APPENDIX A: METHODS FOR LABORATORY STUDY
Incubation of P4 Particles at Constant Temperature and Moisture Content
tion) diameter was 1.79 0.06 (3.2% relative stan-
PRODUCTION OF PARTICLES
dard deviation). After the diameter was mea-
White phosphorus was obtained as sticks (16.1
sured, each particle was transferred with a for-
mm in diameter), stored in water, from Aldrich
ceps from the petri dish to an amber vial contain-
Chemical Co. (Milwaukee, Wisconsin). One stick
ing cold reagent-grade water. Particles were
of P4 was placed in an 18.3-cm-diameter glass
placed in sediment samples within a few hours of
dish under 3 cm of reagent water, and a razor
production.
blade was used to obtain a 2-mm slice. The edges
of the slice were cut away so that only P4 from the
PREPARATION OF SEDIMENT SAMPLES
interior of the stick was used. The mass of each
slice was approximately 700 mg. The piece of P4
Sediments
was transferred under water to a test tube
Uncontaminated sediment from Eagle River
(13 100 mm), and the test tube was then placed
Flats was air-dried and homogenized. A set of
in a 1-L beaker containing reagent-grade water.
samples at one test temperature required approx-
Additional test tubes containing reagent-grade
imately 40 kg of air-dried sediment. The sediment
water were placed in the 1-L beaker. These test
was air-dried in a fume hood at room tempera-
tubes served to isolate the particles of P4 once
ture (22C) for two weeks. Since ERF sediments
they are produced.
are silt and clay size, the sediments hardened as
The 1-L beaker containing the test tubes and P4
they dried. During drying, the hardening sedi-
were placed on a Corning hotplate and the water
ment was broken apart with a large stainless steel
heated to 54C (10C higher then the melting
spoon and mixed thoroughly. A mortar and pes-
point of P4). The beaker was removed from the
tle was used to break apart the hard clumps. To
hotplate; then 3-L droplets obtained from the
thoroughly homogenize the sediment, the sedi-
molten P4 using a Gilson Microman Positive Dis-
ment was processed in 1-L batches in a Cuisinart
placement Pipet (size M25) equipped with dis-
(Model DLC-X) processor. The moisture content
posable capillaries and pistons. Droplets of this
of the air-dried, homogenized sediment was de-
size maintain a spherical shape. Each droplet was
termined gravimetrically (difference in weight
transferred under water to individual test tubes
before and after heating at 105C for 24 hours).
(only one droplet was placed in each test tube
The ERF sediment air-dried in our laboratory was
since molten P4 droplets merge to form a larger
approximately 2% moisture (on a dry weight ba-
droplet). The test tubes containing the P4 droplets
sis).
were cooled in a refrigerator (4C). P4 can super-
cool (i.e. remain liquid below the melting point);
Determination of moisture contents to be tested
thus the water had to be cooled well below 44C
The moisture content levels were chosen to re-
to ensure solidification of the P4.
flect those that may be expected in exposed Eagle
To measure the diameter of each particle, each
River Flats sediments. Following the thawing
particle was transferred to a glass petri dish con-
each spring of the ice covering Eagle River Flats,
most of the flats is covered by water, and sedi-
taining reagent-grade water, and the diameter
was obtained using an SPI (Swiss Precision In-
ments throughout the flats are saturated. Follow-
struments) 6-in. caliper with 0.1-mm gradations.
ing drainage through gullies and evapotranspira-
Previously we have measured diameters of 127 P4
tion, the area covered by water gradually shrinks
particles produced in this laboratory by the meth-
in size until the flats is periodically reflooded by
od described above. The mean ( standard devia-
high tides exceeding 31 ft. Thus the area exposed
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