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Paper No. 23
Presentation Time: 9:00 AM-6:00 PM
DEVELOPMENT OF ROCK PHOSPHATE-AGAROSE GEL BEADS TO MONITOR THE RELEASE OF LEAD INTO STREAM WATER FROM A CONTAMINATED INDUSTRIAL SITE
Rock phosphate and other phosphorus fertilizers containing apatite group minerals have been used to effectively fix bioavailable Pb in soil as the extremely water-insoluble mineral pyromorphite. In this study, we used rock phosphate to develop a sensing device for use in stream water that could be used to assess the efficiency of Pb remediation in contaminated soils and mine tailings. Rock phosphate powder was immobilized within agarose gel beads, which were prepared by dropping a heated rock phosphate-agarose mixture into mineral oil. Initial laboratory studies showed the rapid concentration of Pb in aqueous solutions onto the prepared beads. The beads were placed into nylon mesh bags so they could be suspended in stream water and remain in constant contact with flowing water. Field tests were carried out at the site of an abandoned and unremediated industrial site in northwestern Pennsylvania (USA) where concentrated sulfuric acid was recycled for regional oil refineries between ca. 1870 and 1917. The soil at the currently unvegetated site is highly contaminated with up to 43,000 mg/kg total Pb and other metals, due to the extensive use of Pb pans and tank liners for acid processing. A soil extraction method simulating human stomach digestion indicated that the relative human bioaccessibility ranged from 5 to 44% of the total Pb soil concentrations. Rock phosphate bead bags were placed at various locations in a stream that bisected the contaminated site, and these were recovered periodically over a three-month period of time. Total acid digestion of phosphate beads left below the site showed that they accumulated Pb being transported by stream water from the site, despite aqueous Pb concentrations in water that were below ICP-MS analysis detection limits. The phosphate bead approach may thus facilitate the long-term monitoring of Pb remediation efficiency at similar contaminated industrial and mining sites.