Factors affecting the biokinetics of technetium ( 95mTc) in marine macroalgae

Abstract

Technetium (Tc) biokinetics were investigated in marine macroalgae using 92mTc as tracer. Green and red algae accumulated Tc (VII) to a very low degree (CF ≅ 1–20); however, a much higher affinity for pertechnetate was found in some brown algal species (CF > 10 3). Comparative tests with different species of brown algae revealed that technetium does not accumulate similarly in all species of this group. Moreover, no significant differences in radionuclide uptake were noted between brown algae exposed to Tc in either the IV or VII oxidation states. Bioaccumulation of technetium appears to be a metabolically controlled process since uptake did not occur in heat-killed individuals and both light and temperature significantly enhanced the accumulation of technetium in brown algae. Dissection of Sargassum vulgare following the uptake phase showed that the rapidly growing air bladder, leaf-like laterals and small branches contained higher Tc concentrations and retained a greater fraction of the radioactivity than the older, cylindrical main axis. Pertechnetate retention in two brown algae was found to be significantly different; their biological half-lives for Tc differed by an order of magnitude ( T b 1 2 = 19 and 196 days ). During depuration, loss took place more rapidly from the younger portions of the seaweed, as evidenced by the highest concentration and greatest fraction of Tc retained in the older, cylindrical main axis. Provided certain precautions are taken, brown algae such as Cystoseira compressa and S. vulgare would serve as good bioindicator organisms for the presence of Tc contamination in marine waters.