Station, this overall focus on Western diets has lead to surprises relative to expectations. For example, tea plants at the time of the release did not yet have new leaves
(those harvested), eliminating foliar uptakes as a pathway. Nonetheless, some tea
leaves harvested the following season still showed substantial radiocesium uptake.
As gelatinous organisms are essentially wholly absent from Western diets, there has
been far less study on cesium retention. Thus, there are surprises in store with regards
to human dietary concentrations of radiocesium in jellyfish. It is hoped that this
survey of various gelatinous organisms will help serve as a first approximation of
expected outcomes in dietary jellyfish such as Rhizostomatidae and Stomolophidae.
2 Methods
Organisms were collected off the coasts of Oregon and Washington either directly
from surface trawls or via dip nets. Collections are from 2012–2014, conducted as
part of research cruises conducted by the National Marine Fisheries Service. After
identification, samples were kept frozen until processed. Before radio-analysis,
samples were first baked to dryness at 100 °C, before being carefully dry ashed at a
maximum temperature of 450 °C and a maximum temperature increase of 100 °C
per hour. Recovery of cesium through ashing was verified to be unity, within the
range of counting uncertainty (r = 4.074%), by processing IAEA-414 freeze dried
fish tissues [5]. Samples were analyzed for Cs-137 concentrations on a high-purity
germanium c spectrometer. The 72.5 mm diameter, 68 mm long closed-end coaxial
detector has 70% relatively efficiency and 2.0 keV resolution [full-width at
half-maximum] at 1.33 meV and 1.0 keV at 122 keV. To account for differences in
detection geometry arising from differing volumes of ash, samples of known
activity were counted at various fill volumes and a weighted least-squares fit for the
absolute efficiency based on the fill volume was produced. Uncertainties in count
rates, mass, geometry-altered efficiency, and chemical yield (on the basis of the
yield using the IAEA-414 standards) were propagated.
3 Results and Discussion
Initial analyses of 1000 g by wet weight (standard sub-sample weight for other
phyla being analyzed) yielded no detectable concentrations. Increasing this to the
entire mass of each collection yielded detectable levels in only 1 of all collections
despite wet weights up to and exceeding 10,000 g. Table 1 reports the results of
radio-analysis for the 7 collections reported here. However, the minimum detectable
activity (MDA) as based on the Currie limit
1 and reported in terms of Bq/kg
1
The Currie limit is based on a decision level that produces a 5% false positive rate, and defines the
minimum activity necessary at such a decision level to expect a 5% false negative rate.
312
D.R. Neville and K.A. Higley
(those harvested), eliminating foliar uptakes as a pathway. Nonetheless, some tea
leaves harvested the following season still showed substantial radiocesium uptake.
As gelatinous organisms are essentially wholly absent from Western diets, there has
been far less study on cesium retention. Thus, there are surprises in store with regards
to human dietary concentrations of radiocesium in jellyfish. It is hoped that this
survey of various gelatinous organisms will help serve as a first approximation of
expected outcomes in dietary jellyfish such as Rhizostomatidae and Stomolophidae.
2 Methods
Organisms were collected off the coasts of Oregon and Washington either directly
from surface trawls or via dip nets. Collections are from 2012–2014, conducted as
part of research cruises conducted by the National Marine Fisheries Service. After
identification, samples were kept frozen until processed. Before radio-analysis,
samples were first baked to dryness at 100 °C, before being carefully dry ashed at a
maximum temperature of 450 °C and a maximum temperature increase of 100 °C
per hour. Recovery of cesium through ashing was verified to be unity, within the
range of counting uncertainty (r = 4.074%), by processing IAEA-414 freeze dried
fish tissues [5]. Samples were analyzed for Cs-137 concentrations on a high-purity
germanium c spectrometer. The 72.5 mm diameter, 68 mm long closed-end coaxial
detector has 70% relatively efficiency and 2.0 keV resolution [full-width at
half-maximum] at 1.33 meV and 1.0 keV at 122 keV. To account for differences in
detection geometry arising from differing volumes of ash, samples of known
activity were counted at various fill volumes and a weighted least-squares fit for the
absolute efficiency based on the fill volume was produced. Uncertainties in count
rates, mass, geometry-altered efficiency, and chemical yield (on the basis of the
yield using the IAEA-414 standards) were propagated.
3 Results and Discussion
Initial analyses of 1000 g by wet weight (standard sub-sample weight for other
phyla being analyzed) yielded no detectable concentrations. Increasing this to the
entire mass of each collection yielded detectable levels in only 1 of all collections
despite wet weights up to and exceeding 10,000 g. Table 1 reports the results of
radio-analysis for the 7 collections reported here. However, the minimum detectable
activity (MDA) as based on the Currie limit
1 and reported in terms of Bq/kg
1
The Currie limit is based on a decision level that produces a 5% false positive rate, and defines the
minimum activity necessary at such a decision level to expect a 5% false negative rate.
312
D.R. Neville and K.A. Higley