presumptive evidence for the presence of a dispersible ligand in higher
138
pa/g *
1,700
Least Mobile Species
Molecular
Diffusicn
Weight,
Coefficient
g/moale
1077
x
Hesson
Salkum
Muscateen
Ritzville
Quillayute
3 .0
2. 5
2 4
1 5
1 3
1,790
5,000
7,200
8,100
21,000
13,000
24
47
9
55
36
pg/g*
139
pa/g of soll.
*Plutonium added at a ievel of 620,000
53
centration,
_
Soils
Several conclusions may be drawn from studies of the soil chemistry of Pu
which have important implications in terms of the potential role of the
soil microbiota in influencing Pu behavior in soil. Definition of Pu
solubility by filtration or diffusion alone is complicated by Pu chemistry,
but, in conjunction, the measurements suggest that mobile Pu is largely
particulate.
However, a fraction of the mobile Pu is available to plants.
mmr a4
eos ea .
NAAN
5 8
methods employed.
Insight into this possibility was not provided by
comparison of Pu behavior in different soils, as might be expected, because
the estimated concentrations and molecular weights of the mobile species
were not related to the soil properties measured.
Pug (DTPA) 4
with insufficient stability and/or concentration to be detected by the
Control
The comparison of filtration and diffusion data indicates that the mobile
Pu in incubated soils was in the form of hydrated oxide of hydroxide ina
continuum of sizes.
If it can be assumed that Pu in particulate form was
not available to plants, it is possible that the small fraction of Pu
taken up by plants was present in soil as reaction or dissolution products
Weight,
g/mole
This concentration of Pu in soil approximated
the quantity of water-soluble Pu passing the 0.0015 uw ultrafiltration
membrane (Table 1).
Hypothetical globular proteins in this size range
would have average molecular weights < 10,000.
Particies of Pu(OH}, or
hydrated oxides would have molecular weights of 200,000 to 500,000.
Estimated molecular weights for these least mobile species calculated from
diffusion coefficients were between 600,000 and 900,000. Thus, it would
appear, as in the case of the most mobile species, that the least mobile
species of Pu were particulate Pu(OH)}, or hydrated oxides.
Coefficient
x 1076
of 150 - 1200 pg/g (Table 2).
Treatment
The estimated diffusion coefficients for the least mobile Pu components
ranged from 2,3 - 3.1 x 107? cm’/sec with corresponding soil concentrations
Soil Con-
the molecule was a
Molecular
if
piffusion
However,
Most Mobile Species
through this membrane.
Plutonium in Soils from
Estimated Concentrations and Molecular Weights of Mobi Je
1977).
Measured Diffusion Coefficients (Garland and Wildung,
than 500 would pass
hydrated PuO; sphere of similar dimensions, it would have a molecular
weight between 10,000 and 25,000 approximating the molecular weights of
the most mobile Pu species as determined from diffusion coefficients.
This fraction, therefore, likely consisted of small particles of Pu(OH),y
or hydrated oxide.
Table 2.
Applying diffusion principles to characterization of mobile Pu spectes in
soila, Garland and Wildung (1977) estimated the concentrations and molecular
weight of mobile Pu in five surface soils representing a range in particle
size distributions, pH (4.4-6.2) organic C (0.7 to 12.5%) and cation
exchange capacities (14 to 45 meq/100 g). The diffusion coefficients
calculated for the most mobile species in the five soils varied From 1.5
to 3.0 x 10°* cm’/sec (Table 2}.
Estimated concentrations and molecular
weights of the most mobile Pu components in the five soils ranged from 93
to 55 pe/g and from 5000 to 21,000, respectively. Thus, estimated concentrations of the most mobile Pu species were of the same order of magnitude as
those observed by water extraction and subsequent ultrafiltration through
the 0.0010 pp membrane (Table 1). This membrane retained Pu-DTPA (molecular
weight 1700). Hypothetical globular peptides of molecular welghts less
Soil Concentration,
concentration in the Muscatine soil.