Environmental Engineering Reference
In-Depth Information
22.4 URANIUM IN TOTAL SUSPENDED PARTICULATES
The largest number of measurements of U in air has been performed under a U.S. Environmental
Protection Agency (EPA) program named Environmental Radiation Ambient Monitoring System
(ERAMS). The ERAMS air program consists of 50 stations collecting air particulates on ilters.
The ERAMS ilters were analyzed for U starting in the late 1970s. Presently annual composites of
the air particulate ilters are analyzed for U and Pu.
The longest running program for the collection and measurement of air particulates was con-
ducted at the Argonne National Laboratory (ANL), Argonne, IL. Begun in 1973, their air sampling
program includes an off-site station to assess the background concentrations of nuclides of interest,
including U, Th, and Pu.
Published data from the EPA and ANL sampling programs were evaluated to assess the U air
concentration in the continental United States (Stevenson and Pan 1996). The U concentrations
were examined from 25 ERAMS sites and an anomaly was found for stations in the northern and
mid-section of the United States. This was conirmed by the independent air ilter collections and
measurements of U performed at ANL. The 40% decrease in the air concentrations of U at these
sites was attributed to “regulatory compliance in reducing emissions from fossil burning facilities.”
The data from 22 ERAMS locations averaged 2.1 ± 0.7 μBq
238
U m
−3
(170 pg U m
−3
). Only the
ANL data were useful to investigate seasonal variations as the ERAMS compost samples overlapped
seasons. At ANL the samples showed a slight rise in April (Spring rise), a low point in August and
another small rise in November. It was thought that the November rise was due to emissions from a
local coal burning electrical generating plant. The non-carbonaceous residues from the TSP collec-
tions have been analyzed for U and the concentrations were found to relect the U concentration in
soil. The
234
U/
238
U ratio for 22 ERAMS sites was 1.14 ± 0.24, indicative of the U source, soil.
The U concentrations in surface air are shown in Table 22.1. The impact of land mass, climate,
and industrialization is apparent. Basically, there is no soil contribution at the remote sites, the
ground being frozen year round or at oceanic locations. Even the remote sites in Antarctica show a
difference between the pristine environment and human encampments. The global average concen-
tration of U in air as adopted by UNSCEAR (2000a) of 1 μBq m
−3
is based almost exclusively on
data obtained in the mid-latitudes of the Northern Hemisphere.
22.5 THORIUM IN TOTAL SUSPENDED PARTICULATES
Measurements of the Th concentration in air are sparse. This was partially due to the dificulties
encountered with radiochemical separation, speciically unacceptable reagent and material blanks.
Again the Argonne National Laboratory's Environmental Monitoring Program has the longest run-
ning record of Th in air Measurements. As stated earlier for their U in air measurements, the impact
of regional sources causes a marked decrease with time. The ANL data are included in Table 22.2
as they are unremarkable when compared with other measurements. Again, measurements of the
ashed ilter residues indicated that the Th was derived from soil. The activity concentrations of Th
in air are in the same general range as those for U.
22.6 PLUTONIUM IN TOTAL SUSPENDED PARTICULATES
Measurements of a long-lived alpha emitter Pu were necessitated by widespread public concern
over the potential hazard from global fallout, the entry of the SNAP 9 satellite to the atmosphere
(1963), and the nuclear accident at Chernobyl (1986). The measurements of Pu in TSP on a global
basis began in 1966. By the use of the known Pu to
90
Sr ratio (0.017), estimations of atmospheric
Pu in TSP were extended back to 1963 for SASP samples. The USDOE EML SASP network results
for Pu were part of an extensive review by Harley (1980). He estimated that some 15PBq (400 kCi)
had been produced and dispersed globally. Hardy et al. (1973) accounted for over 12PBq (330 kCi)
without estimating the deposition around test sites. The measurements of Pu on a global scale
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