Phytoavailability of zirconium in relation to its initial added form and soil characteristics

The various uses of zirconium (Zr) in chemical and nuclear industries generate a potential risk of environmental contamination by this element. This study was performed on two agricultural soils, an acidic soil (A) and a clayey calcareous soil (B), collected in the Meuse/Haute Marne experimental site of the French National Agency for radioactive waste management (Andra). Distribution coefficients (Kd), defined as the ratio of Zr concentration in the solid phase (mol/kg) to Zr concentration in the solution (mol/l), were obtained for both soils. Their high values (6,000 < Kd < 30,000 l/kg) suggest a rapid and strong retention of Zr on the soil constituents. Chemical extractions (0.01 M CaCl2, Calcium chloride, 0.005 M DTPA, Diethylene Triamine Penta Acetic acid, and 0.1 M NaPP, Sodium Pyrophosphate) showed that organic matter had a high affinity for the added Zr. Soil–plant transfer experiments showed low plant uptake. A significant absorption of Zr was, however, observed for the two studied plants, tomato (Lycopersicon esculentum L. cv. St. Pierre) and pea (Pisum sativum L. cv. “express”). For the most available forms of Zr (acetate and oxychloride), concentrations reached from 8 to 57 mg Zr/kg dry weight of roots. Zr is mainly accumulated in plant roots and is more absorbed by tomato than by pea. Zr bound to root cell walls (i.e. apoplastic Zr) concentrations, determined by HCl extraction, are significantly much lower than root absorbed Zr concentrations. Transfer to roots seemed to be more effective in the acidic soil and was strongly dependant on Zr added form.