isooctane from each sample, the dry weight of
are also the cause of acute poisoning of waterfowl;
each sediment subsample was measured and
thus, we designed and tested a second composit-
white phosphorus concentrations were calculated
ing approach to detect the presence of these parti-
cles.
using dry sediment mass.
Following subsampling for the GC analysis,
Sieved composite samples
approximately 80 mL or 120 g of sample remained,
The tight grid spacing required to detect a hot
and we examined this sediment for white phos-
spot results in numerous samples, adding up to a
phorus particles by spreading each sample on an
large volume of sediment. If the objective of sam-
aluminum plate and heating until all water evapo-
pling is to detect milligram-size white phospho-
rated. If white phosphorus particles were present,
rus particles, and the sediment is fine silt and clay,
we detected them by observing a localized area of
samples can be pooled and white phosphorus par-
intense smoke and flame, and the formation of a
ticles isolated from the bulk of the sediment by
bright orange residue. Particles greater than 0.3
mm in diameter (26 g) can be detected using this
passing the samples through a 30-mesh (0.59-mm)
sieve. The material remaining on the mesh can
method (Walsh et al. 1995). These samples were
then be examined for white phosphorus particles.
not sieved because the amount of sediment was
We collected samples on square and triangular
small.
grid patterns, based on the assumptions that the
contaminated hot spots are circular with radii of
Stirred composite samples
1.0 m. Additional samples were collected based on
The stirred compositing method produced 15
the assumption that the hot spot radius was 0.5 m
subsamples from each of the four composites tak-
and β equals 10%. To maintain proper grid spac-
en, for a total of 60 subsamples. To each of the sub-
ing, quadrates and triangles were constructed
samples, we added 40 mL of isooctane to extract
from 3/4-in. i.d. CPVC pipe and fittings.
the white phosphorus. After shaking the samples
At the grid nodes, a measured volume (50 mL)
for 18 hours, we collected the isooctane extract and
of sediment was collected using a syringe corer
a 1-L aliquot was analyzed by GC-NPD. Each
(2.65-cm i.d., 9-cm length) and samples were com-
subsample was allowed to dry in a fume hood,
bined in a wash bucket equipped with a 30-mesh
and the air dry weight determined. Concentra-
sieve (Forestry Supply, Jackson, Mississippi, Part
tions were expressed as mass of white phosphorus
No. 77255) to produce one composite sample for
(g) per dry sediment mass (g).
the 7- 20-m area. The wash bucket was held un-
derwater, and the sediment stirred to wash away
Sieved composite samples
its fine-grained part and reduce the volume of the
To detect the presence of white phosphorus, the
sample. Previously, when ERF sediments were
sieved composite samples were warmed to room
sieved in this way, the volume was reduced by a
temperature, and headspace Solid-Phase Micro
factor of about 100, depending on the amount of
Extraction (SPME) followed by gas chromatogra-
organic matter present. Each composite sample
phy was performed (Walsh et al. 1996b). When the
was placed in a glass jar equipped with a septa cap
SPME method indicated that white phosphorus
and refrigerated in the dark until analysis. Dupli-
was present, we examined the sample using a dis-
cate samples were taken for each grid shape and
secting microscope, picking out white phosphorus
spacing.
particles and measuring them with a micrometer.
When we observed no more particles under the
Laboratory tasks
microscope, the sample was spread in a thin layer
Discrete samples
on an aluminum pan and heated to ignite any
The 53 discrete samples from the 1.82-m-square
remaining white phosphorus particles, as described
grid were analyzed in duplicate using the stan-
above.
dard method of analysis for white phosphorus in
sediment (USEPA 1995). For this method, white
Data analysis
phosphorus is solvent-extracted from 40-g wet
Discrete samples. All descriptors of populations,
subsamples, and the solvent is analyzed by gas
such a mean, standard deviation, and variance, as
chromatography (GC). This method determines
well as statistical tests such as ANOVA, assume
the total mass of white phosphorus present in a
that data are normally distributed. So, concentra-
sample, and the results are expressed in concen-
tion estimates obtained from the duplicate analy-
tration units (g/g). Following removal of the
ses for the discrete samples were plotted on nor-
8
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