Seasonal variation of technetium-99 in Fucus vesiculosus and its application as an oceanographic tracer

The concentration of 99Tc was determined in archived time series seaweed samples collected at Klint (Denmark). The results demonstrate a significantly seasonal variation of 99Tc concentrations in Fucus vesiculosus with maximum values in winter and minimum values in summer. The mechanism driving this seasonal cycle was explored. With the measured 99Tc concentration in seawater collected in the same location and date as for seaweed, the concentration factor of F. vesiculosus to 99Tc was investigated. Constant value of concentration factors of 99Tc independence of sampling date, with an average value of (1.9 ± 0.5) × 105 L/kg, were obtained. This indicates that F. vesiculosus can be used as a reliable bio-indicator to monitor 99Tc concentration in seawater. [Display omitted] •99Tc concentrations in Fucus vesiculosus show a seasonal cycle.•99Tc in F. vesiculosus are higher value in winter and lower in summer.•99Tc in seaweed follows the trend in seawater from the same location and date.•Concentration factors (CFs) of 99Tc in seaweed are independent of sampling date.•An constant CF of (1.9 ± 0.5) × 105 L/kg for F. vesiculosus is measured.