Medically-derived radionuclides levels in seven heterogeneous urban wastewater treatment plants: The role of operating conditions and catchment area

Abstract

In nuclear medicine radionuclides are administered to patients both for diagnosis or treatment. Subsequently, the excreta from patients, enriched in radionuclides, enter the sewerage networks and reach wastewater treatment plants (TPs). Characterization of inflow wastewaters, sewage effluents and sewage sludges in the seven different urban WWTPs in the Barcelona Metropolitan Area (BMA) has been done and 131I, 99mTc, 111In, 67Ga and 123I concentrations were determined by gamma-spectroscopy. In order to explain the diversity of nuclear medicine short-lived radionuclide concentrations found in the BMA, mean sewage sludge ages and wastewater hydraulic retention times were determined, NM services located and patient management guidelines described. Results were found to vary greatly among the different TPs in inflow wastewaters, sewage effluents and sewage sludges. 131I and 99mTc activity concentrations showed the highest values in most of the inflow wastewaters, sewage effluents and sewage sludges. In the integrated analysis of the present findings, a large-sized TP (320,000 m3/d) from the BMA urban wastewater treatment system shows higher levels and detection frequencies of medically-derived radionuclides. The maximums detected in the sludges from this TP, are partly explained by the relatively low sewage sludge ages. Furthermore, inflow wastewater hydraulic retention times and sludge ages in the TPs are long enough for decay of the short-lived nuclear medicine radionuclides studied (t1/2 ≤ 8d) in such a way that TPs work as abatement systems and decrease the levels of radioactivity both in the effluent and in the final sludge. An integrated analysis of 7 TPs from the same system has been carried out to go further into the dynamics of medically-derived radionuclides in it.