Radioactive Status and Spatial Distribution of Anthropogenic 137Cs in the Coastal Environment of Sri Lanka

The Fukushima nuclear power plant (FNPP) accident in 2011 caused the release of radioactive material into the environment, is drawing attention important of monitoring the marine environment in this region. Radionuclides with a long half-life can remain in the environment for long periods of time and It has been necessary to establish the baseline levels and conduct regular monitoring of marine radioactivity in sea water and sediments of Sri Lanka to enable comparisons of any possible contamination events in the future. In this study, the activity concentration of 137Cs (Cesium-137) and 134Cs (Cesium-134) was measured selected locations around the coastline of Sri Lanka. Locations were selected to cover the coastal area as uniformly as possible. The classical ammonium molybdophosphate (AMP) pre-concentration method has been used routinely to determine 137Cs in seawater. Method validation was done by using the proficiency testing (IAEA-TEL 2018) solution which contained 2010 Bq m-3 of 137Cs activity. All samples were analysed by high resolution gamma spectrometry with relative efficiency of 32.6% for 72,000 seconds (20 hours) in order to improve the counting statistics. The radioisotope, 137Cs, which has a half-life of 30.17 years, ranged in concentration from 0.33 Bqm-3 to 0.94 Bqm-3, with an average of 0.73 Bqm-3 in 2019. 134Cs was not detected. A previous study in 2013 reported that 137Cs ranged from 0.72-1.72 Bq m-3 with an average of 1.20 Bq m-3. Variation in the 137Cs activity concentration in sea water may be due to factors such as scavenging to sediment, biogeochemical processes or primary productivity prevailing in the region. To understand the temporal variation of 137Cs in surface sea water, published data for the Indian ocean at locations adjoining Sri Lanka coast were assessed. Surface seawaters is shown the declining trend of 137Cs concentration based on the assumption that the 137Cs concentrations decrease exponentially with time, and this study data also shows good agreement with recent publications suggestions. Effective half-life of 137Cs in surface water was calculated to be 15.1 year on average in the rage from 13.1 to 17.8 years in surface waters in all the monitoring areas. These results indicating that 137Cs contents do not significantly affect marine biota because the dose rates were still below from the established dose rate of 10 μGy h-1. Apart from fallout, there has been no substantial input from any source, including the operation of nuclear power plants in Sri Lanka coast. (author)