Medically-Derived (131)I as a Tool for Investigating the Fate of Wastewater Nitrogen in Aquatic Environments.

Medically derived (131)I (t1/2 = 8.04 d) is discharged from water pollution control plants (WPCPs) in sewage effluent. Iodine's nutrient-like behavior and the source-specificity of (131)I make this radionuclide a potentially valuable tracer in wastewater nitrogen studies. Iodine-131 was measured in Potomac River water and sediments in the vicinity of the Blue Plains WPCP, Washington, DC, USA. Dissolved (131)I showed a strong, positive correlation with δ(15)N values of nitrate (δ(15)NO3(-)) in the river, the latter being a traditional indicator of nutrient inputs and recycling. Surface water δ(15)NO3(-) values ranged from 8.7 to 33.4‰; NO3(-) + NO2(-) concentrations were 0.39-2.79 mg N L(-1) (26-186 µM). Sediment profiles of particulate (131)I and δ(15)N indicate rapid mixing or sedimentation and in many cases remineralization of a heavy nitrogen source consistent with wastewater nitrogen. Values of δ(15)N in sediments ranged from 4.7 to 9.3‰. This work introduces (131)I as a tool to investigate the short-term fate of wastewater nitrogen in the Potomac River and demonstrates the general utility of (131)I in aquatic research.

Comment on "radioactive fallout in the United States due to the Fukushima nuclear plant accident" by P. Thakur, S. Ballard and R. Nelson, J. Environ. Monit., 2012, 14, 1317-1324.

The May 2012 paper "Radioactive fallout in the United States due to the Fukushima nuclear plant accident" (P. Thakur, S. Ballard and R. Nelson, J. Environ. Monit., 2012, 14, 1317-1324), does not address medical patient excreta as a source of (131)I (t1/2 = 8.04 d) to the environment. While (131)I is generated during fission reactions and may be released to the environment from nuclear power plants, nuclear weapons tests, nuclear fuel reprocessing and weapons production facilities, it is also produced for medical use. Iodine-131 administered to patients, excreted and discharged to sewer systems is readily measureable in sewage and the environment; the patient-to-sewage pathway is the only source of (131)I in many locations.

Iodine-131 in sewage sludge from a small water pollution control plant serving a thyroid cancer treatment facility.

Iodine-131 (half-life = 8.04 d) is the most widely used radionuclide in medicine for therapeutic purposes. It is excreted by patients and is discharged directly to sewer systems. Despite considerable dilution in waste water and the relatively short half-life of I, it is readily measured in sewage. This work presents I concentrations in sewage sludge from three water pollution control plants (WPCPs) on Long Island, NY. Iodine-131 concentrations ranged from 0.027 ± 0.002 to 148 ± 4 Bq g dry weight. The highest concentrations were measured in the Stony Brook WPCP, a relatively small plant (average flow = 6.8 × 10 L d) serving a regional thyroid cancer treatment facility in Stony Brook, NY. Preliminary radiation dose calculations suggested further evaluation of dose to treatment plant workers in the Stony Brook WPCP based on the recommendations of the Interagency Steering Committee on Radiation Standards.

Behavior of medically-derived 131I in the tidal Potomac River.

Iodine-131 (t1/2=8.04 d) is administered to patients for treatment of thyroid disorders, excreted by patients and discharged to surface waters via sewage effluent. Radionuclides generally behave like their stable analogs; therefore, medically-derived (131)I is useful as a transport-reaction tracer of anthropogenic inputs and the aquatic biogeochemistry of iodine. Iodine-131 was measured in Potomac River water and sediments in the vicinity of the Blue Plains Water Pollution Control Plant (WPCP), Washington, DC, USA. Concentrations measured in sewage effluent from Blue Plains WPCP and in the Potomac River suggest a relatively continuous source of this radionuclide. The range of (131)I concentrations detected in surface water was 0.076±0.006 to 6.07±0.07 Bq L(-1). Iodine-131 concentrations in sediments ranged from 1.3±0.8 to 117±2 Bq kg(-1) dry weight. Partitioning in the sewage effluent from Blue Plains and in surface waters indicated that (131)I is associated with colloidal and particulate organic material. The behavior of medically-derived (131)I in the Potomac River is consistent with the nutrient-like behavior of natural iodine in aquatic environments. After discharge to the river via sewage effluent, it is incorporated into biogenic particulate material and deposited in sediments. Solid phase sediment profiles of (131)I indicated rapid mixing or sedimentation of particulate debris and diagenetic remineralization and recycling on short time scales.

Medically-derived 131I in municipal sewage effluent.

This work presents (131)I (t(½) = 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 (131)I 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 (T(s)) of iodine is 3 d in this plant. The T(s), 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 (131)I entering the Stony Brook WPCP leaves in sewage effluent, not in sewage sludge. Patient treatments can result in continuous discharges of (131)I to surface waters where it can be used as a tracer of sewage-derived material and to understand the behavior of (131)I in aquatic environments.