Comprehensive radioecological monitoring of freshwater ecosystems in the vicinity of Rooppur NPP (People's Republic of Bangladesh)

Abstract

The paper presents experience of developing and maintaining a system of radioecological monitoring of freshwater ecosystems in the vicinity of Rooppur Nuclear Power Plant (Bangladesh). Components of freshwater ecosystems in the zone of NPP impact are both very informative for determining the environmental state and very important for conducting economic activities. Therefore, the issue of assessing and predicting quality of freshwater ecosystems in the vicinity of NPP is relevant for ensuring radiation and environmental safety. During the studies, we developed a detailed monitoring program; selected observation points for the state of surface water and groundwater at different distances from Rooppur NPP; determined monitoring objects (water, bottom sediments, higher aquatic vegetation, and fish), list of parameters to be studied, observation regulation, methods, and regulatory and technical support. Among the indicators controlled we considered the following ones: physicochemical properties of water and bottom sediments; radionuclide content of components of freshwater ecosystems including natural (⁴⁰K, ²²⁶Ra, and ²³²Th) and technogenic (⁹⁰Sr, ¹³⁷Cs, and ³H) radionuclides; and content of 19 heavy metals, as well as chemical pollutants. Monitoring studies were conducted in 2014–2017, considering climatic peculiarities of the region at different periods of the year. Radionuclides in environmental objects were determined by spectrometry and radiochemistry; heavy metals – by atomic absorption and plasma emission analysis methods. It was established that higher aquatic vegetation in the Padma River is found not in all seasons. In December, it was almost absent. The maximum species diversity was registered in June. Differences between surface water and groundwater in the vicinity of Rooppur NPP were distinguished for several physical and chemical characteristics. Values of drinking water total mineralization and hardness were higher than that of surface water by 2–3 times. This is due to Padma River water composition, the basis of which is meltwater and rainwater. Organic pollutants content in surface water and groundwater was below detection limits or at minimum ones (benzopyrene – less than 0.01 μg·L⁻¹; phenols – 1.3–3.5 μg·L⁻¹; and petroleum products – 0.01–0.043 mg·L⁻¹). Activity concentration of ¹³⁷Cs in Padma River water did not exceed 0.18 Bq·L⁻¹ (with a mean of 0.07 Bq·L⁻¹) during the observation period. The content of ⁹⁰Sr was 0.02–0.12 Bq·L⁻¹, and the concentration of ³H varied in the range of 0.8–2.1 Bq·L⁻¹. Mean specific activity of ⁹⁰Sr in bottom sediments was 0.5–1.8 Bq·kg⁻¹, and ¹³⁷Cs – 0.8–2.1 Bq·kg⁻¹. Specific activity of ³H in bottom sediments was less than 3 Bq·kg⁻¹, except for 3 samples in 2017 (12–30 Bq·kg⁻¹), which was most likely due to a local pollution. Specific activity of ⁹⁰Sr in higher aquatic vegetation was 0.4–3.9 Bq·kg⁻¹, and ¹³⁷Cs – 0.4–1.0 Bq·kg⁻¹. In drinking water, activity concentrations of radionuclides were as follows: ¹³⁷Cs – 0.03–0.27 Bq·L⁻¹; ⁹⁰Sr – 0.01–0.16 Bq·L⁻¹; ³H – 0.4–1.2 Bq·L⁻¹. Specific activity of ⁹⁰Sr in fish was 0.02–1.6 Bq·kg⁻¹.The content of ¹³⁷Cs in fish was 0.26–0.3 Bq·kg⁻¹. Analysis of monitoring data on heavy metal levels in components of freshwater ecosystems in the vicinity of Rooppur NPP showed that for a number of elements their increased concentrations were recorded, most of which belong to monsoon season. In Padma River surface water, a repeating increase in As, Cd, Mn, and Al concentrations was noted, and in bottom sediments – an increase in As, Cd, Ni, Co, and Zn content, which was associated with anthropogenic impact and increasing runoff of pollutants during monsoon rains. Repeatedly increased As and Mn concentrations were noted in drinking water of Rooppur NPP 30-km zone. In separate samples, there was an increase in Fe and Al content. This might be due to both natural peculiarities of the region (relatively high As content in aquifers) and the state of water supply systems. Obtained results and developed network of radioecological monitoring of freshwater ecosystems would make it possible to register a change in the situation and to identify impact of Rooppur NPP operation on human population and the environment.

Keywords: Bangladesh, Rooppur NPP, water resources, freshwater ecosystems, Padma River, drinking water, radioecological monitoring, radionuclides, heavy metals, chemical pollution