PARENT SESSION
14 - Radioecology
2:10 PM to 5:20 PM, Monday, 13 May 2002
Session Chair: Gerzabek, Martin ¹, Kirchner, Gerald ², ^{1 2} .
Lehar B

(14-03) The effect of soil structure on plant uptake of contaminants: First results.

Centofanti, Tiziana^*,1, Penfield, Robin², Frossard, Emmanuel¹, Flühler, Hannes², Albrecht, Achim¹, ¹ Institute of Plant Sciences, Experimental Station Eschikon, ETH Zürich, Lindau, Switzerland² Institute of Terrestrial Ecology and Soil Physics, Schlieren, Switzerland

ABSTRACT- Contaminant uptake by plants has been extensively studied in systems, where plants were grown in soils homogeneously labeled with radionuclides. Experiments done in monoliths and acidic forest soil have shown that the distribution of surface applied radionuclides is heterogeneous, delineated by the flow paths in the soil. We tested the importance of soil structure on contaminant distribution and availability in two experiments: (1) with ¹³⁴Cs and a dye tracer (used to visualize the zones of preferential flow compared to the matrix) applied to the surface of an un-tilled agricultural soil and (2) with the tracer mixed into the same but homogenized soil. Maize (Zea Mays L. cv. Corso) was grown in both soils for two months and ¹³⁴Cs was measured, after harvest, in plant and soil samples. In the field the radionuclide distribution was heterogeneous with zones of enrichment along the flow paths (stained area) and very low concentration in the matrix (unstained area), confirming our previous results. The uptake of ¹³⁴Cs was higher in the structured soil (6-20 Bq/kg) than in the homogenized soil (<5 Bq/kg). Roots grown in the homogenized soil explored the entire soil volume, presenting a higher root weight density (0.6-2 g/cm³) than the roots grown in the field (0.3-0.6 g/cm³ in the upper 0-20cm and ~0.1 g/cm³ in the lower 20-40cm). The different patterns of Cs uptake by maize observed in both systems can be interpreted as follows. In the structured soil Cs reacted with a small surface of soil located around the zones of water preferential flow which were exploited by roots, whereas in the homogenized system Cs was sorbed on a much greater surface created during soil homogenization and became less available. This suggests that risk assessment models, which rely on input variables obtained under homogenized soil conditions, could underestimate plant uptake.

Key words: soil structure, plant uptake, contaminat availability, root distribution