Concentrations of iodine-131 have been measured in sewage effluent from a small plant serving a large medical centre in the US.Iodine-131 from a single inpatient treatment may be discharged in sewage effluent for many days.
This paper reports on 131I(half-life=8.04 days)concentrations in sewage effluent from the Stony Brook Water Pollution Control Plant(WPCP),a small plant serving a regional thyroid cancer treatment facility in Stony Brook,New York.
The primary source of 131I is excreta from thyroid cancer inpatients treated at the Stony Brook University Medical Center.The concentrations detected in sewage effluent ranged from 1.8±0.3 to 227±2 becquerels/litre(Bq L−1).
Based on several time series measurements following known inpatient treatments,the mean sewage half-life(Ts)of iodine is 3 days in this plant.Ts is analogous to a radioactive half-life,and describes the time it takes for half of a wastewater component to be removed from a WPCP.
Flow recycling,or activated sludge,which is used to maintain bacterial populations necessary for sewage treatment,causes iodine to remain in this plant for far longer than its hydraulic retention time.
The experimental results suggest that most 131I entering the Stony Brook WPCP leaves in sewage effluent,not in sewage sludge.
Patient treatments can result in continuous discharges of 131I to surface waters,where it can be used as a tracer of sewage-derived material,and to understand the behaviour of 131I in aquatic environments.
