TRACING NON-FALLOUT NUCLEAR CONTAMINATION IN HUDSON RIVER SEDIMENTS WITH PLUTONIUM, NEPTUNIUM, AND CESIUM ISOTOPE RATIOS: SOURCES AND TRANSPORT

Isotope ratios of ¹³⁷Cs, ²³⁷Np, ²³⁹Pu, and ²⁴⁰Pu measured in sediment cores from five locations in the Hudson River drainage basin show clear evidence of input from non-fallout sources. Different sources of nuclear contaminants exhibit unique isotopic signatures, which can be used to identify and resolve inputs from multiple sources. This approach can lead to a better understanding of the transport behavior, fate, and relative importance of particle reactive nuclear contaminants originating from Knolls Atomic Power Laboratory (KAPL) and Indian Point Nuclear Power Plant (IPNPP), which lie within the drainage basin. Our work to date indicates: 1) Contamination derived from activities at KAPL is present in Mohawk River sediments is a chronic source of contamination to sediments at all sites sampled in the Hudson River Estuary, indicating transport distances of greater than 200km. In a sediment core collected in the Mohawk River ~1km downstream of KAPL, we observe ¹³⁷Cs, ²³⁹Pu, and ²⁴⁰Pu inventories 1-2 orders of magnitude greater than those expected from global fallout deposition. We estimate the ²⁴⁰Pu/²³⁹Pu and ¹³⁷Cs/²³⁹Pu end-member isotopic composition of KAPL-derived contamination to be 0.049 ± 0.002 and 0.0280 ± 0.0013, respectively. 2) Non-fallout ¹³⁷Cs in effluent releases from IPNPP, identified by ¹³⁷Cs/²³⁹Pu ratios significantly higher than average global fallout, is present in sediments collected in close proximity to the facility as well as those collected ~30km downstream. 3) An additional source of contamination has contributed excess ¹³⁷Cs to sediments collected in the Upper Hudson River ~60km above its confluence with the Mohawk River. We can not currently attribute this contamination to any known source. 4) Using isotopic information, we can resolve inputs from specific sources. By resolving and comparing the KAPL-derived ²³⁹Pu contributions in a core from the Mohawk River and one in the Hudson River Estuary (over 200km downstream), we estimate a dilution factor of ~106 and recommend that a series of dilution factors obtained from additional coring sites along the Mohawk and Hudson Estuary should allow us to constrain sediment inputs from the Mohawk River and other tributaries emptying into the Hudson Estuary as well as identify areas of sediment deposition and storage.