Cesium-137 dynamics within a reactor effluent stream in South Carolina

Cesium-137 dynamics were studied in a blackwater creek which had received production reactor effluents from the Savannah River Plant in South Carolina. Most 137Cs in the water column is dissolved or in colloidal form and is believed to originate primarily through outflow from an upstream contaminated reservoir. All ecosystem components in the stream have high 137Cs concentration factors. Radiocesium concentrations are highest in filamentous algae (332 pCi/g-dry) and suspended particulate matter (100 to 200 pCi/g). Other food chain bases had much lower 137Cs levels. Most consumer populations averaged 10 to 50 pCi/g. Radiocesium concentrations decreased in transfers between food chain bases and primary consumers or filter feeders. Omnivores and small predators have similar 137Cs concentrations with bioaccumulation occurring by top-carnivores. Radiocesium levels are around 100 pCi/g in largemouth bass and water snakes. Foodweb components in the stream have reached a dynamic equilibrium in 137Cs concentrations despite a 10-year absence of reactor operations. Radiocesium levels are apparently being maintained through long-term 137Cs cycling in the upstream reservoir and surrounding flood plain forest systems. Rainfall and other physical processes influence the seasonal 137Cs fluctuations in stream components. (auth)