Screening Level Assessment of Arsenic and Lead Concentrations in Glass Beads Used in Pavement Markings

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.

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.