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 = 106x 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 decision-making. 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 bio-accessible arsenic levels in the beads were below instrument detection limits, and extractable and bio-accessible 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 riskwhile meeting retroreflective performance criteria. (Author/publisher)
Samenvatting