Uptake and Retention of Cesium 137 and Zinc 65 by Seaweeds1

Uptake and retention of Cs137 and Zn by seaweeds were observed under various environmental conditions. Concentration factors and biological half‐lives varied widely among species, Zn65 showing generally higher levels of uptake and retention. No significant relationship between growth rate and either concentration factor or biological half‐life was found among the species tested. Both uptake and loss of Cs137 were stimulated by light, but some Cs137 movements occurred in the dark. Both exogenous substrate (glutamate) and previous exposure to light stimulated Cs137 uptake in the dark. Exposure to nitrogen in the dark inhibited both influx and efflux of Cs137. Neither darkness nor anoxia caused appreciable net loss of absorbed Cs137. Cs137 was not extensively adsorbed by cell walls or killed tissue. Influx and efflux of Cs were proportional, respectively, to the external and internal Cs concentrations. Intracellular Cs appears to be largely ionic, with Cs movements being closely related to metabolism. Zn65 was highly concentrated by living and killed algae and by cell walls. Light had a variable effect on Zn65 movements. Zinc uptake at different external Zn concentrations agreed with the Freundlich adsorption equation. Adsorption exchange appears to be an important mechanism of Zn movements in seaweeds.