Cost-benefit analysis of health risks caused by indicative dose from drinking water consumption.

The effective dose annual limit in European Union member states for doses above natural background is 1 mSv. This includes ingestion, inhalation and external dose to a member of public. For doses received due to ingestion of drinking water, parametric value for annual indicative dose is 0.10 mSv. As the name indicates, parametric value is not a limit value: when the parametric value is exceeded, a risk estimation needs to be carried out. Assessment of health risks is done in various fields, however, it is unclear how to do this for drinking water in a situation where the parametric value for indicative dose is exceeded but the annual effective dose limit is not. Approach for risk assessment through cost-benefit analysis is proposed to find the upper limit for investment in a water treatment plant that is justified for lowering the indicative dose of drinking water to a level equal to the parametric value. When a water treatment process cannot be improved with financial resources equal to or below the upper limit of investment, the risk caused by radionuclide ingestion with drinking water can be considered low enough that it is acceptable for the society as a whole. Case study based on the situation in Estonia is brought as an example.

Long-term monitoring of water treatment technology designed for radium removal-removal efficiencies and NORM formation.

A drinking water treatment plant in Viimsi, Estonia, was monitored over three years for iron, manganese, radium-226, radium-228, as well as their daughter nuclides, in order to determine the efficiency of the treatment process, gain an insight into the removal mechanisms and interactions between radium, iron, and manganese, and assess the overall longevity and performance of the technology along with the possible build-up of NORM in the treatment process. During the study, samples were collected from raw water, first and second stage filtrate, consumer water, backwash water and filter materials. The results show consistent removal efficiency for iron and manganese, as well as an average of over 85% removal for radium with a slight decline over time. The backwash process has been optimised for maximum radium removal from the filters, while keeping concentrations in the backwash water below exemption levels. However, the accumulation of radium and thorium occurs in the filter material, exceeding exemption levels in the top layer of the filter columns in less than a year. By the end of the observation period, activity concentrations in the top layer of the columns were above 30 000 Bq kg-1 for Ra-226 and Ra-228, and around 15 000 Bq kg-1 for Th-228. Radionuclides are not homogenously distributed in the filter columns. In order to estimate the average activity concentrations in the filter media, the height distribution of radionuclides has to be accounted for. Two years and two months after commissioning the treatment plant, the average activity concentrations of Ra isotopes in the filter columns were in the range 10 000 Bq kg-1, while Th-228 activity concentration was roughly 3500 Bq kg-1.

Long-term monitoring of a water treatment technology designed for radium removal - removal efficiencies and NORM formation.

A drinking water treatment plant in Viimsi, Estonia was monitored over three years for iron, manganese, radium-226, radium-228, and their daughter nuclides in order to determine the efficiency of the treatment process, get an insight of the removal mechanisms and interactions between radium, iron, and manganese, and assess the overall longevity and performance of the technology and possible build-up of NORM from the treatment process. During the study, samples were collected from raw water, first and second stage filtrate, consumer water, backwash water, and filter materials. The results show a consistent removal efficiency for iron and manganese, as well as an average of over 85% removal for radium with a slight decline with time. Backwash process has been optimized for maximum radium removal from the filters, while keeping the radium concentrations in the backwash water below exemption levels. However, accumulation of radium and thorium occurs in the filter material, exceeding exemption levels in the top layer of the filter columns in less than a year. By the end of the observation period, activity concentrations in the top layer of the columns were above 30 000 Bq/kg for Ra-226 and Ra-228, and around 15 000 Bq/kg for Th-228. Radionuclides are not homogenously distributed in the filter columns. In order to estimate the average activity concentrations in the filter media, the height distribution of radionuclides has to be accounted for. Two years and two months after commissioning of the treatment plant average activity concentrations of Ra isotopes in the filter columns were in a range of 10 000 Bq/kg while Th-228 activity concentration was roughly 3500 Bq/kg.