Influence of clay mineral type and organic matter content on the uptake of ²³⁹Pu and ²⁴¹Am by plants

Abstract

The uptake of ²³⁹Pu and ²⁴¹Am from different clay mineral-organic matter-sand mixtures simulating contrasting soil types was examined in growth chamber experiments. The mixtures represented various combinations of organic matter (0, 5 and 10%), kaolinite (11 type) and montomorillonite (21 type) clay minerals, each at the levels of 5, 10 and 25%, and purified quartz sand (as filler). Results indicated a marked reduction in uptake of both ²³⁹Pu and ²⁴¹Am with increase in organic matter as well as clay content of the mixtures. The Pu Concentration Ratios (CRs) ranged from (2.5-7.0)×10^-3 in the case of kaolinite-organic matter mixtures, and from (0.9-5.5)×10^-3 in the case of montmorillonite-organic matter mixtures. The corresponding values of Am Concentration Ratios (CRs) obtained were (1.9-725.4)×10^-3 in the case of kaolinite-organic matter mixtures, and between (0.7-3.5)×10^-3 for the montmorillonite-organic matter mixtures. Reduction in the uptake of ²⁴¹Am with increasing clay content was more pronounced in the montmorillonite clay-organic matter mixtures as compared to that in the case of kaolinite-organic matter mixtures. While similar qualitative reduction in ²³⁹Pu CRs with increasing clay content was observed, the reduction was less marked than in the case of ²⁴¹Am. The values for Am CRs were higher than the corresponding Pu CRs in kaolinite based mixtures whereas in the case of montmorillonite-organic matter mixtures Pu CRs exceeded the Am CRs. Increasing organic matter content and its interaction with both kaolinite and montmorillonite clay minerals were found to be equally effective in reducing the uptake of ²³⁹Pu as well as ²⁴¹Am by plants.