Some aspects of the assay of technetium in environmental waters

Technetium, as technetium -99, is present in environmental waters as a result of radioactive effluent discharges from nuclear installations. It is necessary to be able to measure aqueous technetium levels if accurate models are to be developed to predict the long term effects of technetium releases on man. As natural waters contain little -3 technetium, less than μg dm-3 ,relatively large samples are required ( >500 cm3). A method has been developed in which the technetium in the sample can be rapidly concentrated onto an anion-exchange column after the removal of ruthenium isotopes by a precipitation procedure. Further decontamination is achieved by washing the anion-exchange resin with sodium hydroxide prior to removing the technetium with sodium thiocyanate. The bulk of the concentrated technetium (> 75%) can be removed from the resin into less than 15 cm 3 of eluent and further concentration is achieved by extracting the technetium into butan-2-one. The butan-2-one can be evaporated onto a planchette and the technetium levels determined by measuring the amount of B-radiation emitted from the final concentrate. The method has been shown to be capable of removing between ca. 10-15 g and 10 -6 g of technetium from 500 cm 3 of water and has been used successfully with samples ranging from natural waters to nuclear installation effluent. Technetium in natural waters may be lost from solution onto soils and this has important consequences if environmental technetium levels are to be measured. Experiments have been carried out to investigate Some of the factors which influence technetium sorption onto soil and microbial action has been shown to play an important role in determining the rate at which technetium is lost from solution. Other parameters found to affect technetium sorption onto soil include the chemical form of the technetium and the type of water used in the experiment.