molecular weight fractions of naturally occurring colored organic acids are
responsible for most of the chelating capacity in surface waters.
and Ardakani
(1972)
Stevenson
reported that metals bound to the larger fractions were
less available to plants and less mobile in soil solution.
larger diameter organics reduced
otherwise sequestering Pu.
Pu uptake, presumably
In this study the
by chelating an
The smaller diameter organics greatly increased
Pu uptake.
This may be due to decreased Pu precipitation and adsorption to
glass.
Organic matter in soil solutions decreased Pu availability tc plants
(Schulz et al.,
1976).
Pillai et al.
(1976)
found humics maintained more Pu
in solution than sea water alone but precipitated removing Pu over a long
period of time.
Smaller diameter organics may also facilitate Pu uptake by
crossing the cell membrane as a Pu-organic complex or by juxtapositioning
Pu on the cell.
Metal organic complexes may readily penetrate cell membranes,
thus chelating agents may transport metals into cells in quantities greater
than would normally occur
Table 4.
:
cellular
Effects of 4 organic fractions on A. hydrophila
237 Pu
(Doyle etal.,
Low molecular weight humic acid fractions and fulvic acids may penetrate the
cell membranes of phytoplankton
concentration after 6 hr.
1974).
weight humic acids
(F I and F
(Prakash et al.,
II)
1973)
probably do not.
but
the higher molecular
Prat et al.
(1961)
and
Pr&t and Pospisil (1959) report that humic acids cannot penetrate plant cell
237pyt4 Removed From Medium
Treatment
Final cell _density
(cell x 10/+ml~
Removed/Cell
1078 pei 237put4eceil”!
% Total Removed
4.3 + 20"
14 + 6¢
5.4
TSB + F I
5.1 + 2.24
742
B
3.2
TSB + F II
3.6 + 1,44
10 + 2 B
3.2
Tsp + Fort
3.1 + 1.2"
15 + 2 c
4.2
TSB + F IV
5.6 + 2.17
51 +9
26.0
TSB
Means not significantly
+ 2 S..
*N = 4, a = 0.05, confidence intervals =
by A, B or c.
different from one anothér are denoted
membranes.
Humic substances that penetrate cell membranes are inhibitory to
all cellular processes (Prdét, 1968).
transport across the cytoplasmic membrane, while Saunders
(1957)
stated that
humic acids may stimulate cell membranes of phytoplankton, thereby allowing an
influx of bound metals.
ACKNOWLEDGMENTS
This research was supported by Contract E(38-1)-819 between the University of
Georgia and the U. S. ERDA.
R. M. Wallace, and E. L. Wilhite helped with
Pu**
preparation.
R. Geiger and L. A. Briese aided in data collection and
J. Cc. Corey helped with all phases of the study.
539
538
The important point is that all naturally
occurring organics do net increase or decrease Pu uptake but some increase Pu
uptake while others cause a decrease. Waris (1953) suggested that humic substances may directly affect the cytoplasmic membrane.
Chaminade (1956) reported
humic acids stimulate growth of violet epidermal cells by allowing mineral