended 

solids to lead in filtrate varies from 4:1 in the rural 

compartment to 27:1 in the urban compartment. 

100 

so 

0 

_ 

-

SHWll SUSPENDED SOLIDS 

^-^ j FILTRATE 

,,,II, I ,ii ' f ^ 

-

/V/ ^ 

^ 

Figure 6-26. Lead distribution between filtrate and suspended 

solids In stream water from urban and rural compartments."0 

The concentration of lead usually reported represents a somewhat arbitrarily defined solute fraction, 

separated from the nonsolute fraction by filtration. 

Most filtration techniques cannot be relied on to 

remove all colloidal-sized particles. Upon acidification of the filtered sample, which is usually done to 

preserve it before analysis, the colloidal material 

that passes through is dissolved and reported in that 

form. Usually the solids removed from a surface 

water sample by filtration are not analyzed for lead. 

But even the lead in rainfall can be mainly particulate, and thus it will be necessary to obtain more information on the amounts of lead transported in 

nonsolute form87 before a valid estimate can be obtained of the effectiveness of runoff in transporting 

lead away from areas where it has been deposited by 

atmospheric fallout and rain. 

6.4.2.2 ORGANIC 

The organic components of soil-water system are 

an extremely diverse group of compounds that includes carbohydrates, amino acids, phenolic and 

quinonic compounds, organic acids, nucleic acids, 

enzymes, porphyrins, and humic materials.87 In addition to the natural organic compounds present in 

soils, streams and lakes contain organic sediments 

and suspended solids that have been derived from 

municipal, agricultural, and industrial wastes. These 

wastes include carbohydrates, proteins, nucleic 

acids, enzymes, lipids, and many other organic compounds found in living systems. In addition, oils, 

plasticizers, polymers, and many other organic compounds are discharged to natural waterways by manufacturing and chemical industries. The interaction 

of lead with these organic compounds is still not well 

understood, but most of these organic materials can 

confidently be expected to form complexes with lead 

(and other metals), since they all contain available 

donor sites for complexation. A discussion of metal 

complexation is presented in Chapter 3 and Appendix B. 

The presence of fulvic acid (a constituent of soil 

humic materials) in water has been shown to increase 

the rate of solution of lead sulfide 10 to 60 times 

over that of a water solution at the same pH that did 

not contain fulvic acid.8792 At pH values near 7, 

soluble lead-fulvic acid complexes were present in 

solution. At initial pH values between 7.4 and about 

9, the lead-fulvic complexes partially decomposed, 

and lead hydroxide and carbonate were precipitated. At initial pH values of about 10, the leadfulvic acid complexes again increased. This increase 

was attributed to dissociation of phenolic groups at 

high pH values, which increases the complexing 

capacity of the fulvic acid. But it may also have been 

due to the formation of soluble lead-hydroxyl complexes. 

In summary, the complexing of lead by most of the 

common sulfur-, phosphorus-, oxygen-, and 

nitrogen-containing ligands means that lead will accumulate in living and nonliving organic components of soil-water and sediment-water systems. The 

living and nonliving organic components are not independent, of each other, but they are constantly 

interacting as the living components metabolize the 

nonliving components of the system and then die, 

contributing their remains to the pool of nonliving 

compounds in the system. The fate of heavy metals 

in this process has not been elucidated; but the sediment in a contaminated surface-water body will 

serve as a large reservoir that can provide lead and 

other metals to the biota of the system even after 

6-22 
heavy-metal pollutants have ceased to be introduced. Most attention has been given to the heavy 

metals dissolved in the water phase of surface water 

rather than to the complexed metals in the sediment 

phase, though sediments probably contain a higher 

amount of lead.87 

The biotransformation of lead to volatile tetramethyl lead constitutes one mechanism by which 

lead may leave sediment-water systems. The direct, 

biological methylation of certain inorganic lead 

compounds by lake sediment microorganisms has 

been reported.93-

94

 All the lake sediments tested 

were able to transform trimethyl lead to tetramethyl 

lead,93 but only some of the sediments were able to 

transform lead nitrate and lead chloride into 

tetramethyl lead. No biotransformation occurred 

when the lake sediments were incubated with lead 

oxide, lead hydroxide, lead bromide, lead cyanide, 

or lead palmitate.93 Certain pure bacterial isolates 

(see Chapter 8) from these lake sediments were 

shown to transform trimethyl lead to tetramethyl 

lead in the anaerobic incubation system used.93 

The conversion of the tri- to the tetramethyl lead 

salt was subsequently postulated to be chemical 

rather than biological, proceeding via formation and 

then decomposition of an organic sulfide intermediate, (Me3Pb)2S.95

 Using a system containing no 

sulfides, however, other workers showed the production by microorganisms of Me4Pb from Me3Pb

 + 

much in excess of yields expected from the 

stoichiometry of redistribution reactions of lead 

alkyl compounds in aqueous solutions.94 Thus, the 

alkylation appears to be direct and biological. The 

alkylation of lead, unlike that of mercury, was not 

mediated by methylcobalamin, as shown when 

equimolar amounts of Me3PbOAc, Me3PbCI, 

Me2PbCl2, and Pb(N03)2 were substituted for inorganic mercury in an aqueous test system (~pH 

7).95 Taylor and Hanna,96 however, have recently 

demonstrated that prolonged incubation of 

methylcobalamin with a fine suspension of lead oxide (Pb304) in an aqueous medium results in partial 

demethylation of the corrinoid. This chemical 

demethylation of MeB12 by Pb3 04 was shown to be 

highly pH dependent, with no demethylation occurring at pH 7, and 61 percent occurring at pH 2. 

Trace r studie s with [ 14C]-methyl-labeled 

methylcobalamin indicated that demethylation of 

MeB12 by Pb(IV) was accompanied by a proportional volatilization of the label. These results 

are in agreement with the known instability of 

monoalkyl lead compounds in aqueous media as described by Wood.97 

The alkylation of lead, then, unlike that of mercury, does not appear to result in nonvolatile, toxic 

organolead that could undergo biomagnification in 

the food chain. Volatile TML generated in situ 

would be expected to escape from a body of water. 

The possible uptake of tetramethyl lead by aquatic 

organisms during its passage to the surface of a body 

of water is unknown. 

6.4.3 Plants 

Lead is transferred from the atmosphere to the 

soil and vegetative compartments of the environment by dry and wet deposition. Considerable attention has been devoted to determining the amount 

and localization of lead in roadside and smelter 

areas, but little information is available regarding its 

chemistry and effects in those areas. Motto el al.98 

suggested that plant uptake is probably related better to soluble rather than total lead in soils. Wilson 

and Cline99 concluded that only 0.003 to 0.005 percent of total lead in soil is available for plant uptake. 

The soil solution is affected by all the reactions that 

occur as the constituents are changed through addition to or depletion from the soil. Ultimately, the 

composition of the soil solution is controlled by the 

solubility of the various mineral phases in the soil. 

The long-term effects of lead in soils are uncertain. 

Only recently has attention been given to the 

solubility relationships of PbS04, Pb3(P04)2, and 

PbC03 as possible controlling mechanisms for the 

amount of lead in soils.44 If PbC03 is involved as a 

reaction product, there is the possibility that soils of 

high pH, upon becoming acidic, could release lead 

at some future time.100 The question of chemical 

identity of lead in plants is still largely unanswered. 

Hamp and Ziegler101 have suggested that lead associated with plant surfaces in nature may be largely 

lead phosphate. Zimdahl,102 citing studies conducted at Colorado State University and the University of Illinois, reported the identification of lead 

pyrophosphate in bean roots and lead orthophosphate in soybean root. The results of later solubility 

studies of the two compounds suggested that lead 

pyrophosphate should be the dominant form in 

plants. 

The process by which lead is taken up by plants, 

which may be passive,85103 is favored under conditions of low soil pH.104

 MacLean et al.105 have suggested that soil management practices such as the addition of organic matter, lime, and phosphate may 

be appropriate in contaminated soils to reduce the 

availability of lead for plant uptake. They found that 

the concentration in oats and alfalfa varied inversely 

6-23 
P.88 

with pH and organic matter, and that addition of 

phosphate reduced the uptake of lead; they suggested that the pH effect was due to repression of 

lead solubility at the higher pH values. John and 

Van Laerhoven106 found little difference in uptake 

by oats and lettuce when lead was derived from 

water-insoluble lead carbonate as opposed to the 

more water-soluble lead chloride or nitrate. Hence 

the formation of lead carbonate as a result of liming 

would not explain the pH effect. 

Work at the University of Illinois and at Colorado 

State University, cited by Zimdahl,102 has shown 

that uptake by several plant species is inversely proportional to soil lead content and is greatest under 

conditions of low pH and low phosphorus. The binding or exchange capacity of soils, related to organic 

content, is extremely important as a determinant of 

lead availability to plants. Chelating agents can 

modify the uptake and possibly the movement of 

heavy metals by plants, but the relative importance 

of natural chelating substances is hard to evaluate at 

this time.102 Zimdahl,102 citing a number of studies 

regarding chelation of lead with EDTA, concludes 

that the extent of lead movement within the plant is 

still unresolved. He questions whether studies with 

synthetic and highly ionized chelating agents such as 

EDTA actually reflect what is happening in nature. 

In a study conducted at the University of Illinois107

 (cited by Zimdahl102), it was shown that the 

roots of hydroponically grown corn acquired a surface lead precipitate and slowly accumulated 

crystalline lead in the cell walls. The surface precipitate formed quickly and independently of plant activity. Two compounds were postulated but not 

identified. The lead entering the root was concentrated in some but not all dictyosome vesicles. After 

precipitation had occurred in the dictyosome vesicle, cell-wall precursors were added to the vesicle by 

apposition of vesicles or by internal secretion. As the 

lead-containing crystals grew, more cell-wall 

material was added, so that the entire vesicle eventually moved to the periphery of the cell to achieve 

fusion with the cell wall. Lead deposits were thereby 

concentrated at the cell wall and not within 

mitochondria or other organelles.102 Although this 

sequence of events was observed in the root tips, 

deposits were observed throughout the plant, and it 

was suggested that a similar process occurred in all 

plant tissues.102 

The deposition of lead on the leaf surfaces of 

plants where the particles are often retained for long 

time periods must also be considered.32108109 Several studies have shown that plants near roadways 

exhibit considerably higher levels of lead than those 

farther away. In most instances, the higher concentrations were due to lead particle deposition on 

plant surfaces.32 Studies have shown that particles 

deposited on plant surfaces are often very difficult to 

remove completely by simple washing techniques 

considered characteristic of the treatment that 

would be used in a household kitchen.IOS.I 10,111 

Leaves with hairy surfaces seem able to retain (and 

attract) particles via an electrostatic mechanism. 

Other types of leaves are covered with a cuticular 

wax sufficiently sticky to preclude the removal of 

particles. Thus rainfall does not serve as a particularly effective means of removing the deposited particles.110

 Animals or humans consuming the leafy 

portions of such plants can certainly be exposed to 

higher than normal levels of lead. Fortunately, a 

major fraction of lead emitted by automobiles is 

deposited inside a typical highway right-of-way, so 

at least part of this problem is alleviated. 

The particle deposition on leaves has led some investigators to stipulate that lead may enter plants 

through the leaves. This would typically require, 

however, that the lead particles be dissolved by constituents of the leaf surface and/or converted to the 

ionic form via contact with water. The former 

possibility is not considered likely, since cuticular 

waxes are relatively inert chemically. Zimdahl and 

Arvik85 have shown in a rather elegant set of experiments that entry of ionic lead through plant leaves is 

of minimal importance. By using the leaf cuticles of 

several types of plants essentially as membranes, 

they found that even high concentrations of lead ions 

would not pass through the cuticles into distilled 

water on the opposite side. 

The results of the studies discussed above 

generally indicate the following: 

1. The uptake of lead by plants from soil is 

highly dependent on the chemical equilibria 

prevalent in the soil in question. The uptake 

can probably be controlled through treatment of the soil with materials (e.g., lime, 

phosphate fertilizers, etc.) that affect these 

chemical equilibria. 

2. Although uptake rates are enhanced at lower 

soil pH levels, the majority of the lead taken 

up remains in the plant roots; only smaller 

fractions are translocated to the shoots. 

3. Deposition and retention of lead particles on 

plant surfaces can serve as a route of animal 

or human exposure to automotive lead. Thus 

crops grown near sources of high traffic 

6-24 
should probably be considered suspect 

unless appropriate safety precautions are 

taken. 

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P.92 

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7/5(6):455-460, 1973. 

6-28 
7. ENVIRONMENTAL CONCENTRATIONS 

AND POTENTIAL EXPOSURES 

7.1 AMBIENT AIR EXPOSURES 

Several studies on concentrations of lead in the 

ambient air have been undertaken. These studies 

were generally intended to survey the levels and distributions of lead in the general air environment and 

around sources. They usually were not designed in 

conjunction with epidemiological studies of the concurrent effects of lead on man or other organisms. 

Yet that is the context in which these studies must 

now be interpreted to shed the most light possible on 

the concentrations likely to be encountered in 

various environmental settings. 

Measurements taken with high-volume samplers, 

dust-fall buckets, and particle size fractionators are 

included in these studies; however, with the exception of the NASN data from 1970 through 1974, 

quality control and interlaboratory comparability 

are unspecified. The effectiveness of some filter 

media in collecting very small lead-containing particles has been questioned; this subject is discussed in 

Chapter 4. The studies show that: 

1. Lead typically occurs in urban airborne suspended particles 0.5 fim or less in mass median equivalent diameter at annual average 

concentrations ranging from <0.1 to 5 

/xg/m3, with an overall average of 1 to 2 

Mg/m3. 

2. Urban concentrations of lead have declined 

somewhat since 1970. 

3. Suspended particles in rural air samples contain lead at concentrations ranging from 

<0.01 to 1.4 /ug/m3, with an overall average 

of about 0.2 /j.g/m3. 

4. Monthly average concentrations of lead in 

urban settleable particles range from 3 to 12 

mg/m2-mo. 

5. Indoor concentrations of lead are quite 

variable, but are generally one- to two-thirds 

the concentrations of adjacent outdoor 

levels. 

A discussion of the NASN measurements follows. 

Summaries of additional studies can be found in Appendix C. 

7.1.1 National Air Surveillance Network (NASN) 

Data 

Since 1957, samples of suspended particulate matter collected at some 300 urban and 30 nonurban 

NASN sites have been analyzed for trace metals, including lead. Only data beginning with 1966 are 

summarized here, however, because the procedure 

used before 1966 was found to recover only about 50 

percent of the lead actually present. The emission 

spectrograph^ method now employed in the 

analysis has sufficient sensitivity to permit detection 

of lead in all urban and most nonurban samples. 

Summaries of the data for urban and nonurban 

NASN sites for 1966 through 1974 are presented in 

Tables 7-1 and 7-2, which categorize the sites by 

four successive annual average concentration 

ranges.'

 2 The majority of the urban sites (91 percent 

of the site-years) reported annual averages below 2.0 

Mg/m3, and the majority of nonurban sites (86 percent of the site-years) reported annual averages 

below 0.2 ,y,g/m3. 

Samples collected by the NASN from 1970 

through 1974 were combined for analysis into quarterly composites. Tables 7-3 and 7-4, respectively, 

give the cumulative frequency distributions of urban 

and nonurban quarterly composite values for 1970 

through 1974.' 

Urban NASN sites for which annual average concentrations have been 3.0 figlm3

 or greater are listed 

in Table 7-5. 1 2 Highest concentrations for shorter 

intervals (quarterly and 24-hr) have been included, 

where available, in order to indicate the variation in 

concentration with averaging time and potential 

peak exposure conditions. A large number of 

Southern California cities are included in the list 

because of the heavy automobile traffic in these 

areas. Both the annual average and maximum values 

at Los Angeles County sites were consistently high, 

7-1 
P.94 

TABLE 7-1. NUMBER OF NASN URBAN STATIONS WHOSE 

DATA FALL WITHIN SELECTED ANNUAL AVERAGE LEAD 

CONCENTRATION INTERVALS, 1966-19741 •* 

TABLE 7-2. NUMBER OF NASN NONURBAN STATIONS 

WHOSE DATA FALL WITHIN SELECTED ANNUAL AVERAGE 

LEAD CONCENTRATION INTERVALS, 1966-197412 

Year 

1966: 

No. stations 

Percent 

1967: 

No. stations 

Percent 

1968: 

No. stations 

Percent 

1969: 

No. stations 

Percent 

1970: 

No. stations 

Percent 

1971: 

No. stations 

Percent 

1972: 

No. stations 

Percent 

1973: 

No. stations 

Percent 

1974: 

No. stations 

Percent 

1966-1974: 

No. stations 

Total percent 

< 0.5 

9 

9 

4 

3 

14 

9 

5 

2 

9 

5 

— 

16 

9 

20 

15 

19 

15 

96 

8 

Concentration interval, ug 

0.5-0.99 

40 

42 

37 

32 

67 

45 

46 

25 

54 

33 

23 

21 

67 

37 

76 

55 

69 

53 

479 

38 

1.0-1.9 

40 

42 

63 

55 

54 

36 

103 

57 

80 

50 

64 

58 

84 

47 

36 

26 

38 

29 

562 

45 

2.0-3.9 

6 

6 

9 

7 

10 

6 

23 

12 

15 

9 

21 

19 

12 

7 

4 

3 

4 

3 

104 

8 

/m3 

4.0-5.3 

— 

— 

— 

0 

0 

0 

6 

1 

Total 

95 

100 

113 

100 

146 

100 

178 

100 

159 

100 

109 

o o o O 00 o 

137 

100 

130 

100 

1247 

100 

Year 

1966: 

No. stations 

Percent 

1967: 

No. stations 

Percent 

1968: 

No. stations 

Percent 

1969: 

No. stations 

Percent 

1970-1971: 

No. stations 

Percent 

1972: 

No. stations 

Percent 

1973: 

No. stations 

Percent 

1974: 

No. stations 

Percent 

1966-1974: 

No. stations 

Total percent 

< 0.03 

— 

1 

5 

1 

5 

— 

— 

— 

10 

29 

9 

39 

3 

19 

24 

15 

Concentration interval 

0.03-0.099 

10 

52 

7 

35 

15 

75 

11 

52 

— 

— 

4 

12 

7 

31 

5 

31 

59 

36 

0.10-0.19 

6 

32 

10 

50 

4 

20 

9 

43 

7 

70 

9 

26 

6 

26 

6 

38 

57 

35 

ng'm3 

0.20-0.45 

3 

16 

2 

10 

— 

— 

1 

5 

3 

30 

11 

33 

1 

4 

2 

12 

23 

14 

Total 

19 

100 

20 

100 

20 

100 

21 

100 

10 

100 

34 

100 

23 

100 

16 

100 

163 

100 

TABLE 7-3. CUMULATIVE FREQUENCY DISTRIBUTIONS OF QUARTERLY LEAD MEASUREMENTS 

AT URBAN STATIONS BY YEAR, 1970 THROUGH 1974' 

(/u.g/m3) 

Year 

1970 

1971 

1972 

1973 

1974 

No. 

quarterly 

composites 

797 

717 

708 

559 

594 

Min 

LD" 

LDa 

LD» 

LDa 

0.08 

10 

0.47 

0.42 

0.46 

0.35 

0.36 

30 

0.75 

0.71 

0.72 

0.58 

0.57 

50 

1.05 

1.01 

0.97 

0.77 

0.75 

Percentile 

70 

1.37 

1.42 

1.25 

1.05 

1.00 

90 

2.01 

2.21 

1.93 

1.62 

1.61 

95 

2.59 

2.86 

2.57 

2.08 

1.97 

99 

4.14 

4.38 

3.69 

3.03 

3.16 

Max. 

5.83 

6.31 

6.88 

5.83 

4.09 

Arithmetic 

Mean 

1.19 

1.23 

1.13 

0.92 

0.89 

Std. 

dev. 

0.80 

0.87 

0.78 

0.64 

0.57 

Geometric 

Std. 

Mean dev. 

0.99 1.84 

1.00 1.89 

0.93 1.87 

0.76 1.87 

0.75 1.80 

a

 LD = limit of detection. 

TABLE 7-4. CUMULATIVE FREQUENCY DISTRIBUTIONS OF QUARTERLY LEAD MEASUREMENTS 

AT NONURBAN STATIONS BY YEAR, 1970 THROUGH 1974' 

(ng/m3) 

1970 

1971 

1972 

1973 

1974 

124 

85 

137 

100 

79 

0.003 

0.003 

0.007 

0.015 

0.007 

0.003 0.003 0.003 0.003 0.267 0.383 0.628 

0.003 0.003 0.003 0.003 0.127 0.204 0.783 

0.007 0.007 0.107 0.166 0.294 0.392 0.950 

0.015 0.015 0.058 0.132 0.233 0.392 0.698 

0.007 0.053 0.087 0.141 0.221 0.317 0.496 

1.471 

1.134 

1.048 

0.939 

0.534 

0.088 0.190 

0.047 0.155 

0.139 0.169 

0.110 0.149 

0.111 0.111 

Year 

No 

quarterly 

composites Min 10 30 50 

Percentile 

70 90 95 99 Max. 

Arithmetic 

Std. 

Mean dev. 

Geometric 

Std. 

Mean aev. 

0.040 3.72 

0.008 4.80 

0.090 2.59 

0.068 2.77 

0.083 2.30 

7-2 
TABLE 7-5. NASN STATIONS WITH ANNUAL AVERAGE LEAD 

CONCENTRATIONS 23.0 Mg/m31<

2 

Year and 

station 

1966: 

Phoenix, Ariz. 

Burbank, Calif. 

Los Angeles, Calif. 

Pasadena, Calif. 

1967: 

Los Angeles, Calif. 

1968: 

Burbank, Calif. 

Glendale, Calif. 

Long Beach, Calif. 

Los Angeles, Calif. 

Pasadena, Calif. 

1969: 

Fairbanks, Alaska 

Phoenix, Ariz. 

Burbank, Calif. 

Glendale, Calif. 

Los Angeles, Calif. 

San Juan, Puerto Rico 

Dallas, Tex. 

1970: 

Burbank, Calif. 

Glendale, Calif. 

Los Angeles, Calif. 

San Juan, Puerto Rico 

Dallas, Tex. 

1971: 

Anaheim, Calif. 

Burbank, Calif. 

Santa Ana, Calif. 

Los Angeles, Calif. 

1972: 

Burbank, Calif. 

Glendale, Calif. 

Los Angeles, Calif. 

San Juan, Puerto Rico 

1973: 

Burbank, Calif. 

Average 

3.2 

3.7 

3.6 

3.6 

3.1 

4.4 

3.0 

3.3 

3.9 

3.5 

3.2 

3.1 

3.5 

3.1 

4.6 

3.8 

3.0 

4.9 

3.5 

4.5 

3.7 

3.2 

3.3 

5.3 

3.5 

4.6 

3.2 

3.5 

3.1 

5.0 

4.0 

Maximum 

Quarterly 

composite 

8.1 

6.0 

11.0 

4.3 

5.4 

— 

— 

— 

— 

— 

4.8 

7.1 

4.7 

4.5 

5.7 

4.2 

5.2 

5.8 

4.2 

5.6 

4.1 

3.8 

4.0 

6.2 

4.6 

6.3 

6.7 

5.2 

4.8 

6.9 

5-2 

24-hr 

— 

'' — 

— 

— 

— 

14.0 

7.5 

12.0 

10.0 

8.3 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

— 

apparently because of location, topography, and 

meteorological conditions that favor retention of 

pollutants in the air over the area. 

Ambient particulate lead data from NASN were 

studied for trends over the 10-year period from 

1965 through 1974. Figure 7-1 shows the 10th, 50th, 

and 90th percentiles for data from 92 NASN urban 

sites.3 Urban lead concentrations as described by the 

50th percentiles increased from 1965 until 1971 and 

then declined from about 1.1 ,ug/m3 to 0.84 

/xg/m3 — about a 24-percent decrease, with most of 

this decline occurring between 1972 and 1973. The 

other percentiles exhibit a similar pattern. This 

general pattern describes the trend for most of the 

sites studied. Trends in the percentage of lead in the 

total particulate matter measured also follow this 

pattern, which indicates that the trends in lead are 

not just a result of general particulate controls but 

are a direct result of decreases in lead emissions. 

E 

•a 

\—i—i—i—i—i—r 

90TH PERCENTILE 

Figure 7-1. Seasonal patterns and trends In quarterly average 

urban lead concentrations.3 

The seasonal pattern in quarterly composite 

values (solid lines in Figure 7-1) shows that the highest levels of airborne lead occurred in the winter 

quarters (first and fourth) and the lowest levels in 

the summer quarters (second and third). In contrast, 

automotive emissions of lead would be expected to 

be greater in the summer for two reasons: (l) 

gasoline usage is higher in the summer, and (2) lead 

content is raised in summer gasolines to replace 

some of the more volatile high-octane components 

that cannot be used in summertime gasolines. Evidently summertime meteorological conditions expedite the movement of these larger emissions more 

quickly and widely through the atmosphere on their 

way to subsequent destinations in vegetation, crops, 

soil, and water. 

Since about the 1970 model year, automobiles 

have been built with lower-compression engines that 

can use lower-octane gasoline and thus gasoline with 

lower lead content. As a result of this engine 

modification, practically all cars built since 1970 

are able to use regular gasoline instead of the more 

leaded premium fuels. Figures 7-2 and 7-3 show, 

respectively, the percentage of the total, market for 

regular and premium gasolines and the trend in lead 

content of gasolines.4 The results of the engine 

modifications can be clearly seen in the lower lead 

content in gasoline (both in regular and premium 

grades) and in the subsequent increase in regular 

gasoline sales and decrease in premium sales. These 

7-3 
P.96 

factors, coupled with the use of a modest amount of 

low-lead and no-lead gasoline introduced at about 

this same time, are identified as principally responsible for the observed decrease in ambient lead concentrations over this period. The increasing use of 

unleaded gasoline resulting from EPA regulations, 

which is reflected in Figure 7-2, will lead to even 

lower levels of atmospheric pollution in the future. 

The effect of these changes is enough to override the 

general increase in annual gasoline consumption of 

about 5 percent typical of recent years (except 

1974). This increase in gasoline consumption probably does not proportionately affect many urban 

monitoring sites (which are chiefly center-city locations) because their neighborhoods are generally at 

or near traffic saturation. There may even be instances of a reduction in vehicle miles traveled in 

downtown areas because of car pooling, improved 

mass transit systems, and the loss of business activity 

to suburban shopping centers. 

O 30 

Iz 

UJ 

U 

F. 20 

I I I I I I I I I I I I I I I I 

REGULAR GAS SALES 1%) 

f 

PREMIUM GAS SALES 1%) 

UNLEADED GAS SALES (%l _ 

62 64 66 68 70 72 74 76 

Figure 7-2. Nationwide trends In regular, premium, and 

unleaded gasoline sales, 1960-1976.4 

In addition to the NASN study, a number of other 

studies involving major cities and rural areas have 

been undertaken. These data support the NASN 

results (see Appendix C). 

7.1.2 Airborne Particle Size Distribution 

In 1970, a cascade impactor network was established by EPA in six cities (Cincinnati, Chicago, 

Denver, Philadelphia, St. Louis, and Washington, 

D.C.) to collect particulates of different size ranges 

for subsequent analysis for lead and other metals.5 

The samples, collected once every 2 weeks for a full 

I l I I I l l 

60 62 64 66 70 72 74 76 

Figure 7-3. Nationwide trends In lead content ot regular and 

premium gasoline, 1960-1976.4 

year, were analyzed for size distribution. Samples 

from each city were also composited quarterly and 

analyzed for lead by optical emission spectroscopy. 

The average annual total lead concentration as 

determined in this study ranged from a high quarter 

of 3.2 jLtg/m3 in Chicago to a low quarter of 1.3 

/ng/m3 in Washington, D.C. The average mass median diameter for lead particles ranged from 0.69 

fim in St. Louis to 0.42 fim in Washington, D.C. 

Fifty-nine to 74 percent of the lead was associated 

with particles smaller than I fim in diameter. Quarterly and annual particle size distribution data are 

presented in Table 7-6. 

7.1.3 Vertical Gradients of Lead in the Atmosphere 

Very few studies have been conducted to determine the variation of lead concentrations with height 

above the ground. Of those that were found, all contained the premise, either explicitly or implicitly, 

that the concentrations being studied derived principally from automotive emissions. Of the studies 

found in the literature, none were adequately 

designed to establish the lead concentration versus 

height relationship. Such a study would require 

simultaneous measurement (preferably continuous) 

at given height intervals over a long period of time 

(a minimum of l year). Even then, the results would 

be valid only for a location having the same characteristics and experiencing the same atmospheric conditions. A single set of concentration values obtained over short and variable time intervals is not 

sufficient to draw conclusions regarding general exposure conditions. 

7-4 
TABLE 7-6. QUARTERLY AND ANNUAL SIZE 

DISTRIBUTIONS OF LEAD-BEARING PARTICLES FOR SIX 

CITIES. 1970S 

TABLE 7-7. LEAD IN AIR ON MAIN STREET, BRATTLEBORO, 

VERMONT, SEPTEMBER 12and 13,1972»« 

(ng/m3) 

City and 

quarter 

of year 

Average 

concentration. 

jj.g/m3 

Average 

mass 

median 

diameter. 

utr\ 

Chicago, III.: 

1 2.9 

2 3.5 

3 3.5 

4 2.9 

Total year 3.2 

Cincinnati, O.: 

1 1.0 

2 2.2 

3 1.9 

4 2.1 

Total year 1.8 

Denver, Colo.: 

1 2.0 

2 1.1 

3 1.4 

4 3.0 

Total year 1.8 

Philadelphia, Penn.: 

1 1.5 

2 1.2 

3 1.8 

4 1.9 

Total year 1.6 

St. Louis, Mo.: 

1 1.9 

2 1.6 

3 1.8 

4 1.8 

Total year 1.8 

Washington, D.C: 

1 1.3 

2 1.0 

3 1.3 

4 1.8 

Total year 1.3 

1.43 

0.51 

0.56 

0.54 

0.68 

0.25 

0.41 

0.54 

0.65 

0.48 

0.43 

0.58 

0.52 

0.56 

0.50 

0.36 

0.38 

0.70 

0.45 

0.47 

0.46 

0.63 

0.78 

0.95 

0.69 

0.36 

0.39 

0.41 

0.54 

0.42 

Percentage 

of particles 

5//.m 

41 

65 

65 

64 

59 

79 

74 

69 

67 

72 

76 

68 

69 

66 

70 

74 

74 

62 

70 

70 

68 

63 

59 

53 

62 

76 

73 

74 

71 

74 

Darrow and Schroeder6 measured lead concentrations at eight heights above street level in Brattleboro, Vermont. The values found are shown in 

Table 7-7. The average traffic flow was reported to 

be 7500 cars per day. The concentration levels 

shown in Table 7-7 are considerably higher than 

those usually reported in other cities. The investigators attributed the higher values to greater collection 

efficiency and lower sampling heights, but this was 

not confirmed. The sampling times were short and 

variable. General conclusions regarding the relationship of concentrations versus height cannot be 

drawn from these data. 

Height Sampling times 

above 8:36a.m. 10:20 a.m. 1:20p.m. 

street, ft 10:15 a.m. 12:00 noon 3:00 p.m. 

3:25 p.m. 4:35 p.m. 9/12 

4:25 p.m. 1:02 p.m. 9/13 

1" 

2 

3 

4 

5

C 

7 

8 

30 

8.94 

8.22 

7.15 

7.84 

4.40 

8.15 

3.85 

5.31 

7.56 

17.38 

21.11 

2.40 

3.01 

4.25 

a

 Average air lead value for 54.38 m3 air = 8.54 ^ g Pb/m3. 

D

 1-. 2-, 3-. and 4-ft heights: Average air lead values lor 13.53 m3 air = 8.01 M 9 

Pb/m3. 

c

 5-. 7-, 8-, 30-ft heights: Average air lead values for 40.85 m3 air = 3.96 n g Pb/m3. 

Edwards7 has reported measurements made in 

downtown Fort Collins, Colo. Measurements were 

made in a street canyon formed by two- and threestory buildings (average height, 9 m). With a 2.3 

m/sec wind from the Northeast (street running 

north-south), lead concentrations along the east side 

of the street canyon ranged from 11.3 /i,g/m3 at street 

level to 4.0 /u,g/m3 at roof level. On the west side of 

the street, concentrations ranged from 0.9 /ug/m3 at 

street level to 1.3 /xg/m3 at roof level. Values for two 

additional sampling points above the rooftops on 

each side of the street were 0.4 ttg/m3 (east side) and 

0.9 /xg/m3 (west side). Lead concentrations 2 to 5 

blocks away ranged from 0.1 to 0.3 Mg/m3. These 

data reflect the wide variability that can be expected 

in urban traffic environments. Under moderate 

cross-wind conditions, concentrations within the 

canyon were strikingly anisotropic, and street-level 

concentrations along the upwind building faces were 

substantially higher than along the downwind face. 

With different wind regimes, different building configuration, and different stability conditions, the distribution of concentration values would also be 

different. 

Barltrop and Strelow8 conducted an air sampling 

program at a proposed nursery site under an elevated motorway. The height of the motorway was 

9.3 m. Air samplers were operated at five to seven 

sites from Monday to Friday, 8 a.m. to 6 p.m. for 1 

year. The maximum individual value observed was 

18 /xg/m3. The 12-month mean ranged from 1.51 

Mg/m3 to 1.35 /xg/m3, with standard deviations of 

0.91 and 0.66, respectively. The authors reported 

that the airborne concentrations were independent 

of height from ground level up to 7 m. 

PedCo-Environmental9 measured lead concentrations at heights of 5 and 20 ft at sites near streets in 

7-5 
P.98 

Kansas City, Mo. and Cincinnati, O. The sampling 

sites in Kansas City were described as unsheltered, 

unbiased by localized pollution influences, and not 

immediately surrounded by large buildings. The 

Cincinnati study area was located in a primarily residential area with one commercial street. Samplers 

were operated for 24-hr periods from 8 a.m. to 8 

a.m.; but a few 12-hr samples were collected from 8 

a.m. to 8 p.m. Data were obtained at Kansas City on 

35 days and at Cincinnati on 33 days. The range and 

average values reported are shown in Table 7-8. In 

all cases except two, the measured concentrations 

were higher at 5 ft than at 20 ft. Note that the 

difference between the east side and west side of the 

streets was approximately the same as the difference 

between 5 and 20 ft in height. 

TABLE 7-8. AIRBORNE LEAD CONCENTRATIONS AT 5- AND 

20-FT ELEVATIONS ABOVE STREET LEVEL* 

(Mg/m3) 

Location Range 

Kansas City 0.8-4.0 

Cincinnati 0.1-4.6 

East side of street 

20 ft 5 ft Did. 

1.7 2.0 0.3 

0.9 1.4 0.5 

Averages 

West side of street 

20 It 5 ft Diff. 

1.5 1.7 0.2 

0.6 0.8 0.2 

These data reflect the strong influence of the 

geometry of the boundary layer, wind, and atmospheric stability conditions on the vertical gradient of lead resulting from automobile emissions. 

The varability of concentration with height is further 

complicated by elevated emissions (i.e., from 

stacks). Concentrations measured from sampling 

stations on the roofs of buildings several stories high 

may not reflect actual human exposure conditions, 

but neither would a single sampling station located 

at ground level in a building complex. The height 

variation in concentration resulting from vertical 

diffusion of automobile emissions is likely to be 

small compared to temporal and spatial variations 

resulting from surface geometry, wind, and atmospheric conditions. 

7.2 MOBILE SOURCE EXPOSURES 

Several major studies have been undertaken to 

determine the lead levels in the air and in settled 

dust near busy highways that are far from any stationary lead source. Among the most intensive of 

these studies was the Los Angeles Catalyst Study of 

1974-1975, undertaken by EPA to measure the impact of the catalytic converter on air quality near a 

major traffic lead source.10 , 

Table 7-9 summarizes the 24-hr ambient concentrations of lead observed at two sites (A and C) 

on opposite sides of a major freeway during the 

calendar year 1975. In addition to the monthly 

average concentration at each site, the monthly 

average cross-freeway difference in concentrations 

(C-A) and ratio of concentrations (C/A) are shown 

in the table. Finally, the percentage of hours in the 

month when winds were from the directional sector 

that is most favorable to the detection of cross-freeway differences is shown in the righthand column. 

The favorable wind direction interval is approximately 160° to 290° and was defined on the basis of 

concentration of carbon monoxide, which is a tracer 

for mobile-source pollutants. 

TABLE 7-9. MONTHLY AVERAGE LEAD CONCENTRATIONS 

FOR 1975 LOS ANGELES CATALYST STUDY'" 

Month 

Site A. 

Mg/m3 

SiteC. 

jjg/mJ 

Difference. 

C-A 

Ratio. 

C/A 

% 

Favorable 

wind 

direction8 

January 

February 

March 

April 

May 

June 

July 

August 

September 

October 

November 

6.0 

4.1 

3.2 

2.8 

1.8 

1.4 

1.9 

2.8 

3.7 

4.2 

4.8 

6.2 

4.8 

5.2 

6.0 

7.4 

8.1 

8.0 

8.4 

8.5 

7.3 

6.6 

0.2 

0.5 

2.0 

3.3 

5.6 

6.8 

6.1 

5.7 

5.0 

3.3 

1.7 

1.03 

1.18 

1.63 

2.14 

4.06 

5.68 

4.27 

3.00 

2.30 

1.74 

1.37 

28.2 

35.2 

43.3 

47.6 

65.6 

71.2 

68.0 

61.6 

59.5 

49.4 

31.6 

8

 From A to C (S + SW + W winds). 

A very strong seasonal effect is observed in the 

data, with concentrations at Site C exceeding those 

at Site A by only 3 percent in January, increasing to 

a maximum difference of over 400 percent in June, 

and subsequently decreasing during the fall months 

(no data were collected during the month of December). As expected, there is a strong linear relationship between the occurrence of favorable wind 

direction and the observed cross-freeway difference 

in lead concentration. The correlation coefficient 

between the two variables is 0.96, indicating that 

almost all of the variation in the cross-freeway concentration of lead may be accounted for by the 

seasonal variation in the occurrence of favorable 

wind direction. 

In a study conducted in London, England,11 ambient air levels of organic lead were measured at urban sites. Concentrations of 0.04 to 0.11 Mg organic 

Pb/m3 were found on streets of varying widths and 

traffic flow. These values were 0.3 to 2.6 percent of 

total airborne lead. The level of organic lead inside 

a busy tunnel was 0.02 figlm3, or 0.1 percent of the 

total airborne lead. Not surprisingly, organic lead 

concentrations measured at a busy service station 

7-6 
ranged from 0.21 to 0.59 figlm3

, or 3.9 to 9.7 percent of total airborne lead at that site. At a less busy 

service station, the concentration of organic lead 

was 0.07 Mg/m3.

 o r

 4.2 percent of total airborne lead 

at that site. 

Data obtained in a number of other studies on 

lead in dusts near roadways are summarized in Tables 7-10 and 7-11. The above data demonstrate that 

abnormally high concentrations of lead are found in 

the air and dust near major roadways, and that people who live or work (e.g., traffic policemen, service 

station and garage attendants) in these areas are exposed to high lead concentrations. 

For comparison, Table 7-12 summarizes lead in 

dusts from nominally residential urban areas. These 

concentrations have a wider range than those in 

traffic-oriented dust samples. They are higher in the 

vicinity of an identified point source such as the El 

Paso smelter, but the majority of the readings are 

lower than those of the traffic-oriented samples. 

7 3 POINT SOURCE EXPOSURES 

Several studies have been undertaken to investigate lead levels in the vicinity of various point sources 

of lead emission such as smelters or battery plants. 

By far the most complete and informative studies are 

TABLE 7-10. LEAD DUST ON AND NEAR HEAVILY 

TRAVELED ROADWAYS 

Sampling site 

Washington, DC : 

Busy intersection 

Many sites 

Chicago: 

Near expressway 

Philadelphia: 

Near expressway 

Brooklyn: 

Near expressway 

New York City: 

Near expressway 

Detroit: 

Street dust 

PhiladelphiaGutter (low exposure) 

Gutter (low exposure) 

Gutter (high exposure) 

Gutter (high exposure) 

Miscellaneous U.S. Cities: 

Highways and tunnels 

Netherlands: 

Heavily traveled roads 

Concentration 

jig Pb/g 

12820 

(4000-8000)12 

6600 

(3000-8000)13 

(900-4900)1" 

200015 

(966-1213)16 

1507 

(270-2626)" 

3262 

(280-8201)1' 

(10000-20000)18 

500019 

TABLE 7-11. LEAD CONTENT IN OR ON ROADSIDE SOIL AND GRASS 

AS A FUNCTION OF DISTANCE FROM TRAFFIC AND GRASS DEPTH IN PROFILE* 

Site and distance 

from road, m 

Lead content, iig/g dry weight 

Grass 

0-5 cm 

soil death 

5-10 cm 

soil deDth 

10-15 cm 

soil denth 

West ot U.S. 1, near Plant 

Industry Station, 

Beltsville, Md.: 

8 

16 

32 

West of southbound lanes, 

Washington-Baltimore Parkway, 

Bladensburg.Md.: 

8 

16 

32 

West of Interstate 29, 

Platte City, Mo.: 

8 

16 

32 

North of Seymour Road, 

Cincinnati, O.: 

8 

16 

32 

68.2 

47.5 

26.3 

522 

378 

164 

460 

260 

108 

416 

104 

69 

51.3 

30.0 

18.5 

21.3 

12.5 

7.5 

31.3 

26.0 

7.6 

540 

202 

140 

242 

140 

61 

150 

101 

55 

300 

105 

60 

112 

104 

55 

29 

14 

10 

98 

60 

38 

95 

66 

60 

11 

8.2 

6.1 

a

 Adapted from Lagerwerff and Specht (cited in Reference 20). 

7-7 
P.100 

TABLE 7-12. LEAD DUST IN RESIDENTIAL AREAS 

Sampling site 

Concentration, 

M9 Pn/g 

Philadelphia: 

Classroom 

Playground 

Window frames 

Boston and New York: 

House dust 

Brattleboro, Vt.: 

In home 

Birmingham, England: 

In home 

New York City: 

Middle class 

residential 

El Paso, Texas, 

Smeltertown 

dust at: 

0-1 mile 

1-2 miles 

2-3 miles 

> 4 miles 

Philadelphia: 

Urban industrial 

Residential 

Suburban 

2000 

3000 

17501? 

(1000-2000)21 

(500-900)6 

50001" 

(608-742)15 

36853 

(2800-103750)22 

2726 

(100-84000)22 

2234 

(100-29386)22 

2151 

(200-22700)22 

3855 

(929-15680)23 

614 

(293-1030)23 

830 

(277-1517)23 

those carried out by Yankel et al.24 and Landrigan et 

al.25 in the neighborhood of a smelter in Silver 

Valley, Idaho. Consequently, the data from these 

studies will be described here in some detail. Other 

studies carried out in Solano County, Calif.; Omaha, 

Neb.; El Paso, Tex.; Helena Valley, Mont.; 

Missouri; Helsinki, Finland; Meza River Valley, 

Yugoslavia; and Ontario, Canada, are summarized 

in Appendix C. Their findings are in substantive 

agreement with those of the Idaho study. 

Yankel and von Lindern24 defined five study 

areas arranged concentrically around the smelter 

and two control areas. Area 1 consisted of homes 

within 1 mile of the smelter; Area 2, 1 to 2-1/2 miles 

from smelter; Area 3, 2-1/2 to 6 miles; Area 4, 6 to 

15 miles; and Area 5, 15 to 20 miles. Environmental 

samples, including surface soil, house dust, paint, 

grass, and garden vegetables were collected at the 

homes in each area, as were blood samples from the 

resident children aged 1 to 9 years. The mean lead 

levels found in the ambient air, soil, and house dust 

all decreased with increasing distance from the 

smelter. As mentioned in Chapter 12, the blood lead 

levels of the resident children followed a similar 

pattern. 

Ambient air lead levels were measured by highvolume samplers stationed throughout the Silver 

Valley. A highly significant relationship between 

distance from the smelter and ambient air lead concentration was found, and this relationship was used 

to estimate the ambient air lead level for any location in the study area. The mean annual ambient air 

lead levels near a smelter for two different years 

(1974, 1975) are shown graphically in Figure 7-4. 

Similar results were obtained for the lead content of 

soil and house dust. As noted in Chapter 12, the 

children's blood lead levels correlate quite closely 

with ambient air lead levels, although this result 

should not be interpreted as suggesting that direct 

inhalation of lead is the principal exposure mechanism involved. One result of this pivotal study was 

that some specific emergency measures were taken in 

E 

"a 

l~~l AUG. 1974 

ES3 AUG. 1976 

1.5 T 1.8 

JLM 1 2 3 4 5 6 7 

BY AREA ISEE TEXT! 

Figure 7-4. Annual ambient air lead concentration near a 

smelter, by area, before the August 1974 and August 1975 surveys.24

 Area 1 Is within 1 mile of smelter; Area 2 Is 1 to 1-1/2 

miles from smelter; Area 3, 2-1/2 to 6 miles; Area 4, 6 to 15 

miles; and Area 5,15 to 20 miles. 

7-8