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Size-fractionated plutonium isotopes in a coastal environment
M H Dai1, K O Buesseler, J M Kelley
1Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA. mdai@whoi.edu
Journal of Environmental Radioactivity
|May 31, 2001
Summary
This study analyzed plutonium isotopes in the Gulf of Maine, finding a single source from global fallout. Most plutonium was in small molecular weight fractions, indicating conservative mixing in seawater.
Area of Science:
- Environmental Science
- Radiochemistry
- Oceanography
Background:
- Plutonium (Pu) isotopes are significant anthropogenic radionuclides in marine environments.
- Understanding Pu distribution is crucial for assessing its fate and transport in oceans.
Purpose of the Study:
- To investigate the size distribution and isotopic composition of plutonium in Gulf of Maine seawater.
- To determine the source and behavior of plutonium in this marine ecosystem.
Main Methods:
- Seawater samples were size-fractionated using 1 kD cross-flow ultrafiltration (CFF).
- Plutonium isotopes (239Pu, 240Pu, 241Pu) were purified radiochemically.
- Isotopic analysis was performed using thermal ionization mass spectrometry (TIMS).
Main Results:
- A consistent 240Pu/239Pu atom ratio of 0.18 indicated a single source, global fallout.
- The majority of plutonium was found in the low molecular weight fraction (< 1 kD).
- Colloidal plutonium concentrations decreased with depth, suggesting conservative mixing.
Conclusions:
- The plutonium in the Gulf of Maine originates from a single, contemporary source (global fallout).
- Cross-flow filtration did not cause significant isotopic fractionation.
- Plutonium's vertical distribution is mainly governed by conservative mixing, with limited particle reactivity.