Comparative uptake of plutonium from soils by Brassica juncea and Helianthus annuus

Abstract

Plutonium uptake by Brassica juncea (Indian mustard) and Helianthus annuus (sunflower) from soils with varying chemical composition and contaminated with Pu complexes (Pu–nitrate [239Pu(NO3)4], Pu–citrate [239Pu(C6H5O7)+], and Pu–diethylenetriaminepentaacetic acid (Pu–DTPA [239Pu–C14H23O10N3]) was investigated. Sequential extraction of soils incubated with applied Pu was used to determine the distribution of Pu in the various soil fractions. The initial Pu activity levels in soils were 44.40–231.25 Bq g−1 as Pu–nitrate, Pu–citrate, or Pu–DTPA. A difference in Pu uptake between treatments of Pu–nitrate and Pu–citrate without chelating agent was observed only with Indian mustard in acidic Crowley soil. The uptake of Pu by plants was increased with increasing DTPA rates, however, the Pu concentration of plants was not proportionally increased with increasing application rate of Pu to soil. Plutonium uptake from Pu–DTPA was significantly higher from the acid Crowley soil than from the calcareous Weswood soil. The uptake of Pu from the soils was higher in Indian mustard than in sunflower. Sequential extraction of Pu showed that the ion-exchangeable Pu fraction in soils was dramatically increased with DTPA treatment and decreased with time of incubation. Extractability of Pu in all fractions was not different when Pu–nitrate and Pu–citrate were applied to the same soil. More Pu was associated with the residual Pu fraction without DTPA application. Consistent trends with time of incubation for other fractions were not apparent. The ion-exchangeable fraction, assumed as plant-available Pu, was significantly higher in acid soil compared with calcareous soil with or without DTPA treatment. When the calcareous soil was treated with DTPA, the ion-exchangeable Pu was comparatively less influenced. This fraction in the soil was more affected with time of incubation. The lowest extractable Pu was from a pH 6.55 Crockett soil that contained the highest clay compared to the other two soils. Extractable soil Pu was largely affected by soil pH and the amounts of clay, salt, metal oxide, and carbonate.