title: Prediction of Pb speciation in concentrated and dilute nutrient solutions.
abstract: Despite the presence of numerous studies in the literature examining the phytotoxicity of Pb, there is a lack of precise quantitative data on limiting concentrations of Pb for plant growth. Using the PhreeqcI chemical equilibrium model, simulations were conducted to examine the speciation of Pb in concentrated and dilute nutrient solutions. Due to the higher P concentration of Hoagland's solution (1000microM), precipitation of chloropyromorphite (Pb5(PO4)3Cl) was predicted to occur at lower pH values, and at lower Pb concentrations, than for a dilute nutrient solution (2microM P). Although nutrient solutions prepared in the glasshouse were supersaturated (and Pb concentrations were substantially higher than predicted by modeling), they confirmed the importance of the P concentration in influencing the precipitation of Pb. Given the low solubility of Pb-phosphates, nutrient solutions with low P concentrations should be utilized, and plant growth should be related to measured Pb concentrations rather than to the quantity of Pb initially added.
authors.affiliation: School of Land, Crop and Food Sciences, The University of Queensland, St. Lucia, Queensland 4072, Australia. p.kopittke@uq.edu.au
authors.forename: P M
authors.initials: PM
authors.lastname: Kopittke
authors.forename: C J
authors.initials: CJ
authors.lastname: Asher
authors.forename: N W
authors.initials: NW
authors.lastname: Menzies
mesh_terms: D011232:Chemical Precipitation; D002712:Chlorides; D003198:Computer Simulation; D006812:Humic Substances; D006863:Hydrogen-Ion Concentration; D007854:Lead / Q000633:toxicity*; D008954:Models, Biological; D063245:Plant Development; D010944:Plants / Q000187:drug effects*; D012989:Soil Pollutants / Q000633:toxicity*; D012995:Solubility; D018675:Toxicity Tests / Q000379:methods*
chemical_list: D002712:Chlorides; D006812:Humic Substances; D012989:Soil Pollutants; D007854:Lead