of ancient gaswork soils. Effect of polycyclic aromatic hydrocarbons (PAHs) on plant germination. Organic Geochemistry, Elsevier, 1999, 30 (8) ABSTRACTThe phytotoxicity of various contaminated soils was assessed by plant inventories on ancient industrial fields, and by phytotoxicity tests. Industrial fields are well colonised by numerous weedy plants. Phytotoxicity was tested with pure PAHs, ancient industrial soils, soil leaches, liquid tar and tar volatile compounds. Both field studies and toxicity tests show that contaminated samples can be classified into two categories: first, a recently excavated soil/liquid tar that was foul-smelling and phytotoxic, and second, an 'aged', surface soil that was weathered and nonphytotxoic. Plant germination and growth are strongly inhibited by the presence of volatile, water-soluble low molecular-weight hydrocarbons (< 3 rings) such as benzene, toluene, xylene (BTX), styrene, indene, naphthalene and other possibly toxic substances. On the other hand, high molecular weight PAH (3-5 rings) did not show any phytoxicity under the conditions studied. These findings suggest that once low molecular weight aromatic hydrocarbons are removed e.g. by volatilization, biodegradation, weathering, tillage and fertilising, plants should be able to grow.

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Abstract. Uranium behaviour in soils is controlled by actions and interactions between physico-chemical and biological processes that also determine its bioavailability. In soil solution, uranium (+VI) aqueous speciation undergoes tremendous changes mainly depending on pH, carbonates, phosphates and organic matter. In a first approach, plants (Phaseolus vulgaris) were grown using hydroponics to allow an easy control of the composition of the exposure media. The latter, here an artificial soil solution, was designed to control the uranium species in solution. A geochemical speciation code was used to perform the solution speciation calculations. On this theoretical basis, three domains were defined for short-duration well-defined laboratory experiments in simplified conditions: pH 4.9, 5.8 and 7 where predicted dominant species are uranyl ions, hydroxyl complexes and carbonates respectively. For these domains, the influence of plant growth stage on transfer was determined. The Free Ion Model (or its derivated the Biotic Ligand Model) was tested to determine if U uptake was governed by the free uranyl species or if other metal complexes could be assimilated. The effect of different variables on root assimilation efficiency and phytotoxicity was explored: presence of ligands such as phosphates or carbonates and competitive ions such as Ca 2+ at the 3 pHs.

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Early studies have shown that cesium (Cs + ) competes with the macronutrient potassium (K + ) for uptake by plants. The present study investigates the effect of K + supply on Cs + uptake and translocation in Arabidopsis thaliana. Taking advantage of the frequent use of this model plant in + concentration above 100 µM. We propose that non-selective cation channels, likely involved in Cs + uptake under K + -sufficient conditions according to previous studies, could also mediate Cs + uptake under K + -starvation and high Cs + concentrations. Finally, evidences for Cs + translocation mediated by K + channels are discussed.