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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

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Publication Number:  FHWA-HRT-14-021    Date:  January 2014
Publication Number: FHWA-HRT-14-021
Date: January 2014


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

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).

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.