Date of Award
Doctor of Philosophy in Environmental Engineering - (Ph.D.)
Civil and Environmental Engineering
John R. Schuring
Glass beads are embedded in pavement markings to obtain retroreflectivity which plays a crucial role in the lighting-up effect needed for safe driving. Elevated metal and metalloid concentrations of As, Sb, and Pb have recently been observed in imported glass beads. The main objective of this research was to assess the environmental impact associated with applying these imported glass beads in highway markings. To achieve this objective, total metal concentrations were measured using two techniques: hydrofluoric acid digestion followed by inductively coupled plasma mass spectroscopy (HF/ICP-MS), and field portable x-ray fluorescence (FP-XRF) spectroscopy. A number of leaching studies were conducted and included two standard United States Environmental Protection Agency (U.S. EPA) methods: the toxicity characteristic leaching procedure (TCLP) and the synthetic precipitation leaching procedure (SPLP). In addition, a factorial study was conducted to determine the impact of environmentally relevant factors such as pH, chemicals applied on roadways, particle size, and time on metal and metalloid leaching. To compare results among the three types of studies (TCLP, SPLP, and factorial study), a select batch of glass beads with elevated concentrations was used. FP-XRF was observed to be as reliable a tool for measuring total metal and metalloid concentrations and is recommended over the use of HF/ICP-MS. Results demonstrated that the most important factors affecting leaching were pH and time. For anions such as HAsO42- and SbO3-, leaching increased with increasing pH, while for cations including Pb2+, it increased as pH decreased. Sequential extraction was conducted as well to better understand the form of metals and metalloids associated with the glass beads. While 3% were extracted in the exchangeable (As, Mn, and Ba) and the oxidizable forms (Pb), greater than 97% of metals and metalloids were associated with the glass matrix. Further studies to assess leaching as a function of total concentration in the imported batch were conducted for 30 days. Non-parametric statistics were applied to test concentrations that resulted in excess of the groundwater quality criteria. Results demonstrated that the New Jersey Default Leachate Groundwater limits for As were exceeded for 98% of the samples tested. In case of Pb, these limits were exceeded for 58% of the samples and with Sb 15%. These results suggest a potential environmental impact to groundwater used as a drinking water source when either storing glass beads in bulk or disposing of the roadway marking material in bulk.
Sandhu, Nimrat K., "Leaching of metals and metalloids from highway marking glass beads and the potential environmental impact" (2012). Dissertations. 345.