Screening Level Assessment of Arsenic

and Lead Concentrations in Glass Beads 

Used in Pavement Markings

PUBLICATION NO. FHWA-HRT-14-021 JANUARY 2014

Research, Development, and Technology

Turner-Fairbank Highway Research Center

6300 Georgetown Pike

McLean, VA 22101-2296
FOREWORD 

This report provides results of an assessment of the potential risk to human health posed by 

occupational and residential exposure to arsenic and lead concentrations found in glass beads 

used in pavement markings. The study used glass beads from samples of inventories from 

15 State transportation departments to ascertain minimum screening levels based on both 

carcinogenic and noncarcinogenic effects, with the lower value selected as the final 

recommended screening level. The recommended screening levels were determined to be 

220 ppm for arsenic, based on the child resident scenario, and 580 ppm for lead, based on the 

worker scenario. These determined screening levels are greater than the maximum content of 

200 ppm for arsenic and 200 ppm for lead in glass beads prescribed in MAP-21 (the Moving 

Ahead for Progress in the 21st Century Act); therefore, the values specified in the existing 

legislation are considered protective of health based on currently available data. 

The report is divided into three sections. The first section provides a detailed characterization of 

arsenic and lead concentrations in commercially available glass beads in current use on U.S. 

roadways, including the total, extractable, and bioaccessible arsenic and lead content in glass 

bead samples provided by State transportation departments. The second section describes the 

modeling methodology used to estimate the potential for adverse human health effects associated 

with arsenic and lead in glass beads used in pavement markings. The third section provides the 

human health screening levels for arsenic and lead in glass beads that are considered protective 

of human health. The results of the screening level assessment indicate that currently available 

products pose minimal health risk to humans while meeting retroreflective performance criteria. 

Monique R. Evans 

Director, Office of Safety 

Research and Development 

Notice 

This document is disseminated under the sponsorship of the U.S. Department of Transportation 

in the interest of information exchange. The U.S. Government assumes no liability for the use 

of the information contained in this document. 

The U.S. Government does not endorse products or manufacturers. Trademarks or 

manufacturers’ names appear in this report only because they are considered essential to the 

objective of the document. 

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve 

Government, industry, and the public in a manner that promotes public understanding. Standards 

and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its 

information. FHWA periodically reviews quality issues and adjusts its programs and processes to 

ensure continuous quality improvement. 
TECHNICAL REPORT DOCUMENTATION PAGE 

1. Report No. 

FHWA-HRT-14-021 

2. Government Accession No. 3. Recipient’s Catalog No. 

4. Title and Subtitle 

Screening Level Assessment of Arsenic and Lead 

Concentrations in Glass Beads Used in Pavement Markings 

5. Report Date 

January 2014 

6. Performing Organization Code: 

7. Author(s) 

Bryan Boulanger, Paul Carlson, Harry Fatkin, and Aditya 

Raut-Desai 

8. Performing Organization Report No. 

9. Performing Organization Name and Address 

Texas A&M Transportation Institute 

The Texas A&M University System 

College Station, Texas 77843-3135 

10. Work Unit No. 

TRAIS 

11. Contract or Grant No. 

DTFH68-09-E-00105 

12. Sponsoring Agency Name and Address 

Office of Infrastructure Research & Development 

Federal Highway Administration 

6300 Georgetown Pike 

McLean, VA 22101-2296 

13. Type of Report and Period Covered 

Final Report 

14. Sponsoring Agency Code 

15. Supplementary Notes 

Projects were performed with the cooperation and participation of the Environmental Protection Agency 

Project Title: Development of Roadway Guidance Information 

16. Abstract 

Retroreflective glass beads used in pavement markings are a critical component of highway safety. Glass beads 

meeting American Association of State Highway and Transportation Officials (AASHTO) M247 specifications 

are the current industry standard. AASHTO M247 glass beads are fabricated using reclaimed glass cullet, 

offering cost effective performance while beneficially reusing sources of industrial and commercial waste glass. 

However, reclaimed glass cullet may contain elevated levels of arsenic and lead that can be passed through to the 

final product. Concern regarding the presence of arsenic and lead in retroreflective glass bead products within the 

U.S. marketplace resulted in recently adopted legislation that sets a 200 part-per-million (ppm = 

106

 x massmetal/massbeads) limit for both arsenic and lead for beads used on U.S. roadways. While the scientific 

justification for the 200 ppm limit is not immediately clear, the proposed legislation is regarded as a good-faith 

attempt to limit the risk associated with the presence of arsenic and lead in the beads. 

This research developed a preliminary understanding of the risk associated with the presence of arsenic and lead 

in glass beads used in pavement marking systems to support decisionmaking. Researchers tested 15 samples of 

commercially available glass beads in current use on U.S. roadways from State transportation department 

stockpiles. The mean total concentration observed in the sampled beads across replicates was 71 ppm arsenic and 

54 ppm lead. Extractable and bioaccessible arsenic levels in the beads were below instrument detection limits, 

and extractable and bioaccessible levels of lead in the beads were present at less than 3.6 ppm as a maximum 

mean value. Based on laboratory-generated characterization data, field investigations, available literature data, 

and the developed model, reasonably conservative screening levels for arsenic and lead in glass beads were 

determined to be 220 ppm and 580 ppm, respectively. Lead and arsenic levels observed in glass bead samples 

provided by State transportation departments were within the determined screening limits, indicating that 

currently available products pose minimal health risk while meeting retroreflective performance criteria. 

17. Key Words 

Pavement markings, glass beads, health, human 

health, environment, risk assessment, arsenic, 

lead, retroreflectivity, extractable, bioaccessible 

18. Distribution Statement 

No restrictions. This document is available to the public 

through the National Technical Information Service, 

Springfield, VA 22161. 

19. Security Classif. (of this report) 

Unclassified 

20. Security Classif. (of this page) 

Unclassified 

21. No. of Pages 

92 

22. Price 

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized 
ii 
iii 

TABLE OF CONTENTS 

EXECUTIVE SUMMARY .......................................................................................................... 1

AIM 1: CHARACTERIZATION OF ARSENIC AND LEAD 

CONCENTRATIONS IN COMMERCIALLY AVAILABLE GLASS 

BEADS IN CURRENT USE ON U.S. ROADWAYS .............................................. 2

Assessment of Arsenic and Lead Content in Commercially Available Glass Beads ..........2

Arsenic Speciation ...............................................................................................................4

Relationship Between Retroreflectivity and Total Arsenic Content ....................................5

AIM 2: SCREENING LEVEL RISK ASSESSMENT TO ASSESS THE 

IMPACTS OF OCCUPATIONAL AND RESIDENTIAL EXPOSURE 

TO ARSENIC AND LEAD WITHIN GLASS BEADS ........................................... 6

CSEM Development for Arsenic and Lead Glass Bead Occupational and Residential 

Exposures .......................................................................................................................6

Arsenic and Lead Concentrations in Mixed Glass Bead/Soil Samples Taken From a 

Glass Bead Storage and Transfer Facility ......................................................................7

Arsenic and Lead Screening Levels Resulting in Minimum Risk From Residential 

and Occupational Exposures to the Beads .....................................................................9

Guidance to Support Decisionmaking .................................................................................9

SECTION 1. CHARACTERIZATION OF ARSENIC AND LEAD 

CONCENTRATIONS WITHIN COMMERCIALLY AVAILABLE GLASS 

BEADS IN CURRENT USE ON U.S. ROADWAYS .................................................. 11

INTRODUCTION................................................................................................................. 11

EXPERIMENTAL METHODS .......................................................................................... 12

Sampling ............................................................................................................................12

Reagents and Standards .....................................................................................................13

ICP-MS Analysis ...............................................................................................................13

Method for Determining Total Arsenic and Lead in Glass Bead Samples ........................14

Method for Determining Extractable Arsenic and Lead in Glass Bead Samples ..............15

Method for Determining Bioaccessible Arsenic and Lead in Glass Bead Samples ..........15

Method Comparison for Analysis of Total Arsenic and Lead Analysis in Glass Beads ...16

Retroreflectivity Measurements .........................................................................................16

Arsenic Speciation Determination .....................................................................................17

Estimation of Glass Bead Mass in Site Soil Samples ........................................................17

Analysis of Total Metals in Respirable Fraction of Soil Samples .....................................18

Quality Assurance/Quality Control (QA/QC) ...................................................................18

RESULTS AND DISCUSSION ........................................................................................... 19

QA/QC ...............................................................................................................................19

Total Arsenic and Lead ......................................................................................................19

Extractable Arsenic and Lead ............................................................................................21

Bioaccessible Arsenic and Lead ........................................................................................22

Comparison of Total Metal Content in Glass Beads Evaluated from Different 

Methods........................................................................................................................22
iv 

Relationship Between Total Arsenic Content in Glass Beads and the Retroreflective 

Performance of the Beads ............................................................................................26

Speciation of Metals in Leachate From Glass Beads .........................................................27

Characterization of Arsenic and Lead Content in Mixed Glass Bead and Soil Samples 

Taken From a Bead Storage and Transfer Facility ......................................................28

CONCLUSIONS ................................................................................................................... 29

SECTION 2. PROPOSED MODEL FOR THE ASSESSMENT OF HUMAN 

HEALTH RISKS ASSOCIATED WITH GLASS BEADS USED FOR 

PAVEMENT MARKING .............................................................................................. 31

INTRODUCTION................................................................................................................. 31

Background of Bead Workflow .........................................................................................32

Bead Manufacturing ...........................................................................................................36

Bead Blending ....................................................................................................................36

Bead Transport ...................................................................................................................37

Bead Storage and Transfer .................................................................................................37

Bead Application ...............................................................................................................37

Road Marking Wear and Degradation ...............................................................................38

Bead Removal/Disposal .....................................................................................................39

Human Exposures Associated With the Bead Workflow ..................................................39

EXPOSURE ASSESSMENT ............................................................................................... 40

Potential Exposure Scenarios .............................................................................................40

Occupational Exposure Scenarios ......................................................................................40

Residential Exposure Scenarios .........................................................................................40

Recreational Exposure Scenarios .......................................................................................41

Agricultural Exposure Scenarios .......................................................................................42

EXPOSURE PATHWAYS ................................................................................................... 42

Worker Exposure Pathways ...............................................................................................44

Residential Exposures ........................................................................................................45

MIGRATION PATHWAYS ................................................................................................ 45

Air Pathway .......................................................................................................................46

Groundwater Pathway ........................................................................................................46

MODELING METHODS .................................................................................................... 48

Equations Used to Calculate Exposure to Heavy Metals for Each Receptor Modeled 

in the Exposure Scenarios ............................................................................................48

Risk Evaluation and Calculation of Permissible Levels of Exposure (Cancerous and 

Non-Cancerous Human Health Screening Levels) ......................................................50

Final Bead Screening Level ...............................................................................................53

SECTION 3. MODEL-DERIVED HUMAN HEALTH SCREENING LEVELS FOR 

ARSENIC AND LEAD IN GLASS BEADS ................................................................. 55

INTRODUCTION................................................................................................................. 55

Parameter Data Available for Development of the Modeling Method ..............................55

Receptor-Specific Exposure Parameters ............................................................................55

Contaminant and Site-Specific Exposure Parameters ........................................................58
v 

Bead-Specific Exposure Parameters ..................................................................................62

Concentration of Metals in Glass Beads and Leaching Potential ......................................67

RISK EVALUATION RESULTS ....................................................................................... 72

GUIDANCE FOR DECISIONMAKING ........................................................................... 79

ACKNOWLEDGMENTS .......................................................................................................... 81

REFERENCES ............................................................................................................................ 83
vi 

LIST OF FIGURES 

Figure 1. Photo. Magnified light table image of AASHTO M247 Type I bead sample 

included in this study. ......................................................................................................... 2

Figure 2. Graph. Relationship between mean arsenic content and mean retroreflectivity of 

each sample of glass beads evaluated within this research. ................................................ 6

Figure 3. Equation. Formula for determining sample size. ........................................................... 12

Figure 4. Equation. Formula to calculate total metals content. .................................................... 14

Figure 5. Equation. Formula to calculate extractable metals content of glass beads. ................... 15

Figure 6. Equation. Formula to calculate the oral bioaccessible content of arsenic and 

lead in glass bead samples. ............................................................................................... 16

Figure 7. Equation. Formula to calculate total mass of glass beads in a representative 

sample. .............................................................................................................................. 18

Figure 8. Equation. Formula to calculate the percentage of glass beads within a site soil 

sample. .............................................................................................................................. 18

Figure 9. Graph. Total mean arsenic and lead (ppm) content in the glass beads supplied 

by the State transportation department participants. ......................................................... 21

Figure 10. Graph. Relationship between mean arsenic content and mean retroreflectivity 

of each sample of glass beads evaluated within this research. ......................................... 27

Figure 11. Photo. Application of glass beads to long line markings. ........................................... 38

Figure 12. Photo. Close-up of glass bead application to long lines. ............................................. 39

Figure 13. Diagram. Conceptual site exposure model for pavement-marking beads. .................. 43

Figure 14. Equation. Formula to calculate intake of metals due to incidental ingestion. ............. 49

Figure 15. Equation. Formula to calculate exposure concentrations for inhalation of 

metals. ............................................................................................................................... 49

Figure 16. Equation. Formula to calculate intake of metals due to ingestion of beadimpacted groundwater. ...................................................................................................... 50

Figure 17. Equation. Formula to calculate ILCR for direct contact through ingestion. ............... 51

Figure 18. Equation. Formula to calculate ILCR for inhalation exposures. ................................. 51

Figure 19. Equation. Formula to calculate CSL for protection of human health. ......................... 52

Figure 20. Equation. Formula to calculate HQ for direct contact. ................................................ 52

Figure 21. Equation. Formula to calculate HQ for inhalation. ..................................................... 52

Figure 22. Equation. Formula to calculate NCSL. ........................................................................ 52

Figure 23. Equation. Formula to calculate GW SL. ..................................................................... 53

Figure 24. Equation. Formula to calculate PEF. ........................................................................... 58

Figure 25. Equation. Formula for deriving the inverse of the mean concentration at the 

center of the source (Q/C). ................................................................................................ 59
vii 

LIST OF TABLES 

Table 1. Mean ± standard deviation of arsenic and lead content (ppm) in glass beads 

provided by State transportation department participants .................................................. 3

Table 2. Intra-method comparison for total arsenic and lead in the 15 glass bead samples ........... 4

Table 3. Arsenic speciation in leachate water in contact with beads .............................................. 5

Table 4. Mean glass bead content (by weight) and mean ± standard deviation total arsenic 

and lead (ppm) in site soil samples ..................................................................................... 8

Table 5. Screening levels for arsenic and lead from each scenario ................................................ 9

Table 6. MDL and PQL for arsenic and lead for total, extractable and bioaccessible 

metals ................................................................................................................................ 19

Table 7. Total arsenic and lead content (ppm) in glass beads provided by State 

transportation department participants .............................................................................. 20

Table 8. Total arsenic and lead content (ppm) in SRM ................................................................ 21

Table 9. Extractable and bioaccessible arsenic and lead content (ppm) in glass beads 

provided by State transportation participants ................................................................... 22

Table 10. Comparison of arsenic content (ppm) in glass beads from intra-method 

evaluation .......................................................................................................................... 24

Table 11. Comparison of lead content (ppm) in glass beads from intra-method evaluation. ....... 25

Table 12. Mean ± standard deviation retroreflectivity and total arsenic content for each 

bead sample evaluated in this research ............................................................................. 26

Table 13. Arsenic speciation observed in samples of bead leachate generated from an 

up-flow cartridge system ................................................................................................... 28

Table 14. MDL and PQL for arsenic and lead for total, extractable, and bioaccessible 

metals for storage yard soil samples ................................................................................. 28

Table 15. Glass bead content (by weight), total arsenic and lead (ppm) in site soil 

samples, and total arsenic (ppm) in respirable fraction of site soil samples. .................... 29

Table 16. Summary of total, extractable, and bioaccessible arsenic and lead in all of the 

samples analyzed in this study .......................................................................................... 30

Table 17. Bead workflow elements and release potential ............................................................. 33

Table 18. Exposure parameters for glass bead assessment due to direct exposures. .................... 56

Table 19. Calculation of particulate emission factor .................................................................... 60

Table 20. Extractable and bioaccessible fraction of arsenic and lead in bead samples 

expressed as a percentage of the total content .................................................................. 61

Table 21. Toxicity data for glass bead assessment ....................................................................... 63

Table 22. Estimates of bead loading to soil per year .................................................................... 65

Table 23. Estimated glass bead application and loss rate for line applications. ........................... 66

Table 24. Summary of statistics for bead analysis ........................................................................ 69

Table 25. Summary of TTI/TAMU leaching studies for arsenic—December 2012 .................... 70

Table 26. Summary of TTI/TAMU leaching studies for lead—December 2012 ......................... 71

Table 27. Summary of glass bead risks for arsenic ...................................................................... 73

Table 28. Estimated groundwater risk for arsenic ........................................................................ 74

Table 29. Summary of glass bead screening levels for arsenic .................................................... 76

Table 30. Calculations of adult blood lead concentrations ........................................................... 77

Table 31. Calculations of adult lead screening levels ................................................................... 78
LIST OF ABBREVIATIONS 

AAS Atomic Absorption Spectroscopy 

AASHTO American Association of State Highway and Transportation Officials 

ACS American Chemical Society 

AGBMA American Glass Bead Manufacturing Association 

ALM Adult Lead Model 

ATSDR Agency for Toxic Substances and Disease Registry 

ATV All-Terrain Vehicle 

BDL Below the Detection Limit 

BQL Below the Quantitation Limit 

CFR Code of Federal Regulations 

CSEM Conceptual Site Exposure Model 

CSL Cancer Screening Level 

DAF Dilution-Attenuation Factor 

DI Deionized 

EPA Environmental Protection Agency 

FDOT Florida Department of Transportation 

FHWA Federal Highway Association 

FP-XRF Field-Portable XRF 

GW SL Groundwater Screening Level 

HI Hazard Index 

HPLC High Performance Liquid Chromatography 

HQ Hazard Quotient 

ICP-MS Inductively Coupled Plasma-Mass Spectrometry 

IEUBK Integrated Exposure Uptake Biokinetic Model 

ILCR Incremental Lifetime Cancer Risk 

KOH Potassium Hydroxide 

MAP-21 Moving Ahead for Progress in the 21st Century Act 

MDL Method Detection Limit 

NCSL Non-Carcinogenic Screening Level 

NIST National Institute of Standards and Technology 

NJIT/RU New Jersey Institute of Technology/Rowan University 

NRMRL National Risk Management Research Laboratory 

PEF Particulate Emission Factor 

PNNL Pacific Northwest National Laboratory 

PQL Practical Quantitation Limit 

QA/QC Quality Assurance/Quality Control 

RSL Regional Screening Level 

SRM Standard Reference Material 

TAMU Texas A&M University 

TFHRC Turner-Fairbanks Highway Research Center 

TTI Texas A&M Transportation Institute 

UCL95% 95-Percent Upper Confidence Limit 

XRF X-Ray Fluorescence 
1 

EXECUTIVE SUMMARY 

Retroreflective pavement markings are a critical component of highway safety. Although many 

types of retroreflective elements can be added to pavement-marking systems, glass beads 

meeting the American Association of State Highway and Transportation Officials (AASHTO) 

M247 specification are the industry standard for providing cost effective retroreflectivity 

performance. Currently, AASHTO M247 glass beads are created from reclaimed glass cullet 

consisting of recycled glass from industrial and commercial sources. This reclaimed glass cullet 

feed may contain heavy metals, such as arsenic and lead, which can be passed through to the 

glass bead products used throughout the transportation industry. Based on the potential risk 

associated with the presence of arsenic and lead in the beads, MAP-21—the Moving Ahead for 

Progress in the 21st Century Act (Public Law 112-141) signed into law on July 6, 2012—

adopted a 200 part-per-million (ppm = 106

 x massmetal/massbeads) limit of both arsenic and lead in 

commercially available beads used on domestic roadways. 

This research developed a preliminary understanding of the risk associated with the presence of 

arsenic and lead in glass beads used in pavement-marking systems to support decisionmaking. 

To meet the project goal, two aims were established. The first was to characterize arsenic and 

lead concentrations in commercially available glass beads in current use on U.S. roadways. This 

aim was achieved by 1) evaluating the total, extractable, and bioaccessible arsenic and lead 

content in glass bead samples provided by State transportation departments; 2) determining the 

speciation of arsenic within leachate from beads; and 3) evaluating the relationship between total 

arsenic content in glass beads and the retroreflective performance of the beads. 

The second aim was to perform a screening level risk assessment to assess the impacts of 

occupational and residential exposure to arsenic and lead within glass beads. This aim was 

achieved by 1) developing a conceptual site exposure model (CSEM) for occupational and 

residential exposures to arsenic and lead in glass beads; 2) analyzing arsenic and lead 

concentrations in mixed glass bead/soil samples taken from a glass bead storage and transfer 

facility; and 3) estimating the arsenic and lead screening levels resulting in minimum risk from 

residential and occupational exposures to the beads. 

The principal findings of this research are summarized by aim within this executive summary. 

Details of the methods, results, and outcomes of each aim’s research evaluations are provided in 

the individual sections of this report. The sections include the following: 

 Section 1: Characterization of arsenic and lead concentrations with commercially 

available glass beads in current use on U.S. roadways (Aim 1 Research). 

 Section 2: Proposed model for the assessment of human health risks associated with glass 

beads used for pavement marking (Aim 2 Research). 

 Section 3: Model-derived human health screening levels for arsenic and lead in glass 

beads (Aim 2 Research). 
2 

Section 3 of the report concludes with recommended guidance to support decisionmaking and 

recommendations for safe storage, handling, application, and removal of glass beads used in 

pavement markings. These recommendations are also presented in this executive summary. 

AIM 1: CHARACTERIZATION OF ARSENIC AND LEAD CONCENTRATIONS IN 

COMMERCIALLY AVAILABLE GLASS BEADS IN CURRENT USE ON U.S. 

ROADWAYS 

Assessment of Arsenic and Lead Content in Commercially Available Glass Beads 

Methods 

Samples of AASHTO M247 glass beads were requested from State transportation department 

inventories in current use in pavement-marking operations. These samples of glass beads 

(see figure 1) were shipped directly to Texas A&M University Transportation Institute (TTI) in 

quart- to gallon-size resealable plastic bags packaged in boxes. After all the glass beads were 

received and cataloged, 15 of the received Type I samples were randomly selected for analysis. 

Subsamples weighing 100 g of each sample were collected into new resealable, zipper bags and 

renamed by a technician to blind the laboratory staff running the sample extractions and analysis 

from the identity and location of the provided samples. 

Figure 1. Photo. Magnified light table image of AASHTO M247 Type I bead sample 

included in this study. 

Three subsamples from each of the 15 randomly selected bead samples were used to determine 

the total, extractable, and bioaccessible fractions of arsenic and lead in the beads. The total 

metals digestion was performed following the Pacific Northwest National Laboratory (PNNL) 

Potassium Hydroxide (KOH) Fusion digestion method, extractable metals extraction was 

performed following Environmental Protection Agency (EPA) Method 3050B, and the 

bioaccessible extraction was performed according to the in-vitro oral bioaccessibilty method.(1)

The resulting digestion and extraction solutions were analyzed by inductively coupled plasmamass spectrometry (ICP-MS) according to EPA Method 6020A. 

Additional studies were performed to determine the comparability of four methods used to assess 

total arsenic and lead contents in the glass beads. These four methods were: 1) the PNNL KOH 

fusion digestion followed by ICP-MS analysis, 2) EPA Method 3052 (microwave assisted 

hydrofluoric acid digestion) followed by ICP or atomic absorption spectroscopy (AAS) analysis 
3 

to evaluate metals in siliceous solids, 3) bench-top XRF (X-ray fluorescence), and 4) FieldPortable XRF (FP-XRF).(2, 3) A National Institute of Standards and Technology (NIST) standard 

for metals in glass, Standard Reference Material (SRM) 612, was also analyzed for total metals 

using KOH fusion and EPA Method 3052. 

Findings 

Table 1 provides the mean total, extractable, and bioaccessible arsenic and lead content 

measured in the 15 samples of glass beads. Lead and arsenic were measured in all 15 samples of 

glass beads following total digestion of the beads at a mean concentration of 71 and 54 ppm, 

respectively. The mean arsenic and lead content observed in the beads were below the currently 

proposed limit of 200 ppm. However, large variability in total arsenic and lead content was 

observed between replicates of the same bead sample. Repeat analysis of both the replicates and 

of additional subsamples within the batch reproduced the variability. Analysis of NIST 

SRM 612, however, resulted in mean measured concentrations of arsenic and lead at 94 percent 

and 86 percent of the expected value with minimal variability between replicates. Therefore, the 

observed variability of arsenic and lead in the beads was determined to be caused by actual 

variability of metals content within the supplied samples. 

Table 1. Mean ± standard deviation of arsenic and lead content (ppm) in glass beads 

provided by State transportation department participants. 

Bead 

Total (ppm) Extractable (ppm) Bioaccessible (ppm) 

Arsenic Lead Arsenic Lead Arsenic Lead 

AA 75 ± 27 79 ± 50 BDL 0.38  0.1 BDL BQL 

AC 11 ± 8 22 ± 19 BDL 0.74  0.5 BDL 3.6  5.4 

BD 65 ± 36 67 ± 58 BDL 0.21  0.1 BDL BQL 

BE 55 ± 24 89 ± 62 BDL 0.70  0.3 BDL BQL 

BI 53 ± 25 100 ± 71 BDL 3.29  1.0 BDL 1.7  2.4 

DA 62 ± 31 176 ± 154 BDL 0.252x10-3 BDL BQL 

DB 70 ± 40 161 ± 186 BDL BDL BDL BDL 

DC 82 ± 65 199 ± 246 BDL BQL BDL BQL 

DD 61 ± 27 3 ± 7 BDL BDL BDL BDL 

EA 51 ± 30 13 ± 13 BDL BDL BDL BDL 

FH 50 ± 20 72 ± 36 BDL 0.31  0.1 BDL 0.190.01 

GA 49 ± 34 10 ± 9 BDL BDL BDL BDL 

GB 52 ± 22 38 ± 33 BDL BDL BDL BDL 

GC 45 ± 15 15 ± 6 BDL BDL BDL BDL 

GD 35 ± 37 28 ± 26 BDL BDL BDL BDL 

ppm = parts per million 

BDL = below detection limit (< 0.07 g/g for arsenic, < 0.004 g/g for lead) 

BQL = below quantification limit (< 0.1 g/g for arsenic and lead) 

μ μ

μ
4 

The extractable and bioaccessible arsenic and lead contents were significantly lower than the 

total arsenic and lead content of the beads. Reportable levels of arsenic were not observed in 

either the extractable metal or bioaccessible metal extraction solutions in any of the samples. 

When observed, mean concentrations of 0.8 ppm for extractable lead and 1.8 ppm for 

bioaccessible lead were measured. However, lead was only present in 7 of the 15 extractable 

metal solutions and in 3 of the bioaccessible metal solutions. The results of the arsenic and lead 

analysis indicate that while both metals are present in the glass matrix within the sampled beads 

(total metal digestions), the levels of arsenic and lead that leave the matrix under environmental 

(extractable metals by Method 3050B) or intestinal (oral bioaccessibility method) exposures are 

significantly lower. 

The mean arsenic and lead content returned by each of the four evaluated methods across the 

15 bead samples are shown in table 2. Although results of the intra-method comparison for 

analysis of total arsenic and lead in the glass bead samples were not in agreement for the 

samples, agreement was achieved between the results of KOH fusion and EPA Method 3052 for 

the NIST SRM 612 standard. While a systematic approach was used to evaluate the cause of the 

observed difference in the samples but not in the control, method or instrumental errors that 

could explain the observed difference were not identified. Therefore, because KOH fusion gave 

the overall most conservative (highest) estimate of arsenic and lead content observed in the 

beads, the authors report KOH fusion results in this technical report to represent a conservative 

(upper value) estimate of the total arsenic and lead content in the bead samples.

Table 2. Intra-method comparison for total arsenic and lead in the 15 glass bead samples. 

Method 

Arsenic Lead 

No. of Samples 

with 

Measurable 

Arsenic 

Mean Content 

When Present 

(ppm) 

No. of Samples 

with 

Measurable 

Arsenic 

Mean Content 

When Present 

(ppm) 

Portable XRF 2 of 15 8.5 3 of 15 15 

Bench-top XRF 6 of 15 1.0 10 of 15 15 

EPA Method 15 of 15 1.3 15 of 15 8.2 

KOH Fusion 15 of 15 51 15 of 15 68 

XRF = X-ray fluorescence 

EPA = Environmental Protection Agency 

KOH = potassium hydroxide 

Arsenic Speciation 

Speciation of arsenic in water has a significant impact on the toxicity of arsenic in aqueous 

systems. Because the beads are used and stored in locations where they could come into contact 

with rainfall, there was interest in determining the resulting speciation of arsenic within bead 

leachate for future risk assessments. 

Methods 

Subsamples of three glass bead samples (AA, DC, and EA) were placed in an up-flow cartridge 

reactor, and laboratory-prepared water (pH of 7) was passed through the cartridges at a flow rate 
5 

of 30 mL/h. Cartridge effluents were sampled after 1 h, preserved with 1 percent hydrochloric 

acid, and refrigerated until they were analyzed. Speciation was achieved using a highperformance chromatograph with a reversed phase column operating within a binary mobile 

phase coupled to an ICP-MS. A complete description of the analytical method for speciation can 

be found in Section 1 of this report. 

Findings 

The speciation analysis of arsenic revealed the presence of both arsenite (As3+) and arsenate 

(As5+) as the two predominant species of arsenic in solution. Table 3 presents the results for the 

analysis. While total arsenic levels (As3+ + As5+) in the pure leachate exceeded the 10 g/L 

drinking water maximum contaminant level for arsenic, under environmental conditions, the 

impact of leachate on existing groundwater or surface water reserves would be minimal for these 

samples because of dilution. 

Table 3. Arsenic speciation in leachate water in contact with beads. 

Sample

As3+ 

( g/L) 

As5+ 

( g/L) 

AA 3.02 8.92 

DC ND 14.7 

EA 1.42 10.6 

ND = Non-detectable 

Relationship Between Retroreflectivity and Total Arsenic Content 

The relationship between arsenic content and retroreflective performance was evaluated because 

of historical use of arsenic within glass production as a high-temperature oxidant for removing 

imperfections in glass. The researchers were curious to evaluate whether higher arsenic levels 

would correlate to higher retroreflectivity measurements. 

Methods 

Retroreflective performance measurements were conducted by creating pavement markings 

containing glass beads on metal sheets. Immediately following paint application, glass beads 

were applied on the surface using a bead dispenser for even, but random and dispersed, 

application on the paint. After curing, a Delta LTL-X retroreflectometer was used to measure the 

retroreflectivity of the pavement-marking samples. Pearson’s product moment correlation 

coefficient (r) was determined to assess the direction and the strength of the correlation between 

the arsenic content of the beads and their retroreflective performance. 

Findings 

Figure 2 shows the relationship between retroreflectivity and total mean arsenic content within 

the glass beads for all 15 samples. The correlation r for the dataset was determined to be 0.564, 

suggesting a positive moderate correlation may exist between the arsenic content and 

retroreflective performance. However, additional samples should be analyzed to determine 

whether a correlation actually exists. In this study, the range of mean arsenic contents was 

μ

μ μ
6 

limited to between 15 and 88 ppm. The retroreflectivity data, however, demonstrate that suitable 

performance can be achieved at low arsenic levels within the beads. 

Figure 2. Graph. Relationship between mean arsenic content and mean retroreflectivity of 

each sample of glass beads evaluated within this research. 

AIM 2: SCREENING LEVEL RISK ASSESSMENT TO ASSESS THE IMPACTS OF 

OCCUPATIONAL AND RESIDENTIAL EXPOSURE TO ARSENIC AND LEAD 

WITHIN GLASS BEADS 

CSEM Development for Arsenic and Lead Glass Bead Occupational and Residential 

Exposures 

The conceptual site exposure model was developed to assess the workflow of beads within their 

product lifecycle, perform a human health exposure assessment based on bead workflow, 

develop exposure assessment models to evaluate screening level concentrations in glass beads 

that are protective of human health, and identify existing sources of data for use within the 

developed modeling. CSEM development was based on field observation of human interactions 

with the glass beads during manufacturing, transportation, storage, application, and disposal of 

old marking residues. All field observations were conducted in an arid environment during 

warm, dry, and low wind conditions (< 15 mi/h). Although observations were made in an arid 

environment, this assessment considers a range of environmental conditions. Additional 

information used in this assessment was obtained through interviews with individuals involved in 

the glass manufacturing and highway marking industries. 
7 

Based on the completed exposure assessment, the proposed risk assessment model focused on 

three specific exposure scenarios: 

 Scenario 1—Worker: roadway marking crew employee exposed through incidental 

ingestion, dermal contact, and inhalation of fugitive dust emissions. 

 Scenario 2—Adult Resident: resident living in close proximity to an active bead storage 

yard or on top of a former storage yard exposed through ingestion of contaminated 

drinking water, incidental ingestion, dermal contact, and inhalation of fugitive dust 

emissions. 

 Scenario 3—Child Resident: resident living in close proximity to an active bead storage 

yard or on top of a former storage yard exposed through ingestion of contaminated 

drinking water, incidental ingestion, dermal contact, and inhalation of fugitive dust 

emissions. 

The proposed modeling framework focuses on developing quantitative measures to evaluate the 

screening level concentrations of arsenic and lead in glass beads that result in an increased risk. 

The quantitative assessment requires calculation of two components: 1) the level of metal uptake 

or air concentration as a function of each individual exposure route, and 2) the permissible level 

of exposure (screening level) due to either cancerous or non-cancerous end points considering 

the combined intake from the multiple routes of exposure affecting a single receptor. All 

calculations are based on EPA guidance documents addressing human exposure to soil, water, 

air, and food.(4) The contaminant exposures calculated for each receptor, environmental medium, 

and pathway combination are the basis for estimating the potential risk or hazard to exposed 

individuals. 

The full list of equations used to determine the intake of metals applicable to every exposure 

scenario and the calculations used to evaluate the cancer and non-cancerous human health 

screening levels for direct contact, inhalation, and ingestion of bead-impacted groundwater are 

found in section 2. The proposed model (presented in section 2) was externally peer-reviewed 

prior to use of the model to predict screening level concentrations of arsenic and lead found in 

section 3. 

Arsenic and Lead Concentrations in Mixed Glass Bead/Soil Samples Taken From a Glass 

Bead Storage and Transfer Facility 

During the CSEM model development, the mass percentage of beads in soil at a storage facility 

and the resulting arsenic and lead content within mixed glass bead/soil samples was determined 

to be an important parameter. Initial assumptions used in the model included the assumption that 

all of the soil in a bead storage facility was composed of spilled beads with a concentration 

equivalent to the highest measured arsenic and lead content. To arrive at a more realistic 

conservative assessment, five samples of soil from a bead storage facility where beads had been 

stored and transferred for more than 20 years were collected and analyzed for bead mass content. 

The resulting arsenic and lead concentration in the mixed sample were determined. A control soil 

sample selected from a nearby vacant lot was used for comparison. 
8 

Method 

Surface soil samples were collected, weighed, and then sieved on U.S. Sieve #30, #40, #50, and 

#80. The fraction of soil retained on each sieve was weighed and kept separately. An inclined 

plane made of a strip of Plexi-Glass® and a light table was used to manually separate glass 

beads, based on roundness, color, and translucence, from a representative portion of each 

fraction of soil. The beads separated from each fraction were then weighed. A portion of the 

original, non-sieved sample was digested following the PNNL KOH method followed by ICPMS analysis of the digested solutions according to EPA Method 6020A. 

Findings 

Table 4 lists the average glass bead content in site soil samples collected from a bead storage and 

transfer facility (along with a nearby vacant field). The difference in the content of glass beads is 

owing to different sampling locations within the facility. The glass bead soil content varied from 

19 percent to a maximum of 78 percent, with an average bead to soil content of 42 percent. 

Reportable levels of arsenic were observed in only two of the five site samples. However, lead 

was observed in all samples and in the control at concentrations ranging from 11 ppm to 

120 ppm. The concentrations observed in the mixed bead samples are in excess of the 

background concentration by 33 percent to 400 percent. While it may be reasonable to assume 

that elevated arsenic and lead content in the storage facility samples are associated with the 

presence of glass beads, the glass bead content in field site soil sample does not correlate with 

the metal content in site soil samples. Based on the historical use at this site, the initial 

assumption that site soils would have higher concentrations of both arsenic and lead does not 

appear to be valid. 

Table 4. Mean glass bead content (by weight) and mean ± standard deviation total arsenic 

and lead (ppm) in site soil samples. 

Sample 

ID 

Glass Bead 

Content in 

Soil (Weight 

Percent) 

Total Arsenic 

(ppm) 

Total Lead 

(ppm) 

Sample 1 25 2.9 ± — 120 ± 160 

Sample 2 20 BDL 40 ± 19 

Sample 3 48 7.6 ± 0.5 35 ± 2.1 

Sample 4 41 BDL 14 ± 11 

Sample 5 78 BDL 12 ± 5.1 

Control 0 BDL 24 ± 12 

ppm = parts per million 

BDL = below detection limit (< 0.07 g/g for arsenic, < 0.001 g/g for lead) 

 — indicates only one viable data point 

μ μ
9 

Arsenic and Lead Screening Levels Resulting in Minimum Risk From Residential and 

Occupational Exposures to the Beads 

Reasonably conservative screening levels for protection of human health risk from glass bead 

exposures were determined for each evaluated exposure scenario identified during field 

investigations of bead workflow. Exposure pathways included in the model were incidental 

ingestion of beads, incidental inhalation of beads, and ingestion of bead contaminated 

groundwater. The potential for leaching of arsenic to groundwater was evaluated using 

laboratory-generated characterization data. Lead and arsenic toxicity data used in the risk 

evaluation are from the Risk Assessment Information System maintained by the Oak Ridge 

National Laboratory. 

The developed model indicates that while the majority of risk is associated with the ingestion 

pathway, current concentrations in the beads are within EPA’s acceptable risk range of E-6 to 

E-4. Therefore, there is a low likelihood of adverse human health effects due to exposure to 

beads released to the environment. Table 5 presents the bead screening levels for arsenic and 

lead based on the evaluated exposure scenarios for all combined pathways. The presented results 

assume a source that is 42-percent beads diluted with soil (based on field-analyzed samples at a 

bead storage facility). Screening levels are generated based on both carcinogenic and noncarcinogenic effects, with the lower value selected as the final screening level. The 

recommended screening levels were determine to be 220 ppm for arsenic based on the child 

resident scenario and 580 ppm for lead based on the worker scenario. 

Table 5. Screening levels for arsenic and lead from each scenario. 

Scenario 

Screening Level (ppm) 

Arsenic Lead 

Adult Resident 

 Carcinogenic 620 NA 

 Non-cancer 12,000 580 

Child Resident 

 Carcinogenic 220 NA 

 Non-cancer 1,700 1,050 

Worker 

 Carcinogenic 1,000 NA 

 Non-cancer 17,000 580 

ppm = parts per million 

NA = not applicable

Note: Bolded values represent the most conservative screening levels and 

are the recommended screening levels for arsenic and lead in glass beads. 

Guidance to Support Decisionmaking 

The determined screening levels for arsenic and lead are above the current maximum content of 

200 ppm arsenic and 200 ppm lead adopted in legislation. Therefore, the existing legislation is 

determined to be protective of human health when all currently available data are considered. In 

addition, based on laboratory and field sample characterization completed in this study, the mean 
10 

arsenic and lead concentrations observed in the beads were below the 200 ppm limit currently 

adopted in legislation. Therefore, the proposed limit should not present a hurdle to using existing 

beads already in the commercial markets for pavement-marking purposes. 

Although current risk levels are minimal, field observations of bead workflow processes did 

identify easy-to-implement practices that would further reduce exposure. In the occupational 

setting, employees were observed handling the beads without gloves or masks. Concern was 

raised during the visits and during the model peer-review process that employees might be 

exposed to high levels of silica from bead dust that could lead to silicosis. Wearing gloves and 

respirators to protect against potential silica exposures would have the added benefit of reducing 

exposure to arsenic and lead. 

The model also predicted potential concern regarding the impact of bead storage facilities on 

residential groundwater due to leaching of arsenic and lead from the beads that may occur within 

some climates. Current practices of bead storage prevent rainfall from leaching arsenic and lead 

from stored beads to groundwater. Efforts to reduce bead spillage during transfer would also 

reduce the likelihood that bead-contaminated media could affect groundwater. Existing locations 

with long-term histories of bead (and or cullet) storage and transfer may present a challenge to 

groundwater where shallow groundwater tables are present. 

Although application of the beads does result in bead loss to the surrounding environment, long 

line applications in which bead loss may reach up to 30 percent under poor application practices 

or conditions does not appear to present a risk to human health or the environment. During long 

line applications (roadway center and edge line markings), bead loss occurs over a long distance 

and the beads quickly scatter. Long line application is also performed using bead drop equipment 

in a manner that does not expose employees to the lost beads. Short line applications (cross 

walks and intersections), however, do result in greater worker exposure and higher 

concentrations of spilled beads accessible to the general public. Efforts should be made to reduce 

excess bead loss during short line applications. Employees putting down beads should wear 

gloves to reduce exposure, and beads should be dropped so that the majority land on the binder 

(paint, thermoplastic, or epoxy). In particular, efforts should be made to reduce excess bead loss 

in short line applications in locations with curbs and gutters because of the potential slipping 

hazard. 

Line removal presents a separate set of potential risks. To minimize exposure to arsenic and lead 

from glass beads during marking removals, employees should wear gloves, eye protection, and 

respirators if they are performing removal techniques that generate dust. Grinding, sand-blasting, 

or water blasting systems used to remove the lines should be equipped with vacuum recovery 

systems to reduce dust removal. Additional investigations into dust exposures during marking 

removal are advised. 

As a final comment, arsenic and lead in glass beads may be a minor concern for environmental 

health and safety compared with other components in pavement-marking systems. A thorough 

review of the risk posed by residential and occupational exposures to components in other 

marking systems is advised to alleviate potential concerns for environmental and worker safety. 

 
11 

SECTION 1. CHARACTERIZATION OF ARSENIC AND LEAD CONCENTRATIONS 

WITHIN COMMERCIALLY AVAILABLE GLASS BEADS IN CURRENT USE ON U.S. 

ROADWAYS 

INTRODUCTION 

Improving the visibility of pavement markings can significantly contribute to reducing highway 

mortality owing to lane departures. For pavement markings to be visible to the drivers under 

limited visibility conditions, they must be retroreflective. Retroreflective pavement markings 

reflect the incoming light from vehicle headlamps back toward the vehicle. Pavement markings, 

which would otherwise scatter light from vehicles, are made retroreflective by embedding 

retroreflective elements in the marking material. Currently, glass beads complying with 

AASHTO M247 regulations are the industry standard for providing cost effective retroreflective 

performance. 

The most common feed material used in the production of AASHTO M247 glass beads is 

reclaimed glass cullet. Reclaimed glass cullet commonly consists of glass from residential 

glassware, such as cathode-ray tubes from televisions, windowpanes, stained glass, incandescent 

bulbs, and other industrial and commercial sources. This reclaimed glass cullet feed may contain 

heavy metals, such as lead and arsenic, that can be passed through to the final recycled glass 

bead products used throughout the transportation industry. Arsenic and lead are naturally 

occurring metals present in mineral-based materials used to make glass and were also added to 

glass to achieve specific industrial purposes such as improved clarity or performance. 

Two existing studies have previously reported on the composition and leachability of heavy 

metals found in glass beads. The New Jersey Department of Transportation/Federal Highway 

Association (FHWA) sponsored leaching study carried out by New Jersey Institute of 

Technology/Rowan University (NJIT/RU) and the American Glass Bead Manufacturing 

Association (AGBMA) funded study carried out at Texas A&M University (TAMU)/TTI each 

examined heavy metal contents present in glass beads.(5, 6) Both studies confirmed the presence 

of heavy metals within glass bead samples and quantified the total metal content and leached 

amount of metal by conducting leaching studies. While the two previous studies report the 

composition and leachability of heavy metals in glass beads, the representativeness of the sample 

sets examined within each study in comparison with the metals content of samples actually in 

use within commerce was unknown. Therefore, this research aimed to determine the arsenic and 

lead composition of beads currently in use on roadways with the United States. 

The confirmed presence of metals in glass beads has raised concern regarding the potential risk 

of heavy metals in glass beads on human health and the environment. Particular concern focuses 

on the occupational safety of workers who are subject to exposure to glass beads during 

manufacturing, transport, and application of glass beads to pavement markings. Based on the 

potential risk associated with the presence of arsenic and lead in the beads, MAP-21: the Moving 

Ahead for Progress in the 21st Century Act (Public Law 112-141) signed into law on July 6, 

2012, adopted 200 ppm arsenic and 200 ppm lead as the maximum permissible levels allowable 

in glass bead formulations used within the industry. Additional legislation is also proposed 

within several states to limit maximum amounts of arsenic and lead in glass beads. 
12 

This study was conceived and carried out to begin a formalized, but preliminary, assessment of 

risk associated with occupational and residential exposures to arsenic and lead in glass beads 

used to provide retroreflectivity to pavement markings. This goal of this research component was 

to characterize arsenic and lead concentrations of commercially available glass beads in current 

use on U.S. roadways. To meet the goal, four objectives were explored: 

 Objective 1—Evaluate the total, extractable, and bioaccessible arsenic and lead content 

in glass bead samples provided by State transportation departments. 

 Objective 2—Evaluate the relationship between total arsenic content in glass beads and 

the retroreflective performance of the beads. 

 Objective 3—Determine the speciation of arsenic within leachate from beads. 

 Objective 4—Analyze arsenic and lead concentrations of mixed glass bead/soil samples 

taken from a glass bead storage and transfer facility. 

The team conducting the research consisted of Bryan Boulanger, formerly of TAMU’s 

Department of Civil Engineering, and Paul Carlson from TTI. Dr. Boulanger was the lead for 

Objectives 1, 3, and 4, and served as the overall project coordinator and point of contact. 

Dr. Carlson was the lead for Objective 2. Project formulation also included contributions from 

Dr. Tolyamat from the EPA’s National Risk Management Research Laboratory (NRMRL), 

Dr. Taylor from EPA’s Office of Solid Waste, and Mr. Andersen of FHWA’s Turner-Fairbank 

Highway Research Center (TFHRC). This research was carried out in Dr. Boulanger’s 

laboratories at TAMU and in Dr. Carlson’s laboratories at TTI. An intra-method comparison for 

total metals analysis among TAMU, EPA, and FHWA research laboratories was also conducted 

as part of Objective 1. The three laboratories involved included Dr. Boulanger’s laboratories at 

TAMU, Dr. Tolyamat’s Laboratories at NRMRL’s Center Hill Facility, and Mr. Arnold’s 

Laboratories at FHWA’s TFHRC. The research covered in this report was conducted between 

April 1, 2010, and June 30, 2012. 

EXPERIMENTAL METHODS 

Sampling 

A total of 15 samples of AASHTO M247 Type I beads acquired from State transportation 

departments were evaluated as part of this study. The sample size used in this study was 

calculated at the 95 percent confidence interval based on the sample size determination formula 

provided in figure 3, where n is the sample size, is the underlying standard deviation of metals 

concentrations in the beads based on past analysis, and B is the specified error of estimation. 

Figure 3. Equation. Formula for determining sample size. 



nൌ ൤1.96σ

B ൨

2
13 

The underlying standard deviation of metals concentrations for this estimation was taken from 

previous analysis of arsenic content in glass beads during the TAMU/TTI AGBMA funded 

study. The mean ± standard deviation arsenic contents from Batch 1 and Batch 3 beads in this 

previous study were 83.3 ± 1.42 ppm and 393 ± 6.93 ppm, respectively. Based on an allowable 

margin of error of 1 percent, the corresponding sample sizes were determined to be 11.2 and 12, 

respectively. A final selected sample size of 15 satisfied the statistical criteria based on 

95 percent confidence interval and 1 percent allowable error. 

Based on the final selected sample size, Dr. Carlson made the request for samples from his 

contacts within State transportation departments. All samples from the transportation 

departments were shipped directly to Dr. Carlson in quart- to gallon-size resealable zipper bags 

packaged in boxes. Each of the samples received were cataloged upon receipt. Once all the 

samples had arrived, a team member collected the samples, took out 100 g subsamples of each 

bulk supplied material, and renamed the samples to blind the laboratory staff running the sample 

extractions and analysis from the identity and location of origin of the provided samples. 

Three subsamples from each of the 15 bead samples were used to determine the total, 

extractable, and bioaccessible contents of arsenic and lead in the beads. KOH fusion digestion 

was carried out to assess the total arsenic and lead content, EPA Method 3050B was carried out 

to assess the extractable arsenic and lead content, and the in-vitro oral bioaccessibility method 

was used to assess the bioaccessible arsenic and lead content in the beads. The resulting solutions 

from each of these methods were analyzed by ICP-MS. Because the ICP-MS analytical method 

is common throughout, it is detailed first below, followed by the three processing methods. 

Reagents and Standards 

Deionized (DI) water was produced in the laboratory using a Barnstead NanopureTM DI water 

system. DI water was used for preparing reagents, generating standards, and conducting 

experiments. Specpure® analytical standards for arsenic and lead were purchased from Alfa 

Aesar. Nitric acid (American Chemical Society (ACS) grade), hydrochloric acid (ACS grade), 

potassium nitrate (ACS grade), potassium hydroxide (ACS grade), and sodium hydroxide (ACS 

grade) were purchased through Fisher Scientific. Oxalic acid (ACS grade) was purchased from 

VWR International. Glycine (98.5–101.5 percent) and hydrogen peroxide (ACS grade, high 

purity) were purchased from JT Baker. SRM 612—Trace Elements in a Glass Matrix, was 

purchased from NIST. 

ICP-MS Analysis 

Analysis was carried out as described in EPA Method 6020A: ICP-MS. An ELAN® DRC II 

ICP-MS system housed within TAMU’s Center for Chemical Characterization was used to 

quantify the concentration of arsenic and lead in solutions produced from the total metal, 

extractable metal, and orally bioaccessible metal extractions. All samples were preserved in 

1 percent (volume/volume) nitric acid and kept at 4 °C while in storage. Samples were allowed 

to come to room temperature before analysis. 

The Method Detection Limit (MDL) for each of the eight heavy metals using ICP-MS was 

determined according to 40 Code of Federal Regulations (CFR) Appendix B to Part 136, 
14 

“Definition and Procedure for the Determination of the Method Detection Limit.” The MDL is 

the minimum concentration of a substance that can be measured and reported with 99 percent 

confidence that the analyte concentration is greater than zero. The practical quantitation limit 

(PQL) was then set based on the greater of the MDL or the lowest analyzed calibration standard. 

A four-point calibration was used to quantitate analytes in a range from 1 to 100 g/L. Samples 

in which the analytes were present at concentrations above the highest calibration standard were 

diluted to within the calibration range and reanalyzed. 

Method for Determining Total Arsenic and Lead in Glass Bead Samples 

The KOH fusion process (procedure number APSL-03) developed by the PNNL was used to 

dissolve a portion of the subsampled beads for total bulk bead metals content analysis.(2) In this 

procedure, recycled glass beads from each batch were crushed using a porcelain mortar and 

pestle and passed through a #140 U.S. mesh sieve (< 100 m). Researchers weighed 

0.25 ± 0.075 g of the crushed beads and transferred them into a 7 mL carbon crucible. 

Approximately 1.8 ± 0.4 g of potassium hydroxide and 0.2 ± 0.1 g of potassium nitrate were 

added to the crushed beads, and the contents were mixed by swirling. The crucible and its 

contents were heated using a Bunsen burner until the mixture melted and all visible 

effervescence subsided. Allowing all the effervescence to subside was a minor modification to 

the original method that allowed for reproduction of the arsenic and lead concentrations in the 

SRM.(2) The digestate was then allowed to cool to room temperature. 

Approximately 5 mL of DI water was added to dissolve the cake-like crystalline melt, and the 

resulting solution was transferred to a 1,000 mL volumetric flask. Additional 5-mL aliquots of 

DI water were repeatedly added to the crucible until all of the melt was dissolved. The solution 

in the flask was diluted to approximately 500 mL total volume using DI water and acidified 

using 25 ± 5 mL of concentrated nitric acid to dissolve any precipitate. Researchers added 

0.3 ± 0.1 g of oxalic acid crystals to dissolve any additional observed precipitate that was not 

dissolved with the nitric acid addition. The flask contents were then filled to 1,000 mL mark with 

DI water. A 15-mL aliquot of the sample was extracted from the flask, labeled appropriately, and 

stored at 4 °C until ICP-MS analysis. 

The total metals content of glass beads was calculated from the measured concentrations using 

the formula in figure 4: 

Figure 4. Equation. Formula to calculate total metals content. 

Where: 

C = concentration of metal in fusion solution, g/L. 

 = volume of solvent, L. 

M = mass of beads, g. 

μ

μ

Total Metal ቆ

μgmetal

gbead

ቇ =

C×∀

M

μ


15 

Method for Determining Extractable Arsenic and Lead in Glass Bead Samples 

The extractable metals content of the glass beads was analyzed by EPA method 3050B.(7) High 

purity ACS grade nitric acid and high purity ACS grade hydrogen peroxide were used for this 

test. Refluxing columns were used as vapor recovery devices, and a water bath capable of 

heating up to 100 °C was used as the heat source. ICP-MS was used for analysis of samples. 

Researchers measured 1.0 ±0.01 g of each glass bead sample and placed them in a circular 

flask/digestion vessel into which a 1:1 (volume:volume) mix of nitric acid was added. The 

sample was heated to 95 °C in a water bath and then refluxed for 15 min. 

After cooling, an additional 5 mL of concentrated nitric acid was added, and the sample was 

heated to 95 °C in the water bath and refluxed for 30 min. Because fumes were not observed, 

additional nitric acid addition and refluxing was not performed, and the sample was heated for 

2 h without boiling at 95 °C and then cooled. Researchers added 2 mL of DI water and 3 mL of 

30-percent hydrogen peroxide solution to the flask, and this was heated to 95 °C until 

effervescence was minimal. Upon cooling, the 30-percent hydrogen peroxide solution was added 

in 1-mL aliquots, and the above procedure repeated until effervescence was not observed. No 

more than 10 mL of hydrogen peroxide solution was added to the samples. The sample was 

heated at 95 °C without boiling for 2 h. The sample was then cooled and filtered using Whatman 

filter paper no. 41 and diluted to 100 mL. A 15-mL aliquot of the sample was extracted, labeled 

appropriately, and stored at 4 °C until analysis was conducted by ICP-MS. 

The extractable metals content of glass beads was calculated from the measured concentrations 

using the formula in figure 5: 

Figure 5. Equation. Formula to calculate extractable metals content of glass beads. 

Where: 

C = concentration of metal in extraction solution, g/L. 

 = volume of solvent, L. 

M = mass of beads, g. 

Method for Determining Bioaccessible Arsenic and Lead in Glass Bead Samples 

The in-vitro oral bioaccessibility method developed by Kelly et al. was used to determine the 

bioaccessibility of arsenic and lead in the glass bead samples.(1) This method was found to 

directly correlate results from in-vivo bioavailability testing protocols for heavy metals. The 

Kelley et al. method was selected for use in evaluation of the accessibility of metals for 

biouptake because the in-vitro test is faster and eliminates in-vivo testing. 

The in-vitro oral bioaccessibility method was run in a 0.4 M glycine solution with a pH adjusted 

to 1.5 ± 0.05 with hydrochloric acid. Researchers weighed 0.1 g of each bead and placed them in 

a high-density polyethylene bottle containing 100 mL of the pH-adjusted glycine solution. The 

reactors were tied using zip-ties to rotators (Barnstead Thermolyne LABQUAKE®) and placed 

Extractable Metal ቆ

μgmetal

gbead

ቇ =

C×∀

M

μ


16 

in an environmentally controlled, orbital shaker chamber (LabLine Orbit Environ-Shaker, 

Model # 3948, Lab-Line Instruments Inc., Melrose Park, IL). The rotators were operated at their 

maximum rotation speed of 8 rpm (which was a modification of the original 30 rpm used in the 

Kelly et al. method), and the chamber temperature was maintained at 37 ± 5 °C for an hour. 

After 1 h, the rotators were turned off, and the samples were allowed to settle for 5 min. A 

15-mL aliquot of the solid free supernatant was extracted from each bottle, labeled appropriately, 

and stored at 4 °C before ICP-MS analysis. 

The oral bioaccessible content of arsenic and lead in the glass bead samples was calculated from 

the measured concentrations using the formula in figure 6: 

Figure 6. Equation. Formula to calculate the oral bioaccessible content of arsenic and lead 

in glass bead samples. 

Where: 

C = concentration of metal in glycine solution, g/L. 

 = volume of solvent, L. 

M = mass of beads, g. 

Method Comparison for Analysis of Total Arsenic and Lead Analysis in Glass Beads 

Four methods were compared for their ability to evaluate arsenic and lead contents in glass beads 

used in pavement markings: 1) the KOH fusion method followed by ICP-MS, 2) EPA Method 

3052 (microwave assisted hydrofluoric acid digestion) followed by ICP or AAS performed at 

EPA to evaluate metals in siliceous solids, 3) bench-top XRF performed at FHWA, and 4) FPXRF performed at Florida Department of Transportation (FDOT). Subsamples from glass beads 

(with the exception of sample AA) received at TAMU were sent to each agency for testing. SRM 

612 was also analyzed for total arsenic and lead by EPA and TAMU.(2, 3) 

Retroreflectivity Measurements 

The retroreflective performance measurements were conducted by creating pavement marking 

samples containing glass beads on metal sheets. The metal sheets were painted using a shoe to 

put down the paint. The shoe was dragged along the metal sheet to spread the paint with a 

uniform thickness of 15 mils over the entire length of each pavement marking sample. 

Immediately following application of the paint, glass beads were applied on the surface using a 

bead dispenser for even, but random and dispersed, application on the paint. Three replicate 

markings were used to assess the retroreflectivity of each glass bead sample. After curing, the 

markings for 24 h, a Delta LTL-X retroreflectometer was used to measure the retroreflectivity of 

the pavement-marking samples in units of millicandela per square meter per lux (mcd/m2

 lx). 

The retroreflectivity was measured in two directions: in the direction of the paint application and 

the opposite direction. The retroreflectometer was used to take five independent measurements 

Bioaccessible Metal ቆ

μgmetal

gbead

ቇ =

C×∀

M

μ
17 

from each direction, which were summed to determine the final retroreflectivity value for each 

sample. 

Arsenic Speciation Determination 

Researchers placed 80-g subsamples of glass bead samples AA, DC, and EA in an up-flow 

cartridge reactor. The cartridges, previously described by Boulanger, were 25 mm in diameter 

and 265 mm in length.(5) pH-adjusted DI water at a pH of 7 was passed through the cartridges at 

a flow rate of 30 mL/h. Researchers sampled 10 mL subsamples of the cartridge effluents after 

1 h. Samples were preserved with 1 percent hydrochloric acid and refrigerated at 4 °C until they 

were placed in a cooler and shipped to EPA’s NRMRL overnight. Received samples were 

transferred to a refrigerator at EPA prior to analysis using a coupled high-performance 

chromatography (HPLC) ICP-MS system. All samples were analyzed within 2 weeks of their 

receipt. 

Arsenic speciation was completed in the EPA’s NRMRL under the guidance of Dr. Mallik 

Nadagouda. An Agilent 1100 series high-performance chromatograph was used to 

chromatographically resolve arsenic species on a ZORBAX Eclipse® XDB-C18 (5 mm by 

4.6 mm (inside diameter) by 250 mm) column using a binary eluent system. The binary mobile 

phase consisted of DI water with either 5 mM tetrabutylammonium hydroxide (eluent A) or 

2.5 mM ammonium phosphate (eluent B) that is adjusted to a pH of 6.0. pH adjustment was 

accomplished for eluent A using phosphoric acid and eluent B using ammonium hydroxide. A 

100 L injection introduced the sample to the front of the column, and a linear elution gradient 

with a flow rate of 1 mL/min was used. The linear gradient program used included 0 percent B 

from 0 to 1.5 min, ramped to 50 percent B at 4 min, held at 50 percent until 6 min, ramped to 

100 percent B at 8 min, and returned to 0 percent B at 12 min. 

The HPLC’s effluent was sent to an Agilent 7500cc ICP-MS using 0.25 mm inner diameter 

polyetheretherketone tubing. The ICP-MS was operated in standard resolution mode for arsenic 

(m/z 75). Eluent flow was introduced into the ICP-MS through a micro-concentric nebulizer cell. 

Full operation parameters of the ICP-MS used in this method can be found in the Almassalkhi 

reference.(8) A seven-point external calibration curve ranging from 1 to 150 g/L (As3+/As5+) 

was used to quantify the analytes. 

Estimation of Glass Bead Mass in Site Soil Samples 

Approximately 50 g of each site soil sample was subsampled and weighed. A particle size 

distribution using a series of U.S. Sieve #30, #40, #50, and #80 was performed, and the fraction 

of soil retained on each sieve was weighed and kept separately. An inclined plane made of a strip 

of Plexi-Glass® and a light table was used to manually separate glass beads, based on roundness, 

color, and translucence, from a representative portion of each fraction of soil. The glass beads 

from each fraction were weighed and collected. The total glass bead mass in 50 g of soil sample 

was calculated using the equation in figure 7. 

μ

μ
18 

Figure 7. Equation. Formula to calculate total mass of glass beads in a representative 

sample. 

The glass bead content in the site soil samples were calculated using the equation in figure 8: 

Figure 8. Equation. Formula to calculate the percentage of glass beads within a site soil 

sample. 

Analysis of Total Metals in Respirable Fraction of Soil Samples 

The respirable fraction (< 10 m size) of soil samples and blank samples was obtained by 

modifying the wet sieving process, which is a common procedure to extract dust from soil 

samples.(9, 10, 11) Approximately 50 g of site soil sample was wet sieved using a U.S. Sieve #10, 

#50, #230, and #800 using DI water. Water and soil particles passing through U.S. Sieve #800 

were collected and stored in a glass beaker. Water from each sample was allowed to evaporate, 

leaving behind flakes of soil particles. The soil was scraped out with a spatula and stored in 

polypropylene tubes, and analyzed for total arsenic using KOH fusion digestion and ICP-MS 

analysis. 

Quality Assurance/Quality Control (QA/QC) 

QA/QC efforts focused on several areas, including prevention of cross contamination, ensuring a 

representative subsampling from the initially provided samples, experimental controls and 

replicates, and QA/QC related to instrumental analysis. Cross contamination prevention included 

controls on sample handling that involved marking the subsamples. Any materials coming into 

contact with the glass beads during the experiment were also pre-screened for the likelihood of 

cross contaminating the glass beads. The DI water used in all laboratory experiments, the 

1 percent nitric acid solution used for diluting samples, and the glycine solution used in the 

bioaccessible extraction were also evaluated for their background arsenic and lead content. 

Experiments were carried out in triplicate to produce data between environmental factors that 

could be compared using statistical approaches. For every extraction procedure, a method blank, 

which consisted of analysis without using any sample, was generated. DI blanks and method 

blanks were also generated for all experimental procedures. The total content of arsenic and lead 

in the SRM 612 (glass wafer) was determined using the KOH fusion process. 

Instrumental QA/QC followed the guidelines outlined in EPA Method 6060A, and the MDL was 

determined as described in 40 CFR Appendix B to Part 136. Interferences were not observed for 

arsenic and lead, and the instrument limit of detection and resulting MDLs were able to observe 

quantifiable concentrations of these two components within the experimentally derived samples. 

Total	Glass	Beadsൌ ෍ ሺGlass	beads	in	representative	portionሻ	. Weight	of	fraction	of	soil

Weight	of	representative	portion

%	Glass	beads 	ሺby	weightሻൌ Weight	of	total	glass	beads

Weight	of	soil	sample ሺ~50	gሻ

μ
19 

RESULTS AND DISCUSSION 

QA/QC 

Table 6 reports the MDL in terms of the mass of metal per mass of glass bead (ppm) for the 

analysis of total, extractable, and bioaccessible metals in glass beads. Because the MDLs were 

lower than the lowest calibration standard (1 g/L), the lowest calibration standard became the 

PQL. Analytes with a concentration between the PQL and the MDL are reported as below the 

quantitation limit (BQL). Analytes detected in the sample that were below the MDL but still had 

a measured value are reported as below the detection limit (BDL). Analytes with a no observable 

measured response are reported as non-detectable. Interferences were not observed for arsenic 

and lead within the experimentally derived samples. 

For the total metal extraction, 0.25 g of glass beads was used in the KOH fusion method, and the 

final samples of extract were made up in 1 L of solution. For the extractable and bioaccessible 

extractions, 1 g of glass beads was used, and the final extract volume was 100 mL. Therefore, the 

MDLs for arsenic and lead in the glass beads for the extractable metal and bioaccessible metal 

extractions are different than the total metal extractions. 

Table 6. MDL and PQL for arsenic and lead for total, extractable and bioaccessible metals. 

Metal Limit 

Total 

(ppm) 

Extractable 

(ppm) 

Bioaccessible 

(ppm) 

Arsenic MDL 3 0.07 0.07 

PQL 4 0.1 0.1 

Lead MDL 0.16 0.004 0.004 

PQL 4 0.1 0.1 

ppm = parts per million 

MDL = method detection limit 

PQL = practical quantitation limit 

Total Arsenic and Lead 

The total arsenic and lead contents in the glass beads measured using the KOH fusion method are 

presented in table 7 and figure 9. Arsenic content in all the glass beads examined was less than 

100 ppm, while lead content was less than 200 ppm. NIST reports a nominal arsenic content of 

50 ppm and a certified lead content of 38.57  0.2 ppm in the SRM 612 wafers. The arsenic and 

lead content obtained by the KOH fusion method for the SRM are shown in table 8. The results 

for total metal analysis in glass beads show large standard deviations for both arsenic and lead, 

indicating a high degree of variability within the replicates of each bead sample. However, less 

than 6-percent variability was observed between three SRM replicates for both arsenic and lead 

over six analyses of the material. 

Because all QA/QC checks were met with the instrument, and acceptable results were obtained 

for the SRM, variability associated with instrument and methodology was ruled out. The 

variability in glass beads could be associated with varying sources of glass and varying amounts 

of heavy metals in the recycled glass and glass cullet used for manufacturing glass beads. The 

inconsistency of the reclaimed product used to make the glass beads could result in a very high 

μ
20 

concentration of heavy metals in some glass beads. This variability in different samples and 

subsamples of glass beads used in pavement markings has also been observed in a previous study 

by NJIT/RU and TTI.(5, 6) In the future, extraction methods may need to be modified to process a 

larger subsample to reduce the chance of selecting a high metal content glass bead randomly. 

Table 7. Total arsenic and lead content (ppm) in glass beads provided by State 

transportation department participants. 

Bead 

Arsenic 

(ppm) 

Lead 

(ppm) 

AA 75 ± 27 79 ± 50 

AC 11 ± 8 22 ± 19 

BD 65 ± 36 67 ± 58 

BE 55 ± 24 89 ± 62 

BI 53 ± 25 100 ± 71 

DA 62 ± 31 176 ± 154 

DB 70 ± 40 161 ± 186 

DC 82 ± 65 199 ± 246 

DD 61 ± 27 3 ± 7 

EA 51 ± 30 13 ± 13 

FH 50 ± 20 72 ± 36 

GA 49 ± 34 10 ± 9 

GB 52 ± 22 38 ± 33 

GC 45 ± 15 15 ± 6 

GD 35 ± 37 28 ± 26 

ppm = parts per million 

 
21 

Figure 9. Graph. Total mean arsenic and lead (ppm) content in the glass beads supplied by 

the State transportation department participants. 

Table 8. Total arsenic and lead content (ppm) in SRM. 

Arsenic (ppm) Lead (ppm) 

Measured Expected Measured Expected 

SRM 612 47  5 50a 33  6 38.57  0.2b

ppm = parts per million 

a

Nominal arsenic concentration in glass matrix 

b

Certified lead concentration in glass matrix 

Extractable Arsenic and Lead 

The extractable arsenic and lead in the glass beads measured using EPA method 3050B is 

presented in table 9. The concentrations of arsenic were below the MDL (0.07 ppm) for all the 

glass beads. For lead, one sample was measured between the MDL (0.004 ppm) and PQL 

(0.1 ppm) and was reported as BQL. Using the PQL as a lower limit of calibration, lead was 

observed within the extractable metals extracts in 7 of the 15 samples at reportable 

concentrations. When observed, the levels of lead ranged from 0.21  0.002 to 3.29  1.00 g 

extractable lead per gram of bead. Therefore, when present, lead within the extractable metals 

extracts was up to 2.5 percent of the total observed lead in the beads. 

0

50

100

150

200

250

AA AC BD BE BI DA DB DC DD EA FA GA GB GC GD

Total Mean As and Pb (μg/g of bead)

Bead

Arsenic Lead

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22 

Table 9. Extractable and bioaccessible arsenic and lead content (ppm) in glass beads 

provided by State transportation participants. 

Bead Extractable (ppm) Bioaccessible (ppm) 

Arsenic Lead Arsenic Lead 

AA BDL 0.38  0.1 BDL BQL 

AC BDL 0.74  0.5 BDL 3.6  5.4 

BD BDL 0.21  0.1 BDL BQL 

BE BDL 0.70  0.3 BDL BQL 

BI BDL 3.29  1.0 BDL 1.7  2.4 

DA BDL 0.252x10-3 BDL BQL 

DB BDL BDL BDL BDL 

DC BDL BQL BDL BQL 

DD BDL BDL BDL BDL 

EA BDL BDL BDL BDL 

FH BDL 0.31  0.1 BDL 0.190.01 

GA BDL BDL BDL BDL 

GB BDL BDL BDL BDL 

GC BDL BDL BDL BDL 

GD BDL BDL BDL BDL 

ppm = parts per million 

BQL = below quantification limits (<0.1 g/g for arsenic and lead) 

BDL = below detection limits (< 0.07 g/g for arsenic, < 0.004 g/g for lead) 

Bioaccessible Arsenic and Lead 

The bioaccessible arsenic and lead content in the glass beads measured is also presented in 

table 9. Bioaccessible arsenic concentrations were not in the reportable range for all the glass 

beads because the observed value was below the MDL (0.07 ppm). For lead, several of the 

measured values fell between the MDL (0.004 ppm) and PQL (0.1 ppm). Using the PQL as a 

lower limit, lead in the bioaccessible extracts was less than 0.7 percent of the lowest observed 

total lead concentration. 

Comparison of Total Metal Content in Glass Beads Evaluated from Different Methods 

The intra-method comparison for the analysis of total arsenic and lead in the glass beads 

included the following methods: 1) KOH fusion digestion followed by ICP-MS analysis, 2) EPA 

Method 3052 (microwave assisted hydrofluoric acid digestion) followed by ICP or AAS analysis 

to evaluate metals in siliceous solids, 3) bench-top XRF, and 4) FP-XRF. NIST SRM 612 was 

also analyzed for total arsenic and lead using KOH fusion and EPA Method 3052.(2, 3) KOH 

fusion digestions and ICP-MS analysis were completed at TAMU, EPA Method 3052 and ICP or 

AAS analysis was completed at the EPA’s NRMRL, bench-top analysis XRF was completed on 

μ

μ μ
23 

a Panalytical system at FHWA’s TFHRC, and portable XRF analysis was completed within 

FDOT’s laboratories. 

Table 10 and table 11 provide a summary of the mean total arsenic and lead content 

(respectively) for each of the analyzed samples using the four methods. Results of the intramethod comparison were not in agreement for the samples, although agreement was achieved 

between the KOH fusion method and EPA Method 3052 for the NIST SRM 612 standard. One 

possible explanation for the observed difference was a difference in glass bead preparation 

specified within the methods. KOH fusion digestion required that all glass beads and SRM 

samples be crushed and sieved prior to analysis. The EPA Method 3052 digestions included 

whole beads that were not crushed or sieved; however, because the SRM was received as a disk, 

crushing the SRM was required before digestion. The portable XRF samples were not altered, 

but the bench-top XRF samples were fused prior to analysis. Because the methods did not agree, 

but did meet their respective QA/QC specifications, additional work was carried out to determine 

the cause of the difference between KOH fusion (an alkaline digestion) and EPA Method 3052 

(an acidic digestion). However, crushing the beads did not result in a substantial change in 

measured arsenic or lead content when digested according to EPA Method 3052. 

Sieving the crushed beads was ruled out as a source of error (due to potential metal 

contamination from the sieve or due to size selectivity of crushed glass beads). However, 

processing the SRM samples by crushing and sieving them prior to KOH fusion digestion did not 

indicate an issue because the SRM recovery was acceptable. Further analysis of beads and SRM 

to evaluate the effects of crushing and sieving did not result in any explanation of the difference 

in measured concentrations between the two methods when the methods were followed as 

described. (However, running KOH fusion on whole beads greatly reduced both arsenic and lead 

content measured in the samples.) 
24 

Table 10. Comparison of arsenic content (ppm) in glass beads from intra-method 

evaluation. 

Sample ID 

Total Arsenic Content (ppm) 

Portable XRF EPA 3052 KOH Fusion Bench-top XRF 

AC ND 0.9 15 1.2 

BD ND 5.5 48 1.6 

BE ND 1.1 56 ND 

BI ND 1.0 60 ND 

DA 7 1.0 47 ND 

DB ND 0.9 57 0.7 

DC ND 1.3 68 ND 

DD 10 0.5 47 1.1 

EA ND 1.3 43 ND 

FH ND 2.6 58 1.0 

GA ND 0.3 53 ND 

GB ND 0.4 58 0.4 

GC ND 1.2 52 ND 

GD ND 0.5 53 ND 

SRM — 43 48 — 

ppm = parts per million 

XRF = X-ray fluorescence 

EPA = Environmental Protection Agency 

KOH = potassium hydroxide 

ND = not detected 

— indicates not analyzed 
25 

Table 11. Comparison of lead content (ppm) in glass beads from intra-method evaluation. 

Sample ID 

Total Lead Content (ppm) 

Portable XRF EPA 3052 KOH Fusion Bench-top XRF 

AC ND 4.1 30 12 

BD 19 6.0 84 15 

BE ND 10 120 11 

BI 15 8.6 130 22 

DA ND 2.2 230 ND 

DB ND 2.4 93 19 

DC ND 2.2 100 ND 

DD ND 3.8 4.2 9.2 

EA ND 2.7 17 ND 

FH 12 5.6 55 18 

GA ND 33 14 ND 

GB ND 7.1 45 14 

GC ND 23 17 14 

GD ND 3.2 16 ND 

SRM — 42 36 — 

ppm = parts per million 

XRF = X-ray fluorescence 

EPA = Environmental Protection Agency 

KOH = potassium hydroxide 

ND = not detected 

— indicates not analyzed 

Instrumental errors were also ruled out by analyzing extracts on more than one analytical 

platform. The cross-over analysis between platforms (which was also conducted in different 

laboratories) reproduced the extract concentrations for the digestions. Therefore, after ruling out 

sources of method and instrumental error, the observed difference is considered to be caused by 

either intra-replicate variability of arsenic and lead in the glass beads or a matrix interference/ 

enhancement present in the glass beads but absent in the SRM. 

Despite using a systematic approach to evaluate the cause of the differences in total metals 

content measured using the four methods, no method or instrument errors arose that explained 

the observed difference. Overall, KOH fusion provided the result closest to the nominal arsenic 

and certified lead content of the SRM for glass. In addition, several literature reports indicated 

better digestion of metals from glass through alkali fusion methods compared with acid 

digestion.(12, 13) However, the metals considered in these studies were trace metals such as 

rhenium, zirconium, hafnium, thallium, and uranium. Finally, because KOH fusion gave the 

overall most conservative (highest) estimate of arsenic and lead content observed in the beads 

while meeting QA/QC limits, the authors felt most comfortable performing subsequent 

digestions using this method. 
26 

Relationship Between Total Arsenic Content in Glass Beads and the Retroreflective 

Performance of the Beads 

The relationship between arsenic and retroreflective performance was evaluated because of the 

historical use of arsenic within glass production as a high temperature oxidant to remove 

imperfections in glass. The researchers were curious to evaluate whether higher arsenic levels 

would also correlate to higher retroreflectivity measurements, which would have implications for 

the performance of the beads placed on the roadway surface. The retroreflective performance of 

the bead samples was determined by creating pavement-marking samples on metal slabs and 

measuring the resulting marking retroreflectivity using a retroreflectometer. The Pearson’s 

product moment correlation coefficient was determined and used to assess the direction and the 

strength of the correlation between the arsenic content of the beads and their retroreflective 

performance. 

The total arsenic levels found through KOH fusion digestion followed by ICP-MS analysis were 

used to assess the relationship between arsenic content and the measured retroreflectivity of the 

beads applied within a pavement marking. Table 12 and figure 10 show the relationship between 

retroreflectivity and total mean arsenic content within the glass beads for all 15 samples. 

Table 12. Mean ± standard deviation retroreflectivity and total arsenic content for each 

bead sample evaluated in this research. 

Sample ID Retroreflectivity (mcd/m2.lx) Arsenic (ppm) 

AA 347 ± 10 63 ± 18 

AC 243 ± 8.7 15 ± 2.6 

BD 347 ± 36 48 ± 13 

BE 438 ± 52 56 ± 29 

BI 321 ± 6.8 60 ± 25 

DA 170 ± 39 47 ± 7.0 

DB 336 ± 52 57 ± 38 

DC 407 ± 65 88 ± 48 

DD 293 ± 18 47 ± 3.1 

EA 276 ± 14 43 ± 30 

FH 476 ± 34 58 ± 12 

GA 348 ± 19 53 ± 40 

GB 338 ± 26 58 ± 23 

GC 345 ± 11 52 ± 5.3 

GD 380 ± 28 53 ± 47 

ppm = parts per million 
27 

Figure 10. Graph. Relationship between mean arsenic content and mean retroreflectivity of 

each sample of glass beads evaluated within this research. 

The calculated Pearson’s product moment correlation coefficient for all 15 samples shown in 

figure 10 is 0.564. The coefficient indicates a positive moderate correlation between the two 

factors, suggesting that a correlation may exist between the arsenic content and retroreflective 

performance. However, additional samples should be analyzed to determine whether a 

correlation actually exists. In this study, the range of observed arsenic contents was limited to 

between 15 and 88 ppm. Arsenic contents of previously analyzed beads were an order of 

magnitude greater than the beads analyzed from State transportation department samples, and 

these high arsenic beads and beads with lower arsenic content (below 15 ppm) should be 

included in additional studies that explore this correlation. The retroreflectivity data, however, 

also demonstrate that suitable retroreflectivity performance can be achieved at low levels of 

arsenic. 

Speciation of Metals in Leachate From Glass Beads 

Arsenic speciation in water plays an important role in determining its potential toxicity to 

exposed organisms. Because glass beads were determined to leach arsenic, understanding the 

speciation of arsenic within the leachate solutions became of interest. The speciation analysis of 

arsenic revealed the presence of both arsenite (As3+) and arsenate (As5+) as the two predominant 

species of arsenic in solution. Table 13 presents the results for the analysis. While total arsenic 

levels (As3+ + As5+) in the pure leachate exceeded the 10 g/L drinking water maximum 

containment level for arsenic, under environmental conditions, the impact of leachate on existing 

μ
28 

groundwater or surface water reserves would be minimal for these samples owing to dilution. 

However, speciation data are considered during the human health risk assessment. 

Table 13. Arsenic speciation observed in samples of bead leachate generated from an 

up-flow cartridge system. 

Sample

As3+ 

( g/L) 

As5+ 

( g/L) 

AA 3.0 8.9 

DC ND 15 

EA 1.4 11 

ND = not detected 

Characterization of Arsenic and Lead Content in Mixed Glass Bead and Soil Samples 

Taken From a Bead Storage and Transfer Facility 

Five soil samples were collected from a glass bead storage and transfer facility of a pavementmarking company to study the contribution of glass beads to the total metal content within beadimpacted media samples. The bead storage facility has been storing beads on site for more than 

20 years. Because beads were evident upon visual examination, the site samples served as a realworld exposure scenario for bead-impacted environmental media. The MDL for the field sample 

analysis was determined separately because a new ICP-MS was installed in the later stages of 

this study, and a new matrix was used. The field site MDLs are given in table 14. Because the 

MDLs were lower than the lowest calibration standard (1 g/L), the lowest calibration standard 

became the PQL. 

Table 14. MDL and PQL for arsenic and lead for total, extractable, and bioaccessible 

metals for storage yard soil samples. 

Metal Limit Total (ppm) 

Extractable 

(ppm) 

Bioaccessible 

(ppm) 

Arsenic MDL 2.8 0.07 0.07 

PQL 4 0.1 0.1 

Lead MDL 0.44 0.011 0.011 

PQL 4 0.1 0.1 

ppm = parts per million 

MDL = method detection limit 

PQL = practical quantitation limit 

Table 15 lists the average glass bead content in site soil samples collected from a bead storage 

and transfer facility. The difference in the content of glass beads is owing to different sampling 

locations in the vicinity of the facility, including the storage zone and the transfer zone. The glass 

beads’ content varied from 19 percent to a maximum of 78 percent. Because most of the workers 

at the glass beads manufacturing facility do not wear protective equipment other than a hard hat, 

they are likely exposed to a high volume of glass beads through various routes of exposure, 

including direct contact and inhalation. 

μ μ

μ
29 

Table 15 presents the total metal content of site soil samples containing glass beads. While total 

arsenic was only reportable in sample locations 1 and 3, the concentrations of lead in the storage 

facility soil samples ranged between 11 and 122 ppm. The elevated arsenic and lead content in 

the soil samples over the control may be associated with the presence of glass beads. However, 

the glass bead content in field site soil sample does not correlate with the metal content in site 

soil samples. A detailed study, with more samples from a variety of facilities, is needed to assess 

the contribution of glass beads to the total metal content of the soil. 

Table 15 presents the total arsenic content in the respirable portion (< 10 m in size). The 

concentrations of total arsenic were below the MDL (0.70 g/L in aqueous phase) for all 

samples and are reported as BDL. These preliminary findings indicate that studies involving 

more samples from multiple facilities are required to evaluate the contribution of glass beads to 

total arsenic content in the respirable fraction of the soil. 

Table 15. Glass bead content (by weight), total arsenic and lead (ppm) in site soil samples, 

and total arsenic (ppm) in respirable fraction of site soil samples. 

Sample ID 

Weight 

Percentage of 

Glass Beads in 

Soil 

Arsenic 

(ppm) 

Lead 

(ppm) 

Arsenic in 

Respirable Fraction 

(ppm) 

Sample 1 24.5 2.9 ± —1 120 ± 160 BDL 

Sample 2 19.8 BDL 40 ± 19 BDL 

Sample 3 48.0 7.6 ± 0.5 35 ± 2.1 BDL 

Sample 4 41.2 BDL 14 ± 11 BDL 

Sample 5 78.3 BDL 12 ± 5.1 BDL 

Control 0 BDL 24 ± 12 BDL 

SRM — BDL 22 ± 4.6 BDL 1

Only one reportable data point out of three replicates 

ppm = parts per million 

SRM = standard reference material 

— indicates not applicable 

BDL = below detection limit (< 2.8 g/g for arsenic, < 0.44 g/g for lead) 

CONCLUSIONS 

Table 16 summarizes the overall number of samples and number of replicates per sample 

examined in this research. It also provides the mean total, extractable, and bioaccessible arsenic 

and lead contents measured in the entire sample set of glass beads analyzed in this study. While 

an intra-method comparison for total arsenic and lead content in the beads did not result in 

agreement among the four methods evaluated, KOH fusion digestion coupled to ICP-MS 

analysis reproduced the SRM content of both analytes to within 94 percent of the target value for 

six samples of SRM analyzed in triplicate. In addition, spiked addition controls demonstrated 

106  12 percent recovery of the known addition for both lead and arsenic in all spiked samples 

when KOH fusion was used. Therefore, the researchers have confidence that KOH fusion 

followed by ICP-MS analysis is a suitable method for measuring arsenic and lead content in the 

glass beads.

μ

μ

μ μ
30 

Arsenic speciation was observed in laboratory-generated samples of leachate under neutral pH 

conditions. Arsenate (As5+) ranged from 8.9 and 15 g/L in the leachate solution; whereas 

arsenite (As3+) was present below 3.0 g/L in the leachate. Arsenic and lead were also present in 

bead-impacted soil samples collected from a facility used for more than 20 years to store and 

transfer beads on site. When present, arsenic had a mean content in the site soils of less than 

5.5 ppm. Lead was detected in all of the samples at contents ranging 12 to 120 ppm. (Control site 

lead content was 24 ppm.) Overall glass content within collected samples from the site ranged 

from 20 to 78 percent by weight, with an average content of 42 percent by weight. 

Based on laboratory and field sample characterization completed in this study, the mean 

concentrations observed in the beads were below the 200 ppm arsenic and lead limit adopted in 

the recently approved MAP-21 legislation. Therefore, the proposed limit should not present a 

hurdle to using existing beads already in the commercial markets for pavement marking 

purposes. 

Table 16. Summary of total, extractable, and bioaccessible arsenic and lead in all of the 

samples analyzed in this study. 

Method 

No. of 

Samples 

No. of 

Replicates 

Per 

Sample 

Arsenic Lead

Frequency of 

Reportable 

Detection 

(percent) 

Mean 

Content 

When 

Present 

(ppm) 

Frequency of 

Reportable 

Detection 

(percent) 

Mean 

Content 

When 

Present 

(ppm) 

Total 15 9 100 54 100 71 

Extractable 15 3 0 — 47 0.8 

Bioaccessible 15 3 0 — 20 1.8 

ppm = parts per million 

— indicates not detected in any sample 

μ

μ
31 

SECTION 2. PROPOSED MODEL FOR THE ASSESSMENT OF HUMAN HEALTH 

RISKS ASSOCIATED WITH GLASS BEADS USED FOR PAVEMENT MARKING 

INTRODUCTION 

The use of glass beads in pavement markings presents the potential for contaminant release to 

the environment and subsequent human exposure. This section presents the proposed modeling 

methodology used to estimate the potential for adverse human health effects associated with 

arsenic and lead in glass beads used for pavement marking. 

Specifically, this section presents the development of the human health risk model, including the 

following: 

 An assessment of the workflow of pavement-marking beads within their product 

lifecycle. 

 Identification of the potential for human exposures based on the bead workflow. 

 Evaluation of the migration of contaminants from beads to human exposure points. 

 Methodology and equations used to determine exposures. 

 Methodology and equations used to determine a screening level concentration of arsenic 

and lead within the glass bead products that is protective of human health. 

The risk evaluation methodology is based on observation of human interaction with the 

workflow of glass beads in the environment. The workflow includes interactions during 

manufacturing, transportation, storage, application, and disposal of old marking residues. The 

exposure assessment considered human exposures over a range of potential scenarios that could 

lead to contact with beads. The scenarios that captured the most likely and reasonably 

conservative exposures based on field observations were included in the exposure model 

development. The process of developing the model identified a number of important parameters. 

The required parameters were assembled from literature or laboratory measurement of glass 

beads where applicable. For some parameters, however, literature was either not available or 

demonstrated significant variability among the available sources of data. Parameters that were 

considered key to the development of the risk model and which indicated significant variability 

in parameter values are specifically highlighted in the text. 

The field observations of glass bead production, storage, application, and removal were 

conducted in an arid environment during warm, dry, and low wind conditions. Roadway marking 

operations are generally conducted during periods of low winds (< 15 mi/h) to minimize bead 

and paint loss. Although observations were made in an arid environment, this assessment 

considers a range of environmental conditions. Additional information used in this assessment 

was obtained through interviews with individuals involved in the glass manufacturing and 

highway marking industries. 

The laboratory investigations presented in section 1 were used to establish the total, extractable, 

and bioaccessible arsenic and lead content used in the model. Because of uncertainty regarding 
32 

the source of the beads used in the metals analysis in experiments prior to the September 2012 

TTI/TAMU report, the risk evaluation presented in this report focuses on arsenic and lead using 

the most recently available bead analysis. 

The bead workflow assessment was conducted using English units because those are most 

commonly used in the United States for the applicable processes. The remaining portions of the 

document use SI units because English units are not used for the chemical analyses that support 

development of the risk-assessment models. 

Background of Bead Workflow 

Table 17 identifies the different stages and potential points of release of arsenic and lead within 

glass bead workflow. Use of glass beads as a reflective material in roadway line markings is 

decades old. Glass beads used in pavement markings are applied to the roadway on top of a base 

material that is a paint, epoxy, or thermoplastic. The beads are dropped either by a painting 

machine (specially designed truck or hand-cart) or by hand spreading. The bead sizes range from 

a fine table salt crystal up to a small ball bearing. Bead application rates, which are on the order 

of 192 lb/mi for a single 6-inch-wide line, result in a significant amount of beads that are not 

bound to the base material and are released to the environment. Additional releases of beads 

from markings may occur through wear due to traffic abrasion and weather, as well as during 

removal of the markings, such as when preparing a roadway for re-marking. 

Portions of the workflow associated with the glass beads are presented in table 17, which 

describes each of the steps where beads are used and potentially released to the environment. The 

basic elements of the bead workflow include the following: 

 Manufacturing. 

 Transportation. 

 Storage/transfer. 

 Application. 

 Wear/abrasion. 

 Removal/disposal. 

Beads are typically manufactured by melting crushed recycled glass cullet (large glass blocks) in 

an up-flow furnace to form the spherical glass particles. The formed particles are then passed 

through sieves of various sizes to isolate beads of desired size fractions that are mixed in the 

product formulation. Once sieved, the glass beads may be coated for various purposes (e.g., to 

prevent moisture accumulation, to achieve better paint adherence). The beads are then packed in 

large super-sacks (2,000-lb bags), smaller 50-lb bags, or in customer-specified packaging. 
33 

Table 17. Bead workflow elements and release potential. 

Bead Workflow Element Description of Release Release Potential 

1.Beads arrive palletized and packaged to 

prevent moisture contamination 

Rupture of a 2,000-lb bag possible. Majority of contents would be recovered. 

Low (localized to storage yard) 

a.Where moisture contamination has 

occurred, workers may use hands/tools to break apart the clumps of beads resulting in direct contact. 

Minimal loss while receiving/recovering/ transferring beads 

Low (localized to storage yard) 

2.Bead bags are opened and used in one of 

two ways: 

a.Vacuum beads into painting vehicle 

storage containers. Worker exposure to beads may occur while manipulating the vacuum nozzle or opening/resealing the bead bags. Where vacuum transfer is not functional, bead bags may be cut and contents dumped into vehicle storage bins, resulting in potential worker contact with beads. Beads may also be spilled into the yard, increasing the potential for exposure. 

Where a vacuum transfer is used, potential for release is limited to the opening and closing of bead bags. Dumping of beads from bags has greater potential for release than does vacuum transfer. 

Moderate (localized to storage yard) 

b.Pour beads into a bucket for hand 

application. Beads may be contacted during transfer and may be spilled, requiring handling during pickup. 

Minimal loss while recovering/transferring beads 

Low (localized to storage yard) 

3.Vehicle application of beads may require 

workers to manipulate nozzles, resulting in bead contact. Excess beads (up to 15 percent) are released to the environment. 

Excess beads applied to lines are released to the environment. For an application requiring six lines, a rate of 192 lb applied per 6-inch-wide line per mile results in a total of 1,150 lb/mi. For a loss rate of 15 percent of applied material, a total of 175 lb are released per mile of roadway, and assumed to be distributed 6 ft on either side of the roadway. In general, roads are remarked every 2 to 5 years. 

Moderate (large quantity, widely dispersed), most significant where roadside curbs have the potential to concentrate beads 
34 

Bead Workflow Element Description of Release Release Potential 

4. Application of beads by hand (without 

gloves) results in direct contact with beads. Excess beads are released to the environment. 

Loss rate is greater than machine application (up to 25 percent), with a bead usage of approximately 210 lb/mi. Typical applications require 300 ft of marking in a small residential neighborhood (perhaps near a school zone with many crosswalks) per year. 

Moderate (small quantity, potentially localized), most significant where curbing concentrates beads 

5.Worker inspecting applied lines may contact 

the surface and dislodge beads. 

Worker contact with the lines may result in minimal bead loss. 

Small (very small amount, widely dispersed) 

6.Line abrasive wear and weathering 

During lifetime of line, beads are slowly released from the line as a result of abrasive wear and weathering. Assume that 85 percent of the original load (1,150 lb/mi for six 6-inch lines) adhered to the line. Further assume that 25 percent of the adhered beads are released each year due to traffic wear and weathering. 

Moderate (large quantity, widely dispersed, long duration release), most significant where curbing concentrates beads 

7.Line removal of beads and substrate may 

include use of hand tools or vehiclemounted equipment. When vacuum is not used to remove material, workers may contact beads. When vacuum is used, bead contact in the field is limited; however, it may occur when removing material from storage tank. Removal methods include mechanical grinding, hydraulics, etc. 

Assume that lines are repainted when remaining retroreflectivity is 25 percent of original value, equivalent to retention of 25 percent of adhered beads, which is approximated as 250 lb/mi for a roadway section with six 6-inch lines. Releases may occur when vacuum removal of debris is not used, or when removed material is incorrectly stored in the marking company storage yard. 

Moderate (Potential is moderate in the field because vacuum trucks capture nearly all debris. Vacuumed material may be released in the storage yard. Mitigation measures are highly variable in practice.) 
35 

The packed beads are shipped by truck, air, rail, and train to the end users who are the pavementmarking agencies (either public entities or private corporations). Beads are completely covered 

during transport to prevent contamination of the beads by moisture. Although the beads may be 

shipped a significant distance, there are few recorded incidents of spills due to crashes. 

The pavement-marking agency, either a state/local entity or a private company, receives the 

beads and may store the packed beads in any number of ways. The storage areas may be covered 

with tarps or open air (with paved or bare ground). The storage yards may or may not include 

catch-basins to collect any material runoff. The beads are well protected from the elements by 

the shipment packaging because they tend to form clumps in the presence of moisture, leading to 

problems when used in the pavement-marking vehicles. 

The packaged beads are taken from storage and opened for use in pavement-marking 

applications. Beads in super-sacks are transferred to specially designed vehicles with internal 

bead holding tanks that are isolated from the environment. Their transfer is generally 

accomplished with a vacuum attachment incorporated into the pavement-marking vehicle, but 

occasionally the super-sacks are hoisted above the vehicle and gravity fed into the storage tank. 

The super-sacks may also be transported from the storage yard into the field and staged for later 

use. Smaller bead bags are opened and poured into buckets for jobs requiring hand application of 

beads. 

In the field, beads are applied to the pavement markings either by vehicle or by hand. Pavementmarking vehicles apply paint, thermoplastic, or epoxy substrate from one set of nozzles, followed 

by a stream of beads through other sets of nozzles. The nozzles are designed to result in beads 

that are buried halfway in the substrate for the best combination of adhesion and retroreflectivity, 

a measure of the line visibility at night. To achieve uniform bead coverage on the substrate, 

excess beads are applied, resulting in some bead loss along the edges of the marking. For smaller 

applications (e.g., small intersections, crosswalks), beads may be thrown onto the substrate by 

hand or, in some cases, using small fertilizer spreaders. 

A portion of the beads that adhere to the substrate are slowly dislodged over a period of time 

owing to traffic wear and weathering until a fraction of the original number of beads are left and 

re-marking is required. For highways, re-marking occurs every 2 to 5 years on average, whereas 

the frequency is approximately 3 years for urban areas. The markings are generally re-applied 

when 25 percent of the original retroreflectivity remains on the roadway. When re-marking is 

needed, the old marking material is either covered by new markings or is removed from the 

roadway before laying the new markings. 

Removing the remnants of old roadway markings generally involves mechanical, hydraulic, or 

chemical methods. Specially designed vehicles use an attachment that includes a hydraulic jet 

and vacuum system to remove the marking material and collect the waste. The slurry is 

contained within a holding tank on the vehicle for disposal, and very little material is lost to the 

environment. Where systems are used without vacuum recovery, the old marking material is 

generally left along the roadside. 

Each of these steps in the bead workflow and the potential for exposure are discussed in greater 

detail in the following subsections. 
36 

Bead Manufacturing 

The bead manufacturing process is a multistep process. The process starts when recycled glass 

cullet is received by the manufacturer. The cullet arrives via truck or rail and is stored in piles on 

the property (often exposed to the ambient conditions) until the cullet is turned into beads. The 

cullet is moved from the storage pile to large hoppers using a pay loader. The cullet is then 

passed through a series of grinders that breaks the cullet down into pea-size pellets. During the 

grinding portion of the process, dust suppression controls are typically used. 

In the primary manufacturing process used in industry today, the ground pellets are then 

introduced into an up-flow furnace. The pellets are melted in the lower portion of the furnace, 

and the molten glass rises due to temperature-driven convection and advective air flow. The flow 

rate through the furnace, combined with the temperature within the furnace, creates the spherical 

beads as the molten glass rises, cools, and re-solidifies within the furnace. The process to create 

the beads results in formation of beads across several particle size fractions. The formed beads 

are then passed to additional hoppers and are immediately sieved to isolate beads of the desired 

particle size, which are then stored in bins until formulated into products. 

Products are formulated by combining beads of different particle sizes together to achieve the 

final blend. Beads from different bins are fed by gravity through a chute, and the resulting mix of 

various bead sizes are packaged into super-sacks, 50-lb bags, or other customer-defined 

packaging. 

Worker exposure to the beads occurs at three main points: 

1. During formulation of the product as the blended beads are fed into their final packaging. 

2. During QA/QC testing. 

3. As a result of spilled beads. 

During product formulation, workers aid in the process by manually aligning the chute to the 

packaging for the super-sacks. For the 50-lb bags, the workers hold the bags while they are 

filled. Samples of each formulated product are tested to ensure the correct particle size 

distribution and spherical shape. Workers within the quality control laboratory come into 

incidental contact with the beads during testing. Workers may also come into contact with the 

beads that are spilled during the process. However, once the beads are packaged, worker 

exposure to the beads is minimal. The packaged beads are transported in sealed packaging 

around the manufacturing floor using a palate and forklift. The beads are stored within the 

facility until they are loaded via forklift for transport to the consumer. Workers may also be 

exposed to heavy metals through contact with the glass cullet in addition to exposure to metals in 

the formulated bead products. 

Bead Blending 

At some locations within the United States, both domestic beads and foreign beads are blended 

into final products without onsite bead manufacturing. Worker exposure to the beads at these 
37 

operations is similar to worker exposure to beads occurring during bead formulation described in 

the preceding subsection. 

Bead Transport 

The potential for bead release during transport from the manufacturer to the pavement-marking 

agency is minimal. Because the products are individually packaged in sacks and covered with a 

water-protective barrier, such as a tarp, during transport, the loss of beads and exposure to the 

driver are low. The beads are delivered to the consumer and off loaded into storage using a 

forklift. 

Bead Storage and Transfer 

The end user of the beads is either a public entity or a private contractor that marks roadways. 

The agency receives the palletized beads in either a super-sack or a 50-lb sack. The large sacks 

are either opened in the storage yard, where beads are transferred into the specially designed 

marking vehicles, or taken unopened into the field where they are staged for later use. The 

smaller bags are used where the markings are limited in size and/or where hand application of 

beads is the most practical approach. 

Beads may be spilled during receipt and storage, but localized releases mainly occur during 

transfer of beads to equipment in the storage yard. The extent to which released beads migrate 

outside of the yard is a function of a number of factors, the two most important being yard 

construction (e.g., protective coverings, land slope, design features such as sumps) and climate 

(arid/dust, wet/leaching). Materials released within the storage yard are of particular interest 

because they may accumulate over time. Considering the durability of the beads and the low 

associated rate of break-down, a storage yard used over many years could accumulate a 

significant concentration of beads. The transfer of beads to equipment outside of the yard will 

also potentially result in releases to the environment; however, the beads would be distributed 

over a wide area reducing the likelihood of accumulation. 

Bead Application 

The potential exists for a significant amount of beads to be released into the environment while 

being applied to the base marking material. To ensure good coverage, excess beads are often 

applied and a level of overspill is accepted as industry practice. Methods to curtail bead loss are 

in limited use (e.g., vertical drops, zero relative velocity nozzles, bead sheaths). The low cost of 

the beads makes more precise application or the use of recovery devices relatively uneconomical. 

The degree to which beads become mobilized is based on many factors (including weather, 

physical characteristics of the roadway, and street sweeping frequency), as well as the type of 

markings being applied. The general classes of roadway line markings are short (lines for 

intersections, traffic signals, and crosswalks) and long lines (lines applied over distance using 

specially designed vehicles). The application of beads to short lines is generally accomplished 

with small, single operator equipment or by hand spreading. The amount of bead loss is not 

quantified; however, an amount similar to that for long lines was observed in the field for an 

urban area with gutters (which tends to accumulate beads) along the roadside. 
38 

For long lines, bead application is accomplished through automated bead drop delivery systems 

that place beads onto the marking material in a continuous process figure 11 and figure 12). In 

general, beads are fed by gravity from a holding vessel to the bead drop nozzles. The amount of 

beads deposited and the direction of bead release is governed by manual adjustment of the nozzle 

aperture. In some cases, multiple nozzles may be used to provide additional bead loading for 

wide lines or to allow higher vehicle speeds. 

Road Marking Wear and Degradation 

A portion of the beads that were successfully applied to the base coat of marking material will be 

abrasively removed as a result of traffic wear and weathering. The majority of the detached 

beads will be intact, and little chipping/crushing of beads is expected to occur. The fraction of 

beads removed can be expressed relative to the loss of reflectivity of the lines. Where lines have 

lost 25 percent of the reflectivity, it can be inferred that 25 percent of the adhered bead load 

(assumed to be 85 percent of the applied bead load) has been removed by wear. At the point that 

re-marking is required, an additional layer of beads and base material is applied on top of the 

remaining line, or the remaining line/base material is removed. Application of several layers of 

lines prior to removal and re-application is typical.

Figure 11. Photo. Application of glass beads to long line markings. 
39 

Figure 12. Photo. Close-up of glass bead application to long lines. 

Bead Removal/Disposal 

The final disposition of the beads and base material used in roadway markings, owing to 

reaching the maximum feasible number of layers or to demolition and removal of the road itself, 

may result in release of beads to the environment. The line remnants are removed by a number of 

methods (including abrasives, water jets, and chemical removal), and the resulting material is 

either collected using a vacuum or released to the environment. When vacuum attachments are 

used, very little material is lost to the environment and releases are dependent on ultimate 

disposition of the vacuumed material in a landfill or at the equipment storage yard. In the case of 

mechanical removal without vacuum, the majority of remnant material (including beads or 

pulverized bead fractions) is likely to be lost to the environment, and a portion may become 

airborne. In addition, the beads would be concentrated because the remaining beads are held 

together in the base material that would also be removed. Because some base materials (such as 

epoxy and thermoplastic) would retain the beads in one area and prevent them from dispersing, 

the concentrations associated with removed marking material may be increased.

Human Exposures Associated With the Bead Workflow 

Human exposure to glass beads using in pavement markings may occur at any phase in the 

workflow lifecycle of the beads. Field observations of manufacturing environments, storage 

facilities, product applications, and product removal were carried out to determine the 

individuals who are most likely to experience significant exposure to beads released to the 

environment. The results of the field observations are reported in the next section.
40 

EXPOSURE ASSESSMENT 

The exposure assessment presented in this section outlines the individuals and pathways by 

which humans come in contact with contaminants associated with glass beads during the product 

lifecycle. In the exposure assessment, information regarding the characteristics of bead 

contamination is combined with assumptions regarding the source of contamination and presence 

of potential receptor populations, to elucidate the nature of human health exposures. The 

exposure assessment includes discussions concerning exposure scenarios, pathways of exposure, 

and migration pathways (used to establish the environmental fate of the beads). 

Potential Exposure Scenarios 

Populations that could potentially be exposed to glass beads include workers, residents, 

recreational users, and consumers of agricultural goods. Although some exposures are more 

plausible than others, all of the potential exposure scenarios listed below were considered for 

further evaluation. When the field observations indicated a particular scenario was insignificant 

relative to other scenarios for the same media, that scenario was no longer considered viable and 

was eliminated from the exposure pathway assessment. 

Occupational Exposure Scenarios 

The occupational exposure scenario is based on individuals who work on a roadway marking 

crew or manufacturing workers. The two occupational scenarios are similar, with the primary 

difference being that manufacturing workers will be exposed to beads only. Roadway marking 

crews may be exposed to both beads and soil that has been affected by the beads. 

Marking crew employees include two distinct populations of workers who experience exposures 

related to the handling of beads: those who apply markings and those who remove markings. 

However, the same person or persons may work on all tasks required by a marking crew. 

Manufacturing workers may also be exposed during the direct handling of the product (either 

during packaging or transferring of beads). 

Field observations indicated that worker exposure during transportation of bead products is 

minimal because of the handling practices employed to keep the beads free of residual moisture. 

Therefore, worker exposure during transport is not considered further. However, other exposures 

associated with the bead lifecycle are further evaluated in this assessment for the marking crew 

worker and manufacturing worker scenarios. 

Residential Exposure Scenarios 

The residential scenario is based on an individual property affected as a result of proximity to 

either a roadside where beads have been applied to markings or a bead storage yard. Field 

observations indicate that exposures associated with roadway marking application would be less 

significant than residential exposures due to concentration of beads released to the bead storage 

yard. Therefore, the residential scenario focused on exposures associated with the bead storage 

yard of a pavement-marking agency and not on application of the beads along a property line. 
41 

Individuals (either adults or children) living on the affected property may be exposed both 

indoors and outdoors to contaminated soil, water, food, and air originating from a bead storage 

yard. The resident may be exposed to contamination migrating from a storage yard that is on 

property adjacent to the residence, or in the most conservative approach, the residence may have 

been built directly on top of a former bead storage yard. 

Where a former storage yard is now a residential area, individuals may contact contaminated soil 

during daily outdoor activities. A resident may also track contamination indoors, resulting in 

continued exposure. If beads were left exposed to precipitation in the storage yard, the potential 

exists for heavy metals to leach to groundwater, which may result in additional exposure 

pathways (through drinking affected groundwater or irrigating a home garden). In the case of a 

residence adjacent to a bead storage facility, the possibility exists for metals to migrate into 

offsite residential soil, particularly in arid climates where wind-generated dust is prevalent. Also 

associated with the offsite resident is the potential for juvenile trespassing into the adjacent bead 

storage facility. 

For both the resident onsite and offsite scenarios, there is a potential for exposure via ingestion 

of fish from a contaminated surface water body, consumption of home-grown vegetables 

(gardening), or consumption of home-raised livestock products (chickens or chicken eggs, for 

example). Additional residential exposure may occur to individuals near schools where 

numerous crosswalks are frequently re-marked and, particularly, where streets are curbed 

allowing beads to accumulate. The sparkling appearance of the beads may draw attention and be 

attractive to school children, increasing their likelihood of exposure. However, exposures 

mentioned within this paragraph are considered speculative, and if they occur, they will be 

infrequent and short in duration. Therefore, to address the most significant and likely scenarios, 

the residential exposures included in the development of this methodology are those associated 

with residents living in close proximity or on top of a bead storage yard and the trespasser 

accessing the storage pile from an offsite residence. 

Recreational Exposure Scenarios 

The recreational scenario is based on an individual who rides all-terrain vehicles (ATV) along 

roadways or who fishes from water bodies affected by beads. Where a sufficient amount of beads 

has accumulated, dust may be inhaled by the ATV rider or taken up by aquatic organisms, 

resulting in potentially significant exposure. The level of exposure is highly dependent on 

climate and the fate of beads in the environment. 

Because of the expected low concentration of beads estimated and observed for roadside soils, 

roadside recreational activities are unlikely to result in significant exposures. In arid climates 

where dust generation is more prevalent, a rider is also more likely to wear a face mask filter to 

reduce dust inhalation. For areas with higher precipitation, the mass of beads is likely to be 

insufficient to significantly affect aquatic biota. In the absence of evidence of elevated roadside 

bead concentrations, the recreational scenario is not evaluated further. 
42 

Agricultural Exposure Scenarios 

The agricultural scenario is based on a farm situated beside a roadway where beads have been 

applied. Beads accumulating in farmland may result in uptake into crops or livestock and 

subsequent human exposure. Although this scenario is possible, the area affected by beads would 

likely be limited, resulting in contamination of only a fraction of any total farmland. Coupled 

with the low frequency of bead application (perhaps every 5 years in rural areas), the agricultural 

scenario is unlikely to result in significant exposures and is not considered further in this 

assessment. 

EXPOSURE PATHWAYS 

Evaluation of exposure pathways allows the risk assessment to focus on the pathways with the 

most significant potential to contribute to adverse human health effects. Exposure pathways are 

considered complete when four elements are present: 1) a contaminant source, 2) a transport 

mechanism to a receptor location, 3) a receptor present at the location, and 4) an exposure 

pathway to the receptor. Incomplete exposure pathways are eliminated from further 

consideration. Pathways are categorized as either direct (where the point of exposure is the 

source of contamination) or indirect (where a transport medium is needed to connect the source 

to the receptor). Potential exposure pathways are evaluated for each of the exposure scenarios 

(see figure 13). 

The manufacturing worker is exposed to beads daily in the course of production and packaging. 

The marking crew worker is exposed to the beads daily in the course of product handling, 

application, and removal. The marking crew worker is exposed in the field during line 

application; however, based on field observations, the majority of their exposure is likely to be in 

the storage yard where beads are stored and prepared for use or during line removal without a 

vacuum. While worker exposure during roadway marking removal is possible, some states 

require that the removed waste marking material be collected with a vacuum, essentially 

eliminating exposures in the field. Therefore, the focus of the evaluation of exposure pathways is 

the bead storage yard for the marking crew worker and the production/blending process for the 

manufacturing worker. 

The residents are assumed to either live adjacent to an active bead storage yard, or under the 

most conservative scenario, a residential area may also be built on top of a former bead storage 

area. The residential soil is assumed to be contaminated by past bead releases or from airborne 

transport of beads from an adjacent bead yard. The residential trespasser is assumed to live 

adjacent to an active storage yard. 
43

Figure 13. Diagram. Conceptual site exposure model for pavement-marking beads. 
44

Although the inhalation pathway provides the potential for exposure, it is unlikely to be 

significant. The arsenic and lead are atomically bound to the beads and are not likely to volatilize 

under ambient conditions. While the beads may be crushed, they are unlikely to be reduced to 

particles small enough to be entrained in air due to wind scour. Therefore, only the portions of 

the intact beads that are small enough to be inhaled are used as the inhalation source. 

There is a low potential for leaching of metals from beads and subsequent sorption to soil 

particles that may then be inhaled. The extractable portion of metals from glass beads was shown 

to be low, and the fraction of leached metals sorbed to soil particles small enough to be inhaled 

would be minimal. However, the inhalation pathway is included in this assessment to estimate 

the potential for toxic effects due to silicon exposure. 

For dermal pathways, beads are assumed to adhere to skin, similar to soil, resulting in an 

absorbed dose. Because metals typically result in low dermal exposures relative to the ingestion 

pathway, the dermal pathway was not quantified in the risk evaluation. Food-related pathways 

(home-grown vegetables/livestock) are also possible, but are not currently considered a 

significant source of exposure and were not included in the assessment. 

In all cases, exposures are considered to occur from contact with beads and from metals lost 

from beads into the surrounding media. Laboratory data indicate that arsenic and lead may be 

leached out of the beads to soil and to groundwater; however, the potential is limited. The 

ingestion exposure pathway assumed that bead contaminants are absorbed through the gastrointestinal tract and into the blood stream. 

Worker Exposure Pathways 

The worker exposure is assumed to occur throughout the work day. The worker is exposed to 

both direct (ingestion) and indirect (inhalation) pathways. Potential pathways of exposure 

included in the risk evaluation were as follows: 

 Incidental ingestion of beads. 

 Inhalation of fugitive bead particulates (if no controls are used). 

As indicated previously, the dermal pathway was not included because of the low absorption of 

metals and uncertainty in the availability of bead contamination for dermal absorption. In 

addition, the potential for contamination of soil due to migration of contamination from beads is 

low. Therefore, only direct bead ingestion (and not soil ingestion) is included in the risk 

evaluation. 

These pathways have the potential to be complete exposure pathways based on the four 

components of exposure outlined previously. Exposure via ingestion assumes that the source of 

contamination is the beads, the receptor is the worker handling the beads, and the worker may 

incidentally ingest the contamination if not wearing protective equipment. The inhalation 

exposure pathway assumes that the source is the spilled beads, the migration pathway is 

re-suspension of fugitive dust, the receptor is the worker, and the worker may inhale respirable 

particles if not wearing protective equipment. 
45

Residential Exposures 

Adult and child residential exposures occur throughout the day both inside a residence and 

outdoors. The resident would be exposed by direct pathways (ingestion) and indirect pathways 

(air, water, food). Direct pathways are applicable if the residence is built on top of a former 

storage yard, otherwise all residential exposures are indirect because a mechanism is required to 

transport contamination from the adjacent storage yard. 

Potential indoor and outdoor exposures included in the risk evaluation were as follows: 

 Incidental ingestion of beads. 

 Ingestion of groundwater contaminated by bead leachate. 

 Inhalation of fugitive particulates. 

As indicated previously, the dermal pathway was not included because of the low absorption of 

metals and uncertainty in the availability of bead contamination for dermal absorption. 

The food ingestion pathways were not included in the evaluation because of the low leaching 

potential identified in laboratory studies. Similarly, the potential for contamination of soil 

because of migration of contamination from beads is low and soil ingestion is not included in the 

risk evaluation. 

Outdoor exposures occur while residents are playing or working in the bead-bearing soil and are 

assumed to be limited to ingestion of beads, inhalation of particulates due to wind scour, and 

ingestion of groundwater contaminated by bead leachate. 

MIGRATION PATHWAYS 

The exposure scenarios associated with the identified receptors include both direct and indirect 

pathways. The estimation of exposure via the indirect pathways requires modeling of bead 

contamination through environmental media. The general modeling methods proposed for use in 

the bead assessment are based on EPA guidance documents for the development of human health 

based soil screening levels, as described below. 

The two potential migration pathways identified for heavy metals in glass beads used in 

pavement markings were as follows: 

 Airborne suspension of respirable particulate matter affected by beads and subsequent 

inhalation by a receptor. 

 Leaching of heavy metals from beads into infiltrating water, migration to a groundwater 

aquifer, withdrawal of potable water through a residential well, and subsequent ingestion 

by a receptor. 

Developed equations and parameter values for each of these pathways are presented in the 

following subsections.
46

Air Pathway 

The inhalation exposure pathway is based on suspension of particulate matter that a human could 

inhale into the bronchial passages of the lungs. Therefore, the assessment of the inhalation 

exposure requires an estimate of both the amount of material suspended in the air and the 

fraction of that material that could be taken into the lungs. In general, the inhalation pathway for 

metals is of less concern than the ingestion pathway; however, details of the inhalation pathway 

are presented for completeness.(14)

The suspension of soil into the air could be due to human activity in the area of contamination 

(e.g., vehicle traffic) or environmental causes (e.g., wind scour). The exposure scenario under 

consideration is based on the pavement-marking company storage yard as the source of 

contamination, which is subject to vehicle traffic. However, the vehicle speeds are likely to be 

low, and traffic would be infrequent, although this variable is difficult to quantify. Therefore, 

suspension of bead material due to wind scour is likely to be a more consistent and frequent 

source of airborne contamination and is used as the basis for further model development. 

General equations for human health exposure to airborne contamination are based on the air 

concentration of respirable particles. The size of particles that are considered respirable is based 

on the deposition velocity of particulates in air and filtering ability of the human respiratory tract. 

Calculation of air exposure concentrations for the modeling methods will be based on the amount 

of respirable material suspended into the air due to wind scour from the soil matrix containing 

the beads. Models describing the wind scour of soil are based on the concept of a threshold wind 

speed that can entrain particulates in the air.(15) A particle size of 75 m is considered the limit 

for wind suspension. For the bead model, it is assumed that the distribution of contamination in 

the bulk beads is similar to the distribution of contamination in the smaller size fractions. The 

“unlimited reservoir” wind suspension model assumes that 60 percent of the erodible material 

would pass a 1-mm screen, which is consistent with standards for Type I and II beads, requiring 

that > 90 percent be less than 0.85 mm in diameter.(15, 16) 

To provide a conservative value for the amount of respirable particulates in the air, the source 

area is assumed to have no vegetation and no surrounding buildings or trees that might 

significantly reduce the wind speed at the ground surface. Although only a small portion of the 

beads (< 5 percent for AASHTO type II beads) are in the respirable range, it is assumed that the 

distribution of bead sizes approximates the distribution of particle sizes in soil used to develop 

the wind scour model.(16) 

Groundwater Pathway 

The potential for migration of contaminants out of the glass beads and into groundwater is 

significant in the evaluation of human health risks. Groundwater ingestion pathways include two 

elements: 1) the leaching of contaminants out of glass beads and into infiltrating water, and 

2) the migration of leachate to the groundwater and subsequent extraction from a residential 

well, resulting in human exposure by ingestion. The leaching of contaminants depends on the 

partitioning between the bead matrix and surrounding pore water, and an important parameter in 

the evaluation of leaching from the solid matrix is the partition coefficient (i.e., the distribution 

μ
47

coefficient). The partition coefficient is defined as the ratio of the total metals content in a solid 

matrix to the metals content in the liquid matrix. Higher partition coefficients indicate that the 

metal is more likely to be retained in the solid matrix. The partition coefficient can be used to 

estimate the concentration of contamination in liquid that is in equilibrium with contaminants in 

soil, which can then be used to determine the impact on groundwater. 

The migration of leachate to groundwater and subsequent ingestion through a residential well is 

highly dependent on site-specific factors related to weather conditions, soil properties, and 

characteristics of the groundwater aquifer. The relationship between the concentration of a 

contaminant in leachate and the concentration in groundwater can be expressed as a dilutionattenuation factor (DAF). In general, a high infiltration rate and low groundwater velocity leads 

to a low DAF, indicative of groundwater concentrations that are more significantly affected by 

the leachate. 

A reasonably limiting DAF is approximately 10 for a low-flow aquifer with a significant 

infiltration rate. Although a lower groundwater velocity leading to a DAF < 10 is possible, 

aquifers with a DAF < 10 are less likely to be used for potable water because the capacity for the 

aquifer to provide a consistent volume of potable water to a household would be reduced. In 

addition, at very low groundwater velocities, the transport time of contaminants leaching from 

beads and traveling to a well would approach the exposure duration for a resident of 30 years. 

The use of a DAF of 10 is considered conservative because DAF values of approximately 4,000 

are reasonable for high-flow aquifers with minimal infiltration. 

The use of a DAF provides a simplified approach for a screening level assessment and is based 

on a number of modeling assumptions, including the following: 

 Contamination is uniformly distributed within the source area. 

 The contaminant source is in contact with the surface of the aquifer (no unsaturated 

zone). 

 Water is withdrawn from the aquifer at the down-gradient edge of the contaminated area 

from a well screened within the contaminant mixing zone. 

The edge of the contaminated area is used as the point of exposure because it represents a 

location that is significantly affected and feasible for exposure. Groundwater accessed in this 

area is assumed to mix with leachate to a depth that might be feasible for access to drinking 

water, yet the dilution is less than at locations further down-gradient from the contaminant 

source that might also be used for household purposes. 

These assumptions are consistent with EPA recommendations for calculation of screening levels 

protective of residential groundwater use.(14) For calculation of a site-specific DAF, the generic 

evaluation may be refined based on additional data collection or interpretation.
48

MODELING METHODS 

Based on the completed exposure assessment, the risk evaluation modeling methods focused on 

the following three particular exposure scenarios: 

 Scenario 1—Worker: roadway marking crew employee exposed through incidental 

ingestion and inhalation of fugitive dust emissions. (Inhalation scenario assumes no 

protective masks are worn.) 

 Scenario 2—Adult Resident: adult living in close proximity to an active bead storage 

yard or on top of a former storage yard exposed through ingestion of contaminated 

drinking water, incidental ingestion of beads, and inhalation of fugitive dust emissions. 

 Scenario 3—Child Resident: child living in close proximity to an active bead storage 

yard or on top of a former storage yard exposed through ingestion of contaminated 

drinking water, incidental ingestion of beads, and inhalation of fugitive dust emissions. 

A trespassing juvenile exposure scenario was considered but not evaluated because the resident 

exposure was considered to be more limiting. An occupational exposure scenario for the 

manufacturing worker was also considered but not included in the risk evaluation. It was 

assumed that occupational exposures would be controlled through the use of dust suppression 

methods and/or use of personal protective equipment where necessary. 

The proposed modeling framework focuses on developing quantitative measures to evaluate 

potential risk and develop screening level concentrations of metals in the glass beads that are 

protective of human health. The quantitative assessment requires calculation of the following 

two components: 

 The level of metal uptake or air concentration as a function of each individual exposure 

route. 

 The permissible level of exposure (screening level) due to either cancerous or noncancerous end points, considering the combined intake from the multiple routes of 

exposure affecting a single receptor. 

The calculations are based on EPA guidance documents addressing human exposure to soil, 

water, air, and food.(4) The contaminant exposures calculated for each receptor, environmental 

medium, and pathway combination are the basis for estimating the potential risk or hazard to 

exposed individuals. 

Equations Used to Calculate Exposure to Heavy Metals for Each Receptor Modeled in the 

Exposure Scenarios 

Exposure equations are specific to each environmental medium (soil, water, and air) and 

pathway of exposure. The calculations of intake for each receptor due to ingestion of beads or 

bead-impacted soil, inhalation of particulate matter associated with beads or bead-impacted soils, 

and ingestion of bead-impacted groundwater are presented within this subsection. The developed 

equations apply to each scenario, and all direct solid matrix exposures are assumed to occur from 
49

the top 150-mm layer of soil or from the glass bead product itself. The quantified exposures are 

then compared with the toxicity values to determine the potential for adverse health effects. 

Lead does not have established toxicity data for the evaluation of risk; instead, the exposures are 

related to blood lead levels to determine the potential for adverse health effects. The risk 

evaluation for beads used the U.S. EPA models, Adult Lead Model (ALM), and the Integrated 

Exposure Uptake Biokinetic Model (IEUBK) for children to estimate human health risks from 

lead exposure. 

Because this risk evaluation focuses on arsenic and lead, the equations used are based on metals 

exposures for the exposure pathways described below. Because lead is evaluated with specific 

EPA models, the following equations are applied to exposures to arsenic. 

Intake Due to the Incidental Ingestion of Beads or Bead-Impacted Soil 

Figure 14 presents the equation to estimate the intake of metals from beads or bead-impacted soil 

due to incidental ingestion. 

Figure 14. Equation. Formula to calculate intake of metals due to incidental ingestion. 

Where: 

Cs = exposure concentration in solid matrix (mgmetal/kgmatrix). 

IRs = ingestion rate of solid matrix (kgmatrix/day). 

EF = exposure frequency (days/year). 

ED = exposure duration (years). 

FI = bioavailable fraction (unitless). 

BW = body weight (kg). 

AT = averaging time (days) for carcinogens or non-carcinogens. 

Exposure Concentrations Associated with Inhalation of Beads or Bead-Impacted Soils 

The inhalation pathway is based on an air concentration representing an average over the 

exposure duration. Figure 15 presents the equation used to calculate exposure concentrations for 

inhalation of metals from small beads, bead dust, or from bead-impacted soils. 

Figure 15. Equation. Formula to calculate exposure concentrations for inhalation of metals. 

  BW AT

C IR EF ED FI Intake mg kg day s s metal



    /  

AT

C EF ED (VF + PEF ) Exposure Concentration (mg m )=

-1 -1 s

metal

3    /
50

Where: 

Cs = exposure concentration in solid matrix (mgmetal/kgmatrix). 

EF = exposure frequency (days/year). 

ED = exposure duration (years). 

VF = chemical-specific volatilization factor (m3

/kgmetal). 

PEF = particulate emission factor (m3/kg). 

AT = averaging time (days) for carcinogens or non-carcinogens. 

Note that chemical-specific VF is only applicable for soil contaminants that volatilize 

significantly. Because metals do not generally volatilize, the VF-1 term in figure 15 is 0. 

Intake Due to Ingestion of Bead-Impacted Groundwater 

Figure 16 presents the equation used to estimate the intake of metals from groundwater used as a 

drinking water source. 

Figure 16. Equation. Formula to calculate intake of metals due to ingestion of beadimpacted groundwater. 

Where: 

Cw = exposure concentration in water (mgmetal/L). 

IRw = ingestion rate of water (L/day). 

EF = exposure frequency (days/year). 

ED = exposure duration (years). 

BW = body weight (kg). 

AT = averaging (days) for carcinogens or non-carcinogens. 

Risk Evaluation and Calculation of Permissible Levels of Exposure (Cancerous and NonCancerous Human Health Screening Levels) 

The final step in the risk evaluation combines the exposure assessment and toxicity data to 

estimate human health risks and generate screening levels. Potential human health effects are 

characterized as either carcinogenic or non-carcinogenic when calculating the screening levels 

for each constituent via each exposure pathway. 

The probability of cancer effects is assumed to be linearly related to the exposure level of a 

human receptor to a contaminant in an environmental matrix. An increased probability of cancer 

effects is assumed to occur with any increased exposure, regardless of magnitude. In other 

words, there is no threshold for cancer effects and some impact, however small, is expected at 

any level of exposure. In contrast, non-cancer effects are based on the concept of a threshold of 

exposure. Below the threshold, no adverse effects are expected; however, exposures exceeding 

the threshold only indicate an increased likelihood of the occurrence of the adverse health 

effects. 

BW AT

C IR EF ED Intake mg kg day w w



   ( /  ) 
51

For this evaluation, carcinogenic effects are defined as an increased probability of cancer 

incidence, or an Incremental Lifetime Cancer Risk (ILCR). An acceptable ILCR of 1 additional 

cancer per 100,000 exposed individuals (also expressed as 0.00001 or 1E-05) is proposed as the 

target risk level for determining screening levels of individual metals in glass beads associated 

with carcinogenic effects. 

Non-carcinogenic effects may be manifested in any number of health impacts (including skin 

lesions, reproductive effects, and kidney damage) and are represented by a Hazard Quotient 

(HQ). An HQ is a ratio of the intake of contaminants (or exposure concentration for inhalation) 

to a reference value. The reference concentration is considered a threshold level below which 

there is a low probability of adverse health effects. For this evaluation, an HQ of 1.0 is proposed 

as the target level for determining the screening levels of individual metals in glass beads 

associated with non-cancer effects. 

The target ILCR and HQ are selected considering the acceptable target risk range established by 

the EPA.(17) The upper end of the risk range is an ILCR of 1 in 10,000 or 1E-04, with a lower 

threshold of 1 in 1,000,000 or 1E-06. For non-carcinogenic effects, a Hazard Index (HI) of 1 is 

the point of departure for considering mitigation of exposures. The HI is the sum of HQs for 

individual metals over all pathways. 

The screening levels established for bead exposure must account for the multiple contaminants 

present in the beads and multiple pathways of exposure. An individual would experience an 

increased risk from each constituent and protective screening levels account for the exposure 

from the combination of contaminants. 

Calculating Direct-Contact Cancer Screening Levels 

Figure 17 presents the equation for calculating the ILCR for direct contact with beads or beadimpacted soils through the ingestion exposure pathways. 

Figure 17. Equation. Formula to calculate ILCR for direct contact through ingestion. 

The equation in figure 18 is used to calculate the ILCR for inhalation exposures. 

Figure 18. Equation. Formula to calculate ILCR for inhalation exposures. 

ILCRs are calculated specific to a particular contaminant, exposure pathway, and receptor. The 

slope factor relates the intake level to the probability of increased cancer. The cancer slope 

factors are determined from animal experiments and data from accidental human exposures 

where available 

The overall ILCR for an individual constituent is then calculated as the sum of the ILCRs for the 

exposure pathways (ingestion, inhalation). The ILCRs for the constituents are then summed to 

provide an overall ILCR for the exposure scenario. 

Calculated ILCR = Intake (mgmetal/kg-d) x Cancer Slope Factor (risk per mgmetal/kg-d)

Calculated ILCR = Exposure Concentration (mgmetal/m3) x Inhalation Unit Risk (risk per mgmetal/m3)
52

If the ILCRs are calculated for a unit concentration in the exposure media (e.g., 1 mg/kg), the 

ILCR can be used to calculate the cancer screening level (CSL) for protection of human health 

with the equation in figure 19. 

Figure 19. Equation. Formula to calculate CSL for protection of human health.

The resulting screening level is protective of human health for cancer effects from the exposure 

pathways included in the assessment. The equation in figure 19 can also be used to generate 

screening levels representative of a single exposure pathway (such as ingestion, inhalation) by 

substituting the calculated ILCR for the individual pathway for the calculated ILCR for all 

pathways.

Calculating Direct Non-Cancerous Screening Level 

Figure 20 presents the equation for calculating the HQ for direct contact with beads or beadimpacted soils through the ingestion exposure pathways. 

Figure 20. Equation. Formula to calculate HQ for direct contact. 

Figure 21 presents the equation for calculating the HQ for inhalation. 

Figure 21. Equation. Formula to calculate HQ for inhalation. 

As indicated, the equation and parameters are specific to the pathway under consideration. The 

reference dose is generally expressed in mgmetal/kg-d and the reference concentration in 

mgmetal/m3

. These reference values are based on animal experiments or exposure to humans. 

The overall HQ for an individual constituent is then calculated as the sum of the HQs for 

ingestion and inhalation exposure. The sum of the HQs for all constituents considered in the 

exposure is the HI and reflects the overall potential for toxic effects from bead exposure. 

If individual HQs are calculated assuming a 1 mg/kg media concentration, then the results can be 

used readily to determine the non-carcinogenic screening level (NCSL) using the equation in 

figure 22. 

Figure 22. Equation. Formula to calculate NCSL. 

CSL (mgmetal/kgmatrix) = Media Concentration (1 mgmetal/kgmatrix) x Target ILCR (1x10-6)

 Calculated ILCR 

HQ = Intake (mgmetal / kg – d)

Reference Dose (mgmetal / kg – d)

HQ = Exposure Concentration (mg/m3

)

Reference Concentration (mg/m3)

NCSL (mgmetal/kg) = Media Concentration (1 mgmetal /kg) x Target HQ

Calculated HQ 
53

The resulting screening level is protective of human health for non-cancer effects via the 

pathways considered in the assessment. The above equation can also be used to generate 

screening levels that are representative of a single exposure pathway (such as ingestion or 

inhalation) by substituting the calculated HQ for the individual pathway for the calculated HQ 

for all pathways.

Calculating Indirect Contact Screening Levels: Ingestion of Bead-Impacted Groundwater 

The development of the screening level for consumption of bead-impacted groundwater is based 

on permissible levels of metals in groundwater for residential use, in this case the EPA Regional 

Screening Levels (RSL). The screening levels for protection of groundwater are based on an 

ILCR of 1E-06 or an HQ of 1 used for individual contaminants. 

The concentration of contaminants in beads is then related to the acceptable groundwater 

concentration based on the assumed leach rate of metals from beads and dilution of contaminants 

leaching into the affected aquifer (which is the DAF). Figure 23 presents the equation used to 

calculate the bead groundwater screening level (GW SL). 

Figure 23. Equation. Formula to calculate GW SL. 

Final Bead Screening Level 

The overall screening level for any medium from direct and indirect exposures is determined by 

comparing the screening levels based on carcinogenic effects with those for non-carcinogenic 

effects. The lowest value for each medium is selected as the final screening level for protection 

of human health within a given scenario. By evaluating each medium independently, combined 

exposures to soil and water are not represented in the screening levels. Because of the 

conservative assumptions incorporated in the evaluation, a combined exposure using the current 

model would lead to a highly conservative screening level. Where combined exposures to soil 

and groundwater are considered feasible, refinements to the modeling assumptions could provide 

more representative screening levels. 

The calculated screening levels for each of the scenarios evaluated will include: 

 Scenario 1—Worker: roadway marking crew employee exposed through incidental 

ingestion and inhalation of fugitive dust emissions. 

The overall soil screening level for individual constituents is the lowest value of: 

o CSL (ingestion, inhalation pathways combined). 

o NCSL (ingestion, inhalation pathways combined). 

GW SL (μgmetal/gbead) = Target GW Conc. (μgmetal/L) x DAF x Measured Bead Metals Conc (μgmetal/gbead) x 

Fraction of Beads in Source Area 

Estimated Leachate Metals Conc. (μgmetal/L) 
54

 Scenario 2—Adult Resident: living in close proximity to an active bead storage yard or 

on top of a former storage yard exposed through ingestion of contaminated drinking 

water, incidental ingestion, and inhalation of fugitive dust emissions. 

The overall soil screening level for individual constituents is the lowest value of: 

o CSL (ingestion, inhalation pathways combined). 

o NCSL (ingestion, inhalation pathways combined). 

The overall groundwater screening level for individual constituents is the lowest value of: 

o CSL (ingestion pathway). 

o NCSL (ingestion pathway). 

 Scenario 3—Child Resident: living in close proximity to an active bead storage yard or 

on top of a former storage yard exposed through ingestion of contaminated drinking 

water, incidental ingestion, and inhalation of fugitive dust emissions. 

The overall soil screening level for individual constituents is the lowest value of: 

o CSL (ingestion, inhalation pathways combined). 

o NCSL (ingestion, inhalation pathways combined). 

The overall groundwater screening level for individual constituents is the lowest value of: 

o CSL (ingestion pathway). 

o NCSL (ingestion pathway). 

The equations used to determine the screening level concentrations for each route of exposure 

within each scenario are the same; however, the parameters used for each scenario are different 

based on how the receptor interacts with the beads (or bead-impacted media) within each 

exposure pathway. Section 3 details available data included in the exposure assessment and 

reports modeling effort results used to set the screening levels for arsenic and lead in glass beads. 
55

SECTION 3. MODEL-DERIVED HUMAN HEALTH SCREENING LEVELS FOR 

ARSENIC AND LEAD IN GLASS BEADS 

INTRODUCTION 

Parameter Data Available for Development of the Modeling Method 

The calculations outlined in section 2 are the basis for development of the human health 

screening levels. Each of the calculations contains parameters that must be defined before using 

the developed model. This section assigns a representative value to parameters used to determine 

intake or exposure concentrations and, in some cases, discusses the range of parameter values 

considered. The screening levels are then recommended based on the developed model run with 

the identified parameters. The developed CSEM is used to determine the arsenic screening level, 

and the ALM and IEUBK models are used to determine the screening level for lead based on 

each evaluated exposure scenario. 

It is important to acknowledge the risk associated with the uncertainty inherent in the risk 

assessment and to explicitly state that any preliminary calculation of human exposures to metals 

in glass beads released to the environment will necessarily be based on numerous assumptions 

and generalizations. The use of generic input parameter values provides results that might be 

applicable across a range of possible site locations with region-specific considerations (e.g., 

weather, geology). In addition, available data derived from laboratory investigations are also the 

source of variability in the estimated screening levels. Where applicable, key uncertainties 

requiring additional sources of data (or further refinement) prior to using the presented modeling 

methodology are discussed. Parameters specific to individual receptors, contaminants, or the 

beads are also presented in the following subsections. 

Receptor-Specific Exposure Parameters 

Each receptor has particular metabolic or behavioral parameters that must reflect the activities 

associated with each scenario, and these parameter values are specific to each receptor under 

evaluation. The population of individuals representing the receptor group is incorporated into the 

values selected for these parameters to provide a conservative but reasonable estimate of 

exposure. General parameter values available from EPA’s risk assessment guidance documents 

that are used to determine arsenic screening levels are summarized in table 18. 
56

Table 18. Exposure parameters for glass bead assessment due to direct exposures. 

Parameter Units 

Adult 

Resident 

Child 

Resident Worker 

Ingestion Exposure 

Soil ingestion rate mg/day 50 200 50 

Bioavailable fraction unitless 0.1 0.1 0.1 

Exposure frequency days/year 350 350 250 

Exposure duration years 30 12 25 

Body weight kg 80 45 80 

Carcinogen averaging time days 25,550 25,550 25,550 

Non-carcinogen averaging 

time days 10,950 4,380 9,125 

Conversion Factor—

Chemicals kg/mg 0.000001 0.000001 0.000001 

Inhalation Exposure 

Particulate emission factor m3/kg 5.39E+08 5.39E+08 5.39E+08 

Volatilization factor m3/kg chemical 

specific 

chemical 

specific 

chemical 

specific 

Exposure frequency days/year 350 350 250 

Exposure duration years 30 12 25 

Body weight kg 80 45 80 

Carcinogen averaging time days 25,550 25,550 25,550 

Non-carcinogen averaging 

time days 10,950 4,380 9,125 

Notes: Exposure parameters are consistent with EPA guidance document for ingestion and inhalation 

exposures. 

Bioavailable fraction of 10 percent is a conservative estimate based on bead measurements (see table 9). 

The worker exposure is assumed to represent light industrial activities, which excludes any 

heavy excavation or similar work, but does include contact with the bead/soils. The residential 

exposure is based on an adult and child who spend time both indoors and outdoors. While 

outdoors, the child/juvenile is assumed to play in the soil and beads. The adult is assumed to 

work in the beads and soil doing landscaping or similar activities. The following subsections 

describe receptor-specific parameters used in the assessment, including body weight, exposure 

duration, exposure frequency, ingestion rates, skin surface area, and soil/bead adherence factors. 

Body Weight 

The body weight used in the analysis for the worker is based on a conservative estimate for 

adults of 80 kg.(18) Similarly, the adult resident is based on an average adult of 80 kg. The body 

weight of the child is assumed to be 45 kg, which is an average of both sexes from ages 6 to 

18 years old.(19) The juvenile trespasser is assumed to be exposed from age 8 to 18 years, so a 

body weight of 45 kg is also representative of this receptor. 
57

Exposure Duration 

The exposure duration for the worker of 25 years is based on a conservative estimate of the 

length of employment for an adult.(20) Although it is likely that the occupational exposure 

duration would be significantly shorter, the conservative value is assumed to reduce the potential 

for underestimates of risk in the assessment. 

The residential adult exposure duration is based on a conservative estimate of the length of time 

spend in one residence of 30 years.(4) The residential child is assumed to live in one household 

from ages 6 to 18, an exposure duration of 12 years. The trespasser exposure occurs for a period 

of 10 years, assuming that older teenagers are less likely to continue trespassing into the storage 

yard. Similar to the worker exposure, the conservative values are proposed for the resident to 

provide protective results. 

Exposure Frequency 

The frequency of exposure for a marking crew worker is based on a typical schedule of 5 days 

per week for a total of 250 days in a year (assuming 2 weeks of vacation). However, the 

application of roadway markings is a weather -dependent job, and work is only conducted on 

days with low wind and no precipitation. In some areas of the country, weather conditions may 

prevent work on all but approximately 120 days each year. On days that are not suitable for 

applying markings, workers may be employed with the removal of old markings. Therefore, 

marking crew workers would be on the job for 250 days each year; however, the balance 

between the time spent applying lines and removing old lines would differ regionally. 

A resident is typically assumed to be at home for all but 2 weeks each year, or a total of 350 days 

annually. Although it is likely that the exposure frequency would be significantly shorter, the 

conservative value is proposed. The trespasser is assumed to access the bead storage yard five 

times each week, for a reasonably conservative exposure frequency of 250 days each year. 

Ingestion Rate 

The ingestion rates of soil and water are specific to each receptor. The soil pathway applies to 

both marking crew worker and residential exposures, but not to the manufacturing worker. The 

water ingestion pathway is only applied to the residents who drink contaminated well water 

(assuming workers drink from municipal water systems). 

Soil/Bead Ingestion: The soil/bead ingestion rate is based on the amount of soil/beads adhered 

to the hands, which is subsequently ingested throughout the day. It is assumed that beads behave 

similarly to soil, and that the concentration of contaminants in soil/beads that are ingested are 

consistent with the relative concentrations in soil (i.e., no preferential ingestion of highly 

contaminated particles). 

For workers and adult residents, the average ingestion rate is assumed to be 50 mg/day.(18) It is 

assumed that the worker is engaged in light industrial activities and does not do any excavation 

work that might increase contact with soil and thereby increase the ingestion rate. Residents 

contact soil/beads while engaged in landscaping or other similar activities. 
58

The average child ingestion rate of 200 mg/day is used in the assessment.(19) A resident child 

may exhibit pica, which is a condition that results in excessive soil ingestion (approximately 

2,000 mg/day). However, the pica receptor is highly unlikely and, therefore, is not used as the 

basis for child soil ingestion. 

Water Ingestion: The water ingestion rate applies only to residents who use potable water from 

a well that extracts groundwater that has been affected by a bead storage yard. The resident adult 

is assumed to ingest groundwater at a rate of 2.7 L/day on average.(18) Similarly, it is assumed 

that the child ingests water at the same rate as an adult.(19)

Contaminant and Site-Specific Exposure Parameters 

Parameters that are metal specific are used to quantify exposure mechanisms that are dependent 

on the properties of the contaminant under evaluation. The exposure equations reflect the 

particular rates of uptake into humans and/or food products, based on the magnitude to which 

constituents may move through the human body or migrate from soil to other media. Sitespecific parameters represent hydrogeology or climate conditions that affect the calculation of 

screening levels. 

The following subsections describe contaminant-specific and site-specific parameters used in the 

assessment, including the gastrointestinal absorption factor, particulate emission factor (PEF), 

groundwater transport factors, bioavailability factors, environmental half-life, and toxicity 

factors. 

Gastrointestinal Absorption Factor 

The gastrointestinal absorption factor describes the absorption rate of contaminants that are 

ingested in beads through the gastrointestinal system. The bioaccessible fraction of arsenic and 

lead in glass beads reflects a wide range of values and is a source of uncertainty in the proposed 

modeling methodology. In the presented model, a gastrointestinal adsorption factor of 0.003 is 

used.(21) 

Particulate Emission Factor 

The PEF is used to determine the dust load in the air and the resulting air concentration for the 

exposed receptors. The dust load is dependent on soil, weather, and activity factors. The 

equations used in the PEF calculation are presented in figure 24 and figure 25. 

Figure 24. Equation. Formula to calculate PEF. 

Where: 

Q/C = inverse of mean concentration at center of source (g/m2

-s per kg/m3). 

V = fraction of vegetative cover (unitless). 

Um = mean annual wind speed (m/s). 

Ut = equivalent threshold value of wind speed at 7m height (m/s). 

F(x) = experimentally derived function dependent on Um/Ut (unitless). 

PEF (m3/kg) = Q/C x 3600 (seconds/hour) 

0.036 x (1-V) x (Um/Ut)

3

 x F(x)
59

Figure 25 presents the formula for deriving the value of Q/C. 

Figure 25. Equation. Formula for deriving the inverse of the mean concentration at the 

center of the source (Q/C). 

Where: 

A, B, C = experimentally derived constants based on air dispersion modeling for specific climate 

zones. 

Asite = area of contamination (acres). 

Table 19 presents the results of the PEF calculation, which describe the emission rate of particles 

that have a diameter of 10 m or less. (18)

Groundwater Transport Factors 

The groundwater transport parameters are used to describe the lateral migration of contaminants 

that have been leached to groundwater. In general, it is assumed that the concentration of 

contaminants in the leachate is the concentration that reaches the groundwater. This assumption 

results in conservative groundwater concentrations because some contaminants will likely not 

reach groundwater but will remain sorbed to particles in the vadose zone. Once they reach the 

groundwater, contaminant transport may be retarded relative to groundwater flow within the 

aquifer or may disperse significantly relative to the advective motion of the aquifer. Both of 

these mechanisms would tend to reduce the contaminant concentration in groundwater. 

Groundwater transport factors also have a site-specific component related to the site 

hydrogeology and weather conditions. 

To be conservative, a DAF of 10 is used to evaluate contaminant migration through groundwater. 

Calculated DAFs that range over several orders of magnitude are likely for sites throughout the 

United States. The DAF is linearly related to the screening level for ingestion of groundwater in 

the residential exposure scenarios, and a tenfold increase in DAF would increase the screening 

level by an order of magnitude. Therefore, the DAF is a source of a significant and key 

uncertainty that needs to be carefully considered for each specific site when using the current 

modeling methodology. In addition, if a residential groundwater well was screened across both a 

contaminated and uncontaminated zone in a bead-impacted aquifer, further dilution of 

groundwater contaminants would occur within the well.

Q/C = A x exp[ln(Asite)-B]2

C

μ
60 

Table 19. Calculation of particulate emission factor. 

Scenario Parameters for Dispersion 

Factor 

Calculation 

Q/C 

Dispersion 

Factor 

(g/m2-s per 

kg/m3) 

Measured 

Average 

Wind Speed 

at Elevation 

of 7 m 

(Um) 

(m/s) 

Threshold 

Friction 

Velocity

(m/s) 

Equivalent 

Value of 

Threshold 

Wind Speed 

at 7 m 

(Ut) 

(m/s) 

Parameter for 

Determination 

of Equation 

Describing 

f(x) 

(unitless) 

F

D

(u

A B C 

Nationwide 16 19 216 82.9 4.69 0.21 11.36 2.10 

Northeast 

(Hartford, CT) 13 19 215 65.4 3.80 0.17 9.20 2.10 

Southeast 

(Atlanta, GA) 15 18 204 71.6 4.10 0.19 9.93 2.10 

Central 

(Minneapolis, 

MN) 

16 19 216 82.9 4.70 0.21 11.38 2.10 

Northwest 

(Boise, ID) 11 20 225 63.0 3.90 0.18 9.45 2.10 

Southwest 

(Phoenix, AZ) 10 19 212 53.5 2.80 0.13 6.78 2.10 

Notes: Calculation based on equations presented in the EPA Soil Screening Guidance and supporting sources.(14, 15) Values for Minneapolis, MN, were found to represent the 90th percentile of results derived from air dispersion modeling for 29 cities in thVariables for site area, fraction of vegetative cover, sand percentage in soil, and measured annual average wind speed are user-entered va

are calculated as described in EPA.(14) Parameters A, B, and C for the Dispersion Factor Calculation were generated by EPA from atmosp

simulations for sites across the country and best fit regression analysis of the results. Table assumes a 1-acre source area with no ground cover and a roughness height of 0.1 cm (open ground). 
61

Bioavailability Factors 

The bioavailability, biotransfer, and bioaccumulation factors are used to describe the 

contaminants’ availability to biological organisms and the potential for concentration into food 

items such as vegetables, livestock, or fish. Recent laboratory analysis of the bioaccessibility of 

arsenic and lead in glass beads, as presented in table 9, indicate an average for bioaccessible lead 

of 1.8 ppm compared with a total lead average of 71 ppm, or an average bioaccessible fraction of 

approximately 2.5 percent. Table 20 presents the calculated bioaccessible fraction, which ranged 

from 0.06 to 16 percent, indicating significant variability in the parameter. No extractable or 

bioaccessible arsenic was observed. 

Table 20. Extractable and bioaccessible fraction of arsenic and lead in bead samples 

expressed as a percentage of the total content. 

Bead Group 

Percentage of 

Total Lead as 

Extractable 

Percentage of Total 

Lead as 

Bioaccessible 

AA 0.48 0.13 

AC 3.36 16.36 

BD 0.31 0.15 

BE 0.79 0.11 

BI 3.29 1.70 

DA 0.14 0.06 

DB NA NA 

DC NA NA 

DD NA NA 

EA NA NA 

FH 0.43 0.26 

GA NA NA 

GB NA NA 

GC NA NA 

GD NA NA 

Overall 

Average 1.3 2.7 

NA = not available because results were below detection limits 

Environmental Half-Life 

The environmental half-life is a parameter that describes the persistence of glass beads once they 

are released to the environment and is considered site specific. It is assumed that the glass beads 

are extremely stable and remain intact under typical environmental conditions, with the 

exception of beads removed by mechanicals means that might result in crushing of beads. Beads 

removed from the base material (paint, thermoplastic) by vehicle traffic are assumed to be intact, 

as are beads released into a storage yard.
62

Toxicity Factors 

The toxicity factors are used to define, for each constituent, the potential for adverse health 

effects based on the magnitude of exposure for each receptor and pathway for each constituent. 

Contaminant speciation and complexation are a significant consideration in assigning a value for 

toxicity parameters. 

Arsenic speciation in leachate from beads was measured and indicated that the dominant species 

is arsenic (V) in laboratory experiments (table 13). Although specific toxicity data are not 

available for particular arsenic species, studies have indicate that arsenic (III) is a generally more 

toxic form of arsenic. The full toxicological profile for arsenic is available from the Agency for 

Toxic Substances and Disease Registry (ATSDR) at http://www.atsdr.cdc.gov/toxprofiles/ 

tp2.pdf. The ATSDR profile for lead is available at http://www.atsdr.cdc.gov/toxprofiles/ 

tp13.pdf. Table 21 summarizes the toxicological parameters used in this study’s modeling 

approach for arsenic. 

Bead-Specific Exposure Parameters 

Parameters that are bead specific reflect exposure mechanisms that depend on the properties of 

the beads under evaluation. The following subsections describe bead-specific parameters used in 

the assessment, including the concentration of the beads in the bead/soil source material, the 

concentration of metals in beads, and the leaching rate of metals from the glass beads. 

Mass of Beads in Bead/Soil Source 

The quantity of beads present in the environment as a result of bead loss during storage and 

application is an important parameter in the risk evaluation. The fraction of beads in the source 

material affects the magnitude of the exposure to humans. The following section presents 

estimates of bead loss, as well as field measurements of the bead fraction observed at an active 

bead storage facility. 
63 

Table 21. Toxicity data for glass bead assessment. 

Constituent 

Chemical 

Abstracts 

Service 

(CAS) No. 

Exposure 

Point 

Concentration

(EPC) Units 

Oral 

Reference 

Dose 

(RFDo) 

(mg/kg-d) 

Absorbed 

Dermal 

Reference 

Dose 

(ADRFD) 

(mg/kg-d) 

Inhalation 

Reference 

Concentration 

(RFCi) (mg/m3) 

Oral Slope 

Factor 

(SFO) 

(mg/kg-d)-1

Inha

Uni

(I

( g

Arsenic (at 54 ppm) 7440-38-2 22.8 mg/kg 3.00E-04 1.00E-02 1.50E-05 1.50E+00 4.3Arsenic (at 62 ppm) 7440-38-2 26.1 mg/kg 3.00E-04 1.00E-02 1.50E-05 1.50E+00 4.3

NA = not applicable Notes: Toxicity data from the EPA(21)

EPC—exposure point concentration in bead/soil assuming 42-percent beads in the source. Arsenic concentrations of 54 and 62 ppm are the arithmetic average and 95-percent upper confidence limit (UCL95%), respectively. 

μ
64

Table 22 provides available data for estimating the bead concentrations in environmental media 

for various bead loss scenarios. The estimates presented in table 22 are based on the bead 

workflow elements and release potential outlined in table 17. The release potential values have 

been converted from English to SI units for use in the model equations. 

The estimated bead concentration in the soil of a storage yard assumes that an area of 4,050 m2 is 

used to store and transfer beads and that the beads are mixed into the soil to a depth of 150 mm. 

If approximately 4.5 kg were spilled daily for 250 days each year, a total of 1,125 kg of beads 

would be mixed into the soil annually, resulting in a bead concentration in soil of approximately 

1,500 ppm after 1 year. 

Bead loss to the environment may also occur during application of the beads onto pavement 

markings. During application, bead loss is expressed as a percentage of the total beads applied. 

The total bead load applied is a regulated quantity in some states. Table 23 presents an estimate 

of bead mass loss rate in kg/km, based on typical pavement marking paint and bead application 

rates. The application scenarios are shown in English units, with the final bead mass loss rate 

converted to SI units. Actual bead mass loss depends on the number and width of the pavement 

markings, operational characteristics of the application equipment, speed of application, and 

other factors. 

The bead load estimate above is based on a four-lane undivided highway with a central turning 

lane, and the following 6-inch lines: 

 Left shoulder—continuous. 

 Lane 1 and 2 divider—dashed. 

 Left double line for central turn lane—continuous/dashed. 

 Right double line for central turn lane—continuous/solid. 

 Lane 3 and 4 divider—dashed. 

 Right shoulder—continuous. 

Based on worker interviews and field observations, typical bead loss percentages are assumed to 

be 15 percent of the applied load. With a total estimated bead application rate of 1,150 lb/mi (see 

table 17), the resulting 15 percent bead loss rate is approximately 49 kg/km. The quantity of 

beads lost to the roadside can be used to provide an estimate of soil concentrations at residential 

locations near roads. Assuming that all beads are blown to one side of the road, and that they are 

mixed into the soil to a depth of 50 mm and to a width beside the road of 2 m, then the total 

mixing soil volume is 100 m3/km. For a typical silty loam soil with a density of approximately 

1.28 g/cc or 1.28 × 106

 g/m3 or 1,280 kg/m3, the mixing mass of soil for each kilometer is 

128,000 kg. The resulting bead concentration in the roadside soil would be 49 kg of beads in 

128,000 kg of soil or 385 ppm. 
65 

Table 22. Estimates of bead loading to soil per year. 

Scenario (Soil Location) 

Affected 

Area 

(m2) 

Affected 

Depth 

(m) 

Soil 

Density 

(kg/m3) 

Soil 

Mass 

(kg) 

Typical 

Bead 

Loss 

(kg/event)

Release 

Frequency(events/yr) 

Annual 

Bead 

Mass 

Released

(kg) 

Estimat

Bead 

Concentra

in Soil 

(kgbead/kg

Storage Yard 4,050 0.15 1,280 777,600 4.5 250 1,125 0.0015 Rural Roadside During Application 2,000 0.05 1,280 128,000 49 1 49 0.0004 Roadside Due to Line Degradation 2,000 0.05 1,280 128,000 69 1 69 0.0005 Roadside Total 2,000 0.05 1,280 128,000 118 1 118 0.0009 

Notes: Assumes storage yard area is approximately 1 acre or 4,050 m2. 

Assumes area affected for the roadside scenario is approximately 2 m wide, approximately 50 mm deep and 1 km long. Soil density is that for silty loam (1,280 kg/m3). 

Bead mass for the storage yard assumes 4.5 kg per day over 250 days each year, or an annual release of 1,125 kg. Bead mass for the roadside during application assumes 1,150 lb/mi application rate for six continuous 6-inch-wide lines with a bead loss 175 lb/mi. Bead mass for line degradation assumes 25 percent of the bead load on the line (85 percent of total applied load) is released in a year, or akilometer of roadway. Bead mass for the total roadside is sum of the releases from the original line application and line degradation, per kilometer of road, assumsame year. 
66 

Table 23. Estimated glass bead application and loss rate for line applications. 

Line 

Width 

(inches) 

Paint Volume 

Application 

Rate 

(gallon/line-mi) 

Bead 

Application 

Concentration

(lb/gal) 

Bead Line 

Mass 

Application 

Rate 

(lb/line-mi)

Number of 

Lines per 

Roadway 

Bead Roadway

Mass 

Application 

Rate 

(lb/roadwaymi) 

Bead Loss 

Percentage

(%) 

Bead Ma

Loss Rate

English Un

(lb/mi) 

4 12 10 120 6 720 15 108 6 16 12 192 4 770 15 115 6 16 12 192 6 1,150 15 175 

Notes: All quantities are estimates based on data from several State transportation departments. Site-specific information is used wher

estimates. 
67

In general, lines are replaced when reflectivity has dropped to 25 percent of the original value, 

which is assumed to occur within 3 years within the model calculations. Therefore, during 

1 year, approximately 25 percent of the original line load will be released to the environment. 

For the example presented in table 22, the total applied load is 324 kg/km, with 275 kg/km 

adhering to the lines and 49 kg/km lost to the roadside initially. An additional loss of 

approximately 69 kg/km may occur over a period of a year through line degradation. 

Field investigations have measured the fraction of beads in soil at one bead storage yard to 

provide perspective on the estimated bead concentrations (table 15). The storage yard has been 

used for at least 20 years and indicated a range of bead fractions (by weight) of 20 percent to 

approximately 78 percent and averaging 42 percent, or 420,000 mg/kg. The field measurements 

indicate that the estimated bead loss calculation presented in table 22 may be an underestimate 

by approximately an order of magnitude. However, it is not clear to what depth the beads were 

mixed into the soil during field measurements, which could account for the discrepancy. 

In actuality, the mass balance of contaminants in the beads has not been included in the modeling 

methodology. The methodology currently proposes that the total mass of metals in the released 

beads is available for both direct contact and migration to groundwater individually. In reality, 

the bead mass lost to leaching would no longer be available for ingestion, dermal contact, or 

inhalation, thereby reducing the exposure concentration of metals for the direct contact receptor. 

Similarly, bead mass removed from the marking crew storage yards by wind scour or ingestion 

would no longer be subject to leaching. These conservative assumptions provide an additional 

margin of protectiveness in the calculations. 

Concentration of Metals in Glass Beads and Leaching Potential 

The evaluation of long-term exposures requires an understanding of the long-term releases from 

beads to the environment. Most significantly, metals may migrate from glass beads through 

interactions with precipitation and migrate to the groundwater. The modeling of bead leaching 

over a period of time similar to the long-term exposure duration of the receptors provides the 

most representative assessment of risk. 

In the environment, beads are incorporated into the soil matrix, and any interactions with 

infiltrating water would be complex and include partitioning of contaminants among the beads, 

soil, and water in the pore spaces of the soil/bead matrix. As contaminants in beads go into 

solution, they may interact with soil particles and adsorb to the surface. Over time, contaminants 

may repeat this process, with the general effect of retarding the movement of some portion of the 

contaminants from freely moving with the infiltrating water through the soil column and into the 

underlying groundwater system. In addition, some portion of the contamination will remain in 

the soil matrix and never reach the groundwater. For calculation of groundwater protection 

screening levels, it is conservatively assumed that contaminants leaching from beads are not 

retained or retarded by the soil matrix, and instead travel unimpeded to a groundwater aquifer 

that is used for drinking water. 

To determine long-term groundwater concentrations, it is important to understand the magnitude 

and rate of contaminant leaching from beads. The residential receptor is assumed to ingest 
68

groundwater over a period of 30 years; therefore, an average concentration over that period of 

time is most representative of the exposure scenario. 

The results of leaching experiments may be used to estimate exposure over a lifetime by 

assuming that the leachable mass in beads enters the environment during a 1-year period. 

Experimental results may also determine whether beads in the environment longer than 1 year 

are inert and are not a source of further contamination to groundwater. 

Calculating the groundwater concentration requires an estimate of either the mass of 

contamination entering the aquifer, which can be based on the mass of contaminants that can be 

leached, or the concentration of contaminants in the leachate. These estimates can be made 

through general assumptions regarding the leaching potential of beads or through experimental 

analysis. For the development of groundwater screening levels, the mass of contamination 

leaving the beads and entering groundwater on an annual basis may be calculated from the 

experimental data, which are discussed in the following sections. 

An additional consideration is the physical location of the bead contamination within the bead 

structure. If contamination is coating the bead surface, it may leach quickly, leading to high 

initial water concentrations that quickly decline. Contamination within the bead matrix may 

provide lower initial water concentrations that persist longer. Continuing laboratory studies may 

provide data to clarify leaching dynamics. 

The leaching rates used in the evaluation are necessary to describe the following processes: 

leaching rate of contaminants from glass beads to groundwater, leaching rate of contaminants to 

soil, and leaching of contaminants in a mixture of soil and beads to groundwater. Two older 

studies are available for determining the leaching rates of metals from glass beads: the TAMU 

study published in 2011 and NJIT/RU study.(22, 23) The TAMU study evaluated the leachability of 

metals from glass beads present in an up-flow column system as a function of pH, short-term 

exposures to high-intensity ultraviolet light, short-term exposures to high temperatures, and 

particle size. The NJIT/RU study also evaluated leaching in batch reactors as a function of pH 

and particle size. In addition, the NJIT/RU study evaluated leaching using the simulated 

precipitation leaching procedure and toxicity characterization leachate procedure, and a longterm leaching experiment conducted over a period of 160 days. 

Section 2 of this report presents findings of the most recent study conducted on a large sample of 

beads from across the United States to provide a more representative study of beads actually in 

use on roads. Laboratory characterization of the State transportation department provided beads 

indicated a total arsenic concentrations ranging from 11 to 82 ppm with an overall average of 

54 ppm. Total lead ranged from 3 to 199 ppm, with an overall average of 71 ppm. Statistical 

analysis of these datasets with EPA software is summarized in table 24 for arsenic and lead.(24)

The 95-percent upper confidence intervals for arsenic and lead are 62.14 and 118.6 ppm, 

respectively. Estimates of human health risk are presented for exposure to both the mean and 

95-percent upper confidence limit (UCL95%) concentrations in source materials for comparison. 

 
69

Table 24. Summary of statistics for bead analysis. 

Parameter Arsenic Lead 

Minimum 11 3 

Maximum 82 199 

Arithmetic Average 54.4 71.47 

UCL95% 62.14 118.6 

Distribution Normal Gamma 

Notes: All concentrations in ppm. 

UCL95% is the 95-percent upper confidence limit on the mean concentration. 

Statistics are based on the average concentrations in glass beads (table 7). 

The EPA software ProUCL version 4.1, was used to generate the statistics.(24) 

The potential leaching of metals was evaluated by comparing the total metals analysis to the 

extractable metals in laboratory experiments. Similarly, the bioaccessible fraction of metals was 

determined by comparing total and bioaccessible measurements. Extractable arsenic was not 

detectable in all samples and was similarly not detectable in the bioaccessibility analysis. 

Extractable lead was measured at up to 3.4 percent of the total measurement, and bioaccessible 

concentration was up to 16.4 percent of the total (see table 20). The time series analysis of 

column leaching studies indicated that lead concentrations were all below detection, and arsenic 

leachate concentrations were below detection within 48 hours (table 25 and table 26). The 

laboratory data indicate that there is a low likelihood of significant leaching of arsenic and lead 

from pavement-marking beads. 
70 

Table 25. Summary of TTI/TAMU leaching studies for arsenic—December 2012. 

Arsenic Data (ppm) Sampling Time (hours) 

Bead 

Group 

Total Arsenic 

by KOH 0 1 2 4 8 12 24 

AA 130 0.59 0.12 0.15 0.17 BQL 0.14 0.20 

BD 138 0.13 BDL BDL BDL BDL 0.12 0.29 

BE 74 BDL BDL ND ND ND BDL 0.18 

BI 54 BDL BDL ND BDL BDL BQL 0.13 

DA 129 BDL ND ND BDL BDL BDL ND 

DB 130 BDL BDL ND ND ND BDL 0.14 DC 146 0.27 BDL BDL BDL BDL BDL BDL 

DD 122 BDL BDL ND ND ND BDL BDL 

EA 97 0.13 BDL ND BDL BDL ND ND 

FH 45 0.12 ND ND ND ND ND ND 

GA 57 0.10 ND ND ND ND ND ND 

GB 55 0.16 ND ND ND ND ND ND GC 45 0.26 BDL ND ND ND ND ND 

GD 56 0.14 BDL BDL ND ND ND ND 

KOH = potassium hydroxide ND = not detected BDL = below detection limit BQL = below quantitation limit 
71 

Table 26. Summary of TTI/TAMU leaching studies for lead—December 2012. 

Lead Data (ppm) Sampling Time (hours) 

Bead 

Group 

Total lead by 

KOH 0 1 2 4 8 12 

AA 21 ND ND ND ND ND ND 

BD 17 BQL ND ND ND ND ND 

BE 6 ND ND ND ND ND ND 

BI 4 BQL ND ND ND ND ND 

DA 8 BQL BDL ND BDL ND ND 

DB 6 ND ND ND ND ND ND DC 10 BQL ND ND ND ND ND 

DD ND ND ND ND ND ND ND 

EA ND ND ND ND ND ND ND 

FH 124 BQL ND ND ND ND ND 

GA ND ND ND ND ND ND ND 

GB 20 ND ND ND ND ND ND GC 8 ND ND ND ND ND ND 

GD 66 ND ND ND ND ND ND 

KOH = potassium hydroxide ND = not detected BDL = below detection limit BQL =below quantitation limit 
72

RISK EVALUATION RESULTS 

The estimate of human health risk from glass bead exposures was based on the residential and 

worker scenarios. Exposure pathways included in the evaluation were incidental ingestion and 

inhalation of re-suspended particulates. Although the laboratory data indicate a low likelihood of 

metal leaching from beads, the groundwater ingestion pathway has been evaluated for 

completeness. 

Toxicity data used in the risk evaluation of arsenic are presented in table 21, and the results of 

the risk evaluation for beads in soil are presented in table 27. The exposure of receptors to 

arsenic at the average concentration resulted in risks of 8.8E-7, 2.5E-6, and 5.4E-7 for the adult, 

child, and worker, respectively. All carcinogenic risks are within the EPA acceptable risk range 

of E-6 to E-4. The majority of risk is via the ingestion pathway with insignificant risk owing to 

inhalation. The hazards for arsenic were all below the threshold hazard of 1, indicating a low 

likelihood of adverse human health effects due to exposure to beads released to the environment. 

These calculations were based on a source that was 42-percent beads. 

Also presented in table 27 are results for exposures at the UCL95% arsenic concentration of 

62 ppm for comparison. All risks and hazards are within the acceptable range and are not likely 

to present a health hazard. These calculations also assumed that the source material was 

42-percent glass beads in the soil. 

The potential for leaching of arsenic to groundwater is evaluated in table 28. Laboratory 

experiments yielded conflicting results regarding the leaching of arsenic and lead from glass 

beads. The risk evaluation was based on the most conservative leachate concentration observed 

(speciated arsenic (V) at 15 g/L). Additional conservatism is included in the calculation 

because these leachate concentrations were assumed to persist for the duration of the exposures 

(up to 30 years in the case of the adult resident). The estimated groundwater concentration of 

0.63 g/L is below the Federal Maximum Contaminant Level of 10 g/L but exceeds the EPA 

RSL of 0.045 g/L. The estimated risk associated with arsenic in groundwater was 1.4E-5, 

which is within the acceptable risk range, even with the inclusion of conservative assumptions in 

the calculations. The results indicate that adverse human health impacts are unlikely via the 

groundwater pathway. 

μ

μ μ

μ
73 

Table 27. Summary of glass bead risks for arsenic. 

Exposure Pathway

Adult Resident Child Resident Indust

ILCR HQ ILCR HQ ILCR 

Arsenic (54 ppm) 

Bead Ingestion 8.8E-07 4.6E-03 2.5E-06 3.2E-02 5.2E-07 Bead Inhalation 6.2E-11 2.7E-03 2.5E-11 3.0E-03 9.8E-11 Totals 8.8E-07 7.3E-03 2.5E-06 3.5E-02 5.2E-07 

Arsenic (62 ppm) 

Bead Ingestion 1.0E-06 5.2E-03 2.9E-06 3.7E-02 6.0E-07 Bead Inhalation 7.1E-11 3.1E-03 2.8E-11 3.4E-03 1.1E-10 Totals 1.0E-06 8.3E-03 2.9E-06 4.0E-02 6.0E-07 

ILCR = incremental lifetime cancer risk HQ = hazard quotient ppm = parts per million Notes: Beads were assumed to represent 42 percent of the bead/soil source. Arsenic concentrations of 54 and 62 ppm are the arithmetic average and UCL95%, respectively (table 24). 
74 

Table 28. Estimated groundwater risk for arsenic. 

Constituent 

MCL 

( g/L) 

Tap Water RSL

( g/L) 

Concentration 

in Leachate 

( g/L) 

Estimated 

Groundwater 

Concentration 

( g/L) 

Esti

Groun

R

Arsenic 10 0.045 15 0.63 1.4

Notes: Tap water RSL is based on carcinogenic effects to an adult/child at a risk level of 1E-6. Maximum contaminant level (MCL) is a federally promulgated standard that accounts for economic and human health considerations. Concentration in leachate is an upper bound based on speciated arsenic analysis of bead sample DC. The majority of sa

indicated < 0.7 g/L of extractable arsenic. Estimated groundwater concentration assumed that the bead source is diluted to 42 percent of the soil matrix and a DAF 

the aquifer. Groundwater concentration is calculated as: Leachate Conc ( g/L) × 0.42 × (1/10) = 0.63 g/L. Estimated groundwater risk is based on the tap water RSL, and is calculated as: Tap water RSL ( g/L) × Groundwater Concentration ( g/L)/1E-6. 

μ μ μ μ

μ

μ μ

μ μ
75

Table 29 presents the bead screening levels for arsenic based on the exposure scenarios and 

pathways evaluated. Results are presented assuming a source that is 100-percent beads, as well 

as a source that is 42-percent beads diluted with uncontaminated soil. Screening levels are 

generated based on both carcinogenic and non-carcinogenic effects, with the lower value 

selected as the final screening level. For all scenarios (residents and industrial) the carcinogenic 

exposure via bead ingestion was the most significant pathway. Screening levels based on noncarcinogenic exposures were approximately an order of magnitude less stringent than those for 

carcinogenic effects. For an undiluted source, screening levels for the adult, child, and industrial 

worker were 252, 90, and 421 ppm, respectively. When considering a source that is 42-percent 

beads, the screening levels are 600, 220, and 1,000 ppm, respectively. The final screening level 

recommendation of 220 ppm is based on a child exposure to source material that is 42-percent 

beads. 

The evaluation of lead used EPA models for adults and children as presented in table 30 and 

table 31. The exposures to lead and resulting blood lead levels are compared with the acceptable 

level of 10 g of lead per dL of blood. The ALM indicated a blood lead concentration of 

approximately 1.9 g/dL, and the ALM calculated screening level was 580 ppm. The IEUBK 

model for child lead exposure estimated a blood lead level of ~0.6 g/dL, and the IEUBK 

calculated screening level was > 1,000 ppm. The adult and child lead modeling indicates that 

adverse health effects are not likely due to lead exposures. These results are based on the 

UCL95% concentration of 118 ppm for lead in undiluted beads, which represents a conservative 

exposure that is unlikely to be exceeded. 

μ

μ

μ
76 

Table 29. Summary of glass bead screening levels for arsenic. 

Exposure Pathway

Adult Resident Child Resident Ind

Carcinogenic 

NonCancer Screening Level Carcinogenic Non- Cancer Screening Level Carcinogenic 

Undiluted Bead Source 

Ingestion 2.6E+02 5.0E+03 2.6E+02 9.1E+01 7.0E+02 9.1E+01 4.4E+02 7Inhalation 3.7E+06 8.4E+03 8.4E+03 9.2E+06 7.7E+03 7.7E+03 2.3E+06 1Screening Level 2.6E+02 3.1E+03 2.6E+02 9.1E+01 6.5E+02 9.1E+01 4.4E+02 4

Diluted Bead Source (42% beads) 

Ingestion 6.2E+02 1.2E+04 6.2E+02 2.2E+02 1.7E+03 2.2E+02 1.0E+03 1Inhalation 8.7E+06 2.0E+04 2.0E+04 2.2E+07 1.8E+04 1.8E+04 5.6E+06 2Screening Level 6.2E+02 7.5E+03 6.2E+02 2.2E+02 1.5E+03 2.2E+02 1.0E+03 1

Notes: All units are ppm. Values in bold are the final screening values. Carcinogenic target incremental lifetime cancer risk (ILCR) was 1.0E-5. Target HI was 1.0. Beads were assumed to represent 42 percent of the bead/soil source (table 15). 
77 

Table 30. Calculations of adult blood lead concentrations. 

Variable Description of Variable Units 

GSDi and PbBo 

from Analysis of 

NHANES 1999–

2004 

PbS Soil lead concentration μg/g or ppm 118 

Rfetal/maternal Fetal/maternal PbB ratio — 0.9 

BKSF Biokinetic Slope Factor g/dL per g/day 0.4 

GSDi Geometric standard deviation PbB — 1.8 

PbB0 Baseline PbB g/dL 1.0 

IRS Soil ingestion rate (including soil-derived indoor dust) g/day 0.050 

IRS+D Total ingestion rate of outdoor soil and indoor dust g/day 0.050 

WS Weighting factor; fraction of IRS+D ingested as outdoor soil — 0.750 

KSD Mass fraction of soil in dust — 0.500 

AFS, D Absorption fraction (same for soil and dust) — 0.17 

EFS, D Exposure frequency (same for soil and dust) days/yr 350 

ATS, D Averaging time (same for soil and dust) days/yr 365 

PbBadult PbB of adult worker, geometric mean μg/dL 1.4 

PbBfetal, 0.95 95th percentile PbB among fetuses of adult workers g/dL 3.3 

PbBt Target PbB level of concern (e.g., 10 g/dL) g/dL 10.0 

P(PbBfetal > 

PbBt) 

Probability that fetal PbB > PbBt, assuming 

lognormal distribution Percent 0.0% 

NHANES = National Health and Nutrition Examination Survey — indicates unitless Notes: Absorption fraction is based on maximum bioaccessible lead measurements for bead group AC. Source: http://www.epa.gov/superfund/lead/products.htm#alm .

μ

μ

μμ

μ μ
78 

Table 31. Calculations of adult lead screening levels. 

Variable Description of Variable Units 

GSDi and PbBo 

from Analysis of 

NHANES 1999–

2004 

PbBfetal, 0.95 95th percentile PbB in fetus g/dL 10 Rfetal/maternal Fetal/maternal PbB ratio — 0.9 BKSF Biokinetic Slope Factor μg/dL per g/day 0.4 GSDi Geometric standard deviation PbB — 1.8 PbB0 Baseline PbB μg/dL 1.0 IRS Soil ingestion rate (including soil-derived indoor dust) g/day 0.050 AFS, D Absorption fraction (same for soil and dust) — 0.16 EFS, D Exposure frequency (same for soil and dust) days/yr 350 ATS, D Averaging time (same for soil and dust) days/yr 365 PRG Screening Level ppm 1,051 

NHANES = National Health and Nutrition Examination Survey — indicates unitless Notes: Absorption fraction is based on maximum bioaccessible lead measurements for bead group AC, Source: http://www.epa.gov/superfund/lead/products.htm#alm 

μ

μ
79 

GUIDANCE FOR DECISIONMAKING 

The risk evaluation methods outlined in this report have been developed to provide reasonably 

conservative screening levels for protection against adverse human health effects. The exposure 

evaluation has documented the current understanding of potential human interaction with beads 

during use by workers and after release to the environment. 

The determined screening levels for arsenic and lead are above the current maximum content of 

200 ppm arsenic and 200 ppm lead adopted in MAP-21, the Moving Ahead for Progress in the 

21st Century Act. Therefore, the existing legislation is determined to be protective of human 

health when all currently available data are considered. 

The analysis includes a number of conservative assumptions: 

 Bead leaching observed over 48-h laboratory experiments are representative of long-term 

releases from beads in the environment. 

 Bead concentrations are represented by using UCL95% statistics from the laboratory 

results. 

 Bioaccessible and extractable fractions of metals from beads are represented by upper 

bound estimates from the laboratory results. 

 The fraction of beads in the bead/soil matrix are represented by the average observed in 

the field. 

Environmental exposures are likely to be lower than those estimated in this risk evaluation. 

Because the application of conservative assumptions does not result in unacceptable risk to 

human health, less intense exposures would be similarly protective. 

Although current risk levels are minimal, field observations of bead workflow processes did 

identify easy-to-implement practices that would further reduce exposure. In the occupational 

setting, employees were observed handling the beads without gloves or masks. Concern was 

raised during the visits and during the model peer-review process that employees may be 

exposed to high levels of silica from bead dust that could lead to silicosis. Wearing gloves and 

respirators to protect against potential silica exposures would have the added benefit of reducing 

exposure to arsenic and lead. 

The model also predicted potential concern regarding the impact of bead storage facilities on 

residential groundwater owing to leaching of arsenic and lead from the beads that may occur 

within some climates. Current practices of bead storage prevent rainfall from leaching arsenic 

and lead from stored beads to groundwater. Efforts to reduce bead spillage during transfer would 

also reduce the likelihood that bead contaminated media could affect groundwater. Existing 

locations with long-term histories of bead (and or cullet) storage and transfer may present a 

challenge to groundwater where shallow groundwater tables are present. 

Although application of the beads does result in bead loss to the surrounding environment, long 

line applications in which bead loss may reach up to 30 percent under poor application practices 
80 

or conditions does not appear to present a risk to human health or the environment. During long 

line applications (roadway center and edge line markings), bead loss occurs over a long distance 

and the beads quickly scatter. Long line application is also performed using bead drop equipment 

in a manner that does not expose employees to the lost beads. Short line applications (cross 

walks and intersections), however, do result in greater worker exposure and higher 

concentrations of spilled beads accessible to the general public. Efforts should be made to reduce 

excess bead loss during short line applications. Employees putting down beads should wear 

gloves to reduce exposure, and beads should be dropped so that the majority land on the binder 

(paint, thermoplastic, or epoxy). In particular, efforts should be made to reduce excess bead loss 

in short line applications in locations with curbs and gutters because of the potential slipping 

hazard. 

Line removal presents a separate set of potential risks. To minimize exposure to arsenic and lead 

from glass beads during marking removals, employees should wear gloves, eye protection, and 

respirators if they are performing removal techniques that generate dust. Grinding, sand-blasting, 

or water blasting systems used to remove the lines should be equipped with vacuum recovery 

systems to reduce dust removal. Additional investigations into dust exposures during marking 

removal are advised. 

As a final comment, arsenic and lead in glass beads may be a minor concern for environmental 

health and safety compared with other components in pavement-marking systems. A thorough 

review of the risk posed by residential and occupational exposures to components in other 

marking systems is advised to ease potential concerns regarding environmental and worker 

safety. 
81 

ACKNOWLEDGMENTS 

Completion of this research would not have been possible without the following individuals 

whom we gratefully acknowledge: 

 Dr. William James from the TAMU Center for Chemical Characterization. 

 Karen Mangalgiri and Heidi Wood from the Boulanger Research Group for their help and 

advice in research design, data acquisition, and data interpretation. 

 Drs. Thabet Tolyamat, Timothy Taylor, and Mallik Nadagouda from EPA. 

 Carl Andersen and Terry Arnold, FHWA. 

 Paul Vinik, FDOT. 

 All the support staff at TTI and the TAMU Zachry Department of Civil Engineering 

business office for their help in project administration. 

83 

REFERENCES 

1. Kelley, M.E., Brauning, S. E., Schoof, R.A., and Ruby, M.V. (2002). Assessing Oral 

Bioavailability of Metals in Soil. Columbus, Ohio: Battelle Press. 

2. Brinkley, A.L. (1994). Characterization of Rocky Flats and Oak Ridge Glass Containing 

Mixed Wastes. Retrieved December 23, 2011 from 

http://dspace.mit.edu/handle/1721.1/28108. 

3. EPA (1996). Method 3052. Retrieved December 23, 2011, from EPA 

http://www.epa.gov/osw/hazard/testmethods/sw846/pdfs/3052.pdf. 

4. EPA (1989). Risk Assessment Guidance for Superfund (RAGS), Volume I, Human 

Health Evaluation Manual (Part A) Interim Final, EPA/540/1-89/002. 

5. Boulanger, B., Desai, A.B.R., and Carlson, P. (2011). Heavy Metal Content and Leaching 

Potential of Recycled Glass Beads Used in Pavement Markings: Texas Transportation 

Institute. 

6. Axe, L.B., Jahan, K., Sandhu, N. K., Ramanujachary, K.V., Ndiba, P.K., and Magdaleno, 

F. (2011). Heavy Metal Contamination in Highway Marking Glass Beads. New Jersey 

Department of Transportation. 

7. EPA (1996). Method 3050B. Retrieved April 4, 2011, from EPA 

http://www.epa.gov/osw/hazard/testmethods/sw846/pdfs/3050b.pdf. 

8. Almassalkhi, B. (2009). Arsenic Speciation, Detection, and Quantification Using High 

Performance Liquid Chromatography and Inductively Coupled Plasma Mass 

Spectrometry. University of Cincinnati, Master’s Thesis. 

9. Ljung, K., Siah, W.S., Devine, B., Maley, F., Wensinger, A., Cook, A., and Smirk, M. 

(2011). Extracting Dust from Soil: Improved Efficiency of a Previously Published 

Process. Science of the Total Environment, 410–411, 269–270. doi: 

10.1016/j.scitotenv.2011.07.061. 

10. Ljung, K., Torin, A., Smirk, M., Maley, F., Cook, A., and Weinstein, P. (2008). 

Extracting Dust from Soil: A Simple Solution to a Tricky Task. Science of the Total 

Environment, 407(1), 589–593. doi: 10.1016/j.scitotenv.2008.09.007. 

11. Misra, K., Mehta, R.K., and Lan, P. (2001). Remediation of Radium From Contaminated 

Soil. Ohio: EPA. 

12. Neo, N., Yamazaki, S., and Miyashita, Y. (2009). Data Report: Bulk Rock Compositions 

of Samples from the IODP Expedition 309/312 Sample Pool, ODP Hole 1256D1. Paper 

presented at the Proceedings of the Integrated Ocean Drilling Program, Washington, DC. 
84 

13. Uchida, S., Tagami, K., and Tabei, K. (2005). Comparison of Alkaline Fusion and Acid 

Digestion Methods for the Determination of Rhenium in Rock and Soil Samples by ICPMS. Analytica Chimica Acta, 535(1–2), 317–323. doi: 10.1016/j.aca.2004.11.065. 

14. EPA (2002). Supplemental Guidance for Developing Soil Screening Levels for 

Superfund Sites. Office of Solid Waste and Emergency Response (OSWER) 9355.4-24. 

December 2002. 

15. Cowherd, C., Jr., Muleski, G.E., Englehart, P.J., and Gillette, D.A. (1985). Rapid 

Assessment of Exposure to Particulate Emissions from Surface Contaminated Sites, 

Midwest Research Institute, Kansas City, Missouri, 64110, EPA/600/8-85/002. 

16. AASHTO (2009). Standard Specifications for Glass Beads Used for Pavement Markings, 

American Association of State Highway and Transportation Officials, Designation M247-09, 444 N Capitol St. NW, Suite 249, Washington, DC 20001. 

17. EPA (1991). Role of Baseline Risk Assessment on Remedy Selection Criteria. OSWER 

Directive 9355.0-30, April 22, 1991. 

18. EPA (2011). Exposure Factors Handbook. 2011 Edition, U.S. Environmental Protection 

Agency, Washington, DC, EPA/600/R-09/052F, 2011. 

19. EPA (2008). Child-Specific Exposure Factors Handbook, National Center for 

Environmental Assessment, Office of Research and Development, EPA/600/R-06/096F. 

20. EPA (1997). Exposure Factors Handbook. Office of Research and Development, 

Washington, DC. EPA/600/P-95/002Fa. 

21. EPA (2012), Pacific Southwest Region 9 Regional Screening Levels Retrieved December 

15, 2012, from EPA http://www.epa.gov/region9/superfund/prg/index.html. 

22. TAMU (2011). Heavy Metal Content and Leaching Potential of Recycled Glass Beads 

Used in Pavement Markings, Texas Transportation Institute, The Texas A&M University 

System, College Station, Texas 77843-3135, April 1, 2011. 

23. NJIT-RU (2010). Heavy Metal Contamination in Highway Marking Glass Beads, New 

Jersey Institute of Technology and Rowan University for the New Jersey Department of 

Transportation, Trenton, NJ 08625, December 2010. 

24. ProUCL version 4.1 from http://www.epa.gov/osp/hstl/tsc/software.htm. 

HRDS-10/01-14(WEB)E