title: Organic acids inhibit the formation of pyromorphite and Zn-phosphate in phosphorous amended Pb- and Zn-contaminated soil.
abstract: Pyromorphite (PY) and some zinc phosphates (Zn-P) are very sparingly soluble minerals and hence can immobilize Pb and Zn in contaminated soils. However, mechanisms leading to the poor efficiency of PY and Zn-P formation in contaminated soils amended with P still remain unclear. We studied the influence of two low molecular weight organic acids (LMWOA) - oxalic acid and citric acid and diethylene triamine pentaacetic acid (DTPA) - in PY and Zn-P formation in a P-amended contaminated soil. Despite the high levels of metals (∼4% Pb and 21% Zn) in the study soil, the addition of up to 1% inorganic P transformed only up to 37% and 17% of the total Pb and Zn to PY and Zn-P, respectively. Semi-quantitative estimates from a linear combination fitting of X-ray absorption near edge spectra (LC-XANES fitting) showed that the formation of PY decreased from 37% to 3% of the total Pb in the presence of oxalic acid and the addition of 1% P. The reduced PY formation may be associated with the increase in organic-bound Pb from 9% to 54% and decrease in carbonate associated Pb from 42% to 12% with oxalic acid addition as indicated by a chemical sequential extraction (SE) technique. Citric acid seemed to have a less adverse effect in PY formation than oxalic acid. Our data also suggests both oxalic and citric acids have less adverse effects on the efficiency of Zn-P formation. From this study we conclude that the abundance of LMWOA in soil environments can be one factor contributing to the poor efficiency of P amendments practices to effectively immobilize Pb and Zn in metal contaminated soils.
authors: University of Northern British Columbia, Natural Resources and Environmental Studies, Prince George, BC, Canada V2N4Z9. debela@unbc.ca
authors: F
authors: F
authors: Debela
authors: J M
authors: JM
authors: Arocena
authors: R W
authors: RW
authors: Thring
authors: T
authors: T
authors: Whitcombe
mesh_terms: D000143:Acids / Q000737:chemistry*; D019343:Citric Acid / Q000737:chemistry; D008903:Minerals / Q000737:chemistry*; D009930:Organic Chemicals / Q000737:chemistry*; D019815:Oxalic Acid / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry*; D010758:Phosphorus / Q000737:chemistry*; D058441:Rhizosphere; D012989:Soil Pollutants / Q000737:chemistry*; D017967:Zinc Compounds / Q000737:chemistry*
chemical_list: D000143:Acids; D008903:Minerals; D009930:Organic Chemicals; D010710:Phosphates; D012989:Soil Pollutants; D017967:Zinc Compounds; C471364:pyromorphite; C043952:zinc phosphate; D010758:Phosphorus; D019343:Citric Acid; D019815:Oxalic Acid