Detection of Lead Mobilization From Soil at An Abandoned Sulfuric Acid Recycling Plant Using Rock Phosphate-Immobilized Gel Beads.

Sulfuric acid used to clarify kerosene at oil refineries in Titusville, PA in the 1800s was recycled at a nearby acid plant.  This facility cleaned the spent acid of accumulated tar and restored it to full strength by distillation.  In this study, we examined the unvegetated site of an acid plant that was active between ca. 1870 and 1917.  The soil at the site was highly contaminated with up to 43,000 mg/kg total Pb, distributed spatially in a way consistent with the former locations of Pb distillation pans and lead-lined storage tanks.  Other metals, especially antimony, were also found in high concentrations.  An acid extraction method simulating human stomach digestion indicated that the relative human bioaccessibility of the Pb at the site ranged from 5 to 44% of the total Pb concentrations.  

 

Rock phosphate and other phosphorus fertilizers have been used previously to effectively fix bioavailable Pb in soil as extremely insoluble pyromorphite-like minerals.  In this study, we immobilized rock phosphate in beads prepared from two different gel matrices, calcium alginate and agarose.  These were put into mesh bags, placed at various locations in a stream that bisected the contaminated industrial site, and recovered every month over a three-month period of time.  Total acid digestion of the phosphate beads indicated that they were effective in the detection of Pb being transported in stream water from the site, despite aqueous Pb concentrations in water that were below ICP-MS analysis detection limits.  Calcium alginate-based beads disintegrated over time, suggesting the influence of a calcium-chelating agent in the stream water.  The phosphate bead approach may facilitate the long-term monitoring of Pb remediation effectiveness at similar contaminated sites.