title: Biogeochemistry of fluoride in a plant-solution system.
abstract: Fluoride (F-) pollutants can harm plants and the animals feeding on them. However, it is largely unknown how complexing and chelating agents affect F bioavailability. Two studies were conducted that measured F- bioavailability and uptake by rice (Oryza sativa L.). In the first study, rice was grown in solution culture (pH 5.0) with 0, 2, or 4 mM F- as KF to compare the interaction of F- with humic acid (HA) and with a conventional chelating agent, N-hydroxyethylenthylenediaminetriacetic acid (HEDTA). In the second study, F was supplied at 0, 0.5, 1.0, and 2.0 mM KF with an additional 2 mM F- treatment containing solution Ca at 2x (2 mM Ca) the level used in the first study, to test the effect added Ca had on F- availability and uptake. Total biomass was greatest with HEDTA and F- < 1 mM. Leaf and stem F concentrations increased exponentially as solution F- increased linearly, with nearly no F partitioning into the seed. Results suggest that F was taken up as HF0 while F- uptake was likely restricted. Additionally, F- competed with HA for Ca, thus preventing the formation of Ca-HA flocculents. The addition of soluble Ca resulted in the precipitation of CaF2 solids on the root surface, as determined by tissue analysis and energy dispersive X-ray spectroscopy.
authors.affiliation: Plants, Soils, and Biometeorology Dep., Utah State Univ., Logan, UT 84322-4820, USA. cmackow@cc.usu.edu
authors.forename: C L
authors.initials: CL
authors.lastname: Mackowiak
authors.forename: P R
authors.initials: PR
authors.lastname: Grossl
authors.forename: B G
authors.initials: BG
authors.lastname: Bugbee
mesh_terms: D001682:Biological Availability; D002118:Calcium / Q000493:pharmacokinetics; D004492:Edetic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D005457:Fluoridation; D005459:Fluorides / Q000493:pharmacokinetics*; D006801:Humans; D006812:Humic Substances; D012275:Oryza / Q000378:metabolism*; D018517:Plant Roots / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000493:pharmacokinetics*
chemical_list: D006812:Humic Substances; D014874:Water Pollutants, Chemical; D004492:Edetic Acid; D005459:Fluorides; C026060:N-(hydroxyethyl)ethylenediaminetriacetic acid; D002118:Calcium