Inventories and sorption-desorption trends of radiocesium and radiocobalt in James River estuary sediments

Anthropogenic radionuclides (¹³⁷Cs,¹³⁴Cs,⁶⁰Co) have been introduced to the James River estuary as a result of low-level releases from the Surry Reactor site since 1973 and worldwide atmospheric fallout from nuclear weapons tests since the early 1950s The total radionuclide burden in the estuary sediments has been estimated by integrating radionuclide activities in 29 box cores and extrapolating these integrated values over surface areas subdivided on the basis of sediment type, rates of accumulation, and proximity to the reactor release site. Our results indicate that 30% of the⁶⁰Co, but only 15% of the¹³⁴Cs released from the reactor site, has been retained in the estuary sediments, and about 40% of the¹³⁴Cs and⁶⁰Co sediment inventory is in areas that represent less than 5% of the total estuarine surface area. Depletion of the¹³⁴Cs in downstream sediments forms a noticeable trend in the James River estuary, and we postulate that seawater cation competition and exchange is primarily responsible.