INITIAL INVESTIGATIONS OF LEAD CHROMATE TRAFFIC PAINT IN THE MIDWEST UNITED STATES: CHARTING A PATH FORWARD FOR INVESTIGATING A POTENTIAL SOURCE OF LEAD AND HEXAVALENT CHROMIUM POLLUTION

Lead is globally recognized as a neurotoxin while hexavalent chromium is extensively recognized as a carcinogen. The nature and forms of these metals in the environment are therefore of high concern for both human health and environmental ecosystems. One potentially widespread form of both of these metals is lead chromate (PbCrO4) which contains lead as Pb2+ and chromium as Cr6+. In particular, lead chromate is a historic traffic paint pigment with a poorly constrained history of use. To date, its occurrence is confirmed southwestern portions of the state of Ohio and in the city of Philadelphia, Pennsylvania, yet the extent of its occurrence in historical and extant traffic paint remains poorly constrained. A survey of yellow traffic paint is currently underway across multiple midwestern states (e.g., Ohio, Indiana, Illinois) in order to assess whether PbCrO4 is common, what the nature of this paint is, and whether there are indications of the pathways through which this material may be cycling through the environment. Where observed using scanning electron microscopy (SEM), PbCrO4 is shown to occur in a variety of textures including nanometer-scale particles on the order of 200 to 100 nm in maximum diameter, to larger aggregates of particles that are several tens of micrometers in diameter. Some samples also display a record of partial dissolution and there is evidence of dispersal into soils and aquatic environments at local scales. These initial observations suggest that 1) PbCrO4can be transported from road surfaces into surface water systems, soils, and air; 2) that detailed systematic geographic studies are warranted and 3) that a comprehensive survey of traffic paint in the U.S. is justified. Future investigations should involve transmission electron microscopy (TEM) to better constrain PbCrO4 nanoparticle dimensions and dissolution processes. Dissolution behavior of PbCrO4 in simulated rainwater and road treatment conditions should also be evaluated. Owing to the well-recognized toxicity of lead and hexavalent chromium, when present, PbCrO4 may pose some environmental health risk for persons working in road construction, environmental remediation, as well as children which are at higher risk for soil exposure.