Another Radiation Source To Consider: Hospital Sewage

Researchers found higher than expected levels of radioactive iodine at a Long Island sewer plant that receives effluent from the thyroid cancer treatment center at Stony Brook University, they report in the latest issue of Health Physics.
The research highlights the need for studies of wastewater treatment plants that receive effluent from thyroid cancer treatment facilities, say researchers Paula S. Rose and Lawrence R. Swanson of Stony Brook's Marine Sciences Research Center.
"This study highlights that medical use can cause substantial fluctuations of I-131 in sewage sludge and the general need for more surveys of I-131 in municipal WCPCs (Wastewater Polution Control Plants)," they write in the August 2013 issue of Health Physics (subscription required).
Rose and Swanson found a concentration of radioactive iodine four times higher than previously published studies of the Stony Brook plant, and at levels that sometimes exceeded the federal dose limit for members of the public.
The measured I-131 peaked at the euiqvlent of 3.68 millisieverts per year, which is slightly higher than the estimated dose Americans receive from background radiation. That measurement does not account for other radionuclides, however, and the researchers say the dose at Stony Brook may sometimes be higher than the study recorded.
The federal level for occupational exposure is 50 times higher than the level for exposure to the public (50 millisieverts per year for workers, compared to 1 mSv per year for the public), but the researchers nonetheless recommend Suffolk County reconsider the possibility of radiation exposure to workers at the treatment plant.
"Further evaluation of treatment plant worker dose at this plant has been recommended to the Suffolk County Sewer District based on the radiation doses presented here."
The researchers studied three wastewater treatment plants on Long Island, but found the highest doses at Stony Brook, perhaps because a relatively small treatment plant there serves a regional thyroid cancer center. The Stony Brook Medical Center treats about 60 inpatient thyroid cancer patients per year.
Iodine-131 can be both a cause of thyroid cancer and a solution. Cancers can develop when the thyroid absorbs I-131 instead of stable iodine, and can be included in the cure after doctors remove the thyroid gland and use I-131 to destroy remaining cells. Patients dosed with I-131 become temporarily radioactive, as does their urine. "Patient excreta" are exempt from regulation in the U.S., and are therefore released into sewer systems.
Iodine 131 has a half life of about eight days.
"Iodine-131 is readily measured in sewage sludge at the Stony Brook WPCP," according to the study. "The primary source of this radionuclide is excreta from thyroid cancer inpatients treated at the Stony Brook University Medical Center. Frequent inpatient treatments, flow recycling, and sewage sludge removal practices cause 131I to remain in sewage sludge for at least 13 days after patients have left the hospital."