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IN-VITRO FORMATION OF PYROMORPHITE VIA REACTION OF PB SOURCES WITH SOFT-DRINK PHOSPHORIC ACID
Citation:
Scheckel*, K G. AND J A. Ryan*. IN-VITRO FORMATION OF PYROMORPHITE VIA REACTION OF PB SOURCES WITH SOFT-DRINK PHOSPHORIC ACID. SCIENCE OF THE TOTAL ENVIRONMENT 302(1-3):253-265, (2003).
Description:
Similar results were observed Pyromorphite (Pb5(PO4)3C1) is a Pb mineral whose rapid kinetic formation and thermodynamic stability (Nriagu, 1973, 1974) has gained much attention in recent years as a mechanism to diminish Pb toxicity. Our research examined the in-vitro formation of pyromorphite (Ksp=10.25)to significantly reduce Pn bioavailability via the reaction of PbC12 and Pb paint with cola soft drinks (regular, caffeine-free, and diet) that contain phosphoric acid. X-ray diffraction (XRD) spectroscopy was employed to identify and quantify the crystal phases. The experiments consisted of a two-phase experimental design to simulate stomach and gastrointestinal (GI) conditions comprised of an initial reaction system (stomach) at pH 2.0 for 1 hour at 37 degrees C and second-phase cxonditions (GI tract) at pH 7.0 for 5 hours at 37 degrees C. The results showed that available Pb in solution was quickly transformed to pyromorphite by a precipitation mechanism. The PbCI2 experiments observed over90% Pb removal from solution within 30 seconds and nearly all (>93-100%) of the Pb was converted to pyromorphite within 6 hours. Similar results were observed in the Pb-paint system in which all of the available Pb initially present in solution was stablized as pyromorphite within a short eaction period. While only 70% of the total PBb in the paint was converted to pyromorphite, there were minimal amounts of Pb in solution. It appeared the dissolution mechanism allowing Pb in the paint to be realeased into the cola solution was repressed and was attributed to precipitation of pyromorphite on the surfaces of Pb-paint particles that inhibited further Pb release. The results of this research indicate that the in-vivo formation of pyromorphite in children that ingest Pb-contaminted material (soil, dust, paint) with a phosphate source, such as a cola soft drink, may significantlly reduce Pb bioavailability and allow passage of the pyromorphite material through the GI tract with minimal Pb absorption into the body.