Medically-derived 131I in municipal sewage effluent

This work presents 131I (t½ = 8.04 d) 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, NY, USA. The concentrations detected in sewage effluent ranged from 1.8 ± 0.3 to 227 ± 2 Bq L−1. The primary source of 131I is excreta from thyroid cancer inpatients treated at the Stony Brook University Medical Center. Based on several time series measurements following known inpatient treatments, the mean sewage half-life (Ts) of iodine is 3 d in this plant. The Ts, analogous to a radioactive half-life, describes the time it takes for half of a wastewater component to be removed from a WPCP. Flow recycling, or activated sludge, used to maintain bacterial populations necessary for sewage treatment causes iodine to remain in this plant 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 behavior of 131I in aquatic environments.

► Concentrations of 131I in sewage effluent from a small plant serving a large medical center.
► Iodine-131 from a single patient treatment may be discharged in sewage effluent for many days.
► Medical treatments can be a continuous source of 131I to surface waters.