The plant availability of 137 Cs in soils varies widely between soil types. The source of this variation was analyzed in a pot trial. Thirty topsoils covering a wide range in textural classes were contaminated with 137 Cs and incubated for 41 days prior to 19 days plant growth. The plant-soil 137 Cs concentration ratio (TF) varied from 0.002 to 2.6 g g -1 between soils. The soil-soil solution 137 Cs concentration ratio (K D ) varied from 123 to 167 000 mL g -1 between soils. The log TF was negatively correlated with log K D , but the correlation was weak (R 2) 0.10). The plant-soil solution 137 Cs concentration ratio (CF) was however significantly related to the K concentration in soil solution. At K concentrations up to 1 mM, the CF decreased more than 2 orders of magnitude with increasing K concentrations. Above 1 mM K, the CF was almost unaffected by K supply. A twoparameter nonlinear model for the log TF was fitted to the K concentrations and K D values and explained 94% of the variance. It is concluded that plant availability of 137 Cs in mineral soils varies extensively between soils due to differences in 137 Cs retention, affecting 137 Cs supply to roots, and to differences in K availability, affecting the 137 Cs root uptake process.

Soil microbial processes are readily disturbed by added zinc (Zn) in laboratory ecotoxicity tests. This study compares Zn toxicity between freshly spiked soils and soils that have been contaminated with Zn in the field. Soils were sampled in three transects (< 80 m) toward galvanized electricity transmission towers (pylons). The soil total Zn concentrations gradually increased in each transect from background values (25-82 mg Zn/kg) to elevated Zn concentrations near the pylon (226-595 mg Zn/kg). Soil samples taken at the furthest distance from the Zn source were spiked with ZnCl2 to a range of total Zn concentrations similar to those in the transect. Nitrification, respiration, and N-mineralization rates were significantly reduced by added Zn in laboratory-spiked soils and were 9 to 95% (mean 32%) of the control values at largest doses depending on soil type and the microbial process. In contrast, these processes were either unaffected by soil Zn (p > 0.05) or increased significantly with soil Zn concentrations in the transect soils. These increases could not be explained by soil pH or % soil organic carbon. Leaching soils after spiking significantly lowered the toxic effects of Zn on nitrification or on substrate-induced respiration. The soil solution Zn concentrations of field soils were always smaller than in spiked soils at equivalent total Zn. Highest soil solution Zn concentrations were always lower than the soil-solution EC50s of spiked soils. It is concluded that there is a large discrepancy in microbial responses to elevated Zn between spiked soils (unleached) and field-contaminated soils and there is a need to explain this discrepancy in terms of Zn availability, adaptation processes, and additional soil factors controlling the microbial processes.

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137Cs uptake rates and distribution within the plant were investigated for clover, maize, sunflower and radish under five different nutritional scenarios. Nutritional scenarios differed in cationic composition only: K + concentration ranged from 0.25 to 5 mM, Ca 2+ from 1.89 to 3.60 mM. 137Cs uptake and distribution depended both on species and on the ionic composition of the growth medium. Differences between the species were maximal at the lowest K + concentration. Ranking of the species with respect to 137Cs level in the plant was also dependent on the external K + concentration. It is concluded that crop selection as a measure to reduce 137Cs contamination of the food chain should not occur without taking into consideration the external K + concentration.