DISSOLUTION EXPERIMENTS OF YELLOW TRAFFIC PAINT CONTAINING LEAD CHROMATE (PBCRO4)

Pollution from heavy metals in urban environments is a topic of growing concern because many metals, including Pb and Cr, are a human health hazard. Exposure to Pb and Cr has been linked to the inhibition of neurological development, and toxic, carcinogenic (for dissolved Cr(VI)), effects on many organs. Yellow traffic paint (YTP), a blend that may contain crocoite (PbCrO₄), organic polymers, and binders, is a potential source of both Pb and Cr(VI). Recently, YTP has been studied for its potential contribution to pollution but detailed dissolution experiments have not been performed. To prepare for these experiments, YTP and asphalt were collected in Philadelphia from a road surface. The collected samples and synthetic PbCrO₄ were analyzed with X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX) for both ESEM and TEM, and X-ray fluorescence; using this multi-analytical approach we determined mineral phase occurrence, morphometry, dimensional distributions, crystal structure, and elemental composition. The XRD results demonstrated that the primary crystalline phases present in YTP were calcite, crocoite, dolomite, and rutile. Three batch dissolution experiments, with YTP, asphalt, and synthetic PbCrO₄ were performed to simulate ingestion (1 hour at 37 °C in gut fluid), inhalation (1 week at 37 °C in lung fluid or Gamble’s solution), and environmental interaction (1 week at 23 °C in rain water). Elemental releases were determined with inductively coupled plasma-optical emission spectrometry (ICP-OES), and results indicated that little to no Pb and Cr were leached from the YTP during the three experimental procedures. The ESEM and TEM procedures performed above were repeated at the end of each dissolution experiment. The ESEM results for YTP showed similar dimensional distributions after gut, lung, and rain interactions and similar Pb/Cr values before and after the experiments. Our results suggest that YTP surface transformations (e.g., redox states) should be further investigated. Our approach using an unprecedented multi-analytical methodology will potentially help to inform YTP regulations.