Detection and tracing of the medical radioisotope¹³¹I in the Canberra environment

Abstract

Abstract. The transport and radioecology of the therapeutical radioisotope 131 I has been studied in Canberra, Australia. The isotope has been detected in water samples and its activity quantified via characteristic J-ray photo peaks. A comparison of measurements on samples from upstream and downstream of the Canberra waste water treatment plant shows that 131 I is discharged from the plant outflow into the local Molonglo river. This is consistent with observations in other urban environments. A time-correlation between the measured activities in the outflow and the therapeutical treatment cycle at the hospital identifies the medical treatment as the source of the isotope. Enhanced activity levels of 131 I have been measured for fish samples. This may permit conclusions on 131 I uptake by the biosphere. Due to the well-defined and intermittent input of 131 I into the sewage, the Canberra situation is ideally suited for radioecological studies. Furthermore, the 131 I activity may be applied in tracer studies of sewage transport to and through the treatment plant and as an indicator of outflow dilution following discharge to the environment.