Leaching of arsenic, lead, and antimony from highway-marking glass beads

Glass beads embedded in pavement markings provide retroreflectivity to ensure safe driving. Recently, elevated concentrations of arsenic (As), antimony (Sb), and lead (Pb) have been observed in glass beads imported to the US. After an initial assessment of total concentrations in glass beads, a factorial study was conducted to determine the impact of environmentally relevant factors on leaching: pH (4, 7, and 10), chemicals applied on roadways (NaCl, CaCl2, KCH3COO, and KCl), ionic strength (10-2-10-1 M), particle size (>100 and <37 μm), and time (18 h to 160 days). Additional leaching studies included the US EPA toxicity characteristic leaching procedure (TCLP) and synthetic precipitation leaching procedure (SPLP). Results demonstrated that the most important factors affecting leaching were pH and time. For anions of As and Sb, leaching tended to increase with increasing pH, whereas for the cation Pb, leaching increased as pH decreased. As expected, leaching increased with a decrease in particle size. Although the TCLP results revealed greater leaching than the SPLP, concentrations were one to two orders of magnitude less than concentrations observed in the factorial experiments.