The {sup 129}Iodine bomb pulse recorded in Mississippi River Delta sediments: Results from isotopes of I, Pu, Cs, Pb, and C

Journal Article · Wed Mar 01 04:00:00 EST 2000 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/S0016-7037(99)00364-6· OSTI ID:20020876

Oktay, S D; Santschi, P H; Moran, J E; Sharma, P

Anthropogenic sources from nuclear reprocessing discharges and bomb test fallout have completely overwhelmed the natural signal on the surface of the earth in the last 50 years. However, the transfer functions in and out of environmental compartments are not well known due to temporal variations in the sources of {sup 129}I and to a lack of knowledge regarding the forms of iodine. From a vertical profile of {sup 129}I/{sup 127}I ratios in sediments located in the Mississippi Delta region in approximately 60 meters water depth, the {sup 129}I input function to this region was reconstructed. Dates in the core were assigned based on the plutonium peak at 20 cm depth (assumed to have been deposited in 1963) and the excess {sup 210}Pb profile in the same depth interval, and below that, based on the steadily decreasing {sup 240}Pu/{sup 239}Pu ratios from a ratio of 0.18 at 22 cm to 0.05 at 57 cm depth, the 1953 horizon. Atom ratios of {sup 129}I/{sup 137}I Cs, decay corrected to 1962, the year of maximum radionuclide production, are about 0.3, very close to the production ratios of about 0.2 during atomic bomb tests. This evidence, combined with other observations, strongly suggests that {sup 129}I in Mississippi River Delta sediments originates from atomic bomb fallout eroded from soils of the Mississippi River drainage basin, with little alteration of the isotopic ratios during transport from watershed to coastal deposits. Based on these observations and on laboratory evidence, the authors propose a conceptual model which explains this correspondence and the low {sup 129}I/{sup 127}I ratios. Differences in mobilities of the different chemical forms of {sup 129}I and {sup 127}I, as well as the variances in chemical forms of {sup 129}I from nuclear bomb fallout versus nuclear fuel reprocessing, are proposed to have created such a correspondence between I-isotope ratios and bomb fallout nuclides, without revealing recent inputs from nuclear fuel reprocessing releases to the northern hemisphere observed in watersheds of the USA and Europe.

• Research Organization: Texas A and M Univ., Galveston, TX (US)
• OSTI ID: 20020876
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 6 Vol. 64; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
CARBON ISOTOPES
CESIUM 137
IODINE 129
LEAD 210
MISSISSIPPI RIVER
NEVADA TEST SITE
NUCLEAR WEAPONS
PLUTONIUM ISOTOPES
RADIOECOLOGICAL CONCENTRATION
RIVER DELTAS
SEDIMENTS
TESTING
WATERSHEDS