size were only evident in those particles incu-
cle. In three instances, one at each temperature
bated at moisture contents below saturation. Al-
tested, the particle was located without sieving,
most all particles were translucent, and there
and the sediment in direct contact with particle
was no evidence of the oxidized coating that
was analyzed. P4 concentrations in this associated
sediment were 0.2 (4C), 0.5 (15C) and 6.6 g/g
forms when P4 is stored in water. Some particles
(20C).
developed an orange tinge over part of the sur-
face, similar to the color that develops when P4
Residual mass of P4 particles. P4 particles were re-
covered from all samples incubated at 4C. At this
is exposed to light. This color change may have
been an artifact from the microscope light used
low temperature, there were no significant reduc-
to locate the particles.
tions of the masses of P4 particles found, except
The particles were difficult to locate. The moist
the particles isolated at the last sampling interval
sediment surrounding the particles was not visi-
(58 days) at the lowest moisture content (Fig. 10a),
bly changed. Some unsaturated samples (s = 0.64)
where the mass for each particle was approxi-
that were incubated at 20C for 10 days were al-
mately half that of the original mass.
For samples incubated at 15C (Fig. 10b), there
lowed to air-dry. Then a razor blade was used to
slice through the region where the particle was
were no changes in particles incubated at satura-
tion or above; however, there were significant re-
ductions in particles incubated at the two lowest
moisture contents (s = 0.45 and 0.64) during 30
days of incubation. Following incubation for 57
days at 15C, no P4 was detected in the samples at
the two lowest moisture contents. At s = 0.82, P4
loss was inconsistent. P4 was undetectable in
some samples after only one week of incubation
but was persistent in other samples for 38 days,
the last sample taken.
At 20C (Fig. 10c) there were no changes in par-
ticles incubated at saturation or above; however,
there were significant reductions in particles in-
cubated at the two lowest moisture contents (s =
0.45 and 0.64) after only one day of incubation.
Again at s = 0.82, P4 loss was inconsistent. P4 was
undetectable in some samples after only 10 days
of incubation but was persistent in other samples
for over 20 days (the last sampling interval).
Based on the data obtained in the laboratory,
Figure 9. Void in dry sediment formed as P4
persistence for 2-mm-diameter particles can be
particle sublimed. Dark-colored hygroscopic
estimated. In a previous study, most particles iso-
oxidation products are visible in the sediment
lated from Eagle River Flats sediments were
surrounding the void.
smaller than 2 mm (Racine et al. 1993). For moist
sediments that were well below saturation (s <
0.6) at 20C, 99.9% of the mass was lost in one day
planted. In each case, a small (1.8-mm), spherical
and 99.999% was lost by 10 days. At 15C, 99.9%
void with smooth sides was found. Sediment sur-
was lost by 30 days and >99.999% was lost by 60
rounding the void was slightly lighter in color
days. Only a 50% loss was observed at 4C at the
then the rest of the sediment. Previously we have
lowest moisture content after 56 days; thus, at this
observed the formation of a dark, wet, phosphate-
rich halo around P4 particles in very dry sediments
low temperature, particles can persist for several
(<10% moisture) (Racine et al. 1994) (Fig. 9). Sedi-
months or longer in unsaturated sediments. Since
FPO
ments for this experiment were always moist;
no loss of mass was observed in saturated sedi-
therefore, water-soluble oxidation products could
ments at any temperatures, P4 particles can be
freely diffuse away from the particle. Occasionally
assumed to persist indefinitely in saturated sedi-
a whiff of "smoke" was visible when the sedi-
ments. For sediments that have moisture contents
ments were probed (Table 6). In almost all cases,
slightly less than saturation, loss of P4 mass can
the sediment had to be sieved to find the P4 parti-
occur but at an unpredictable rate.
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