Radioactivity of anthropogenic origin in the Tejo Estuary and need for improved waste management and environmental monitoring

Abstract

The Tejo Estuary is a large water body surrounded by seven municipalities and industries with liquid effluent discharges containing contaminants that reach the estuary. This is the case for man-made radionuclides used in nuclear medicine, present in liquid effluents discharged by medical facilities. Radionuclide measurements in seaweeds, mussels, fish, water and sediments sampled along the North bank of the estuary revealed the presence of 131I and 99mTc, originating from nuclear medicine facilities in Lisboa. Concentrations reached 90 Bq kg−1 (wet weight) of 99mTc in fish, and 18 Bq kg−1 (wet weight) of 131I in mussels, and were even higher in the water. Another anthropogenic source of radionuclides is industrial waste, such as phosphogypsum the by-product of phosphoric acid production stockpiled at the South bank of the estuary. Main radionuclides present in phosphogypsum are 226Ra, 210Pb, 210Po and uranium. Concentrations of 226Ra in phosphogypsum are about 1000 Bq kg−1, which is a high value in comparison with 226Ra in soils of the Tejo valley, <100 Bq kg−1. 226Ra, in particular, is dissolved by rainwater from phosphogypsum stacks and seeps into the estuary. Other potential sources of radioactivity are discharges from naval nuclear powered vessels and merchant ships transporting radioactive materials that berth in the Lisboa harbour. A whole survey of the estuary indicated low concentrations of 137Cs in sediments, mostly attributed to radioactive fallout. Since waste discharges are undergoing deep modifications due to enhanced urban waste treatment, but economic activities have changed and the use of radiopharmaceuticals increases, the periodic radioactivity monitoring of the Tejo Estuary is advised and should provide feedback to enhanced waste management.