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

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 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.